WORLD
(I
BANK
TECHNICAL
PAPER
NO.
421
EneegySeries
WTP421 March 1999
Work in progress for public discussion
Evaporative Air-Conditioning Applicationsfor Environmentally FriendlyCooling
GelitJan Bom Robert Foster Ebel Dijkstra Tummer-s AMIaija
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(List continues on the inside back cover)
WORLD BANK TECHNICAL
PAPER NO. 421
EnergySeries
Evaporative Air-Conditioning ApplicationsforEnvironmentally FriendlyCooling
GertJanBom RobertFoster EbelD#jkstra Marja Tummers The WorldBank Washington,D.C.
Copyright © 1999 The International Bank for Reconstruction and Development/THE WORLD BANK 1818H Street, N.W. Washington, D.C. 20433,U.S.A. All rights reserved Manufactured in the United States of America First printing March 1999 TechnicalPapers are published to communicate the results of the Bank's work to the development community with the least possible delay. The typescript of this paper therefore has not been prepared in accordance with the procedures appropriate to formal printed texts, and the World Bank accepts no responsibility for errors. Some sources cited in this paper may be informal documents that are not readily available. The findings, interpretations, and conclusions expressed in this paper are entirely those of the author(s) and should not be attributed in any manner to the World Bank, to its affiliated organizations, or to members of its Board of Executive Directors or the countries they represent. The World Bank does not guarantee the accuracy of the data included in this publication and accepts no responsibility for any consequence of their use. The boundaries, colors, denominations, and other information shown on any map in this volume do not imply on the part of the World Bank Group any judgment on the legal status of any territory or the endorsement or acceptance of such boundaries. The material in this publication is copyrighted. The World Bank encourages dissemination of its work and will normally grant permission promptly. Permission to photocopy items for internal or personal use, for the internal or personal use of specific clients, or for educational classroom use is granted by the World Bank, provided that the appropriate fee is paid directly to Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923,U.S.A.,telephone 978-750-8400,fax 978-7504470.Please contact the Copyright Clearance Center before photocopying items. For permission to reprint individual articles or chapters, please fax your request with complete information to the Republication Department, Copyright Clearance Center, fax 978-750-4470. All other queries on rights and licenses should be addressed to the World Bank at the address above or faxed to 202-522-2422. ISSN: 0253-7494 Gert Jan Bom, Ebel Dijkstra, and Marja Tummers are development consultants at Ecozone, Haarlem, the Netherlands. Robert Foster is a project engineer at New Mexico State University, Las Cruces. Libraryof Congress Cataloging-in-Publication Data Evaporative air-conditioning: applications for environmentally friendly cooling / Gert Jan Bom . . .[et al.].
p. cm. - (World Bank technical paper; 421. Energy series) Includes bibliographical references (p. ). ISBN 0-8213-4334-3 1. Air conditioning. 2. Evaporative cooling. I. Bom, Gert Jan. II. Series. TH7687.E94 1998 697.9'3-dc2l 98-31273 CIP
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Contents
Foreword.............................................................
ix
Abstract.............................................................
xi
Acknowledgments .............................................................
xiii
Abbreviations, Symbols, and Glossary .............................................................
xv
1. Introduction.............................................................
l1 Benefits of Evaporative Cooling .............................................................. 2 Opportunities and Limitations .............................................................. 2 Environmental Benefits.............................................................. 2 Direct Evaporative Air-Conditioning .............................................................. 3 Residential Coolers .............................................................. 3 Indirect Evaporative Air-Conditioning .............................................................. 4 Desiccant-Assisted Evaporative Air-Conditioning .............................................................. 4 Commercial Evaporative Air-Conditioners .............................................................. 5 Comparing Vapor-Compression and Evaporative Air-Conditioning ................................................. 5 Outlook .............................................................. 5
2. Opportunities and Constraints.............................................................. 9 Climatological Factors ............................................................. 9 Comfort Issues ............................................................. 10 Expected Performance of Evaporative Air-Conditioning ............................................................. 12 Power Supply ............................................................. 13 Water Supply ............................................................. 13 Advantages of Evaporative Versus Vapor-Compression Air-Conditioning .................................... 13 3. Economics............................................................. Economics of Residential Coolers ............................................................. Investment Costs ............................................................. Market Situation .............................................................
15 15 16 18
4. Technology ............................................................. Direct Evaporative Air-Conditioning ............................................................. Indirect-Direct Evaporative Air-Conditioning ............................................................. Desiccant Cooling .............................................................
21 21 26 29
5. Choosing and Maintaining Equipment ............................................................. Available Equipment .............................................................
31 31
v
vi
Evaporative Air-Conditioning, Applications for Environmentally Friendly Cooling
Direct Evaporative Air-Conditioning Recommended Air Change Rate for Design Wet-Bulb (WB) Conditions .......................................................... Maintenance ..........................................................
33 33
6. Solar EvaporativeAir-Conditioning.......................................................... 37 The Market.......................................................... 37 Optimizing Evaporative Air-Conditioning Design for Solar Operation .......................................... 38 7. Introductionand Local Manufacturein Developing Countries......................................................... 41 Maintenance ........................................................... 41 Installation and Sizing.......................................................... 41 Manufacturing Requirements ........................................................... 41 Know-How .......................................................... 43 8. CommercialEvaporativeAir-Conditioning .......................................................... Commercial versus Residential Cooling .......................................................... Commercial Kitchen Evaporative Air-Conditioning .......................................................... Laundry and Dry Cleaning .......................................................... Extreme Heat Conditions .......................................................... Industrial Applications .......................................................... Factory Air-Conditioning Design Considerations ........................................................... Agricultural Applications-Poultry .......................................................... Greenhouses ..........................................................
45 45 46 46 46 47 47 48 49
Bibliography..........................................................
69
.
Annexes
1. 2. 3.
Introduction to Evaporative Cooling .......................................................... 53 Suitability of Evaporative Air-Conditioning in Different Climate Zones ........................................ 57 List of Manufacturers and Suppliers .......................................................... 63
Boxes 2.1 Relative Humidity and Wet-BulbTemperature .......................................................... 5.1 A Simple Sizing Example .......................................................... Figures
1.1 1.2 1.3 2.1 2.2 2.3 3.1 3.2 3.3 3.4 4.1 4.2 4.3 4.4 4.5
Typical Direct Evaporative Air-Conditioner .3 Roof-Mounted Downdraft Evaporative Air-Conditioning Unit, El Paso, Texas .4 Direct Evaporative Air-Conditioner for Transport Use .7 Modified Evaporative Air-Conditioning Comfort Zone Taking into Account Increased Airflow Compared with ASHRAE Comfort Zone Based on Vapor Compression Air-Conditioning .11 Annual Energy Use Summary: Vapor Compression Air-Conditioning (SEER= 9.5 for Phoenix, Arizona, USA).14 Annual Energy Use Summary: Indirect/Direct Evaporative Air-Conditioning (2,000scfm, for Phoenix, Arizona, USA).14 Typical Investment Costs for Evaporative Air-Conditioning in the United States .16 Typical Investment Costs for Evaporative Air-Conditioning in India .17 Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioning for the United States .17 Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioning for India .18 Simplified Evaporative Air-Conditioning Process .22 Psychrometric Process for Direct Evaporative Cooling, Mexico.22 Comnonly Available Rigid Cellulose Pads Provide Superior Saturation and Cooling Compared with Ordinary Aspen Pads .24 Close-up of Rigid Cellulose Pad Made of Corrugated Paper .24 Common Cabinets for Residential Coolers in India .26
10 32
Contents
4.6 4.7 4.8 4.9 4.10 6.1 6.2 7.1 8.1 8.2 8.3 A1.1 Al.2 A1.3 A1.4 A1.5 A1.6 Al.7 A1.8 A2.1 A2.2 A2.3 A2.4 A2.5 A2.6
v2i
Cutaway of a Direct Evaporative Air-Conditioning ................................................................... 27 Plate-Type Indirect-Direct Evaporative Air-Conditioning ................................................................. 27 Indirect-Direct Evaporative Air-Conditioners on a Public School Rooftop, Colorado Springs, USA.................................................................. 28 Indirect-Direct Evaporative Air-Conditioning Process ..................................................................29 Ventilation Cycle Desiccant Cooling System .................................................................. 30 A Solar-Powered Evaporative Air-Conditioner .................................................................. 37 Evaporative Cooler Coupled with Solar Power (System installed by a homeowner in Chaparral, New Mexico, USA).................................................................. 39 Evaporative Air-Conditioners in Kamla Market, New Delhi, India ................................................. 42 Typical Evaporative Air-Conditioning Application for Poultry Houses .......................................... 49 Evaporative Cooling Pad Section of Rigid Cellulose Pads ................................................................. 50 External Evaporative Air-Conditioners on a Research Greenhouse, New Mexico State University, Las Cruces, New Mexico.................................................................. 50 Psychrometric Chart and Saturation Line .53 Complete Psychrometric Chart .53 Wet-BulbDepression of Ambient Air .54 Saturation Effectiveness for an 80 Percent Effective Evaporative Cooling Pad .54 Saturation Effectiveness of 80 Percent for Evaporative Cooling Pads at Different Ambient Conditions .54 Effectof Indirect Evaporative Cooling on Ambient Airstream .54 Effect of Combined Indirect Evaporative Cooling Coupled with Direct Section.55 Energy-Saving Effect of Using a Smaller Coil Coupled with Indirect and Direct Evaporative Cooling Sections.55 Suitability of Evaporative Air-Conditioning: Africa .57 Suitability of Evaporative Air-Conditioning: Asia .58 Suitability of Evaporative Air-Conditioning: Australia .59 Suitability of Evaporative Air-Conditioning: Europe .60 Suitability of Evaporative Air-Conditioning: North America.61 Suitability of Evaporative Air-Conditioning: South Arnerica .62
Tables 1.1 Vapor-Compression versus Evaporative Air-Conditioning ................................................................. 6 2.1 Effectiveness of Evaporative Cooling by Climate Type .................................................................... 9 2.2 Relation between Wet-Bulb Temperatures and Effectiveness of Evaporative Air-Conditioning .................................................................. 10 2.3 Evaporative Air-Conditioning Performance in Selected Locations at 1 Percent Cooling Design Conditions .................................................................. 12 2.4 Benefits of Evaporative Air-Conditioning Versus Vapor Compression Air-Conditioning ............13 5.1 Available Residential Evaporative Air-Conditioning Equipment ..................................................... 31 5.2 Useful Cooling Chart: Percentage of Useful Cooling for Direct Evaporative Air-Conditioning Output ................................................................... 34 6.1 Available Packaged Solar Evaporative Air-Conditioning Equipment .............................................. 38 6.2 Design Measures to Optimize Evaporative Air-Conditioning for Solar Power .............................. 38 7.1 Work Involved in Manufacturing Evaporative Air-Conditioning .................................................... 42
Foreword
Although evaporative coolers cannot be used in all countries and at all times, they are generally very much underutilized in places where they can be used successfully. This is unfortunate, both for the potential user, the country, and the global environment. Benefits include lower cooling equipment costs and a much reduced electricity bill for the user, reduced electrical energy and power demand at peaktimes for the country, and lower greenhouse gas and CFC/HFC emissions for us all. This handbook is designed for those who do not know evaporative coolers, but might be convinced to try using or promoting them. It provides the advantages and disadvantages of using evaporative coolers while comparing them to the commonly used, energy guzzling, and expensive vapor compression air conditioners. Existing markets where evaporative coolers are currently used, local manufacturing possibilities, operational aspects are discussed along economic and global aspects. A world-wide list of manufacturers and suppliers is included in the Annex.
James Bond Director Energy, Mining and Telecommunications Department
ix
Abstract
As the harmful environmental effects of chloro-fluorocarbons (CFCs) and greenhouse gases have become better known, interest has grown in environmentally friendly cooling technologies. Evaporative air-conditioning (EAC) is such a technology. Whereas conventional vapor compression air-conditioning (VAC)uses CFCs as cooling liquids, EAC uses water. EAC technology is simple, functional, and has both residential and commercial applications in industrialized and developing countries. EAC can provide superior cooling and ventilation while consuming less energy (and hence contributing less to greenhouse gas emissions) than VAC. EAC works best in hot, dry climates, but it can be used in more humid climates as well. This paper elucidates some of the technical characteristics and fields of application for EAC and outlines the climatic conditions under which EAC can be most effectivelyemployed. The document begins with a general outline of the applications and limitations of EAC and explains the differences between "direct" and "indirect" EAC. Chapter 2 discusses the applicability of EAC in different climates and explains the use of wet-bulb temperature as a useful tool for predicting the applicability of EAC. Chapters 3 and 4 discuss the economics of EAC versus VAC in terms of energy consumption, required investments, and life-cyclecosts. Production costs, the paper points out, are low enough so that EACs can be manufactured relatively easily in the developing world, as is now being done in South Asia and the Middle East. Chapters 5 and 6 review the market for EACs and try to show how EAC can increase individuals' "feeling of comfort." Chapter 7 explains the basic technology of EAC.The difference between direct and indirect coolers is elaborated on through the use of a psychrometric chart. The hardware components of the EAC are explained: pads, motor, pump, and fan. Chapter 8 lists the equipment available on the market. It also points out that the capacity of the cooler and the size of the room to be cooled are key elements in selection of an EAC.A simple example is given to aid in sizing. Like any sort of mechanical equipment, EACs need to be maintained regularly to perform well and last longer. Maintenance requirements for each component are discussed in chapter 9. EACs require little energy, and because the presence of strong sunshine coincides with the need for cooling, a link with solar energy appears to be attractive. In chapter 10 the usefulness of solar EAC and the present market situation are outlined. EAC is an attractive cooling solution, for industrial as well as for less developed countries too. The requirements for the introduction of a relatively new technology like EAC are discussed in Chapter 11.In Chapter 12 the usefulness of EAC for commercial applications is outlined. Commercial kitchens, laundry and dry cleaning and industrial applications are three areas where EAC could be useful.
xi
Abbreviations, Symbols,and Glossary
Design temperatures: outdoor temperatures at a fixed percentage more temperate than worst-case figures, which are a standard air-conditioning system design parameter. Enthalpy: total heat content of air-water vapor atmospheric gas. Not altered by adiabatic cooling. Evaporative air-conditioning: lowering of dry-bulb temperature as air passes over water. Two methods using evaporating water to cool air: (1) direct, which is adiabatic and humidifies the air; and (2) indirect, which is nonadiabatic and cools the air being treated. Indirect evaporative air-conditioner. a heat and mass transfer device used to sensibly cool a primary airstream, without addition of moisture, by means of an evaporatively cooled secondary airstream. Since the secondary air provides wet-bulb depression, it represents a heat sink to the primary air. Latent heat load: heat carried by water vapor in air; varies with humidity. Wet-bulb temperature is an index to latent heat. Saturation (cooling) effectiveness: the primary air dry-bulb temperature reduction divided by the primary air entering dry-bulb temperature less the entering secondary wet-bulb temperature. Temperature, dry-bulb: the air temperature measured by a dry temperature sensor. Temperature, wet-bulb: the temperature measured by a temperature sensor covered by a water-moistened wick and exposed to air in motion. When properly measured, it is a close approximation of the temperature of adiabatic saturation.
xv
Introduction Evaporative air-conditioning (EAC) technologies are being used increasingly in residential and commercial applications worldwide. EAC technologies-which rely on water as a coolant rather than on chemical refrigerants-are economical to produce and use and have important environmental benefits. This paper introduces the technical aspects of EAC, reviews EAC's scope of application, and surveys the specific climatic conditions under which EAC can be used most effectively in industrialized and developing countries. Under the right conditions and applicafions, EAC can provide excellent cooling and ventilation with minimal energy consumption using water as the working fluid and avoiding the use of ozone-destroying chlorofluorocarbons (CFCs). Policymakers in particular should become better informed about EAC because of the opportunities it affords to reduce the use and emission of CFCs and hydrofluorocarbons (HFCs), the reduction in CO2 emissions that come from the energy efficiency of the technology, and the potential for mitigating problems of peak electricity demand during the hot season in many countries. The viability of using EAC will depend on the particular application and on the local climatic conditions. For example, for comfort cooling, EAC is most suited to dry regions, although technical improvements such as indirect/direct and desiccant-assisted systems widen the zone of applicability. On the other hand, some commercial applications of EAC are suitable even in humid climates. In general, several sectors have significant reasons for considering employing EAC technologies: * Utilities.Dissemination of EAC appliances can serve as a significant demand-side management (DSM) tool for utilities. Power savings of EAC technology versus VAC are on the order of 70 percent for direct EAC and 50 percent for indirect EAC. This differential presents substantial peak-saving opportunities for utilities that can promote the use of EAC within their service areas. * Governments.For goverrnent agencies and planners, cost savings from reduced electrical consumption can be realized directly by incorporating EAC technology into buildings and other installations. In addition, government planners should encourage use of EAC technologies as a relevant technology alternative to VAC that will save consumers money, reduce overall electrical demand, reduce pollution emissions, and help meet international treaty obligations related to reducing pollutant emissions. 1
2
Evaporative Air-Conditioning: Applications for Environmentally Friendly Cooling
* Consumers.Consumers who use EAC at home can save money on cooling costs. The typical capital, installation, and operation costs are significantly lower for EAC technologies than for VAC technologies. Moreover, EAC technology is simple enough so that most homeowners can maintain their own units. * Privateenterprise.The manufacture and sale of EAC appliances presents significant opportunities for both small and large enterprises. It is particularly suited to manufacture even in relatively poor developing countries because-unlike the comparatively complex technical requirements for production of chemical air-conditioners-EAC production requires only the basic infrastructure and skills mix related to sheet metal, motor, pump, and fan fabrication. Hence, marketers of EACs can underbid VAC prices while maintaining comparatively high profit margins. In the right climates, EACs can gain far more than a "niche" market: in some of the larger cities in the southwestern United States and northern Mexico, for example, 95 percent of the residential airconditioning market is taken by EAC units, most of them manufactured locally.
Benefits of Evaporative Cooling The following benefits of EAC can be cited: * * * * * * * * * * * *
Significant local fabrication and employment Substantial energy and cost savings No chlorofluorocarbon (CFC)usage Reduced peak demand Reduced CO2 and power plant emissions Improved indoor air quality Life-cyclecost effectiveness Easily integrated into built-up systems Wide variety of packages available Provide humidification when needed Easy to use with direct digital control (DDC) Greater regional energy independence
Opportunities and Limitations EAC works best for comfort cooling where it is hot and dry. EACs are widely used in the Middle East, Australia, the Indian subcontinent, Eastern African, northern Mexico, and the southwestern United States. Residential EACs are known in India as desertcoolers,and in such desert or dry-steppe climates EACs do give "significant relief" during the hot months. "Significant relief" is considered to be provided when the final supply-air temperature leaving the EAC is about 20' to 250C (680to 77°F). Even in a tropical savanna climates such as in the northeast of Brazil, the Sahel region of Africa, the southwest Dominican Republic, EAC can be useful in some comfort cooling applications and also for many commercial applications such as greenhouses and poultry houses. A limiting factor for the application of EAC is the definition of comfort. A residential cooler bringing down the temperature from 450to 30°C(1130to 860T) may still be appreciated even if it does not provide "significant" relief. Environmental Benefits EAC technologies represent significant enviromnental benefits related to reducing CFC/HCFC use and for obviating C02 and other emissions, as well as for reducing peak electrical demand. For example, the
Introduction
3
4 million EAC units in operation in the United States provide an estimated annual energy savings equivalent to 12 million barrels of oil and an annual reduction of 5.4 billion pounds of CO2 emissions. They also avoid the need for 24 million pounds of refrigerant traditionally used in residential VAC systems. Similar energy savings and environmental benefits are also made by commercial applications of evaporative cooling technologies in the United States and elsewhere. Through increasing use of EAC technologies, countries can save energy, reduce power plant emissions, obviate CFC usage, and improve indoor air quality. Basic air conditioning with water is a relatively simple process. Direct Evaporative
Air-Conditioning
Direct EAC is the simplest, the oldest, and the most widespread form of air-conditioning. This system typically uses a fan to draw hot outside air into a dwelling through a porous wetting medium. Heat is absorbed by the water as it evaporates from the porous wetting medium, and the air thus leaves the EAC at a lower temperature. The amount of cooling provided is determined by efficiency of the wetting medium, the fan, and the overall design and construction of the unit. A critical component in EAC is the use of water. This may vary from a few liters per day in small residential coolers to perhaps a hundred liters or more in pad-and-fan EAC systems in greenhouses and complicated duct-systems in laundries and hotel kitchens. Residential
Coolers
A residential EAC typically consists of a cubical box of sheet metal or plastic containing large vertical filter "pads," an electric-motor-driven fan, a water pump, a water distribution system, and a water sump at the bottom. As Figure 1.1 and Figure 1.2 show, the fan draws in warm outside air through the wetted media, cooling the air. The water pump lifts the water from the sump through the distribution system to the top of the pads from where it trickles down by gravity back to the water sump. The cooled air is then delivered either directly through a grille into a single room or into a duct distribution system. This is a "direct" EAC in which the cooled and saturated outside air flows into the room, displacing the hot air. It is simple and cheap but is not sufficient for indoor comfort cooling once ambient wet-bulb temperatures reach 21°C (69.8°F).
Figure1.1. TypicalDirect EvaporativeAir-Conditioner Distribution Manifold
Inlet Air
d. Wetted Media
Conditioned Air Recirculation Pump
Source:Authors.
4
Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling
Figure1.2. Roof-MountedDowndraftEvaporativeAir-ConditioningUnit, El Paso,Texas
7."~
~
~
~
~~~~.
Source: R. Foster.
Indirect EvaporativeAir-Conditioning Indirect-direct EAC is a method established only over the past 15 years. It is not as widely used as direct EAC, but it is gaining in popularity because it cools air more than direct EAC, and cools the air down from higher wet-bulb temperatures. hindirect EAC accomplishes these effects by building an additional step into the cooling process. That is , the incoming air is cooled first with a normal air-to--airheat exchanger. This is the "indirect" stage because it does not add moisture to the supply air. Instead, only one side of the heat exchanger is cooled with evaporating water as the supply air passes through the other side, dropping in temperature
as it does. Only then, as it passes through the direct EAC stage, is the
supply air moisturized. The final air leaving an indirect-direct EAC unit is generally 3.5C (6.30 F) cooler than what could be achieved with a direct EAC unit alone. Because it cools the air first without moisturizing it, the indirect-direct process also allows the EAC unit to provide more comfort in slightly more humid areas. Commonly these units achieve 65 percent indirect stage efficiency (performnancefactor), which allows an ambient wet-bulb temperature of up to 250 C to provide acceptable room temperatures for real comfort. Two-stage air-conditioners combinLingindirect and direct EAC are becoming popular in the United States and Australia, particularly in locations where slightly higher wet-bulb temperatures (i.e.,conditions of higher ambient humidity) do not permit sufficientlycomfortablesupply-air temperatures via direct EAC. On the downside, however, the two-stage units have higher construction and maintenance costs.
Desiccant-Assisted EvaporativeAir-Conditioning The use of dehumidifying chemicals (e.g., desiccants such as silica gel) further widens the scope for EAC. Desiccant technologies can widen the scope for comfort cooling to even the most humid regions. In such systems, the desiccant is used first to dehumidify the ventilation air to a desired state; then, EAC (either direct or indirect or a combination thereof) is used to cool the air to the desired supply-air temperature.
Introduction
5
CommercialEvaporativeAir-Conditioners Commercial EAC applications are of several types. Commercial comfort cooling applications are used for offices,retail establishments, and so on, as determined by local climates and comfort preferences. In other commercial applications, EAC may be used to moderate the effects of an additional internal heat source that does not depend (only) on the climate or the time of the year. For example, temperatures may rise inside warehouses or buildings because of the operation of ovens, machines, or the presence of livestock. These heat sources sometimes exacerbate already high ambient temperatures. Although the cooling requirements differ as a matter of degree, so to say, cooling of buildings affected by both internal and external sources of heat does require a somewhat different approach from residential cooling to moderate high outside ambient temperatures. For one thing, such commercial EAC systems may well need to be designed for operation the year round rather than just in a "hot season." A commercialkitchen or bakery, for example, might need cooling year-round. Moreover, the internal cooling requirements may be quite localized within the building (e.g., spot-cooling in a manufacturing plant). Another difference between commercial and comfort cooling with EAC is that EAC in some commercial applications is the only practical alternative; that is, where VAC technologies cannot function or compete effectivelybecause of high operating costs. The most salient example here is the cooling towers in a power plant, but on a smaller scale, EAC is the only real alternative in agricultural applications such as greenhouses, where VAC is both inappropriate and far too costly Common commercial applications for EAC include the following: * • • * * -
Commercial kitchens Hotels and restaurants Hospitals Other institutions Laundry and dry cleaning Industrial applications Agricultural applications Poultry sheds - Greenhouses * Schools and offices * Transit buses (Figure 1.3) * Industrial applications - Warehouses - Spot cooling - Factories
ComparingVapor-Compressionand EvaporativeAir-Conditioning Table 1.1 compares the basic characteristics of VAC with those of EAC.
Outlook Worldwide, the potential for EAC is much greater than is currently realized. Investment, operation, and replacement costs can be lowered significantly by foregoing or replacing VAC technologies and using EAC.The potential applications are manifold: from buildings and homes to buses and kitchens. In some developing regions of the world where air-conditioning has scarcely arrived, EAC could bring comfort, as VAC may not be affordable by many because of its high investment and operating costs. Even where the conventional electric grid service is available, EAC may be a viable and economically attractive option, particularly in conjunction with the use of solar photovoltaic (PV) modules.
6
EvaporativeAir-Conditioning:Applicationsfor EnvironmentallyFriendlyCooling
Table 1.1.
Vapor-Compression
versus Evaporative Air-Conditioning
Basic characteristics
Coolant Production residential coolers Sensitivity to humidity for comfort cooling applications Ventilation (indoor air quality) Energy use in a typical residential air conditioner for a 100m3 room. Investment for a residential cooler
Maintenance Annual accumulated costs including power, maintenance, depreciation
Vapor compression AC
Evaporative AC
CFCs/HFCs Small and large scale Applicable in all climate types
Water Small and large scale Applicable in dry hot climates for comfort cooling 100%outside air 350 kWh/yr
20% outside air 1,000kWh/yr Developed country US$1,000-1,600 Less developed country US$600-1,400 Change filters every 2 years In USA: US$500 In India: US$500
Developed country US$200-700 Less developed country US$60-300 Annual pad change for aspen sump coat every 2 years In USA: US$170 In India: US$37
Source:Authors.
Some options expanding and realizing the benefits of EAC are noted below: Low energy use/solar. Small EAC units using solar photovoltaics (PV) are available in several commercial and prototype models. Manufacture and dissemination could be done through commercial channels providing cost-efficient cooling in grid-and non-grid settings. Transfer I of technology. EAC technologies are a fertile field for South-South transfer of technology, in particular with regard to small residential coolers and some agricultural applications. .Support possibilities. EAC has substantial applicability as a demand-side management tool, in government offices and schools. Technical assistance to developing countries, pilot programs, and demonstrations all may provide further opportunities for EAC.
Introduction
Figure 1.3. DirectEvaporativeAir-ConditionerforTransportUse
Note
he EAC unit(onthe
forklift at right) wasbut
by
imatran andisbeinginstalledontoatytransitbusinDenverColorado.
More than 400 buses in the United States and more than 1,200in Australia use evaporative air-conditioning. Source:R. Foster.
7
Opportunities and Constraints
Climatological Factors Unlike vapor-compression air-conditioning, which can work under virtually any climatic conditions, evaporative air-conditioning varies in applicability and efficiencywith the relative humidity of the outside air: that is, the drier the air, the more suitable EAC is and the better it cools. The general climatic parameters for applying EAC for comfort cooling can be superimposed on the world map in terms of three types of climatic zones that are, respectively, highly, moderately, and marginally suitable for EAC (Annex 2 contains maps showing these zones of applicability of EAC for each continent). The climate types are listed in Table 2.1, and for each type the effectiveness of EAC is indicated. This effectiveness is rather constant for desert climates, but for both the steppe and savanna climates, a generalization about applicability masks what may be significant month-to-month variations in the actual comfort derived from EAC. It should be emphasized, moreover, that this sort of zoning provides only a rough indication of suitability; each zone may contain areas that are better or worse suited for EAC than their assignment to the zone would suggest. Moreover, some specialized EAC applications (e.g., in greenhouses or poultry houses) are effective and commonly used in even the most humid of climates outside of these zones. EAC is already popular in the desert climate zones such as the arid southwestern United States, Mexico, Australia, Iran, Iraq, Jordan, Libya, Spain, Sudan, Egypt, India, Pakistan, and South Africa.These Table 2.1. Effectivenessof EvaporativeCoolingby ClimateType Climatetype Desert Steppe Savanna
Generaleffectivenessof EAC Realcomfortduring the wholecoolingseason(e.g.,offices,homes,libraries,restaurants) Realcomfortduring the dry period of the hot seasonand moderatereliefcoolingduring more humid periods Onlycan provide reliefcoolingduringthe hot season(e.g.,warehouses,greenhouses, poultryhouses).
Source:Authors.
9
10
EvaporativeAir-Conditioning:Applicationsfor EnvironmentallyFriendlyCooling
Box 2.1.
Relative Humidity and Wet-Bulb Temperature
Apart from using the rough measure of climate zones or the level of humidity, one can predict the effectivenessof EAC for a particular location fairly accurately using the locally prevailing wet-bulb temperatures (WB).Table 2.2 shows how these are measured. In brief, by adding about 5-C (9°F)to the WB,one knows the effectiveroom temperature that can be reached with EAC. Becausethe WBvaries over seasons and during the course of the day,it does not suffice to use average WB. Rather, one should consider the WB at the time when cooling is most important-for example,around noon.
areas have in common high summer temperatures coinciding with low humidity-that is, high ambient temperatures combined with low wet-bulb temperatures. This combination means that EACs can be very efficient and can provide real indoor comfort (see Table 2.2 and Box 2.1 for a range of benefits). A total of about 20 million EAC units are presently in use worldwide. EAC is largely unknown, however, in many areas with steppe or savanna climates, even though it could constitute a real alternative to VAC. Comfort Issues "Human comfort" depends on a range of factors ranging from temperature, humidity, and air movement to clothing and culture. What is comfortable for one person in one society may be entirely uncomfortable for another. Someone who has long lived without VAC may find an artificially air-conditioned environment uncomfortable, whereas people who take VAC for granted in their homes and workplaces may avoid being outside during hot weather all together. Standards
Comfort zones are often shown on standard psychrometric charts and have been developed to indicate regions where a person is "comfortable." In the United States, the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE)has developed comfort zones based on psychrometric charts. However, these standard types of comfort charts have more limited relevance related to evaporative air-conditioning. First, standard comfort zones are based on air velocities typical of vapor-compression air-conditioning systems, not the higher air velocities used with evaporative air-conditioners. Second, the traditional comfort zones used today (unlike those of the past) have horizontal, constant humidity-ratio (constant dew point) lines supposedly aimed to minimize respiratory diseases, mold growth, and similar problems. Relative humidity boundary lines are just as effective (and were previously used) and would distort comfort analysis less. Tests have shown that human comfort is a continuum, not confined between dewpoint lines. Consequently, the standard comfort zones commonly used face shortcomings relative to EAC.
Table 2.2. Wet-bulb temperature
15-210 C 21-230 C 23-270 C
Source:ECI.
Relation
between
Wet-Bulb
Temperatures
and Effectiveness Typical
Type of EAC Unit
Direct Direct Indirect / direct Direct Indirect / direct
of Evaporative
supply air temps (Dry-bulb)
17-230 C 23-250 C 22-230 C 25-300 C 23-260 C
Air-Conditioning
Cooling
effectiveness
Real comfort Moderate relief Real comfort Some relief Moderate relief
Opportunitiesand Constraints
11
TheModified Comfort Standard for Evaporative Air-Conditioning The effect of a given air stream on a person can be determined by an effective temperature chart, as is commonly used when calculating wind chill. By increasing the velocity of movement, air feels cooler.For evaporative air-conditioning, it is more reliable to consider a comfort zone bounded by relative humidity and extended to take into account the cooling effect of increased airflow, as shown in Figure 2.1.
Figure2.1. ModifiedEvaporativeAir-ConditioningComfortZone Takinginto Account IncreasedAirflow Comparedwith ASHRAE ComfortZone Basedon VaporCompressionAir-Conditioning 23.9
Wet-Bulb Temperature
(°C) 18.3
90_L_g ModifiedComlbrtZone
2i
7.2
<
AtArddt ioning
70
12.7 18.3 23.9 29.4 35.0 40.6 Dry-BulbTemperature(0C)
Source:ECI.
Actual Comfort The actual comfort derived from EAC for a given dry and wet-bulb temperature depends on the following factors: * Saturationeffectivenessof the evaporativeair-conditioner.Only if the saturation effectiveness is 100 percent can the temperature of the air leaving the air-conditioner be equivalent to the wet-bulb temperature. This depends on the condition and quality of the medium, heat losses from the motor, fan, and pump, and heat absorption through exposure of the air-conditioner cabinet to direct solar gain. Typicalsaturation efficienciesare between 60 and 90 percent for commercially available media. * Heat absorptionof the spaceto be cooled.This depends on exposure of walls and roof to solar gain, shading, number, size, and location of windows and construction materials. * Heatgenerationin the space.Number of people present in the room, their activity and the presence of heat generating equipment such as copy machines, stoves, television, and computers. * Sizing of the EAC unit. * Properinstallationand airflows.Cooled air should be properly divided and directed so as to most effectively "wash" the space and occupants to be cooled. * Activity of the occupants.Sedentary people require less cooling than physically active persons. EACmay only be the only realistic way to provide a high level of comfort for every day of the year in many desert climates. In some locations, EAC maybe acceptable for users willing to experience less than full comfort from the EAC for a few hours on the hottest days of the year because the slight discomfort does not outweigh the extra costs associated with VAC.
12
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Expected Performance of Evaporative Air-Conditioning The expected performance for both direct and indirect/direct EAC units commonly found in the market for selected locations worldwide is given in Table 2.3.
Table 2.3. EvaporativeAir-ConditioningPerfornancein SelectedLocationsat 1 PercentCoolingDesign Conditions Location
1% designconditions DB/WBa
Directsupply Air DBb
Indirect/Direct Supply Air DBC
Asia/Pacific Alice Springs, Australia
39.4/20.0
22.9
17.6
Beijing,China Bangalore, India Christchurch, New Zealand Melbourne, Australia Kabul, Afghanistan Singapore, Singapore
35.0/23.31 35.5/23.3 27.8/17.8 34.4/20.6 36.7/17.8' 32.2/26.1
25.1 25.2 19.3 22.6 20.6 27.0
22.1 22.2 16.4 18.9 15.6 25.6
43.9/20.0 36.1/18.3 33.3/17.2 38.3/16.7
23.6 21.0 19.6 19.9
17.1 16.1 15.0 13.7
38.9/23.3la 34.4/21.1la
25.6 23.1
22.1 19.0
35.6/20.0
22.3
18.2
28.9/20.0 32.2/19.4 28.9/20.6 29.4/20.6
21.3 21.4 21.8 21.9
19.0 17.9 19.7 19.7
35.6/20.0 33.9/15.0 35.6/16.1 42.2/18.9 38.9/23.9 33.9/18.9 28.9/15.6 37.8/17.8'
22.3 17.8 18.1 22.4 26.1 21.1 17.6 20.8
18.2 12.2 13.3 16.1 22.2 17.2 13.9 15.2
Middle East Riyadh, Saudi Arabia Ankara, Turkey Jerusalem, Israel Tehran, Iran
Africa Cairo, Egypt Casablanca, Morocco
Europe Madrid, Spain
South/CentralAmerica Cali, Colombia Santiago, Chile Caracas, Venezuela San Jose, Costa Rica
NorthAmerica Los Angeles, California, USA Denver, Colorado, USA Albuquerque, New Mexico,USA Las Vegas,Nevada, USA Dallas, Texas, USA Guadalajara, Mexico Mexico City, Mexico Ciudad Juarez, Mexico
a. Temperatures in °C, 1%Dry-bulb/Mean Coincident Wet-bulbdesign conditions (ASHRAE). 1. 1%design dry bulb condition and 5%design wet-bulb condition (U.S.Army). la. (ASHRAE). b. Direct saturation effectivenessof 85% is assumed; dry-bulb supply temperature °C. c. All casesassume an overaUperformance factor of 65% for the indirect process and asaturation effectivenessof 85%for the direct process; dry-bulb supply temperature 'C. Source:ECI.
Opportunitiesand Constraints
13
Power Supply The power requirements for EAC units can range from 100Wfor the smallest units to more than 1,000W for the larger packaged sizes. Because a packaged EAC unit has a low-mass fan and a centrifugal water pump, it creates little demand for extra current during start-up. This means that if the unit requires a current of 1 amp for operation, a power supply of 1 amp is also sufficient for starting. In contrast, a VAC of, say, 1,200Wand 5 amps would require a starting current of at least 10 amps. In developing countries where power demand often exceeds the supply, voltage drops are not uncommon. This is detrimental to VAC units because the compressor motor has to supply a constant torque and may draw too much current and burn its windings. EAC units on the other hand are much more tolerant of voltage fluctuations because both the fan and the centrifugal pump draw less current at lower voltage and thus simply run at a lower speed without overheating. Water Supply The water consumption of most packaged EACunits varies from 5 to more than 100liters per day depending on cooler size, ambient temperature, relative humidity, and operating hours. The units can be directly connected to the main water line, controlling the water feed through a float valve, or they can be manually filled for smaller indoor units. Accessto a water supply is a prerequisite for EAC.The units with automatic water feed can make do with a relatively smallreservoir,but the manually filled units use a larger reservoircapacity commensurate with the water consumption so as not to require refilling more than once or twice a day. Advantages of Evaporative Versus Vapor-Compression Air-Conditioning EAC has several significant benefits over VAC (Table2.4 summarizes the comparative benefits). For one thing, EAC consumes significantly less energy than VAC. The only power-consuming components of a direct evaporative cooler are fans and small water pumps; in contrast, VACs and heat pumps are more complex, having more fans and a compressor (see Figure 2.2 for a summary of use by VACs).People living in dry regions that require cooling thus can realize large energy (and cost) savings by using EAC instead of VAC systems. As noted, the energy savings of EACs vary with humidity levels and temperatures. Direct systems in low humidity regions typically yield energy savings of 60 to 80 percent over VAC systems. Indirect/direct systems yield 40 to 50 percent energy savings in moderate humidity zones (Figure 2.3). Indirect systems with vapor-compression second stages can provide adequate comfort cooling in high-humidity zones with savings of up to 25 percent. Table 2.4. Benefitsof EvaporativeAir-ConditioningVersusVaporCompressionAir-Conditioning Item Power consumption
Indoorair quality Refrigerants Maintenance Fabrication Pollutionemissions Waterconsumption Localemployment
Source:Authors.
EAC 50to 70%Lowerthan AC Muchbetter using100%outsideair Water Annualpad changefor aspen, fiveyear pad changefor cellulose Simple No CFCemissions lowerpower plant emissions High (evaporationand bleed-off) High for fabrication,distribution, installation,and maintenance
VAC High Poorwith 20%outsideair CFCs,HFCs,HCFCs Bi-annualfilter change Moderatelycomplicated CFC,HFC,HCFCemissions high power plant emissions Moderate(waterneededat the power plant) Moderatefor fabrication, high for distribution,installation, and maintenance
14
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Figure 2.2. Annual Energy Use Summary: Vapor CompressionAir-Conditioning (SEER = 9.5for Phoenix, Arizona, USA) 12,000
s
-
10,000
E
8,000
2
6,000
>,
4,000
NbO
2,000 0 Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Month
*
Natural gas
Electricity
Source:ECI.
Figure 2.3. Annual Energy Use Summary: Indirect/Direct Evaporative Air-Conditioning (2,000 scfn,for Phoenix, Arizona, USA) 12,000 ,_ 10,000 8,000 >
6,000
b
4,000 2,000 0 Jan
Feb
Mar
Apr
May Jun
Jul
Aug
Sep
Oct
Month
Natural gas Source:ECI.
*
Electricity
Nov
Dec
3 Economics
In general, evaporative air-conditioners are much less expensive to purchase and operate than vaporcompression air-conditioners. It must be noted, however, that these two cooling technologies must be compared with care because VACcan always provide full comfort (provided the unit is adequately sized for the load and the owner is willing to pay the electric bill), but EAC cooling depends on local climatological conditions. Thus it is only in settings where both EAC and VAC can provide comfort cooling that a true comparison can be made. Beforedelving into the economics of EAC and VAC, it is worth enumerating several elements that play a role in the economics of both types of cooling: * * • * * *
Cost of the cooler Cost of installation Length of the cooling season Cost of electricity Cost of water Interest rate.
Economics of Residential Coolers Worldwide, the most widespread EAC applications are small- and medium-sized packaged residential coolers. More than 20 million residential units are installed around the globe. They are produced in different ways. In India, small enterprises use a labor-intensive production process (1 million units a year are manufactured by some 300 to 400 enterprises in New Delhi alone). These "desert coolers," made of sheet metal, wood fiber pads, and a simple pump, find their way onto the market either as finished products or as kits and are transported and installed all over India. The other fabrication techniques are more sophisticated. For example indirect-direct EAC production in Australia and the United States use coated sheet metal, plastics or fiberglass, efficient cellulose paper pads, computerized thermostats, and bleed-offs. These units are marketed with glossy brochures and exported to a number of countries. Prices vary as much as production. In India, the smallest coolers are about US$35 and the largest US$150or more. In Australia and the United States, direct EAC outdoor units sell for US$300to US$700,and simple
15
16
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
indoor units are available for US$40 and up; however, the largest and most expensive units sell for more than US$1,200. The investment cost for a direct-indirect system is roughly double that for a direct EAC unit (and in fact approaches the level as VAC). However, the direct-indirect EAC's power consumption is only about 25 percent higher than direct EAC on an annual basis, and the total cost of electricity and maintenance for indirect-direct EAC systems amounts to only about 50 percent of that of conventional VACs of comparable performance. Investment
Costs
Figure 3.1 compares typical total investment costs of EAC and VAC systems for different room sizes (20, 60 and lOOm2 ) for the United States. In all cases EAC is the cheaper option.
Figure 3.1. TypicalInvestment Costsfor EvaporativeAir-Conditioningin the United States 2,500 ,
2,000-
-
1,500
E
1,000,
-
_
500-
20 EAC
20 AC
60 EAC
60 AC
100EAC
100 AC
Room size in sq m for EAC and AC
ES Installationcost
Costcooler
Source:R. Foster.
It is striking that although the cost of EAC coolers in the United States is low, the cost of installation is relatively high, because of the labor involved in placing the cooler, connecting it to water and electric power sources, and providing a drain for the flush water. The same has been done for India in Figure 3.2. Here the difference between EAC and VAC is much
more pronounced because EAC units are made by small wayside industries at very low cost, whereas VAC units are either imported or made by large, inefficient industries at much higher cost. The cost of installation in India is low because labor is cheap. These typical investment costs for India and the United States illustrate that the relative economic merits of EAC are more pronounced in devel-
oping countries than in the industrialized world. Life-Cycle Costs
The life-cycleand operationalcosts have alsobeen analyzedfor these two countries,as depictedin Figures 3.3and Figure3.4.
Economics
Figure 3.2.
Typical Investment
Costs for Evaporative Air-Conditioning
in India
1,000800
Cei-
600 400 -
i
2000
20 EAC
20AC
60 EAC
60 AC
100EAC
100AC
Room size in sq m for EAC and AC Installation cost
Cost cooler
Source:R. Foster.
Figure 3.3. States
Typical Life-Cycle Costs: Evaporative Air-Conditioning
versus Air-Conditioningfor
the United
6,000 ,5,000
m)
4,000
8
3,000 2,000 1,000 0 20 EAC
20 AC
60 EAC
60 AC
100EAC
Room size in sq m for EAC and AC *
Depreciation
D Interest Source:R. Foster.
2
Energy
n Maintenance
Water
100AC
17
18
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Figure3.4. TypicalLife-CycleCosts:EvaporativeAir-Conditioningversus Air-ConditioningforIndia 6,000
-_
-
5,000-
rA
4,000
8 3,000 2,000 1,000 0-
,
,
20 EAC
20 AC
60 EAC
60 AC
100EAC
100 AC
Room size in sq m for EAC and AC *
Depreciation
D:Interest
E
Energy
n
Water
Maintenance
Source: R. Foster.
For the calculation of the operational costs it was assumed in all cases that the maintenance is done by a hired professional, which explains the rather high annual maintenance cost for EAC in the United States. In reality, however, many EAC owners do their own maintenance because it is easy and saves money. In developing countries where labor is cheap, maintenance is generally done by professionals. In India, for example, it is common for owners of EAC units to have a maintenance contract with an EAC dealer. Market Situation At least 20 million residential EAC units are in operation worldwide. Of these, some 8 to 10 million are in
India, and more than 4 million are in the United States. Other significant markets also exist in Australia, South Africa, Pakistan, and Saudi Arabia. EAC also has significant market potential in many other areas of the world (e.g., in the Sahel); yet in most of these areas, EAC technology is unknown. A significant reason why EAC units are not in operation in more areas around the world is that half or more of the world's population lives in coastal regions, or within 100 kilometers of coasts, and these areas are typically humid and hence generally not the most favorable sites for EAC units. In contrast, the most favorable climatic conditions for using EAC are in dry and hot desert regions, and these are comparatively sparsely populated. Population differences notwithstanding, sufficient populations live in dry and hot regions to constitute meaningful markets for EACs. In the United States, for example the current sales of direct EACs are more than US$150million per year. Moreover, the recent growth of the U.S. EAC market has been significant, with annual increases of 10 percent reported by manufacturers. California, which traditionally has used VAC, represents one of the world's fastest-growing EAC markets. The California Energy Commission (CEC), noting the 50 to 80 percent energy savings possible with EAC (as opposed to VAC)technologies statewide, adopted energy credits for EAC as part of the Title 24 code compliance program in January 1993.Inclusion of EAC in the Title 24 program facilitates significant prospective growth of the industry in California. The CEC is also promoting an EAC
Economics
19
commercialization program that seeks to accelerate adoption of EAC to maximize its energy saving, environmental, and economic development potentials. Several California utilities are promoting EAC for commercial and residential applications as well. Pacific Gas and Electric (PG&E) offers rebates for commercial use of evaporative cooling equipment. Under the utility's customized program, hybrid and two-stage EACs can receive a US$200/kW reduction as replacements for VAC technologies. PG&E also offers a line-item rebate for the installation of commercial evaporative cooling equipment at US$80per ton displaced of VAC for new construction as part of a "Retrofit Express" program. Locally in California, the Sacramento Municipal UtilityDistrict (SMUD)has a new construction rebate program that provides rebates to EAC in the commercial sector based on calculated energy savings compared with conventional cooling. In late 1992Southern California Edison began offering US$100rebates for installation of residential EAC (direct and indirect-direct) in their service territory. The company has promoted these rebates actively in desert locations, offering an incentive of US$125for replacement of residential VACunits with EACequipment. Southern California Edison also provides and maintains EACs at no cost to qualifying low-income residents in their service area. On the commercial front, the company is interested in energy conservation in the retrofit market and offers rebates at US$75 per ton for direct EAC and US$100per ton for indirect-direct EAC for displaced tonnage of VAC(they use 1,250cfm = 1 ton cooling).About 30 to 50 commercial installations are taking advantage of this program each year. The State of New Mexico is requiring the use of EAC (mainly indirect-direct systems) instead of VAC systems in new public schools and additions. New Mexico places about 100 new EAC applications per year in schools. The Stratospheric Ozone Protection Division of the U.S. Environmental Protection Agency (EPA)has included EAC as an acceptable technology in the EPA's Significant New Alternatives Policy (SNAP) rulings on alternative refrigerants and technologies. This should further encourage the adoption of EAC technologies in the United States. Greenpeace and other environmental organizations are advocating EAC as an environmentally responsible technology worldwide. This type of interest from environmental organizations should also further global market development. The greatest market development problem facing the EAC industry currently is the lack of a normalized test standard for performance ratings. Saudi Arabia and Australia have some limited general test standards. However, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)standards committees on EAC have submitted a proposed test standard for testing indirect evaporative air conditioning equipment adopted by ASHRAE in 1996. Similarly, a proposed ASHRAE test standard for direct EAC units should be adopted in 1998.When these standards are adopted, the industry worldwide will benefit from a proposed certification program for rating EACs based on the ASHRAE test standards by the Evaporative Cooling Institute. This certification program will provide design engineers worldwide with an independent performance-based test standard for rating EACunits. The EAC market should continue to grow worldwide as interest from utilities and countries increases in applying the technology as an energy conservation tool. Given advances with indirect and hybrid systems that widen the climatic range of application, the potential market penetration of this technology is large. Indeed, when coupled with desiccant technologies, EAC could displace VAC technologies in many applications in the coming century.
4 Technology
Direct EvaporativeAir-Conditioning A residential evaporative air-conditioner consists of a cubical box with large, vertical filter-like "pads," a sump at the bottom, an electric-motor-driven fan, a water pump, and a water distribution system (see Figure 4.1). The fan draws in warm outside air through the wet pads, cooling the air. The water pump lifts the water from the sump through the distribution system on top of the pads from where it trickles down by gravity back to the sump. The cooled air is then delivered either directly through a grill into a single room or into a duct system to cool more than one room. This is a "direct" evaporative air-conditioner in which the cooled and humidified outside air flows to the room and removes the heat. An efficient wetted pad can reduce the air temperature by as much as 95 percent of the wet-bulb depression (ambient dry-bulb temperature less wet-bulb temperature), while an inefficient and poorly designed pad may only reduce this by 50 percent, or worse. A simplified process diagram for direct evaporative air-conditioning is shown below. There is actually very little change in energy state of the air (i.e. there is no sensible cooling) other than energy inputs from the fan and makeup water. Direct EAC is simple and cheap but it has the disadvantage that if the ambient wet-bulb temperature is higher than 21°C(69.8°F),the cooling effect is not sufficient for indoor comfort cooling. The saturation effectiveness of a direct evaporative air-conditioner best describes the performance of the unit. Saturation effectiveness is defined as the difference between the entering and exit dry-bulb (DB) temperatures over the wet-bulb (WB)depression and can be defined as follows: Saturation effectiveness = DBI - DB2 DB, -WB1 where DB1 = Entering (typically ambient) dry-bulb temperature DB2 = Exiting dry-bulb temperature WB1 = Entering (typically ambient) wet-bulb temperature 21
22
EvaporativeAir-Conditioning:Applicationsfor EnvironmentallyFriendlyCooling
Figure 4.1.
Simplified Evaporative Air-Conditioning Process Dry air
Water
Moist air
Latent energy 35 0 C
Latent.
e..
energy
DB
Heat needed
:::.
to evaporate
Sensibl energy
water
Direct evaporative
~~~cooler 210 C
heat
D
Water
ha
You feel 21°C
Sensible and latent heat energy
You feel 35°C
Sensible heat in the air is used to evaporate water (transfered to latent energy in the moist air) Source:Authors.
A psychrometric chart, which shows moist air properties, more clearly demonstrates the evaporative cooling process. The initial dry-bulb and wet-bulb temperatures are shown at the start of the process, and the endpoint of the evaporative cooling process is found to the left at the end of the arrow along the line of constant wet-bulb temperature. For example, taking 1 percent design conditions for Ciudad Juarez, Mexico, of 37.7°C (99.9°F) dry-bulb temperature at a mean coincident wet-bulb temperature of 17.7°C (63.9°F), and using evaporative media that has a saturation effectiveness of 85 percent, we find that the evaporative media will change the state of the airstream to a dry-bulb temperature (supply air) of 20.7TC (69.3°F). This process is shown in Figure 4.2 for Ciudad Juarez.
Figure 4.2.
Psychrometric Processfor Direct Evaporative Cooling, Mexico
20.70 CDB for S.E.=85% a
/4/ /
//
\
Evaporative ~~~Direct \ti~~Coling Process
Cd. Jukrez, Mexico 37.7 DBJ17.7°C WB
Dry-Bulb Tempearture °C
Source:ECI.
oa +;o 0
i 2
Technology
23
Direct evaporative coolers do not recirculate air in applications. Instead, air is passed only once through the system and then exhausted. This leads to superior indoor air quality. Evaporative cooling media also act as a wetted filter that scrubs out many contaminants (see also Figure 1.1). Pads The pad-or medium, as it is often called-serves to bring the water and air into contact so that the air can absorb moisture and lower the dry-bulb temperature (cooling effect). An ideal pad should have the following characteristics: * * * * * * *
Minimum resistance to airflow Maximum air-water contact for vaporization Equal distribution of airflow resistance, air-water contact, and water flow Resistance to chemical or biological degradation Ability to self-clean airborne matter Durability and consistent performance over life-cycle Low cost.
In reality, all pads fall short of this ideal and thus require some trade-offs among advantages. There are at present three major types of pads: aspen (or other similar type) wood, rigid pads, and synthetic pads. Each has its own advantages and disadvantages. Aspen Wood Pads. These pads are composed of thin shredded wood slivers, packed loosely to a thickness of 3 to 5 cm. This material is spread equally over the pad-holder surface and held in place by a flexible steel or plastic grid. The thin wood strands absorb water and ensure good diffusion of the water over the surface of the pad, which gives it sufficient cooling characteristics. This good cooling, combined with the very low cost (US075per replacement pad) has made aspen wood the most popularly used pad material worldwide. Aspen pads have some serious deficiencies in performance and durability, however. First, because wood is an organic material, it degrades fairly quickly in humid conditions. In application, this means that the strands decrease in strength and sag under the weight of the water they have absorbed. T'he sagging means that some areas of the pad become more compact, blocking the airflow, while other areas become more open, increasing airflow at the cost of reduced saturation efficiency.This combination leads to reduced cooling.Moreover,dust, pollen, and other airborne organic or inorganic matter are trapped between the strands of the pad, increasing resistance to airflow and imparting unpleasant odors to the cooling air if the pad is not properly dried during daily use. Similarly,when the EAC is turned off and the remaining water in the pad evaporates, it leaves behind a deposit of minerals, called scale. This scale is not completely dissolved when the unit is restarted and it impairs the airflow and blocks the pad. Depending on the intensity of usage, the level at which mineral concentrations are controlled (adequate bleed-off), and the outside air quality (quantity of dust in the air) aspen pads may be replaced once a cooling season or sometimes after two cooling seasons. Even so, optimum performance of the EAC may only be achieved in the first weeks after installation of pads. A properly packed pad may start with 70 percent saturation efficiency but may decline to 50 percent efficiency after only a few weeks, operating at that level or less until it is replaced. Another problem with aspen wood pads is their sensitivity to installation technique. That is, the pads must be installed so as to ensure that the woody material is spread in equal density across the pad's total area. If this is not done, the saturation efficiency will be reduced from the start. Because replacement of pads is needed regularly and appears to be a relatively simple task, many EAC owners will do it-with varying results in terms of efficiency-themselves. Rigid Pads. Rigid pads became available in the early 1980's. They are made of a specially impregnated type of paper or glass fiber and typically use a honeycomb type structure. They are made of strips of corrugated paper alternative with upward and downward slopes, cemented together where the corrugations touch (Figures 4.3 and 4.4). This arrangement eliminates most of the problems associated with aspen wood because rigid pads have the following advantages:
24
EvaporativeAir-Conditioning:Applicationsfor EnvironmentallyFriendlyCooling
Figure 4.3. Commonly Available Rigid CellulosePads Provide Superior Saturation and Cooling Compared with Ordinary Aspen Pads
Source: Munters Corporation.
Figure 4.4.
Close-up of Rigid Cellulose Pad Made of Corrugated Paper
Source:Munters Corporation.
* * * * *
Long and fairly constant service life between three and seven years, depending on maintenance Largely self-cleaning (i.e., dust washes off) No biological deterioration of the pad material More consistent saturation efficiency of about 75 to 90 percent Low pressure drop across the pad.
The disadvantage is that rigid media are more costly (about US$100more on an EAC that would cost US$300if using aspen wood pads). They are also bulkier, which makes them difficult to use in smaller units. At present, about 25 percent of the EACs sold in the United States are fitted with rigid pads, a share
Technology
25
that is growing. In fact, some U.S. manufacturers expect that eventually most EACs will be fitted with rigid pads because of their performance advantages over aspen pads. OtherPad Materials. In a bid to improve on aspen wood, some manufacturers are supplying pads made of woven plastic. The plastic pads avoid many of the disadvantages of aspen wood but have the disadvantage of poor cooling efficiency because of the poor wetting characteristics (low saturation effectiveness) of the plastic material. Other substances have been tried as pad materials such as woven expanded paper, fabrics, wood wool made of pine, fir, cottonwood, cedar, redwood, spruce, plain and etched glass fibers, copper, bronze and galvanized screening, but none of these are extensively used. Country-SpecificPad Materials.In each country where evaporative air-conditioners are used or are intended to be used it may be advisable to look for an inexpensive and easily available indigenous pad material-such as Khus-khus grass in India-or a long-lasting alternative such as a rigid pad. The objective, of course, is to avoid the need for continuous large-scale shipment of pad materials such as aspen wood from the United States or Australia or if corrugated paper from Europe. Cabinet The cabinet of the air-conditioner is usually made of hot dip galvanized steel, coated with baked on high quality paints (see Figure 4.5). Corrosion can be a problem with drip air-conditioners because most parts come into contact with highly oxygenated water and concentrated solutions of waterbome or airborne chemicals. To eliminate corrosion problems some manufacturers supply stainless steel air-conditioners and some others air-conditioners made entirely of polypropylene, polyurethane, or glass fiber. In Australia at least one manufacturer brings an aluminum air-conditioner on the market. Stainless steel air-conditioners are expensive and very sensitive to electrolytic corrosion (one screw of the wrong material may cause corrosion of the whole air-conditioner) and glass fiber or plastic models are subject to deterioration due to ultraviolet radiation. If galvanized steel cabinets are cleaned and repainted inside after every season, they should last 10 years or more. Fan and Motor Small air-conditioners (up to 55m 3 /min of washed air), serving only one or two rooms are often fitted with an axial propeller type fan. These fans, with 2 to 4 blades, operating at 900 to 1,400rpm are noisier than centrifugal types but are about twice as efficient. For higher airflow resistance, as is usually the case for larger air-conditioners delivering air to a duct system, centrifugal fans are more suitable. They are very quiet in operation but the efficiencyis only half of that of an axial fan. Axial fans are usually fitted directly on the motor shaft but centrifugal fans are belt driven and geared down to roughly 1/3 of the motor speed. In general it can be said that the larger the fan and the lower the speed the more quiet it is. The motors for most residential air-conditioners are two-speed, single-phase, shaded-pole and fourpole types in the range of 200 to 1000W.They should have a drip proof construction and a 50°Callowable temperate rise, certified by some recognized authority. More advanced designs are beginning to incorporate variable speed motors. Recirculation Pump The most popular pump is a small submerged centrifugal pump driven through a vertical shaft from an air-cooled motor mounted dry above the waterlevel in the sump. These pumps are inexpensively made (US$15retail price) and may last no more than three to five seasons. They require no maintenance but can be vulnerable to dry running. The capacity is generally not more than 20 1/min against a head of about lm. In many cases there is a small outlet besides the pump discharge for the purpose of continuously
26
Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling
Figure4.5. CommonCabinetsforResidentialCoolersin India
Photo: R. Foster.
bleeding off some of the water circulated to prevent an excess concentration of minerals in the water. To combine this bleeding off with operation of the pump limits the loss of water during operation only. Controls
Direct-drip air-conditioners can generally be run on two speeds, with or without the pump. Operating the air-conditioner without the pump can be desirable when the outside humidity is too high for effective cooling but ventilation still provides some comfort. In the United States and Australia many EACs are now also supplied with an indoor thermostatic control to stop the unit when it gets too cold and start it when it gets too hot. The air outlet of either the air-conditioner or the duct is usually fitted with a bidirectional set of louvers to control the direction of the airflow.
Indirect-Direct EvaporativeAir-Conditioning A two stage air-conditioner combining indirect and direct processes is gaining popularity in the United States in places where the higher wet-bulb temperatures (i.e.,higher ambient humidity) does not permit sufficiently low indoor temperatures from a simple direct air-conditioner. In this system the outside air is precooled in an indirect stage and then further cooled in a subsequent direct stage. The first stage cools the air without adding moisture and in the second stage moisture is added. The result is that the final air temperature leaving the air-conditioner is generally 3.5 °C lower than what could be achieved with a direct air-conditioner only. This expands the application of evaporative air-conditioning considerably to areas with slightly higher wet-bulb temperatures. Commonly 65 percent indirect stage efficiency (performance factor) is reached which allows an ambient wet-bulb temperature of up to 25°C to provide low enough room temperature for real comfort (see Figures 4.6 and 4.7 for pictures of direct and indirectdirect evapoative air-conditioning). The investment cost is however roughly double that of a direct air-conditioner (nearly the same level as for refrigerative air-conditioning) but the power consumption is only about 25% higher on an annual basis than for direct air-conditioners. The total cost of electricity and maintenance for indirect/direct systems amounts to roughly 50 percent of that of vapor-compression for the same performance.
Technology
27
Figure4.6. Cutawayof a DirectEvaporativeAir-Conditioning
Key 1:galvanized and painted steel (or sometimew plastic) housing, 2: louvered pad frame for air-inlet,3: blower wheel and shaft 4: water distribution system (header), 4: motor with belt driven centrifugal fan, 5: thermally protected water pump with bleed-off, 6: extra finish is good against rust, and 7: float valve, also overflow and bottom drain are located in the water sump. Source:ECI.
Figure 4.7.
Plate-Type Indirect-Direct Evaporative Air-Conditioning
Conditioned SupplyAir
SecondaryOutside Air Pad
uts Secondary Outside Air Exhaust Source: ECI.
Air
28
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Many buildings in drier regions that use vapor-compression air-conditioning can replace it with indirect/direct evaporative air-conditioning systems to provide comfort cooling. Residences can also benefit in these regions by employing indirect/direct evaporative cooling as well. One potential problem for retrofit situations is that existing building or residential ducts may be inadequately sized for the increased airflow delivery required by indirect/direct evaporative coolers over vapor-compression systems. For indirect systems, typically a secondary (or scavenger) airstream is used in which the evaporative cooling takes place. One method of doing this is based on using coils with water that has been evaporatively cooled. Water evaporatively cooled through a cooling tower is circulated through a heat exchanger. The supply air to the space is passed over the other side of the heat exchanger. If the evaporatively cooled water is colder than the supply air passing over the heat exchanger fin, than the supply air will be cooled without the addition of moisture to the airstream. The heat removed from the airstream raises the temperature of the water which is returned to the evaporative cooling process to be cooled again through evaporation of some of the water. Obviously, by adding the heated water to the evaporative cycle from an external source this is no longer an adiabatic process. Another common method used employs air-to-air heat exchange, one side of which is wetted. The evaporative cooling occurs on the wet-side and heat is transferred from the conditioned airstream on the dry-side. Figure 4.8 shows a typical type of indirect/direct evaporative air-conditioning system using a plate heat exchanger. The first stage (indirect) sensibly cools the air, which is then passed through the second stage (direct) which evaporatively cools the air. Figure 4.8.
Indirect-Direct Evaporative Air-Conditioners on a Public School Rooftop, Colorado Springs, USA
Source:Norsaire Systems, Inc.
Performance of indirect evaporative cooling is measured by the performance factor which is the ratio of the reduction of the dry-bulb temperature of the dry-side airstream to the initial difference between dry-side dry-bulb and wet-side wet-bulb temperature. The performance factor is affected by equipment size and effectiveness, as well as overall air and water quantities. Industry ratings are normally based on a specific ratio between dry-side and wet-side air quantities. Performance factor =
DB, - DB2 (dry-side) DB1 (dry-side) - WB1 (wet-side)
The indirect process is shown as a sensible cooling process on the psychrometric chart (the identical process for vapor-compression refrigeration). This process follows a line along a constant humidity ratio since no moisture is introduced in the indirect stage. Often a direct stage is introduced after the indirect
Technology
29
stage, and sometimes several indirect stages can be used to further enhance the sensible cooling effect. Some larger commercial units are designed to use the building exhaust air coupled with evaporative cooling on the heat exchanger to provide even better performance. Figure 4.9 shows an indirect/direct evaporative cooling process for Ciudad Juarez, Mexico for 1 percent design conditions of 37.7°C(DB)/ 17.7°C(WB).Whereas when only a direct stage a supply air temperature of 20.7°Cwas possible, adding an indirect stage with a performance factor of 65 percent followed by an 85 percent effective direct stage yields a final supply air temperature of 15°C(DB),which is 5.7°Cless than a direct stage alone. Figure 4.9. Indirect-DirectEvaporativeAir-ConditioningProcess
~~~~~~~al
//
{//
~~ ~
0
~~~~~~~~~~~E
<
151C DBfor /
j~~~~~~~~~lndrc 4,
Process IdDirect P
Process
r
Cd.Juirez, Mexico 37.7DB/17.7°CWB
E
.
Dry-BulbTemperature 'C
Source:ECI.
Desiccant Cooling Evaporative air-conditioning can be coupled with desiccant technologies to expand the range for comfort cooling applications. A desiccant assisted evaporative cooling system is used to dehumidify the ventilation air first with the desiccant to a desired state, and then to use evaporative cooling (either direct or indirect or a combination thereof) to cool the air to the desired supply temperature. Processes developed use either liquid (e.g., trimethylene glycol) or solid (e.g., silica gel) desiccants. Desiccants do not have the environmental problems associated with CFCs. The desiccant must be reactivated with a low grade and inexpensive thermal heat source such as natural gas, solar, geothermal, or waste heat. A desiccant combined with an evaporative air-conditioner provides sensible cooling that can meet cooling comfort needs even in the most humid environments without use of CFCs.A typical desiccant assisted evaporative cooling cycle is shown in figure 4.10.Thermal COPs of 2.0or higher, with an EER of 35 or better for electric parasitic power (fans, pumps, wheel motors) are possible for desiccant-assisted evaporative air-conditioners. Desiccant-assisted evaporative air-conditioners have recently become commercially available in the last couple years, although no residential models exist yet. Size and costs of desiccant equipment are gradually decreasing, which should lead to general acceptance by the marketplace over time, and greater use of evaporative cooling to more humid regions for comfort cooling.
30
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Figure 4.10.
Ventilation Cycle Desiccant Cooling System Outside OUA
Air
houtsidUe air
cooler
~~~~~~~~~~~~~Supply
~~~~~~~~~hot-dry airm
E
dryair~~~~~~~~~ooer~ Air
cR°BdIEva?|Rtay moister
Exhau sHeat
Retu
Air
Source.ECI.
5 Choosing and Maintaining Equipment
Available Equipment EAC units for residential cooling are available in different configurations, sizes, and ratings. Table 5.1 gives an overview. Cooler Selection Portable Coolers. For cooling needs either inside a building or on the porch, spot cooling can be provided by a portable or trolley mounted small capacity air-conditioner. If these air-conditioners are used inside there should be sufficient ventilation to prevent recirculation of air through the air-conditioner otherwise humidity will build up and eventually nullify the cooling effect. Preferably the unit should be placed just inside an open window so that it will mostly draw in outside air, and other windows should be open to allow washed air to escape and not be recirculated. Such portable air-conditioners are sometimes sold without proper instruction and by either expecting too much or operating units incorrectly, customers may be dissatisfied. It is often common for persons whose only prior experience is with vaporcompression air-conditioning to try and incorrectly operate evaporative air-conditioners similarly. Table5.1. AvailableResidentialEvaporativeAir-ConditioningEquipment Type Portable Fixed
Spaceto be cooled
Installation
Singleroom
Window In room Window Window Rooftopor Through-the-wall
Singleroom Tworooms Home(wholehouse)
Source:Authors. 31
Capacities 15-40m3/min 15-40m3/min 20-100m3/min 40-160m3/min 80-300m3/min
32
EvaporativeAir-Conditioning:Applications for EnvironmentallyFriendlyCooling
Window Units. If a whole room and possibly a second room needs to be cooled, a window EAC unit is often used, blowing the cold air directly into the room without any ducting. Although called window units, sometimes an aperture is made in the wall of the house and the air-conditioner is fitted outside on brackets. For the same purpose an air-conditioner can be fitted on the roof and have a single straight vertical duct into the living room whence the cool air can be directed to another room by the opening and closing of doors and windows. Roof mounting is often preferred because it is generally considered more attractive than wall mounting. Home Coolers. For cooling more than two rooms with a single air-conditioner and to cool alternate not adjoining rooms, a ducting may be required and is usually placed between the ceiling and the roof. Thus, it is logical to mount the air-conditioner on the roof. A disadvantage of roof mounting is the more difficult access to the air-conditioners for maintenance. For roof mounting one should also try to avoid running water lines in the attic as to avoid potential freezing of the water lines in winter. Sizing
Rough Sizing. The capacity of air-conditioners is given in m3/min air displacement. As a rule of thumb an air-conditioner size is chosen which provides an air change in the room between once and four times every four minutes, depending on prevailing wet-bulb temperatures (higher means more airchange required), saturation efficiencyof the particular cooler (higher efficiencymeans reduced airchange requirement) and the features of the building (more heat input means more airchange required). See Box 5.1 for an example. Take for example a room with a volume of 46m3 with large window area, high sun exposure, little shading, and poor insulation. The outside air wet-bulb temperature during the hottest time of the day is 26'C. It is not possible to cool this room to full comfort because that would require a wet-bulb temperature of less than 23TC,so only relief cooling can be achieved. The highly unfavorable building features require a maximum airchange and the unfavorable high wet-bulb temperature requires the same. Consequently the air-conditioner for this room should be sized for 1 airchange per minute or an air displacement of 46m3/min. In a different situation where for the same room volume there would only be a single window, no direct sunlight on the walls through shading and trees, good attic ventilation, and an outside wet-bulb temperature 229C,full comfort can be had if the air-conditioner displaces the room air only once every 3 minutes and should thus have a capacity of 12m3/min.
Box 5.1. A SimpleSizing Example Building Size = 20 x 30 x 3 m = 1,800 m3 for 1% Design Conditions of 37'C (DB)/18°C (WB) This would imply an air change based on 18'C WB of every 4.25 to 2 minutes. A more conservative design would use an air change every 2 minutes, while the air change every 4.25 minutes would probably be sufficient for most comfort applications. 1,800 m3 /4.25 = 423 m 3 /min Recalling that the saturation effectiveness is defined as the difference between the entering and exiting dry-bulb (DB) temperatures over the wet-bulb (WB) depression, as given in the equation: Saturation Effectiveness = DB, - DB2 DB1 - WE3 where, DB, = Entering (typically amnbient) dry-bulb temperature DB2 = Exiting dry-bulb temperature WBI = Entering (typically ambient) wet-bulb temperature Assuming a unit with an 85% saturation effectiveness, the supply air temperature DB2 for this unit will be: DB2 = 37°C - (.85(37-18'C)) = 20.9'C
Choosingand MaintainingEquipment
33
Other cases are obviously in between those extremes. A room change of once per minute has been taken as the maximum because higher values will cause unacceptable drafty conditions. The bottom value of one room change per four or five minutes is because with a lower value there would be insufficient mixing of the air causing uneven cooling (i.e., cold and warm places). Using the rough method for sizing inevitably results in some cases of overcooling (need to switch off the unit earlier) and undercooling in which case (if possible) a higher capacity unit must be bought. Some manufacturers provide easy to use paperboard slide rules to aid in these estimations. Following is a recommended air change rate for differing design wet-bulb conditions:
Direct EvaporativeAir-Conditioning Recommended Air Change Rate for Design Wet-Bulb (WB)Conditions For Comfort Cooling: 15.5°CWB 17°CWB 18°CWB 19°CWB 20°CWB 21°CWB
= = = = = =
One air change every 5 to 2 minutes One air change every 4.5 to 2 minutes One air change every 4.25 to 2 minutes One air change every 4 to 2 minutes One air change every 3.75 to 2 minutes One air change every 3.5 to 2 minutes
For Relief Cooling 220C WB 23°C WB 24°C WB
= One air change every 3.25 to 2 minutes = One air change every 3 to 2 minutes = One air change every 2.5 to 2 minutes
Note that these are general air change volumes used. It is not recommended to use less than one air change every 5 minutes for most applications. An accurate method is to calculate the heat load of the structure by the same engineering principles used for refrigerated cooling. With heat loads determined, the cooling system is designed to remove them. To do this the probable washed-air temperature delivery temperature is computed from the outdoor wet-bulb depression and estimated air-conditioner saturating efficiency.If for instance the outside DB is 35°C,the saturating efficiency is assumed to be 80%and the WB22°C, than the DB of the washed air is 35-0.8(35-22)=23.6°C. With a desired indoor design temperature of 27°C, there is a heat gain of 27-23.6=3.4°C.From Table 5.2, it is shown that the heat gain falls within the recommended operating zone and that the useful sensible room cooling is then about 65 percent. Subsequently the volumetric flow of washed-air needed to maintain 27°Cindoor design temperature is calculated based on the previously established heat load i.e. amount of heat to be removed from the room per unit of time and the specific heat of the washed air. For larger structures, building computer simulation models such as DOE2.1E are sometimes used which contain algorithms for EAC for more precise sizing and an evaluation of overall system performance based on TMY or TRYclimatological data.
Maintenance As with any mechanical equipment, EAC units need to be maintained regularly if they are to perform well and last a long time. However the maintenance work is easy and the necessary spare parts and materials are usually readily available. This means that the owner can do the job and so avoids the cost of calling a professional. The majority of the owners in the USA do the maintenance themselves. In India though, where labor is cheap, it is mostly done by professionals and often they have a maintenance
34
EvaporativeAir-Conditioning:Applicationsfor EnvironmentallyFriendlyCooling
Table 5.2. UsefulCoolingChart: Percentageof UsefulCoolingforDirectEvaporativeAir-Conditioning Output Washedair temperaturegain in rooms (Roomdischargetemperatureminus roomentrancetemperature),OC Temperature gain IC air enteringcooler (WB depression'C)
1.7 (%)
2.2 (%)
2.8 (%)
3.3 (%)
3.9 (%)
4.4 (%)
5.0 (%)
6.7
31
42
52
63
73
84
94
7.8
27
54
63
71
80
5.6 (%)
6.1 (%)
89
98
6.7 (%)
7.2 (%)
7.8 t%)
8.3 (%)
8.9 (%)
8.9
23
31
39
47
55
62
70
78
86
94
10.0
21
28
34
42
49
56
63
69
76
84
90
97
11.1
19
25
31
37
44
50
56
62
69
75
81
88
94
100
12.2
17
23
28
34
40
45
51
57
62
68
74
80
85
91
13.3
16
21
26
31
36
42
47
52
57
63
68
73
78
83
14.4
14
19
24
29
34
38
43
48
53
58
63
67
72
77
15.6
13
18
22
27
31
36
40
45
49
54
58
63
67
71
16.7
13
17
21
25
29
33
37
4
46
50
54
58
62
67
17.8
12
16
20
23
27
31
35
39
43
47
51
55
59
62
18.9
11
15
18
22
26
29
33
37
40
44
48
51
55
59
20.0
10
14
17
21
24
28
31
35
38
42
45
49
52
56
21.1
13
17
20
23
26
30
33
36
40
43
46
49
53
22.2
13
16
19
22
25
29
31
34
38
41
44
47
50
12
15
18
21
24
27
30
33
36
39
42
45
48
23.3
Drafty zone
Recommended operating zone
Uneven cooling zone
Source:Adapted from Watt (1986).
contract. The regular maintenance consists of preparing the unit at the beginning of the cooling season by fitting new pads and lubricating the bearings. At the end of the season, the sump should be cleaned out by removing the scaling and repainting the inside. The following paragraphs set out the maintenance requirements for each component and type of problem affecting EACs: Maintenance of Pads Pads typically require regular maintenance or replacement, the frequency depending on the materials, construction, and conditions of use of the unit. * Replacingaspenwoodpads.These generally need to be replaced every 6 months of usage depend-
ing on factors such as dust in the air, adequate water flow, water hardness and adequate bleedoff. In very dusty conditions filters can be used as well. These filters can be deaned and pad life extended. If the water flow is not enough or not equally distributed, dry areas can occur on the pads, accelerating the deposit of scale which can cause localized clogging and increased air velocities in other pad areas, which may lead to water being carried over with air and reaching the fan and motor, causing corrosion. * Regularcleaningof rigidpads.Rigid and some synthetic pads can be cleaned by soaking in a slightly acid solution that effectively dissolves scale deposits. If this is done every few years, such pads
Choosingand MaintainingEquipment
35
can last 7 years or more. If they are not cleaned regularly they may need to be replaced after three to five years, depending on water hardness and bleed-off rates. * Using waterbleed-offto controlscaledeposits.Substantial amounts of water are evaporated in EAC units and because the water contains minerals which are left behind during evaporation, the concentration of minerals steadily increases. If only new (make-up) water was added, the minerals would eventually increase to the point that they reached saturation and would begin to crystallize and be deposited. To avoid this, a small portion of the water is drained from the air-conditioner either constantly or at intervals. The water that is added to the air-conditioner to make up for the water evaporated is the sum of the evaporated water plus the drained-off water. Generally the amount of bleed-off is roughly equivalent to 2 to 5 percent of the total water flow,which keeps the concentration of minerals at an acceptable level. It is difficult however to give rules of thumb here because the content of minerals in the tap water varies widely from place to place. In New Delhi, India, for example, where about four million units are operational during the summer months, no provision is made for bleed-off, and reportedly a once-a-yearcleaning of the sump and removal of scale is deemed "sufficient." However, pad life clearly would be increased even in New Delhi with some small amount of bleed-off. * Scalecontrolusingchemicalwatertreatment.Chemical treatment is not recommended for pads, as it may shorten the life of the pads and may cause manufacturers to void pad warranties. In particular chemical water treatment should not be used if the chemicals could get into the supply airstream (e.g., in a direct evaporative air-conditioner). Ideally, scale control can be optimized with miiimal water consumption. However, some type of scale-management system, preferably a bleedoff, is essential for better performance and lifetime of evaporative air-conditioners media.
Maintenance of FanMotor and Pump The motor sometimes has bearings that need lubricating once a year, or comes with prelubricated and sealed bearings that require no attention. The life of the motor is generally between 3 and 6 years, depending largely on whether spray water is carried from the pad or not. Because rigid pads are less likely to clog, there is less chance of water carry over and motors last longer. Pumps are typically small centrifugal recirculating pumps that have no maintenance requirements. The most commonly used pumps are cheaply mass produced and should last several seasons, however in some countries they don't last more than one season. Replacement pumps should be thermally protected to prevent the pump from dry-running (which is a fire hazard if the pump dry runs, overheats, and catches on fire). CorrosionPrevention for Cabinets The majority of the evaporative air-conditioners are still made of coated galvanized steel. Because of the extremely corrosive properties of both the air and the water inside these air-conditioners, if left unattended, they may become extremely corroded after several years. To prevent this from happening, a once a year (end of season) clean up and inside repainting should be done. If maintained in this manner the cabinet of a well made air-conditioner can last 10 to 15 years. Plastic or glass fiber cabinets need no regular repainting but given the deterioration of these materials when exposed to UV radiation, they may not last as long as well-maintained steel ones.
6 Solar Evaporative Air-Conditioning Because evaporative air-conditioners require relatively little energy, and because the presence of strong sunshine often coincides with the need for cooling, a link between EAC and solar energy appears attractive (see Figures 6.1 and 6.2 for a schematic diagram and a picture). Only a few suppliers offer solarpowered air-conditioners, however, even in the southwestern United States, the heart of the EAC industry. Companies supplying these devices apparently aim for other markets, such as developing countries where grid electricity is not yet common. The Market It is apparent from Table 6.1 that only a very few sources are suppliers of solar EAC. Moreover, inquir-
Figure 6.1. A Solar-Powered Evaporative Air-Conditioner
Solar (PV)panel array
Evaporatingpad media Air distribution baffle
Ambient air in
Water storage with recirculating pump Axial fan
t
Supply air out
Source: ECI.
37
38
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Table 6.1. Available Packaged Solar Evaporative Air-Conditioning Equipment Supplier Jade Mountain Jade Mountain Solar Energie Technik
Type
Rated capacity
Window Home Portable
25 m3/mnin 75 m3/min 10 m3/min
Required solar Approximate cost capacity including PV modules 60 Wp 300 Wp 110Wp
US$1,400 US$4,500 US$2,500
Source:Authors.
ies of suppliers indicate that only a few units have been sold so far (probably only a few hundred, worldwide, to date). The attractiveness of solar EAC depends largely on the availability and cost of electric power. Because photovoltaic (PV) power may cost US$0.25/kWh or more, compared with US$0.10/kWh for power from the grid, PVs are most likely to be cost effective where grid power does not yet reach. Nevertheless, solar evaporative air-conditioning is a proven technology that can be very useful and efficient in such circumstances. Optimizing
Evaporative
Air-Conditioning
Design
for Solar Operation
Because of the high investment cost of solar panels (90 percent of the cost of solar EAC is the cost of the solar array), it is important that the energy requirement of the air-conditioner be as low as possible. Ordinary evaporative air-conditioners are not really designed for minimizing energy need as electric power from the grid is inexpensive. This means that for evaporative air-conditioners to be suitable for solar operation, they should really be redesigned to minimize power consumption. Important points will be the efficiency of the fan (axial rather than centrifugal), motor efficiency, reduced pad resistance (larger area) and a high-efficiency circulation pump. At present, it seems that manufacturers simply replace the AC motors with DC motors or add an inverter to make conventional air-conditioners suitable for solar power. Such measures will make the cooler more expensive but sharply reduce the investment in the solar array and thus the total system cost. Obvious areas for improving the energy efficiency of EAC for solar power are presented in Table 6.2.
Table 6.2.
Design Measures to Optimize Evaporative Air-Conditioningfor Solar Power Average efficiency
Possible improvement
Potential efficiency
Motor
50%
70%
40%
Fan
25%
50%
100%
Pump Pad
1% n.a.
Select optimal DC permanent magnet motor Replace by axial type radial type Drive from fan motor Optimize medium and reduce air velocity
4%
400% 25%
Component
Overall potential reduction in power requirements: Source:Authors.
Component efficiency gain
60%
Solar Evaporative Air-Conditioning
Figure 6.2. EvaporativeCoolerCoupledwith SolarPower(System installedby a homeownerin Chaparral, New Mexico,USA)
Source: ECI.
39
7 Introduction and Local Manufacture in Developing Countries
Maintenance Unlike conventional air-conditioners and fans, evaporative air-conditioners require simple but relatively frequent maintenance and replacement of parts. Some parts, such as the aspenwood pads, need to be replaced after 6 to 12 months, depending on the local water quality. This means that EACmarketing must be accompanied by an after-sale service network and that where sales are just being established, this after-sale network will need to be set up as well.
Installation and Sizing Another important difference between EAC as compared with fans and vapor-compression air-conditioners is that EAC requires some knowledge about airflow direction, distribution, and evacuation for the cooling to be effective. In some cases (e.g., Tunisia, Bangladesh) EACs of the spot-cooling (trolley) type were introduced, but because of lack of proper instruction they were used in closed rooms as if they were vapor-compression air-conditioners. Since EACs require outside air flow, the units did not function properly, causing general disillusionment and failure in the marketplace. The lesson is clearly that EAC must be introduced with adequate and honest information to the users, and replacement materials and trained service personnel should be ensured.
ManufacturingRequirements EAC is essentially a low technology and can be wholly or partially produced in developing countries, depending on the existing industrial base. In India and Pakistan, for example, large numbers of units are being produced entirely locally (see Figure 7.1).
41
42
Evaporative Air-Conditioning: Applications for Environmentally Friendly Cooling
Table 7.1.
Evaporative
in Manufacturing
Work Involved
Component
Air-Conditioning
Type of work
Done where
Cabinet Louvers Grill Motor
Sheet metal working Sheet metal working Sheet metal or wood Motor manufacturing
Fan
Metal stamping, aluminum casting or plastic molding
In house In house In house or purchased Buy from local supplier or import directly Buy from local supplier or import directly
Pad:
Rigid pad
Highly specialized
Wood wool or other locally available pad material
Cottage industry
Buy from local supplier or import directly Buy from local supplier
Source:Authors.
Evaporative
Figure 7.1.
Air-Conditioners
in Kamla Market,
New Delhi, India
~~~
K. Source;R.
Suc; >R .SFoser _
N-
,
1
f-._ _
~~~~A.
F-
3
Introductionand LocalManufacturein DevelopingCountries
43
Certain components are easier to make than others. Electricmotors, fans, and water circulation pumps can only be produced in countries with a reasonably large industrial base, such as India, Pakistan, and China. Yet even where such items cannot yet be made locally, they can be imported, and their source should not be of vital consequence to most manufacturers of coolers because they will be purchasing them for assembly in any case. Table 7.1gives an overview of the items that are needed for building and assembling EACs and who makes or supplies the components. It follows from Table 7.1 that the production of coolers is essentially sheet metal working, while the mechanical items are usually purchased. Such sheet-metal work can be done on a small scale and requires very little in the way of investments in machines, molds, or accommodation. In short, EACs are a good product for small-scale entrepreneurs as well as for larger industries. Know-How Although the production of EACs itself is rather straightforward, a need remains for a good design if the cooler is to work satisfactorily. A "good design" means that motor, fan, pump, and pad should be well matched to obtain good performance, energy efficiency,and cost effectiveness. This industry-specific know-how often falls short of the mark in developing countries where EAC is already popular, and it may be lacking altogether in countries where local production is yet to be initiated. Local enterprises that wish to obtain EAC know-how have basically two options: * Establish a joint venture with an EAC manufacturer in the West. * Secure training from independent experts.
8 Commercial Evaporative Air-Conditioning The principle of evaporative air-conditioning is used not only in residential coolers but also in numerous commercial installations. Direct EAC is used in commercial and industrial applications such as schools, greenhouses, buses, laundries, warehouses, factories, kitchens, and poultry houses. Direct and indirect EACs are also used to provide comfort cooling in many buildings such as schools, libraries, and offices. Commercial versus Residential Cooling Many commercial cooling applications are quite different from comfort cooling. Comfort cooling enhances the well-being of individuals living in homes, working in offices, and so on, in areas where ambient temperatures are high. The use of EAC for comfort cooling thus depends partly on the type of climate and the time of the year and partly on the needs of people for "comfort." In many commercial cooling applications a factor additional to the type of climate and the time of year may well be present. That is, the presence of an additional heat source in the form of machines, ovens, dryers, animals, and so on. In such applications, cooling systems often must be sized and designed to work for the whole year. For example, kitchens often need cooling even during winter. Another important aspect of commercial EAC, in certain places where a heat source can be cooled directly (e.g., spot-cooling in a manufacturing plant), is the air stream. Another difference between commercial cooling and comfort cooling with EAC is that in commercial applications EAC can play a significant role that VAC systems can do only with difficulty or great expense. The best example is that of cooling towers in power plants. Moreover, in some agricultural applications EAC is the only realistic alternative; in greenhouses, for example, VACwould be extremely expensive to operate. Similarly, in horticulture and floriculture, EAC is useful precisely because it adds moisture to the air. Because it is an "air-washer," EAC may have distinctive advantages in other applications as well. Although in some applications-such as in hotels, restaurants, commercial laundries, and kitchens-only the VAC options are typically considered. But managers of such facilities should compare VAC and EAC systems and assess the potential of EAC properly before making decisions on investments. EAC's advantages of ventilation and direct cooling may make it the most appropriate and effective solution. 45
46
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Commercial Kitchen Evaporative Air-Conditioning Makeup air,or exhaust air replacement, is typically needed in food service facilities-by building and health codes, if for no other reason-and EAC can be used to good effectin meeting these requirements. Proper kitchen ventilation in particular has safety implications and requires a well-designed makeup air system. In concert, EAC and makeup air systems can improve the comfort, safety,and efficiencyof commercialkitchens while affording energy savings, improving worker morale, and providing customers better comfort. Cooling Comfort Heating/cooling rooftop makeup air units provide summertime cooling to commercial kitchens through direct evaporative air-conditioning. These systems are ideally suited to commercial kitchens because they provide 100percent fresh air ventilation and cooling,requiring exhaust for proper application, rather than recirculation of air. With its large summer cooling potential of 15°Cor more, this system can increase employee comfort substantially. In many areas of the world, direct evaporatively conditioned air can be introduced through a makeup air unit into the kitchen at between 5 and 10°Cbelow outdoor dry-bulb temperatures or lower depending on ambient conditions. Cost Savings Although VACin kitchens is relatively common, it is certainly not the most efficient approach to comfort, because most of the air introduced through the VACsystem is immediately exhausted by the stove hood before it can recirculate. Thus, constantly running fresh air through a VAC substantially increases the load on the unit and requires purchasing refrigerated air-conditioning capacity well beyond what would be required for the same internal load with a recirculating system. In addition, a typical rooftop refrigerated-heated makeup air unit would be oversized on the heat mode as well and would increase the initial capital cost. By contrast, an EAC unit could supply kitchens with makeup air without water circulation through the pads when cooling was not needed. Sizing Engineers generally size the makeup air unit to match a predetermined amount of air being exhausted by the hood ventilator selected. Proper selection of a makeup air unit of the correct size (the quantity of air that can be delivered by a given unit at the necessary introduction temperature) is the key decision parameter. Temperature rise and air delivery performance vary with different units. The amount of permissible temperature rise necessary in a given application is determined by the winter design conditions for the area in question and by the desired indoor temperature level. Laundry and Dry Cleaning Evaporative air-conditioning in laundry and dry-cleaning operations cross a variety of ambient air-conditions. Evaporative air-conditioning systems perform important cooling and ventilating functions. Evaporative air-conditioning may provide features that give the laundry operator greater cost-effectiveversatility in the interior environment as compared to vapor compression air-conditioning and ventilation alone. Extreme Heat Conditions The heat levels of laundry and dry-cleaning plants are high. ln addition to the solar gain and human heat load occurring in a typical (140to 900 square meter) facility,the equipment used generates a large amount of heat. Heat levels can become unbearably high for finishing (ironing) personnel in particular. Workers
CommercialEvaporativeAir-Conditioning
47
are exposed to heated areas from steam above 80°C.Every plant has a boiler to provide steam for finishing textiles. These units in larger plants are rated as high as 5.3 to 10.5 million KJ/hour (5 to 10 million BTUh).Although boilers are walled off, at least part of their heat is added directly to the heat load of the plant. Other equipment that contributes to the heat environment includes washers and tumblers, and in dry cleaning plants some of the solvent reclamation equipment. EACs can introduce air approximating the ambient wet-bulb temperature for cooling. Some combination of spot and area EACs can reduce heat stress conditions to acceptable levels. Where temperatures are exceedingly high, such as at workstations near large boilers, shielding can be used in combination with spot cooling to reduce radiant heat. Properly directed evaporatively cooled air washing over hot surfaces can reduce radiant heat as well. The climate will determine whether the heat load or the ventilation load will require the larger capability. In moderate climates, the ventilation load may be greater than the airflow required for cooling; the opposite may be true in hot climates. Industrial Applications Evaporative air-conditioners and packaged heat/cool ventilating makeup air units combine many features which make them applicable in diverse industrial applications. EAC systems can be the most economical approach to comfort, increased equipment efficiency,and code compliance under a variety of conditions. The uses of EACs in heat treating, forging, casting, welding, milling, rolling finishing, cleaning and assemblies is also due to safety and comfort concerns for employees and government regulations pertaining to employee welfare. Direct EAC is often used to combat problems such as: * Intense heat, as in many forging, foundry and casting areas. * Low humidity, as in computer and electronic control rooms. * Airborne contaminants, as in welding, plating and cleaning areas. The hot, stagnant conditions present in many casting and furnace rooms may reach indoor dry-bulb temperatures that exceed outdoor temperatures from 100to 15'C, and may reach nearly 70°Cin some extremely hot casting areas. Molten steel at 1,300'C,must be cast by workers. In many basic metal plants where casting, annealing, forging, baking, and drying occur, shutdowns and work slowdowns are typical during summer months. In some factories work reductions and shift stoppages are required if temperatures climb too high. Some plants curtail operations or even close during the peak summer cooling periods. The reasons may be union contracts, walk-outs under hot conditions, and so on. Government regulations vary in different countries, but many countries have legally enforceable occupational heat/ stress standards. Even without government regulations, many industries attempt to relieve the problem of heat in their plants out of basic practicality. Using evaporative air-conditioning in the plant environment can help prevent mandatory and spontaneous work reductions. Spot or area cooling with EAC systems, combined with other heat-control methods such as radiant heat shielding, can effectively meet government heat/stress standards. EAC can increase summertime productivity by as much as 40 to 60 percent in plant areas too large to air-condition with vaporcompression systems. EAC is used in industries including aluminum production and fabrication;electronics assembly;power generation; shop work such as welding, plating and milling; metal fabrication and battery manufacturing. The benefits of cooling hot workers remain essentially the same in most applications: increases work efficiency,lengthened work seasons, lowered costs, code compliance and increases equipment efficiency.
FactoryAir-Conditioning Design Considerations Spot cooling is used in industrial areas where people are in close proximity to high-heat processes and cooling of the entire installation is either inefficient or extremely expensive. Spot cooling with EAC
48
EvaporativeAir-Conditioning:Applicationsfor EnvironmentallyFriendlyCooling
provides two principal benefits: evaporatively cooled air and air movement. The effect of air motion, air temperature and humidity must be combined to derive an index to worker comfort (i.e., effective temperature). Spot cooling essentially isolates the worker from the immediate hot environment by displacing hot air with a stream of cooled air. Thus, the effect on the worker is determined by the outlet air temperature and velocity. Calculations for spot cooling are based on the amount of air being delivered, the heat rise and static pressure in the duct, and the size of the outlet. All of these variables will determine the amount of comfort or relief felt by the worker. Ventilation Control
Makeup air systems, in addition to providing space cooling, help in ventilating high-fume areas and in reducing airborne contaminants in accordance with government standards. Makeup air is typically required by regulation in the design of areas containing plating tanks and paint-spray booths, for example, and it is highly recommended in all areas with industrial exhaust. Makeup air is highly recommended in all areas requiring industrial exhaust. "Air starved" buildings may not be able to provide sufficient flow to operate the hoods, spray booths, and appliances properly. Inadequate makeup air will cause drastic reductions of efficiency that will affect propeller fans and natural drafts; in some instances the flow may be reversed. In addition, some contaminated areas require a large supply-air flow to the dilution of airborne contaminants with or without associated exhaust-for example,areas using industrial solvents. When yearround air supply is needed, heating-cooling-ventilationmakeup air systems or EACs are often specified. Equipment Protection
To last and run efficiently over their design lifetime, many pieces of equipment require appropriate cooling. Again the use of EAC is a valid option, certainly when the use of vapor-compression cooling is too expensive, humidity ratio is not the limiting factor, and ventilation alone is not enough. For example, considerable waste heat is generated in power generation equipment. Whether the power is generated by gas or steam turbines (run on fossil fuel, nuclear energy, or even solar power), the temperatures of the installations in which the turbines run must be kept under 41°C, which is the maximum operating condition for the windings in common alternators. EAC may be used to keep room temperatures lower than 41°C allow generators to operate at overload outputs; the general rule is that approximately 6 percent overload capacity is available for every 4.5°C below rated ambient temperature (usually 41°C) achieved by cooling. Other types of equipment also operate more efficiently under cooler conditions. Electric motors, particularly high-horsepower units (200 HP and larger), can require direct cooling of the windings for proper operation. Agricultural Applications-Poultry Indoor confinement of agricultural livestock is a growing trend worldwide because it yields higher quality and improved productivity. The comfort and well-being of indoor livestock is also becoming of paramount importance from an ethical point of view. Environmental control of livestock housing such as poultry has become an increasingly critical technology in which EAC plays an important part. One of the most commnonareas for applying EACis in poultry houses. Of the farm buildings commonly found in the poultry business, evaporative air-conditioning improves conditions in four major types: the broiler house, the hatchery, the laying house and the processing plant (see Figure 8.1 for an overview). Better Growth Rates and Feed Conversion. Proper evaporative air-conditioning of broiler houses allows birds to achieve a weight gain of from 5 to 8 percent with a corresponding cut in the growth period of 2 to 8 percent. Closely related to poultry growth rates is the factor of feed conversion. Reduced Mortality Rates. Improved Hatch Rates, Increased Egg-Laying Rates and Egg Size. High temperatures-37°C and above-will kill poultry. EAC has been found to decrease poultry production
CommercialEvaporativeAir-Conditioning
49
Figure 8.1. TypicalEvaporativeAir-ConditioningApplicationforPoultry Houses
_ '
T
~~~~Evaporative ~~~~Cooler
FG
Evaporative b(7Cooler,'
Source: ECI.
mortality rates by 35 percent or greater. The use of environmental control with EAC in the hatcheries has been shown to improve hatch rates from 3 to 10 percent. A commercial egg-laying house, or egg ranch, depends in part on lay rate-the number of eggs laid per hen per day-for its profitability. Appropriate EAC systems have reportedly improved overall poultry egg-laying rates by as much as 15 percent increased overall quality, and boosted average egg size from 5 to 6 percent. Improved Conditions for Workers.EAC in poultry houses improves the life and comfort of the birds, as well as their overall productivity, but it also improves conditions for people working in these houses during the summertime heat. In addition, EAC provides ventilation and other benefits of particular value in the poultry environment. Greenhouses Excessive summertime temperatures can reduce plant growth and, if high enough, can kill the plants. Temperatures above 29°Cconstitute a danger to the health and growth of many greenhouse plants, and sustained temperatures above 35°Care a serious threat to most types of plant life. EAC provides significantly lower indoor air temperatures that enhance plant viability, reduce mortality, improve plant size and increase weight. Fan and Pad versus Evaporative Air-Conditioners
Evaporative air-conditioning is used in horticulture, floriculture and other high-productivity greenhouse agricultural systems, where the environmental conditions are critical for production. Basically two systems, with different areas of application, are used. Fan and pad systems have one air inlet into the greenhouse, where the wetted medium is installed and ventilating equipment on the far wall of the building (see Figure 8.2). This approach causes a significant temperature gradient from the inlet side to the ventilation side of the greenhouse because of the heat the air picks up as it travels the length of the greenhouse. The other system uses external packaged coolers that maintain a positive pressure in the greenhouse. They are installed outside the greenhouse and blow humidified air through many polyethylene ducts into the greenhouse (see Figure 8.3). The system maintains a constant overpressure inside the greenhouse, with exhaust air leaving the greenhouse at an exit louver. This approach supplies an even temperature gradient in the greenhouse, since the cooled supply air is delivered through the poly ducts throughout the greenhouse before it picks up additional heat from the greenhouse. This approach creates a more uniform growing environment inside the greenhouse than does the fan and pad system.
50
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Figure 8.2.
Evaporative Cooling Pad Section of Rigid Cellulose Pads
11
~-
I-=-
Pads shown are along west wall of New Mexico State University grower greenhouse maintained by SWTDI in Las Cruces, New Mexico.
Source;ECIL f. l
Additional Crops
_
_11
k
.
EAC can allow an extra growing season for greenhouse crops where summers normally would be too hot, thus increasing annual yields. Where shading is normally required to lower indoor temperatures during summer, it may be reduced or eliminated, depending on the crop, when EAC is used. This can Figure8.3. ExternalEvaporativeAir-Conditionerson a ResearchGreenhouse,New Mexico State University, Las Cruces, New Mexico
-.
Source:ECI.
CommercialEvaporativeAir-Conditioning
51
further increase plant yields. Increasing the velocity of air movement permits shade requiring plants to be grown at higher than recommended light levels without reducing plant quality. Uniformity among individual plants in a crop is enhanced by EAC.Variation among individual plants in a crop is reduced by lower summer temperatures. This effectbenefits commercial growers attempting to increase control over the produce they sell. Both size and the date of harvesting of a crop are more uniform. The former is a benefit in business planning, simplifyingpricing, while the latter affords the grower more control over the seasonality of the crop, allowing better matching of target dates and deadlines. Within limits, high relative humidity (RH) is good for plants; however, RH decreases as temperature rises. EAC provides two benefits to plants under these conditions. The cooling reduces heat stress on a plant, thereby reducing the need for its own "evaporative air-conditioning"-that is, transpiration by its leaves. The increased RH means greater saturation of the air surrounding the leaf, inhibiting the vaporization of water from the leaf itself. Because of the critical nature of temperature in the maintenance of healthy plants, coolingsystems that fail to maintain conditions necessary to the health and development threaten the success of a greenhouse. Fine Tuning Greenhouse Environments with Evaporative Air-Conditioning In warm climates, EAC is useful to ensure that heat-sensitive plants are maintained within safe limits. Cooling may be necessary for plant survival. In milder climates, however, EAC may be used for special greenhouse applications. If a greenhouse that is oriented to low-temperature-preferring plants is desired, EAC can be an essential component, no matter the outdoor climate. To maintain such planned environments, EACs can be operated at night or on cool days. For example, air that is 27°Cand 30percent RH can be cooled to 19°C through EAC. Even at night-when cool-house plants require 7° to 13°C temperatures-an EAC either with or without the pump operating can help maintain proper conditions.
Annex 1 Introduction to Evaporative Cooling Let us first look at the principle of evaporative airconditioning, which can be explained by way of psychrometriccharts.These charts present the moisture ratio versus the temperature, as it is registered by a normal thermometer (the dry-bulb temperature; DB),in a certain situation. The lines in Figure Al.1 connect the points with the same relative humidity RH. At a given temperature air can contain an amount of water vapor. When this amount of water vapor reaches its maximum (100 percent RH), the dewpoint is reached and the water starts to condense. The dew points are connected by the saturation line. The higher the temperature in a certain volume, the more water it can contain in its gaseous stage. In a desert this effect can explain why in the morning, when the temperature is still low, one sometirnes sees drops of water on the scarce vegetation. In the afternoon, when the temperature reaches its maximum, the air feels very dry and hot. T1hesame amount of water is in the air in terms of kilograms of water per kilogram of dry air, but the feeling it gives is completely different.
In Figures A1.2 and A1.3, the effect of EAC is explained. In the cases shown the DB temperature is 40°C, and the air is not saturated with water, RH is only some 15 percent. One can add water, and the temperature will drop until it reaches the saturation line. What happens is that the heat in the air is "absorbed" by the evaporating water. The sensibleheat is transformed into latent heat.The effect is that the temperature is lowered to 20°Cin this case. The difference between 400 and 20° is called the wet-bulb depression.The wet-bulb temperature, or WB, is registered by a normal thermometer that is wrapped in a wet sock or other piece of textile. The constantly evaporating water from the sock causes a drop of the temperature. The WB temperature is always lower than the DB temperature, except when the RH is 100 percentthat is, when the air contains the maximum amount of water it can hold at a given temperature. The WB depression line connects the points with the same enthalpy-the same amount of energy-the sum of latent and sensible heat.
FigureAl.l. Line
FigureA1.2. CompletePsychrometricChart
PsychrometricChartand Saturation Humidity Ratio kg water/kg air J .030 /
3
.025 L
Rain or
Saturation Line
< :3I'
80% 60/
.025
/-
.020 .020
25aDW
*. gi{
Point Temperature
X
.015 7.010
1... 005 15 20 25 30 35 40 Dry-Bulb Temperature °C
.005
00
5 iO 10i.005 1'5 3'5--
10
~~~~~~~~~~~~~~.02
2
.015
100%Relative Humidity .010
5
Humidity Ratio kg water/kg air 4% .030
-45005
45
50
5
Source:The Munters Corporation.
10
15
20 25 30 35 40 45 50 Dry-Bulb Temperature °C
Source:The Munters Corporation.
53
54
EvaporativeAir-Conditioning:Applicationsfor EnvironmentallyFriendlyCooling
Figure A.3.
5
s0J
Wet-Bulb Depression of Ambient Air
lc 15
25
30X
Dwy-5BdbThTh,
20d
40
40
Figure A1.4. Saturation Effectivenessfor an 80 Percent Effective Evaporative Cooling Pad
s
5
la2
t;1
23 3
C
25~~~~~ 30 2 30/
Dl-mmdTcn~ab
3351
43 fi,C
A5
/
5
sC
Source:The Munters Corporation.
Source:The Munters Corporation.
Figure A1.4 explains the cooling effect of an EAC.When water andtiuiai;~~~~~~~~~~~~~~~~~~~~~~~.U dry air are mixed in an Lhgig,=. EAC, the air_; will cool down following the WB depres: ~~~~~~~~25 sion line. The efficiency of a certain EAC defines thiedegree of cooling.In this case, the dry air of 40°C is led through a pad of corrugated paper, which is constantly wetted with water. The appliance has. an 20 15 efficiency of 80 percent, which means it cools the .500 airwith O.80OXWB depressionof40°C-20°C = 16°C.
The outgoing air thus has a DB temperature of 40°C EbcdtRs - 16°C = 24°C. FigureA1.5 explains what happens in different 2w situations when an EAC is used. The arrows point at certain combinations of DB temperature and RH. It is clear that not all these situations are "comfortable." Only certain combinations of DB and RH are 1 20 actually sensed as comfortable by human beings, .010 and this limits the use of the EAC technology -for
F'igureA1.5. SaturationEffectivenessof 80 Percent for EvaporativeCoolingPadsat DifferentAmbient Conditions
FigureA1.6. Effectof IndirectEvaporativeCooling on Ambient Airstream
<
1),Y-BWb
S
.C
T-M~~~
-C
<
bT
Lty-BWb TDs-Bx
C
=
0g
O
15 30
15 c
13 25
40 20
Note: All are 80 percent effective; in drier conditions the coolingeffect is more pronounced than in hu ecid regions. Source: The Munters Corporation.
10
IS
.C
20
2Z
Source:The Munters Corporation.
30
35
40
45
S0
Annex 1: Introduction to Evaporative Cooling
FigureA1.7. Effectof CombinedIndirectEvaporative CoolingCoupledwith DirectSection
FigureA1.8. Energy-SavingEffectof Usinga SmallerCoilCoupledwith Indirectand Direct EvaporativeCoolingSections
025'
10
1S
25/
.025
.010
no,o,2~3 /
~~~~~5
5
.000 co,,
wN.D05
10
C'Il
,.020
20
2
55
30
35
40
04a0,
s
45
S0
DQ-2oOT=00epaoDC
5
10
15
20
%/17
25
30
35
40
45
so
y-Bo1bTon-p-:C
Note: This allows evaporative conmfort cooling to be applied in more huumid regions, as compared wit- direct EAC alone. Source:The Munters Corporation.
Source:The Munters Corporation.
certain applications. In some cases, hovwever,such as greenhouses or cattle sheds, the RH can be increased without any problem. EAC technicians have succeeded in reducing the amounts of water that are in the air, so as to increase the possibilities for applying EAC in humid areas also. Figures A1.6 ard Al .7 explain the effect in an indirect-direct air-conditioner. Before entering the wetting air stream, the air is first cooled by a normal heat exchanger, in which water and air are also mixed. In this case, the DB temperature of the entering air is reduced from 37.7'C to 26.1'C by the heat exchanger. After this, the 26.1'C air is cooled in the direct cooler to a DB of 19.6 C. The indirect cooler in the beginning has
the effect that the direct cooling follows another (lower) WBdepression line. In this way the end of the arrow comes into the "comfortable zone" again. Figure A1.8shows the effectof adding a cooling coil after an indirect evaporative cooling section (using the indirect as a precooler). This allows for a smnaller-sized coil to be used, thus savingenergy over conventional systems. A direct section can be added after this as well ifneeded. Other systems reduce the amounts of water by using desiccants,chemicalsthat can remove the water from the air stream before it enters the direct cooler.Withthese types of combined processes, EAC can be made more efficient in more humid areas.The price of these coolersincreaseswith the more complicated technology.
Annex 2 Suitability of Evaporative Air-Conditioning in Different Climate Zones FigureA2.1. Suitabilityof EvaporativeAir-Conditioning:Africa(Shadedareasindicatesuitability) IE3RD28834
_
axies,cTenwnin0f'tiwis The400V,S )ow
th. ma .. .;n-tinl4. ;n 9h pa of
57
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d
58
EvaporativeAir-Conditioning:Applicationsfor EnvironmentallyFriendlyCooling
FigureA2.2. Suitabilityof EvaporativeAir-Conditioning:Asia (Shadedareasindicatesuitability)
f
4,
*
IBIRD 2835
9
; Suitable Areas
-w-
Stigon
desinUnit ofTh World Bank. , he boustdariea colorade nauonan and anotherinfo=ationshown on this niap do wotkimply. on the part ofTh ol az roup. any judgment on th tegsal tus of any teffitory. or any endorsement or |
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t
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Annex 2: Suitabilityof EvaporativeAir-Conditioningin DifferentClimateZones
FigureA2.3. Suitabilityof EvaporativeAir-Conditioning:Australia(Shadedareasindicatesuitability)
S~~~~~~~~~~~
59
60
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
FigureA2.4. Suitabilityof EvaporativeAir-Conditioning:Europe(Shadedareasindicatesuitability)
3
/S ,7
-
~
i
I
[
<
]
'>
/
/ S\,
/
Suitable Areas
tX
17 IBRD28837
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-
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a
W
/
a /
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J/
X
Tnis map was produced by the Map Design Unit of The World Bank. The boundaries, colors, denominations and any other information shown on this map do not imply, on the part of The World Bank Group, any judgment on the egal z status of any territory, or any enaorsement or acceptance of such boundaries.
1)/ .
JUNE 1997
Annex 2: Suitabilityof EvaporativeAir-Conditioningin DifferentClimateZones
61
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EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
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Annex 3 List of Manufacturers and Suppliers
Complete Evaporative Air-conditioners America:
Baltimore Aircoil Company P.O.Box7322 Baltimore, MD 21227 7595 Montevideo Road Jessup, MD 20794, USA Tel. 410-799-6262,Fax. 410-799-6461 Producesa line ofindirectevaporativeair-conditioners.
AdobeAir, Inc. 500 S. 15th Street Phoenix, Arizona 85034,USA Tel. 602-256-4714,Fax. 602-257-1349 Leading USA manufacturer of a wide range of direct and indirect direct evaporative air-conditioners. Champion Cooler Corporation 5800 Murray Street Air & RefrigerationCorporation Little Rock, Arkansas 72209,USA P.O. Box 565126 Voice501-562-1094,Fax. 501-562-9485 Dallas, Texas 75653,USA Full line of residential evaporative air-conditioners. Voice 214-747-0214,Fax. 214-747-0812 Evaporative air-conditioners and humidification Convair Cooler Corporation equipment for industrial applications. 2007 Texoma Parkway Suite 114 Alton Manufacturing Company Sherman, TX 75090,USA 4830Transport Dr. Voice903-463-7191,Fax. 903-463-9627 Dallas, TX 75247,USA Marketing a range of whole of house evaporative Tel. 214-638-6010,Fax. 214-905-0806 air-conditioners and portable evaporative air-conStandard indirect-direct evaporative units with a ditioners (by Seeley). choiceof drip media in a variety of sheet metal and stainless steel cabinets. Cool Tower Systems, Inc. 8611N. Polk Canyon, Suite 216 Aztec International,LTD Phoenix, AZ 85021,USA 2417Aztec Rd. NE Tel. 02-995-2101,Fax. 602-995-9272 Albuquerque, New Mexico 87107,USA Manufacturers of evaporative air-conditioners Voice 800-545-8306,Fax 505-881-5391 equipment. Indirect and direct air-conditioners standard and custom units and makeup air units. Cool-Fog Systems 26 Pearl St. #Bldg. Bacchus Industries, Inc Norwalk, CT 06850,USA P.O. Box 465, Sunland Park Manufacturers of evaporative sprayers/misters. New Mexico 88063,USA Tel. 505-589-5431 Engineered Commercial Concepts,Inc. Manufacturer of a range of fiberglass cabinet air- P.O. Box 29734 - 2356 Glenda La. conditioners from 85 to 180m3/min. Dallas, Texas 75229,USA Voice214-484-0381,Fax. 214-620-9880
63
64
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
Industrial and commercial direct and indirect evaporative air-conditioners equipment. Stainless steel construction with evaporative media, indirect and direct gas heating. Essick Air Products and Champion Cooler Corporation 5800 Murray Street Little Rock, Arkansas 72209,USA Voice 501-562-1094,Fax. 501-562-9485 Portable, residential and commercial evaporative air-conditioners. EvapcoWest, Inc. P.O. Box 959 Madera, CA 93639,USA Tel. 209-673-2207,Fax. 209-673-2378 Evaporative air-conditioners products. Gustafson E.H. & Company 5115Suffield Terr. Skokie, IL 60077,USA Voice708-966-6155,Fax. 708-966-5662 Manufacturer of air washers utilizing spray coils, evaporative media, and coil sections to provide humidificationand dehumidification for air-conditioning or industrial apparatus. Hastings IndustriesNVari-Cool P.O.Box548 Hastings, Nebraska 68901,USA Tel. 402-463-9821,Fax. 402-462-8041 Manufactures Vari-Cool, an indirect-direct evaporative air-conditioner and direct evaporative airconditioners. Direct air-conditioner capacities from 60m3 /min to 400m3 /min. ICC Technologies 441 North Fifth Street Philadelphia, PA 19123,USA Tel. 215-625-0700,Fax. 215-592-8299 Manufacturer of commercial desiccant assisted evaporative air-conditioners equipment. JanecoInc. dba International Energy Saver Doug Howard 2017S. Cutler Tempe, AZ 85282,USA Voice602-968-3066,Fax. 602-968-5788
Manufacturer of industrial and commercial evaporative air-conditioners systems across a broad range of applications. Products include: evaporative air-conditioners, pre-coolers, cell-cool units, air washers. Modine Manufacturing Company 1500De Koven Ave. Racine, WI 53402, USA Voice414-636-1200,Fax. 414-636-1665 Indirect-fired and direct-fired heating and ventilating equipment with optional evaporative air-conditioners sections in capacities. Norsaire Systems, Inc. 1314West Evans Avenue Denver, CO 80223,USA Voice 303-937-9595,Fax. 303-937-0774 Description: Indirect/Direct evaporative air-conditioners units with a wicked aluminum exchanger or a standard efficiencyplastic exchanger. Phoenix Manufacturing,Inc. 3655E.Roeser Road Phoenix, Arizona 85040,USA Tel. 602-437-1034,Fax. 602-437-4833 Full line of residential air-conditioners, air-conditioner pumps, air-conditioner parts and the 'Power cleaning pump system" Pneumafil Corporation 226 Westinghouse Boulevard, Suite 309 P.O. Box 16348 (28297-8804) Charlotte, NC 28273, USA Voice 704-399-7441,Fax. 704-588-7346 Sheet metal manufacturer of evaporative air-conditioners/filtration systems for the gas turbine cogeneration industry; automotive humidifiers, i.e. media type, spray coil, and spray air washers (high and low velocities). Filtration systems consisting of static self-cleaning barrier type and cartridge pulse type. RainmakerCooling, Inc. 945 Rutland Houston, TX 77008,USA Tel. 713-869-2894 Evaporative spray roof cooling manufacturer.
Annex 3: List ofManufacturersand Suppliers
Rey Industries, Inc. 218 W. 36th Boise, Idaho 83714,USA Voice 208-336-4821,Fax. 208-343-0433 High-velocityspraybank air washers forplant cooling. Reznor EL. McKinley Avenue Mercer, PA 16137,USA Voice412-662-4400,Fax. 412-662-4412 Description: Manufacturer of commercial/industrial heating equipment including an evaporative air-conditioners section. Space-Aire Co. 158 No. Graham Rd. Tipton P.O. Box 888, Pixley,CA 93256,USA Tel. 209-752-2222 Manufactures of a range of fiberglass down draft air-conditioners from 80 to 400 m 3 /min. SPEC-AIR 7249Bosque Rd. Canutillo, Texas 79835,USA Voice915-877-3136,Fax. 915-877-1538 Indirect/Direct evaporative air-conditioners modules and packaged air-conditioners; custom air handlers for institutions and industries; make-up air systems with evaporative air-conditioners; air washers utilizing rigid media; packaged air-conditioners with refrigeration and indirect evaporative air-conditioners; pre-coolers. Sprinkool Systems, Inc. P.O. Box 326 Killeen, AL 35645,USA Evaporative spray roof cooling manufacturer. Southern Equipment Co. 4550 Gustine Ave. St. Louis, MO 63116,USA Voice314-481-0660,Fax. 314-481-8107 High efficiency evaporative air-conditioners to be used as stand alone or package with blowers, and furnaces (unit heaters and duct furnaces). Titon Inc. P.O. Box 6164 South Bend, IN 46660,USA Tel. 219-271-9699,Fax. 219-261-9771
65
Tradewinds 616 So. 55th Ave. Phoernx, AZ 85043,USA Tel. 602-278-1957,Fax. 602-272-9544 Residential and small commercial evaporative airconditioners units. United Metal Products, Inc. 127 S 43rd St. Phoenix, AZ 85034, USA Voice602-275-7622,Fax. 602-275-2428 Industrial, Commercial evaporative Cooling Equipment, Direct, Indirect & Heating type units.
Australia: Bonaire Pyrox 26 Nylex Ave, Salisbury South Australia, 5108 Tel.61-8-282-3110, Fax. 61-8-283-0401 Manufacturer, importer and wholesaler of evaporative air-conditioners equipment. Celair-Malmet P.O.Box373 Leeton NSW 2705 Australia Tel. 011-69-532455, Fax. 011-69-532656 Manufactures a range of evaporative air-conditioners under the trade mark of CELAIR.Product range starts from 40m3 /min to 1600m3 /min. Seely International-ConvairCooler Corporation 1-11Rothesay Ave.,P.O. Box 140 Saint Marys Adelaide South Australia, 5042,Australia Tel. 011-618-276-2355,Fax. 011-618-374-2315 Manufacturer of a range (410-250m3 /min) of polymer cabinet, whole of house evaporative air-conditioners and portable evaporative air-conditioners. Brand names Convair and Breezair. Southernair 29 Aldershot Road Lonsdale, South Australia 5160,Australia Tel. 08 326-3551,Fax. 08 326-3552 Manufacturer of a range of axial fan, roof mounted evaporative air-conditioners with low profile fiberglass cabinet.
66
Evaporative Air-Conditioning: Applications for Environmentally Friendly Cooling
India:
Flippen Valve Company
AmbassadorAir-conditioners Private Lmtd. HA6mbassMohadr Ar-copnditonr Arivate LmtdEl H-6 B-I Mohan Co-op nd. Area
4127 Temple City Blvd. Monte, CA 91734,USA Voice 818-575-1411,Fax. 818-575-1549
New Delhi India Tel. 91-11-683-3258,Fax. 91-11-683-6903 Manufacturer of commercial direct evaporative airconditioners equipment and of evaporative air-conditioners media.
Manufactures extensive line of heavy duty evaporative air-conditioner valves for residential and commercial use.
Kobli andaCoManyiPaharganjManufacturer New Delhi 110 055, India New. De442i110055,Indiacial, Tel. 524428
Cer-Cor
~~~~1149 Central Avenue University Park, IL 60466,USA Tel.708-534-6595or 800-323-9161,Fax.708-534-7581 of cellulose evaporative air-conditioners pads for agricultural, horticultural, commerindustrial and residential applications.
Manufacturers of a range of spot air-conditioners
Goettl Enterprises Inc, Amoy Industries
and wall mounted evaporative air-conditioners.
P.O. box 20246
Solar Air-conditioners:
2301 E. Buckeye Rd, Phoenix AZ 85036,USA Tel. 602-273-7483,Fax. 602-275-2881 Blower wheels and associated items for the evapo-
Jade Mountain Import-Export Company P.O. Box 4616, Boulder CO 80306, USA Tel. 303-449-6601, Fax. 303-449-8266 Mail order of solar powered direct and indirect-direct evaporative air-conditioners from 20 to 100m3 /rnin.
rative air-conditioning industry. New product development programs involving cooling and air movng equipment. Little Giant Pump Company
Solar Energie Technik
P.O.Box 12010
Postfach 1180,D 68801Altluszheim
Oklahoma City,OK 73157-2010,USA
Tel. 06205-3525, Fax. 06205-3528, Germnany. Mail order of a solar powered evaporative spot airconditioner.
Tel. 405-947-2511, Fax. 405-947-8720 Line of non-submersible evaporative tioner pumps.
air-condi-
Munters Corporation
Component Manufacturers:
Evaporative cooling division
Air Moving Market GE Motors P.O. Box 2205 2000 Taylor Street
108 Sixth Street,SE Fort Myers, FL 33907, USA Tel. 813-936-1555, Fax. 813-936-2657 Leading manufacturer of rigid pads
Fort Wayne, IN 46801, USA Voice 219-428-4685, Fax. 219-428-4660 Fan motors for evaporative air-conditioners
Scott Motors Company Al do NM88310 USA
applications.
Tel. 505-434-0633, Fax. 505-434-4895
Dial Manufacturing, Inc.
Manufacturer of evaporative air-conditioner motors.
25 South 51st Avenue
Phoenix, AZ 85043, USA
Manufacturer's Representatives
Tel. 602-278-1100, Fax 602-278-1991 Manufacturer of evaporative air-conditioner replacement parts such as pumps, motors, float valves etc.
A K S Sales, Inc. 606 Northstar San Antonio, Texas 78216, USA
Annex 3: List of Manufacturers and Suppliers
67
Voice 512-344-1845 Manufacturer's representative for evaporative airconditioners, Sno-Bresefor Texas.
U.S. Representatives for Southernair evaporative Air-conditioners. High efficient axial fan residential and commercial air-conditioners.
Barnhart-Taylor, Inc. 1602A E. Yandell El Paso, TX 79902,USA Tel. 915-533-1231,Fax. 915-533-8942 Manufacturers representatives for evaporative airconditioners equipment sold in the Southwest U.S. and northern Mexico.
Consulting Engineering: Anderson, De Bartolo and Pan 2480N. Arcadia Ave. Tucson AZ 85712,USA Tel. 602-795-4500,Fax. 602-881-0413 Consulting engineering specializing in evaporative air-conditioners design
Engineered Air Systems 720 12th Street
McCartney, Jerome J.
Richmond, CA 94802,USA Tel. 510-234-9322
Water Treatment Consultant P.O. Box 498874 Cincinnati, Ohio 45249, USA
FryEquipment Co., Inc. 2600 W. 2nd Ave. Suite 7 Denver, Colorado 80219,USA Voice 303-922-8442,Fax. 303-922-8445 Sales and design engineering desiccant cooling, indirect evaporative air-conditioners systemswith hybrid desiccant and compressorized components.
Voice 513-489-5547 Specializing in chemical water treatment for boilers, cooling towers, evaporative condensers, and closed circuit evaporative air-conditioners.
Meckler, G. PE President Gershon Meckler Associates, P.C. Lincoln Associates 590 Hemdon Parkway, Suite 100 540 Powder Springs St. SW Hemdon, VA22070,USA Suite 29E Voice 703-478-9552,Fax. 703-478-9446 Marietta, GA 30064,USA E conservation, utilization, and management. D of Manufacturers Representative for evaporative air- mechanical and electrical systems for buildings, enconditioners products for Georgia and Alabama. ergy utilization analysis in system design, energy conserving retrofit design for existing facilities, and
Mestek Dallas 4830 Transport Drive Dallas, TX 75247, USA Mountain Air Sales, Inc. 8282 So. State #28 Midvale, UT 84047, USA Tel. 303-937-9595, Fax. 303-937-0774 Robert E. Jones Co. P.O. Box 1129 Newcastle, CA 95658, USA
Wright-Castillo& Associates, Inc. 1268-BAuto Parkway #506 Escondido, CA 92029,USA Voice619-743-6128,Fax. 619-738-9045
life cycle economnicanalysis. Foster, R. Project Engineer, Southwest Technology Development Institute College of Engineering, New Mexico State University P.O. Box 30001, Dept. 3SOLAR Las Cruces, NM 88003-8001, USA Voice 505-646-1846, Fax. 505-646-2960 Analysis and design of direct and indirect evaporative air-conditioning systems, performance testing, building simulation modeling, research and development, training and workshops, solar energy
applications.
68
EvaporativeAir-Conditioning:ApplicationsforEnvironmentallyFriendlyCooling
NM Energy,Minerals and Natural Resources Department Harold Trujillo,Energy Conservation and Management Division 2040South Pacheco Street, Santa Fe,NM 87505,USA Tel.505-827-5900,Fax 505-827-5908 Educating and assisting organizations on the implementing of evaporative air-conditioners, cosponsoring workshops on theory and design. Noble, John M. PE P.O. Box 2615 Taos, NM 87571,USA Voice505-758-2240,Fax. 505-758-2240 Design and analysis of indirect and direct evaporafive air-conditioning systems.
Tecogen,Inc. P.O. Box 9046/45 First Avenue Waltham, MA 02254,USA Tel. 617-622-1323,Fax. 617-622-1252 Desiccant air-conditioning systems. Services: LegalLicensing Ian G. Fierstein Attorney at Law Miller Faucher Chertow Cafferty & Wexler 30 North LaSalle St. Suite 3630 Chicago, IL 60602,USA Voice312-332-3400,Fax. 312-782-4485 Representing developer of industrial process for molding complex and detailed fiberglass parts to produce evaporative air-conditioners.
Bibliography
Brown, W. K. 1991. "Application of Evaporative Cooling Concepts to Save Energy while Imnproving the Indoor and Outdoor Environment. ASHRAE Transactions97(Pt. 2), IN-91-11-1
Nationwide, Commercial Applications for Evaporative Cooling Systems." Washington State Energy Office, ASHRAE Inland Empire Chapter, Spokane, Washington, March 21.
Brown, W. K. 1989. "Humidification by Evapora- McClellan,C. H. 1988."Estimated Temperature Pertion for Control Simplicityand Energy Savings." formance for Evaporative Cooling Systems in ASHRAE Transactions95(Pt.1), Atlanta, GA. Five Locations in the United States." ASHRAE Evaporative Cooling Institute. 1992a. "Commercial Transactions.Atlanta, Georgia. Applications for Evaporative Cooling Systems: McClellan, C. H. 1989. "Evaporative Cooling ApWorkshop Manual." Governors Energy Office, plication Handbook." Sun Manufacturing, El Texas Energy Extension Service,Energy Center, Paso, Texas. ASHRAE-El Paso, University of Texas at El Muller, M. J., 1987. "Handbuch ausgewalter Paso, El Paso, Texas,June 16. Klimastationen der Erde." University of Trier, Evaporative Cooling Institute. 1992b. "Sizing and Forschungsstelle Bodenerosion Mertensdorf, Maintaining Evaporative Cooling Systems: Ruwertal, Germany. Workshop Manual." Governors Energy Office, Peterson, J. L. and B. D. Hunn. 1992."Performance TexasEnergy Extension Service, Energy Center, Evaluation of an Indirect Evaporative Cooler." Evaporative Cooling Institute, ASHRAE-El Conservation and Solar Research Report No. 11, Paso, University of Texas at El Paso, El Paso, Center for Energy Studies, University of Texas, Texas,June 16. Austin, Texas, January. Evaporative Cooling hinstitute.1995."Commercial Applcations for Evaporative Cooling Systems."I Puckorius, P.R., P.T. Thomas, and R. L. Augspurger. WApplingonstaterEneprgyatffieCoolingSHRAems 1995. "Why Evaporative Coolers Have Not Washington State Energy Offkce,ASHRAE in Caused Legionnaires' Disease." ASHRAEJourland Empire Chapter, Spokane, Washington, nall995qanuary): 29-33. March 21. Foster, R. E. 1991. 'Evaporative Air-Conditionin Supple, R., 1982. "Evaporative Cooling for ComFostechnoloiEand1.CvapontributiAlrons tioo*g fort." ASHRAEJournal. 1982(August). Technologies and Contributions to Reducing Greenhouse Gases." Proceedings of the Watt, J. R. 1986.EvaporativeAir-ConditioningHandASHRAE Asia-Pacific Conference on the CFC book.Second Edition. Issue and Greenhouse Effect, Singapore, May. Wu, H., 1989."Performance Monitoring of a TwoFoster, R. E. 1995. "Evaporative Air-Conditioning Technologies:Reducing Energy and CFCUsage
Stage Evaporative Cooler." ASHRAE Transactions. 95(Pt. 1). Atlanta, Georgia.
69
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Recent World Bank Technical Papers (continued) No. 390
Foster, Lawrence, and Morris, Groundwater in Urban Development: Assessing Management Needs and Formulating Policy Strategies
No. 391
Lovei and Weiss, Jr., Environmental Management and Institutions in OECD Countries" Lessonsfrom Experience
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No. 393 Mohan, ed., Bibliography of Publications: Africa Region, 1990-97 No. 394
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Onorato, Fox, and Strongman, World Bank Group Assistancefor Minerals Sector Development and Reform in Member Countries
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Wiens and Guadagni, Designing Rulesfor Demand-Driven Rural Investment Funds: The Latin American Experience
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Miller and Reidinger, eds., Comprehensive River Basin Development: The Tennessee Valley Authority
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Okidegbe and Associates, Agriculture Sector Programs: Sourcebook
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Jaffee, ed., Southern African Agribusiness: Gaining through Regional Collaboration
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Marifio and Kemper, Institutional Frameworks in Successful Water Markets: Brazil, Spain, and Colorado,USA
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C. Mark Blackden and Chitra Bhanu, Gender, Growth, and Poverty Reduction: Special Program of Assistance for Africa, 1998 Status Report on Poverty in Sub-Saharan Africa
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