Five Degrees of Conservation: A Graphic Analysis of Energy Alternatives for a Northern Climate

Five Degrees of Conservation A Graphic Analysis of Energy Alternatives for a Northern Climate

Lance LaVine, Mary Fagerson, and Sharon Roe

Published by the University of Minnesota School of Architecture Distributed by the University of Minnesota Press, Minneapolis 55414

©by Lance La Vine, 1982 ISBN 0-943352-00-2 ISBN 0-943352-01-0 (pbk) Published by the University of Minnesota School of Architecture Distributed by the University of Minnesota Press, 2037 University Ave. S.E., Minneapolis, MN 55414 Printed in the United States of America

Acknowledgments We are grateful to the many people and organizations who made the completion of this study possible. We wish to thank the graduate students whose work in a one quarter solar energy seminar provided the impetus for this study. The criticism of Gunter Dittmar and Dale Mulfinger at the University of Minnesota School of Architecture was valuable in forming the initial goals. Technical assistance in the research was provided at several stages. Daryll Thayer of Thayer and Associates, Solar Engineers, provided much of the instruction in the solar energy seminar. James Ramsey in the University of Minnesota Department of Mechanical Engineering and Sara Heap at Goddard Space Flight Center, National Aeronautics and Space Administration, were helpful in refining the calculations. Production of the book was accomplished with the help of many people. Dennis Barbour, Mark Nelson, Khosrow Rezai, and Frederick Rogers assisted us in the production of the numerous graphics. A special thanks to Li Daxia, our visiting Chinese scholar, for his many hours of drawing and his critical evaluation. We also wish to thank Donna Jansen for her editing assistance. Administrative and financial support from several sources made this study possible. We would like to thank Roger Clemence of the University of Minnesota Graduate School of Architecture for his administrative assistance. Financial assistance was provided by Northern States Power Company, The Graduate School of the University of Minnesota, the Center for Urban and Regional Affairs of the University of Minnesota, and the Minnesota Department of Energy, Planning, and Development. ii

Dedication To George Miller, my friend and running partner, without whose trust this would not have happened. L.L. To my father, who unwittingly aroused my interest in architecture. M.F. To my children, Chris, Sarah, and Susie, who have helped accustom me to chaos. S.R.

iii

Preface Five Degrees of Conservation began as an effort to collect and analyze comparable data on five Minnesota homes that use energy efficient technologies. It evolved into a study of five degrees of technological impact. In the not far distant past, energy efficiency was not a major consideration in designing a home. One simply designed a house based on many other criteria and then put in a furnace to accommodate temperature control. Today, energy efficiency has become a major concern in designing most buildings. The problem is that this concern is rarely linked to other design issues. This book is an attempt to point out some of the impacts that selection of a particular energy-efficient technology may have on a range of design issues. It provides data which can be used early in the design process to make this selection. This data is intended to suggest options for combining technologies with other concerns in a way that will enhance design choices and the home that results. We hope this information will be useful to three groups of people. The homeowner can use this data to plan a comfortable house that will operate efficiently, both as a home fulfilling human needs and as a house contributing to energy conservation. The designer can use layers of information inherent in the graphic format of this book to facilitate the integration of energy issues into the process of design. We believe there are untapped opportunities to generate design ideas from relationships among technologies, lifestyles, form vocabularies and contextural opportunities. Policy makers can use this informaton to gain a clearer understanding of the potential impact of new energy-efficient residential strategies on our region's energy needs. Our severe northern climate reduces the question of whether or not to be energy efficient to how to be energy efficient. This book explores some of the choices that are available to those engaged in this sensible search.

iv

Table of Contents Concerns

Introduction /3 The Five Houses /5 The Logic of the Study Energy Impacts /8

17

Graphic Analysis The The The The The

Fisher House III Scott House /19 Wild River House 127 Bergstedt House /35 Humphreys House /43

Comparisons Analytical Methods

/53

Base Data Analytical Strategy

Comparisons

/57

Amount of Auxiliary Fuel Used Actual vs. Predicted Auxiliary Fuel Inferred vs. Predicted Passive Gain System Performance Range of Uncertainty Costs per BTU Saved 30 Year BTU Savings

Postscript Bibliography

/63 /65

V

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Concerns

1

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Introduction "If the fool would persist in his folly he would become wise."

William Blake Energy efficiency is a natural concern of habitat design. It is not a panacea for all house design problems; nor must it be an obstacle to good design. It is a significant force, especially in northern climates, for generating residential design ideas. Yet, energy conservation is not the most important goal of housing design. Energy-efficient technologies are laudatory only to the degree that they serve, rather than dictate, the design of homes. In the past, designers could avoid the constraints imposed by a concern for energy conservation. A furnace, with its great heat producing capacity and minimal design requirements, could compensate for problems created by indifference to energy issues in even the most thermally inappropriate houses. It liberated designers with brute fossil fuel force, but it made us fuel dependent. New energy efficient technologies are not as benign as furnaces in terms of their design implications. They are not hidden in basements but are integral physical parts of the form and organization of the houses they serve. When these technologies are seen as the singular starting point of residential design there is a danger that all other design decisions will be made to accommodate the needs of this technology. In some cases the technology in question is not particularly demanding in terms of spatial design and hence allows a wide range of options. In other cases, the technology may be extremely demanding; once selected, all other design decisions must be subordinated to the requirements of that technology. Spatial organization in the houses and the needs and expectations of the people who live in them are forced to adapt to the demands of the technology employed. The intended servant becomes the served in the name of oversimplified definitions of environmental success. A home is simply too important a part of our mental and physical well-being to be reduced to technological efficiency. Quick and simple formulas are inadequate substitutes for the essential nature of design processes as the search for solutions to a wide range of human and technological issues. Calculations cannot replace thoughtful consideration of design subtleties that help to create unique environments to fulfill unique personal needs.

3

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The Five Houses Each of the five houses selected for this study is an excellent representative of its respective technology. All have at least one winter of recorded fuel use allowing actual thermal performance to be analyzed. Each house is compared to the other four on the basis of that data. The Fisher House

minimal use of glazing employed (12% of the floor area) and the use of an air to air heat exchanger to reduce the amount of heat lost in ventilating extremely tightly sealed buildings. The result is a twostory, solar salt box, located near Northfield that consumed only 22,000 BTU of auxiliary fuel per square foot of interior space over the course of the 1979-80 heating season. The Wild River House

This large (4200 SF), four-story, moderately well insulated (MI) house is located in Mahtomedi. It is owner built and utilizes conventional conservation technologies including earth sheltering on a portion of its northern exposure, R-24 walls, R-45 ceilings, and triple and quadra glazed windows. Four cords of wood and an electric hot water backup system provided the auxiliary heat required by a family of four for the 1979-80 winter. Average auxiliary fuel use during this heating season was 38,000 BTU/SF.

This home was designed to house the manager of the Wild River State Park and his family. It is a true underground structure (UG) with 18" of earth over much of its roof. Two thirds of the exterior surface of the house is located below grade. In addition to the use of earth to moderate heat losses in this house, the design employs a large amount of south facing glazing (400 SF) and significant thermal storage (260 SF primary masonry storage) to make a substantial passive solar contribution to its space heat needs. This house consumed 44,000 BTU/SF during the 1980-81 winter. The Bergstedt House

The Scott House

This home is a fine example of a new breed of conservation strategies which are referred to as super-insulated (SI) structures. This nomenclature is derived from the level of insulation attained by these houses (R-34 walls and R-61 ceilings), the

This 1730 SF three story house located in Duluth is comprised of an envelope within an envelope (DE). The space between these surfaces serves as a giant air duct for a three story sunspace that covers the southern elevation of the house. The performance of this technology does not lend itself to analysis using conventional techniques. Our results bear this out as the amount of passive solar gain they 5

suggest is greater than the amount of energy assumed to be available from sunlight in Duluth. We have concluded from this disparity that the house acts as a far better conservation strategy than calculated. We include this house both to highlight this calculating problem and to provide reliable auxiliary fuel and cost information pertaining to this strategy. This house consumed 32,000 BTU/SF during the 1980-81 heating season.

energy efficient technology (high insulation levels, minimum window area, and control of infiltration losses) makes few demands on the form of the house. The result is a conventional salt box that the owner desired even before considering energy conservation. Thicker walls, more careful selection of window placement and size, addition of a good vapor barrier, and a heat exchanger for ventilation can accommodate an infinite range of site, form, and lifestyle conditions and desires.

The Humphreys House The earth-sheltered house represents a different degree of the impact of technology on the design of houses. In this case, the technology makes substantial demands on all ensuing design decisions. Limited opportunities for exposure to sunlight and the structural requirements of carrying the heavy loads imposed by earth-covered walls and roofs create a strong set of technological imperatives in this dwelling. It is not surprising that the form taken by houses using this technology tend to be very similar. The familiar extruded section of earthsheltered housing is an intelligent response to the technology. The question is whether it is an equally intelligent and sensitive response to other housing needs.

Alan Humphreys is a unique individual and perhaps in some ways an apt representative of the owners of all these houses. He is an inveterate mental and physical tinkerer. He has coupled his own knowledge with that of a mechanical engineer and an architect to provide a prize-winning solar house design. The house, the only urban example selected for this study, uses a hybrid passive and active solar collection system (A/P) to provide space heat and to charge both diurnal water storage and an annual rock bed storage system located beneath the garage. It represents our only active solar collector (240 SF, air) and the most ambitious attempt of any of these homes to solve the night insulation problem faced by northern climate houses. Mr. Humpreys has designed, built and installed a photo cell activated exterior shutter system (R8) that covers all the south facing glazing of this house. Solar systems, earth sheltering, well insulated walls and ceiling and night insulation have all contributed to reducing this home's consumption of fossil fuel to 44,000 BTU/SF for the 1980-81 heating season. Analysis of the impact of these technologies hinges on how they are used in making design decisions. With the exception of the Fisher House (moderately insulated), fossil fuel conserving technologies were the obvious starting point of the design of these houses. The power of this initial decision to mold an environment appears to have had least impact on the super-insulated house. In this case, the

_fi_

When these same technologies are viewed not as dominant but as integral portions of broader design concerns, their potential to create new linkages between space heating technology and house form may come to fruition. It should be possible to take advantage of the characteristics inherent in each technology to enhance housing environments. When a house is built on an urban lot, as the Humphreys (A/P) House, heat storage mass can be used as a buffer between the interior spaces of the house and the public areas along the street. Earth sheltering can be used to reduce the visual impact of a structure on the environment as in Wild River State Park. Here, the underground building blends with its surroundings to deliver a definite message that the site, not the building, is of prime importance. Interior sun spaces might begin to fulfill their potential as outstanding aesthetic experiences and functionally useful places. The need for thicker walls in heavily insulated structures could serve to enhance spatial senses of enclosure and protection. Wood burning stoves and fireplaces could create social hearths. Thermally oriented windows could enhance the luminescent qualities of the spaces they serve. If energy efficient solutions are to appeal to populations beyond committed conservationists, these kinds of social and aesthetic opportunities will have to be explored.

The Logic of the Study The key to translating this potential into design reality is the ability to visualize these technologies in terms of their thermal performance and, simultaneously, as a function of their spatial impact. The organization of the graphic analysis of these houses is intended to encourage this vision. Energy-efficient technologies of each house are illustrated at three levels of specificity. Each level is documented and dissected to reveal its underlying thermal and spatial characteristics. At the most general level this analysis consists of a portrayal of the interior spatial configuration of the house followed by a graphic analysis of its envelope as a membrane that loses and gains energy during each heating season. The second level of analysis dissects the house in terms of conservation, passive and active solar components. The relative energy contribution and spatial configuration of each of these systems is linked in these diagrams. Systems are then combined in an illustration which is accompanied by an analysis of the amount of auxiliary fuel used by each house. Finally, these systems are analyzed in terms of their predictability, cost per unit of energy saved and range of uncertainity. Each analysis conveys highly detailed design information. Predictability compares actual auxiliary fuel expenditures with those that would have been predicted using the solar load ratio method for calculating passive solar gains. The cost of each system in dollars per million BTU's saved is based on current local building costs. The uncertainty of each system's performance suggests that we should always be careful when making specific claims about the performance of energy efficient components. Our analysis of the strengths and weaknesses of these five houses is not intended to prove which is the right solution to the problem of energy conservation. Our objective is to provide the kind of information necessary to understand how these technologies function in real houses. This understanding is dependent on translating data into comparable forms using the following procedures. Providing Comparable Data Bases Each house presented is defined using the same base data, analytical procedures, and output measures. Climatic data used is appropriate to the location and year in question. Area estimates and auxiliary fuel consumption are developed from uniformly applied assumptions. Analytical techniques employed are those most commonly available to designers and are not modified in any manner to present any of the technologies reviewed in a more favorable or critical light. Results are expressed, for the most part, on a square foot basis allowing comparison independent of size. Each procedure has been standardized to allow the physical characteristics, energy performance, and

construction costs of these strategies to be compared. We would hope that these comparisons would promote intelligent selection and modification of portions of these strategies rather than wholesale acceptance or rejection of technologies in their entirety. Identifying Auxiliary Fuel Use Many energy efficient strategies are presented on the basis of mathematically predicted performance levels unconfirmed by actual recorded data. Reality is messy. People leave doors open, carpenters puncture vapor barriers, and microclimates do not always mirror average climatic conditions. Some researchers would prefer to avoid these issues on the grounds that they create so many uncontrolled variables that analysis of energy technologies would become unscientific. We prefer to view analysis from the opposite perspective. Knowing what happens under actual conditions presents a more realistic picture of the performance and problems of each technology. To that end we have used actual fuel bills and owner estimates of wood burned in these homes as the basis of our analysis. Linking Performance Data to Design Decisions Energy performance and design decision are normally portrayed as separate and only vaguely related phenomena. Floor plans and sections (usually with arrows to indicate air flow) are followed by a single number representing the potential fuel savings of the house in question. It is difficult, if not impossible, under these conditions to determine just what portion of the strategy is responsible for what proportion of energy savings. If individual system performance can be linked to that system's physical characteristics, and these characteristics can be seen as the outcome of design decisions, then design processes can be used to explore new relationships between thermal performance and spatial characteristics. Portraying system performance in conjunction with three dimensional diagrams of system configurations is an effort to provide this link. Defining the Level of Confidence that can be Placed in Energy Projections Numbers frequently have a peculiar ability to appear more conclusive than they are. To alleviate this problem, the analysis of energy consumption of each house is accompanied by a graph showing potential sources of error in that analysis. Given these sources of error, lines on all graphs might better be represented by a band showing the range of outcomes possible for each calculated value. This information is intended to alert designers to the possible margin of error that may be encountered in projecting the amount of energy saved by each technology.

7

Energy Impact It is difficult to present comparisons in a document which is intended to serve as an information source, without implying that conclusions reached represent a definitive judgement of the technologies examined. It is crucial to remember that each house presented here represents a sample of one of its respective technology. This minimal sample size, combined with limitations of the data utilized to analyze thermal performance of these houses, makes any attempt to draw general conclusions from this work unwise. It is not inappropriate, however, to attempt to understand some of the specific consequences of design decisions made in these houses. These comparisons will hopefully stimulate the investigation of the quantitative and qualitative implications of energy technologies employed in houses located in severe northern climates. Conservation vs. Solar Technologies Insulation played a major role in energy conservation even in those houses which claimed to be solar heated. Only the Humphreys House (A/P) gained more energy through a combination of active and passive solar systems than it did through conservation.

Energy Savings of Houses Studied vs. Current Standards The amount of fuel saved by these houses is enormous when compared to the amount saved by houses that meet the standards of the Minnesota Energy Code. Many of these technologies are simple and relatively inexpensive. If more houses built in the region used these technologies, the reduction of fuel required for space heat would be substantial.

8

Dollars Invested vs. Energy Saved by each Technology Greater investment in energy saving technologies does not necessarily result in greater energy savings. Careful matching of components to climatic conditions is critical to energy-efficient performance. In the five houses analyzed, modest south glazing in combination with high insulation levels appears to be the most cost-effective strategy. Increased expenditures in more complex energyefficient technologies not only failed to produce commensurate rates of gain, but resulted in lower absolute performance. Northern climates obviously make unique demands on energy-efficient technologies.

Graphic Analysis

9

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The Fisher House

11

Overview General Characteristics Owner: Location: Designer/ Engineer: Builder: Occupied: Family Size: Occupancy Pattern: House Size: House Type:

Appliances:

Electric hot water Day and Night—62°F

Auxiliary Fuel Consumption:

Annual Total = 161 x 106BTU Annual/ SF = 38xl03BTU Annual/ SF-°F = 5.1BTU

Construction Cost:

Total Cost = $275,000 10% inflation Cost per SF = $53.95 Moderate insulation Green house Triple and quadra glazing Total Cost = $3791 Cost per SF = $.90

Cost of Energy Efficient Technologies:

(106BTU/Mo)

October November December January February March Apr! 1 Annual Total (106BTU/Yr) % of Code Heat Loss % of Heat Loss as Bui It

12

Code Heat Loss

I9.9 34.0 41.0 52.0 48.5 39.8 18.4 253.6

As Bui It Heat Loss

14.8 26.3 31.6 40.4 37.7 30.5 13.3 194.6

I nterna I Gai ns

Actual Auxi 1 iary

Passive Ga i ns

5.1 8.3 9.4 11.6 10.8 9.3 5.1

0.3 0.2 0.3 0.3 0.2 0.3 0.2

10.8 22.3 28.4 36.7 31.1 24.4 7.7

3.7 3.8 2.9 3.4 6.4 6.1 5.6

59.6

1.8

161.4

31.9

Conservation Savi ngs

24.0$ 1.0$

83.0$

16.0$

Dean Fisher June, 1979 2 Adults 2 Children (9 and 12) Adults work Children in School 4217 SF 4 Story 4 Bedroom y/2 Bath 2 Refrigerators 2 Ranges Microwave Dishwasher Laundry Extensive woodworking shop

Auxiliary Heat: Thermostat Setting:

Energy Conscious Technologies:

Performance Data

Fisher Mahtomedi, Minnesota Dale Mulfinger, Architect

Envelope Performance Spatial Organization

Annual Envelope Heat Gains & Losses

Seasonal Envelope Heat Gains & Losses Heat Gains (106 BTU)

Heat Loss

(106 BID)

Auxiliary Heat

Internal Gains

Active Gain

Passive Gai n

Fal 1 October 1- December 10

52.23

42.19

.57

2.27 (9.47)

Wi nter December 11- February 20

88.70

77.43

.58

5.04 (10.69)

Spri ng February 21- Apri I 30

54.59

41.73

.56

3.44 (12.30)

195.52

161.35

1.71

Total Annual

10.75

13

Energy Systems Conservation

Envelope

Insulation

Infiltration

outh Glazing

Direct Gain

Indirect Gain

Collection

Storage

Distribution

Passive

Active

14

System Performance ENVELOPE CHARACTERISTICS Floor Area (sq. ft.) Volume (cubic ft.) Surface Area (sq. ft.) Surface area/ Volume Ratio % Earth Sheltered Total Glass Area (sq. ft.) Glass/ Floor Area Ratio —

4217 40,435 7003 0.17 0.24 480 0.12

INSULATION CHARACTERISTICS R-Value:

Ceiling Above Grade Opaque Below Grade Number of Glazings: South Other Night Insulation on Glazings (sq.ft.) INFILTRATION CHARACTERISTICS Ai r Changes/ Hour Heat Exchanger

45 24 11 3 4

n

Code Heat Loss October November December January February March April Annual Total (103 BTU/ Ft2)

Area of South Glazing ( I n c l u d i n g SE and SW) (sq.ft.) South Glass/ Floor Area

39 61 73 89 88 70 40

60

46

14 23

InternaI Gai ns South 410 .10

210 0 0

INDIRECT GAIN Glazing Area (sq.ft.) Storage Mass (tons) Heat Capacity (BTU/ Lb-°F)

113 208 241 309 309 234 105

1 NO

DIRECT GAIN Glazi ng Area (sq.ft.) Storage Mass (tons) Heat Capacity (BTU/ Lb-°F)

152 269 314 398 397 304 145

$ of Code Hest Loss

SOUTH GLAZING Orientation of Major Glazing

As Bui It ConserHeat vation Loss Savi ngs

200 0 0

October November December January February March Apri I

Pass i ve Solar Gai n

2 2 2 2 2 2 2

29 30 22 26 43 45 43

Annual Total , ( I03 BTU/ Ft2) .

8

% of As Bui It Heat Loss

^

M%

15

System Costs Auxiliary Fuel

Actual Aux i I i ary Heat 82 176 217 281 264 187 60

October November December January February March Apr! I Annual Total (I03 BTU/ Ft2)

38

% of Heat Loss As Bui It

53%

FueI:

Wood

10

Electricity

28

Combined Systems CONSERVATION 1 nsul ation : Cei 1 ing $ 373 W a l l s - Above Grade 433 - Below Grade 1111 Windows - T r i p l e Pane 1008 - Quad Pane 1 135 Mechanical Equipment: S m a l l e r Furnace

-1317 $2743

Total Cost 6

BTU Savings ( 10 BTU/Year) Cost/106BTU/Year

59

$

47

PASSIVE Extra Glazing

1048

Total Cost

$1048

BTU Savings ( 106BTU/Year) 6

Cost/10 BTU/Year

31

$

33

COMBINED SYSTEMS Total Cost

$3791

BTU Savings ( 106BTU/Year) 6

Cost/1 0 BTU/Year

16

91

$

42

System Impacts Actual vs. Predicted Fuel Use (BTU/SF-Day)

Predicted

Actual

102 199 234 300 265 220 100

82 176 217 281 264 187 60

43,000

38,000

October November December January February March

Apr! 1 A n n u a l Total

+130/

% Deviation From Actua I

System Costs/Energy Saved $ Invested/1 06BTU Saved/ Yr.

Moderate ly I nsu I ated Super 1 nsu 1 ated Underground

Conservation

Passive

Active

Total

$ 47

$ 33

$ -

$ 42

25

0

23

403

366

391

Doub le Enve lope Acti ve/Pass i ve Hybrid Average

76 83

318

140

179

853

398 186

30 Year Energy Savings 5 YEARS

30 YEARS

103 BTU/ S.F. CONSERVATION

7^.0

420.2

PASSIVE

37.3

223.6

107.3

643.8

ACTIVE

TOTAL

17

Uncertainty Range of Uncertainty Conservation Gain = Code Heat Loss - As B u i l t Heat Loss 103RTU/SF-Yr

Range of ,, . . , Uncerta i nty

.„ '4.ZZO.D

Calculated Value

..

31.2 - 60.2

31.6 - 47.0

60

46

Solar Gain = As B u i l t Loss - (Actual A u x i l i a r y + Internal Gains) Range of UncertaInty Caleulated Value

0 - H.I 8

31.6 - 4 7 . 0

30.9 - 4 6 . 1

46

38

The large error in as-built heat loss is due to the larger volume of this house which magnifies the uncertainty in the infiltration rate. The uncertainty in auxiliary fuel is due to the large quantity of wood used (4 cords). However, due to the large total auxiliary fuel use in this house, the relative uncertainty is similar to that of the other houses.

18

The Scott House

19

Overview General Characteristics Owner: Location: Designer/ Engineer: Builder: Occupied: Family Size: Occupancy Pattern: House Type:

House Size: Appliances:

Auxiliary Heat: Thermostat Setting: Auxiliary Fuel Consumption: Construction Cost: Energy Conscious Technologies: Cost of Energy Efficient Technologies:

Performance Data (106BTU/Mo) October November December January February March Apr! 1 Annual Total (106BTU/Yr) % of Code Heat Loss % of Heat Loss as

Bui It

20

Code Heat Loss

As Bui It Heat Loss

18.8 31.3 37.1 46.8 39.5 36.0 17.1

4.5 7.4 9.2 11.8 11.0 9.0 4.2

226.6

57.1

Conservation Savi ngs

I nternal Ga i ns

Actual Auxi I iary

14.3 23.9 27.9 35.0 28.5 27.0 12.9

0.3 0.2 0.3 0.3 0.2 0.3 0.2

(4.5) 5.8 7.2 7.8 6.8 6.4 5.2

169.5

1.8

43.7

Passive Gains

0.0 1.4 1.7 3.7 4.0 2.3 0.0

13.1

IJ jo

-tat y/o

77%

20%

Scott Northfield, Minnesota Michael Scott P&M Construction November, 1979 2 Adults 3 Children (2, 2 and 10) 1 Adult and 2 children home 2 Story + Basement 3 Bedroom 2Y2 Bath 2058 SF Refrigerator Range Dishwasher Laundry Electric furnace (hot air) Day and Night = 62°F Annual Total = 44 x 106BTU Annual/SF = 21 x!03BTU Annual/ SF-°F = 2.8BTU Total Cost = $86,000 Cost per SF = $41.95 10% inflation Super-insulated Triple glazing Heat exchanger Total Cost = $4222 Cost per SF = $2.05

Envelope Performance Spatial Organization

Annual Envelope Heat Gains & Losses

Seasonal Envelope Heat Gains & Losses Heat Gains (106 BTU)

Heat Loss 6

(10 BTU)

Auxiliary Heat

Internal Gains

Active Gain

Passi ve Gain

Fal 1 October 1- December 10

24.12

18.46

.57

4.00 (5.09)

Winter December 11- February 20

43.29

38.08

.58

5.72 (4.63)

Spri ng February 21- Apri 1 30

27.14

23.52

.56

6.74 (3.06)

Total Annual

94.55

80.06

1.71

16.46

21

Energy Systems Conservation

Envelope

Insulation

Infiltration

South Glazing

Direct Gain

Indirect Gain

Collection

Storage

Distribution

Passive

Active

22

System Performance SOUTH GLAZING Orientation of Major Glazing Area of South G l a z i n g ( I n c l u d i n g SE and SW) (sq.ft.) South Glass/ Floor Area

SW

Storage Mass (tons) Heat Capacity (BID/ Lb-°F)

0.07

150 0 0

INDIRECT GAIN Glazi ng Area (sq.ft.) Storage Mass (tons) Heat Capacity (BID/ Lb-°F)

0 0 0

October November December January February March Apr! 1 Annual Total ( I03 BTU/ Ft2)

2058 24,690 5849 0.24 0.38 265 0.13

INSULATION CHARACTERISTICS Cei I ing 61 Above Grade Opaque _____ -54 Below Grade _____________ 11 Number of Glazings: South 2 Other 3 Night Insulation on Glazings (sq.ft.) Q

294 506 582 733 662 564 276

71 120 144 185 184 140 68

223 386 438 548 438 424 208

no

28

82

% of Code Heat Loss

ENVELOPE CHARACTERISTICS Floor Area (sq. ft.) Volume (cubic ft.) Surface Area (sq. ft.) Surface area/ Volume Ratio % Earth Sheltered Total Glass Area (sq. ft.) Glass/ Floor Area Ratio

As Bui It ConserHeat vation Loss Savings

150

DIRECT GAIN Glazing Area (sq.ft.)

Code Heat Loss

75/o

1 nterna 1 Ga i ns October November December January February March Apri 1

Pass i ve Solar Gai n

4 4 4 4 4 4 4

0 23 27 58 63 36 0

.8

21

R-Value:

Annual Total ( I03 BTU/ Ft2)

% of As Bui It Heat Loss

3$

20%

INFILTRATION CHARACTERISTICS Ai r Changes/ Hour Heat Exchanger

0.24 YES

23

System Costs Auxiliary Fuel

ActuaI AuxiIiary Heat October November December January February March Apri I

(71) 93 1 13 123 117 100 83

Annual Total (I03 BTU/ Ft2)

21

% of Heat Loss As Bui It

11%

FueI: Wood

0

Electricity

Combined Systems

21

Costs CONSERVATION I nsulation: Cei I ing $ 814 Wai Is - Above Grade 955 - Below Grade 684 Windows - T r i p l e Pane 324 Structure (2X8 Wai Is)

462

Inf i Itration: Vapor Barrier Caulking

142 471

Mechanical Equipment: Heat Exchanger S m a l l e r Furnace

640 -270 $4222

Total Cost 6

170

Cost/106BTU/Year

$ 25

BTU Savings (10 BTU/Year)

PASSIVE Total Cost BTU Savings (10 BTU/Year) 6

Cost/10 BTU/Year

0

11 0

COMBINED SYSTEMS Total Cost BTU Savings ( 106BTU/Year) 6

Cost/1 0 BTU/Year

24

$4222

181 23

System Impacts Actual vs. Predicted Fuel Use (BTU/SF-Day)

Predicted

October November December January February March Apr! 1

56 105 133 172 169 122 52 24,000

Annual Total % Deviation From Actual

Actual

(71) 93 113 123 117 100 83 21,000

+ 15 '°

System Costs/Energy Saved $ lnvested/106BTU Saved/ Yr. Conser- Passive Active Total vation Moderate ly I nsulated Super I nsu I ated Underground Doub le Enve lope Act! ve/Pass i ve Hybrid Average

$ 47

$ 33

25

0

23

403

366

391

$ -

$ 42

76 83

318

140

179

853

398 186

30 Year Energy Savings 5 YEARS

30 YEARS 103 BTU/ S.F.

CONSERVATION PASSIVE

411.8

2471.0

28.4

170.3

440.2

2641.3

ACTIVE TOTAL

25

Uncertainty Range of Uncertainty Conservation Gain = Code Heat Loss - As B u i l t Heat Loss Range of Uncertal nty

10 3 BTU/SF-Yr 94.0 - 1 14.0

57.9 - 92.9

Ca leu I ated Value

82

2 1 . 1 - 36.1

28

110

Solar Gain = As B u i l t Loss - (Actual A u x i l i a r y + Internal Gains) Range of

0-28.3

21.1-36.1

20.5-22.6

28

21

Uncertalnty Caleulated Value

6

The infiltration rate is assumed to be similar to that measured in a similarly constructed house in Saskatchewan (0.2 ACH). This results in a lower uncertainty in the heat loss per degree but also a larger uncertainty in the balance point temperature. There is a resulting increased uncertainty in the heat loss as built. The small uncertainty in auxiliary fuel is due to the fact that no wood was used for heating.

26

The Wild River House

27

Overview General Characteristics Owner: Location: Designer/ Engineer Builder: Occupied: Family Size: Occupancy Pattern: House Type:

House Size: Appliances:

Auxiliary Heat: Thermostat Setting: Auxiliary Fuel Consumption: Construction Cost: Energy Conscious Technologies: Cost of Energy Efficient Technologies:

Performance Data (106BTU/Mo) October November December January February March Apr! 1 Annual Total (106BTU/Yr) % of Code Heat Loss % of Heat Loss as Bui It

28

Code Heat Loss

As Bui It Heat Loss

Conservation Savi ngs

I nterna I Gains

Actual Auxi 1 iary

Passive Gai ns

11.2 14.8 23.8 24.7 19.8 14.7 8.8

7.6 10.7 18.1 19.1 16.6 13.7 8.7

3.6 4.1 5.7 5.6 3.2 1.0 0.1

0.3 0.2 0.3 0.3 0.2 0.3 0.2

5.5 9.0 16.5 16.8 14.2 11.0 (7.0)

1.8 1.5 1.3 2.0 2.2 2.4 1.5

117.8

94.5

23.3

1 .8

80.0

12.7

2%

84%

14$

20%

State of Minnesota Wild River State Park (50 miles north of Minneapolis) McGuire Engler Architects Herb Larson Construction June, 1980 2 Adults 3 Children (6, 12, and 16) Adults home Children in school 2 Story 3 Bedroom 2 Bath 1800 SF Refrigerator Range Dishwasher Laundry Wood furnace Baseboard heat Day up to SOT Night at 65°F Annual Total - 80 x 106BTU Annual/ SF = 44xl0 3 BTU Annual/ SF-°F = 6.5BTU Total Cost = $100,000 Cost per SF = $55.65 Earth covered Large south glazing Masonry and rock storage Total Cost = $13,301 Cost per SF = $7.39

Envelope Performance Spatial Organization

Annual Envelope Heat Gains & Losses

Seasonal Envelope Heat Gains & Losses Heat Gains (106 BTU)

Heat Loss

(106 BTU)

Auxiliary Heat

Internal Gains

Active Gain

Passi ve Gai n

Fal 1 October 1- December 10

14.85

12.59

.57

1.46 (1.69)

W i nter December 11- February 20

25.84

17.54

.58

1.61 (7.72)

Spri ng February 21- Apri 1 30

16.29

13.47

.56

1.96 (2.26)

Total Annual

56.98

43.60

1.71

5.03

29

Energy Systems Conservation

Envelope

Insulation

Infiltration

South Glazing

Direct Gain

Indirect Gain

Collection

Storage

Distribution

Passive

Active

30

System Performance ENVELOPE CHARACTERISTICS Floor Area (sq. ft.) Volume (cubic ft.) Surface Area (sq. ft.) Surface area/ Volume Ratio % Earth Sheltered Total Glass Area (sq. ft.) Glass/ Floor Area Ratio

1800 •19,886 4203 0.21 0.65 432 0.24 4

INSULATION CHARACTERISTICS 14 C e i I ing 20 Above Grade Opaque 11 Below Grade Number of Glazings: South 2 Other 2 Night Insulation on Glazings (sq.ft.)(136)

R-Value:

INFILTRATION CHARACTERISTICS Ai r Changes/ Hour Heat Exchanger

Code Heat Loss October November December January February March Apr! 1

Area of South Glazing (Including SE and SW) (sq.ft.) South Glass/ Floor Area

% of Code Heat Loss

I nterna I Gai ns

Passive So I ar Gai n

4 4 4 4 4 4 4

32 33 25 38 61 44 33

Annual Total (I03 BTU/ Ft2)

1

7

% of As Bui It Heat Loss

2%

1 A,%

South 400

0.22

400

Storage Mass (tons)

47.0

Heat Capacity (BTU/ Lb-°F)

0.21

INDIRECT GAIN

Storage Mass (tons)

o o

Heat Capacity (BTU/ Lb-°F)

0

G l a z i n g Area (sq.ft.)

65 76 101 99 75 19 2

0.3 No

DIRECT GAIN Glazi ng Area (sq.ft.)

135 198 325 343 319 245 162

Annual Total ( I03 BTU/ Ft2)

SOUTH GLAZING Orientation of Major Glazing

200 274 426 442 394 264 164

As Bui It ConserHeat vation Loss Savings

October November December January February March Apr! 1

31

System Costs Auxiliary Fuel

Actua 1 Auxi 1 iary Heat 99 161 296 301 254 197 (125)

October November December January February March Apri 1 Annual Total ( IQ3 BTU/ Ft2)

44

% of Heat Loss As Bui It

84$

FueI: Wood

15

Electrici ty

Combined Systems

29

Costs CONSERVATION Excavation InsuIation: Ceiling Floor Wai Is, Below Grade Structure: Footings Walls Roof Mechanical Equipment: Smaller Furnace

$1980 257 394 617 559 3253 3303 -1092 $9272

Total Cost BTU Savings (10 BTU/Year)

23

6

$ 403

Cost/10 BTU/Year PASSIVE Extra Glazing Heat Storage (Rock) Distribution

3029 900 100

Total Cost

$4029

BTU Savings ( 106BTU/Year) 6

Cost/10 BTU/Year

11

$ 366

COMBINED SYSTEMS Total Cost

$13,301 6

BTU Savings ( 10 BTU/Year) Cost/106BTU/Year

32

34

$ 391

System Impacts Actual vs. Predicted Fuel Use (BTU/SF-Day) October November December January February March Apri I Annual Total

Predicted 97 163 296 288 271 176 113 42,000

% Deviation From Actual

Actual 74 184 245 326 295 230 (119) 44,000

^ ~^'°

System Costs/Energy Saved $ In vested/ 106BTU Saved/ Yr. Conser- Passive Active Total vation Moderate ly I nsul ated Super I nsu I ated Underground Doub le Enve lope Act! ve/Passi ve Hybrid Average

$ 47

$ 33

$

25

0

23

403

366

391

$ 42

76 83

318

140

179

853

398 186

30 Year Energy Savings 5 YEARS

30 YEARS 10 3 BTU/

S.F.

CONSERVATION

64.8

388.7

PASSIVE

35.5

213.0

100.3

601.7

ACTIVE

TOTAL

33

Uncertainty Range of Uncertainty Conservation Gain = Code Heat Loss - As B u i l t Heat Loss 103BTU/SF-Yr

Range of Uncertainty

0 - 17.4

Calculated Value

54.0 - 67.6

50.2 - 65.6

65

12

53

Solar Gain = As B u i l t Loss - (Actual Auxiliary + Internal Gains) Range of Uncertainty Calculated Value

0

- 28 3 -,

50.2 - 65.6 53

37.3 - 50.2 44

The error in the infiltration rate was virtually eliminated by measurement. As a result, the error in the as-built heat loss is reduced. The primary source of error considered in the heat loss as-built was from internal gains.

34

The Bergstedt House

35

Overview General Characteristics Owner: Location: Designer/ Engineer: Builder: Occupied: Family Size: Occupancy Pattern: House Size: House Type:

Appliances:

Auxiliary Heat: Thermostat Setting: Auxiliary Fuel Consumption: Construction Cost: Energy Conscious Technologies: Cost of Energy Efficient Technologies:

Performance Data (106BTU/Mo) October November December January February N'arch Apr! 1 Annual Total (106BTU/'V) % of Code Heat Loss

% of Heat Loss as Bui It

36

Code Heat Loss

As Bui It Heat Loss

Conservation Savi ngs

1 nterna 1 Gains

Actual Auxi 1 iary

Passive Gai ns

17.6 22.5 35.0 34.9 29.0 24.4 16.9

12.3 15.8 25.4 25.2 20.8 17.2 11.6

5.3 6.7 9.6 9.7 8.2 7.2 5.3

0.3 0.2 0.3 0.3 0.2 0.3 0.2

3.1 7.9 18.8 14.7 7.7 (7.4) (6.2)

8.9 7.7 6.3 10.2 12.9 9.5 5.2

180.3

128.3

52.0

1 .8

65.8

60.7

29% \%

c i (/ P I /o

48%

Bergstedt Duluth, Minnesota Charles Williams and Arno Kahn, Architects Commonwealth Labors and Builders March, 1980 2 Adults 2 Children (7 and 10) Adults work Children in school 1730 SF 2 Story + Basement 3 Bedroom 2 Bath Swing Space Refrigerator Range Laundry Freezer Power tools and heavy loads Wood furnace Electric baseboard heat Day and Night = 68-71°F Annual Total = 66 x 106BTU Annual/ SF = 38 x 103BTU Annual/ SF-°F = 4.5BTU Total Cost = $88,000 Cost per SF = $50.87 Double Envelope Super-insulated Large south sunspace Total Cost = $8,558 Cost per SF = $4.95

Envelope Performance Spatial Organization

Annual Envelope Heat Gains & Losses

Seasonal Envelope Heat Gains & Losses Heat Gains (106 BTU)

Heat Loss (106 BTU)

Auxiliary Heat

Internal Gains

Active Gain

Passive Gai n

Fal 1 October 1- December 10

36.27

17.05

.57

4.82 (18.65)

Winter December 11- February 20

57.24

32.90

.58

6.28 (23.76)

Spri ng February 21- Apri 1 30

34.77

15.81

.56

5.92 (18.40)

128.28

65.76

1.71

Total Annual

17.02

37

Energy Systems Conservation

Envelope

Insulation

Infiltration

South Glazing

Direct Gain

Indirect Gain

Collection

Storage

Distribution

Passive

Active

38

System Performance ENVELOPE CHARACTERISTICS Floor Area (sq. ft.) Volume (cubic ft.) Surface Area (sq. ft.) Surface area/ Volume Ratio" % Earth Sheltered Total Glass Area (sq. ft.) Glass/ Floor Area Ratio "" INSULATION CHARACTERISTICS R-Value:

1730 20,753 4432 0.21 0.20 574 0.33

Ceiling Above Grade Opaque Below Grade Number of Glazings: South Other N i g h t Insulation on G l a z i n g s (sq.ft.)

53 37 11 2 2 44

INFILTRATION CHARACTERISTICS Air Changes/ Hour Heat Exchanger

Code Heat Loss October November December January February March Apr! I

327 434 653 651 598 455 325

229 305 473 470 429 321 224

98 129 180

Annual Total 104 ( I03 BTU/ Ft2)

74

30

South - 494 - 0.29

DIRECT GAIN 104

G l a z i n g Area (sq.ft.) — -

Storage Mass (tons) Heat Capacity (BTU/ Lb-°F)

I nterna I Gai ns October November December January February March Apri I

Pass i ve* Solar Gai n

5 5 5 5 5 5 5

172 148 118 190 266 177 100

1

35

0 0

INDIRECT GAIN G l a z i ng Area (sq.ft.)

101

0.5 NO

Orientation of Major Glazing Area of South Glazing ( I n c l u d i n g SE and SW) (sq.ft.) South Glass/ Floor Area

Storage Mass (tons)

181 169 134

% of Code Heat Loss

SOUTH GLAZING

Heat Capacity (BTU/ Lb-°F)

As Bui It ConserHeat vation Loss Savi ngs

390

38.5 0.21

Annual Total ( I03 BTU/ Ft2)

% of As B u i l t , , ]% 48/ Heat Loss ° These are the inferred values for passive solar gain. However, these values are greater than should be possible based on insolation data recorded at the University of Minnesota.*

System Costs Auxiliary Fuel

Actua I Auxi I i any Heat October November December January February March Apr! I

52 152 350 275 158 (139) (119)

A n n u a l Total ( I03 BTU/ Ft2)

38

% of Heat Loss As Bui It

51$ 18

Fue I : Wood

20

Electricity

Combined Systems

Costs CONSERVATION I nsulation:

Cei I ing W a l l s - Above Grade Mechanical Equipment: SmaIler Furnace

$ 123 1629 -1155

Total Cost

$ 597

BTU Savings ( 106BTU/Year)

52

6

Cost/ 10 BTU /Year

$

12

PASSIVE Extra Glazing

3477

Heat Storage (Trombe Wa I I )

1660

Distribution (Double Wai I)

2724

Mechanical Equipment Total Cost

100 $7961

BTU Savings ( 106BTU/Year) 6

Cost/ 10 BTU /Year

61

$ 131

COMBINED SYSTEMS Total Cost

$8558 6

BTU Savings ( 10 BTU/Year) 6

Cost/ 10 BTU /Year

40

113

$ 76

System Impacts Actual vs. Predicted Fuel Use (BTU/SF-Day)

Predicted

October November December January February March Apri 1

Actual

52 152 350 275 158 (139) (119)

183 259 440 409 361 257 183

63,000

Annual Total % Deviation From Actual

38,000

+61%

System Costs/Energy Saved $ In vested/ 106BTU Saved/ Yr.

Moderate ly I nsu I ated Super I nsu I ated Underground

Conservation

Passive

Active

Total

$ 47

$ 33

$

$ 42

25

0

23

403

366

391

Doub le Enve lope Acti ve/Pass i ve Hybrid Average

76 83

318

140

179

853

398 186

30 Year Energy Savings 5 YEARS

30 YEARS

3

103 BTU/ S.F.

CONSERVATION

Incomplete

Incomplete

PASSIVE

Incomplete

Incomolete

ACTIVE TOTAL

326.0

1955.9

41

Uncertainty Range of Uncertainty Conservation Gain = Code Heat Loss - As B u i l t Heat Loss 3

103BTU/SF-Yr

Range of Uncertal nty

0.6-57.4

Calculated Value

90.5-111.1

53.7-89.39

104

74

30

Solar Gain = As Bui It Loss - (Actual Auxi Mary + Internal Gains) Range of Uncertainty

Ca leu lated Value

"7.9-61.0

35

53. 7 - 89. 9

74

28.9-45.8

38

Since little is known about the infiltration rate in double envelope houses, a slightly larger uncertainty ( ± 2 . 0 instead of ±1.5) was assumed. As a result the building heat loss error was large. The solar gain calculated in this way is greater than that theoretically possible based on Baker's insolation data at the University of Minnesota.

42

The Humphreys House

43

Overview General Characteristics Owner: Location: Designer/ Engineer: Builder: Occupied: Family Size: Occupancy Pattern: House Size: House Type:

Appliances:

Auxiliary Heat: Thermostat Setting: Auxiliary Fuel Consumption: Construction Cost: Energy Conscious Technologies:

Cost of Energy Efficient Technologies:

Performance Data fi

(10°BTJ/Mo) October November December January February March Apri I Annual Total (106BTU/Yr) % of Code Heat Loss % of Heat Loss as Bui It

44

Code Heat Loss

As Built Heat Loss

Conservation Savi ngs

I nterna 1 Gai ns

Active Solar Gai n

Actual A ux i I i a ry

Passi ve Gains

11.3 15.1 24.4 25.4 20.3 15.0 9.3

9.0 12.4 20.6 21.4 17.1 12.3 7.3

2.3 2.7 3.8 4.0 3.2 2.7 2.0

0.2 0.1 0.2 0.2 0.1 0.2 0.1

2.5 1.6 1.0 3.2 2.6 3.4 2.0

5.3 9.7 19.0 17.0 12.8 6.4 4.1

1.1 1.0 0.5 1.0 1.6 2.3 1.0

120.7

100.0

20.8

1.1

16.3

74.2

8.4

•\°/ \ /o

16$

74$

P<# o*

1\ ~i°i I/O

Humphreys St. Paul, Minnesota Alan Humphreys Roger Peterson Michael Plautz, Architect Alan Humphreys, General Contractor October, 1979 2 Adults Adults work 1690 SF 2V2 Story 2 Bedroom 2 Bath Energy-efficient appliances Dishwasher Laundry Power tools Electric furnace (hot air) Day and Night = 65°F

Annual Total = 74 x 106BTU Annual/ SF = 44xl0 3 BTU Annual/ SF-°F = 6.5BTU Total Cost = $87,000 Cost per SF = $51.48 Earth sheltering Passive solar greenhouse with water storage Active collector with annual rock storage Domestic hot water solar assist Total Cost = $17,926 Cost per SF = $10.61

Envelope Performance Spatial Organization

Annual Envelope Heat Gains & Losses

Seasonal Envelope Heat Gains & Losses Heat Loss (106 BTU)

Heat Gains (106 BTU)

Auxiliary Heat

Internal Gains

Active Gain

Passive Gai n

Fal 1 October 1- December 10

28.03

21.05

.34

4.42

4.42 (2.22)

Winter December 11- February 20

47.48

38.93

.34

5.73

5.36 (2.48)

Spri ng February 21- Apri 1 30

24.45

14.22

.33

6.15

4.22 (3.75)

Total Annual

99.96

74.20

1.01

16.30

14.00 45

Energy Systems Conservation

Envelope

Insulation

Infiltration

South Glazing

Direct Gain

Indirect Gain

Collection

Storage

Distribution

Passive

Active

46

System Performance ENVELOPE CHARACTERISTICS Floor Area (sq. ft.) Volume (cubic ft.) Surface Area (sq. ft.) Surface area/ Volume Ratio % Earth Sheltered Total Glass Area (sq. ft Glass/ Floor Area Ratio

1690 19,410 4831 0.25 0.38

375

0.22

INSULATION CHARACTERISTICS R-Value:

Ceiling 42 Above Grade Opaque 23 Below Grade 17 2 Number of Glazings: South 2 Other Night Insulation on Glazings (sq.ft.) 375

INFILTRATION CHARACTERISTICS

216 290 455 473 420 280 178

173 238 383 399 352 230 140

Annual Total 70 ( I03 BTU/ Ft2)

58

October November December January February March Apri 1

Gai ns

South

Area of South G l a z i n g ( I n c l u d i n g SE and SW) (sq.ft.)

312

South Glass/ Floor Area

0.18

DIRECT GAIN 120

Glazing Area (sq.ft.)

30

Storage Mass (tons) Heat Capacity (BTU/ Lb-°F)

0.21

INDIRECT GAIN

October November December January February March Apri 1 Annual Total

(I03 BTU/ Ft2)

% of As Bui It 192

G l a z i n g Area (sq.ft.)

12

- rock water - rock water

Passive So lar Gai n

3 3 3 3 3 3 3

21 19 9 20 33 44 19

.6

5

1$

Heat Loss

0<#

O/o

80 2.7 0.21 1.00

COLLECTION

Active So I ar Gai n

Actual Auxi 1 iary Heat

48 32 19 61 55 65 39

100 190 362 324 269 123 82

Air 240

Col lector Area/ Floor Area

0.14

Storage Mass (tons)

80 0.21

Heat Capacity (BTU/ Lbs-°F)

38

M%

1 nterna 1

Orientation of Major Glazing

System Type Col lector Area (sq. ft.) —

68 50

% of Code Heat Loss

SOUTH GLAZING

Heat Capacity (BTU/ Lb-°F)

43 52 72 74

1 NO

Ai r Changes/ Hour Heat Exchanger

Storage Mass (tons)

As Bui It ConserHeat vation Loss Savi ngs

Code Heat Loss

Domestic Hot Water (BTU/ Mo.) — 1.48x106

October November December January February March Apri I Annual Total (I03 BTU/ Ft2)

._

% of Heat Loss As Bui It

14/o

Fuel :

Wood E lectrici ty

44

14%

6 38

47

System Costs Auxiliary Fuel

Actual Auxi I iary Heat

October November December January February March Apr! I

100 190 362 324 269 123 82

Annual Total (I03 BTU/ Ft2)

44

% of Heat Loss As Bui It

74%

FueI:

Wood

6 38

Electricity

Combined Systems

Costs CONSERVATION I nsuIation: Cei I i ng Wai Is Window Shutters Mechanical Equipment: S m a I l e r Furnace

$ 145 366 3000 -1767

Total Cost

$1744 6

BTU Savings ( 10 BTU/Year)

21

6

Cost/10 BTU/Year

83

PASSIVE Extra G l a z i n g Heat Storage: Water Concrete Floor

1408 400 734

Total Cost

$2542 6

8

Cost/10 BTU/Year

$ 318

BTU Savings (10 BTU/Year) 6

ACTIVE Collectors ($14-28/SF) Storage (Rock) Distribution (Ducts) Mechanical Equipment

3560 9137 854 100

Total Cost

$13,640

BTU Savings (10 BTU/Year) 6

Cost/10 BTU/Year

16

$

853

COMBINED SYSTEMS Total Cost

£17,926

BTU Savings (106BTU/Year) 6

Cost/10 BTU/Year

48

45

E

398

System Impacts Actual vs. Predicted Fuel Use (BTU/SF-Day) October November December January February March Apri 1

Predicted Actual 78 100 176 190 346 362 294 324 248 269 123 123 78 82 41,000 44,000

Annual Total % Deviation From Actua 1

It

System Costs/Energy Saved $ lnvested/106BTU Saved/ Yr. Conser- Passive Active Total vation Moderate ly I nsu I ated Super I nsu I ated Underground

$ 47

$ 33

$ -

25

0

23

403

366

391

$ 42

Doub le Enve lope Act! ve/Passi ve Hybrid Average

76 83

318

140

179

853

398 186

30 Year Energy Savings 5 YEARS

30 YEARS

103 BTU/ S.F. CONSERVATION

61.4

368.3

PASSIVE

25.0

149.8

ACTIVE

48.2

289.4

TOTAL

134.6

807.5

Uncertainty Range of Uncertainty Conservation Gain = Code Heat Loss - As B u i l t Heat Loss 103BTU/SF-Yr

Range of Uncertainty

0-29.1

Calculated Value

12

58.3-73.1

44.0-66.2

70

58

Solar Gain = As B u i l t Loss - (Actual Auxiliary + Internal Gains) Range pf Stlty

Calculated ,,Va i ue

0-24.2

,c 15

44.0-66.2

42.0-53.1

co 58

44

The relatively high uncertainty assumed for internal gains (30% instead of 20%) results in a slightly higher uncertainty in the degree day base than would be expected. This increases the uncertainty in the as-built heat loss. The small quantity of wood used results in a small error in the auxiliary fuel. The range of uncertainty in the active solar gain (6.5 - 10.0 x 103BTU/SF-YR) is a result of the uncertainty in the heat loss value used in the FChart method.

50

Comparisons

51

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Analytical Methods Base Data Climatic Data The climatic data base employed in this analysis was taken from U.S. Weather Bureau statistics and from insolation data gathered by Donald Baker of the University of Minnesota. Temperature data for the moderately insulated, super-insulated, underground, and active/passive hybrid houses were based on Minneapolis/St. Paul Weather Bureau figures although these homes represent locations which are as much as eighty miles apart and represent both rural and urban microclimates. The double envelope house was analyzed using Duluth Weather Bureau data. All degree day bases were modified to represent different rates of heat loss. The following chart depicts the balance point for each analysis and the resultant degree day base generated.

Insolation levels were based on Dr. Baker's base horizontal surface measurements which were then converted to energy incident on vertical surfaces by using the Bowes transformation procedure. These levels do not account for discrepancies in local cloud cover conditions. Duluth might deviate most in this regard due to its location adjacent to Lake Superior. The impact of potential differences in insolation levels are perhaps less crucial to this analysis because they are used only to calculate the predicted auxiliary fuel use as compared with actual fuel consumed. Given this use, the insolation figures used, though admittedly not absolutely accurate, probably represent a better data base than is normally applied in the Solar Load Ratio calculating technique.

Degree Days Base 65° F MINNEAPOLIS

October November December January February March Apri I

Dai Iv Average

1979-80

1980-81

DULUTH

Averaqe

1980-81

16 33 47 53 49 37 20

18 33 39 50 46 38 16

20 28 45 47 41 27 16

20 38 51 56 54 44 28

26 35 53 53 49 37 26

Seasona I Total : Fa I I Winter Spri nq

1958 3607 2150

1947 3341

1907

2094

1642

2275 3883 2629

2376

3226

Annual Total

7714

7382

6775

8803

8397

Deviation From Ave. (BTU/S.F.-Yr.) -939 -322 Absol ute -12/o -4% % From Local C l i m a t o l o g i c a l Data, National Oceanic and Atmospheric Administration, Environmental Data Information Service

3731

2290

-406 -5%

Insolation BTU/SF-Day MINNEAPOLIS October November December January February March Apri I Seasona I Tota I : Fa I I Wi nter Spri ng A n n u a l Total Deviation From Ave. (BTU/S.F.-Yr.) Absol ute al 1°

1979-80

1980-81

890.4 719.9 694.7 911 .2 1133.0 1 147.9 863.0

803.3 769.2 708.1 783.2 1145.0 1 100.4 914.8

56146.0 65496.0 70539.0 192181 .0

Dai 1 y Averaqe

Averaqe

1980-81

833.9 740.5 605.6 962.8 986.2 1 1 3 1 .0 726.8

926.0 741 .7 703.9 936.5 1162.3 1175.5 894.9

867.3 762.9 613.6 989.5 1011.7 1158.3 753.7

55059.0 62049.0 71861 .0

54122.0 62300.0 64754.0

57996.0 67059.0 72586.0

55909.0 63794.0 66612.0

188969.0

181176.0

197641 .0

186315.0

- 3212.0

-1 1005.0 -6%

-2%

DULUTH

-11326.0 -6%

Measurement of Solar Radiation on Horizontal Surfaces, by Donald Baker, University of 11 nnesota Conversion to Vertical Surface, by E I don Bowes Technique

53

Physical Characteristics Surface areas and volumes used in this analysis were calculated from plans which ranged in accuracy from sketches (moderately well-insulated and super-insulated houses) to presentation drawings (the passive/active hybrid house) to construction drawings (underground and double envelope houses). Dimensions were checked when possible against the houses as built. R-values for all these surfaces were based on materials as called out on drawings or as defined by the owners of respective houses and conform to values found in the ASHRAE Handbook of Fundamentals (1977). Infiltration rates, with the exception of measured values for the underground house, were based on educated guesses. Both the moderately well-insulated and passive/active hybrid houses were estimated to have one air change per hour because no special efforts were made in these houses to reduce this rate. The .24 air changes per hour used in analyzing the super-insulated house was based on measured figures of other super-insulated houses. The .5 air change per hour level of infiltration in the double envelope house was assumed to be this low because of the inherent integrity of the outer shell of this dwelling. All glazing areas were reduced 20% to account for mullions. Night insulation was used in calculating the heat loss of the double envelope and passive/active hybrid houses. Auxiliary Fuel Estimates of monthly auxiliary fuel use in each house were developed in the following manner. All electric consumption was assumed to be eventually converted to heat. Wood was assumed to weigh 2,900 pounds per cord and contain 9,000 BTU's per pound. Conversion efficiency of stoves was estimated to be 50% yielding approximately 13 million BTU's of useful energy per cord of wood burned. As both utility bills and wood burned per month were estimated values, the total of the auxiliary energy available from these sources was apportioned to each month based on the relative number of degree days and amount of insolation available in each month. The total annual passive gain was calculated from the energv balance equation.

The annual passive gain was apportioned to each month based on the available insolation for that month:

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The monthly passive gain was substituted in the monthly energy balance equation to find the apportioned monthly auxiliary fuel:

L F I A P t m

= = = = = =

calculated heat loss auxiliary fuel internal gains active solar gain passive solar gain annual total monthly total

Internal heat gains were based on estimates of the period of time each house was inhabited assuming that each person generates 12 x 103 BTU per day. Costs All material and labor cost figures were obtained from Dodge Manual and Building Systems Cost Guide for 1980. Please refer to these documents for cost figures given in this study.

Analytical Strategy The general strategy employed in this analysis was premised on a lack of monitored data and level of confidence in calculated values. Conservation gains were simply defined as the difference between the amount of heat the house would be calculated to lose using Minnesota State Energy Code standards (.16 BTU/SF-hr. for exposed vertical surfaces and .033 BTU/SF-hr for exposed horizontal surfaces) and the calculated heat loss of the house as it was built. As both measures are based on ASHRAE calculations, the relative margin of this difference can be taken as a fairly accurate portrayal of conservation savings. Determining the passive and/or active solar gain of each house is a bit less straightforward in the absence of monitored data. We have chosen to represent this quantity as the difference between the calculated heat loss of the house and the auxiliary fuel plus the internal gains calculated for each dwelling. To support this procedure, we suggest that it conforms with the level of confidence which might be ascribed to each of these measures. Auxiliary fuel consumed and internal gains were considered to be the most reliable of these figures. Heat loss calculations were felt to be more reliable than solar gain calculations because they were based on longer and more frequently verified experience. Solar gains were thus inferred. This procedure yielded credible results with the exception of the double envelope house. In this case the amount of energy that would have to be provided by the sun to compensate for the difference between the calculated heat loss and auxiliary fuel use, plus internal gains in this home

would be greater than the amount of insolation theoretically available per square foot of glazing. The total fuel savings of this house is believable. It is the allocation of this savings to respective systems which yields inaccurate results. The double envelope probably has a lower heat loss than calculated. In any case, this house is currently being monitored by the United States Department of Energy. We would hope that the results of their investigation would help to resolve our quandary. Internal gains were estimated using heat gain values for appliances and people listed in Earth Sheltered Housing Design. The heat gain from active solar collectors was calculated using the F-Chart method (Duffie and Beckman, 1980). Passive solar gains were calculated using the Solar Load Ratio method (Balcomb, 1980). The above-grade heat loss of the houses was calculated using:

To calculate the heat loss of the houses as they were built, the heat loss coefficients were calculated using the equation U= 1/R where R = heat resistance of the materials composing the walls or ceilings. The number of air changes per hour for each house was estimated, except in the case of the underground house which was measured at 0.3 air changes per hour. The temperature differential was taken to be the difference between the balance point temperature and the exterior ambient temperature:

where Tb = Balance Point Temperature T0 = Exterior Ambient Temperature The balance point temperature is the temperature of exterior ambient air below which auxiliary heat is required to maintain a set internal temperature. This varies with the internal gains and the building heat loss per degree of temperature differential. b - 1 set

where U = Heat Loss Coefficient (BTU/Hr-SF-°F) A = Surface Area (SF) V = Volume of the House (Ft3) n = Number of Air Changes per Hour AT = Temperature Differential (°F) t = Hours per Day To calculate the heat loss of the houses built to meet the Minnesota Energy Code standards, one air change per hour was assumed and the following heat loss coefficients (U) were used: Walls Ceiling

0.16 BTU/SF-Hr-°F 0.33 BTU/SF-Hr-°F

Daily Internal Gains Daily Building Loss per Degree

The number of degree days for a specific balance point temperature was derived using maximum and minimum daily temperatures. During months when the maximum daily temperature (M) was always below the balance point temperature, the number of degree days for that month (D) were calculated using the following equation:

where Tb = Balance Point Temperature D = Number of Degree Days for Month M = Maximum Daily Temperature m = Minimum Daily Temperature n = Number Days in the Month

Calculation Logic

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There were parts of some days when auxiliary heat was not required, e.g. when a month had one or more days during which the maximum temperature was above the balance point temperature. The number of degree days per day (d) were then calculated. When the maximum temperature was below the balance point temperature, we used the equation:

For the remaining days, during which the maximum temperature was above the balance point temperature, we used the equation:

The range of uncertainty for each house was calculated using the most optimistic and pessimistic assumptions possible within the bounds of reason. The following figures were used to generate these ranges:

Thermostat Setting:

nf i Itration Rate: Moderate I n s u l a t i o n ±0.35 A i r Changes/Hr Passive/Active Hybrid Underground Double Envelope

±0.20 Ai r Changes/Hr

Super I n s u l a t e d

±0.10 A i r Changes/Hr

Internal G a i n s :

The total degree days for these months was the sum of degree days for each day of the month.

60°F - 68°F

A u x i l i a r y Fuel

+4.5 Kwh/Fami ly/Day (Wood)

±i C o r d / D w e l I ing ±2.3

E l e c t r i ci ty:

X 106BTU/ Cord

5% Exterior Use

The below grade heat loss for all houses was calculated using the equation:

For all houses other than the underground, the temperature differential was assumed to be 33°F throughout the heating season. For the underground house, the temperature differential was assumed to be the difference between the interior temperature and the average ground temperature for the specific month at the specific depth below grade. The calculation of conservation savings and inferred passive solar gains involves the propagation of errors through the calculation process. The sources of possible error and their location within the calculation process are indicated in the diagram below.

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The net result of this error analysis identifies the range of values for each house that both conservation and solar gains might legitimately be considered to fall within. On the graphs accompanying the analysis of each house, the maximum values of the ranges are indicated but the minimums are not, as they frequently would indicate zero or in some cases, negative gains.

Comparisons Amount of Auxiliary Fuel Used When the auxiliary fuel used for space heat in each house is normalized to mitigate differences in size and degree days experienced, the performance is as follows: Super-Insulated Double Envelope Moderately Insulated Active/Passive Hybrid Underground

2.8 4.5 5.1 6.5 6.5

BTU/SF-°F BTU/SF-°F BTU/SF-°F BTU/SF-°F BTU/SF-°F

The following chart summarizes the total auxiliary fuel consumed by each house, the BTU's of auxiliary fuel required per square foot of habitable space, and the BTU's of fuel required per square foot of habitable space per °F (a number sometimes referred to as the thermal integrity factor).

Wood

E lectri city

Tota I s 106BTU/Yr

10 3 BTU/SF-Yr

(Cords)

(KWH)

Moderately Insulated

4.0

35,048

161.0

38.3

5.1

Super 1 nsu 1 ated

0

11,439

44.3

21.5

2.8

Underground

1 .50

15,805*

80.1

44.5

6.5

65.8

38.0

4.5

74.3

43.9

6.5

37.0

5.1

Double Envelope

2.50

A c t i v e / P a s s i v e 0.75 Hybrid

9,754** 23,395

Average Average Mi nnesota House

* **

115.0

BTU/SF-DD

14.9

I n c l u d e s Estimated 1963 KWH for A p r i l 1981 I n c l u d e s Estimated 1787 KWH for March and A p r i l 1981

In this comparison, it is important to note that all houses performed significantly better than the average Minnesota house. The most efficient of the houses, the Scott (super-insulated) House, consumed only 21,500 BTU/SF-Yr. or 19% of the energy used by the average Minesota house. Though the least efficient of the five houses, the Wild River House (underground), consumed twice as much auxiliary fuel per square foot as the Scott House, it still used only 39% of the Minnesota average.

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Actual vs. Predicted Auxiliary Fuel Actual versus predicted use of auxiliary fuel in each house is defined as the difference between the amount of auxiliary fuel actually consumed over a heating season versus the amount that would be predicted to be used by the Solar Load Ratio Method as documented in the Passive Solar Handbook, Volume 2 (Balcomb et al, 1980).

the Wild River House (400 SF) and the Humphreys House (312 SF) utilize large areas of south facing glazing. The performance of the double envelope house simply cannot be accounted for using the same calculating techniques applied to the other houses. The auxiliary fuel used by this house was 67% less than predicted and the passive solar gain inferred for this house (60.8 x 106 BTU/YR) is considerably greater than the maximum available over this period of time (49.0 x 106 BTU/YR). A possible explanation for these two findings is that conventional calculating techniques overestimate double envelope heat losses. If this were true, conservation savings would increase for this technology, the passive solar contribution would decrease, and predicted auxiliary fuel using the Solar Load Ratio method would decrease. Two calculating uncertainties may account for this problem. First, the actual R-value of the air space is based on still air in interstitial spaces rather than convective loops. Second, the infiltration rate may be lower than the .5 air changes per hour assumed. In any case, we have not included the double envelope house in system performance or system cost comparisons for this reason.

Inferred vs. Predicted Passive Gain With the exception of the Bergstedt (double envelope) House, actual auxiliary fuel was within 15% of that predicted by the Solar Load Ratio Method. The Wild River House (underground) and the Humphreys House (active/passive solar hybrid) used slightly more fuel than predicted: 5% and 8% respectively. The Fisher (moderately well insulated) and Scott House (super-insulated) used 13% and 14% less fuel, respectively, than predicted. A portion of this discrepancy may be explained by a study (Palmiter, 6th National Passive Solar Conference, 1981) that contends that passive solar gains increase but in decreasing increments as south facing glazing increases from 100 SF to 300 SF. Both Calculated Gain SLR Method (106BTU/ Yr) Moderate ly 1 nsulated Super 1 nsulated Underground Doub le Enve lope Active/ Passive Hybrid

58

I nferred Gai n (106BTU/ Yr)

An interesting comparison is that of the amount of passive solar energy gain that would be predicted by the Solar Load Ratio method and the amount inferred to be gained by subtracting the auxiliary fuel from the calculated heat loss of the house. It would appear that those houses with small ratios of south facing glazing to floor area contributed significantly more solar energy than the Solar Load Ratio Method predicted, while those with large glazing areas contributed less. A possible explanation for this difference may be the effectiveness of night insulation for glazing. A second explanation would be the Palmiter finding that increased glazing delivers decreasing increases in passive solar gain per unit of south facing glazing. South Glazing To Floor Area Ratio

Di f ference (106BTU/ Yr)

Percentage

10.75

31 .43

0.10

20.70

+ 195$

5.03

1 1 .68

0.08

6.65

+ 122%

16.46

12.78

0.22

3.68

- 22%

5.56

- 40$

INCOMPLETE DATA

14.00

8.44

0.18

System Performance These figures yield two major findings. First, conservation accounts for 30xl0 3 BTU/SF of the 37 x 103 BTU/SF that the Fisher, Scott, Wild River, and Humphreys' houses conserved. Thus, 81% of the average energy savings attributed to these four homes was due to improved insulating techniques while 19% (7 x 103 BTU/SF) can be attributed to solar gains. In the extreme instance of conservation (Scott, super-insulated house) 93% of the energy (82 x 103 BTU/SF of 88 x 103 BTU/SF) saved is due to improved insulating techniques. The Humphreys House is the only home of the four to register larger solar than conservation savings. In this house 54% (14.6X10 3 BTU/SF of 26.9xl0 3 BTU/SF) was due to a combination of the house's active and passive solar systems.

10 BTU/S.F.

Moderately I nsu lated Super I nsulated Underground

Total Savi ngs Acti ve Passi ve Conservation Ca leu lated Mi n/Max Calcu lated MI n/Max Calculated Win/Max Calculated Min/Max ( I nferred) 22 4/ 30 8 0/10 14 4/21 (3) 58/107 88 6 0/14 82 59/93 (2) 19 3/ 40 7 3/23 12 0/17 (9)

Doub le Enve I ope Acti ve/Passi ve Hybrid

-

Average

30

12

-

0/29

5 (8) 7 (6)

0/14

10

7/11

65

13/110

27

11 53

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Range of Uncertainty The second conclusion that may be drawn from these figures is that calculated values float in rather broad ranges of possible values. Though deviation from the calculated figure becomes progressively less probable as the extremes of these ranges are approached, it remains clear that our figures constitute best estimates rather than definitive findings. A great deal of this uncertainty would be eliminated with the aid of a small amount of monitored information. Simple monitoring of inside and outside air temperatures, levels of solar radiation on vertical glazing, weight of wood burned, and monthly use of electricity inside the dwelling in addition to infiltration and stove efficiency tests would improve our data and hence reduce our range of uncertainty by a significant degree. Two of these houses (Wild River and Bergstedt) are currently being monitored.

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Costs per BTU Saved The average cost per million BTUs saved annually through conservation for the Fisher, Scott, Wild River and Humphreys House was $140; for passive solar systems this figure was $179; for the active system of the Humphreys House it was $853. The most cost-effective technology was the conservation measures of the Scott House ($25/106 BTU/YR) followed closely by the Fisher House insulation investment ($47/l(T BTU/YR). The least cost-effective technology was the underground house conservation measures with a cost of $403/106BTU/YR.

Though individual houses vary, the pattern appears clear; conservation measures, excluding those unusual and expensive technologies employed in the underground house, are roughly three times as effective as their passive counterparts in terms of dollars invested per BTU's saved.

60

An interesting way to compare these five houses in terms of total energy saved versus dollars invested to save that energy is to rank the houses in terms of level of investment and then to graph energy savings against that investment. This graph clearly depicts a point of diminishing returns in terms of these five homes. The BTU's saved increase rapidly for a minimal increase of investment from the moderately insulated to the super-insulated solution. More complex and expensive technologies are represented by decreasing energy savings per dollar invested. This comparison would indicate that complexity, at least among these five houses, appears to be counter-productive. As these technologies grow to be more extensive and more complex, their cost increases commensurately but auxiliary fuel savings do not. Insulation, the simplest of all the strategies, consistently delivers the highest returns. Whether this trend is the result of our analytic methods, the unique characteristics of the five houses analyzed, or a broader principle remains to be seen.

30 Year BTU Savings The final comparison we would like to present is the fuel savings that the technologies employed in these houses will generate over the next thirty years. This time frame was selected because it represents an estimate of the years each house will be occupied before major maintenance or remodeling changes occur. The use of fuel savings alone as a measure independent of dollar investments or savings is the appropriate final statement of this study as it highlights future regional dilemmas and potentials rather than individual costs and benefits. Single family detached dwellings accounted for 13,400 of the dwelling units constructed in the state of Minnesota during 1980. If those houses were built to conform to the Minnesota State Energy Code, they will require 64.5xl012 BTU of auxiliary fuel energy over the next thirty years. This is certainly a major improvement over the 69.1 x 1012 BTU of fuel that would be consumed if these same houses simply met the standard of the average fuel use of Minnesota houses for space heat. It falls far short of the 23.7xl0 12 BTU that these houses would consume if they achieved the average savings of the five houses of this study. If all these houses were constructed to meet the specification of the most efficient of these solutions, the savings involved would be even more substantial (IS.OxlO 12 BTU). It is difficult to put such large figures into some kind of understandable form. Perhaps if all 1980 single family detached homes met the average auxiliary fuel use of five houses of this study, the potential savings generated over the next 30 years would save enough energy to heat an additional 23,600 of our existing, inefficient homes at their present average rate of fuel consumption for one year.

10 3 BTU/S.F. 5 Year

30 Year

Moderately 1 nsu lated

107

644

Super 1 nsu 1 ated

440

2641

Underground

100

602

Doub le Enve lope

326

1956

Active/Passive Hybrid

135

808

Average

220

1320

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Postscript

We would like to conclude by saluting the owners, designers and builders of these five houses. They are pioneers in an age of uncertainty. It is difficult in an era like the one in which we find ourselves to identify kinds and directions of change in societal thought and values that are currently taking place. Our ability to perceive these changes is clouded by our participation in them. If our attitudes toward the resources of the earth are in transition, houses like the ones studied in this book may be the most tangible evidence of that change. Each manifests a commitment to a new vision of our place within nature's systems that goes far beyond simply reducing fuel bills. In that sense, these houses may not be as representative of five degrees of technological impact as they are manifestations of a new degree of societal awareness for the ecology of our planet.

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Bibliography

ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigeration, and Air Conditioning Engineers, NY (1977). Balcomb, J. D.; Barley, Dennis; McFarland, Robert; Perry, Jr., Joseph; Wray, William; Noll, Scott. Passive Solar Design Handbook, Volume Two (Appendix A) U.S. Department of Energy, Washington, D.C. (1980). Building Systems Cost Guide 1980, Robert Snow Means Co. Inc., Kingston, MA (1980). Dodge Manual, McGraw-Hill Cost Information Systems, McGraw-Hill, NY, (1980). Duffie, John A., and Beckman, William A. Solar Engineering of Thermal Processes, John Wiley and Sons, Wiley-Interscience, NY (1980). Energy Conservation in Buildings, Code of Agency Rules, Department of Administration, Building Code Division, St. Paul, MN (1978). Energy Policy and Conservation Biennial Report, State of Minnesota Department of Energy; St. Paul, MN. (1980). Karlekar, Bhalchandra V., and Desmond, Robert M. Engineering Heat Transfer, West Publishing Company, St. Paul, MN. (1977). Mazria, Edward, The Passive Solar Energy Book, Rodale Press, Emamaus, PA (1979) Palmiter, L. "Annual Load Curves: A new Design Tool," Proceedings of the 6th National Passive Solar Conference 1981, American Section of the International Solar Energy Society, Neward, DE. (1981). Peterson, Roger A. Energy Budgets of Super-Insulated versus Earth-Sheltered Housing in Minnesota, Paper submitted as coursework for Architectural Design, University of Minnesota, Minneapolis, MN. (1980). Earth Sheltered Housing Design, Underground Space Center, University of Minnesota, Van Nostrand Reinhold Co., New York, (1979). Young, HughD. Statistical Treatment of Experimental Data, McGraw-Hill, New York (1962).

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