NATL INST. OF STAND & jECH REFERENCE

isTBsTR 77-1274

Retrofitting an Existing Wood

Frame Residence for Energy

Conservation—an Experimental

Study

D. M. Burch

C. M. Hunt

Thermal Engineering Section

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington. O.C. 20234

July 1977

Final Report

Prepared for ^qq Federal Energy Administration

^c;^ Washington, D.C. 20461

NBSIR 11All^

RETROFITTING AN EXISTING WOOD

FRAME RESIDENCE FOR ENERGY

CONSERVATION-AN EXPERIMENTAL

STUDY

D. M. Burch

C. M. Hunt

Thermal Engineering Section

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20^34

Sponsored by:

The Federal Energy Administration

12th and Pennsylvania, N.W.

Washington, D.C. 20461

July 1977

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman. Under Secretary

Jordan J. Baruch, Assistartt Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. EmMt Ambler, Acting Director
!„
RETROFITTING AN EXISTING WOOD-FRAME RESIDENCE FOR ENERGY CONSERVATION —

An Experimental Study

by

D. M. Burch and C. M. Hunt

ABSTRACT

A wood-frame residence having only limited insulation in the attic

was retrofitted in three stages to reduce its energy requirements for

heating and cooling. The three retrofit stages comprised: reducing air

leaks; adding storm windows; and installing insulation in the floor,

ceiling, and walls. The house was extensively instrumented to evaluate

energy savings and other performance factors. An economic model was

used to evaluate the cost effectiveness of the retrofit options and the

number of years to pay back their initial investment.

The walls of the test house were insulated with three different

types of insulating material: fibrous glass wool, cellulosic fiber, and

urea-formaldehyde foam. The thermal performance of these three insulating materials was measured and compared, both in the field and laboratory.

"Recommended good practices" for moisture protection were applied

when insulation was installed in the test house. The effectiveness of

these measures in preventing damaging moisture accumulation in crawl

spaces and attics was evaluated.

Finally, thermographic surveys were performed before and after the

retrofit: Based on the results of these surveys, criteria for distinguishing between insulated and uninsulated wood-frame cavity walls were

presented.

Key words: Air infiltration; condensation in buildings; energy conservation; energy measurements; fuel-savings; heat-loss reduction;

insulation properties; residential heat loss; retrofitting

houses; thermal conductivity; thermal insulation; thermography.

i
i CONTENTS

ABSTRACT

EXECUTIVE SUMMARY

1. INTRODUCTION

2. DESCRIPTION OF TEST HOUSE

3. ENERGY- CONSERVATION MODIFICATIONS PERFORMED ON THE

TEST HOUSE

3.1 Measures Taken to Reduce Heating and Cooling

Energy Requirements

3.2 Protective Measures for Preventing Moisture

Accumulation in the Attic and Crawl Space

4. HEAT-TRANSFER PROPERTIES

5. AIR-INFILTRATION MEASUREMENTS

5.1 Theory

5.2 Measurement Technique

5.3 Results and Analysis

5.4 Conclusions

6. ENERGY MEASUREMENTS

6.1 Experimental Plan

6.2 Instrumentation and Measurement Technique

6.3 Winter Energy Measurements

6.4 Summer Energy Measurements

6.5 Conclusions

7. ECONOMIC ANALYSIS

7 . 1 Theory

7.2 Results

7.3 Conclusions

ii
CONTENTS

Page

8. COMPARISON OF THE THERMAL PERFORMANCE OF THREE

INSULATING MATERIALS 74

8.1 Guarded-Hot-Plate Measurements 74

8.2 Full-Scale Laboratory Wall Tests 75

8.3 Heat Transmission and Moisture Measurements in

Retrofitted Wall Sections of the Test House 80

8.4 Other Performance Properties of Insulation 94

8.5 Summary of Results 96

9. EFFECTIVENESS OF RECOMMENDED "GOOD PRACTICE" MEASURES

FOR PREVENTING MOISTURE ACCUMULATION 98

9.1 Experimental Plan 98

9.2 Experimental Results 98

9.3 Conclusions 98

REFERENCES 99

NOMENCLATURE 101

CONVERSION TABLE 103

ACKNOWLEDGMENTS 104

APPENDIX A. Description of the Third Stage of the Retrofit A-1

APPENDIX B. Location of Heat Leaks in Residences Using

Infrared Thermography ^"1

APPENDIX C. Location of Air-Leakge Paths in a Residence

Using Pyrotechnic Smoke ^"1

ill

It

I
FIGURES

Page

1. Photograph of the test house. 9

2. Typical cross-section of the house after retrofitting. 10

3. Floor plan of the test house. 11

4. Caulking compound being applied to foundation sill. 15

5. Storm window being installed. 16

6. A photograph of the south side of the test house

showing the awnings. 18

7. Apparatus used to measure air-leakage rates for the

test house. ; 23

8. Pre-retrofit air- infiltration correlation. 27

9. Post-retrofit air- infiltration correlation. 31

10. Schematic diagram of furnace system showing the location

of measuring transducers. 39

11. Photograph of the weather station. ^1

12. Floor plan of test house showing location of

temperature sensors. ^3

13. Measured heating loads for the unoccupied test house

after various stages of the retrofit. ^6

14. Energy-release rates for equipment , lighting, and

occupancy.

15. Heating-load correlations for the occupied test house

after various stages of the retrofit. ^9

16. Heating degree days as a function of outdoor balance

temperature for Washington, D.C. 51

17. Pre- and post-retrofit winter crawl-space temperatures. 55

18. Pre- and post-retrofit winter attic temperatures. 56

19. Pre- and post-retrofit sensible cooling loads. 59

20. Pre- and post-retrofit latent cooling loads. 60

iv
FIGURES

Page

21. Pre- and post-retrofit sununer indoor relative humidities. 61

22. Pre- and post-retrofit daily-average summer crawl-space 63

temperatures.

23. Pre- and post-retrofit daily-average summer basement ; 64

temperatures.

24. Pre- and post-retrofit daily-average summer attic 65

temperatures.

25. Construction details of laboratory test wall. 76

26. Location of measurement transducers on laboratory test 78

wall.

27. Photograph of exterior surface of laboratory test wall 81

showing buckling and warping of the wood siding.

28. Elevation view of wall section of the test house showing 82

measuring station.

29. The effect of mean wall temperature on the thermal 84

conductance of the three separate wall sections.

30. Floor plan of the test house showing location of 86

humidity sensors and places where moisture content

samples were cored out.

31. Variation of indoor relative humidity and relative 88

humidities of embedded sensors.

32. Water blister at exterior surface of U-F wall section. 91

33. Percent linear shrinkage of urea-formaldehyde foam as a 95

function of elapsed time.

TABLES

1. Description of Exterior Building Elements Before the 12

Retrofit (Inside-to-Outside)

2. Thermal Conductivities of Building Components. 19

3. Areas and Pre-Retrofit Thermal Transmittances for 20

Building Components.

V
TABLES

Page

A. Theraal Transmittances for Retrofitted Building 21

Components.

5. Pre-Retrofit Air-Infiltration Measurements. 25

6. Air-Infiltration Rates After Stage 1 of the Retrofit. 28

7. Air-Infiltration Rates After Stage 2 of the Retrofit. 30

8. Air-Infiltration Rates After Stage 3 of the Retrofit. 32

9. Effect of Attic Ventilation on Air Infiltration. 33

10. Summer Air-Infiltration Rates. 34

11. Calculation of Annual Heating Loads. 52

12. Comparison of Reductions in Heat-Loss Rate to 53

Reductions in Annual Heating Load.

13. Pre-Retrofit Steady-State Winter Heat-Loss Calculations. 57

14. Post-Retrofit Steady-State Winter Heat-Loss Calculations. 57

15. Daily-Average Heat-Transfer Rates, Btu/h. 62

16. Cost Estimate for Energy Conservation Options. 70

17. Heating System Efficiencies and Fuel Costs Used for 70

Sample Calculations.

18. Winter Heating Energy Cost and Savings, Dollars. 72

19. Pay-Back Periods for Energy-Conservation Options. 73

20. Thermal Conductivities of Three Insulating Materials 75

Measured in the Guarded-Hot-Plate Apparatus.

21. Experimental Results of Full-Scale Laboratory Wall Tests 79

After Two-Month Exposure.

22. Temperature Coefficients (a) for the Thermal Conductivity 79

Values.

23. Comparison of Measured and Predicted Thermal Conductance 85

Values at Wall Sections Insulated with Loose-Fill

Materials.

vi
TABLES

Pa^e

24. Winter Moisture Contents of Material Samples Removed 89

from Cellulose Wall Sections.

25. Winter Moisture Contents of Material Samples Taken from 89

the Glass-Fiber Wall Section.

26. Winter Moisture Contents of Material Samples Taken from 90

U-F Wall Section.

27. Summer Moisture Contents of Material Samples Removed 93

from Cellulose Wall Section.

28. Summer Moisture Contents of Material Samples Taken from 93

the Glass-Fiber Wall Section.

29. Summer Moisture Contents of Material Samples Taken from 94

the U-F Wall Section.

30. Measured Linear Shrinkage of In Situ U-F Foam of the 94

Test House.

vli

EXECUTIVE SUMMARY

A wood-frame residence having only limited insulation in the attic

was retrofitted in three stages to reduce its energy requirements for

space heating and space cooling. The three stages were: reducing air

leaks; adding storm windows; and installing insulation in the floor,

ceiling, and walls. The house was extensively instrumented to evaluate

energy savings and other performance factors.

Techniques used to reduce air-leakage rates did not produce measurable reductions in heating energy requirement. This was attributed

to the fact that the test house was of tight construction in its original state. The addition of storm windows reduced heating energy re- quirement by 25.2 percent. The installation of insulation in the walls,

ceiling, and floor reduced heating energy consumption by an additional

33.3 percent. The total reduction in heating energy requirement achieved

by all stages of the retrofit was found to be 58.5 percent.

Measurements of daily average cooling loads before and after the

retrofit indicated that the retrofit was not effective in reducing the

cooling energy requirement for this particular test house under the

particular conditions tested. Post-retrofit latent loads were found to

be somewhat less than corresponding pre-retrofit values, whereas postretrofit sensible cooling loads were found to be slightly higher than

corresponding pre-retrofit values. An explanation is given in the

following

As part of the third stage of the retrofit, a plastic-sheeting

vapor barrier was installed over the bare earth of the crawl space and

insulation with a vapor barrier was installed in the floor over the

crawl space. These measures were effective in reducing vapor flow to

the living space and caused a substantial reduction in indoor relative

humidity during the summer. Lower moisture levels within the living

space after the retrofit resulted in lower latent loads. Prior to the

retrofit, there was no insulation in the floor over the crawl space, and

heat loss through the floor provided natural summer cooling for the

house. The insulation placed in the floor over the crawl space precluded

much of the natural cooling provided by heat loss through the floor and

more than offset the benefits derived from additional ceiling insulation. The roof overhung the south wall of the test house and provided

significant shading of the windows from solar radiation, thereby precluding much of the benefit to be derived from awnings. The effect of

storm windows and wall insulation was small due to the fact that daytime

reductions in heat gain were offset by nighttime reductions in natural

cooling of the test house since the windows were kept closed at all

times. The applicability of these findings on summer cooling to similar

houses is discussed in the text.

1
An economic analysis was performed to evaluate the relative merits

of the energy conservation measures. Since the retrofit did not provide

reductions in the cooling energy requirement for this particular test

house, the effect of reduction in the summer energy requirement was not

included in the economic analysis. Sealing air leaks was not foiind to

be cost effective, since this process produced no measurable reduction

in the winter energy requirement. For this set of retrofit experiments,

storm windows were found to be more cost effective than installing insulation, since they required significantly fewer yeaxs to pay back their

initial investment.

A second objective of the study was to compare the thermal performance of three insulating materials commonly used to retrofit the ex- terior walls of residential buildings. The three materials selected for

study were cellulosic fiber, fibrous-glass wool, and urea-formaldehyde

(U-F) foam. The comparisons consisted of thermal conductivity measurements using the guarded-hot-plate apparatus, heat-loss and moisture

measurements performed on a full-scale test wall which was exposed to

simulated winter conditions in the laboratory, and heat-loss and moisture measurements on wall sections of the test house.

Thermal conductivity measurements were performed on specimens of

the three materials in accordance with the guarded-hot-plate standard

method of test given in ASTM C 177-71. Each specimen was prepared so that its density was approximately equal to the typical density of the

insulation material when it is blown into cavity walls. The thermal

resistance (R-value) for all three materials was found to be good. The

thermal resistance (R-value) for the U-F foam was found to be 17 and 19

percent higher than the values for cellulosic fiber or fibrous glass

wool, respectively.

In the laboratory, a full-scale (8 x 8 ft (2.44 x 2.44m)) test

wall, similar in construction to the walls of the test house, was ex- posed to approximately a 5° F (-15° C) winter condition for a two-month

period. The interior surface of the wall was maintained at approximately

75° F (23.9° C) and 45 percent rh. Different sections of the test wall

were insulated with the three insulating materials. Heat-loss rates and

moisture contents of the insulations were measured at the separate

sections of the test wall. Measured heat-loss rates agreed within

approximately 10 percent of corresponding predicted values determined by

the series-resistance method, even though a significant amount of

moisture had accumulated within each of the insulating materials.

The three insulating materials were also installed in 14-foot

(4.3m) wall sections of a test house. Measured thermal conductances of

the separate wall sections were observed to decrease as the mean temperature of the insulation was reduced. Thus, the thermal resistance of

the wall sections increased when the outdoor air temperature became

lower. Measured conductances of the wall sections insulated with

cellulosic fiber and fibrous-glass wool agreed with corresponding values

predicted by the series-resistance method. In the case of the U-F wall

section, measured conductances of this wall section were observed to be

2
higher than corresponding predicted values determined by the seriesresistance method. The higher thermal conductances observed at the U-F

wall section were attributed to the presence of a fissure (void space)

in line with the measuring station, and the possible presence of a portion of the water originally contained in the foam.

After the winter season, in the third week of April, 76 days after

insulation was blown in the walls of the test house, samples of the wood

siding, sheathing, and insulation materials were cored out at various

locations of the separate wall sections. The moisture contents of these

samples were determined using an oven-drying technique.

The moisture contents of the wood siding and sheathing at wall

sections of the test house insulated with the loose-fill materials

ranged from 12 to 15 percent. The average moisture contents of the wood

siding and sheathing at the U-F wall section of the test house were

found to be 23.2 and 33.4 percent, respectively. These values are

considerably higher than corresponding values measured at the other wall

sections, and may be accounted for as follows:

The U-F foam had a wet density of 2.5 Ib/ft"^ (40.1 Kg/m^) . After

the U-F foam had cured in the wall cavity, its dry density was 0.7

lb/ft (11.21 Kg/m-^) . The difference in these densities is due to the

water originally contained in the foam, which represents the introduction into the wall cavity of approximately 0.47 lb of water for each

square foot of exterior wall surface (2.29 Kg/m^). The foregoing results

suggest that much of water originally contained in the foam had migrated

from the U-F foam into the sheathing and wood siding and was unable to

penetrate the oil-base paint system applied to the exterior surface. An

oil-base paint film has a comparatively low permeability to water vapor

and functions somewhat as a vapor barrier. At the end of the winter

season, some blistering of the oil-base paint system at the U-F wall

section was observed.

It should be pointed out that if a more permeable paint system had

been applied to the exterior surface the original moisture of the U-F

foam might have passed through the construction and escaped to the

outside environment. The heat of the following summer was effective in

driving out most of the accumulated moisture.

Other performance properties of the insulations that were investigated included shrinkage and fissures of the U-F foam and settling of

the loose-fill materials.

Approximately three months after the foam was installed in the test

house, the U-F wall section was opened up, and the foam was examined for

shrinkage and fissures. Several fissures were observed. The linear

shrinkage was measured and found to be approximately 2.6 percent.

Fifteen, twenty, and twenty-six months after the installation of the

foam, the U-F wall section was again opened up and the linear shrinkage

was found to be 5.6, 7.3, and 8.1 percent, respectively. In this time

3
period, the rate of shrinkage was observed to occur at approximately a constant rate irrespective of the age of the foam; very little leveling

off in the rate of shrinkage was observed. Aside from the shrinkage,

the foam appeared to be in good condition after 26 months. No new

measurements of conductance were made.

In the case of walls insulated with loose-fill materials, no settling of the materials was observed over an 18-month period. In the

case of the ceiling, gradual settling of the cellulose fiber insulation

occurred during the first 25 days following the installation of the

material, after which settling took place at a reduced rate. At the end

of 25 days, the loose-fill material had settled 3/4 inch (1.91 cm) out

of an initial fill of 6 inches (15.24 cm). Eighteen months after the

installation, the total measured settling was 1-1/2 inch (3.82 cm) out

of an initial fill of 6 inches (15.24 cm), or 25 percent. The bag count

for the cellulose insulation indicated that the cellulose installed had

been initially applied in the ceiling at too light a density.

A third objective of this study was to observe the effectiveness of

"recommended good practice" measures for preventing moisture accumulation. During the third stage of the retrofit, attic ventilation in the

amount of one square foot of ventilation opening for every 300 square

feet of ceiling was provided for the test house, in accordance with FHA

requirements. Also, the existing ceiling insulation was equipped with

a vapor barrier facing downward. The combination of these two protective

measures was effective in keeping the attic dry during the winter.

In the case of the crawl space, a vapor-barrier ground cover was placed over the bare earth of the crawl space, and crawl-space ventilation openings consistent with ASHRAE recommendations were provided.

These protective measures were found to be effective in keeping the

moisture content of wood parts of the floor during the summer below 19

percent. Usually summer moisture problems, such as wood rot, begin to occur when the moisture content approaches the fiber saturation point

(30%). Thus, the protective measures were effective in keeping the

summer moisture content of the wood parts of the floor at a satisfactory

level.

As part of this study, a thermographic survey was performed before

and after the retrofit of the test house. Thermography was shown to be an effective technique for distinguishing between insulated and uninsulated wood-frame cavity walls.

The authors consider the following findings to be significant:

1. Energy conservation actions which reduce the thermal transmittance of the envelope of a building provide reductions in heating

energy requirements not only by reducing heat-loss rates but also by

lowering the outdoor balance temperature for the building. When the

outdoor balance temperature is reduced, there will exist a larger

4
number of heating hours for which the internal heat (from lights, equipment, and people) can provide the required heating energy instead of the

heating plant.

2. Retrofit measures to reduce the air leakage of a well-built house

may not be effective in saving significant amounts of energy. The installa

tion of storm windows to a home may not produce a reduction in air infiltration when the existing windows are equipped with good weatherstripping

3. The installation of storm windows and insulation in the walls,

floors, and ceiling of a frame house produce significant reductions in

the energy requirements for heating, but by themselves may not reduce the

energy requirement for cooling significantly, especially if the daily

average indoor-outdoor temperature difference is small during the summer. Combining night ventilation with daytime air conditioning would probably

increase the energy conservation benefits during the summer for a retrofitted house.

A. The benefit of insulating the floor of a house over a crawl

space should be evaluated on an annual basis, not on a seasonal basis.

The winter benefits of floor insulation are likely to be partly offset

by reduced heat loss to the crawl space during the summer.

5. Water-mixed foam insulation should not be introduced into wall

cavities of existing buildings unless adequate provision is made for the

escape of the moisture. An incorrectly placed vapor barrier may inhibit

the escape of the moisture, resulting in moisture damage to the building.

For this particular test house, an oil-base paint system was applied to

the exterior surface of the test house, which restricted the escape of

the moisture originally contained in the foam. Paint blistering was

shown to result. Similar results would be expected with other vaporimpervious coatings on films.

6. Cellulosic fiber, fibrous glass wool, and urea-formaldehyde foam

were found to have good insulating properties. With regard to other performance properties of the insulating materials, at 18 months, no settling

was observed for either of the dry loose-fill materials installed in the

walls of the test house. For the U-F foam, several fissures were observed

after the foam had cured. Also, linear shrinkage of the foam was observed

to occur at a constant rate. At 26 months, the total amount of observed

linear shrinkage was more than eight percent.

7. When cellulosic fiber is applied at too low a density to ceilings

substantial settling may occur.

5
RETROFITTING AN EXISTING WOOD-FRAME RESIDENCE FOR ENERGY CONSERVATION—

An Experimental Study

by

D. M. Burch and C. M. Hunt

1. INTRODUCTION

This study was carried out under the sponsorship of the Federal

Energy Administration to provide technical information that could be

used in future broad-scale energy-conservation programs for existing

build ings.

Many residences in this country were constructed during times when

energy was cheap and plentiful. During these times, there was little

incentive to employ energy-conserving construction practices, and as a result homes were built to minimize initial building costs. Thus, many

of the present^ homes of this country are essentially uninsulated (i.e. , single-pane windows, little or no weather str ipping , and little or no insulation in the walls, ceiling, and floor).

Approximately 11.7 percent of the nation's energy is used for space

heating and cooling of residential buildings [1]*. Estimates for the

potential energy savings from improving the thermal performance of

existing homes range from 20 to 60 percent.

In an earlier study [2] Anderson exposed to winter conditions four

test houses located in St. Paul, Minnesota. The construction of the

four houses was identical except for the amount of insulation. The

first house was uninsulated; the second, third, and fourth houses were

insulated with blanket insulation throughout in thicknesses of 0.9

(R-3.6), 1.7 CR-6.8), and 2.3 inches (R-9.2), respectively. The savings

in measured fuel consumption for the second, third, and fourth houses

were 27.2, 31.3, and 32.2 percent, respectively. In a recent study [3]

Degelman and Lewis showed that upgrading the thermal resistance of the

ceiling insulation from R-13 to R-19, installing storm windows, and

adding weather str ipping to a house located in Canton, Ohio, produced a 34-percent reduction in energy requirements for space heating and

cooling.

This report presents the results of a retrofit study. The objectives of this study were: (a) to quantify the winter heating and summer cooling energy savings achieved by retrofitting an existing residence

having limited insulation; (b) to compare the thermal performance of

* Numbers in brackets refer to literature references cited at the end

of the text.

6
three different types of insulating materials commonly used to insulate

existing cavity walls; and (c) to evaluate the effectiveness of "recommended good practices" measures [4] for preventing damaging moisture

accumulation in attics and crawl spaces. An economic model is presented

and the cost effectiveness of the retrofit options and the number of

years required to pay back their initial investment is calculated.

Although it is anticipated that significant energy savings are

possible by applying more insulation, adding storm windows, and by

sealing the cracks around the doors and windows, very few empirical case studies are available to assess the actual benefit of such a retrofit.

In the present study, energy measurements were performed on an actual

residence before and after energy conservation measures were implemented, thereby providing substantive data on the energy savings

achieved by the energy conservation measures.

Three insulating materials commonly used to retrofit existing

residential walls for improving their insulating properties are fibrous

glass wool, cellulosic fiber, and urea-formaldehyde (U-F) foam. When

measured in the laboratory with a guarded hot-plate apparatus, all three

of these materials are shown to have good insulating properties. However,

when they are blown into the walls of a residence, their effective

insulating properties may be reduced by certain factors. For example,

loose-fill materials blown into wall cavities sometimes settle, if the

materials are installed at too low a density. In the case of U-F foam,

if the material is not prepared properly, excessive shrinkage may occur,

producing fissures and void spaces where the insulation pulls away from

the studs. The present study examines these factors in a typical woodframe house.

Reference [4] recommends "good practice" measures for reducing

moisture accumulation in attics and crawl spaces. These measures include proper ventilation and the inclusion of a vapor barrier on the

warm-side of installed insulation. For crawl spaces, a vapor-impervious

ground cover is also recommended. These protective measures were implemented in a typical wood-frame house and their effectiveness was examined.

For geographic locations having cold winters, winter moisture

accumulation in exterior walls sometimes poses a serious problem.

Moisture accumulation in the siding and sheathing of exterior walls may

--Cause paint failure, and in serious cases may actually cause warping

and/or buckling of wood siding. In the winter, occupant-related

activities inside a residence release as much as 25 pounds (11.3 Kg) of

water per day [5]. A portion of this water will permeate through the

exterior walls when no vapor barrier is present. The effect of adding

thermal insulation to walls is to reduce the temperature of the siding

and sheathing, thereby increasing the likelihood of condensation. Water

vapor can also enter the wall from the inside through cracks along the

baseboard and around the electrical receptacles. Another source of

moisture accumulation in exterior walls is rain penetration through

7
cracks in the construction. The present study examines moisture accumulation in retrofitted side walls.

Thermography has been shown to be an effective tool for locating

and identifying heat leaks in buildings [6], There has been much recent

interest in establishing criteria which would make it possible to use thermography as a survey tool to distinguish insulated walls from un- insulated walls. In the present study, the feasibility of using thermography as such a survey tool is demonstrated.

2. DESCRIPTION OF TEST HOUSE

The test house selected for the present study was a wood-frame

rambler, bu'ilt in the early 1950' s and located in suburban Washington,

D.C., adjacent to the National Bureau of Standards. It is sometimes

referred to as the Bowman House, a name derived from the former owner. A photograph of the Bowman Hou^e is sho^n in figure 1. This house,

having a floor area of 2054 ft (191.8m ) excluding the unheated basement floor area, is somewhat larger than typical houses in this country,

which range between 1200 to 1500 ft (111 to 139m ). The west side of

the test house (right side as shown in figure 1) contains the living

quarters (living room, dining room, foyer, kitchen, and study) and is

built over a basement, whereas the east side contains the sleeping

quarters and is built over a crawl space.

The house in its original state was typical of many houses having

limited insulation. The walls and floor were without thermal insulation,

while the ceiling had 3-1/2 inches (8.9cm) of glass-fiber blanket-type

insulation laid on top of the ceiling between the joists. A kraft-paper

vapor barrier on the backside of the insulation was placed so that it

faced the ceiling below.

The house initially had single-pane windows with the exception of

a large picture window in the living room which contained insulating

glass. Good weather stripping had been installed around the doors and

windows, and the construction of the house was tight to begin with. The

window area is 16 percent of the wall area and 11 percent of the floor

area

.

The quality of construction of the house indicated that it had been

constructed by skilled carpenters. A description of the floor, ceiling,

roof and exterior walls of the test house prior to the retrofit is given

in table 1. A cross-section of the house after retrofitting is given in

figure 2. The walls of the house were constructed without fire stops,

and diagonal wind braces were used at the corners of the house. A floor

plan of the house is shown in figure 3.

The original heating plant, consisting of an oil-fired forced-air

furnace system was used for the pre-retrofit heating energy measurements. This furnace had an output capacity of 120,000 Btu/h (35,100 W)

and its efficiency was measured and found to vary between 52 and 58

8
9
ASPHALT SHINGLES

ASPHALT ROOFING

PAPER

ROOFING BOARD2x4 TOP PLATE

METAL GUTTERS —

C

REDWOOD SIDING

SHEATHING PAPER

3/4"W00D-FIBER SHEATHING

3-5/8" INSULATION INSTALLED

BETWEEN 2x4 STUDS

(16 In. on CENTER)

OUTSIDE

2x8 JOISTS 16 O.C.

9/I6"gYPSUM PLASTER ON 3/8" GYPSUM-LATH

SHEETROCK

3- 1/2" GLASS- FIBER BLANKET INSULATION

(with kraft paper vapor barrier)

6" LOOSE-FILL CELLULOSE INSULATION

8 CONCRETE BLOCKS

CONCRETE FOOTING

CARPET

3/4" HARDWOOD FLOORING

BUILDING PAPER

3/4" PINE SUBFLOORING

2x10 JOISTS 16 O.C.

6 GLASS-FIBER BATT INSULATION

(VAPOR BARRIER ON TOP SIDE)

CRAWL SPACE

POLYETHYLENE VAPOR BARRIER

Figure 2. Typical cross-section of the house after retrofitting

10
w

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SCREENED

PORCH V DINING ROOM

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KITCHEN

! Clo^ U E IT L

LIVING ROOM FOYER

FIREPLACE

Clos

STUDY

^ 5

I ^los Clos

BEDROOM

BATH

BEDROOM

Cloe

V' Clos r BATH

BEDROOM

I

Clos V BEDROOM

^Clos

33'- 7"

Figure 3. Floor plan of the test house11

77'-2"
I

i

1

Table 1. DESCRIPTION OF EXTERIOR BUILDING ELEMENTS

BEFORE THE RETROFIT (INSIDE-TO-OUTSIDR)

Floor

3/ 4- inch hardwood (oak) floor

building paper

3/4-inch pine subf looring

2 X 10 wood joists placed 16 in. on center

Wall

9/16- inch gypsum' plaster

3/8-inch gypsum-lath sheetrock

2x4 wood studs place 16 in. on center

3/4- inch wood-fiber sheathing

sheathing paper

7/16-inch redwood siding

Ceiling

9/16-inch gypsum plaster

3/8-inch gypsum- lath sheetrock

2x8 wood joists (with 3 1/2-inch glass-fiber blanket

insulation with a draft-paper vapor barrier installed

between the joists)

Sloping Roof

2x8 rafters placed 16 in. on center

3/4-inch wood sheathing

asphalt roofing paper

1/8-inch asphalt shingles

Attic End Walls

2x4 wood studs

3/4-inch wood-fiber sheathing

sheathing paper

7/16-inch redwood siding

12
percent. Warm air was delivered into two separate supply branches which

delivered air to room registers in the west and east sides of the test

house. The rooms, except the bathrooms, were equipped with return air

registers which were connected to a common return plenum for the furnace.

The warm-air supply registers were located at the baseboard level on interior wall partitions, and the return registers were located at the same level on exterior walls. The air-delivery rate^for the blowe^ of

the oil furnace was measured and found to be 1A50 ft /min (0.684 m /s)

After the pre-retrofit heating energy measurements, the oil-fired

furnace was replaced with a 5-ton (i.e., 60,000 Btu/h) air-to-air heatpump system. The duct system of the house was not changed. The heatpump system was equipped with three stages of electric-strip heaters for

providing supplemental heat. The capacity of the electric-strip heaters

was intentionally sized to satisfy the design heating load for the

house. The air-delivery rate for^the blower of^the heat-pump system was measured and found to be 1770 ft /min (0.835 m /s). In a separate

series of measurements the seasonal coefficient of performance of the

heat pump was found to be 1.7A for heating [7],

3. ENERGY-CONSERVATION MODIFICATIONS PERFORMED ON THE TEST HOUSE

3. 1 Measures Taken to Reduce Heating and Cooling Energy Requirements

Immediately following the pre-retrofit winter heating measurements,

3-1/2 inch glassfiber blanket insulation was installed under the basement ceiling.* This insulation was present during the pre-retrofit

summer cooling energy measurements.

During the second winter season, energy-conservation masures were

performed on the test house in three stages to permit the separate

energy savings for each stage to be quantified.

The first stage of the retrofit consisted of reducing air leaks.

Specific measures taken to seal air leaks are listed below:

a. Fireplace damper was repaired.

b. A spring-activated damper for the kitchen ventilation-exhaust was installed.

* This insulation was installed as a sound-absorbing treatment. It was

required for programs unrelated to the present energy conservation

study.

13
c. Caulking compound was applied to cracks around the warm-air

supply ducts where they penetrated the inside walls. Corresponding cracks around the air return ducts were not caulked,

since air leakage through these cracks was considered to be

much less significant than air leakage through the cracks of

the supply ducts.

d. Improved weatherstripping was installed under exterior doors.

e. A board was inserted into a large crack between exterior siding

and foundation wall (foundation sill) followed by the application of a caulking compound (see figure 4).

f . Inside and outside surfaces of exterior walls were repainted.

A latex-paint system was applied to the interior surfaces and

an oil-base paint system to the exterior surfaces.

g. Wall-to-wall carpet was installed, except for the kitchen, the

two rear bedrooms, and the bathrooms.

h. All window panes were reputtied. In addition, the intersections

between the window frames and the house were caulked at various

locations as needed.

i. Weatherstripping was installed around the door to the attic.

The air leaks associated with items a and b above were identified

from a smoke test described in appendix C, and air leaks associated with

items d and e were discovered during a thermographic survey described in

appendix B. It would seem reasonable that if the combination of these

measures were implemented significant reductions in air leakage rates

for the test house should be produced.

The second stage of the retrofit consisted of the addition of woodsash storm windows (see figure 5). During the heating tests, considerable condensation developed on the inside surface of the storm pane. To

permit this moisture to escape to the outside, two 1/8-iAch (0.32 cm)

weep holes were drilled through the bottom rail of the storm windows.

After the weep holes were drilled, the condensation disappeared.

The third stage of the retrofit consisted of applying insulation to

the walls, ceiling, and the floor. Since NBS did not have the equipment or the trained personnel to blow loose-fill insulation into walls

and over ceilings, the third stage work was carried out under contract.

As part of the third stage of the retrofit the following measures were

performed: 6- inch (15.2 cm) glass-fiber batts (R-18.5)* were installed

The R-values for the glass fiber blanket and cellulose insulation

applied to the ceiling were taken from the manufacturer's literature.

14
15
Figure 5. Storm window being installed.

16
under the floor over the crawl space, insulation of three types was blown into the walls of the test house, and 6- inches (15.2 cm) of loosefill cellulose (R-20.8) were blown on top of the existing 3-1/2-inch

(8.89 cm) glass-fiber blanket (R-10.8) in the ceiling. Loose-fill glass

fiber (R-13.7) was blown into one 14-foot (4.27 m) wall section, and U-F

foam (R-14.4) was installed in a second 14-foot (4.27 m) wall section.

The remainder of the walls of the test house were insulated with loosefill cellulose (R-12.6). A detailed description of the third stage of

the retrofit is given in appendix A.

Before the post-retrofit summer cooling energy measurements, aluminum awnings were installed above the windows on the south side of the

test house. A photograph of the south side of the test house after the

awnings were installed is given in figure 6.

3 . 2 Protective Measures for Preventing Moisture Accumulation in

the Attic and Crawl Space

As part of the third stage of the retrofit, the following protective

measures for preventing winter condensation on cold attic surfaces and

summer condensation on cold crawl-space surfaces were in effect after

stage 3 of the retrofit:

Attic

Ventilation area required in FHA Minimu^ Froperty2Standards.

(The net ventilation opening was 7.9 ft (0.734 m ).)

Crawl Space

Ventilation area recommended in ASHR^ Guide. (The net ventilation opening was 0.65 ft (0.060 m ).)

Polyethylene vapor barrier placed over the bare earth

of the crawl space.

Vapor barrier facing the floor present on the backside of

the insulation.

Even though a vapor barrier on the backside of the ceiling insulation

is not considered necessary for the Washington, D.C. area when adequate

_ attic ventilaticy- i is provided, one was present nonetheless. It should

also be pointed out that prior to the third stage of the retrofit the

adjustable louvers of the ventilation openings at the ends of the attic were closed so that ventilation was limited to leakage under the eaves and through the shingles. These were opened as part of stage 3 of the

retrofit to conform with attic ventilation requirements of FHA Minimum

Property Standards.

17
18
4. HEAT-TRANSFER PROPERTIES

The thermal conductivities of common building components needed for

the heat-transfer analysis presented later in the report are given in

table 2.

Table 2. THERMAL CONDUCTIVITIES OF BUILDING

COMPONENTS [4,8,9,10]

Conductivity

Building Component Btu/h* f t •

Hardwood (oak) floor .10

Pine subfloor .07

Wood structural members .068

Gypsum plaster .28

Gypsum-lath sheetrock .12

Wood-fiber sheathing .032

Redwood s id ing .070

Glass-fiber insulation

(blanket/batts) .027

Glass-fiber (loose-fill for walls) .022*

Gypsum board .12

Loose-fill cellulose

° ceiling .023

° walls .024*

Urea-formaldehyde foam .021*

* Based upon NBS measurements discussed later in the report.

The areas used to compute heat flows through building components

were the inside areas for each of the building components. These areas

and their respective calculated pre-retrofit thermal transmit tance

values (U-values) are summarized in table 3.

19

1
Table 3. AREAS AND PRE-RETROFIT THERMAL TRANSMITTANCES

FOR BUILDING COMPONENTS

Building Component Surface Area Thermal Transmittance

ft2 Btu/h-ft^-F

Windows

1/ 2/

Floor (over crawl space) 956. .27

Floor (over basement) 1096. .27 (.069) - -

Ceiling 203A. .081

Wall 1332. .20

Attic access door 20. .50

2/

II Insulating Glass- 80. .65 (.61) —

Single Pane ^7 228. 1.02 (.95)

Doors

° Front " 20.6 .41

° Kitchen 17.4 .62

" Dining Room 33.5 .19

— For the pre-retrofit winter tests there was no insulation in

the floor, whereas for the pre-retrofit summer tests there was

3-1/2 inches (8.89 cm) of glass-fiber blanket insulation in

the floor.

2/ — Sunmer values in parentheses.

3/ — Picture window in the living room.

These thermal transmittance values for the walls, ceiling, and floor

were calculated using the series-resistance method, or

U

i (1)

^ n=l V V

where h , h » inside and outside surface heat-transfer coefficients.

i' o respectively, Btu/h*ft^*F (W/m2.k)

I = thickness of material, ft (m)

k = thermal conductivity, Btu/h-ffF (W/m*k)

2 2

U = thermal transmittance, Btu/h*ft -F (W/m • k)

N « number of layers in the building component

20
Thermal bridges such as studs and joists were treated as parallel heatflow paths with no laterial heat flow between adjacent components. Heattransfer coefficients at the inside and outside surfaces were taken from

Ref. [4].

Thermal transmittance values for retrofitted building components

are given in table 4.

Table 4. THERMAL TRANSMITTANCES FOR RETROFITTED

BUILDING COMPONENTS

Building Components Thernal Transmit tances

Btu/h'ft^-F

Wall (insulated with cellulose)

Wall (insulated with glass fiber)

Wall (insulated with U-F foam)

Floor (over crawl space)

Floor (over basement)

Ceiling

Double-Pane Window

.069

.065

.063

.048

.069

.035 f

.50 -

— The thermal transmittance values for the windows include the

heat- transmission path through the wood sash.

2/ — This thermal transmittance value is for the thickness originally

installed in the ceiling. After 25 days the cellulose was observed to have settled 12.5 percent which produced approximately

a five percent increase in the overall thermal transmittance of

the ceiling.

5. AIR-INFILTRATION MEASUREMENTS

The purpose of the air-inf iltration measurements was to Investigate

the effect of the three stages of the retrofit on the air-inf iltration

rates of the test house. Separate tests were carried out to investigate

the effect of opening the attic ventilation louvers (which occurred

during the third stage of the retrofit) on the air-inf iltration rates

for the test house. Summer air-infiltration measurements were performed

on the house in its original condition and again after all the retrofit

actions had been completed.

21
5. 1 Theory

To determine the rate of air exchange between the test house and

its surroundings, the rate of disappearance of sulfur-hexaf luoride

(SF ) tracer gas was measured. A small quantity of SF^ was released

inside the test house, and the concentration decay rate was measured.

The rate of change of concentration of tracer gas caused by infiltration

was treated as a first-order process expressed by the equation:

- dF = V

(2)

where v = rate at which air enters and leaves the enclosure,

ft^/h (m^/s)

3 3

V = volume of the enclosure, ft (m )

c = concentration of tracer gas at time (t).

Equation (2) may be expressed in the form

V

c = c e

o

(3)

where I denotes the number of volume changes per hour and c is the

initial concentration of tracer gas. The natural logarithm of the

relative concentration, (c/c^) was plotted as a function of time. The

air change rate (I) was taken as the negative slope of a least-squares

fit line through the data points.

5.2 Measurement Technique

Sulfur-hexaf luoride concentrations were measured with a gas chromatograph equipped with an electron-capture detector. A photograph of the

measurement apparatus is shown in figure 7. Sampling and analysis were

performed semi-automatically using a system which has been previously

described [11]. The response of the instrument was logarithmic over the

concentration range of 5 to 15 ppb which was used, in the measurements.

This may be expressed by the relationship:

c = k,«ln (J/J ) + \. (4)

22
23
Here c is the concentration of SF^ in ppb, is the standing current of

the detector, and J is the current with tracer in the detector (it is

the trough of a chromatographic deflection), k is a constant, and A is a SHiall extrapolated value of c at J/J =0. If A = 0, equation (4)

has the form of Beer's law. The instrument was calibrated against

reference mixtures of SF^ in air.

o SF^ was introduced into the return plenum of the heating plant and

distributed throughout the house. Samples were taken from the air

distribution system every ten minutes (600 s) and analyzed for SF^. In

order to maintain good mixing, which is implicit in the use of eq. (5),

the furnace fan was operated continuously. This is more than normal fan

usage, but in addition to providing mixing, it eliminates random fan

operation as a variable in infiltration measurements. Provision was also made to sample independently from different parts of the house. In

the attic four equal length tygon tubes (1/8 in. (0.32 cm) ID) were

connected to a sampling pump through a length of 1/4 in. (0.64 cm)

ID tygon tubing and a solenoid valve. The sampling system has been

described elsewhere [11]. A similar 4-point sampling network was used

in the basement, and the first floor living space was sampled through a sampling network leading to the various rooms. A sampling tube also led

to the crawl space, where occasional spot samples were taken. Infiltration

rates were based on samples taken from the air -distribution system, but

the independent sampling networks made it possible to check on vertical

air movements between the three main parts of the house.

5. 3 Results and Analysis

5.3.1 Winter Air-Leakage Rates

Winter air-leakage rates for the test house in its original state

were measured over a wide range of outdoor temperatures and wind velocities. A summary of these pre-retrofit air infiltration measurements

is given in table 5. In a previous study [12] in which air-infiltration

rates were measured for a test house located inside an environmental

chamber, it was found that in the absence of wind velocity, a good

correlation existed between air-inf iltration rates and the inside-tooutside temperature differences. Other studies [12, 13] have shown that

for residences exposed to wind velocities as well as temperature differences, the rate of air infiltration (I) could be correlated with respect

to these two driving forces with an equation of the form:

I = a + b-AT + c-V (5)

where AT = inside-to-outside temperature difference, °F

V = wind velocity, mph

a, b, c = empirical constants.

24
Table 5. PRE-RETROFIT AIR-INFILTRATION MEASUREMENTS

Air-Infiltration Rate, h""*"

I I , I -I , AT V

meas calc meas calc , (eq. 7)

.22 .19 .03 ' 1.0 4.7

.23 .23 0 2.3 4.8

.20 .28 -.08 5.1 5.2

.42 .39 .03 6.0 11.5

.28 .35 -.07 7.4 7.5

.40 .33 .07 9.3 6.2

.43 .41 .02 9.5 10.0

.38 .44 -.06 10.7 11.0

.54 .43 .11 18.7 6.4

.44 .45 -.01 22.0 6.0

.53 .48 .05 22.5 7.5

.37 .48 -.11 24.5 6.5

A J J J meas calc _ Average deviation = = 0

N

Standard deviation y

I meas - calc/^

i = 1

N-1

25
A least-squares procedure was used to fit the pre-retrofit airinfiltration data to a correlating equation of the form given by eq.(5)

The correlating equation and the corresponding root-mean-square deviation is:

I = 0.11 + 0.0100'AT + 0.0196-V, 6= 0.062. (6)

The root-mean-square deviation (6) is a parameter indicating the amount

of scatter between the data points and their correlating equation.

The pre-retrofit air-infiltration rates were also fitted to a modified form of eq. (5) in which the temperature difference term

b'AT was changed to b'*AT-^'2^ The modified correlating equation, along

with the root-mean-square deviation, is given in eq. (7).

I = 0.0506 + 0.0652-At1/2 + 0.0154-V, 6 = .061 (7)

A plot of eq. (7) is given in figure 8. Under typical winter conditions,

AT = 35" F (19.4° C) and V = 7 mph (3.1 m/s) , the rate of air infiltration

is roughly 0.5 air changes per hour. At design conditions, AT = 55* F

(30.6° C) and V = 15 mph (6.71 m/s), the air-infiltration rate for the

test house is 0.75 air changes per hour. These figures indicate that

the test house in its original state had low air-leakage rates, due to

good construction and good weather stripping around the doors and windows.

The volumetric air-leakage rate per unit envelope area for the test

house of the present study is 0.020 cfm/ft^ area (1.02 x 10"^ m^/s • m^)

at AT = 30° F (16.7° C) and V = 0 mph (0. m/s). The corresponding value

for the townhouse studied in references [12, 15] is 0.022 cfm/ft^

(1.12 X 10-^ m^/s • m2).

Winter air-infiltration rates were also determined after specific

measures were taken to seal air leaks (see section 3.1). A summary of

air-infiltration measurements after stage 1 of the retrofit is given in

table 6. Calculated values were obtained from the pre-retrofit airinfiltration correlation (eq. 7) using measured temperatures and wind

velocities. These provide an estimate of what the pre-retrofit infiltration would have been under the same weather conditions. The average

difference between the measured and calculated infiltration rates was -0.08 air changes per hour, indicating that only a slight reduction in

air infiltration had occurred. Since the statistical uncertainty in the

data as indicated by the RMS deviation for the pre-retrofit air infiltration correlation is approximately 0.06 h"-'-, the calculated reduction

of -0.08 air changes per hour shown in table 6 has low statistical

sign if icance.

26
lO O lO o

H H M 11 > > > >

pa>flpl^«)i0^rO c\J~:0

i-H 'NoiivanidNi aiv do aiv^i

27
TABLE 6. AIR- INFILTRATION RATES AFTER STAGE 1 OF THE RETROFIT

Air-Infiltration Rate, h"^

^meas ^calc "''meas ^calc AT V

(e<i. 7) °F mph

.33 .1*2 -.09 20.1+ U.3

.37 M ^ -.10 31.0 3.6

.UO .50 -.10 31.0 5.5

.39 .li5 -.06 31.1 2.6

.h6 .U6 0 32.5 2.5

.2li .1*5 -.21 33.0 1.8

.55 .09 33.5 2.0

.28 .I46 -.18 31*. 8 1.6

Average deviation, I - I , = -.08 ° meas calc

Standard deviation = .10

28
Aftier the Installation of storm windows (stage 2), no further

reductions in the air-infiltration rates were observed. The results are

shown in table 7. The average difference between the measured and preretrofit calculated infiltration rates was +0.04 air changes per hour,

indicating a slight increase in air infiltration had occurred over the

pre-retrofit values. Since the statistical uncertainty in the data as indicated by the RMS deviation for the pre-retrofit air-infiltration

correlation is greater than the observed change, it is possible that an actual change in air infiltration may not have occurred.

Air-infiltration measurements were also performed after the third

stage of the retrofit. For purposes of calculating energy losses due to

infiltration, new correlation equations were derived for post-retrofit

data after stage 3:

I = 0.221 + 0.00916-AT + 0.229-V, 6 = .064, (8)

I = 0.0549 + 0.101- AT"*"^^ + 0.0236-V, 6 = .064 (9)

Eq. (9) is plotted in figure 9.

After stage 3, a marginal systematic increase in infiltration over

the pre-retrofit values was observed. This is shown in table 8. The

average increase of +0.14 h"-^, as indicated in table 8, would correspond

to an energy expenditure of less than 5 percent of the pre-retrofit

heating loads for the test house. This is no greater than normal error

in the energy measurenent itself. However, there was no a priori reason

to expect any increase in infiltration rate due to the addition of

insulation. Therefore, this effect merits some examination to determine

whether an actual increase occurred or whether it was a spurious effect

arising from some systematic experimental error. It will be noticed in

comparing tables 5 and 8 that the average inside-outside temperature

difference during post-retrofit measurements was greater than the

corresponding pre-retrofit conditions from which eq. (7) was derived.

Therefore, in comparing pre-retrofit and post-retrofit air-infiltration

rates, some extrapolation outside of the range of pre-retrofit data is

required. However, if measurements after stage 3 are compared with

those made after stage 1 and 2, there is also a systematic increase in

average infiltration rates. This latter comparison minimizes any extrapolation outside of the range of the data and also eliminates the effect

of any procedural differences between pre-retrofit measurements and

post-retrofit measurements a year later. Thus, it is concluded that

the marginal increase in air-infiltration rate is real and not an experimental artifact.

As part of stage 3 of the retrofit, it was necessary to increase

the amount of attic ventilation opening to comply with minimum recommended

ventilation requirements of the FHA Minimum Property Standards. To

evaluate the effect of increased attic ventilation, consecutive measurements of air leakage in the living space were carried out under the

alternate conditions of ventilation louvers open and ventilation louvers

closed.

29
TABLE 7. AIR-INFILTRATION RATES AFTER STAGE 2

OF THE RETROFIT

Air-Infiltration Rate, h

-1

I

niAfi a CCU.C uietLS CcLLC

at' V

Ceq. 7) mph

M .U3 0 27.1 2.5

.37 .1*1» -.07 28.1 2.6

.37 .i»5 -.08 29.3 3.0

.55 .50 + .05 32.9 5.0

.37 .1*9 -.12 33.6 1*.2

.6k .li8 .16 35.2 2.6

.1*8 .1*8 0 38. U 1.1*

.53 . .50 .03 39.2 2.5

M .50 -.02 ltO.6 2.2

.5U .55 -.01 1*3.5 1*.1»

.60 •55 .25 1*3.7 li.l*

.63 .53 .10 1*3.3 3.3

M •53 -.08 1*6.7 2.3

.60 .53 .07 1*6.8 2.0

.65 .53 .12 1*7.1 2.0

.68 .56 .12 50.5 3.0

M .58 .16 50.8 3.9

Average deviation, I - I , = O.OU

meas calc

Standard deviation = 0.10

30
il
TABLE 8. AIR-INFILTRATION RATES AFTER STAGE 3

OF THE RETROFIT

Air-Infiltration Rate,h-1

meas calc

(eq. 7)

meas celIc AT

•F

V

mph

.52 ,k2 .10 19.5 5.5

M .13 19.8 U,7

.63 ^ .52 .11 23.3 9.9

.70 .51 .19 25.0 8.6

.59 16 • 25.9 2.8

.70 .26 26.0 3.1* M .Ul .01* 26.0 1.6

.39 .J|2 .03 26.

U

2.3

.U9 .OU 28.3 3,7

.6U .19 31.6 2.U

.56 .50 .06 3U.1 h.3

.69 M .21 37.6 1.8

.61* . .52 .12 38.2 U.5

.70 .55 .15 39.3 6.0

.60 .52 .08 39.6 3.6

.75 •5T .18 Uo.o 7.1

.8U .57 .27 Uo.7 6.8

.71* .60 .lU Ul.l 8.3

Average deviation, I - I , = 0 .1^* meas calo

Standard deviation = 0. 07

32
The results of these special air-infiltration tests are summarized

in table 9. For these consecutive measurements, the effect of opening

the attic ventilation louvers was to increase the rate of air infiltration for the occupied space of the test house by 0.01 air changes per

hour. Since the random scattering of the data points as indicated by

the RMS deviation of the post-retrofit air-infiltration correlation was

0.064 h~l, the measured increase in air-infiltration rate of 0.01

should not be regarded as statistically significant. Thus, these

measurements indicate that closing the attic ventilation louvers produced

no statistically significant reductions in the air-infiltration rates

for the test house.

TABLE 9. EFFECT OF ATTIC VENTILATION ON AIR INFILTRATION.

Air-Infiltration Rate,h

Imeas I -, (eq 9) calc ' ^ I -I > meas calc AT V

•

Open Closed op mph

.70 .57 .13 26.2 k.6

.56 .53 .03 22.9 h.3

.53 .53 0 23.8 3.7

.56 .50 .06 21.8 3.U

.1*3 .U6 • -.03 15.9 k.Q

.k6 .U5 .01 13.5 5.8

.66* .39 .27 9.3 5.7

.30 .38 -.08 10.1 U.8

.37 .38 -.01 11.7 h.O

Average deviation attic open = + 0.02, standard deviation = 0.07.

Average deviation attic closed » 0.01, standard deviation = 0.06.

* Five door openings occurred during this measurement. It was therefore omitted from average. When included: average deviation = 0.07,

standard deviation = 0.13.

33
The preceding paragraphs presented the results of air-infiltration

measurements before and after three stages of retrofit. The data have

been analyzed to determine what differences were produced, whether the

differences were significant, and their possible causes. From the point

of view of the energy required to heat the house, it is concluded that

any improvements obtained by retrofitting were not due to reduction in

air leakage. Different conclusions might have been reached had the

original house been more poorly constructed or had it been placed in a more exposed location under more severe weather conditions. As it was,

the house was surrounded on all sides by trees and dense shrubbery near

the house on the north side, which served somewhat as a windbreak.

In this connection, some wind-tunnel studies by Mattingly and

Peters [16] are of interest. They measured the inside-outside pressure

differences across different surfaces of a model cluster of townhouses,

and from these results estimated the possible air-infiltration rates.

When a model building or simulated trees were placed upwind from the

townhouses, a marked reduction in pressure differences was obtained.

This indicates that trees and other windbreaks may have a significant

effect in reducing air leakage in homes.

5.3.2 Summer Air-Infiltration

Summer air- infiltration rates were measured for the test house in

its original state, prior to the three stages of the retrofit. Summer

air-infiltration rates were also measured after all the stages of the

retrofit had been performed. The results of these measurements are

shown in table 10.

Comparing table 10 to tables 5 and 8, it is seen that both the

pre- and post-retrofit summer air-inf iltration rates are in most cases

lower than values measured in the winter. However, they were obtained

under comparatively mild weather conditions for which the inside-tooutside temperature differences were much smaller than corresponding

winter values. The differences between pre- and post-retrofit infiltration rates were small compared with the random variations in values

themselves.

TABLE 10. SUMMER AIR-INFILTRATION RATES

Pre-Retrofit Post-Retrofit

I h-1

T - T^

o i

"F

V

mph

I h-i

T - T^

o i

"F

V

mph

.27 13.5 3.4 .36 1.2 4.6

.44 12.6 3.0 .19 2.8 4.2

. 25 -3.4 9.5 .16 3.7 2.4

.21 -3.3 6.9 .23 6.4 2.1

. 24 -2.7 7.5

.29 -3.1 7.1

34
The small increase in winter air-infiltration rates which was observed after stage 3 of the retrofit was not observed for the summer. However, it should be noted that the temperature differences between the

living space and the outside, as well as between the living space and

the attic, were opposite to those prevailing in winter.

Separate measurements showed that air movement was predominantly

upward from the living space into the attic under summer as well as winter conditions. In the summer, the temperature of the air in the

attic is usually considerably warmer than the outdoor or indoor air. The

warmer attic air is lighter than the surrounding air, and therefore has

a tendency to rise and leak out of the ventilation openings at opposite

ends of the attic. Air from the living space is apparently sucked into

the attic to compensate for the outflow of air.

5. 4 Conclusions

Air-infiltration measurements performed in the house in its original condition demonstrated that this particular house was of comparatively tight construction. Under typical winter conditions, the airinfiltration rate was approximately 1/2 air change per hour subject to

variations due to weather conditions.

After energy conservation actions were carried out to seal airleakage paths (stage 1 of the retrofit), air-infiltration measurements

indicated only a small reduction in air-infiltration rates, comparable

in magnitude with the normal statistical variation in the data. The

minimal effectiveness of measures taken to seal air-leakage paths was attributed to the tightness of the original house.

The addition of storm windows produced no measured reductions in

air-infiltration rates for the test house. This result was attributed

to the good weather stripping around the original window systems.

A surprising finding was that after insulation was added to the

walls, ceiling, and crawl-space floor, the air-infiltration rates for

the test house marginally increased. Separate measurements demonstrated

that the observed increase in air infiltration probably was not due to

opening the attic ventilation louvers which occurred during the third

stage of the retrofit.

Summer air-infiltration rates were observed to be between 0.16 and

0.44 air changes per hour and were found to be approximately one-half of

typical winter values.

35
6. ENERGY MEASUREMENTS

In this section, the reductions in the energy required for space

heating of the test house resulting from three stages of a retrofit are

experimentally quantified. Winter heating loads for the test house

were determined experimentally and compared with predicted values.

In addition, the reduction in the space-cooling energy requirement

for the test house achieved by the combination of the retrofit actions

was also experimentally investigated.

6.1 Experimental Plan

The experimental plan for quantifying the heating- and coolingenergy savings achieved by the retrofit was to measure first the winterheating (1973-1974) and summer-cooling (1974) loads for the test house

in its original state under a range of outdoor climatic conditions. The

only modifications performed on the test house prior to these investigations were those necessitated by neglect, such as the repair of a leaky

roof

.

During the following winter heating season (1974-1975) , the test

house was retrofitted in three stages. Winter heating loads for the

unoccupied test house were measured after each stage of the retrofit,

permitting the reductions in the heating load to be quantified after

each stage.

During the following summer season (1975) , awnings were InstalJ.ed

over the windows on the south side of the test house. Cooling loads

were measured and compared to pre-retroflt values.

The test house was unoccupied during testing, except for technical

personnel needed to perform measurements. The only internal heat gains

to the living space were a constant lighting load of 660 watts, the heat

release from the equipment for measuring air infiltration (when it was operated), and the metabolic heat released by technical personnel. Heat

released by occupant-related activities has an appreciable effect on the

heating loads of a residence. However, since internal heat gains due to

occupancy would vary from one day to the next and would introduce uncertainties into the measurements, it was decided to first determine the

heating load as a function of outdoor temperature for the unoccupied

house. The heating- and cooling-energy requirements for an occupied

test house would be obtained from a subsequent analysis.

6- 2 Instrumentation and Measurement Technique

6.2,1 Measurement of Heating and Cooling Loads

The two branch supply duct systems feeding conditioned air to the

east and west sides of the test house were insulated for both the preand post-retrofit energy measurements, so that duct losses would represent

36
a small fraction of the heating and cooling loads. Since the duct

losses were small, the heat delivered by the heating plant was assumed

to be equivalent to the heat supplied to the first floor living space.

Based on this assumption, the integrated heating or cooling load (q) is

given by the relation:

P

q= / (C -p-VA) -AT-dt + Wh^ (10)

y P fg o

where

C = specific heat of air, Btu/lb'F (J/Kg'K)

P

3 3 p = densitv of the air, lb/ft (Kg/m )

V = mean duct velocity, ft/min (m/s)

2 2 A = cross sectional area of duct, ft (m )

AT » temperature rise for space heating applications or temperature

drop for space cooling applications, between inlet and outlet

of central air conditioner, °F (°K)

t * time, minutes

W * mass of water collected, lb (Kg)

» latent heat of vaporization of water, Btu/lb'F (J/Kg*K)

P = period of time over which the blower operates.

The first and second terms represent the sensible and latent

portions of the load, respectively. For residential heating application without humidif ication (W=0) , the latent term vanishes, since

no water is removed or added to the structure by mechanical equipment.

For most heating and cooling applications, the factor (Cp-p-V-A) may be

considered to be constant and taken outside the integral. Thus, the

time-varying heating or cooling load for a residence may be measured by

integrating the temperature rise (or temperature drop) across the

heating (or cooling) plant and multiplying this integrated value by the

factor (Cp* p'V* A) . This measurement of the heat delivered by a furnace

system by integrating the temperature rise is similar to a technique

used by Strieker [17].

It should be pointed out that the temperature difference AT is

only integrated when the blower of the mechanical heating and cooling

system is operating and delivering conditioned air to the living space.

In the case of fuel-fired furnaces, a significant amount of thermal

energy is stored in the heat exchanger. When the blower is off, hot air

is delivered to the living space by buoyant forces. When heating loads

37
were measured for the oil-fired furnace system, a cycle-by-cycle calculation for the gravity-force heating energy delivered to the house was

included. This was accomplished by measuring air-delivery rate due to

gravity force (using a hot wire anemometer) and the temperature difference between the supply and return (using a thermopile system) as a function of time. The calculation of heat delivered to the house due

to buoyant forces is regarded as not of high accuracy.

In order to obtain meaningful duct velocity and temperature rise

measurements, it is necessary that the measurements be made at a station

in the duct having nearly uniform temperature profiles. A schematic

diagram of the original oil-fired furnace system showing the location of

the measurement transducers is shown in figure 10. Note that the airdelivery duct system has two major supply branches, one delivering

conditioned air to rooms located over the basement, the other feeding

the rooms located over the crawl space. For the pre-retrofit heatingenergy measurements, uniform temperature profiles were created in each

major supply branch by installing louvered air-mixing devices which

were constructed according to specifications given in reference [18].

The heating energy delivered during blower operation was measured separately for each of two major supply branches. The temperature rise

across the return plenum and the basement supply duct was sensed with an 18-junction chromel-alumel thermopile. Nine of the junctions were

arranged in an equally-spaced grid network and mounted in the return

plenum. The other nine junctions were also arranged in an equallyspaced grid network and mounted in the basement supply branch located

downstream from the louvered air-mixing devices. The temperature rise

between the return plenum and the crawl-space supply branch was sensed

with an identical thermopile system. The millivolt signal from each of

the thermopiles was fed into micro-switching circuits which in turn were

fed into analog integrators. When the blower of the furnace system

operated, the switching circuits applied the millivolt signal of the

thermopiles to the integrators. When the blower stopped, the switching

circuits applied a short-circuit across the integrators, thereby stopping the integration.

During the pre-retrofit heating-energy measurements, duct air velocities were measured at the approximate vicinity of the hot junctions of

the thermopiles with a hot-wire anemometer that had been calibrated in a wind tunnel. In addition, the mass-flow rate was measured indirectly

by using the electric heaters located in each supply branch and in

the theirmopile system.

After the pre-retrofit measurements, the oil furnace was replaced

by a heat pump system, as part of a heat pump study [7]. The system was also equipped with supplemental electric-resistance heating elements.

In the present study, only the electric-resistance heaters were used

to heat the house.

38
HORIZONTAL

LOUVE RED

MIXER^

BURNER AND CONTROLS

FUEL

INLET

FUEL CONSUMPTION

METER

Figure 10. Schematic diagram of furnace system showing the location

of measuring transducers.

39
Smaller temperature differences would be developed across the heatpump system than the oil-fired furnace. It was therefore necessary to

replace the 18-junction thermopiles on the oil-fired system with 36-

junction copper-constantan thermopiles in order to produce larger millivolt signals for operating the integrators. In addition, the louvered

air-mixing devices were removed and air-flow measuring devices were

installed in each supply branch upstream from the hot-junction grid

network of the thermopiles. The air-velocity measuring devices consisted of a honey-comb air straightener , an array of pitot tubes for

measuring the total pressure, and several static pressure ports. By

measuring the pressure difference between the pitot-tube array and the

static pressure ports, it is possible to monitor the velocity head of

the moving air stream.

For the post-retrofit heating energy measurements, the electric

energy supplied to the resistance heating elements and the blower was measured with watt-hour meters equipped with contact closure devices

which produced a contact closure for each revolution of a disk inside

the watthour meter. These contact closures were totalized, and the

accumulated counts were printed out at hourly intervals. The electric

heat supplied to the test house was equal to the electric energy supplied to the resistance heating elements and to the blower, less the

jacket losses of the heat-pump system. Separate measurements demonstrated that the jacket losses were 8 percent of the total electric

energy released by the resistance heating elements and the blower. The

jacket loss was determined by taking the difference between the electric

energy input to the resistance heating elements and the heating energy

delivered to the house measured with the thermopile energy measurement

system.

For the air conditioning tests, the condensate from the refrigeration coil was collected in a cylindrical tank located on an electronic

weighing platform. The total condensate collected at hourly intervals

was determined by feeding a DC voltage from the weighing platform into

a data acquisition system.

6.2.2 Outdoor Weather Parameters

A photograph of the weather station used in the present study is

shown in figure 11. This weather station was located approximately 60

ft (18.3 m) in front of and in line with the west end of the test house.

This particular location was selected so that the wind direction and

velocity sensors, mounted at the 18~ft (5.5 m) level, would be exposed

to the prevailing winter northwest wind. Wind velocity was measured

with a rotating-cup anemometer, and wind direction was measured with a wind-direction vane. The louvered enclosure shown in figure 11 con- tained a copper-constantan thermocouple for measuring outdoor temperature and a humidity sensing element which produced a millivolt signal

proportional to relative humidity. During the pre-retrofit heating

energy measurements, the total solar radiation incident on a horizontal

surface was measured with a pyranometer mounted on top of the louvered

40
Figure 11. Photograph of the weather station.

41
enclosure shown in figure 11. After the pre-retrofit heating energy

measurements, the pyranometer was relocated on the roof of the test

house. The outdoor ambient temperature was also measured with thermocouples installed on the north side of trees located behind the test

house.

6.2.3 Indoor Parameters

Indoor air temperatures were measured using 24-gage copperconstantan thermocouples placed at the 4. 5- ft (1.37-m) level and in the

center of each of the rooms of the house, except for the bathrooms.

These thermocouple locations are depicted with the symbol "•" on the

floor plan of figure 12. In the living room two additional thermocouples were installed vertically in line with one at mid-height. One was placed 3 in (7.62 cm) above the floor and the other 3 in (7.62 cm)

below the ceiling. Three attic air temperature thermocouples were

located along the east-to-west center line of the attic, 1 ft (0.305 m)

above the ceiling joists. These thermocouples were placed approximately

20 ft (6.10 m) from the attic end walls and in the geometric center of

the attic. Two basement air temperature thermocouples were placed along

the broken line A-A (see figure 12), 1 ft (0.305 m) below the floor

joists and approximately 10 ft (3.05 m) from the basement walls. In the

crawl space, two thermocouples were placed along the broken line B-B

(see figure 12), 1 ft (0.305 m) below the floor joists and approximately

10 ft (3.05 m) from the foundation walls.

A relative humidity sensor (the same type that was used in the

weather station) was placed indoors in the center of the living room

next to the mid-height thermocouple. For the post-retrofit measurements, identical relative humidity sensors were installed in the crawl

space, basement, and the attic. In all cases, an ambient air temperature thermocouple was placed next to each humidity sensor.

6. 3 Winter Energy Measurements

6.3.1 Heating Loads for the Unoccupied Test House

For the pre-and post-retrofit heating energy measurements, dailyaverage heating loads were determined for the unoccupied test house

with corresponding daily average outdoor and indoor temperatures, dailyaverage wind velocities, and total incident solar radiation. The dailytotal heating loads for the unoccupied test house were taken to be

equal to the sum of the heating energy delivered to the house by the

furnace plus the constant lighting load and the energy released by airinfiltration equipment when it is operated. An average heating load

for each day of test was calculated by dividing the daily-total heating load by 24-h/day.

42
LEGEND:

• TEMPERATURE SENSORS

SCREENED

PORCH > DINING ROOM

A

B

KITCHEN 1I

BATH I A

LIVING ROOM FOYER

FIREPLACE

Clos

STUDY

I ^ Clos

BEDROOM

BATH

BEDROOM

Clos ^ Clos ^^"bath I

I BEORDROOM

B

Clos v bedJoom

Clos

33'- 7"

Figure 12, Floor plan of test house showing

location of temperature sensors.

77'-

1
The major portion of the heating load to the unoccupied house is

due to heat loss through the exterior building envelope. The dominant

driving force that governs this heat-loss rate is the inslde-to-outside

temperature difference. Another factor affecting the heat-loss rate is

wind velocity. Since the wind velocity and indoor temperature* for each

of the heating load measurements was not the same, it was necessary to

normalize the measurements to equivalent wind velocities and indoor

temperatures in order to obtain meaningful heating load correlations.

The heat- loss rate (q^) due to air infiltration is given by the

relation

where

q_ ' p-C •VI'(T. - T^) (11)

I p i o

3 3

p = density of air, lb/ft (Kg/m )

3 3

V = volume of a residence, ft (m )

I = rate of air infiltration as a function of wind velocity,

h (s )

C = specific heat of air, Btu/lb-F (J/Kg-K)

P

T, - T " inside-to-outside temperature difference, F (K)

1 o The air-infiltration rate (I) is a function of wind velocity. The

heat-loss rate (qj) may be adjusted from one wind velocity to another

by using air-inf iltration values from the pre- and post-retrofit airinfiltration correlations (eqs. (7) and (9)) in relation (11).

The heat- loss rate (q) at one condition, (Tj^ - T ) may be adjusted

to another condition, (T^ - Tq) having a different in3oor temperature

(T!) by the relation

T' - T

q = — . (12) ^a ^ T_, - T

i o

Here q^ denotes the adjusted heat-loss rate.

For the winter heating energy measurements, an attempt was made to

maintain constant indoor temperature throughout the test. However,

small variations in indoor temperature were nonetheless observed to occur from one day to the next.

44
Since the measured daily-average heating loads for the unoccupied

test house are approximately equivalent to heat-loss rates, relations

(11) and (12) were used to normalize the measured heating loads for the

unoccupied test house to the average wind velocity (4.2 mph (1.88 m/s))

and average indoor temperature (67.9° F (19.9° C)) of all the winter

heating energy measurements. Normalized daily-average heating loads

of the unoccupied house before and after the various stages of the

retrofit are plotted as a function of daily-average outdoor air temperature in figure 13. The straight lines were obtained from a leastsquares procedure.

Measured heating loads before and after stage 1 of the retrofit

are seen to be essentially correlated by the same straight line. These

results suggest that measures taken to seal air leaks did not produce

measurable reduction in the heating loads for the unoccupied test

house. This finding is consistent with the results of the air-infiltration measurements which also showed that no statistically significant

reduction in air infiltration occurred as a result of actions taken to

seal major air-leakage paths.

Actually, there was a tendency for the heating loads after stage 1

to be slightly higher than corresponding pre-retrofit values. This

result may have occurred as a result of one or a combination of the

following factors:

" Elimination of heat gains from the chimney to the test house

after the retrofit. After the pre-retrofit heating- energy

measurements, the oil-fired furnace was replaced with a heatpump system.

" Disturbance of ceiling insulation. As part of another study

being conducted at the test house, speakers, microphones, and

electrical outlets were installed in the ceiling. An attempt

was made to preserve the integrity of the glass-fiber ceiling

insulation, but some disturbance of the ceiling insulation

may have occurred nonetheless.

* Lower crawl-space and basement temperatures. The jacket loss

and the temperature of delivered air for the heat pump system

which was installed after stage 1 of the retrofit were much

less than for the oil-fired furnace. This resulted in lower

crawl-space and basement temperatures. However, R-11 blanket

insulation was added to the basement ceiling before stage 1

of the retrofit, which fortuitously maintained the postretrofit floor heat-loss rate at approximately the preretrofit level. Higher heat-loss rates and colder air leakage probably occurred through the floor over the crawl space

after the heat-pump system was substituted for the oil-fired

furnace system.

45
46
6.3.2 Reduction in the Annual Space-Heating Energy Requirement

The diurnal activities of a family occupying a house have a significant effect on its heating loads. The occupants and the operation of

lighting and appliances release significant amounts of heat to the

living space of a house.

In a previous study [15], an energy-release schedule for lighting,

equipment, and occupants was presented. This occupancy schedule was devised for a six-member family living in a four-bedroom townhouse

having a floor area of approximately 1200 ft^ (111 m ). Since the test

house of the present study has roughly 71 percent more floor area, it was necessary to modify the townhouse occupancy schedule. It was assumed

that the energy-release rates for lighting would be twice as large,

whereas the energy-release rates for equipment would be 30 percent

larger. The modified energy-release schedule for equipment, lighting,

and occupants is plotted in figure 14. The daily-average heat-release

rate for this schedule is 4,409 Btu/h (1,291 W)

Over the conditions for which the house was tested, heat was always

delivered by the heating plant during each hour of every test. If the

test house had been occupied, the heat released by occupant-related

activities would never have been sufficient to satisfy the heating load

of the house over the conditions for which the house was tested. Therefore, the daily-average heating load for the test house, having an occupancy schedule of figure 14, would be equal to the heating load for

the unoccupied test house (see figure 13), less the daily-average heatrelease rate for the occupancy schedule of figure 14.

The foregoing procedure was applied to each of the daily-average

heating loads of figure 13. The daily-average heating loads for an occupied test house are plotted in figure 15. A least-squares procedure

was applied to the pre-retroflt and stage 1 data and the following

correlating equation was obtained between heating load (q) expressed

in Btu/h and outdoor temperature (T^) expressed in °F:

q - -938«T + 57,300 (pre-retroflt and stage 1 retrofit). (13)

o A similar procedure applied to the post-retrofit data yielded:

Writing these equations in terms of the Inslde-to-outside temperature

difference gives

q = -532-T + 30,000 (stage 3 retrofit). (14)

q = 938. (67.9 T^) -6,380 (pre-retroflt) (15)

q = 532- (67.9 T ) -6,140 (stage 3 retrofit). (16)

47
48

The first term in the foregoing equations represents the heat-loss rate

from the test house. The second term represents daily-average internal

heat-release from occupancy, lighting, and equipment, and heat gain from

solar radiation through the windows. Recalling that the daily-average

heat-release rate for the occupancy schedule is 4,409 Btu/h (1,291 W)

,

it is seen that the average solar load is calculated to be 1,971 (557 W)

and 1,731 Btu/h (507 W) , respectively, which are not unreasonable

figures.

The outdoor balance temperature is the outdoor temperature for which

heating load for a house is zero. For this particular test house, the

outdoor balance temperatures for the original and completely retrofitted

house are found by setting eqs. (15) and (16) equal to zero and solving

for Tq. The outdoor balance temperatures for the occupied house were

found to be 61.1° F (16.2° C) for the original house and 56.40° F

(13.6° C) for the completely retrofitted house. Performing a heat

balance on the test house and making use of the heat-transfer properties

of section 4, outdoor balance temperatures for the occupied test house

before and after the retrofit are found to be 63.5° F (17.5° C) and

59.0° F (15.0° C) when solar radiation is not considered. The effect of

including solar radiation in the steady-state heat balance would further

reduce the calculated outdoor balance temperatures. Based on the foregoing considerations, the empirically determined outdoor balance temperatures are very plausible.

Since insufficient stage 2 experimental data were available to

empirically determine the outdoor balance temperature, it was necessary

to resort to a semi- empirical technique to obtain the stage 2 heating

load correlation. The coefficient factor (938.) of eq. (15) represents

the overall heat-transfer coefficient in Btu/h* °F for the test house

before the retrofit. Using the heat-transfer properties given in

section 4, it was found that the addition of storm windows would reduce

the overall heat-transfer coefficient of the test house by 119 Btu/h* °F

(62.7 W/K) . The coefficient factor of eq. (15) was changed from 938 to

819, and an outdoor balance temperature of 60.1° F (15.6° C) was calculated for the stage 2 data. Then using this empirically-determined

outdoor balance temperature, the following correlating equation for the

stage 2 data was obtained from a least-squares procedure:

q = 748 (67.9 - T ) - 5,851 . (17)

o The number of annual heating degree days for Washington, D. C. given

in reference [4] is 4,224. The value of 4,224 is based on an outdoor

balance temperature of 65° F (18.3° C) . The outdoor balance temperature

for each of the correlating equations is different from 65° F (18.3° C)

.

Therefore, to calculate the annual heating-energy requirement for

each of the correlating equations, it is necessary to use the actual

number of heating degree days for the reference temperature of that

particular correlation. Heating degree days for Washington, D.C. (1957)

are plotted versus outdoor balance (reference) temperatures in

figure 16. These values were obtained by searching actual weather data

for Washington, D.C.

50
4600

4400 -

4000

3600

O 3200

UJ

o

UJ

o 2800

i2 2400

2000

1600

XjlL

51

1 1 1

53 55 57 59 61

OUTDOOR BALANCE TEMR

63 65

'l^ure 1ft. Heatlne deeree days as a function of outdoor balance temperature

for Washington, D.C.
The annual heating load for a residence is equal to the product of

the adjusted degree days and the energy requirement for space heating

per degree day (derived from the heating load correlations of figure 15).

The calculation of annual heating loads for the various stages of the

retrofit is shown in table 11.

TABLE 11. CALCULATION OF ANNUAL HEATING LOADS

Energy Requirement Adjusted Annual Heating Energy

Retrofit per Degree Day Degree Days* Load Savings

Stage Btu/DD DD Therms %

Pre-retrofit

(also Stage 1) 22,501 3,350 753.8 Q

Stage 2 17,945 3,140 563.5 25.2

Stage 3 12,752 2,450 ' 312.4 33.3

TOTAL 58.

5

Corresponding to the particular outdoor balance temperature of each of

the heating load correlations of figure 15.

The reduction in the annual heating load resulting from the addition of

storm windows was 25.2 percent. The installation of insulation in the

walls, ceiling, and floor produced a further 33.3 percent reduction.

The combination of all stages of the retrofit resulted in a 58.5 reduction in the annual heating load.

If it is assumed that the separate energy savings achieved by

insulating the floor, ceiling, and walls for stage 3 of the retrofit are

proportional to the predicted reductions in the heat-loss rates (see

tables 13 and 14 of section 6.3.3), the percent savings in heating

energy requirement are found to be 19.7 percent for the walls, 6.1 percent for ceiling, and 7.5 percent for the floor. It should be pointed out

that if the ceiling had been uninsulated to begin with, the effect of

adding insulation to that part would have been much greater.

The first terms of the heating load correlations for the occupied

test house, eqs. (15), (16), and (17), represent the heat-loss rate

from the test house after various stages of the retrofit. Comparing

these terms for the various stages of the retrofit, it is seen that the

addition of storm windows reduced the heat-loss rate by 20.3% and the

addition of insulation to the walls, ceiling, and floor reduced the

heat-loss rate by an additional 23.0%. The total reduction in heat-loss

rate achieved by all stages of the retrofit was 43.3%.

Reductions in heat-loss rate and corresponding reductions in annual

heating loads are compared for the various stages of the retrofit in

table 12.

52
TABLE 12. COMPARISON OF REDUCTIONS IN HEAT-LOSS RATE TO

REDUCTIONS IN ANNUAL HEATING LOAD

Retrofit

Stage

Reduction in

Heat-Loss Rate

%

Reductions in

Annual Heating Load

%

Pre-retrof it

(and Stage 1)

0 0

Stage 2 20.3 25.2

Stage 3 23.0 33.3

Combination 43.3 58. 5

Reductions in annual heating loads are clearly seen to be larger than

corresponding reductions in heat-loss rate.

Retrofit actions which reduce the thermal transmittance of the

exterior envelope of a building provide reduction in annual heating loads

by two mechanisms. They reduce the heat-loss rate and lower the outdoor

balance temperature for a building. When the outdoor balance temperature

is reduced, there will exist a larger number of heating hours for which

the internal heat (from lights, equipment, and people) can provide the

required heating energy, instead of the heating plant. This result

causes the number of heating-degree days to be essentially reduced,

which in turn means reduced heating energy requirement for the building.

The foregoing results suggest that a "modified" degree-day method

which utilizes a variable outdoor balance temperature and adjusted

degree days should be used to evaluate reductions in annual heating load

provided by energy conservation modifications to the exterior envelope

of a building. It will provide significantly more accurate results than

the traditional base-65 degree-day method. A difficulty in using a "modified" degree-day method is that the outdoor balance temperature

depends not only on the overall thermal transmittance of the building

envelope but also on the amount of heat released from occupant-related

activities which varies over a wide range from one family to the next.

6.3.3 Comparison of Measured and Calculated Heat-Loss Rates

The purpose of this section is to compare measured heat-loss rates

to corresponding calculated values determined by a steady-state method.

Since heated air was delivered only to the first-floor occupied space.

53
this region was used as the control volume for the heat balance. For

these calculation*:, measured temperatures for the crawl space (figure 17),

attic space (figure 18) arid basement, at the average outdoor conditions

for the data set, were used in the calculation of heat loss through the

floor and ceiling.

The rates of heat transmission (q ) through the separate surfaces

of the house were calculated using the steady-state relation:

q = U-A- (T - T ) (18)

c i o

2 2 where U = thermal transmittance, Btu/h-ft -F (W/m -K)

2 2 A = surface area, ft (m )

T - T = air-to-air temperature difference across the surface,

^ ° °F (°K).

Heat loss du^ to air infiltration was calculated using eq. (11).

For this calculation, the temperature of infiltrating air was taken to

be at the temperature of outdoor air. Separate tracer-gas measurements

showed that when tracer was released in the attic space, none would

subsequently appear in the living space. However, some infiltration was

found to occur from the crawl space to the living space. This latter

infiltration process caused a portion of the infiltrating air to enter

the test house at higher temperatures than the outdoor air. However,

for the present analysis, the temperature of infiltrating air was taken

to be at the temperature of the outdoor air.

Using eqs. (11) and (18) and making use of the heat-transfer properties given in section 4, pre- and post-retrofit air infiltration correlations (eqs. (7) and (9)), and measured crawl-space, basement, and attic

temperatures, steady-state heat-loss calculations were performed for the

house in its original state (table 13) and for the completely retrofitted

house (table 14). For these calculations, the indoor and outdoor temperatures were taken to be equal to the mean values observed during the

winter heating-energy measurements, namely, T^ = 67.9° F (18.9° C) , and

Tq = 31.8° F (-0.1° C) . The wind velocity was taken to be the mean

value observed during the pre- and post-retrofit heating energy measurements (i.e., V = 7.9 mph (3.5 m/s) and V = 3.5 mph (1.6 m/s) , respectively).

For the pre-retrofit steady-state heat-loss calculations, comparing

the predicted heat-loss rate of 34,336 Btu/h (10,060 W) from table 13 to

the corresponding measured value of 33,900 (9,933) (first term of

eq. (15)), we see that the predicted value is only 436 Btu/h (128 W)

,

or 1.3 percent higher than the measured value. Also, for the postretrofit steady-state heat-loss calculation, comparing the predicted

heat-loss rate of 20,993 Btu/h (6,151 W) (from table 14), to the cor- responding measured value of 19,205 (5,627) (first term of eq. (16)), we

see that the calculated value is only 1,788 Btu/h (524 W) higher or 9.3

percent higher than the measured value.

54
55
56
TABLE 13. PRE-RETROFIT STEADY-STATE WINTER HEAT-LOSS CALCULATIONS

Heat-Losa Path Heat-Loss Rate. Btu/h Percent of Total

Walls 9617. 28.0

Ceiling 4020. 11.7

Floor

•* over crawl space 3201. ( -i/.n-t 9.3

Windows

** 3493 over basement 292. 1 * .9

° single pane 8395. , 24.4)

insulating glass 1877.)

^"»^'^-

5.5/ - Doors 924. 2.7

Air Infiltration 6010. 17.5

(I = 0.51 h )*

TOTAL 34,336. 100.

*Based on pre-retrofit air-infiltration correlation (eq. 7).

TABLE 14. POST-RETROFIT STEADY-STATE WINTER HEAT-LOSS CALCULATIONS

Heat-Loss Path Heat-Loss Rate, Btu/h Percent of Total

Walls

Windows

cellulose 2845.1

glass fiber 210. > 3284. 15.6

** urea formaldehyde 229.)

Ceiling 2057. 9.8

Floor

" crawl space 844.) in?? ^'^ basement 233. f " 1.1

:}

double pane 4115. ( ^^^^ 28.5

" insulating glass 1877,

Doors 924. 4.4

Air Infiltration 7659. 36.5

(I =• 0.65 h

' )*

TOTAL 20,993. 100.

*Based upon post-retrofit air-infiltration correlation (eq. 9)

57
The foregoing comparison of measured and calculated heat-loss rates for

the test house supports the validity of the heating energy measurements.

6. A Summer Energy Measurements

6.A.1 Measured Cooling Loads

Both pre-retrofit and post-retrofit cooling loads were measured for

the unoccupied test house. For these measurements, the only internal

load inside the test house was a constant lighting load of 660 W. The

windows were kept closed throughout the measurements, therefore no benefit was realized from using cool night air for cooling. The

daily-average indoor temperature averaged 73.3° F (22.9° C) for the preretrofit measurements and 74.4° F (23.6° C) for the post-retrofit

measurements

.

The daily-average sensible and latent cooling loads for the preand post-retrofit measurements are plotted in figures 19 and 20. Note

that the post-retrofit sensible loads (figure 19) tended to be slightly

higher than the pre-retrofit sensible loads. For the case of latent

loads (figure 20), the post-retrofit loads tended to be lower than

corresponding pre-retrofit values. The benefit of reduced latent loads

was offset by increased sensible loads, so that the retrofit is seen to

have little or no effect on the total cooling loads for the test house.

6.4.2 Analysis of Cooling Energy Measurements

The reductions in latent load were attributed to a change in the

relative humidity levels in the living space. As shown in figure 21,

the relative humidity in the first-floor living space was significantly

reduced after the retrofit. The reduction in indoor relative humidity

was attributed principally to the polyethylene film which was placed

over the bare earth of the crawl space as part of the retrofit. The

effect of this ground cover was to substantially reduce the moisture

content of the crawl-space air. Separate tracer gas measurements showed

that there was an exchange of air between the crawl space (and basement)

and the living space when the air-delivery system of the heating plant was in operation. It was hypothesized that one mechanism by which

crawl-space air infiltrated into the first-floor living space was through

air leaks at the seams of the return-air ducts. In addition, the vapor

barrier on the backside of the glass-fiber batts which were installed in

the floor over the crawl-space may have reduced the permeation of water

vapor through the floor.

The reduction in latent load (Aq^) may be estimated from the

relation:

Aq = p-V-I-h -Aou, (19)

L tg

58
59
I
a.

5

LU

9

CO

>

<

<

% 'AiiaiwnH 3Aiivi3ii yooaNi
where p = density of air, lb/ft (Kg/m )

3 3

V = volume of the enclosure, ft (m )

I = air infiltration rate, h

^

h^^= latent heat of vaporization for water, Btu/lb (J/Kg)

Aio = reduction in indoor humidity ratio between the pre- and

post-retrofit cooling tests, lb (Kg) H^O per lb (Kg) air.

Taking the air- infiltration rate for the house to be the mean of the

summer air-infiltration measurements (I = 0.26 h~l) and making use of

the relative humidity data of figure 21, the reduction in latent load is

found to be 745 Btu/h (218 W) . This approximates the difference between

the pre- and post-retrofit latent load correlations shown in figure 20.

When comparing pre- and post-retrofit sensible cooling loads, it

should be pointed out that the daily-average indoor temperature for the

post-retrofit cooling-load measurements was 1.1° F (0.61° C) higher

than the pre-retrofit measurements. If the post-retrofit measurements

had been performed at an indoor temperature of 73.3° F (22.9° C) instead

of 74.4° F (23.6° C) then the post-retrofit cooling loads would have

been higher than the values actually measured. This would have caused

the difference between the pre- and post-retrofit sensible loads to have

been greater than the values actually measured. An analysis of the increase in sensible loads that occurred after the retrofit follows.

Comparisons of the pre- and post-retrofit daily average crawlspace, basement, and attic temperatures are given in figures 22, 23,

and 24, respectively. Note that both the crawl-space and basement

temperatures are lower than the indoor air temperatures, so that the

living space is always losing heat to the space below. The large amount

of scatter in the daily-average attic temperature correlations was attributed to differences in solar radiation from one day to the next.

The addition of thermal insulation in the floor over the crawl space

reduced a prior summer benefit of heat loss from the living space to the

crawl space, whereas the installation of additional insulation to the

ceiling reduced heat gains through the ceiling. Pre- and post-retrofit

daily-average heat-transfer rates through the ceiling and floor are given in table 15.

TABLE 15. DAILY-AVERAGE HEAT-TRANSFER RATES, Btu/h

Component Pre-retrof it Post-retrofit Change

Ceiling Heat-Gain Rate 1,451 861 590

Floor Heat-Loss Rate 1,518 615 903

62

a.

iU

3

o

>

<

>-<

a

X.(Uu

3

4-1 (0u

0)a

E

C

Q>E

V

X

.13

01

3

0(1 u

>

I4-1

(T; O

a

T)c

03

I(U

<u3

•H

do ' dWai 1N3W3SV9 • AV AllVQ

O-l
T—I—I

\—I

\—\—I—!—I—

do "dwai Dinv • AV Aiiva
The foregoing daily-average heat-transfer rates were calculated using

the steady-state heat conduction equation (eq. 19). For these calculations, daily-average crawl space (figure 22), basement (figure 23), and

attic (figure 24) temperature were used at an outdoor temperature of

73.3" F (22.9° C)

.

The results of table 15 show that the installation of insulation in

the floor over the crawl space and additional insulation to the ceiling

produced reduction in the heat-loss rate through the floor which more

than offset the reduction in the rate of heat gain through the ceiling.

The net effect of these two retrofit actions was to cause a net decrease

in the daily-average rate of heat loss of 313 Btu/h (91.7 W) . This

decrease is of the same order of magnitude as the difference in cooling

loads between the pre- and post-retrofit measured sensible cooling loads

of figure 19.

A qualitative evaluation of the effectiveness of the awning for

reducing heat gain may be ascertained by considering the photograph of

the installed awnings shown in figure 6. This photograph was taken at

approximately noon time. The overhanging roof is seen to shade most of

the area of each window on the south side of the test house. The additional shading derived from the awnings is seen to be small.

Some qualitative understanding of the effect on the post-retrofit

cooling loads of adding storm windows and insulation to the walls may be

obtained by noting that the daily-average outdoor temperature was very

nearly equal to the daily-average indoor temperature. Thus, the dailyaverage heat gain through the window and the walls over the observed

range of weather conditions should be approximately zero. In other

words, the reductions in heat gain during the day are offset by reductions

in natural cooling at night. Thus, storm windows and wall insulation

would be expected to have a small effect in reducing summer cooling

energy requirements for this particular test house and the conditions

over which it was tested.

The following factors unquestionably influenced the results.

1. At the test conditions over which the comparison of pre- and

post-retrofit cooling loads was made, the daily-average outdoor

air temperature was very nearly equal to the daily-average

indoor air temperatures. If the tests had been conducted under

warmer conditions for which no natural night cooling was possible, then the retrofit actions undoubtedly would have

produced a net reduction in cooling loads.

2. The test house of the present study was surrounded by trees

and received much shading from solar beam radiation.

3. The test house was unoccupied; the only internal load was a constant lighting load of 660 W.

66
4. The roof overhung the south wall of the test house and

provided significant shading of the windows from solar

radiation, thereby precluding much of the benefit that could

be derived from awnings.

5. Finally, the windows of the test house were not opened at night

to take advantage of natural ventilation cooling of the house.

Thus, the walls and windows were holding in heat which therefore had to be removed mechanically.

The foregoing analysis indicates that insulating the floor of a residence

tends to increase the energy required for summer cooling, and that the summer benefit of wall insulation is probably related to the daily average

temperature difference between indoors and outdoors during the cooling

season. It also suggests that opening the windows at night would probably have been beneficial in reducing the energy required for cooling.

6. 5 Conclusions

Energy conservation measures taken to reduce air-leakage rates did

not produce measured reductions in heating-energy requirements. This

was attributed to the fact that the test house was of tight construction

to begin with. The addition of storm windows reduced heating-energy

requirements by 25.2 percent. The installation of insulation to the

walls, ceiling, and floor reduced the energy requirement for space heating by an additional 33.3 percent. The total reduction in heating energy

achieved by all stages of the retrofit was found to be 58.5 percent.

The analysis of heating-energy requirements showed that energy

conservation actions which reduce the thermal transmittance of the

exterior envelope of a building provide reductions in annual heating

loads by two mechanisms. They reduce the heat-loss rate and lower the

outdoor balance temperature. When the outdoor balance temperature for

a building is reduced, there will exist a larger number of heating hours

for which the internal heat (from lights, equipment, and people) can provide the required heating energy instead of the heating plant. These

results suggest that a "modified" degree-day method which utilizes a variable outdoor balance temperature and adjusted degree days should be

used to evaluate reductions in the annual heating load provided by

energy conservation modifications to the exterior envelope of a building.

Measurements of daily-average cooling loads before and after the

retrofit indicated that the retrofit was not effective in reducing the

cooling energy requirements for this particular test house under the

particular conditions tested. The post-retrofit daily-average latent

loads were found to be slightly less than corresponding pre-retrofit

values, whereas the post-retrofit sensible daily-average cooling loads

were found to be slightly higher than the pre-retrofit values.

67
The reduction in latent loads was caused by lower humidity levels

in the living space which were attributed to a polyethylene ground cover

placed over the bare earth of the crawl space and a vapor barrier on the

backside of the insulation installed in the floor over the crawl space.

The increase in sensible loads after the retrofit was attributed to

the fact that the installation of insulation in the floor over the crawl

space produced reductions in the heat loss through the floor which more

than offset the reduction in heat gain through the ceiling due to additional insulation in the ceiling. The net effect of these two energy

conservation actions was to cause a net increase in the sensible cooling

load for the air conditioner. The effect of installing awnings over the

south-facing windows was small due to the overhanging roof which provided

significant shading of these windows from solar radiation, thereby precluding much of the benefit that could be derived from the awnings. The

effect of storm windows and wall insulation was small, largely due to the

fact that reductions in heat gain during warmer daytime hours were offset by reductions in natural cooling of the test house during cooler

nighttime hours.

Insulating a house and adding storm windows also tends to lower the

summer balance temperature (above which mechanical cooling is needed)

and therefore increase the number of hours during which cooling Is re- quired. However, most of this increase could be satisfied with a wholehouse fan instead of an air conditioner. The effects of floor and wall

insulation on the summer cooling loads described above for this test

house indicate that the benefits of various retrofit options may vary

with climate and need to be analyzed on an annual basis rather than for

winter and summer only.

7. ECONOMIC ANALYSIS

The purpose of this section is to present an economic model which

may be used to evaluate the economic merit of various retrofit options.

Since the retrofit on this particular test house did not provide reductions in cooling energy requirements, the effect of summer energy

savings was not included in the economic analysis.

7.1 Theory

This economic analysis assumes that money would have to be borrowed

at a prevailing interest rate to perform one or more of the retrofit

options which were applied to the test house of the present study. Of

particular concern is the number of years required for the cumulative

annual savings to pay back the initial investment. The net annual savings (AS) is related to the initial investment value (C) by the relation:

c = -l^:^:) I -AS for p i D. (20)

68
When P = D, equation (20) is an indeterminant form. Applying the rule

of L'Hospital, eq. (20) reduces to C = L*AS. Here D denotes the discount rate* which was taken in the present analysis to be 10 percent,

and P is the annual rate of fuel price increase, which was taken to be

8 percent for oil and electricity and 10 percent for gas. Solving for

the pay-back period (L) we obtain:

fl _C D - P "| log.. L AS •

1 + Pj

L = — for ? ^ D. (21)

1°«10

When P = D, eq. (21) is an indeterminant form. Applying the rule of

L'Hospital, eq. (21) reduces to L = C/AS.

In estimating the cost for the specific energy conservation options,

it was assumed that the homeowner would use his own labor to reduce

major air leaks (stage 1), whereas he would pay an insulating contractor

to install storm windows and to insulate the floor, ceiling, and walls.

Cost estimates for the specific items of the retrofit are summarized in

table 16. The figure of $780 for storm windows is based on an installed

cost of $!J0 for a storm window up to 100 united inches** and $0.60 per

each additional united inch. An important point that should be made is

that some of the windows of the test house were considerably smaller than

standard double-hung windows. Since the installed cost for a storm window up to 100 united inches is constant, the cost for installing storm

windows for this test house was greater than for a house having standard

double-hung windows. Thus the payback period for having storm windows

installed on the test house of the present study will be longer than

that for a house having standard-size double-hung windows.

The cost figure of $550 for a 6-inch (15.24-cm) fill of loose-fill

cellulose was based on $0.25 per square foot installed. The figure

used to estimate the cost of installing 6-inch (15.2A-cm) glass-fiber

batts in the floor was $0.30 per square foot of floor. And finally,

the cost of installing loose-fill insulation into cavity walls was

$0.60 per square foot. These cost estimates were based on typical 1975

prices and were taken from reference [19]. The total cost for all

items to retrofit the test house was $2840.

* A discount rate is a factor used to convert cash flows occurring in

different time periods to a common basis for comparison purposes.

** United inches » the sum of the height and width of a storm window

in inches.

69
TABLE 16. COST ESTIMATE FOR ENERGY CONSERVATION OPTIONS

1. Stage 1 (Reducing Major Air Leaks) $190.00

2. Stage 2 (Storm Windows) $780.00

3. Stage 3 (Installation of Insulation in Walls,

Ceiling, and Floor)

a. Ceiling $550.00

b. Floor over crawl space

Insulation $360.00)

* Polyethylene ground cover $ 40.00> $480.00

Pipe Insulation $ 80. Oo)

c. Wall $840.00

Total Cost of Retrofit $2,840.00

Since the monetary savings in fuel cost achieved by a retrofit depend upon the efficiency of the heating system and the cost of the fuel

being used, a sample calculation was performed for four different types

of heating systems. The assumed thermal efficiencies and fuel costs used

for the four different heating systems are summarized in table 17.

TABLE 17. HEATING SYSTEM EFFICIENCIES AND FUEL COSTS USED

FOR SAMPLE CALCULATIONS

System Efficiency Cost per Therm in

(coefficient of Fuel Cost conditioned space

Heating System performance) $ per Therm $

Gas-fired

forced air 0.60 0.24 0.40

Oil-fired

forced air 0.55 0.26 0.47

Electric

forced air 0.92* 0.88 0.81

Alr-to-a ir

heat pump 1.74** 0.88 0.51

* An efficiency for an electric heating plant less than unity was used

to account for jacket losses.

**A coefficient of performance of 1.74 means that one unit of electric

energy input produces 1.74 units of heat output.

70
The foregoing system efficiencies (or coefficient of performance)

are assumed typical seasonal values rather than steady-state values often

cited by equipment manufacturers.

The winter heating-energy cost (HC) for the four separate heating

systems may be calculated from the relation:

HC - HL-FC/n (22)

where HL " annual heating load in therms

FC * fuel cost, $ per therm

n efficiency of heating plant or coefficient of performance of

cooling equipment.

7.2 Results

7.2.1 Heating-Energy Costs

Using the annual heating loads for the test house after various

stages of the retrofit (table 11) and the cost per therm in the conditioned space (table 17), annual winter heating-energy costs were

determined for four types of heating systems. The results are summarized

in table 18.

They show that the monetary savings achieved by the various energy

conservation options are very sensitive to the fuel costs and the efficiency

of the heating plant. Note from table 18 that the total annual dollar

savings achieved by the retrofit for the gas, oil, electric and heatpump systems are 176.4, 207.5, 357.6, and 225.1, respectively.

7.2.2 Pay-Back Periods

The number of years to pay back the initial investment for the

various energy conservation options for the four heating systems are

summarized in table 19. These pay-back periods, with the exception of

the payback periods for ceiling insulation, are consistent with values

published in reference [20].

It is interesting to note that for this set of retrofit experiments,

-storm windows were found to be more cost effective than installing insulation, requiring significantly fewer years to pay back their initial

investment.

The payback periods for installing additional ceiling insulation

are longer than values cited in reference [20]. The longer payback

periods for ceiling insulation compared to reference [20] are probably

due to the fact that the effect of winter solax gains on the roof

71
—or

o >

CO

o

CO

C\J OJ

CM

a; (A oo

cvj

COON

00o > O a)

CM

rH o

OJ

(U CO d o

c:> rH

VX3 oo

l/N CM

(0

o >

CO

ON

oo ooH o

CM

rH +J

d) cn (2 o

oo

ITN 00

OO

VO

CM

OO

vo'

CO n

o > o oa CO

vo o

o

rH

VO

rH +J

(U CO O

OO

ITN CM

CM

ITN CMH

P

COO

-pCO

CM

0)

CO +JCO

oo

<ubO p

CO

COc

•H>

COH

-pO

E-t

7
were not considered in that report. Also, the add it.itjnal six inr^hes

inches oV ceiiiru': insulation installed equaled two inches more than

the economically optimum amount cited in reference [20]. Using more than

the economically optimum amount would cause the payback periods for the

celling insulation to be longer.

TABLE 19. PAY-BACK PERIODS FOR ENERGY-CONSERVATION OPTIONS

Stage of Pay Back Period, Years

Retrofit Gas Heat Oil Heat Electric Heat Pump

Stage 1 Inf inite Inf inite Infinite Inf in i t e Stage 2 10.2 9.6 5.4 8.8

Stage 3 17.4 17.5 9.5 15.9

(18.6)* (18.9)* (10.2)* (19.2)*

wall 14.2 13.8 7.5 12. 5

" ceiling 29.9 34.8 17.4 31.1

floor 15.9 15.7 8.6 14.3

(19.3)* (22.1)* (11.8)* (20.0)*

Combination of

stages 1-3 16.1 15.9 8.7 14.5

* Includes cost of vapor-barrier ground cover and pipe insulation.

If the test house had been located in a geographic location having

much colder winters, the pay-back periods would have been considerably

shorter. Including the effect of the retrofit on summer cooling loads

in the economic analysis would have had the following effect on the

payback periods. Reduced summer heat gains due to the installation of

additional ceiling insulation would decrease the payback periods for the

ceiling insulation. Reduced summer heat loss due to the insulation installed under the floor over the crawl space would increase the payback

periods for the floor insulation.

It should be emphasized that the energy savings and payback periods

depend upon heating-plant efficiency, energy cost, number of heating

degree days, thermal characteristics of the house, discount rate, and the

amount of annual fuel price increase. It was not the purpose of this

section to present solutions for all possible variations of the above

parameters, but rather to present an economic model that could be used

to evaluate the economic merits of energy conservation options.

73
7 . 3 Cone luslons

In retrospect, no money should have been spent on sealing air leaks,

and perhaps less insulation should have been added to the ceiling. For

this particular test house, paying to have storm windows installed was found to be more cost effective than having insulation installed, requiring significantly fewer years to pay back the initial investment.

8. COMPARISON OF THE THERMAL PERFORMANCE OF THREE INSULATING MATERIALS

This section describes laboratory and field measurements to compare

the thermal performance of three different insulating materials commonly

used to retrofit exterior cavity walls. The insulation materials

selected for study included cellulosic fiber, fibrous-glass wool and

urea-formaldehyde (U-F) foam. The thermal conductivities of the three

materials were measured using a guarded-hot-plate apparatus. Heattransmission and moisture measurements were performed on a full-scale

test wall that was exposed to simulated winter conditions in the laboratory. Similar measurements were also conducted on wall sections of a test house insulated with the three materials. Other performance properties such as shrinkage and settling were also investigated.

8. 1 Guarded-Hot-Plate Measurements

Measurements of thermal conductivity and density were made on test

specimens of the three different insulating materials in accordance with

the guarded-hot-plate test method given in ASTM C 177-71. Each test

specimen was prepared so that its density was approximately equal to the

density as installed in the walls of the test house. The test specimens

were intentionally not oven dried, but instead allowed to reach moisture

equilibrium with respect to room air at 75° F (23.9° C) and 40 percent

rh, so that the thermal conductivity measurements would be more representative of installed insulating materials.

Table 20 summarizes the thermal conductivity measurements. The

measured values of thermal conductivity of cellulosic fiber are in

close agreement with values reported by Tye [9]. Measured thermal

conductivity values for fibrous glass wool are consistent with values

measured by Bankvall [10 J and values reported by ASHRAE [A]. The three

materials are seen to have good insulating properties as indicated by

thermal conductivity measurements. The thermal conductivity of U-F

foam is seen to be slightly lower than that of the other two materials.

It should be pointed out that differences in thermal conductivity

may exist between the same type of insulating materials obtained from

different manufacturers. For example, in the case of cellulose insulation, different manufacturing processes combined with various forms of

newsprint material can lead to variations in coarseness and density of

the material, which in turn may lead to differences in the thermal

conductivity.

7A
TABLE 20. THERMAL CONDUCTIVITIES OF THREE INSULATING MATERIALS

MEASURED IN THE GUARDED-HOT-PLATE APPARATUS

Thermal

Insulating Moisture Content Density Meem Temp. Conductivity R-value

Material % (by weight) lb/ft

°F Btu-in ft -h-"? — 2

Before test After Test ft -h-^F Btu. in

Cellulose 9-9 9-5 3.5U 75.8 0.288 3.UT

Fibrous

Glass Wool 1.0 0.7 2.11 75.8 0.267 3-75

UreaFormaldehyde , Foam l6.8 l6.8 0.60 75.7 0.2U6 U.07

8. 2 Full-Scale Laboratory Wall Tests

A full-scale laboratory test wall was exposed to a simulated

winter condition on the exterior side and to typical indoor conditions

at the inside surface for a two-month period. Different sections of

the test wall were insulated with the three insulating materials. At

the conclusion of the exposure period, measured thermal conductance

values for the separate sections were compared with corresponding predicted values using the series-resistance method outlined in reference [4].

8.2.1 Description of Test Specimen

A test wall, 8 ft high and 8 ft wide (2.AA m by 2.44 m) , similar in

construction to the walls of the test house, was built in the laboratory.

The construction details of this test wall are shown in figure 25. It

had six cavities between studs placed 16 in (40.6 cm) on center. As in

the case of the test house, an oil-base paint system was applied to the

exterior (cold-side) surface, and a latex paint systen was applied to

the interior (warm-side) surface.

«As viewed from the inside surface, cellulose fiber was blown into

the first two wall cavities on the left, fibrous glass wool Into the

two center cavities, and U-F foam into the remaining two cavities on

the right. When the U-F foam was installed, the redwood siding was not

attached to the wall for about a week, to permit some of the original

water contained in the foam to excape through the comparatively permeable sheathing. The same procedures were used for Installing each of the

insulation materials into the laboratory test walls as were used for the

wall sections of the test house.

75
76
8.2.2 Instrumentation

Front and side views of the test wall showing the location of the

humidity transducers are given in figure 26. Each pair of wall cavities

insulated with different material was Instrumented in a similar manner. Surface and ambient air temperatures were measured with 24-gage copperconstantan thermocouples. Heat-flow meters were spot-glued to the

inside wall surface. They were connected in series for each of the

three insulated sections and the output signals were fed into an analog

integrator for the purpose of averaging. The relative humidity at the

inside surface was measured with a motorized psychrometer placed at the

mid-height level. Thermocouples were embedded in the insulation at the

top and bottom of the wall cavities.

8.2.3 Experimental Procedure

The experimental procedure was to install the laboratory test wall

into a wall test apparatus which maintained the exterior side of the

test wall at a temperature of 5+2° F (-15+1.1° C) and approximately 95%

rh. The Interior side of the test wall was exposed to the laboratory

environmental condition which was maintained at 75+3° F (23.9+1.7° C)

and 45+3% rh. The wall test apparatus consisted of a refrigerated

enclosure, one side of which was open and fitted with a frame for

supporting the laboratory test wall. The foregoing conditions were

maintained for a two-month period. At the conclusion of the testing

period, heat-flow rates were measured and samples of the insulating

materials were cored out and their moisture contents were determined by

comparing the wet weight of the samples with their corresponding dry

weight after oven drying.

8.2.4 Experimental Results

The experimental results of the laboratory wall test are shown in

table 21. The moisture contents at the end of the exposure period were

found to be greater than corresponding winter values for the test house

(see tables 24-26). This finding is not surprising, since the interior

surface of the laboratory test wall was exposed to a substantially

higher Indoor relative humidity than the test house, and the exterior

surface of the laboratory test wall was exposed to much colder outdoor

conditions. The moisture contents were much greater at the bottom of

the glass-fiber and U-F section, which may be due to colder temperatures

within the insulation at the bottom of these sections. Also, note that

the amount of accumulated moisture within the cellulose material is very

nearly the same at the top and bottom of the wall section.

The measured thermal conductance values given in column 7 of table 21

were obtained by dividing the heat flow through the wall by the surfaceto-surface temperature difference. The predicted thermal conductance

values of column 8 were obtained by the series-resistance method. The

77
LOCATION OF MEASURING SENSORS • HUMIDITY

INSIDE AMBIENT TEMPERATURE

A OUTSIDE "

» TEMPERATURE

O HEAT FLOW

SIDE VIEW FRONT VIEW

Figure 26. Location of measurement transducers on

laboratory test wall.

78
thermal conductivity (k) for the insulating material used in the thermal

conductance calculation was adjusted to the mean temperature of the

insulation using the relation:

k = k + a-AT (23) m

where k * measured thermal conductivity at mean temperature of ° guarded-hot-plate measurement, Btu^in/h-ft (W/m«K)

a » temperature coefficient of thermal conductivity,

Btu»in/h.ft2.»F2 (W/m.k^)

AT = mean temperature of wall section minus the mean temperature

of guarded-hot-plate measurement, °F (K)

The mean temperature of the insulation was approximately 76° F for the

thermal conductivity measurements and approximately A0° F for the laboratory wall test. The temperature coefficients (a) for the thermal conductivity values are given in table 22.

TABLE 21. EXPERIMENTAL RESULTS OF FULL-SCALE LABORATORY WALL TESTS AFTER

TWO-MONTH EXPOSURE

Wall Insulation Moisture Thermal Conductance

Insulating Meetn Temp. Density Content Btu/h»ft '^F %

Ivlaterial °F Ib/ft^ % (by weight) Measured Predicted

Top . Bottom Top Bottom

Cellulose k6 36 h.k l8.6 17.^ .O65 .063 3.1

Glass

Fiber k2 3h 1.7 9-8 2k. 3 .069 .062 10.1

U-F Foam U5 * 0.7 ^+9-0 76.3 .051 .05U -5.9

• Data not available.

TABLE 22. TEMPERATURE COEFFICIENTS (a) FOR THE THERMAL

CONDUCTIVITY VALUES

Material Btu-in/h*ff°F^ W/m'K^ Reference

Cellulose 4.0 x 10"^ 1.0 X 10"^ 9

Glass fiber 7.3 X

10"^ 1.9 X

10"^ 10

U-F Foam 6.3 X 10"^ 1.6 X

10"'^ Manufacturer 's

literature

79
Since the thermal conductivity measurements were performed on test

specimens having approximately the same density as the installed material,

it was not necessary to correct the thermal conductivity values for

differences in density.

The measured thermal conductance values agree quite favorably with

corresponding predicted values even though a large amount of moisture

was present in the insulation materials, the percent difference being

less than 10 percent. This was attributed to the fact that much of the

moisture was concentrated in a thin layer of ice which was observed at

the interface between the insulating material and sheathing. The bulk

of the insulating material appeared to be comparatively dry.

After the two-month test period at an exterior temperature of 5° F

(-15.0° C) , the refrigeration system was adjusted to maintain 36° F

(2.2° C) on the cold side. The 36° F (2.2° C) condition was maintained

for 28 days, at the conclusion of which the refrigeration system was

turned off and the test wall was allowed to come to thermal equilibrium

with respect to ambient air at approximately 75° F (23.9° C) . The

floating condition was maintained for 33 days, after which significant

buckling and warping of the wood siding was observed (see figure 27).

The buckling and warping of the wood siding was attributed to high

moisture content of the wood siding.

8. 3 Heat-Transmission and Moisture Measuronents in Retrofitted Wall

Sections of the Test House

8.3.1 Heat-Transmission Measurements

The purpose of this section is to compare thermal conductance

values measured in retrofitted wall sections of the test house with

corresponding predicted values, using the series-resistance method.

8.3.1.1 Instrumentation

The heat-flow rates through wall sections of the test house insulated

with the three types of insulating materials were measured with heatflow meters. The heat-flow meters were circular disks 2.0 in (5.08 cm)

in diameter and 0.13 in (0.33 cm) thick, made of polyvinylchlor ide filler

material, each having an embedded thermopile. Heat flux, upon passing

through the wafer, caused a temperature difference to be developed across

the wafer, which in turn caused a millivolt signal to be produced proportional to the heat-flow rate. At a station A feet above the bottom

of the wall section, six heat-flow meters were spot-glued to the inside

wall surface and equally spaced between adjacent wall studs, as shown in

figure 28. The six heat-flow meters were series-connected and the output

signal was fed into an analog integrator. The integration of the heatflow signal was necessary because instantaneous heat-flow rates were

observed to possess large fluctuations due to the cyclic operation of

the heating plant. The heat-flow measuring station also contained a

80
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81
FLOOR

LEVEL

16"

THERMOPILE

JUNCTIONS

-e—e—e—e

-g—e2.3?* HEAT-FLOW METERS

—

WALL STUDS

2"

4'-0"

Figure 28. Elevation view of wall section of the test house showing h

measuring station.

82
6-junction thermopile for measuring the surface-to-surface temperature

difference. This thermopile was placed 2 in (5.08 cm) above the row of

heat-flow meters, as shown in figure 28. Three copper-constantan thermo

couple junctions were attached to the inside surface with aluminum

adhesive tape. The other three junctions were attached at corresponding

locations at the outside wall surface. This thermopile produced a millivolt signal proportional to the surface-to-surface temperature

difference across the wall section. This millivolt signal was also fed

into an analog integrator.

8.3.1.2 Experimental Results

The thermal conductances of the separate wall sections are plotted

versus mean wall temperature in figure 29. The thermal conductance

values were obtained by dividing the average heat-flow rate over a twelv

hour nighttime period by the average surface-to-surface temperature

difference over the same period. The mean wall temperature was taken to

be the mean temperature between the inside and outside wall surfaces.

The straight-line correlations were obtained from a least-squares

procedure applied to the raw data.

It is interesting to note that the thermal conductances of all the

wall sections decreased as the mean temperature of the insulation was

reduced. This behavior is consistent with the fact that the thermal

conductivity of all three materials decreased as the temperature of the

niaterlal decreased, as indicated by eq. (23) and the temperature coefficients for thermal conductivity given in table 22.

The thermal conductance of the U-F wall section (see figure 29) is seen to be substantially higher than corresponding values of the other

wall sections. This result is inconsistent with the findings of the

guarded-hot-plate measurements (section 8.2) and the full-scale laboratory wall tests (section 8.3) which showed that U-F foam had somewhat

better insulating properties than loose-fill glass fiber or cellulose.

After the heat-loss measurements were performed, the inside wall surface

at the measuring station of the U-F wall section was removed in order to

examine the U-F material for shrinkage and fissures (void spaces where

the foam had pulled apart). A cleavage, one inch in width, was observed

directly in line with the heat-flow measuring station. The presence of

this fissure undoubtedly contributed to the high measured thermal conduc

tance values at the U-F wall section.

Another factor which could have contributed to the higher heat-loss

rates observed through the U-F wall section was the moisture content of

the foam, although the data obtained on the wall specimen in the laboratory, and reported in table 21, shows relatively good agreement between

predicted thermal conductance and the thermal conductance measured in a specimen with 50-76% moisture content. The heat-loss measurements were

carried out approximately 45 days after the U-F foam had been installed.

A humidity transducer installed between the foam and the wood-fiber

sheathing indicated that a saturated condition existed there at the time

83
.20

.18

T

1

\—I—

r

1—

r

$: .16

S .14

.12

.10

.08

.06

.04

.02

WALL SECTION

• GLASS FIBER

A UREA- FORMALDEHYDE FOAM

CELLULOSE

1 L

44 46 46 50 52 54 56 58 60

Figure 29. The effect of mean wall temperature on the thermal

conductance of the three separate wall sections.

84
of the heat- loss measurements (see figure 31, section 8.3.2.1). This

result suggests that some of the original moisture contained in the foam

was still present at the time of the heat-loss measurements.

In table 23, measured and corresponding predicted thermal conductance

values for the cellulose and glass-fiber wall sections are compared. For

the comparison, the insulation was taken to be at a mean temperature of

46° F (7.8° C) . The predicted values were determined by applying the

series-resistance method to the portion of the wall containing insulation.

Since none of the heat-flow meters were placed over studs, the high conductance heat-flow path through the portion of the wall containing studs was not included in the calculation of conductances. The thermal conductivity of the insulating materials used in the thermal conductance calculations was adjusted to a mean insulation temperature of 46* F (7.8* C)

using eq. (23) and the temperature coefficients of thermal conductivity

given in table 22.

TABLE 23. COMPARISON OF MEASURED AND PREDICTED THERMAL

CONDUCTANCE VALUES AT WALL SECTIONS INSULATED

WITH LOOSE-FILL MATERIALS

2 Thermal Conductance, Btu/h*ft -F

Wall Section Measured Predicted

Cellulose .060 .062

Glass-fiber .064 .056

From table 23, it can be seen that the measured thermal conductance

of the cellulose wall section is slightly less than the predicted value,

whereas the thermal conductance of the glass-fiber wall section is somewhat higher than the predicted value.

8.3.2 Moisture Measurements

Material samples of the wood siding, sheathing, and insulation were

cored out at wall sections insulated with the three insulating materials

at the end of the winter season. The moisture contents of these samples

were determined using an oven-drying technique, and compared.

8.3.2.1 Relative Humidities in Insulated Wall Cavities

Ten days after the test house was insulated, small narrow-range

humidity and temperature sensors were installed between the insulating

material and- the sheathing midway between the studs. The specific

location of these humidity sensors is denoted with the symbol "M" on

the floor plan in figure 30. The U-F foam and glass-fiber wall sections

are indicated on figure 30. Other parts of the wall were insulated with

85
w

©

LEGEND:

H MOISTURES SENSORS EMBEDDED IN WALLS

S MOISTURE-CONTENT SAMPLES

S— h-*N

1 BEDROOM Clos BEDROOM

1^

Clos UF FOAM

Zu\sQ) 02S 2M

33'- 7"

-2M

77'-2'

1

Figure iO. Floor plan of the test house showing location of humltHty

sensors and r>lac<»R uHptp '"o-'sture content samples were cored nut

36
cellulose. At those locations where two sensors are indicated (denoted

by the symbol "2M") , humidity sensors were installed approximately 1 ft

(0.305 m) below the ceiling level and 1 ft (0.305 m) above the floor

level. At locations where only one sensor is indicated, the sensor was

installed 1 ft (0.305 m) below the ceiling, except in the living room,

where it was installed 1 ft (0.305 m) above the floor level. The installation procedure was to drill 1-inch (2.54-cm) holes through the wood

siding and sheathing, install the sensors, and replug the holes. These

particular sensors responded to relative hiimidity only in the narrow

range from 85 to 100 percent. Relative humidities less than 85 percent

would not produce an instrument response.

A graph showing the variation of relative humidities indicated by

the embedded rh sensors is given in figure 31. Since the rh sensors

were embedded at the interface between the sheathing and the insulation,

they indicate the presence of moisture in both sheathing and insulation.

The relative humidity at the interface between the U-F foam insulation

and the sheathing remained at a saturated condition for approximately AO

days after the retrofit, at which time the relative humidity began to

decrease slowly. The relative humidity at the interface between the

glass-fiber insulation and the sheathing gradually increased, while

relative humidities at the interface between the loose-fill cellulose

and sheathing were not sufficient to produce an instrument response

(i.e. less than 85 percent rh)

8.3.2.2 Moisture Accumulation

At the end of the winter heating season, in the third week of April

(1975), 76 days after insulation was blown into the walls, (2-1/4 in

(5.72 cm) diameter) circular samples of the wood siding, sheathing, and

insulation were cored out at various locations. Locations where material

samples were taken are shown on the floor plan of figure 30. Where the

symbol "2S" appears, samples were taken from the top of the wall approximately 1 foot (0.35 m) below the ceiling level and at the bottom

approximately 1 foot (0.305 m) above the floor level. Where the symbol

"S" appears, samples were taken only at the top of the wall. Shortly

after the samples were cored out, replacement circular pieces of sheathing and wood siding were installed using glue.

The experimental procedure was to place the samples in sealed jars

immediately after they were removed. Shortly thereafter, these jars

were weighed. The jars were subsequently unsealed and placed in an oven

and heated to 212° F (100° C) , with the exception of U-F foam samples

which were heated to 100° F (37.8° C) . After the samples were oven

dried, they were again weighed. The percent moisture content (f ) (by weight) was determined from the relation:

W - W

f = X 100 (24) m w Ja where W and W are the wet and dry weights of the material, respectively. " 87
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88
The moisture contents of the material samples removed from cellulose

wall sections are shown in table 24.

TABLE 24. WINTER MOISTURE CONTENTS OF MATERIAL SAMPLES

REMOVED FROM CELLULOSE WALL SECTIONS

Moisture Content, % (by weight)

Wood

Sid ine Sheathine

Outside

Insulation

Corp

Insi<

Insula

1 Top 11.2 10.9 13.5 11.9

1 Bottom 12.0 13.0 15. 6 15.3

2 Top 10.8 11.3 13. 2 16.0

2 Bottom 8.6 10.7 13.0 12.5

3 Top 11.8 14.1 16.3 14.1

3 Bottom 12.1 12.3 15.7 14.7

6 Top 15.3 10.5 13.6 13.2

Average 11.7 11.8 14.4 14.0

* See figure 30 for location identification.

The average moisture content of the insulation adjacent to the cold

exterior surface is seen to be only slightly higher than the average

moisture content of samples adjacent to the warm inside surface. This

observation suggests that the moisture content of cellulose tends to become uniformly distributed.

The moisture contents of material samples taken from the glass-fiber

wall section are shown in table 25. The moisture contents of the glassfiber insulation are seen to be clearly lower compared to values for

cellulose insulation, but the moisture contents of the wood siding and

the sheathing at this section are somewhat higher than corresponding

samples taken from wall sections insulated with cellulose.

TABLE 25. WINTER MOISTURE CONTENTS OF MATERIAL SAMPLES TAKEN

FROM THE GLASS-FIBER WALL SECTION

Moisture Content, % (by weight)

Location*

5 Top

5 Bottom

Average

Wood

Siding

12.3

16.8

14.6

Sheathing

14.0

15.5

14.8

Outside

Insulation

Core

8.1

11.0

9.6

* See figure 30 for location identification,

Inside

Insulation

Core

10.1

3.2

6.7

89
The moisture contents of material samples removed from the U-F wall

section are shown in table 26,

TABLE 26. WINTER MOISTURE CONTENTS OF MATERIAL SAMPLES

TAKEN FROM U-F WALL SECTION

Moisture Content, % (by weight)

Outside

Insulation

Sheathing Core

Inside

Insulation

Location* Core

Wood

Siding

4 Top

4 Bottom

Average

24.8

21.6

23.2

28.1

38.6

33.4

8.0

12.9

10.5

9.4

12.3

10.9

* See figure 30 for location identification.

The moisture contents of the U-F foam itself are comparable with

values for the other insulation material. However, the moisture contents

of the sheathing and wood siding samples taken from the U-F wall section

are much higher than corresponding values for the other wall sections.

An explanation is given in the following:

The wet density of U-F foam when it is installed is 2.5 Ib/ft"^

(40.0 Kg/m ) . After the foam has cured and dried, its density is

0.7 Ib/ft-^ (11.2 Kg/m^) . The difference in these density figures is due

to the original water content of the foam. This amount of water corresponds

to approximately 0.47 lb per ft^ of wall (2.29 Kg/m2)

.

The water originally contained in the wet foam apparently migrated

from the U-F foam into the sheathing and siding and could not readily

penetrate the oil-base paint film applied to the exterior surface of the

wall. Published data indicate that three layers of oil-base paint have a perm rating of 0.3 to 1.0 (1.72 to 5.75 x lO'l^Kg/Pa- S -m^) [4]. The

exterior walls of the test house contained several layers of oil-base

primer and top coat, which probably functioned as a vapor barrier.

At the end of the winter season, some blistering of the oil-base

paint at the U-F wall section was observed. Two large blisters (one at

the top and one at the bottom of the section) were present. A photograph

of the water blister at the top is shown in figure 32. Many small

blisters also occurred under the double-hung window at this wall section.

At the end of the summer season, the small blisters disappeared, but the

two large blisters remained.

The foregoing experimental results show that when U-F is blown into

wood-frame cavity walls during the winter, the water originally contained

in the foam will move outward into the wood siding and sheathing. When

a vapor- impermeable paint system is applied to the exterior surface,

this moisture may not be able to escape to the outdoor environment and

90

can lead to paint peeling and blistering. If a more permeable paint

system (such as a latex paint system) had been applied to the exterior

surface, the accumulated moisture might have escaped more readily to

the outdoor environment.

At the end of the following summer season, samples of wood siding,

sheathing, and insulation were again cored out at wall sections insulated

with the three different materials, and the moisture contents of these

samples were determined. The heat pump in the test house was operated

throughout the summer and maintained the indoor temperature at approximately 74.4° F (23.6° C) and at a dew point of approximately 58° F

(14.4° C) . Summer moisture contents of material samples are given in

tables 27, 28, and 29 for the cellulose, glass-fiber, and U-F wall

sections, respectively.

Comparing the moisture contents of samples cored from the cellulose

wall section at the end of the winter season (table 27) to corresponding

samples cored at the end of the summer (table 24), it can be seen that

the moisture contents of the wood siding, sheathing, and insulation

tended to be approximately the same. Note that for both the summer and

winter measurements the moisture contents of the inside and outside

insulation cores at the cellulose wall section were very nearly the

same.

An examination of summer moisture content values taken from the

glass-fiber wall section (table 28) show that the moisture contents

of the inside insulation cores were considerably greater than those of

outside insulation cores. During the summer season, the flow of vapor

is predominantly from the outside to the inside. Moisture tends to

accumulate within the insulation layer adjacent to the cooler interior

surface.

The summer moisture contents of material samples cored from the U-F

wall section (table 29) show that much of the original water that had

become entrapped in the wood siding and sheathing was able to migrate

inward and escape during the summer. However, the slightly elevated

moisture contents of the wood siding and sheathing, and the fact that the

outside insulation cores contained more moisture than the inside cores,

would indicate that the wood siding and sheathing may still have been

losing moisture.

92
TABLE 27. SUMMER MOISTURE CONTENTS OF MATERIAL SAMPLES REMOVED

FROM CELLULOSE WALL SECTION

Moisture Content, % (by weight)

nf WU TnQiil xnouxouxoiiAn xnsiae

Location* Siding Sheathing Outside Inside Wall Covering

1 Top 12 12 13 13 8

1 Bottom 16 12 16 14 9 (11)

2 Top 10 10 14 , 16 10

2 Bottom 8 9 15 14 9

3 Top 11 13 17 18 8

3 Bottom 13 14 18 18 8

6 Top 11 12 25 14 9

Average 11.6 11.7 15.5*** 15.3 8.7

* See figure 30 for location identification

** Plaster (wood) *** The moisture content for 6 Top is not included in the average. .

TABLE 28. SUMMER MOISTURE CONTENTS OF MATERIAL SAMPLES TAKEN FROM

THE GLASS-FIBER WALL SECTION

Moisture Content. % (by weight)

Wood Insulation Core Inside

Location* Siding Sheathing Outside Inside Wall Covering

5 Top 12 14 3 22 9

5 Bottom 12 14 3 18 9

Average 12 14 3 20 9

* See figure 30 for location identification.

93
TABLE 29. SUMMER MOISTURE CONTENTS OF MATERIAL SAMPLES TAKEN

FROM THE U-F WALL SECTION

Location*

Moisture Content, % (by weight)

Wood

Siding Sheathing

21

11

16

Insulation Core

Outside Inside

A Top 17

A Bottom 13

Average 15

* See figure 30 for location identification.

22

14

18

17

14

15.5

Inside

Wall Covering

15

9

12

8.4 Other Performance Properties of Insulations

The shrinkage, fissuring, and settling properties of in situ insulating materials were also observed on the test house.

8.4.1 Shrinkage and Cleavage in the U-F Foam

The U-F wall section was opened up periodically to observe the condition of the foam. On these occasions, the linear shrinkage away from the

studs was measured at several locations and average shrinkage figures

were calculated. Average shrinkage figures of the foam of the test house

are given in table 30.

TABLE 30. MEASURED LINEAR SHRINKAGE OF IN SITU U-F

FOAM OF THE TEST HOUSE

Elapsed Time

Months

3.1

14.8

20.1

2 6.2

Linear Shrinkage

%

2.6

5.6

7.3

8.1

These data are plotted in figure 33. It can be seen that the percent

linear shrinkage of the in situ foam of this particular house has been

occurring at an approximately constant rate. After 26.2 months, there

has been very little leveling off in the rate of shrinkage. Since the

composition and density of the U-F foam are known to have an effect on

the rate and extent of linear shrinkage, the data in table 30 may not be

characteristic of all U-F foam applications.

Several small fissures (void spaces where the foam has pulled apart)

were also observed in the in situ foam. They ranged from 3/8 in (.95 cm)

to 1 in (2.54 cm) in width.
10

* 6

O

z

(T 4 X

</) 3

2

1 1 1 1 1 1 1 1 i i 1 1 1 1

i

%^— _

1 1 1 1 1 1 1 1 1 1 1 1 1 1 8 10 12 14 16 18 20 22 24

ELAPSED TIME, MONTHS

26 28 30

Figure 33. Percent linear shrinkage of urea-formaldehyde foam insulation

as a function of elapsed time.

95
8.4.2 Settling of Loose-fill Insulation

Settling of the loose-fill cellulose insulation installed in the

ceiling was observed over a period of 18 months following the installation. The settling that occurred during the first 25 days was 3/4 in

(1.91 cm) or 12.5 percent, of the initial thickness of 6 in (15.24 cm).

Eighteen months after the installation, the total measured settling was

1-1/2 in (3.82 cm), or 25 percent out of an initial fill of 6 in (15.24 cm).

Part of the settling of the loose-fill cellulose may have been due

to compression of the existing 3-1/2 in (8.89 cm) of glass-fiber blanket

insulation over which the cellulose had been applied. However, it is

doubtful that the glass-fiber insulation would exhibit slow long-term

compression, since glass fiber is one of the most nearly perfect elastic

materials which exists. In addition, the bag count for the cellulose

insulation used to insulate the ceiling indicated that the loose-fill

cellulose had been initially installed at too low a density.

In the case of the walls, holes were drilled at the top of the wall

cavities of the glass-fiber and cellulose wall sections. These holes

were sealed with plastic plugs, permitting periodic inspections for

settling. No settling of either loose-fill material was observed over

a period of eighteen months. • j.,^

8. 5 Summary of Results

Thermal conductivity measurements using the guarded-hot-plate

apparatus showed that cellulosic fiber, fibrous glass wool, and U-F foam

have high thermal resistances (R-values) . The U-F foam was found to

have somewhat higher thermal resistance values than the other two

mater ials.

Heat-loss and moisture measurements were performed on a full-scale

laboratory test wall which was exposed to a temperature of approximately

5° F (-15° C) at the exterior surface and a typical indoor condition at

the interior surface for a two-month period. Separate sections of the

laboratory test wall were Insulated with the three different insulating

materials. Measured thermal conductances of the separate wall sections

agreed with corresponding predicted values determined by the seriesresistance method, even though a large amount of moisture was present in

the form of ice on the exterior side of the insulation.

Heat-transmission measurements were also performed on separate wall

sections (insulated with the three different insulating materials) of

the test house. Measured thermal conductances for the glass-fiber and

cellulose wall sections agreed with corresponding predicted values

determined by the series-resistance method, whereas the measured thermal

conductance of the U-F wall section was considerably higher than predicted value. The higher measured thermal conductance at the U-F wall

section was attributed to a 1-in (2.54 cm) fissure (or void space),

which was discovered directly in line with the heat-flow measuring

station.

96
At the end of the winter season, after the insulation was installed

in the exterior walls of the test house, the moisture content of the

wood siding and sheathing of the cellulose and glass-fiber wall sections ' was determined by an oven-drying technique and found to range between 12

and 15 percent (by weight)

The average moisture content observed at the end of the winter sea- son for the wood siding and sheathing at the U-F wall section were 23 and

33 percent, respectively. These values are considerably higher than

corresponding values observed at other wall sections. At the end of the

winter season, paint blistering was observed at the U-F wall section.

The comparatively higher moisture contents observed at the U-F wall

section were attributed to the original moisture content of the foam.

When the foam was initially installed, it contained approximately 0.47

lb of water per ft^ of exterior wall (2.29 Kg/m2) . The original moisture

in the foam migrated into the siding and sheathing and was unable to

penetrate the oil-base paint system applied to the exterior surface.

Oil-base paint is known to have a low permeance for water vapor. If a more permeable paint system had been used, the original water of the

foam probably might have been able to escape to the outdoor environment

without blistering the paint.

The U-F wall section was opened up on several occasions and the foam

was examined for linear shrinkage. The percent linear shrinkage was

observed to increase at an approximately steady rate during the period of

observation. After 26.2 months, the average linear shrinkage was found

to be approximately 8.1 percent.

Eighteen months after the cellulose and glass-fiber insulations

were installed in the walls of the test house, no settling of the loosefill materials was observed. Eighteen months after cellulose was installed

over the existing glass-fiber ceiling insulation, the height of the

cellulose above the ceiling had decreased by 25 percent. The bag count

of the cellulose used to insulate the ceiling indicated that it had

been installed at too low a density.

9. EFFECTIVENESS OF RECOMMENDED "GOOD PRACTICE" MEASURES FOR

PREVENTING MOISTURE ACCUMULATION

The effectiveness of recommended "good practice" measures [4] for

preventing winter moisture accumulation in attics and summer moisture

accumulation in crawl spaces was also investigated.

97
9. 1 Experimental Plan

The experimental plan for evaluating the effectiveness of recommended

"good practice" measures for preventing potentially dangerous moisture

accumulation was to employ the following measures during the third stage

of the retrofit:

a. Vapor-barrier cover over the bare earth of the crawl space,

b. Recommended attic ventilation,

c. Recommended crawl-space ventilation,

d. A vapor barrier on the warm side of the ceiling and

floor insulation.

Item d is not a requirement for the Washington, D.C. location, but it was included as part of the retrofit, nonetheless. During the remainder

of the winter season, periodic inspections of the test house for visible

condensation were performed. Material samples were cored from the attic

at the end of the winter season and from the floor over the crawl space

at the end of the summer season, and the moisture contents of these

samples were determined.

9. 2 Experimental Results

IT At the end of the winter season, 76 days after the insulation had

been installed in the test house, samples of the glass-fiber blanket

insulation and cellulose were removed at locations where the light fixtures

penetrated the ceiling. These locations were considered to be spots

where moisture-laden air could readily pass into the insulation from the

living space below.

The moisture content was 1 percent for the glass-fiber specimen and

13 percent for the cellulose specimen. These moisture contents were

probably related to the equilibrium moisture contents of the two materials. In addition, the underside of the roof was never observed to be

wet from condensation.

At the end of the summer season, wood samples of the sill plate

above the foundation wall and center pier were cored out, and the

moisture contents of these samples were found to be 19 and 16 percent

(by weight), respectively. This amount of accumulated moisture is much

less than the fiber saturation point (30 percent, by weight). Usually,

moisture problems such as wood rot due to fungi begin to occur when the

moisture content approaches the fiber saturation point [21].

9. 3 Conclusions

The recommended "good practice" measures were found to be effective

in preventing damaging winter moisture accumulation in wood parts of

crawl spaces for the test house and for the conditions under which it

was tested. 98
References

1. Patterns of Energy Consumption In the United States, Stanford

Research Institute, 1972.

2. Anderson, D. B., Heat Loss Studies In Four Identical Buildings to

Determine the Effect of Insulation, ASHRAE Transactions, Vol. 48,

19A2.

3. Degelman, L. D. , and Lewis, S. A., Single Family Dwelling and Natural

Resource Consumption Effects and Energy Budget, Seminar paper presented at the 1973 ASHRAE annual meeting held at Boston, Massachusetts.

4. ASHRAE Handbook of Fundamentals , The American Society of Heating,

Refrigeration, and Air Conditioning Engineers, 1972.

5. Anderson, L. D. , Condensation Problems: Their Prevention and Solution, USDA Forest Service Research Paper FPL 132, Forest Products

Laboratory, Madison, Wisconsin, 1972.

6. Paljak, Ivar, and Pettersson, Bertll, Thermography of Buildings,

Swedish Council of Building Research, Lund Institute of Technology,

Lund, Sweden, 1972.

7. Kelly, G. E., and Bean, J. W. , Dynamic Performance of a Residential

Alr-to-Alr Heat Pump, Building Science Series 93, National Bureau of

Standards, 1977.

8. Nottage, H. B., The Thermal Properties of Building Materials Used

In Heat Flow Calculations, ASHRAE Research Bulletin No. 2, Vol. 53,

1947.

9. Tye, R. P., Heat Transmission In Celluloslc Fiber Insulating Material,

Journal of Testing and Evaluation, Vol. 2, No. 3, American Society

of Testing and Materials, 1974.

10. Bankvall, Claus G. , Natural Convection Heat Transfer In Insulated

Structures, Report 38, Division of Building Technology, Lund Institute of Technology, Lund, Sweden, 1972.

11. Hunt, C. , and Treado, S., A Prototype Semi-Automated System for

Measuring Air Infiltration In Buildings Using Sulfur Hexafluorlde

as a Tracer, NBS Technical Note 898, 1976.

12. Hunt, C. M. , and Burch, D. M. , Air Infiltration Measurements In a Four-Bedroom Townhouse Using Sulfur Hexafluorlde as a Tracer Gas,

ASHRAE Transactions, Vol. 81, Part I, 1975.

99
13. Bahnfleth, D. R. , Moseley, T. T., and Harris, W. S., Measurement of

Infiltration in Two Residences, Part I: Technique and Measured

Infiltration, Part II: Comparison of Variables Affecting Infiltration, ASHRAE Transactions 63, pp. 453-476, 1957.

14. Coblentz, C. W. , and Achenbach, P. R. , Field Measurements of Air

Infiltration in Ten Electrically Heated Houses, ASHRAE Transactions

69, pp. 358-365. 1963.

15. Peavy, B. A., Burch, D. M. , Powell, F. J., and Hunt, C. M. , Comparison of Measured and Computer-Predicted Thermal Performance of a FourBedroom Wood-Frame Townhouse, Building Science Series 57, National

Bureau of Standards, 1975.

16. Mattingly, G. F. , and Peters, E. F. , Wind and Trees - Air Infiltration Effects on Energy in Housing, Center for Environmental Studies

Report No. 20, Princeton University, May, 1975.

17. Strieker, S., Measurement of Heat Output of Residential Furnaces,

ASHRAE Transactions, Vol. 76, Part II, 1970.

18. Faison, T. K. , Jr., Davis, J. C. , and Achenbach, P. R. , Performance

of Louvered Devices as Air Mixers, Building Science Series 27,

National Bureau of Standards, 1970.

19. Jacobs, M. , and Petersen, S., Making the Most of your Energy Dollars

in Home Heating and Cooling, NBS Consumer Information Series 8,

National Bureau of Standards, June, 1975.

20. Petersen, S. R. , Retrofitting Existing Housing for Energy Conservation: An Economic Analysis, Building Science Series 64, National

Bureau of Standards, December, 1974.

21. Scheffer. T. S. , and Verrall, A. F. , Principles for Protecting Wood

Buildings from Decay, USDA Forest Service Research Paper FPL-190,

Forest Products Laboratory, Madison, Wisconsin, 1973.

100
Nomenclature

A = area, ft (m ) AS = annual savings, $

c * Tracer gas concentration

C = initial cost

C = constant pressure specific heat, Btu/lb'T (J/Kg«K)

P

D = discount rate

e = emissivity

2 2

E = radiated energy, Btu/h-ft (W/m ) FC = fuel costs

f = moisture content TM 2 2

h = heat-transfer coefficient, Btu/h'ft (W/m 'K)

h_ = latent heat of vaporization of water, Btu/lb'*F (J/Kg»K)

HC = heating costs

HL « annual heating load, therms (J)

I = air infiltration rate, h~^

k » thermal conductivity, Btu/h*ft***F (W/m*K)

I » layer thickness, ft (m) n » layer index

N = number of layers

P = period of time or annual fuel price increase

q = heat delivered to the house or heat-transfer rate, Btu/h (W)

t = time, min. (s)

T = temperature, **F (K)

2 2

U = thermal transmittance, Btu/h* ft '"F (W/m -K)

3 3 V » rate at which air enters and leaves an enclosure, ft /h (m /s)

V =» velocity, ft/min (m/s)

3 3 V = volume, ft (m ) W = mass, lb (kg)

2 a = temperature coefficient of thermal conductivity, Btu'in/h'ft

(W/m-K^)

6 = deviation

n = efficiency of heating plant or coefficient of performance for

air conditioning equipment

101
;

A = constant

3 3

p = density, lb/ft (Kg/m ) a = Stefan-Boltzmann constant

0) = humidity ratio, lb (Kg) H-0 per lb (Kg) dry air

Subscripts

a = air properties or normalized quantity

c = heat loss by conduction

d = dry property

i = inside surface

I = air infiltration

L = latent load

m = measured value

o = outside surface or initial time

w = wet property

102
Conversion Factors to Metric (SI) Units

Physical To Convert

Quantity Symbol From To Multiply By

Length i ft m 3.05 X lO""^

Area A

^ 2

ft 2

m

-2

9.29 X 10

Volume V ft

3

m

-2

2.83 X 10

Temperature T Fahrenheit Celsius t^= (t^-32)/l

Temp. Diff. AT Fahrenheit Kelvin K = (ATj/1.8

Mass lb Kg 4.54 X lO"-*-

Density P Ib/ft^ Kg/m^ 1.602 X lO"""

Thermal

Conductivity k Btu-in/h*ft^ ••F W/m-K 1.442 X lO""*"

Thermal

Transmit tance

(or Conductance) U Btu/h'ft^'**F W/m^-K 5.68

Thermal Resistance R h-ft^-°F/Btu m^-K/W 0.176

Heat Flux Rate q/A Btu/h-ft^ W/m^ 3.15

Heat Flow q Btu/h W 2.93 X 10"

Volumetric Flow

Rate V ft /min 3, m /s 4.72 X lo"^

Velocity V f t/min m/s 5.08 X

10"^

Specific Heat C

P

Btu/lb-'F J/Kg-K 4.19 X 10^

Permeance 2

perm Kg/Pa* s*m 5.72 X lO'-''^

103
ACKNOWLEDGMENTS

Staff members of the Building Environment Division of CBT provided

much assistance and support during the period of research and preparation of this report.

The authors are grateful to Paul Achenbach, David Didion and

George Kelly for their many ideas, conceptual approach, and technical

suggestions prior to and during the experimental phases of the study,

and to Steve Petersen for suggestions concerning the economic technique

for evaluating the cost effectiveness of the retrofit measures. The

authors are indebted to Rollin Baumgardner for many helpful suggestions

concerning retrofit techniques and moisture condensation in buildings.

Appreciation is also expressed to C. Siu for conducting the guarded-hotplate measurements; to Walter Ellis for his technical assistance in the

installation of the instrumentation and day-to-day operation of the ex- periment; to John Grimes for designing, constructing, and testing the

full-scale laboratory test wall; to James Allen for carrying out the

smoke and thermographic measurements; to Dee Showalter for assisting in

the smoke measurements; to John Bean for reducing the energy data; to

Mary Reppert for editing the manuscript; and to Tammy Mewshaw and

Shirley Baile for typing this report.

Mr. Reid Hartsell, general technical representative. Federal Energy

Administration, provided liaison for this report, and his patience and

encouragement are appreciated by the authors.

104
Appendix A

Description of the Third Stage of the Retrofit

1. Introduction

The third stage of the retrofit consisted of applying insulation in

the walls and the floor, and installing additional insulation in the

ceiling. Since NBS did not have the equipment nor the trained personnel

to blow loose-fill insulation into walls and over ceilings, the thirdstage work was performed under contract.

2. Installing Additional Insulation in the Ceiling

Six inches (15,24 cm) of loose-fill cellulose insulation were blown

on top of the existing 3-1/2 in (8.89 cm) of glass-fiber blanket ceiling

insulation. The cellulose insulation was poured from bags into the

blowing machine shown in figure A-1. At the bottom of the blowing

machine, the rotation of an agitator broke up the cellulose into smallsize particles which were subsequently fed into a blower. The blower

pumped the insulating material through a 2-1/2 in (6.35 cm) diameter

hose which was used to distribute the insulating material uniformly on

top of the existing ceiling insulation (see figure A-2) . Loose-fill

cellulose was also blown under and up to the top surface of the 6-ft

(1.83 m) wide catwalk that ran the length of the attic.

3 . Insulating the Walls

Loose-fill cellulose insulation was blown into the wall cavities,

with the exception of the northeast bedroom where loose-fill glass fiber

was blown into the north exterior wall and U-F foam was blown into the

east exterior wall. The technique used to install loose-fill cellulose

in most portions of the wall was to drill a 1-1/4 inch (3.18 cm) hole

through the siding and the sheathing, approximately 1 foot (0.305 m)

above the floor and 1 foot (0.305 m) below the ceiling. The cellulose

material was fed into the blowing machine and forced to pass through the

flexible hose. A flow-reducing nozzle with a sight glass (for observing

the flow of cellulose) and a flow-control lever was mounted at the end

of the hose, as shown in figure A-3. The nozzle was inserted into the

hole in the wall cavity and the flow of insulating material was initiated

by activating the flow-control lever. Upon detecting the stoppage of

flow through the sight glass, the equipment operator would de-activate

the flow control lever and move the nozzle to the ne?ct hole.

Loose-fill glass-fiber insulation was blown into the north wall of

the northeast bedroom. The application technique was to drill a 2-9/16

in (6.51-cm) hole through the siding and the sheathing at the bottom and

top of each wall cavity. Insulating material was pumped through a 3-in

(7.62-cm) diameter flexible hose into a 2-1/2 in (6.35 cm) nozzle which

was inserted into the hole as shown in figure A-4. Blowing loose-fill

A-1
Figure A-1. Loose-fill cellulose insulation being poured

into blowing machine.

A-2
exo

o

3 d

o o ^ +J

nj M -H C 3

•H CO

OJ 60

CO C

O -H iH r-H rH di

•H CO

I X

0) OJ

COO 0) O rC

CN

I <

60

•rl

Figure A-4. Glass fiber being blown into a wall section.

Aglass fiber into walls requires larger holes, since the glass fibers are

long and have a tendency to get hung up in a small reducing nozzle.

Urea-formaldehyde (U-F) foam insulation was blown into the east

wall of the northeast bedroom. The application technique was to drill

four 1-inch (2.54 cm) holes, approximately 2 feet (0.610 m) apart vertically, in each of the wall cavities. The U-F foam was successively

applied from the bottom to the top holes, completely filling the wall

cavity (see figure A-5) . When the foam was initially applied, its wet

density was 2.5 Ib/ft^ (40.1 Kg/m^) . Figure A-6 is a photograph of the

technical representative for the U-F foam measuring the wet density of

the U-F foam material. The technical representative also determined " the setting time of the U-F foam after it left the foaming apparatus.

The setting time was found to be less than 1 minute. These are very

important tests which should be performed prior to blowing U-F material

into the wall cavities, since they provide a good indication of the

correctness of the composition of the material. After drying, its

density was 0.7 Ib/ft^ (11.21 Kg/m^) . Three hoses transporting U-F

resin, a catalytic foaming agent, and compressed air were connected to

the applicator gun (shown in figure A-5) in which the constituents were mixed in proper proportions to produce U-F foam.

4. Insulating the Floor

Six-inch (15.24 cm) foil-faced glass-fiber batts were installed

between the floor joists over the crawl space (see figure A-7) . The

foil was placed in contact with the underside of the floor. The insulation was held in place with flexible thin rods called "tiger teeth."

The domestic water pipes in the crawl space were also insulated to provide freeze protection. A polyethylene vapor barrier was placed over the

bare earth of the crawl space to prevent moisture of the earth from

migrating into the crawl space.

A-6

Technical representative measiiring wet density

of the U-F foam.

A-8


Appendix B

Location of Heat Leaks in Residences

Using Infrared Thermography

1. Introduction

As part of the energy conservation study conducted on the test

house, a thermographic survey using an infrared (IR) television system

was performed before and after energy conservation measures were implemented. The purpose of the survey performed prior to the retrofit was

to identify major heat leaks which could be treated as part of the retrofit. The purpose of the survey performed after the retrofit was to determine the effectiveness of the retrofit in treating these previously

discovered heat leaks. A thermographic survey of the exterior walls of

the test house was performed after insulation was blown into the walls

to identify void spaces where insulation was missing. Finally, another

survey of the retrofitted test house was performed during the following

summer to determine if the same void spaces (previously observed in the

winter season) could be observed in the summer when the inside-tooutside temperature difference was much smaller.

2. Description of Thermographic Equipment

Infrared thermography is based on the principle that all surfaces

emit energy in the form of electromagnetic radiation. The amount of

self-emitted radiated energy is proportional to the emissivity of the

surface and the fourth power of the absolute temperature, or

E = e.a.T^^ * (B-1)

2 2 where E = radiated energy, Btu/h-ft • (W/m )

e = surface emissivity

T = absolute temperature, °R (K)

2 4 2 4 a = Stef an-Boltzmann constant, Btu/h-ft -"R (W/m K )

A photograph of the infrared television system used for the present

study is shown in figure B-1. The equipment from right to left consists

of an IR television camera, black-and-white television monitor, a color

television monitor, and a temperature-profile display monitor. Upon

sensing the radiation emitted from a surface, the IR television camera

produces a video signal. The IR camera consists of an optical scanning

system with a liquid-nitrogen cooled indium-antimonide photovoltaic

detector having high sensitivity in the spectral range of 2.0 to 5.6

micrometers (10~^)

The video signal from the IR camera is processed in the black-andwhite television monitor where it is converted into a thermal picture in

B-1
B-?.
which the gray tones in the picture approximately correspond to surface

tanperatures. A photograph of the thermal picture is called a "thermogram." Video signals are also fed into the color television monitor

where ten individually color-coded isotherms are displayed on the color

television screen to produce a thermal picture in which the temperature

range has been subdivided into ten regions, each coded with a separate

color. The temperature profile display monitor selects a single horizontal trace line of the black-and-white television picture and displays

this line such that the temperature change throughout the line is shown

as a vertical displacement.

The color thermograms* of the present study were obtained by taking

photographs, using conventional camera equipment, of the color television

display, respectively. Ten regions of different temperatures are

displayed in different colors. The temperature spectrum from the coldest

region (coded black) to the warmest region (coded white) is displayed at

the bottom of each color thermogram.

3 . Comparison of Thermographic Surveys Performed

Before and After the Retrofit

A thermographic survey was performed before the retrofit for the

purpose of identifying specific heat leaks which could be eliminated by

some retrofit procedure. After the house was retrofitted, a second

survey was performed to examine the success of the retrofit. In this

section, three photographs are presented in each figure. The first

photograph is a conventional photograph in the visible spectrum of a surface of the house; the second photograph is a thermogram (in the IR

spectrum) of the same part prior to the retrofit; and the third photograph is a thermogram (in the IR spectrum) of the same part of the test

house taken after the retrofit. All thermographic pictures were taken

at night to eliminate solar radiation effects.

The dates and temperature conditions for the two thermographic

surveys are given in table B-1:

Table B-1. Conditions for the Two Thermographic Surveys

Date

Inside

Air Temp.

°F

Outside

Air Temp.

°F

Temp

Diff.

°F

Pre-retrofit

survey March, 74 81.0 41.0 40

Post-retrofit

survey March, 75 70.0 29.0 41

* This NBSIR report shows the thermograms only in black and white. A

Building Science Series report covering this research will present

the thermograms in color. B-3
I

The indoor air temperature for the pre-retrofit thermographic survey

was intentionally elevated, so that the inside-to-outside temperature

difference would be approximately the same as that for the post-retrofit

survey. When performing a thermographic survey, a large inside-tooutside temperature difference is desirable, so that the contrasts in

the thermal picture between insulated and non- insulated regions will be as large as possible. Another important consideration necessary for a meaningful comparison between thermograms (say before and after retrofit)

is that the inside-to-outside temperature differences be the same for

the two cases. The wind velocities were not measured during the two

surveys, but visual observations would indicate low wind velocities for

both surveys, probably less than 5 mph (3.61 m/s)

.

An overall view of the whole test house is given in figures B-2a,

b, c. Comparing the pre-retrofit thermogram (figure B-2b) to the postretrofit thermograms (figure B-2c) , it is seen that the contrast between

the test house and the surroundings is much greater in the pre-retrofit

thermogram than the post-retrofit thermogram. This decrease in contrast

in the post-retrofit thermogram is due to comparatively colder exterior

surfaces (with respect to the surroundings) for the insulated test

house. Thus, we see that the contrast (temperature difference) between

a building and its surrounding environment may be used as a qualitative

indication to determine whether wood-frame cavity walls are Insulated.

Thermographic surveys of the east end of the test house before and

after the retrofit are presented in figures B-3a, b, c. In the postretrofit thermogram the contrast (temperature difference) between the

left and right parts of the wall section is due to the difference in the

heat loss characteristics of wall sections insulated with different

insulating materials. The wall section on the left is insulated with

loose-fill cellulose, whereas the wall section on the right is insulated

with urea-formaldehyde foam. It can be seen that the cellulose wall

section is approximately two color-coded isotherm units colder than the

U-F wall section. The lower outside surface temperature of the cellulose

wall section clearly demonstrates that, at the time this particular

thermogram was taken , the insulating properties of the cellulose material

were better than those of the urea-formaldehyde foam. It should be

pointed out that the post-retrofit thermogram was taken only 17 days

after the U-F foam was installed, when the U-F material still contained

significant residual moisture which may have considerably reduced its

insulating properties. The embedded relative humidity transducer mounted

inside the wall between the U-F foam and the sheathing showed a saturated

condition at the time this infrared picture was taken. The rectangularly

shaped dark region between the windows on the pre-retrofit thermogram is a closet. Since the interior of the closet is an unheated space, less

heat is lost through the exterior wall where the closet is located,

resulting in lower exterior surface temperatures at this location.

Note, however, after insulation is added to the walls, it is no longer

possible to distinguish the closet in the thermogram. This suggests

that for thermograms taken at an inside-to-outside temperature difference

B-4

Overall view of exterior surfaces of the test house,

(b) Thermogram before retrofit.

B-6
Figure B-2. Overall view of exterior surfaces of the test house,

(c) Thermogram after retrofit.

B-7
Figure B-3. East end of test house,

(a) Conventional photograph.

B-8
Figure B-3. East end of test house,

(b) Thermogram before retrofit.

B-9
Figure B-3. East end of test house,

(c) Thermogram after retrofit.

B-10
of approximately 40'' F (22.2° C) , the ability to see closets in thermograms of the exterior surfaces may be used as a qualitative indication

to distinguish between insulated and uninsulated wood-frame cavity

walls.

As a final comment on this pair of thermograms, the foundation wall

of the post-retrofit thermogram appears saturated white. On the particular day that the post-retrofit thermographic survey was performed, the

afternoon temperatures were comparatively warm, followed by significantly

lower temperatures in the evening. It was hypothesized that the foundation wall apparently stored heat in the afternoon. It was believed that

this stored heat was released in the evening, as shown in the postretrofit thermogram. It should be pointed out that, when a part of a thermal picture (such as the windows of figure B-3) is displayed in

white or black, its temperature level may not be determined, since the

extent of which the temperature level is into saturation is not known.

Figures B-4a, b, and c are a thermographic survey of the door

leading from the dining room to the screened-in back porch. These

pictures were taken from inside the dining room. The black region (cold

spots) in the pre-retrofit thermogram (figure B-4b) is due to an air

leak under the door. The sensitivity (total temperature range display

in the thermal picture) is the same for both the pre- and post-retrofit

thermograms. Observed differences may therefore be regarded as being due

to the differences in surface temperatures. Note that in the postretrofit thermogram (figure B-4c) the application of improved weatherstripping at the bottom of the door is seen to be effective in eliminating the previously observed air leak.

Figures B-5a, b, and c are a thermographic survey of the interface

between the ceiling and the wall above the large picture window of the

living room taken before and after the retrofit. A dark line has been

superimposed on these photographs to assist in identifying the interface between the wall and the ceiling. In the pre-retrofit thermogram

(figure B-5b) a cold black region can be seen in the ceiling surface

where it intersects the wall. An inspection of this location from the

attic showed that the insulation was in place. It was believed that

cold air leaking through the eaves of the attic was able to penetrate

through the ends of glass-fiber blanket insulation and cause the cold

spot. Note that in the post-retrofit thermogram (figure B-5c) 6 inches

(15.24 cm) of loose-fill cellulose over the top of the existing 3-1/2

inch (8.89 cm) glass-fiber blanket was successful in eliminating the

cold spot along the ceiling.

Figures B-6a, b, and c are a thermographic survey of an upper

corner of the northeast bedroom. A dark line has been superimposed on these photographs to assist in identifying the interface of various

surfaces of the room. The red and pink regions (region 1) shown in the

pre-retrofit thermogram (figure B-6b) are cold spots on the ceiling due

to compressed glass-fiber ceiling insulation. When blanket insulation

is compressed, it loses some of its insulating properties and allows

B-11
(a) Conventional photograph.

B-12
Interior surface of dining room door.

Thes-Tiogram after retrofit.

B-13
Figure B-4. Interior surface of dining room

(c) Thermogram after retrofit.

B-14
Figure B-5. Interior view of ceiling-wall interface above

the bay window in living room.

(a) Conventional photograph.

B-15
Figure B-5. Interior view of ceiling-wall interface above

the bay window in living room.

(b) Thermogram before retrofit.

B-16
Figure B-5. Interior view of ceiling-wall interface above

the bay window in living room.

(c) Thermogram after retrofit.

B-17
B-18
Figure B-6. Interior view of upper corner of northeast bedroom,

(b) Thermogram before retrofit.

B-19
I

I

j Figure B-6. Interior view of upper corner of northeast bedroom,

(c) Thermogram after retrofit.

B-20
more heat loss. The post-retrofit thermogram (figure B-6c) indicates

that the installation of loose-fill cellulose over the top of the

existing glass-fiber blankets has eliminated the cold spots on the

ceiling.

4 . Winter Thermographic Survey of the Extermior Walls

After the Retrofit

The following post-retrofit thermographic survey was taken on March 3, 1975, during the evening when the inside-to-outside temperature

difference was 44° F (24.4° C)

Figure B-7 is a thermogram of the U-F wall section after the retrofit. The blue area above the window (region 1) is a cold spot on the

inside wall due to an air space between a regular stud and a jack stud.

A jack stud is an extra stud inserted in a wall to support a window

frame. Notice the maroon-shaded area (region 2) depicting a cold spot,

probably where U-F foam of two regions did not completely flow together.

Also, note that the region where the heat-flow measuring station was

placed (region 3) appears to be free of any void spaces. However, when

the inside wall surface was removed at this location, a one- inch fissure

was discovered at this location which caused the measured heat-loss

rates to be greater than the predicted values (as indicated in section

8.3 of the report)

Figure B-8 is a thermogram of one section of the inside surface of

the south wall. The dark spot is a cold spot on the inside surface due

to a void space in the wall cavity which is not filled with cellulose

insulating material. The diagonal member shown in the thermogram is a wind brace. The hole through which insulation was blown was drilled

below the wind brace. When cellulose insulation was blown into the wall

cavity, the wind brace prevented the space from being filled with insulating material.

Figure B-9 is a thermogram of the inside surface of the east wall

of the southeast bedroom. Again, the diagonal member shown in the

thermal picture is a wind brace. In this case, void spaces are located

below the wind brace. The holes for blowing insulation into these

cavity spaces were drilled below the wind brace. Insufficient cellulose

insulating material was blown into these spaces, as indicated by the

void spaces.

Figure B-10 is a thermogram of the inside surface of a glass-fiber

wall section. Again insufficient glass fiber material was installed as indicated by the void spaces.

In the thermograms of inside surfaces shown in figures B-8 through

B-10, it can be seen that wall studs can be distinguished in the thermal

picture. In the pre-retrofit thermographic survey, it was difficult to see wall studs for inside-to-outside temperature differences at approximately 40° F (22.7° C) . Thus, the ability to see wall studs in thermograms

of inside wall surfaces of a wood-frame house may be used to distinguish

between insulated and uninsulated wood-frame cavity walls.

B-21
Figure B-7. Winter thermogram of inside surface of U-F wall section.

B-22
Figure B-8. Winter thermogram of inside surface of cellulose

wall section in dining room.

B-23
Figure B-9. Winter thermogram of inside surface of cellulose wall

section in southeast bedroom.

B-24
Figure B-10. Winter thermogram of inside surface of glass-fiber

wall section in northeast bedroom.

B-25
5. Sununer Thermographic Survey of the Exterior Walls

After the Retrofit

Summer thermographic pictures were taken at the same location where

winter heat leaks had been previously identified (see figures B-7 through

B-10) to determine if uninsulated regions (void spaces) could still be

detected during the summer when inside-to-outside temperature differences

were much smaller. A summer thermographic survey was performed after

the retrofit on September 5, 1975. For these measurements the indoor

temperature was approximately 69° F (20.6° C) , whereas the outdoor

temperature ranged between 74° F (23.3° C) and 75° F (23.9° C) . Thus,

the inside-to-outside temperature difference was about 6° F (3.3° C) .

Figures B-11 and B-12 are summer thermograms of cellulose and

glass-fiber wall sections shown in figures B-9 and B-10, respectively.

Notice that the uninsulated void spaces may still be identified. Thermograms of the wall sections shown in figures B-7 and B-8 were not successfu

in identifying the void spaces seen during the winter. It is therefore

concluded that summer thermographic surveys, performed when the insideto-outside temperature differences are small, may be only partially

successful in identifying uninsulated void spaces in retrofitted walls.

6. Conclusions

Thermographic surveys were performed during the winters before and

after the house was retrofitted. Thermography was shown to be an effective technique to distinquish between insulated and uninsulated

wood-frame cavity walls. For instance, the following characteristics

observed in the winter, when there exists at least a 40° F (17° C)

inside-to-outside temperature difference, indicate that exterior woodframe cavity walls of a house are uninsulated:

° Studs do not stand out in contrast with respect to the

insulated portion of the wall when viewed from the inside.

° Exterior walls stand out in contrast with the surroundings

when viewed from the outside.

Closets next to exterior walls appear as cold spots when

viewed from the outside.

The absence of the foregoing characteristics indicates that wood-frame

cavity walls are insulated.

Summer thermographic surveys, performed when the inside-to-outside

temperature difference was small, were only partially successful in

identifying uninsulated void spaces in insulated wood-frame cavity

walls.

B-26
Figure B-11. Summer thermogram of the inside surface of the cellulose

wall section in southeast bedroom.

B-27
Summer thermogram of the inside surface of the glass-fiber

wall section in northeast bedroom.

B-28
Appendix C

Location of Air -Leakage Paths in a Residence

Using Pyrotechnic Smoke

1. Introduction

Specific air-leakage paths were identified in the test house using

white pyrotechnic smoke. The experimental procedure was to fill a portion of the test house with white pyrotechnic smoke, and subsequently

pressurize the interior of the house. The air-leakage paths were then

identified through visual observations and photographed.

2. Instrumentation and Experimental Procedure

White pyrotechnic smoke was released in each room of the test

house using either the drum-type distributor (figure C-1) or the combination fan and metal trash basket (figure C-2)

In the case of the drum-type smoke distributor, two pyrotechnic

smoke generators were ignited and placed inside the cylindrical drum.

The operation of the electrically-driven blower mounted at the base of

the cylindrical container caused smoke to effuse through holes at the

top periphery of the drum. For the other smoke distribution system, two

smoke generators were ignited and placed inside metal trash baskets. The

fan blew air across the top of the container causing the smoke to mix

with the indoor air.

After the smoke had filled a portion of the interior of the test

house, the inside of the house was pressurized using a 1/2-horsepower

(373 W) centrifugal blower connnected to a sealed window panel with a 12-inch (30.48 cm) diameter flexible hose. A photograph of the centrifugal blower and flexible hose connection to the window is shown

in figure C-3.

The inside-to-outside pressure difference was measured with a Hook

gage. The air-delivery rate of the centrifugal blower and the wind

speed were measured using a rotating vane anemometer.

Since the centrifugal blower was not of sufficient capacity to obtain an adequate inside-to-outside pressure difference for the whole

house, it was decided to segment the test house into approximately equal

sections by closing and taping the interior doorway in the center hallway. It should also be pointed out that performing smoke tests on segmented portions of the test house has the additional advantage of reducing the exterior surface requiring monitoring. Due to time conflicts

with other aspects of the energy conservation study, smoke tests were

performed only on the living quarters.

C-1

I;

The smoke test on the living quarters was performed before any of

the retrofit measures were implemented to reduce air leaks. The drain

waste-water traps were filled with water, since this is the way a house

would normally be operated. In addition, the return and supply air

registers were sealed with aluminum duct tape, since the primary objective was to locate the major air leaks of the exterior envelope of the

test house. It would have been useful to perform a separate smoke test on the duct syston. However, experimental constraints did not permit

such a test to be conducted.

During the smoke test, the wind speed above the test house, the

air-delivery rate of the centrifugal blower, and the inside-to-outside

pressure differences were measured. The smoke generators were ignited

and the living space of the house was allowed to fill with smoke. Subsequently, the house was pressurized and the air-leakage paths were

located by visual observations. Smoke leakage was monitored on the

four faces and the roof of the test house. In addition, smoke leakage

through the floor and ceiling were observed from the basement and the

attic spaces, respectively. Points of smoke leakage were marked with

colored chalk and photographically documented.

3 . Discussion of Test Results

Prior to conducting the smoke test, the air-delivery rate of the

centrifugal blower was measured and found to be 1970 ft^/min (0.682

m-^/s) . This air -delivery rate corresponds to approximately 13.7 induced

air changes per hour, which is roughly twenty-eight times the natural

rate under typical winter conditions. Inside-to-outside pressure

differences measured at various locations are given in table C-1.

Table C-1

Location Inside-to-outside pressure difference, in H7O

Living Room .1034

Kitchen .1040

Dining Room .0920

Half Bath .0917

Foyer .0919

Study or Den .0913

Average .0958

C-5
The inside-to-outside pressure difference remained comparatively constant and did not vary much firom one room to another. An important

consideration in conducting smoke tests is that the pressure difference

remain approximately constant across the various exterior surfaces of

the test structure.

The wind velocity was measured before and after the test and

ranged between 0.5 and 3 mi/h (0.224 and 1.34 m/s).

A major air-leakage path was through the chimney as shown in

figure C-4. An inspection of the fireplace damper revealed that it was not seated properly and a large crack existed between the damper

frame and the damper. Another major path of air leakage was through

the kitchen ventilation-exhaust opening, as shown in figure C-5. An

inspection of the kitchen ventilation-exhaust opening revealed that the

hinge of the damper had become seriously corroded and the damper was

frozen in an open position. Another major air-leakage path was through

the ceiling as observed from the attic space. In this case, the smoke

was observed to be effusing through the large crack where the chimney

penetrated the ceiling and at the eaves where the sloping roof meets

the attic floor. It was postulated that the path for the smoke effusing

near the eaves was through the wall cavities of the exterior walls. The

smoke may have entered the wall cavity through cracks along the baseboard. Other observed air-leakage paths include cracks under the doors

and around the windows. These paths were much less pronounced than the

other major air-leakage paths previously noted.

4. Conclusion

A smoke test was shown to be an effective research technique for

locating specific air leaks for a residence. As a result of the findings

of the smoke test, the following specific measures were taken to seal

air-leakage paths of the test house:

** The fireplace-damper system was repaired.

** A spring-activated kitchen ventilation-exhaust damper was

installed.

* The window panes were reputtied as needed.

* The window frames were recaulked as needed.

C-6


. --Tl4A (I. - V. 7-73)

u s. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. I'llHI.K A 1 ION OK KI-.l'OK I' NO. NBSIR 77-1274

2. Ciov't Ac'Cf.s.s i(in No.3. Rt < ipu nt '.s Acccs.sion No.

4. Til I I-: AND SUBTITI.l- RETROFITTING AN EXISTING WOOD-FRAME

RESIDENCE FOR ENERGY CONSERVATION-AN

EXPERIMENTAL STUDY

5. Publication Date July 1977

6. I'l-rforming Organization Code

7. AU rilOR(S)

D.M. Burch and CM. Hunt

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRKS.S

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Worlc Unit No. U62 6U00

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Addres.s- (Street, City, State, ZIP)

Federal Energy Administration (FEA)

Washington, D.C. 20^461

13. Type of Report & Period Covered

Final - 2-year repori.

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) A wood-frame residence having only limited insulation in the attic was retrofitted in

three stages to reduce its energy requirements for heating and oocling. The three

retrofit stages comprised: reducing air leaks; adding storm windows; and installing

insulation in the floor, ceiling, and walls. The house was extensively instri:imented

to evaluate energy savings and other performance factors. An economic model was

used to evaluate the cost effectiveness of the retrofit options and the number of

years to pay hack their initial investment.

The walls of the test house were insulated with three different types of insulating

material: fibrous glass wool, cellulosic fiber, and urea- formaldehyde foam. The

thermal performance of these three insulating materials was measured and compared, both

in the field and laboratory.

"Recommended good practices" for moisture protection were applied when insulation was

installed in the test house. The effectiveness of these measures in preventing damagir^

moisture acciomiilation in crawl spaces and attics was evaluated.

Finally, thermographic surveys were performed before and after the retrofit. Based on the results of these surveys, criteria for distinguishing between insulated and uninsulated wood-frame cavity walls were presented.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Air infiltration; condensation in buildings; energy conservation; energy measurements;

fuel savings; heat-loss reduction; insulation properties; residential heat loss; retrofitting houses: thermal cnndncti vt t.y • t.hp-rmal in=;nlflt 1 nn -J t.hp^-rmng-rapliy

18. AVAILABILITY ^ Unlimited

\Z ' For Official Distribution. Do Not Release to NTIS

'^rder From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. Cl^

E Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

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(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

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UNCLASSIFIED

21. NO. OF PAGES

157

22. Price

$7.50

USCOMM-DC 2e042-P74