NBS BUILDING SCIENCE SERIES 105

Retrofitting an Existing Wood-Frame

Residence for Energy Conservation

An Experimental Study

U.S. DEPARTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS "^^^f^^
NATIONAL BUREAU OF STANDARDS

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I«tkm«1 loruu of Stan OCT U

NBS BUILDING SCIENCE SERIES 105

Retrofitting an Existing Wood-Frame

Residence for Energy Conservation

An Experimental Study

D. M. Burch

C. M. Hunt

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

Sponsored by:

The Federal Energy Administration

12th and Pennsylvania Avenue, N.W.

Washington, D.C. 20461

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

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued July 1978

z
Library of Congress Cataloging in Publication Data

Burch, Douglas M.

Retrofitting an existing wood-frame residence for energy

conservation. (NBS building science series ; 105)

Includes bibliographic references. Supt. of Docs, no.: Cl3.29/2:105

1. Dwellings—Energy conservation. 2. Wooden-frame

houses—Thermal properties. 3. Wooden-frame housesInsulation. I. Hunt, Charles Maxwell, 1911-joint author. II. Center for Building Technology. III. Title. IV. Series: United

States. National Bureau of Standards. Building science series

105. TA435,U58 no. 105 [TJ163.5.D86] 690'.021s [696] 77-27819

National Bureau of Standards Building Science Series 105

Nat. Bur. Stand. (U.S.), Bidg. Sci. Ser. 105, 82 pages (July 1978) CODEN: BSSNBV

Supersedes NBSIR 74-1274

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1978

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20234

(Order by SD Catalog No. Cl3. 29/2:105) Stock No. 003-003-01885-6 Price $3

(Add 25 percent additional for other than U.S. mailing)
CONTENTS

Page

CONVERSION FACTORS TO METRIC (SI) UNITS viii NOMENCLATURE ix

ABSTRACT x

EXECUTIVE SUMMARY 1

1. INTRODUCTION 5

2. DESCRIPTION OF TEST HOUSE 7

3. ENERGY-CONSERVATION MODIFICATIONS PERFORMED ON THE

TEST HOUSE 11

3.1 Measures Taken to Reduce Heating and Cooling

Energy Requirements 11

3.2 Protective Measures for Preventing Moisture

Accumulation in the Attic and Crawl Space 13

4. HEAT-TRANSFER PROPERTIES 15

5. AIR-INFILTRATION MEASUREMENTS 17

5.1 Theory 17

5.2 Measurement Technique 18

5.3 Results and Analysis 18

5.4 Conclusions 22

6. ENERGY MEASUREMENTS 23

6.1 Experimental Plan 23

6.2 Instrumentation and Measurement Technique 24

6.3 Winter Energy Measurements 27

6.4 Summer Energy Measurements 33

6.5 Conclusions 36

7. ECONOMIC ANALYSIS 39

7.1 Theory 39

7.2 Results 41

7.3 Conclusions 42

8. COMPARISON OF THE THERMAL PERFORMANCE OF THREE

INSULATING MATERIALS 43

8.1 Guarded-Hot-Plate Measurements 43

8.2 Full-Scale Laboratory Wall Tests 44

8.3 Heat-Transmission and Moisture Measurements in Retrofitted Wall Sections of the Test House 47

iii
Page

8.4 Other Performance Properties of Insulation 52

8.5 Summary of Results 53

9. EFFECTIVENESS OF RECOMMENDED "GOOD PRACTICE" MEASURES

FOR PREVENTING MOISTURE ACCUMULATION 55

9.1 Experimental Plan 55

9.2 Experimental Results 56

9.3 Conclusions 56

10. REFERENCES 57

ACKNOWLEDGMENTS 58

APPENDIX A. Description of the Third Stage of the Retrofit 59

APPENDIX B. Location of Heat Leaks in Residences Using

Infrared Thermography 63

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

Using Pyrotechnic Smoke 71

LIST OF FIGURES

Fig. 1. Typical cross-section of the house after retrofitting 8

Fig. 2. Floor plan of the test house 8

Fig. 3. Caulking compound being applied to foundation sill 12

Fig. 4. A photograph of the south side of the house showing the awnings 12

Fig. 5. Apparatus used to measure air-leakage rates for the test house 18

Fig. 6. Pre-retrofit air-infiltration correlation 19

Fig. 7. Post-retrofit air-infiltration correlation 20

Fig. 8. Schematic diagram of furnace system showing the location of

measuring transducers 25

Fig. 9. Photograph of the weather station 26

Fig. 10. Floor plan of test house showing location of temperature sensors 27

Fig. 11. Measured heating loads for the unoccupied test house after

various stages of the retrofit 28

Fig. 12. Energy-release rates for equipment, lighting, and occupancy 29

Fig. 13. Heating-load correlations for the occupied test house after

various stages of the retrofit 29

Fig. 14. Heating degree days as a function of outdoor balance temperature

for Washington, D.C 30

Fig. 15. Pre- and post-retrofit winter crawl-space temperature 31

Fig. 16. Pre- and post-retrofit winter attic temperatures 32

Fig. 17. Pre- and post-retrofit sensible cooling loads 33

Fig. 18. Pre- and post-retrofit latent cooling loads 33

Fig. 19. Pre- and post-retrofit summer indoor relative humidities 33

Fig. 20. Pre- and post-retrofit daily average summer crawl space

temperatures 34

Fig. 21. Pre- and post-retrofit daily average summer basement

temperatures 35

iv
Page

Fig. 22. Pre- and post-retrofit daily average summer attic temperatures 35

Fig. 23. Construction details of laboratory test wall 45

Fig. 24. Location of measurement transducers on laboratory test wall 45

Fig. 25. Photograph of exterior surface of laboratory test wall showing

buckling and warping of the wood siding 47

Fig. 26. Elevation view of wall section of the test house showing

heat-flow measuring station 47

Fig. 27. The effect of mean wall temperature on the thermal conductance

of the three separate wall sections 48

Fig. 28. Floor plan of the test house showing location of humidity

sensors and place where moisture content samples were cored out 49

Fig. 29. Variation of indoor relative humidity and relative humidities

of embedded sensors 50

Fig. 30. Water blister at exterior surface of U-F wall section 51

Fig. 31. Percent linear shrinkage of urea-formaldehyde foam insulation

as a function of elapsed time 52

Fig. A-1. Loose-fill cellulose insulation being poured into blowing

machine 59

Fig. A-2. Loose-fill cellulose being blown on top of the existing

ceiling insulation 59

Fig. A-3. Cellulosic fiber being blown into the wall of the test house 60

Fig. A-4. Glass fiber being blown into a wall section 60

Fig. A-5. Urea-formaldehyde foam being blown into a wall section 60

Fig. A-6. Technical representative measuring wet density of the U-F foam 60

Fig. A-7. Glass-fiber batts being installed under the floor in the crawl

space 61

Fig. B-1. Infrared television system 63

Fig. B-2. Overall view of exterior surfaces of the test house

(a) Conventional photograph 64

Fig. B-2. Overall view of exterior surfaces of the test house

(b) Thermogram before retrofit 64

Fig. B-2. Overall view of exterior surfaces of the test house

(c) Thermogram after retrofit 65

Fig. B-3. East end of test house

(a) Conventional photograph 65

Fig. B-3. East end of test house

(b) Thermogram before retrofit 65

Fig. B-3. East end of test house

(c) Thermogram after retrofit 65

Fig. B-4. Interior surface of dining room door

(a) Conventional photograph 66

Fig. B-4. Interior surface of dining room door

(b) Thermogram before retrofit 66

Fig. B-4. Interior surface of dining room door

(c) Thermogram after retrofit 66

Fig. B-5. Interior view of ceiling-wall interface above the bay

window in living room

(a) Conventional photograph 67

Fig. B-5. Interior view of ceiling-wall interface above the bay

window in living room

(b) Thermogram before retrofit 67

V
Page

Fig. B-5. Interior view of ceiling-wall interface above the bay

window in living room

(c) Thermogram after retrofit 67

Fig. B-6. Interior view of upper corner on northeast bedroom

(a) Conventional photograph , 67

Fig. B-6. Interior view of upper corner on northeast bedroom

(b) Thermogram before retrofit 68

Fig. B-6. Interior view of upper corner of northeast bedroom

(c) Thermogram after retrofit 68

Fig. B-7. Winter thermogram of inside surface of U-F wall section 68

Fig. B-8. Winter thermogram of inside surface of cellulose wall section

in dining room 68

Fig. B-9. Winter thermogram of inside surface of cellulose wall section

in southeast bedroom 69

Fig. B-10. Winter thermogram of inside surface of glass-fiber wall

section in northeast bedroom 69

Fig. B-11. Summer thermogram of the inside surface of the cellulose wall

section in southeast bedroom 70

Fig. B-12. Summer thermogram of the inside surface of the glass-fiber

wall section in northeast bedroom 70

Fig. C-1. Drum-type smoke distributor 71

Fig. C-2. Fan and metal trash basket used to distribute white

pyrotechnic smoke 71

Fig. C-3. Centrifugal blower connected to the window panel with a flexible hose 71

Fig. C-4. Major air leakage path through the chimney 72

Fig. C-5. Major air leakage path through kitchen ventilation exhaust

opening 72

LIST OF TABLES

Table 1. Description of Exterior Building Elements Before the

Retrofit (Inside-to-Outside) 8

Table 2. Thermal Conductivities of Building Components 16

Table 3. Areas and Pre-Retrofit Thermal Transmittances for

Building Components 16

Table 4. Thermal Transmittances for Retrofitted Building

Components . 16

Table 5. Pre-Retrofit Air-Infiltration Measurements 19

Table 6. Air-Infiltration Rates After Stage 1 of the Retrofit . 20

Table 7. Air-Infiltration Rates After Stage 2 of the Retrofit 20

Table 8. Air-Infiltration Rates After Stage 3 of the Retrofit 21

Table 9. Effect of Attic Ventilation on Air Infihration 21

Table 10. Summer Air-Infiltration Rates 22

Table 11. Calculation of Annual fieating Loads 30

Table 12. Comparison of Reductions in Heat-Loss Rate to Reductions in Annual Heating Load 31

Table 13. Pre-Retrofit Steady-State Winter Heat-Loss Calculations 32

Table 14. Post-Retrofit Steady-State Winter Heat-Loss Calculations 32

Table 15. Daily-Average Heat-Transfer Rates, Btu/h 36

Table 16. Cost Estimate for Energy Conservation Options 40

Table 17. Heating System Efficiencies and Fuel Costs Used for

Sample Calculations 40

vi
Page

Table 18. Winter Heating Energy Cost and Savings, Dollars 4 ) Table 19. Pay-Back Periods for Energy-Conservation Options 4]

Table 20. Thermal Conductivities of Three Insulating Materials

Measured in the Guarded-Hot-Plate Apparatus 44

Table 21. Experimental Results of Full-Scale Laboratory Wall Tests After Two-Month Exposure 46

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

Values 46

Table 23. Comparison of Measured and Predicted Thermal Conductance

Values at Wall Sections Insulated with Loose-Fill

Materials 48

Table 24. Winter Moisture Contents of Material Samples Removed

from Cellulose Wall Sections 50

Table 25. Winter Moisture Contents of Material Samples Taken from

the Glass-Fiber Wall Section 51

Table 26. Winter Moisture Contents of Material Samples Taken from

U-F Wall Section 51

Table 27. Summer Moisture Contents of Material Samples Removed

from Cellulose Wall Section 51

Table 28. Summer Moisture Contents of Material Samples Taken from

the Glass-Fiber Wall Section 52

Table 29. Summer Moisture Contents of Material Samples Taken from

the U-F Wall Section . 52

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

Test House 52

vii
CONVERSION FACTORS TO METRIC (SI) UNITS

Physical

Quantity Symbol

To Convert

From To Multiply By

Length \ ft m 3.05 X 10-1

Area

\/ /"\ 1 1 1 mo V OlUlIlt: A

V

ft2

fl-3 m2

m

9.29 X 10-2

? fi.'i. V 1 n -2

1 emperature T ranrtrnntriL I -

f -oL) \ J. .O

1 t-y-i *-\ 1 |it~t~ 1 t:mp. L/irr. A T Fal 11 trllllcll IN. t:l V 111 K - f ATr:")/1 8

IVl abb Xu A '^A V 1 0 1 ^.O'i X lU

Density P lb/ft3 kg/m^ 1.602 X 101

Thermal

Conductivity Btu-in/h-ft2-°F W/m-K 1.442 X 10-1

1 nermdi

Transmittance

(or Conductance) ; 7 Dtu/n rt"- r O.OO

1 nerniai ixesistance pi\ n rt^ r/Dtu m 2 • k' /W u. i /o

T-4o:jf neat riux Pliiv T^^fo ixate n / A CJ/ /I Ri.,, /U . £(.2 Dtu/n rt^ W/Kr«2 vv /m"^

Heat Flow Btu/h W 2.93 X 10-1

Volumetric Flow

l\a It; It/ f f 3 /mi ITlinn VCl'^l s 4t. / Z X iU —

V trioci L

y

V ft/min m/ s o.uo X lu

Specific Heat Btu/lb-°F J/kg-K 4.19 X 103

Permeance perm kg/Pa • s

• m^ 5.72 X 10-11

viii
NOMENCLATURE

A = area, ft^ (m2)

AS - annual savings, $

c - tracer gas concentration

C = initial cost Cp = constant pressure specific heat,

Btu/lb-°F (]/kg-K)

D = discount rate

e = emissivity £ = radiated energy, Btu/h -ft^ (W/m2)

fC = fuel costs

= moisture content

h = heat-transfer coefficient,

Btu/h-ft2-°F (W/m2-K)

he = latent heat of vaporization of water,

Btu/lb-°F (i/kg-K)

HC = heating costs HL = annual heating load, therms (j)

1 - air infiltration rate, h-^

k = thermal conductivity,

Btu/h-ff°F (W/m-K)

5 = 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)

f = time, min. (s) T = temperature, °F (K)

U - thermal transmittance, Btu/h -ft^-^F (W/m2-K)

V = rate at which air enters and leaves an

enclosure, ft^/h (m^/s)

V = velocity, ft/min (m/s) V" = volume, ft^ (m^)

W = mass, lb (kg)

OC = temperature coefficient of thermal

conductivity, Btu • in/h • ft^ • °F^ {W/m-K2)

5 = deviation

V = efficiency of heating plant or

coefficient of performance for air conditioning equipment

A. = constant P = density, Ib/ft^ (kg/m^)

8 = Stefan-Boltzmann constant

(jO = humidity ratio, lb (kg) H2O per lb (kg) dry air SUBSCRIPTS

1! = air properties or normalized quantity

c = heat loss by conduction

d = dry property

I = inside surface

1 = air infiltration L = latent load m = measured value

0 = outside surface or initial time w - wet property

ix
ABSTRACT insulating materials was measured and compared,

both in the field and laboratory.

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

"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 accu- mulation 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.

X
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 eval- uate 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 the heating energy requirement 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 be- fore 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, as explained below.

As part of the third stage of the retrofit, a plasticsheeting 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 sum- mer 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 over- hung 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. 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 reduction in the summer

energy requirement was not included in the eco- nomic analysis. Sealing air leaks was not found to be cost effective, since this process produced no

measurable reduction in the winter energy require- ment. For this set of retrofit experiments, storm windows were found to be more cost effective than installing insulation, since they required significantly fewer years 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 exterior walls

of residential buildings. The three materials

selected for study were cellulosic fiber, fibrousglass 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 per- formed 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 per- formed 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 2.44 m)) test wall, similar in construction to the

walls of the test house, was exposed 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 sec1
tions of the test wall. Measured heat-loss rates agreed within approximately 10 percent of corre- sponding 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-ft (4.3 m) 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 be- came lower. Measured conductances of the wall

sections insulated with cellulosic fiber and fibrousglass 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 higher than

corresponding predicted values determined by the

series-resistance method. The higher thermal con- ductances 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 deter- mined 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/m3). After the U-F foam had cured in the wall cavity, its dry density was 0.7 Ib/ft^ (11.21 kg/m3). 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/m2). The foregoing results suggest that much of the 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

fissuring 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 percent linear shrinkage of the in situ foam was observed to occur at a constant rate for 20.1 months, after which it leveled off to a value of

8.1 percent. Aside from the shrinkage, the foam

appeared to be in good condition after 35.2 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 a 35-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 % in (1.91 cm)

out of an initial fill of 6 in (15.24 cm). Eighteen

months after the installation, the total measured

settling was IV2 in (3.82 cm) out of an initial fill of 6 in (15.24 cm), or 25 percent. The bag count for the cellulose insulation indicated that the cellulose had been initially installed 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 accord- ance with FHA requirements. Also, the existing

ceiling insulation was equipped with a vapor barrier facing downward. The combination of these

2
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 percent). Thus, the protective measures were effective in keeping the summer moisture

content of the wood parts of the floor at a satis- factory 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 are a larger number of heating

hours during 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 installation 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, tind ccilin); 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 indooroutdoor 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.

(4) 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, resulting in paint

blistering. Similar results would be expected with

other vapor-impervious coatings on films.

(6) Cellulosic fiber, fibrous glass wool, and urea- formaldehyde foam were found to have good

insulating properties. With regard to other per- formance properties of the insulating materials, at 35 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

leveled off to a value of 8.1 percent.

at a constant rate for 20.1 months, after which it

(7) When cellulosic fiber is applied at too low a density to ceilings, substantial settling may occur.

3

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

energy-conservation programs for existing

buildings.

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 weatherstripping,

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 [l].' 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 four test houses located in St. Paul, Minnesota, to winter

^Numbers in brackets refer to literature references cited

at the end of the text.

5
conditions. 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 (R-6.8), and 2.3 in (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 weatherstripping 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 a residence which

had limited insulation; (b) to compare the thermal

performance of three different types of insulating

materials commonly used to insulate existing cavity

walls; and (c) to evaluate the effectiveness of "recommended good practice" 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 are calculated.

Although it is assumed 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, loosefill 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

wood-frame 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 lbs (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 cracks in the construction. The present

study examines moisture accumulation in retrofitted side walls.

Thermography has proven an effective tool for locating and identifying heat leaks in buildings [6]. There has been much recent interest in establish- ing criteria which would allow the use of thermography as a survey tool to distinguish

insulated walls from uninsulated walls. In the present study, the feasibility of using thermography

as such a survey tool is demonstrated.

6
2. DESCRIPTION OF

TEST HOUSE

The test house selected for the present study was

a wood-frame rambler, built 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 House is shown above. This house,

having a floor area of 2054 ft^ (191.8 m-) excluding

the unheated basement floor area, is somewhat

larger than typical houses in this country, which

range between 1200 to 1500 ft^ (111 to 139 m^).

The west side of the test house (right side as shown

in the above photograph) 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 3Vi in (8.9 cm) 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.

7
The house initially had single-pane windows with

the exception of a large picture window in the

living room which contained insulating glass. Good

weatherstripping 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 1. 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 2.

TABLE 1. DESCRIPTION OF EXTERIOR

BUILDING ELEMENTS

BEFORE THE RETROFIT

(INSIDE-TO-OUTSIDE)

ASPHALT SHINGLES

ASPHALT ROOFING PAPER ROOFING BOARD-

2x4 TOP PLATE

METAL GUTTERS

REDWOOD SIDING

SHEATHING PAPER —j|-

3/4"W0OD-FIBER SHEATHING

3-5/8' INSULATION INSTALLED BETWEEN 2x4 STUDS ^

(ISin on CENTER!

2x4 SOLE PLATE

2x10 HEADER

2x6 SILL PLATEe" CONCRETE BLOCKS

CONCRETE FOOTING

2x8 JOISTS 16 OC

9/I6"'gyPSUM PLASTER ON 3/8 ' GYPSUM-LATH SHEETROCK

3-[/2"GLASS-FIBER BLANKET INSULATION

(with kraff paper vopor barrier) 6"L00SE-FILL CELLULOSE INSULATION

CARPET

3/4" HARDWOOD FLOORING

BUILDING PAPER

3/4" PINE SUBFLOORING

- 2x10 JOISTS I6"0C-

^6 GLASS-FIBER BATT INSULATION

(VAPOR BARRIER ON TOP SIDE) CRAWL SPACE POLYETHYLENE VAPOR BARRIER

Figure 1. Typical cross-section of the house after retrofitting.

Floor

3/4-in hardwood (oak) floor building paper

3/4-in pine subflooring

2 X 10 wood joists placed 16 in on center

Wall

9/16-in gypsum plaster

3/8-in gypsum-lath sheetrock 2x4 wood studs placed 16 in on center

3/4-in wood-fiber sheathing

sheathing paper

7/16-in redwood siding

Ceiling

9/16-in gypsum plaster 3/8-in gypsum-lath sheetrock 2x8 wood joists (with 3V2 in glass-fiber blanket

insulation with a kraft-paper vapor barrier installed between the joists)

Sloping Roof

2x8 rafters placed 16 in on center

3/4-in wood sheathing

asphalt roofing paper

1/8-in asphalt shingles

Attic End Walls 2x4 wood studs

3/4-in wood-fiber sheathing

sheathing paper

7/16-in redwood siding Figure 2. floor plan of the test house.

8
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 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 blower

of the oil furnace was measured and found to be

1450 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 heat-pump

system. The duct system of the house was not changed. The heat-pump 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). Thus duct leakages may have been

greater when the heat pump was used as opposed

to the oil-fired furnace system. In a separate series of measurements the seasonal coefficient of per- formance of the heat pump was found to be 1.74

for heating [?].

9

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, 3V2 in glass fiber blanket

insulation was installed under the basement ceiling. 2 This insulation was present during the preretrofit summer cooling energy measurements.

During the second winter season, energyconservation measures 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:

2This insulation was installed as a sound-absorbing

treatment. It was required for programs unrelated to the present energy conservation study.

11
a. Fireplace damper was repaired.

b. A spring-activated damper for the kitchen

ventilation exhaust was installed.

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 fig. 3).

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 loca- tions as needed.

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

Figure 3. Caulking compound being applied to foundation sill.

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 wood sash-storm windows (see photo at the front of this chapter). 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 Vs in (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 floor. Since

NBS did not have the equipment or the trained personnel to blow loose-fill insulation into walls and over ceilings, this work was carried out under

contract. The following measures were performed:

6-in (15.2 cm) glass-fiber batts (R-18.5)3 were

installed under the floor over the crawl space, insulation of three types was blown into the walls

of the test house, and 6-in (15.2 cm) of loose-fill cellulose (R-20.8) were blown on top of the exist- ing 31/2-in (8.89 cm) glass-fiber blanket (R-10.8) in the ceiling. Loose-fill glass fiber (R-13.7) was

blown into one 14-ft (4.27 m) wall section, and U-F

foam (R-14.4) was installed in a second 14-ft (4.27

m) wall section. The remainder of the walls of the

test house were insulated with loose-fill 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 4.

Figure 4. A photograph of the south side of the house showing

the awnings.

"The R-vaiues for the glass-fiber blanket and cellulose insulation applied to the ceiling were taken from the manufacturer's literature.

12
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 three of the retrofit:

Attic

Ventilation area required in FHA Minimum

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

Crawl Space

Ventilation area recommended in ASHRAE

Guide. (The net ventilation opening was 0.65

ft^ (0.060 m2).)

O Polyethylene vapor barrier placed over tlie bare earth of the crawl space, o 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 ventilation 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 three of the retrofit to conform with attic ventilation requirements of FHA Minimum Property

Standards.

13

These thermal transmittance values for the walls,

ceiling, and floor were calculated using the series- resistance method, or

H = 1 ^ ' /

where /!/, ~ inside and outside surface

heat-transfer coefficients,

respectively,

Btu/h-ft^-F {WIm-- K)

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.

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

The above photograph shows the NBS guarded-hot-plate

apparatus.

15
II = thickness of material, ft (m)

k = thermal conductivity,

Btu/h-ffF (W/m- K> U = thermal transmittance,

Btu/h-ft2-F iWlm^-K)

N = number of layers in the

building component

Thermal bridges such as studs and joists were

treated as parallel heat-flow paths with no lateral heat flow beween adjacent components. Heattransfer coefficients at the inside and outside

surfaces were taken from ref. [4].

TABLE 2. THERMAL CONDUCTIVITIES

OF BUILDING COMPONENTS

[4, 8, 9, 10]

Conductivity

Building Component Btu/h ff F Hardwood (oak) floor 0.10 Pine subfloor .07 Wood structural members .068 Gypsum piaster .28 Gypsum-lath sheetrock .12 Wood-fiber sheathing .032 Redwood siding .070

Glass-fiber insulation

(blanket/batts) .027

Glass-fiber (loose-fill for walls) .022^ Gypsum board .12

Loose-fill cellulose

0 ceiling .023

o walls .024^ Urea-formaldehyde foam .021^

Based upon NBS measurements discussed later in the

report.

Thermal transmittance values for retrofitted build- ing components are given in table 4.

TABLE 3. AREAS AND PRERETROFIT THERMAL

TRANSMITTANCES FOR

BUILDING COMPONENTS

Surface Thcrnial Building Area Transmittance

Component ft^ Btu/h-ft^F

Floor (over crawl space) 956.0 0.27

Floor (over basement) 1096. .27 (.069)^'° Ceiling 2034. .081 Wall 1332. .20 Attic access door 20. .50 Windows

0 Single Pane 228. 1.02 (0.95)^

o Insulating Glass'- 80. 0.65 (0.61)° Doors

o Front 20.6 .41 o Kitchen 17.4 .62

0 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 3V2 in (8.89 cm) of glass-fiber blanket insulation in the floor. Summer values in parentheses.

Picture window in the living room.

TABLE 4. THERMAL TRANSMITTANCES

FOR RETROFITTED

BUILDING COMPONENTS

Thermal

Building Transmittances

Components Btu/hft^F

Wall (insulated with cellulose) 0.069 Wall (insulated with glass fiber) .065 Wall (insulated with U-F foam) .063 Floor (over crawl space) .048 Floor (over basement) .069 Ceiling .035^ Double-pane Window .50b

^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. The thermal transmittance values for the windows

include the heat-transmission path through the wood

sash.

16
AS SHOWN IN THERMOQRA

5. AIR-INFILTRATION

MEASUREMENTS

The purpose of the air-infiltration measurements

was to investigate the effect of the three stages of the retrofit on the air-infiltration rates of the test house. Separate tests were carried out to investi- gate the effect of opening the attic ventilation louvers (which occurred during the third stage of the retrofit) on the air-infiltration 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.

5.1 THEORY

To determine the rate of air exchange between the

test house and its surroundings, the rate of disappearance of sulfur-hexafluoride (SFp) 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:

dc_

di

V (2)

17
where v = rate at which air enters and

leaves the enclosure,

ft3/h (m3/s)

V- - volume of the enclosure,

ft^ (m^)

c - concentration of tracer gas

at time U).

Equation (2) may be expressed in the form

V

c = c e /-.v o (3)

where / denotes the number of volume changes

per hour and is the initial concentration of

tracer gas. The natural logarithm of the relative concentration, (c/Cq) was plotted as a function of

time. The air change rate (/) was taken as the negative slope of a least-squares fit line through

the data points.

5.2 MEASUREMENT TECHNIQUE

Sulfur-hexafluoride concentrations were measured

with a gas chromatograph equipped with an

electron-capture detector. A photograph of the measurement apparatus is shown in figure 5.

Figure 5. Apparatus med to measure air-leakage rates for the

test house.

Sampling and analysis were performed semiautomatically using a system which has been

previously described [ll]. 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 U{]1]^) +k . (4)

Here c is the concentration of SFo in ppb, is the standing current of the detector, and ] is the cur- rent with tracer in the detector (it is the trough of

a chromatographic deflection), ^ is a constant, and

X is a small extrapolated value of c at - 0. If A.= 0, eq(4) has the form of Beer's law. The

instrument was calibrated against reference mixtures of SFe in air.

SFf, was introduced into the return plenum of the heating plant and distributed throughout the house. Samples were taken from the air distribution system every 10 min (600 s) and analyzed for SFp. In order to maintain good mixing, which is implicit in the use of eq (3), 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 {Vs, in (0.32 cm) ID) were connected to a sampling pump through a length of Vi in (0.64 cm)

ID tygon tubing and a solenoid valve. The sampling system has been described elsewhere [ll]. A

similar four-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 sum- mary of these pre-retrofit air-infiltration measure- ments 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- infiltration rates and the inside-to-outside temperature differences. Other studies [12, 13] have

18
shown that for residences exposed to wind

velocities as well as temperature differences, the

rate of air infiltration (J) could be correlated with

respect to these two driving forces with an

equation of the form:

+ h -AT + c .V (5)

^here AT

V

a, b, c

inside-to-outside temperature difference, °Fwind velocity, mph

empirical constants.

TABLE 5. PRE-RETROFIT AIRINFILTRATION MEASUREMENTS

Air-Infiltration Rate, h

' At

°F V

mph

I meas 'calc

(eq. 7) meas calc

0.22 0.19 0.03 1.0 4.7

.23 .23 0 2.3 4.8

.20 .28 -.08 5.1 5.2

.42 .39 .03 b.O 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

. 1 . . meas cat. Average deviation = — = 0

Standard deviation =/ In/

V y y mens ' K'alc) i

1 = 1 N-1

to /;' • A/'''''. The mcjdificd correlating equation,

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

/ = 0.0506 + 0.0652 • At''^ + 0.0154 • V, 6 = .061

(7)

A plot of eq (7) is given in figure 6. 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 = 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 weatherstripping around the doors and windows.

PRE-RETROFIT AIR-INFILTRATION CORRELATION

I = .0506 + 0 0652-AT''^ + 0 OlSa v RMS DEV = 061

I .5

J L

15 20 25 30 35 40 45 50

INSIDE-TO-OUTSIDE TEMP, DIFF , °F

Figure 6. Prc-retrofit nir-infiltration correlation.

A least-squares procedure was used to fit the

pre-retrofit air-infiltration data to a correlating

equation of the form given by eq (5). The correlating equation and the corresponding root-meansquare deviation is:

/ = 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 • AT was changed

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 lO""* m^/s • m') at AT = 30°F (16.7°C) and K = 0 mph (O. m/s). The corre- sponding value for the townhouse studied in references [12, 15] is 0.022 cfm/ft' (1.12 x 10-* m^/s . m^).

Winter air-infiltration rates were also determined

after specific measures were taken to seal air leaks

(see sec. 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 air-infiltration correlation (eq 7) using measured temperatures and wind velocities. These provide an estimate of what the pre-retrofit

19
TABLE 6. AIR-INFILTRATION RATES AFTER

STAGE 1 OF THE RETROFIT

Air-Infiltration Rate, h"'

' meas 'calc ^meas 'calc V

(eq. 7) or mph

0.33 0.42 -.09 20 A 4.3 .37 .47 -.10 31.0 3.6

.40 .50 -.10 31.0 5.5

.39 .45 -.06 31.1 2.6

.46 .46 0 32.5 2.5

.24 .45 -.21 33.0 1.8

.55 .46 .09 33.5 2.0

.28 .46 -.18 34.8 1.6

Average deviation, ^rneas"'calc " ~0 08 Standard deviation = 0.10

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. This is only

slightly larger than the normal statistical variation

of 0.06 /!"'. However, the benefits of reducing

leaks in the building envelope could have been

partially offset by increased duct leakage because

of the higher operating capacity of the heat pump

system. Any component of the duct leakage not

passing into the living space would be treated as

infiltration.

After the installation of storm windows (stage 2), no further reductions in the air-infiltration rates were observed. The results are shown in table 7.

TABLE 7. AIR-INFILTRATION RATES AFTER

STAGE 2 OF THE RETROFIT

Air-Infiltration Rate

^meas leak ^meas'^calc At V

(eq 7) °F mph

0.43 0.43 0 27.1 2.5 .37 .44 -.07 28.1 2.6

.37 .45 -.08 29.3 3.0

.55 .50 +.05 32.9 5.0

.37 .49 -.12 33.6 4.2

.64 .48 .16 35.2 2.6 .48 .48 0 38.4 1.4

.53 .50 .03 39.2 2.5

.48 ,50 -.02 40.6 2.2

.54 .55 -.01 43.5 4.4

.80 .55 .25 43.7 4.4

.63 .53 .10 43.3 3.3

.45 .53 -.08 46.7 2.3

.60 .53 .07 46.8 2.0

.65 .53 .12 47.1 2.0

.68 .56 .12 50.5 3.0

.74 .58 .16 50.8 3.9

Average deviation, 'rneas~^calc = 0-04 Standard deviation = 0.10

The average difference between the measured and

pre-retrofit 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 preretrofit 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, 5 = .064,

(8)

/ = 0.0549 + 0.101 • ATi/2 + 0.0236 • V, b = .064

(9)

Eq (9) is plotted in figure 7.

0 5 10 15 20 25 30 35 40 45 50

INSIDE-TO-OUTSIDE TEMP. DIFF , °F

Figure 7. Post-retrofit air-infiltration correlation.

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 /i-i, 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 measurements themselves. However,

there was no a priori reason to expect any increase

in infiltration rate due to the addition of insulation.

20
TABLE 8. AIR-INFILTRATION RATES AFTER

STAGE 3 OF THE RETROFIT

Air-Infiltration Rate, h-'

Imeas Icalc 'meas 'calc At V

(eq 7) °F mph

0.52 0.42 0.10 7i Q7 . J J.J

.54 .41 .13 19.8 A 7

.52 .11 23.3 0 0

.70 .51 .19 25.0 o .o .59 .43 .16 25.9 9 ft .70 .44 .26 26.0 il .45 .41 .04 26.0 1X . Ao

.39 .42 .03 26.4 z.

.49 .45 .04 28.3

.64 .45 .19 31.6 2 4

.56 .50 .06 34.1 4^ .69 .48 .21 37.6 1.8

.64 .52 .12 38.2 4.5

.70 .55 .15 39.3 6.0

.60 .52 .08 39.6 3.6

.75 .57 .18 40.0 7.1

.84 .57 .27 40.7 6.8

.74 .60 .14 41.1 8.3

Average deviation, imeas~'calc " ^.14 Standard deviation = 0.07

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-infiltra- tion 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

in order to comply with minimum recommended

ventilation requirements of the FHA Minimum

Property Standards. To evaluate the effect of increased attic ventilation, consecutive measure- ments of air leakage in the living space were

carried out under the alternate conditions of

ventilation louvers open and ventilation louvers

closed.

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 about 0.02 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-', the measured

increase in air-infiltration rate of about 0.02 should

not be regarded as statistically significant. Thus,

these measurements indicate that opening 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"' At

°F

V

mph

'meas leak

(eq 9)

' meas "calc Open Closed

0.70 0.57 0.13 26.2 4.6 0.56 .53 .03 22.9 4.3

.53 .53 0 23.8 3.7

.56 .50 .06 21.8 3.4 .43 .46 -.03 15.9 4.8

.46 .45 .01 13.5 5.8

.66* .39 .27 9.3 5.7

.30 .38 -.08 10.1 4.8

.37 .38 -.01 11.7 4.0

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.

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.

21
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 build- ing 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.

TABLE 10. SUMMER AIR-INFILTRATION

RATES

Pre-Retrofit Post-Retrofit

I To-Ti V I To-Ti V

h-' °F mph h-' °F mph

0.27 13.5 3.4 0.36 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

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

that both the pre- and post-retrofit summer air- infiltration 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-to-outside 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.

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

air-infiltration rate was approximately Vi air change per hour subject to variations due to weather conditions.

After energy conservation actions were carried out

to seal air-leakage 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

weatherstripping 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.

22
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 heatingand cooling- energy savings achieved by the retrofit was to measure first the winter-heating

(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 investi- gations 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

23
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 installed over the windows on the south side of the test house. Cooling loads were

measured and compared to pre-retrofit 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 W,

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 resi- dence. 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 pre- and

post-retrofit energy measurements, so that duct

losses would represent 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

iq) is given by the relation:

P

q = y (Cp- P -V A) • AT dt + W hf^ (10)

0

where

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

P - density of the air, lb/ft3 (kg/m3)

y - mean duct velocity,

ft/min (m/s)

A - cross sectional area of

duct, ft2 (m2)

At = temperature rise for space heating applications or temperature drop for space cooling applications,

between inlet and outlet

of central air conditioner,

°F (K)

f = 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 humidification (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 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.

24
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 shov^^n in figure 8. Note that the

air-delivery 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 preretrofit heating-energy 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

HORIZONTAL LOUVEREO

, MIXER,

METER

Figure 8. Schematic diagram of furnace system showing the

location of measuring transducers.

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 equallyspaced grid network and mounted in the return plenum. The other nine junctions were also arranged in an equally-spaced 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 signals

from each of the thermopiles were fed into microswitching circuits which in turn were fed into analog integrators. When the blower of the furnace

system operated, the switching circuits applied the

millivolt signals 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 the thermopile 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.

Smaller temperature differences would be developed across the heat-pump 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 pres- sure 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

25
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

direction vane. The louvered enclosure shown in figure 9 contained 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

enclosure shown in figure 9. 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.

A photograph of the weather station used in the present study is shown in figure 9. 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 wind6.2.3 Indoor Parameters

Indoor air temperatures were measured using

24-gage copper-constantan 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 10. 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 fig. 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 fig. 10), 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 midheight 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.

26
77'-2"

LEGEND:

• TEMPERATURE SENSORS

Figure 10. Floor plan of test house showing location of temperature sensors.

6.3 WINTER ENERGY MEASUREMENTS

6.3.1 Heating Loads for the Unoccupied

Test House

For the pre- and post-retrofit heating energy

measurements, daily-average heating loads were

determined for the unoccupied test house with

corresponding daily average outdoor and indoor

temperatures, daily-average wind velocities, and

total incident solar radiation. The daily-total

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

air-infiltration 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.

The major portion of the heating load to the unoccupied house is due to heat loss through the

exterior building envelope. The domin.int driving

force that governs this heat-loss r.ilc is I he inside- 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 measure- ments to equivalent wind velocities and indoor

temperatures in order to obtain meaningful

heating load correlations.

The heat-loss rate iq due to air infiltration is given by the relation:

Cp-v-i-a, (11)

p

V

1

T,-T,

density of air, Ib/ft^ (kg/m3)

volume of a residence,

ft3 (m^)

rate of air infiltration as a function of wind velocity, h-' is-') specific heat of air, Btu/lb-F (j/kg-K)

inside-to-outside temperature difference, °F (K)

The air-infiltration rate (/) is a function of wind

velocity. The heat-loss rate (<?/) may be adjusted

from one wind velocity to another by using air- infiltration values from the pre- and post-retrofit

air-infiltration correlations (eqs (7) and (9)) in relation (11).

The heat-loss rate {q) at one condition, (T,- - Tq)

may be adjusted to another condition, (T',- - Tg)

having a different indoor temperature (T'/) by the

relation

Here denotes the adjusted heat-loss rate.

(12)

''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.

27
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 11. The straight lines were obtained from a least-squares procedure.

I • PRE-RETROFIT

) POST-RETROFIT AFTER PHASE 1 A POST-RETROFIT AFTER PHASE 2

X POST-RETROFIT AFTER PHASE 3

DAILY AV. OUTSlOE AIR TEMP.,''F

Figure 11. Meastired Iwating lands tortlw unoccupied test house

after various stages of the retrofit.

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 measure- ments 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:

pre-retrofit heating-energy measurements, the

oil-fired furnace was replaced with a heat- pump system.

o 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.

o 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 post-retrofit floor heat-loss

rate at approximately the pre-retrofit 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.

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 1 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 12, The

daily-average heat-release rate for this schedule is 4,409 Btu/h (1,291 W).

° Elimination of heat gains from the chimney to the test house after the retrofit. After the Over the conditions for which the house was

tested, heat was always delivered by the heating

28
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 12, would be equal to the heating load for the unoccupied test house (see fig. 11), less the daily-average heat-release rate for the occupancy

schedule of figure 12.

EQUIPMENT EQU

t.-\^ LIGHTING

^!S0\ OCCUPANCY

DAILY AV. HEAT-RELEASE RATE = 4409 BTU/H

i

0 2 4 6 8 10 12 14 16 18 20 22 24 TIME OF DAY, HOURS

Figure 12. Energy-release rates for equipment, lighting, and

occupancy.

The foregoing procedure was applied to each of the

daily-average heating loads of figure 11. The

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

procedure was applied to the pre-retrofit 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- To + 57,300

(pre-retrofit and stage 1 retrofit). (13) A similar procedure applied to the post-retrofit data yielded:

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

Writing these equations in terms of the inside-to- outside temperature difference gives

q = 532 -(67.9 - Tq) -6,140 (stage 3 retrofit). fl6)

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.

j • PRE.RETROFd

I POST.OETROFIT, PHASE 1

* POST.REIROflT, PHASE 2

O POST-RETROFIT, PHASE 3

30 40 50

DAILY AV. OUTSIDE AIR TEMP , ^F

q = 938 -(67.9 - Tg) -6,380 (pre-retrofit) (15)

Figure 13. Heating-load correlations for the occupied test house

after various stages of the retrofit.

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 Tg. 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.

29
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 heattransfer 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:

Cj = 748 (67.9 - To) - 5,851. (17)

Comparing eqs (15) and (17), it is seen that the

overall heat-transfer coefficient for the test house

is seen to be reduced 190 Btu/h' °F (100 W/K),

compared to a theoretical computed difference of 119 Btu/h-°F (62.7 W/K). The difference in these

figures may be due in part to the uncertainty of the stage 2 correlating equation caused by insuffi- cient data (i.e., only four data points).

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 out- door balance (reference) temperatures in figure 14. These values were obtained by searching actual weather data 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

fig. 13). The calculation of annual heating loads

for the various stages of the retrofit is shown in table 11.

The reduction in the annual heating load resulting

from the addition of storm windows was 25.2

T I 53 55 57 59 61 OUTDOOR BALANCE TEMP, °F

Figure 14. Heating degree days as a function of outdoor

balance temperature for Washington, D.C.

TABLE 11. CALCULATION OF ANNUAL

HEATING LOADS

Energy Adjusted Annual

Requirement Degree Heating Energy

Retrofit per Degree Days a Load Saving!

Stage Day,Btu/DD DD Therms %

Pre-retrofit

(also Stage 1) 22,501 3,350 753.8 0 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 13.

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 sec. 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

30
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 percent and the addition

of insulation to the walls, ceiling, and floor reduced

the heat-loss rate by an additional 23.0 percent.

The total reduction in heat-loss rate achieved by all stages of the retrofit was 43.3 percent.

Reductions in heat-loss rate and corresponding

reductions in annual heating loads are compared

for the various stages of the retrofit in table 12.

TABLE 12. COMPARISON OF REDUCTIONS

IN HEAT-LOSS RATE TO

REDUCTIONS IN ANNUAL

HEATING LOAD

Reduction in Reductions in Retrofit Heat-Loss Rale Annual Heating

Stage % Load, %

Pre-retrofit 0 0

(and Stage 1) 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 trans- mittance 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 out- door 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" degreeday 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, this region was used as the control volume for the heat balance. For these

calculations, measured temperatures for the crawl

space (fig. 15), attic space (fig. 16) and basement, at the average outdoor conditions for the data set, were used in the calculation of heat loss through

the floor and ceiling.

y 40 _

<

a.

<

q:u 30 —

0 I I I I I I 1 0 10 20 30 40 50 60

OUTSIDE AIR TEMP..°F

Figure 15. Pre- and post-retrofit winter crawl-ipnce temperatures.

The rates of heat transmission (q^) through the

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

q^ = U-A-{Ti~To) (18)

where U = thermal transmittance,

Btu/h- ft2 °F (W/m2 • K)

A = surface area, ft^ (m^)

31
T,- - To = air-to-air temperature

difference across the

surface, °¥ (K).

PRE-RETROFIT

POST -RETROFIT

PRE-RETROFiT

(3-1/2- in Gloss-Fiber Existing Irs )

POST- RETROFIT

(6-in Loose-Fill Cellulose Added

Over Existirig Ins 1

OUTSIDE AIR TEMP, °F

Figure 16. Pre- and post-retrofit winter attic temperatures.

Heat loss due 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 infil- trating 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.

Usmg 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 To = 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).

TABLE 13. PRE-RETROFIT STEADY-STATE

WINTER HEAT-LOSS

CALCULATIONS

Heat-Loss

Path

Walls

Ceiling

Floor

o over crawl space

o over basement

Windows

o single pane

o insulating glass Doors

Air Infiltration

(I = 0.51 h-i)'' TOTAL

Heat-Loss Rate, Btu/h

9617.

4020.

3201.

292.

8395.

1877.

924. 6010.

34,336.

3493.

10,272.

100.

Percent of Total

28.0

11.7

9.3

0.9

24.4

52.7 17.5

:=1 29.9

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

TABLE 14. POST-RETROFIT STEADY-STATE

WINTER HEAT-LOSS

CALCULATIONS

Heat-Loss

Path

Walls

o cellulose o glass fiber o urea formaldehyde

Ceiling

Floor

o crawl space

o basement

Windows

o double pane

o insulating glass Doors

Air Infiltration

(I = 0.65 h-i)'' TOTAL

Percent of Total

15.6

9.8

4.0

1.1

28.5

4.4 36.5

100.

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

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

post-retrofit steady-state heat-loss calculation,

comparing the predicted heat-loss rate of 20,993

Btu/h (6,151 W) (from table 14), to the corre- sponding 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.

32
The foregoing comparison of measured and

calculated heat-loss rates for the test house

supports the validity of the heating energy

measurements.

6.4 SUMMER ENERGY MEASUREMENTS

6.4.1 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 pre-retrofit measurements and

74.4 °F (23.6 °C) for the post-retrofit measurements.

The daily-average sensible and latent cooling loads

for the pre- and post-retrofit measurements are

plotted in figures 17 and 18. Note that the

post-retrofit sensible loads (fig. 17) tended to be

slightly higher that the pre-retrofit sensible loads. For the case of latent loads (fig. 18), the postretrofit 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 19, the relative humidity

in the first-floor living space was significantly

reduced after the retrofit. The reduction in indoor

1—

• POST-RETROFIT

PRE-RETROFIT

POST-RETROFIT

70 72 74 76 78 80 82

DAILY AV. OUT DOOR AIR TEMP., °F Figure 17. Pre- and post-retrofit sensible cooling loads.

86 88 90 92 94 96

Figure 18. Pre- and post-retrofit Intent cooling Figure 19. Pre- and post-retrofit summer indoor relative

loads. humidities.

33
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 (A'?^) may be

estimated from the relation:

Aqj_ = p -V-J-hr -Ao), (19)

p

V

I

hfg

density of air, Ib/ft^ (kg/m^)

volume of the

enclosure, ft^ (m^)

air inflitration

rate, h-^ latent heat of vaporization for water,

Btu/lb (;/kg)

A O) = reduction in indoor

humidity ratio between the pre- and post-retrofit cooling tests, lb (kg) H,0 per lb (kg) air.

Taking the air-infiltration rate for the house to be

the mean of the summer air-infiltration measure- ments (] = 0.26 /i-i) and making use of the relative humidity data of figure 19, 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 18.

When comparing pre- and post-retrofit sensible cooling loads, it should be pointed out that the daily-average indoor temperature for the postretrofit 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.

72

70

68

66 1

64 <

62 %

60 u

> 58 <

<

56

54

52

50

1

\—\—\—\—

r

PRE-RETROFIT |NO FLOOR INSI

• POST RETROFIT

PRE RETROFIT

J L

i

•

POST-RETROFIT

(6-IN FLOOR INS)

J L J I I L

60 62 64 66 68 70 72 74 76 78 80 82 84

DAILY AV . OUT DOOR AIR TEMP., °F

Figure 20. Pre- and post-retrofit daily average summer crawl space temperatures.

34
Comparisons of the pre- and post-retrofit daily average crawl-space, basement, and attic temperatures are given in figures 20, 21, and 22,

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 m 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.

80

78 -

76 -

74

72

70

68 -

66

64

62

60

58 -

"1 r "I—I—I

\—

PRE-RETROFIT (NO FLOOR INSI

POST RETROFIT

PRE RETROFIT

(3!6-IN GLASS FIBER FLOOR INS.|

60 62 64 66 68 70 72 74 76 78 80

DAILY AV. OUT DOOR AIR TEMP , °F

Figure 21. Pre- and post-retrofit daily average summer basement temperatures.

1—I—!—I

\—\—\—I—!—I—

I /

- I I I I

I I \—I—I—I—I—I

\—I—I—I—

' 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92

DAILY AV. OUT DOOR AIR TEMP., »F

Figure 22. Pre- and post-retrofit daily average summer attic temperatures.

35
TABLE 15. DAILY-AVERAGE HEATTRANSFER RATES, Btu/h

Pre- Post- Component retrofit retrofit Change

Ceiling Heat-Gain

Rate 1,269 719 550

Floor Heat-Loss Rate 1,459 595 864

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 (fig. 20), basement (fig. 21), and attic (fig. 22) temperatures were used at an outdoor temperature of 73.3 °F (22.9 °C). The

indoor air temperature was taken to be 73.3 °F (22.9 °C) for the pre-retrofit calculations and

74.4 °F (23.6 °C) for the post-retrofit calculations.

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 314 Btu/h (91.9 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 17. 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 4. 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

daily-average 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.

4. The roof overhung the south wall of the test house and provided significant shading of the windows from solar radiation, thereby pre- cluding 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 the heating-energy requirement. This was

attributed to the fact that the test house was of

tight construction to begin with. The addition of storm windows reduced the heating-energy

requirement 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

36
in heating energy requirement achieved by all stages

of the retrofit was found to be 58.5 percent.

The analysis of the heating-energy requirement

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 large 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 requirement for this particular test house

under the particular conditions tested. The postretrofit 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.

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 retrtjfit 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 required. However, most of this increase could be satisfied with a whole-house 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 the cooling energy

requirement, 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:

39
When P = D, eq (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:

log 10 L ^5 1 + Pj

log

V 1 + D/

for P it D.

(21) When P = D, eq (21) is an indeterminant form.

Applying the rule of L'Hospital, eq (21) reduces to L = aAS.

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-in (15.24-cm) fill of

loose-fill cellulose was based on $0.25 per ft^ installed. The figure used to estimate the cost of

installing 6-in (15.24-cm) glass-fiber batts in the

floor was $0.30 per ft^ of floor. And finally, the

cost of installmg loose-fill insulation into cavity walls was $0.60 per ft-. 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.

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 $30

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

TABLE 16. COST ESTIMATE FOR ENERGY

CONSERVATION OPTIONS

1. Stage 1 (Reducing

Major Air Leaks)

2. Stage 2 (Storm Windows)

3. Stage 3 (Installation of Insulation in Walls, Ceilmg, and Floor)

a. Ceiling

b. Floor over crawl

space

o Insulation $3o0.00

° Polyethylene

ground cover $ 40.00

o Pipe Insulation $ 80.00

c. Wall

Total Cost of Retrofit

$190.00

$780.00

$550.00

$550.00

$480.00

$840.00

32,840.00

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 dif- ferent 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

Heating

System

System

Efficiency

(coefficient of performance)Fuel Cost

$ per Therm

Cost per Therm in conditioned

space $

Gas-fired

forced air 0.60 0.24 0.40

Oil-fired forced air .55 .26 .47

Electric forced air .92^ .88 .8'i-^. q y

Air-to-air heat pump 1.74^ .88 .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.

^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.

The foregoing system efficiencies (or coefficient of performance) are assumed typical seasonal values rather than steady-state values often cited by

equipment manufacturers.

40
The

si

Item

Table 17

Sec. 7.2

Table 18

Change

in Section 7.1 Electric forced air system, cost per therm - $0.81 to 0.96

1 Last line, 3rd figure (saving in electricity)

in Sec. 7.2.1, electric fuel costs and savings -

flTable 19 in Sec. 7.2.2, payback periods, electric systems

(August 1978

from 357.6 to 423.7

610.6 to 723.7

456.4 to 541.0

253.0 to 299.9

154.2 to 182.7

203.4 to 241.1

357.6 to 423.8

5.4 to 4.5

9.5 to 7.9

10.2 to 8.4

7.5 to 6.3

17.4 to 14.3

8.6 to 7.1

11.8 to 9.8

The winter heating-energy cost (HC) for the four

separate heating systems may be calculated from

the relation: HC = HL-FCIV (22)

where HL = annual heating load in therms

fC = fuel cost, $ per therm

77 = 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 heat-pump systems are

176.4, 207.5, 3^.^, 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.

TABLE 18. WINTER HEATING ENERGY COST AND SAVINGS, DOLLARS

GAS OIL ELECTRIC HEAT PUMP

Fuel Cost Fuel Cost Fuel Cost Fuel Cost

Stage of Study Cost Savings Cost Savings Cost Savings Cost Savings

Pre-retrofit (Stage 1) 301.5 0 354.3 0 elO.6 0 384.4 0

Stage 2 225.4 76.1 264.8 89.5 450.4 154.2 287.4 97.0

Stage 3 125.0 100.4 140.8 118.0 253.0 203.4 159.3 128.1

Total Savings 176.4 207.5 357.6 225.1

TABLE 19. PAY-BACK PERIODS FOR

ENERGY-CONSERVATION

OPTIONS

Stage of Retrofit

Pay Back Period, Years Gas Heat Oil Heat Electric Heat Pump

Stage 1 Stage 2 Stage 3

0 u'all 0 ceiling 0 floor

Infinite 10.2

17.4 (18.6)3 14.2

29.9

15.9

(19.3)3

Infinite 9.6 17.5

(18.9)3 13.8

34.8

15.7

(22.1)3

Infinite 5.4 9.5 (10.2)3

7.5 17.4

8.6 (11.8)3

Infinite 8.8 15.9

(19.2)3 12.5

31.1

14.3

(20.0)3

Combination

of stages 1-3 16.1 15.9 8.7 14.5

3 Includes cost of vapor-barrier ground cover and pipe insulation.

41
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

solar gains on the roof was not considered in that

report. Also, the additional six inches of ceiling insulation installed equaled two inches more than

the economically optimum amount cited in refer- ence [20]. Using more than the economically

optimum amount would cause the payback periods

for the ceiling insulation to be longer.

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 in- crease 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.

7.3 CONCLUSIONS

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.

42
8. COMPARISON OF THE

THERMAL PERFORMANCE

OF THREE INSULATING

MATERIALS

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.

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. Heat-transmission

and moisture measurements were performed on a

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

43
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| and values reported by ASHRAE [4].

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 cellu- lose 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.

TABLE 20. THERMAL CONDUCTIVITIES OF THREE INSULATING MATERIALS

MEASURED IN THE GUARDED-HOT-PLATE APPARATUS

Insulating Material Moisture Content % (by weight)

Density

lb/ft' Mean Temp.°F

Thermal

Conductivity

/ Btu in \

R-value /ft2h°F\

Before test After test Vft^h°F/ \ Btu in /

Cellulose 9.9 9.5 3.54 75.8 0.288 3.47

Fibrous Glass Wool 1.0 0.7 2.11 75.8 0.267 3.75

Urea- Formaldehyde

Foam 16.8 16.8 0.60 75.7 0.246 4.07

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 corre- sponding 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 (2.44 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 23. 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 system 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.

8.2.2 Instrumentation

Front and side views of the test wall showing the

location of the measurement transducers are given

in figure 24. Each pair of wall cavities insulated with

different material was instrumented in a similar

44
Figure 23. Construction details of lahorntori/ test wall.

manner. Surface and ambient air temperatures were

measured with 24-gage copper-constantan

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.

LOCATION OF MEASURING SENSORS • HUMIDITY

INSIDE AMBIENT TEMPERATURE A OUTSIDE " " TEMPERATURE O HEAT FLOW

SIDE VIEW FRONT VIEW

Figure 24. Location of measurement transducers on

laboratory test wall.

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 (-ISil.l °C) and

approximately 95 percent rh. The interior side of the test wall was exposed to the laboratory envi- ronmental condition which was maintained at 75±3°F i23.9±1.7°C) and 45±3 percent 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 labora- tory 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

45
TABLE 21. EXPERIMENTAL RESULTS OF FULL-SCALE LABORATORY

WALL TESTS AFTER TWO-MONTH EXPOSURE

Wall

Insulating Material

Insu Mean[ation Temp.

'F DensityIb/ft^

Moisture Content % (by weight)Thermal Conductance

Btu/hft^°F %

Diff. Top Bottom Top Bottom Measured Predicted

Cellulose 46 36 4.4 18.6 17.4 0.065 0.063 3.1

Glass

Fiber 42 34 1.7 9.8 24.3 .069 .062 10.1

U-F Foam 45 0.7 49.0 76.3 .051 .054 -5.9

*Data not available.

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 surface-to- surface temperature difference. The predicted

thermal conductance values of column 8 were

obtained by the series-resistance method. The

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 = kffj + a AT (23)

k^ = measured thermal

conductivity at mean

temperature of guardedhot-plate measurement,

BtuMn/h-ft2-°F (W/m-K)

CX = temperature coefficient of thermal conductivity,

Btu-in/h-ft2-°F2 (W/m-K2)

AT = mean temperature of wall

section minus the mean

temperature of guardedhot-plate measurement,

°F (K)

The mean temperature of the insulation was

approximately 76 °F for the thermal conductivity

measurements and approximately 40 °F for the

laboratory wall test. The temperature coefficients

( ot) for the thermal conductivity values are given

in table 22.

TABLE 22. TEMPERATURE COEFFICIENTS ( a ) FOR THE THERMAL

CONDUCTIVITY VALUES

Material Btuin/hft2°F2 W/mK^ Reference

Cellulose Glass Fiber U-F Foam

4.0 X 10-

7.3 X 10-

6.3 X 10-

1.0 X 10-

1.9 X 10-

1.6 X 10-

910 Manufacturer's

literature

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

fig. 25). The buckling and warping of the wood

siding was attributed to high moisture content of the wood siding.

46
Figure 25. Photograph of exierior surface of laboratory ksi wall showing buckling and warping of the wood siding.

8.3 HEAT-TRANSMISSION AND

MOISTURE MEASUREMENTS 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.

Instrumentation: The heat-flow rates through wall

sections of the test house insulated with the three

types of insulating materials were measured with

heat-flow 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 polyvinylchloride filler material, each having an embedded thermopile.

Heat flux, upon passing through the wafer, causes

a temperature difference to be developed across the wafer, which in turn causes a millivolt signal

to be produced proportional to the heat-flow rate. At a station 4 ft 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 26. The six heat-flow meters were series-connected and the

output signal was fed into an analog integrator.

The integration of the heat-flow 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 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.

16"

THERMOPILE

-e—e— —e—e—e23

HEAT-FLOW METERS ^

-WALL STUDS

Figure 26. Elevation view of wall section of the

test house showing heat-flow measuring station.

as shown in figure 26. Three copper-constantan

thermocouple 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.

Experimental Results: The thermal conductances

of the separate wall sections are plotted versus mean wall temperature in figure 27. The thermal

conductance values were obtained by dividing the average heat-flow rate over a twelve-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 material

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 fig. 27) is seen to be substantially higher than

corresponding values of the other wall sections.

47
£ .14 —

WALL SECTION • GLASS FIBER UREA- FORMALDEHYDE FOAM CELLULOSE

6 48 50 52 54 56 MEAN WALL TEMPERATURE, "F

Figure 27. The effect of wean wall temperature on

the thermal conductance of the three separate wall sectiom.

This result is inconsistent with the findings of the guarded-hot-plate measurements (sect. 8.2) and the

full-scale laboratory wall tests (sect. 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 conductance 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, show relatively good agreement between

predicted thermal conductance and the thermal

conductance measured in a specimen with 50-76

percent moisture content. The heat-loss measure- ments 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 of the heat-loss measurements (see fig. 29, sec. 8.3.2). 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 msulation 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 con- ductance 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

Thermal Conductance Btu/hft^F

Wal! Section Measured Predicted

Cellulose 0.060 0.062

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 ovendrying technique, and compared.

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 28. The U-F foam and glass-fiber wall

48
M MOISTURES SENSORS EMBEDDED IN WALLS

S MOISTURE-CONTENT SAMPLES

77'-2"

Figure 28. Floor plan of the test house shoiving location of humidity sensors and place where moisture content samples were cored out.

sections are indicated on figure 28. Other parts of the wall were insulated with 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 indi- cated, 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-in (2.54-cm)

holes through the wood siding and sheathing,

install the sensors, and replug the holes. These

particular sensors responded to relative humidity

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 29. 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 mterface between the U-F foam insulation and the sheathing remained at a saturated condition for approximately 40 days after the retrofit, at which time the relative humidity

began to decrease slowly. The relative humidity at the mterface 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).

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 wails,

(2% 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 28. Where the symbol "2S" appears, samples were taken from the top of the wall approximately

1 ft (0.305 m) below the ceiling level and at the bottom approximately 1 ft (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 (fm) (by weight) was determmed from the relation:

X 100 (24)

where Wj^, and are the wet and dry weights of the material, respectively.

The moisture contents of the material samples

removed from cellulose wall sections are shown in table 24.

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.

49
108 70

RH MEASURED

WITH EMBEODED SENSOR

INDOOR RELATIVE HUMIDITY U-F FOAM (TOP ANIDBOTTONI ] GLASS FIBER ( BOTTOM I GLASS FIBER (TOP)

MATERIAL SAMPLESCORED OUT

ELAPSED TIME AFTER THE RETROFIT, DAYS

Figure 29. Varintion of indoor ri'lntive humiditxi and relative humidiHes of embedded

sensors.

TABLE 24. WINTER MOISTURE CONTENTS

OF MATERIAL SAMPLES

REMOVED FROM CELLULOSE

WALL SECTIONS

Moisture Content, % (by weight)

Outside Inside Wood Insulation Insulation Location 3 Siding Sheathing Core Core

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 28 for location identification.

The moisture contents of material samples taken

from the glass-fiber wall section are shown in table

25. The moisture contents of the glass-fiber 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.

The moisture contents of material samples

removed from the U-F wall section are shown in table 26.

The moisture contents of the U-F foam itself are comparable with values for the other insulation

materials. However, the moisture contents of the sheathing and wood siding samples taken from the U-F wall section are much higher than corre- sponding 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 lb/ft3 (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 10-"kg/Pa • 5 -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 30. Many small blisters also occurred

50
TABLE 25. WINTER MOISTURE CONTENTS OF MATERIAL SAMPLES TAKEN FROM THE

GLASS-FIBER WALL SECTION

Moisture Content, % (by weight)

Outside Inside Wood Insulation Insulation Location^ Siding Sheathing Core Core

5 Top 12.3 14.0 8.1 10.1

5 Bottom 16.8 15.5 11.0 3.2 Average 14.6 14.8 9.6 6.7

^See figure 28 for location identification.

TABLE 26. WINTER MOISTURE CONTENTS

OF MATERIAL SAMPLES

TAKEN FROM U-F WALL

SECTION

Moisture Content, % (by weight)

Outside Inside Wood Insulation Insulation Location ^ Siding Sheathing Core Core

4 Top 24.8 28.1 8.0 9.4 4 Bottom 21.6 38.6 12.9 12.3 Average 23.2 33.4 10.5 10.9

^See figure 28 for location identification.

Figure 30. Water blister at exterior surface of U-fwall section.

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 foam 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 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 24) to corresponding samples

cored at the end of the summer (table 27), it can be

TABLE 27. SUMMER MOISTURE CONTENTS

OF MATERIAL SAMPLES

REMOVED FROM CELLULOSE

WALL SECTION

Moisture Content, % (by weight)

Location

^ Wood

Siding Sheathing

Insulation Core

Inside Wall Outside Inside 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

f^See figure 28 for location identification Plaster (wood)

""The moisture content for 6 Top is not included

in the average.

51
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 wail 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.

TABLE 28. SUMMER MOISTURE CONTENTS

OF MATERIAL SAMPLES TAKEN

FROM THE GLASS-FIBER WALL

SECTION

Moisture Content, % (by weight)

Location ^ Wood

Siding Sheathing

Insulation Core

Inside Wall Outside Inside Covering

5 Top 12 14 3 22 9

5 Bottom 12 14 3 18 9 Average 12 14 3 20 9

^ See figure 28 for location identification.

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.

TABLE 29. SUMMER MOISTURE CONTENTS

OF MATERIAL SAMPLES TAKEN

FROM THE U-F WALL SECTION

Moisture Content, % (by weight)

Location ^ Wood

Siding Sheathing

Insulation Core

Inside Wall Outside Inside Covering

4 Top 17 21 22 17 15

4 Bottom 13 11 14 14 9 Average 15 16 18 15.5 12

^See figure 28 for location identification.

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 Linear Shrinkage

Months %

3.1 2.6 14.8 5.6 20.1 7.3 26.2 8.1 35.2 8.1

These data are plotted in figure 31. It can be seen

that the percent linear shrinkage of the in situ foam

of this particular test house increased at a constant

rate for 20.1 months, after which it leveled off to a value of 8.1 percent. 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.

1—I—I—I

\—I—I—I—I—I I \ I I r

I I I

I I I I I I I I I I I I I I I—

I

0 2 4 6 a 10 12 14 IG ie 20 22 24 26 28 30 32 34 36 38 ELAPSED TIME, MONTHS

Figure 31. Percent linear shrinknge of urea-formaldehyde foam

insulation as a function of elapsed time.
Several small fissures (void spaces where the foam

has pulled apart) were also observed in the in situ foam. They ranged from % in (0.95 cm) to 1 in (2.54 cm) in width.

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

Vi 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 IV2

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 SVz 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 thirty-five months.

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 materials.

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 series-resistance method, even though a large

amount of moisture was present in the form of ice at 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 C(.)nductances 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.

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 season 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 constant

rate for 20.1 months, after which it leveled off to a value of 8.1 percent.

Thirty-five months after the cellulose and glassfiber insulations were installed in the walls of the

test house, no settling of the loose-fill materials was

53
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.

54
9.1 EXPERIMENTAL PLAN

The experimental plan for evaluating the effective- ness 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.

55

9. EFFECTIVENESS OF

RECOMMENDED 'GOOD

PRACTICE ' MEASURES

FOR PREVENTING

MOISTURE ACCUMULATION

The effectiveness of recommended "good practice"

I measures [4] for preventing winter moisture

accumulation in attics and summer moisture

i accumulation in crawl spaces was also investigated.
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

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 cellu- lose 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 the attic and summer moisture accumulated in wood

parts of the crawl space for this particular test house

and for the conditions under which it was tested.

56
10. 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, 1942.

3. Degelman, L. D., and Lewis, S. A., Single Family

Dwelling and Natural Resource Consumption Effects and Energy Budget, Seminar paper presented at the 1975 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, Bertil, Thermography of Buildings, Swedish Council of Building Research,

Lund Institute of Technology, Lund, Sweden, 1972.

7. Kelly, G. E., and Bean, ]. W., Dynamic Performance

of a Residential Air-to-Air Heat Pump, Nat. Bur. Stand. (U.S.), BIdg. Sci. Ser. 93, 18 pages (Mar. 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 Cellulosic Fiber Insulating Material, Journal of Testing and

Evaluation, Vol. 2, No. 3, American Society of Testing and Materials, 1974.

10. Bankvall, Claus C, 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 SemiAutomated System for Measuring Air Infiltration in Buildings Using Sulfur Hexafluoride as a Tracer, Nat.

Bur. Stand. (U.S.), Tech. Note 898, 24 pages (Mar.

1977).

12. Hunt, C. M., and Burch, D, M., Ajr Infiltratjon Measurements in a Four-Bedroom Townhouse Using

Sulfur Hexafluoride as a Tracer Cas, ASHRAE

Transactions, Vol. 81, Part I, 1975.

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. ]., and Hunt,

C. M., Comparison of Measured and ComputerPredicted Thermal Performance of a Four-Bedroom

Wood-Frame Townhouse, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 57, 62 pages (Apr. 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, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 27, 22 pages (Mar.

1970).

19. Jacobs, M., and Petersen, S., Making the Most of your Energy Dollars in Home Heating and Cooling,

Nat. Bur. Stand. (U.S.), Consumer Info. Ser. 8, 16

pages (Oct. 1975).

20. Petersen, S. R., Retrofitting Existing Housing for Energy Conservation: An Economic Analysis, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 64, 76 pages (Dec.

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.

57
ACKNOWLEDGMENTS

Staff members of the Building Thermal and Service

Systems 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 con- ducting the guarded-hot-plate measurements; to Walter Ellis for his technical assistance in the

installation of the instrumentation and day-to-day

operation of the experiment; 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 f^artsell, general technical representative. Federal Energy Administration, provided liaison for

this report, and his patience and encouragement

are appreciated by the authors.

58
APPENDIX A

DESCRIPTION OF THE

THIRD STAGE

OF THE RETROFIT

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 third-stage work was per- formed under contract. INSTALLING ADDITIONAL INSULATION

IN THE CEILING

Six inches (15.24 cm) of loose-fill cellulose insulation were blown on top of the existing 3% 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 small-size

particles which were subsequently fed into a blower. The blower pumped the insulating material

through a IVi in (6.35 cm) diameter hose which was used to distribute the insulating material

uniformly on top of the existing ceiling insulation

(see fig. 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.

Figure A-2. Loose-fill cellulose being blown on top of the

existing ceiling insulation.

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 IV4 in (3.18 cm) hole through the siding and the sheathing, approximately 1 ft (0.305 m) above the floor and 1 ft (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 next 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 ZVi in (6.35 cm) nozzle which was inserted into the hole

as shown in figure A-4. Blowing loose-fill glass

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.

59
The application technique was to drill four 1-in (2.54 cm) holes, approximately 2 ft (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

fig. 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

Figure A-3. Cellulosic fiber being blown into the walls

of the test house.

Figure A-4. L^lass fiber being blown into a wall sedit

Figure A-5. Urea-formaldehyde foam being blown

into a wall section.

Figure A-6. Technical representative measuring wet density of the U-F foam.

60
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 correct- ness 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 fig. A-5) in which

the constituents were mixed in proper proportions

to produce U-F foam.

INSULATING THE FLOOR

Six-inch (15.24 cm) foil-faced glass-fiber batts were

installed between the floor joists over the crawl

space (see fig. 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.

Figure A-7. Glass-fiber batts being installed under the floor in the crawl space.

61

APPENDIX B

LOCATION OF HEAT LEAKS

IN RESIDENCES USING

INFRARED THERMOGRAPHY

INTRODUCTION

As part of the energy conservation study con- ducted 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-to- outside temperature difference was much smaller. 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)

where £ = radiated energy, Btu/h-ft2-(W/m2)

e = surface emissivity

T = absolute temperature, R (K) o - Stefan-Boltzmann constant,

Btu/h-ft2- R^ (W/m2K4)

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 \x (lO"''m).

Figure B-1. Infrared television system.

The video signal from the IR camera is processed

in the black-and-white television monitor where it

is converted into a thermal picture in which the gray tones in the picture approximately correspond

to surface temperatures. 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 iso- therms 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.

63
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.

°r

Temp.

Diff. °F

Pre-retrofit survey March, 74 81.0 41.0 40

Post-retrofit survey March, 75 70.0 29.0 41

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-to-outside

temperature difference is desirable, so that the

contrast 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 (fig. B-2b) to the post-retrofit

thermograms (fig. 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 indica- tion to determine whether wood-frame cavity walls are insulated.

Figure B-2. Overall view of exterior surfaces of the test house.

(a) Conventional photograph.

Figure B-2. Overall view of exterior surfaces of the test house.

(b) Thermogram before retrofit.

64
Figure B-2. Overall view of exterior surfaces of the test house.

(c) Thermogram after retrofit.

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 post-retrofit 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

Figure B-3. East end of test house.

(a) Conventional photograph.

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

Figure B-3. East end of test house.

(b) Thermogram before retrofit.

Figure B-3. East end of test house.

(c) Thermogram after retrofit.

65
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 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 distin- guish between insulated and uninsulated woodframe 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 post-retrofit 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 to 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

Figure B-4. Interior surface of dining room door.

(a) Conventional photograph.

from inside the dining room. The black region (cold

spots) in the pre-retrofit thermogram (fig. 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 postretrofit thermograms. Observed differences may

therefore be regarded as being due to the

differences in surface temperatures. Note that in the post-retrofit thermogram (fig. B-4c) the

application of improved weather-stripping at the

bottom of the door is seen to be effective in eliminating the previously observed air leak.

Figure B-4. Interior surface of dining room door.

(b) Thermogram before retrofit.

Figure B-4. Interior surface of dining room door.

(c) Thermogram after retrofit. 66
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 (fig. 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

Figure B-5. Interior view of ceiling-wall interface above the bay

window in living room.

(a) Conventional photograph.

Figure B-5. Interior view of ceiling-wall interface above the bay

window in living room.

(b) Thermogram before retrofit.

insulation and cause the cold spot. Note that in the

post-retrofit thermogram (figure B-5c) 6 in (15.24

cm) of loose-fill cellulose over the top of the

existing SVi in (8.89 cm) glass-fiber blanket was

successful in eliminating the cold spot along the

ceiling.

Figure B-5. Interior view of ceiling-wall interface above the bay

window in living room.

(c) Thermogram after retrofit.

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 (fig. 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 more heat loss. The post-retrofit thermogram (fig. 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.

Figure B-6. Interior vieiv of upper corner of northeast bedroom.

(a) Conventional photograph.

67
Figure B-7. Wintt'r tlwrmogram of inside surface of U-F wall

section.

Figure B-O. Interior view of upper corner of northeast hedrooni.

(b) Thermogram before retrofit.

Figure B-6. Interior view of upper corner of northeast bedroom.

(c) Thermogram after retrofit.

WINTER THERMOGRAPHIC SURVEY OF

THE EXTERIOR 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 maroonshaded 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

Figure B-8. Winter therwograni of inside surface of cellulose wall section in dining room.

68
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 insul- ating 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 woodframe house may be used to distinguish between

insulated and uninsulated wood-frame cavity walls.

i

Figure B-9. Winter thermogram of inside surface of cellulose wall section in southeast bedroom.

Figure B-10. Winter thermogram of inside surface of glassfiber wall section in northeast bedroom.

SUMMER 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 figs. 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 fig- ures B-7 and B-8 were not successful in identifying the void spaces seen during the winter. It is therefore concluded that summer thermographic

surveys, performed when the inside-to-outside temperature differences are small, may be only

partially successful in identifying uninsulated void

spaces in retrofitted walls.

CONCLUSIONS

Thermographic surveys were performed during the winters before and after the house was retrofitted. Thermography was shown to be an effective

69
Figure B-11. Summer thermogram of the inside surface of the

cellulose wall section in southeast bedroom.

technique to distinguish 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 wood-frame cavity walls of a house

are uninsulated:

o Studs do not stand out in contrast with

respect to the insulated portion of the wall when viewed from the inside.

o Exterior walls stand out in contrast with the

Figure B-12. Summer thermogram of the inside surface of th glass-fiber wall section in northeast bedroom.

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 indi- cates 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.

70
APPENDIX C

LOCATION OF

AIR-LEAKAGE PATHS

IN A RESIDENCE USING

PYROTECHNIC SMOKE

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.

INSTRUMENTATION AND

EXPERIMENTAL PROCEDURE

White pyrotechnic smoke was released in each room of the test house using either the drum-type

distributor (fig. C-1) or the combination fan and

metal trash basket (fig. 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.

Figure C-1. Drum-iype smoke distributor.

Figure C-2. fan and metal trash basket used to distribute white

pi/rotechnic smoke.

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 connected to a sealed window panel

with a 12-in (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.

Figure C-3. Centrifugal blower connected to the ivindow panel with a flexible hose.

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 adeuqate 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

71
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.

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 system. 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 differ- ences 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.

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 (0.882 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 H2O

Living Room 0.1034 Kitchen .1040 Dining Room .0920 Half Bath .0917 Foyer .0919 Study or Den .0913 Average .0958

The inside-to-outside pressure difference remained

comparatively constant and did not vary much

from 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 mph (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 ventila- tion-exhaust opening, as shown in figure C-5. An

inspection of the kitchen ventilation-exhaust

opening revealed that the hinge of the damper had

Figure C-4. Major nir leakage path through the chimneif.

Figure C-5. Major air leakage path through kitchen exhaust

opening.

72
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.

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:

o The fireplace-damper system was repaired.

° A spring-activated kitchen ventilation-exhaust

damper was installed.

o The window panes were reputtied as needed.

° The window frames were recaulked as needed.

73
U.S. DEPT. OF COMM. bibLiocraphic data

SHEET

1. PUBLICATION OR REPORT NO. NBS ESS 1052. Gov't Accession

No.

3, Recipient's Accession No.

4. TITLE AND SUBTITLE

Retrofitting an Existing Wood-Frame Residence

for Energy Conservation—An Experimental Study

5. Publication Date July 1978

6. Performing Organization Code

/. A U 1 nUK(o)

D, M. Burch and C. M. Hunt

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

10. Pro)ect/Task/Worlc Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Federal Energy Administration

12th and Pennsylvania Avenue, NW

Washington, D.C. 20461

13. Type of Report & Period

oV c r t ci Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 77-27819

16. ABSTRACT (A 200-word or less factual summary of most sigpificant 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 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 those 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 preformed before and after the retrofit. Based on the results of these surveys, criteria for distinguishing bewteen 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 conductivity; thermal insulation; thermography.

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