Sss/oxNBSIR 76-1182

The Thermal Performance of a

Two-Bedroom Mobile Home

G. J. Teitsma

Dow Chemical Co.

Midland, Michigan 48640

and

Bradley A. Peavy

Thermal Engineering Section

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

January 1977

Final Report

Prepared for Federal Energy Administration

Washington, D. C. 20461

NBSIR 76-1182

THE THERMAL PERFORMANCE OF A

TWO-BEDROOM MOBILE HOME

G. J. Teitsma

Dow Chemical Co. Midland, Michigan 48640

and

Bradley A. Peavy

Thermal Engineering Section

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

January 1977

Final Report

Prepared for Federal Energy Administration

Washington, D. C. 20461

U.S. DEPARTMENT OF COMMERCE. Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Acting Director

CONTENTS

Page

1. Introduction 1

2. Description of Test Specimen 3

3. Instrumentation and Transducers 12

4. Procedure, Results and Discussion 13

4.1 Thermal Testing Under Steady-State Conditions 13

4.2 Thermal Performance by Thermographic Technique 30

4.3 Air Leakage Analysis 48

4.4 Condensation Potential 62

5. Conclusions and Recommendations 74

5.1 Conclusions 74

5.2 Recommendations 78

6. References 80

7. Conversion Factors 81

Appendix A. Calculations for Heat Transfer A-l

Appendix B. Rationale for Thermal Resistance of

Interior Air Films B-l

THE THERMAL PERFORMANCE OF A TWO-BEDROOM MOBILE HOME

by

G. J. Teitsma and B. A. Peavy

ABSTRACT

Tests were conducted on a mobile home located in an Environmental

Climatic Laboratory for the purpose of evaluating its thermal performance.

The heating demand greatly affected the part-load efficiency of a gas-fired,

forced-air, sealed-combustion furnace system. The practice of installing

oversized heating plants was shown to result in low seasonal operating

efficiencies. Air leakage measurements were performed using a pressurization technique to quantify the amount of air leakage through the various

parts of the mobile home. Separate air infiltration tests using the SF^

tracer-gas technique showed that somewhat higher air infiltration rates

were induced by operation of the mobile home heating plant. A thermographic survey of interior surfaces showed that the technique used to

install the wall insulation may allow wrinkles formed in the surface of the

insulation to form air paths running the height of the wall cavity. Convective air flow through these paths may create heat leaks on the building

surface which can have an impact on the overall heat-loss rate. Separate

tests were also conducted to identify places in the mobile home envelope

having high condensation potential.

Key Words: Air infiltration; energy conservation; mobile home;

part-load efficiency; thermography.

i
<

*

.
1. INTRODUCTION

Rising energy prices and the necessity for conserving our nation's

energy resources should provide a significant incentive to increase the

effectiveness of energy utilization. For residential and commercial

buildings this can be done by providing more efficient heating, ventilation,

and cooling equipment, by more efficient operation and sustained mainte - .

nance of buildings and equipment, and by a building envelope with increased

resistance to heat loss or gain. As in other types of buildings, energy

conserving efforts in the mobile home industry and on existing mobile

homes would result in a significant impact on energy savings. Currently,

mobile homes represent more than 30 percent of new single-family detached

housing , and this percentage is expected to increase over the next

few years.

In order to accomplish savings in this significant segment of

building energy consumption, it is necessary to provide the mobile home

industry and present occupants of mobile homes with techniques and

methods for predicting and evaluating energy utilization. As an effort

to upgrade the standards with regard to energy conservation, the National

Conference of States for Building Codes and Standards (NCSBCS) asked that

the National Fire Protection Association Standard (NFPA) 501B (ANSI A119.1)

Committee develop energy conservation requirements for mobile homes.

NFPA formed an Energy Conservation Task Force to

add such requirements to the mobile home standard and

to a proposed new mobile home installation standard. As part of his

initiative in the energy area, the President has directed the Secretary

of the Department of Housing and Urban Development (HUD) to work in

1
conjunction with the Federal Energy Administration (FEA) and the Department of Commerce (DoC) to ensure that energy conservation standards are

included in the mobile home construction and safety standards.

The present report summarizes the findings of an experimental study

conducted at the National Bureau of Standards (NBS) which was sponsored

by FEA. The objective of this study was to observe measured vs. predicted

thermal performance in order to aid in the establishment of energy conservation design standards with consideration to cost, size, weight, and

performance of mobile homes. The test plan included the instrumentation

and measurement of the thermal performance of a new furnished mobile home,

built in accordance with the Mobile Home Standard, ANSI A119.1, 197^-

The mobile home was installed in the large NBS Environmental Laboratory,

where it was exposed to a variety of climatic conditions.

Because the final location of a mobile home may not be known at the

time of manufacture and because of a number of variables such as altitude

and heating value of the fuel that may affect the furnace output capacity,

it is a common practice in the mobile home industry to install oversized

heating plants in mobile homes. In most instances, the heating output capacity of the heating plant is much larger than the design heating load for

the home in its final location. This study investigates the effect of heating demand on the part-load efficiency of a gas-fired forced-air heating

plant.

Heat loss through air infiltration may represent one-third to one- half the heating load for a mobile home. Measures taken to reduce air leakage will unquestionably have a significant impact on reducing heating

energy requirements. The points where air leakage occurs may not always

be obvious and may sometimes occur in unsuspected places. A recent air

2
leakage study performed on residential buildings [l]*showed that s ignif icant

amounts of leakage occurred through solid walls and ceilings. These parts

were previously thought to be essentially impervious to air leakage.

Similar tests were also conducted on the mobile home of the present

study to quantify the amount of air leakage occurring through different

parts of the structure. Separate tests were also conducted to determine

the effect of the operation of the heating plant on inducing additional

air infiltration.

When mobile homes are constructed, the technique for installation of

insulation in the walls may cause the insulation to wrinkle, creating

air paths running the full height of the wall cavity. In this instance,

significant air flow can be induced due to the thermo-syphon effect

which may decrease the insulation effectiveness. In the present study,

heat leaks due to this phenomenon were investigated.

The condensation of moisture on exposed surfaces and within structural

elements may eventually cause unsightly staining and even wood rotting

which may significantly shorten the life of a mobile home. As part of

the present study, observations were made to identify those parts of the

mobile home that have a high condensation potential.

2. DESCRIPTION OF TEST SPECIMEN

The test specimen was a new, factory-produced two-bedroom mobile home of

nominal dimensions of 50 feet by 12 feet with a 7-foot interior height.

Nominal dimensions include a 4-foot hitch., making the actual length 46 feet.

* Figures in brackets indicate the literature references at the end of

this paper.

3
Figures 1 through 12 show construction phases for the mobile home,

beginning with the chassis (fig. 1). Floor construction included R-4

insulation over 1/16- in asphal t- impregnated underlayment ; 2 x 6-in floor

joists and heating duct running the entire length, comnleted with carnet and

vinyl floor covering. The next step was installation of interior partitions

and bathroom and kitchen. Exterior wall sections were fabricated with R-7

insulation friction-fitted between 2 x 4-in framing, and placed on periphery

of floor; the roof section using R-14 insulation between framing members and

over a 6-mil polyethylene film and a 3/4- in fiberboard ceiling material was thei

lowered over the walls, and the factory construction was completed by the

installation of corrugated aluminum siding on exterior walls, and the

sheet metal roof.

The mobile home was manufactured in Ephrata, Pennsylvania, and transported by tractor to NBS (fig. 13). After it was placed in the NBS high3 bay environmental laboratory of approximately 70,000 ft in volume, the

utilities--electricity , water, natural gas and drainage--were connected.

Supports were placed at various locations under the chassis to take weight

off of the tires, for leveling and to reduce vibration. Also, sheet metal

skirting was installed at the outer periphery between the bottom of the

mobile home and the ground, as shown in figure 14. The home was factoryfurnished with refrigerator, stove, two beds, dining-room table and four

chairs, couch and divan, and curtains and draperies at windows.

k
Figure 1. Chassis of mobile home.

Figure 2. R-4 insulation over asphaltimpregnated underlayment

.

5
Figure 3. Installation of 2 x 6 floor joists.

6
Figure 5* Mobile home floor coverings in place.

Figure 6. Installation of interior partitions.

7
Figure 7* Prefabricated insulated wall sections.

Figure 8. Installed wall sections.

8
Figure 9 * Fabrication of roof section.

10. Roof section being lowered onto walls.

9
Figure 11. Installation of aluminum siding.

Figure 12. Installation of sheet metal roof.

10
Figure 13. Mobile home delivered to NBS.

Figure l4. Mobile home in environmental chamber.

11
The warm-air, gas-fired, sealed-combustion furnace was rated at 56,500

Btu/h input and 45,200 Btu/h output at the bonnet. Air for combustion was

taken from the outdoors at the roof through an outer annulus surrounding

the flue pipe and into the combustion chamber. Combustion products were

discharged to the outside through the inner annulus or flue. Air circulation within the mobile home was by a furnace fan forcing air down through

the heat exchanger of the furnace to the heating duct located below the

floor. Figure 15 shows air registers in the mobile home plan view. The

thermostat was located in the hallway between the doors to the bedroom and

furnace room. For special test purposes, the furnace plenum was used for

the installation of electric resistance heating elements. The voltage supplied to the elements was controlled by a variable transformer for varying

the electric heat input in tests where needed.

For expelling exhaust furnace flue gases, a 12-in diameter flexible

hose was installed over the flue-gas stack located on the roof and connected

to the laboratory outdoor exhaust system. The flexible hose installation

is shown in figure 14.

3. INSTRUMENTATION AND TRANSDUCERS

The electric energy supplied to the mobile home electrical distribution

system was measured using a calibrated 3-wire watt-hour meter equipped with

an impulse generator--a photoelectric device which generated pulses from

revolutions of the disk inside the meter. The pulses were registered by a

counter and printed out at preset time intervals. The same system was used

to measure electric energy input to the electric resistance heating elements

installed in the furnace plenum.

12
The volume of natural gas consumed "by the furnace was measured with

a domestic gas meter that was specially modified, so that the passage

3 of 1 ft of gas caused an electric pulse to be generated. This was

accomplished by placing an excitation voltage across a micro-switch

that rode on the cam shaft of the counter and printed out at preset

time intervals

Ambient air and surface temperatures were measured with 24- gage

copper-constantan thermocouples. Thermocouple strings, suspended by 3/1 6- in

diameter polycarbonate rods, were placed in each room. The location of

these strings is shown in figure 15. Four thermocouples were attached

to each rod and located at 3, 30, 60, and 81 inches above the floor.

Outside air temperature in the environmental chamber was measured by eight

thermocouples placed one foot from outside surfaces of walls and roof. ,

Two thermocouples placed one foot below the chassis of the mobile home

measured the air temperature in the space enclosed by the sheet metal

skirting. Other thermocouples measured temperatures at inside window

surfaces, and temperatures of the supply and return air to the furnace.

.4 . PROCEDURE. RESULTS AND DISCUSSION

In the following sections, procedure, results and discussion are

presented for the various aspects of testing.

4.1 Thermal Testing Under Steady-State Conditions

A. Instrumentation

This series of tests was conducted in an environmental chamber

having the capability of individually controllable temperature and relative humidity from -50 F to 150 F and from 15 percent to 85 percent RH,

respectively. The temperature

13
Ugure 15. Plan view of 46 ft long by 12 ft wide mobile home showing location of

thermocouple strings

lU
and relative humidity can be held constant or caused to cycle on a predetermined schedule. The air within the chamber is circulated at a highchange rate (one air change every two minutes) in order to control the

temperature within the chamber. Control thermocouples are located in

the supply and return air.

Forty-eight 24-gauge copper constantan thermocouples were located

throughout the interior and exterior of the mobile home so that temperature measurements could be used for heat flow calculations. For location

of these thermocouples, refer to section 3 of this report.

Although the gas meter provided the gross energy input to the gas -fired

furnace, it was necessary to measure the efficiency of the furnace

in order to determine the energy input to the mobile home. The continuous operating efficiency was determined using a CO^ combustion gas

analyzer

The furnace on-and-off cycles were observed using clocks and stripchart recorders connected by relays to the furnace. A separate stripchart recorder was used to show furnace blower on-time and furnace burner

(or electrical resistance elements) on-time. These recorders were used

to determine the number of cycles per hour. Two electric clocks were

also connected to the strip-chart circuitry so that one clock recorded

total on-time of the furnace fan during a test and the other clock

recorded total burner on-time. These clocks were used to provide accurate

percent on-time for the fan and the furnace for each test condition.

b. Test methods and conditions

For this series of tests, the chamber and mobile home interior

temperatures were held constant and the mobile home energy consumption

15
was recorded. It was necessary to hold the test chamber at test conditions for at least l6 hours prior to each test to allow the mobile

home to reach equilibrium. A further check on equilibrium conditions

was made at the end of each test by comparing energy consumption for

each hour. Any irregularity of energy demand resulted in test

invalidation

The mobile home was tested under several outside air temperature

conditions, with both natural gas and electric energy inputs and with

and without storm windows. The various steady-state tests are denoted

by the x’s in the following schedule.

Approximate Chamber Temperature . F

-15 0 15 30 ^5

Electric With StormX X X X

Furnace Windows

Without " X X X

Original gas

Furnace

With

Storm Windows

Without "

X XX XX XX XXX

.1 X X X

Modified gas With Storm

Windows X X X X

Furnace

Without "

The average inside air temperature was about 70°F for all tests.

Tests were conducted with the furnace modified to a lower natural gas

input to show the effect of this variable. Tests with the original gas

furnace were repeated to show reproducibility of data. One test was

made at -15 F in order to extend trends established. The chamber temper

atures are described as being approximate since the chamber controls

16
were set at the value shown but equilibrium was often established, with

a +_ 2 F deviation from the set point. Actual temperatures were used

for all calculations.

After reaching equilibrium, each steady-state test was continued

for a period of seven hours. A complete set of data was recorded every

30 minutes for the duration of the test.

One series of tests was run with the furnace modified to a lower

input capacity. The original equipment gas furnace was rated at a

56,500 Btu/h input and a bonnet capacity of 45,200 Btu/h. On special

request, the manufacturer provided a replacement burner orifice to reduce

the input capacity to 30,000 Btu/h or a bonnet capacity of 24,000 Btu/h.

In order to keep the furnace efficiency nearly the same as the original

furnace, the manufacturer also provided a small plate which was used to

partially block the burner chamber draft outlet opening. After installing

the new burner orifice and plate, the continuous running efficiency was

found to be 75 percent (365 F and 4.5 percent CO^) as compared to 72 percent (517 F and 4.5 percent CO^) as determined for the original equipment.

For sealed combustion furnaces the air for combustion is heated by the flue

jacket, whereby the flue jacket losses for the computation of efficiency

are ignored. The efficiency is then computed on the assumption of complete

combustion of the fuel and the temperature and carbon dioxide content of

the combustion products in the flue.

The method used to evaluate the effect of reducing the furnace capacity

oversizing in comparison with the heating load was a comparison of energy

consumption with the two different furnace capacities. The comparative comfort derived from the two furnace sizes was evaluated by determining air

temperature gradient from floor to ceiling under the different test conditions.

17
c. Results and Discussion

The actual energy input was observed over 7-hour test periods and

averaged to obtain energy input data. The observed energy readings were

adjusted to reflect efficiency losses associated with the combustion

heating systems. The electrical resistance furnace was assumed to

operate at 100 percent efficiency and all other electrical inputs were

converted directly to heat. The natural gas energy was based on a heat

3 content of 1027 Btu/ft . This figure was obtained from the local

natural gas utility and was reported to be applicable for the period

of time when the tests were run. The efficiency of the gas furnace

was measured using the CO^ gas analyzer previously described. This

efficiency could not be used directly, however, because of the indeterminate

stack losses occurring during the off-cycle. In order to estimate the

efficiency of the gas furnace under cyclical running conditions, the

energy input to the combustion furnace was compared to the input to

electrical resistance heating under the same test conditions. The

relationship between the measured energy demands in Btu/h as a function

of the inside-to-outside air temperature difference} AT, for the electric

heating tests was found to be:

for mobile home with storm windows

Q

= 1*71.3 + 149.2 AT + 1.076 AT

2

e for mobile home without storm windows

Q = 120.35 + 177.1 AT + 1.081 AT

2

e where = total heating load satisfied by combination of electric resistance heating elements, lights, and furnace fan.

From tests with the gas-fired furnace, the total rate of gas energy

18
consumption, Q , rate of electrical energy consumption from lights and

6

furnace fan, Q , and the temperature difference as measured, the effim

ciency, e, is calculated from the expression:

Q

S

where Q

g

is determined from the relationships given above. These

apparent efficiencies as a function of inside-to-outside temperature

differences are shown in figure 16. These efficiencies were used to

calculate net energy input to the mobile home for each test condition

and compared with the predicted values.

The measured energy input to the mobile home for each of the test

conditions is shown in table 1.

For comparison purposes, the predicted heat loss was calculated

for each of the test conditions. These calculations as shown in

Appendix A were made using the formula, U factors, and areas shown on

table A-l. The construction of the building elements is shown in

section 2 of this report. In these calculations the ASHRAE

design resistances for interior still-air films were not used in the

calculations. This is because of the geometry of the mobile home and

its effect on the radiative heat transfer. Appendix B discusses reasons

for the interior air film resistances used.

Actual temperature differences observed during each test were

used in the heat transfer predictions. Separate temperature differences

were used for transmission losses through walls and roof, and floor areas.

In order to predict heat flow under test conditions, air infiltration

rates had to be considered. The air infiltration rates used in the

calculations were determined on the mobile home using sulfur hexafluoride

19
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1916

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(SF^) as a tracer gas. Section b.3 of this report discusses the infiltration rate of this mobile home as a function of inside-to-outside temperature differences. Infiltration rates were determined both with the furnace

blower running continuously and the blower off. In the steady-state heating

tests, however, the furnace and blower cycled on and off by thermostat

demand. Therefore, the infiltration rate used in the calculations was

estimated to be between the observed rate with and without fan operation

based on the percent on-time of the blower for each test condition. The

percent furnace on-time for the tests with the gas-fire furnace operation

is shown in figure 1 7. The estimated infiltration rate as a function of

inside-to-outside temperature with cyclical furnace operation is shown

in figure 18. These infiltration rates were used in the calculations.

Using the method outlined in the calculation form of Appendix A, the

predicted overall thermal transmittance is determined by dividing the heatloss rate by the actual temperature difference and the thermal envelope

area of 1916 square feet. The measured heat-loss rate is determined in a

like manner, and table 2 gives the measured and predicted thermal transmittance values. Generally, at the lower temperature differences there is

good agreement between the measured and predicted values, but with increase

in temperature difference, the measured values become greater than the predicted values. This seems to indicate a process taking place that is dependent upon increase in temperature difference,, such as the increased buoyant

effect on air. In section 4.2, we note that there is thermos;! phoning of air

in passageways between the insulation and wall paneling due to loose insulation fits at the top and bottom of the stud spaces. These effects are difficult to determine from a predictive analysis because they are indeterminate

and depend upon the workmanship and methods used to install the insulation

and the magnitude of the inside-to-outside temperature difference.

22
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Gross energy (not adjusted for efficiency) input versus inside-tooutside temperature difference is shown in figure 19. Throughout the

tests, it was observed that the inclusion of storm windows caused an

approximate 10-percent reduction in energy consumption under each test

condition. This reduction was close to the predictions from the heat

flow calculations. Previous infiltration studies on this mobile home

(refer to section 4.3) show that the storm windows had only a small

effect on infiltration rates. Therefore, it is assumed that the difference in energy input with and without storm windows is due to heat

transfer through the windows by conduction and convection.

Throughout the tests the furnace was observed to be greatly oversized

for the test conditions. The original furnace configuration was rated at

56,500 Btu/h input and the mobile home was certified to maintain a JO F

interior temperature with an outside temperature of -50 F, assuming a

maximum 15-mile-per-hour wind. This mobile home can be considered to be

equipped with a furnace oversized for the New York State marketing area for

which it was produced. The degree of oversizing of the original furnace can

seen in figures 17 and 19. When the mobile home was tested in the environmental chamber at -15 F with the original furnace configuration, the furnace

burner was operating only 43 percent of the time. Energy input to this furnace was 20,5000 Btu/h or 36 percent of furnace rating when the environmental

chamber was maintained at approximately 0 F.

In order to evaluate the effect of this oversizing, measured

energy consumption was compared between tests run with the original

56,500 Btu/h input furnace and the modified 30,000 Btu/h input. The

I I energy input with the two sized furnaces is shown in table 1. The

actual, gas and electrical energy inputs (not adjusted for furnace

26
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seen that the energy consumption rate was significantly lower for the

modified furnace than for the original-equipment furnace, especially

at the lower inside-to-outside temperature differences where the effect of

oversizing is more pronounced. This is true even though infiltration

rates are assumed to be slightly higher with the smaller furnace because

of the increased furnace blower on-time.

The reduction in energy consumption can be attributed to the

increased percent on-time shown in figure 17, resulting in decreased

time for off-cycle stack losses. The apparent efficiencies shown in

figure 16 were determined by comparing the gross gas furnace input to

the electrical input under the same test conditions, assuming the electric

furnace to be 100 percent efficient. At a temperature difference of 70 F,

both gas furnaces approach their continuous running efficiencies. At 30 F

temperature difference, the difference in efficiency is greater than 10

percent. These low-load operating conditions are common during the

heating season.

The floor-to-ceiling temperature gradients within the mobile home

with each of the furnaces were checked to determine the effect of

furnace sizing on occupant comfort. Table 3 shows these results. These

results indicate that the floor-to-ceiling temperature differences

were not significantly different between the two sizes of gas furnaces.

However, the temperature gradient experienced with the electric furnace

was obviously lower. This could be due to longer running time with

the electric furnace, but this is not known because percent on-times

were not recorded for the electric furnace tests.

28
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The lack of significant effect of furnace oversizing on occupant comfort may be specific to this mobile home design. Floor-to-ceiling temperature gradients in typical residential construction range from 5 to 20 F,

depending upon the type of air distribution system used. It is possible

that the temperature gradients would be affected to a greater degree if

the ducts and registers were designed for better air mixing within the

mobile home.

4 . 2 Thermal Performance by Thermographic Technique

A method for determining the thermal performance of the components

of buildings is use of a thermographic system which detects infrared

radiation emitted from surfaces. The surface temperature in a relatively

narrow temperature range is proportional to the infrared radiation and

relatively warm or cold spots can be quantified and displayed in a scan of

surface temperatures if the surface emittances are known. Such warm and

cold spots can help to identify areas of varying thermal transmittance

due to thermal bridges and internal air movement.

The thermographic technique was also successful in identifying locations of air infiltration and air movement. The relation of warm and cold

areas of walls to thermal performance of walls was investigated.

Refer to figures 20 and 21 and to section 2 of this report for

a description of the wall construction.

4.2.1 Description of thermographic system

A photograph of the thermographic system used for this study is

shown in figure 22. The equipment from right to left consists of an

infrared camera, black-and-white television monitor, a color television

display and a temperature profile adapter. The long-wave radiation that

is emitted and reflected from a surface is sensed by the infrared

30
Figure 20. Elevation View of Mobile Home Wall

31
I

Figure 21. Plan View of Insulated Mobile Home Wall

32
Figure 22. Thermographic System

33
camera and converted into a video signal. The camera consists of an

optical scanning system with liquid-nitrogen-cooled indium-antimonide

photovoltaic detector having a high sensitivity in the spectral range

from 2.0 to 5.6 microns.

The video signal from the camera is processed in the black and white

monitor and converted into a thermal picture in which the black, gray

tones and the white approximately correspond to surface temperatures from

cool to warm, respectively. The image is displayed on the screen of an

oscilloscope for display and can be photographed with a conventional camera.

The video signal is also fed into the color television display where ten

individually color-coded isotherms each represent a step in the temperature

gradient. The temperature profile adapter was not used in this study.

h.2.2 Observations with thermographic equipment

General thermographic observations were made of the inside and outside

of the mobile home. During all of the following thermographic observations, the outside temperature was 0 F and the inside temperature was

72 F. On the outside, it was observed that the skirting around the

base was warmer than the wall surface above, (fig. 23).

Most observations were made of the inside surfaces including

several general observations. The location of wood studs was observable

because the inside surface was slightly colder over the studded areas.

Wall surfaces were observed to be colder toward the bottom as compared

to the top of the wall (fig. 25). The warm heating ducts created an

obvious pattern on the floor. Figure 26 shows an obviously warm floor

register with a resulting warm wall area caused by the heater air

3^
Figure 23. Angular thermograph of exterior sidewall of mobile home.

Dark area (colder) is the aluminum wall surface. Lighter area

(warmer) below is the skirting at base of mobile home , and

white area in lower left is ground surface. Dark area found in

skirting is an air vent (refer to figure lb).

Figure 2k, Warmer horizontal aluminum trim at wall roof juncture.

35
Figure 25. Wall along hallway looking from kitchen area. Walls are colder at the

base of the wall. Cold streaks occur randomly along wall.

Figure 26. Wall at base of double living room window. Warm air register

at lower left is warming the wall surface under left window.

36
warming the wall surface. The general thermographic observations also

\ revealed some air infiltration locations. Figure 27 shows a cold (dark)

area under a window where outside air is leaking in around the window

framing. The wall/floor corner shown in figure 28 is obviously very

cold. Closer observations at this location revealed an air leak at

the wall/floor junction resulting in an interior surface temperature of

29 F in the corner (inside 72 F, outside 0 F).

One thermal characteristic was so dramatic that it created a

dominant thermal pattern on the wall. Cold "streaks" (dark area of

figure 29 ) occurred along the inside of the wall starting at the base

of the wall and extending up into the upper half. Surface temperature

measurements showed these streaks were about 5.5 to 6 degrees F colder

than the warmer areas. The colder area covered about 25 percent of the

surface area between studs.

From these observations, it was hypothesized that cold air must be

in contact with the interior wood paneling. This early hypothesis was later

supported when it was observed that the cold patterns on the wall

correspond directly with locations where the insulation was not in

contact with the wood paneling, leaving an air channel between the

insulation and the paneling.

To test this hypothesis and evaluate various corrective techniques,

a series of changes were made in the wall construction and the resulting

thermal profiles were observed. All of these changes were made in one

location as identified in figure 30.

Since gaps were observed at the top and bottom of the insulation

(fig. 31), it was considered possible that cold air could enter the

37
Figure 27. Window with warm curtain (light area) on right side. Dark

(cold) area on wall under window is due to perceptible cold air

leaking into mobile home.

Figure 28. Living room wall/wall/floor corner. Perceptible air leak in corner created very cold spot, out of camera range. Light area

in lower left is couch.

38
Figure 29. Wall area to left of living-room side-wall window. Picture on wall at upper left, draperies along window on right side of

picture. Dark areas are cold. Note wall studs showing through

in upper center. Location as shown on figure 30.

Figure 30. Location of thermographic investigation of wall performance denoted

by X.

39
Figure 31, Gap between sill plate and bottom of insulation which could allow outside

air in contact with back of inside paneling.

Figure 32. Thermograph of wall test area after sealing outside of

insulation cavity with polyethylene film.

40
cavity, pass under the insulation, rise between the insulation and interior

paneling and then pass to the outside over the insulation at the top. The

exterior aluminum paneling allows more or less free passage of outdoor air

into and out of the wall cavity outside of the insulation.

Six-mil ployethylene film was then attached to the outside surface of

the studs at the test location to prevent cold air from penetrating directly

into the insulation cavity (see fig. 33). After the outside surface was

sealed, the resulting thermographs (see fig. 32) revealed that the cold

pattern still remained with the same configuration as received from the

factory. The surface temperatures were slightly warmer and the intensity

of the cold/warm pattern was not quite as sharp as shown in fig. 29. See

table 4 for surface temperatures at locations A and B of fig. 39. Location A

is a spot where temperatures were lowest, and location B is the warmest

temperature.

After it was determined that sealing the outside surface of the wall

would not prevent the occurrence of cold patterns on the inside surface,

it was reasoned that cold air could be circulating in a closed loop around

the insulation within the stud cavity, without direct air leakage to the

outside, effectively siphoning heat to the outside. This theory was tested

by taping the inside vapor barrier of the insulation to the adjacent wood

studs (see fig. 34). This figure also shows the taped lines outlining areas

of the insulation which were in contact with the back surface of the wood

paneling. Those areas in contact had warmer inside surface temperatures,

supporting the theory that air movement within the stud space was causing

the cold streaking on the inside wall surface.

After taping the vapor barrier to adjacent studs, more thermographs

were taken. The resulting thermal profiles showed that the Inside sealing

process had a greater effect on reducing the cold streaks than drd sealing

the outside of the study cavity. Observations were made

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the cold streaking on the inside surface, sealing the inside surface to

prevent siphoning was obviously more effective (see table 4).

An alternative way to stop air movement within wall cavities and subsequent siphoning of heat to the outside would logically be to fill the

cavity with insulation to remove locations where air could move. This

theory was tested by removing the original insulation (R-7) and replacing

with an R-ll full thick batt. This technique was evaluated with insulation

installed by friction fit (figure 35) and with the insulation stapled

neatly to the faced of the wood studs (figure 36 ).

In both cases, thermographic and thermocouple observations revealed

that the cold streaks were substantially eliminated with full batts. Without neat, mechanically-attached placement, some streaks did occur along the

studs where the insulation was wrinkled due to stuffing the stapleing flanges

of the vapor barrier into the stud space, allowing air passage (see figure

37)* With neat attachment, cold streaking was eliminated and surface

temperatures were very even, as shown in figure 38 . As changes were made

in the insulating system, inside-surface temperatures were recorded with

the thermocouples located at A and B as shown in figure 39 . These temperatures are shown in table 4.

Some conclusions can be drawn. As currently installed, a portion of the

R-7 insulation in the walls is made ineffective by the passage of cold air

through the insulated cavity, siphoning air around the insulation. Although

the surface temperature depression of 5. 5-6.0 degrees F seems rather small,

calculations indicate that this effectively means a reduction in insulation

effectiveness in the cold spot 43
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areas of over 50 percent. Since cold areas appear to constitute approximately 25 percent of the wall area, movement of cold air within the wall

could result in a 9" percent reduction of overall wall resistance. Further,

since wall losses constitute about 40 percent of the total energy loss of

the mobile home, thermal siphoning could account for 4 percent of all energy

loss at a temperature difference of 70 F. It appears that full, thick, properly installed insulation substantially reduces or eliminates air movement

in insulated cavities. The presence of non-insulating sheathing such as the

polyethylene film did not effectively stop air movement and thermal siphoning

Placement of a vapor barrier such as polyethylene film on the outside surface

is not a recommended practice, but was used as an expedient for excluding

outside air from entering into the stud walls, for the purposes of this test.

4. 3 Air Leakage Analysis

4.3.1 Natural air infiltration as a function of stack effect

A separate NBS study was conducted on the air infiltration

characteristics of this mobile home. This work is described in

detail in a report entitled, "Air Leakage Measurement in a Mobile

Home" [2].* For purpose of reference to calculations and observations

in this report, some results from that study are included in

this report.

a. Test method

Infiltration tests were made with sulfur hexafloride (SFg) gas

introduced into the furnace fan and distributed throughout the house.

Tracer concentrations were measured with a gas chromatograph equipped

with an electron capture detector. Samples were introduced into the

* Figures in brackets indicate the literature references at the end of

this paper.

48
chromatograph by means of an automated sampling system. Replicate

samples were collected every 10 minutes from various locations inside

and outside of the mobile home. The infiltration rate of the mobile

home was calculated from the decay of tracer gas concentration as a

function of time. (See above-referenced report for further test

method details. )

b. Observed infiltration rates

The NBS environmental chamber provided the ideal laboratory for

determining infiltration as a function of inside-to-outside temperature

difference. It is generally recognized that this stack effect is one

of the driving forces. Another driving force is the outside wind

pressure.

The initial series of infiltration tests were run with the furnace

blower running continuously. Later tests showed that the furnace blower

had a considerable effect on the infiltration rate. Comparison tests were

made between continuous- fan and no- furnace- fan operation. Without operation

of the furnace fan, air infiltration rates were reduced by about 0.2 air

changes per hour (figure 17). In this test, the air within the mobile

home was circulated by means of fans located within the rooms.

The reason for the large effect of furnace blower operation on

infiltration rate was observed to be an annular gap around the furnace

flue where it penetrated through the ceiling (see figure 40), allowing

the furnace room to communicate almost unobstructed with the vented attic

space. When the fan was operated, the furnace room was under a slight

negative pressure which induced outside air from the attic space.

49
n

i:
Another suspected source of air leakage was through the joints in

the furnace duct under the floor. This was checked by drawing air samples

out from the crawl space under the mobile home during infiltration measurements. These air samples were monitored regularly for SF^ traces, but

none were found. This would suggest that the combination of duct and

bottom board provided an effective seal.

Infiltration rate tests were also run with and without storm windows

on the inside. The effect was found to be quite small. This was because

window frames are not usually sealed to the interior paneling, and infiltration can occur through the resulting gapsj and because the mounting

frame for the storm window is not tightly sealed to the inside wall paneling.

Air leaking through or around the primary window is relatively free to pass

around the inside mounted storm sash.

4.3.2 Pressurized leakage tests

Although actual infiltration rates were determined through the SF^

tracer-gas technique, this study did little to identify the paths of air

infiltration. Some of the infiltration paths were observed with the infrared camera, such as the previously mentioned air leakage under a window and

in the living room corner. This section discusses another attempt to

locate leakage paths by pressurizing the mobile home interior, and measuring air flow rates through the mobile home as various suspected leakage

paths were blocked and unblocked.

a. Test method

Refer to figure 41 for a diagram of the test equipment. An interiormounted axial fan (figure 42 ) was used to pressurize the mobile home and

the total air flow was measured by means of a pitot static-air velocity

measuring device located upstream of the fan (figure 43). The differential

pressure was maintained at a constant 0.20- inch water

51
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Figure k2. Vane axial fan mounted through sealed plywood partition at front

entrance door opening.

Figure U3. Pitot static air velocity measuring device located at plywood barrier.

'Duct leading to velocity measuring device was used to provide laminar

flow of air over pitot static tubes.

53
gage by restricting the size of the open end of the duct extension as

more and more leakage paths were blocked.

Potential air leaks within the mobile home were blocked from the inside with the use of duct tape. As each air leak was blocked the reduction

in air flow was noted. Because the weather outside the environmental test

chamber changed rather dramatically during the test, the temperature and

barometric pressure within the test chamber were recorded at least two times

per day and these variables were used in the calculation of air flow. The

air density was calculated using the equation:

P 1.325

where p = air density in pounds per cubic foot

P = barometric pressure in inches of mercury

-DT = absolute temperature (F + 460)

The air flow rate, Q, in cubic feet per minute, moving through the duct

containing the calibrated pitot tube was calculated using tne equation:

Q = 1096. TA

where A = duct area, .555 ft

h = pitot tube pressure difference in inches of water

There was a question whether to use a pressure or vacuum on the

interior in order to create forced leakage. Previous forced-leakage

studies on conventional homes by G. T. Tamura of the National Research

Council of Canada (nrc) utilized a negative interior pressure and leakage

paths which were blocked from the outside with polyethylene film and tape.

This is a logical way to test conventional homes because it appears that

the pressure envelope is on the exterior surface and it is easier to

54
seal areas with the sealing medium drawn toward the surface rather than

pushed away. Because of the vented exterior wall design used with this

mobile home, the pressure envelope was known to exist at the inside wall

surface. Therefore, the leakage paths were blocked from the inside and

an interior positive pressure was more logical. In addition, equilibrium

values were slower in developing and were more erratic when negative pressure

was applied to the mobile home.

Previous studies by NRC were conducted with a constant inside-tooutside pressure difference of 0.300 inches water gage while these tests

at NBS were run at 0.200 inches water gage. The 0.200- in water gage pressure

was used because it was found that the vane axial fan was capable of maintaining approximately 0.204 inches wg pressure difference without any leakage paths blocked. With this capacity, it was decided to run all tests at

0.200- in wg pressure.

The decision to test at 0.200- in water gage was accompanied by a determination of the relationship between pressure and flow rates. Figure 44

shows that this relationship is apparently linear down to about 0.02 inches

wg pressure difference. As the graph indicated, this relationship was checked

with approximately one half the leakage paths blocked as well as with the

mobile home in its original condition.

The ins ide- Lo-outs idc and pitot-static pressure measurements were

made with a micro-manometer and a standard Hooke gage with micrometer scale.

b. Results and Discussion

The sequence of leak blockage and unblockage as well as their effects

are shown in table 5. In general, the consistency of the effect of blocking

and unblocking leakage locations was very good, with the exception of two

cases; namely, the effect of sealing the wall-ceiling

55
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57

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gage.
juncture and the windows. However, if these two leakage locations are

recognized as being parallel leakage paths through one element (the wall),

it is logical that the sequence of blockage of these parallel paths mayhave an effect on the reduction or increase of air flow. It can be

seen from the figures below that the total leakage through the wall was

virtually the same in both directions.

Variable Decrease in air

flow upon sealing

Increase in air

flow upon unblocking

1. Sealing exterior switches

and outlets

17 19

2. Sealing windows and rear

door

188 240

3. Sealing plywood butt

joints

77 7 6

4. Sealing wall/ceiling

juncture

138 90

Total Effect 420 cfm 425 cfm

The sealing process was accomplished with aluminized duct tape.

Figures 45 through 47 show examples of sealing of suspected air leaks.

After all the obvious and sealable leaks were taped shut, only

approximately JO percent of the initial leakage remained. At

this point, some air was still observed to be leaking at penetrations

through the asphalt -impregnated underlayinent , through the roof vents

and through the exterior-wall-vent openings. This residual leakage is

presumed to be occurring by such means as:

1. permeability through the building materials.

2. inaccessible holes through the ceiling such as electrical

penetrations within partitions and under light fixtures.

58
Figure 45. Panel side joints, wall corner joint, ceiling wall joints and window

sealed with duct tape.

Figure Bathroom exhaust fan sealed shut with duct tape.

59
Figure ^7. Plumbing hole through floor under bathtub sealed with duct tape. Access

gained through hole cut in end bedroom wall.

Figure H8. Bathroom exhaust fan with foam plastic backflow sealing flaps.

6o
3. non-sealable leaks through the floor at the base of the furnace.

4. other miscellaneous locations.

The wall leakage was found to be greater than 40 percent of the

total forced leakage. This is a combination of leakage through the window

construction (the largest portion), through the exterior electrical switches

and outlets, through the wall/ceiling juncture, and through the joints

between plywood panels. Observation of the window construction leads to

the conclusion that much of the total window loss was caused by sealing

the primary window to the exterior surface, which is not the pressure

envelope. It appears that air was leaking between the inside-mounted

storm windows and the exterior mounted primary window, allowing air flow

into the vented wall cavity. This observation was supported by the fact

that air leakage out of the exterior wall base and top vents was reduced

substantially when the total window construction was sealed. Yet, significant leakage through the outside prime window could not be felt while

the window was unsealed on the inside and the house was under pressure.

The leakage through wall switches and outlets was small, considerably

less than anticipated. This tightness is attributed to the close fit

between the electrical box and the paneling and to the air resistance of

the switch or outlet and cover assembly.

The pressurized leakage of the bath exhaust vent may not be indicative of air leakage through this path under normal infiltration pressure

differences. However, this unit could be designed to provide a more

effective seal. As constructed (figure 48), the circular duct is Hampered

with two semi-circular, l/4-inch-thick sheets of open-cell polyurethane

61
foam glued to the fan housing at onLy one point. The fan blows these flaps

up, effectively opening the damper. Unfortunately, the flaps overlap and do

not fit well, allowing some unrestricted air flow. It was noted that warm

air was escaping from the fan vent due to stack effect only, with the interior at 70 F and the chamber at 0 F.

Pressurization tests were used to identify air-flow paths as sources for

potential air leakage. Results of these tests should not be extrapolated to

quantify air infiltration and exfiltration rates. The complex natural

convection forces due to wind and temperature differences are not expected

to behave in the same manner as that for the constant internal pressure.

4 .4 Condensation Potential

a. Instrumentation

Condensation tests on this mobile home were conducted in the environmental chamber. Humidification was achieved with a portable power type

wetted element humidifier located in the kitchen area of the mobile

home. The built-in humidistat was by-passed by setting the humidifier

control to continuous operation. The on-off cycling was controlled

using a humidistat with a hair-type sensing element.

Two full-ranee humidity transducers were utilized to read the

relative humidity

in the living space of the mobile home and the attic space. Four

narrow-range ( 89% to 99%>) lithium-chloride- moisture sensors were

installed in the insulated wall cavity. Two of the sensors were installed

between the interior paneling and the insulation vapor barrier. The

remaining two were installed between the wall-cavity insulation and the

outside aluminum sheathing.

b. Test methods and conditions.

The condensation-potential tests were conducted with the environmental. chamber maintained at approximately 0 F and the the interior of

the mobile home maintained at 72 F by means of the mobile-home thermostat62
controlled furnace. Mixing of.(<the humidified air was accomplished with

a flexible duct and small fan mpving humidified air fpom the living

room to the rear bedroom and through the mining action of the furnace

blower. The furnace blower was allowed to cycle on demand.

These tests were conducted with the interior relative humidity maintained

at approximately 42 percent RH (+17o) . It is recognized that a 42 percent

interior RH is unusual under 0 F weather conditions, but it is possible with

either a portable humidifier (as used in this test) or a furnace-mounted

humidifier. It is also possible to achieve relatively high humidities with

unvented driers, hanging clothes to dry indoors, showers, cooking, or other

high moisture-producing activities within the mobile home. Therefore, it was

decided to test under conditions severe enough to reveal condensation potential.

At the beginning of the test, two full-range humidity transducers

were used to determine consistency of relative humidity throughout the

mobile home. One of the transducers was located in the center of the

living room area and the other transducer was installed in various locations such as the rear bedroom, bathroom and hallway. After it was

determined that the interior fan mixing systems produced even humidities

throughout the mobile home, the second humidity transducer was installed

in the attic space near the center of the mobile home. The transducer

was mounted in the free air space of the attic and the lead-in wire

was inserted through a ceiling light fixture to the mobile home interior.

The condensation-potential tests were conducted over a continuous

two-week period. During this time, the full- and narrow-range sensors

were read at least four times daily to ensure that the interior relative

63
humidity was being maintained at the set point and to observe whether

condensation was occurring in the attic or wall spaces. The full-range

transducers were also observed closely for variations caused by furnace

on-off cycles by taking readings every minute over two 2-hour periods.

In addition to the instrumentation observations, visual observations

were made throughout the testing, including checks for surface condensation and condensation within structural elements. The visual observation

of condensation within the structural elements was accomplished by opening

sections of the wall and roof at the conclusion of the test,

c. Results and discussion

1. Results obtained through instrumentation.

The narrow-range wall-cavity moisture sensors were used

solely for purposes of determining when relative humidities

approached condensation-potential levels. The sensors

located on the inside or the outside of the insulation

showed no reading throughout the test. This would indicate

that relative humidities never exceeded the bottom of the

range (89 percent) for the sensor. This was also true for

the sensor between the paneling and the insulation; however,

it was later found that frost had accumulated in the entire

area surrounding the sensor between the insulation and the

exterior siding. It is assumed that the narrow-range sensor

was not operative at the low temperature on the outside

of the insulation. The results obtained with the wall-mounted

64
narrow-range sensors were not considered meaningful and

no conclusions were based on these results.

The full-range RH transducers located in the attic

and living room areas did provide useful information.

It was observed that the interior relative humidity was

maintained at an approximately constant level as the

humidifier cycled on and off

once each 25 minutes. ' The attic relative

humidity cycled considerably as a direct function of the

furnace-blower operation. It was concluded that when the

furnace blower was on, outside dry air was being drawn

through the attic space into the mobile home. This was

caused by the annular gap around the chimney as shown in

figure 40. This conclusion was later verified by closing

the gap with duct tape and virtually eliminating any effect

on attic relative humidity by the on-off cycles of the

furnace blower. At the location of the RH transducer,

the attic space relative humidities ranged from a low of

80 percent to a high of 9^ percent over the entire two-week

period. With the gap sealed at the chimney, the atti<" snare

RH levels were also within this range but were held more

nearly constant.

2. Results from visual observations

Observations of interior structural condensation

were made by cutting holes through the metal roof to

65
observe attic condensation. Refer to figure 49 for location

of roof cuts. These test cuts were made at the end of the second week of condensation testing while the chamber was still

at 0 F and the interior temperature and relative humidity

were still maintained at 72 F and b2 percent RH.

Roof test cut No. 1 was made near the furnace flue. Observers walking on the roof in the general area of the test cuts

heard cracking noises which were interpreted as indicating possible frost attachment between the metal roof membrane and the

foam-core sheathing. Considerable frost was observed on the

underside of the sheathing and a single droplet of water was

observed on top of the fiberglass roof insulation.

Roof test cut No. 2 was made far removed

from the furnace flue, in an area where the cracking noise

created by roof-top traffic was not predominant. At this

location, very little frost appeared between the metal roof

and the sheathing. This frost consisted of fine frost lines

on the under surface of the metal with no observable frost on the

top side of the ;heathing. A thin film of frost was observed on

the underside of the sheathing (more than on the underside of

the metal roofing). The glass-f iber-batt roof insulation

appeared dry at this location.

Roof test cut No. 3 was made near the bathroom exhaust

vent stack. The previously discussed cracking noises were

very predominant in this general area. Frost was observed

between the metal and the sheathing (more frost at this

66
<>7

Figure

49.

PLAN

VIEW

OF

ROOF
location than at either test cut No. 1 or 2). Considerable

ice and water were observed on the underside of1 the sheathing

and water droplets covered the surface of the batt insulation. See figure 50 .

These roof test cut observations indicated that atticspace condensation was heavily influenced by air leakage through

the penetrations in the ceiling of the mobile home rather than

general diffusion through the ceiling construction (which contained a plastic film vapor barrier). Moisture accumulations'

were obviously heavier near the penetrations (bath exhaust and

furnace f]ue) as observed by both the test cuts and by

noises created by cracking frost and ice observed while

walking over the roof surface.

The bathroom exhaust vent constituted a penetration

into the attic space because the two sections of the exhaust

stack were not properly joined, allowing interior air to go

into the attic space as well as to the outside of the mobile

home. It appeared that the stack effect alone was sufficient to force interior air up through the foam flap "sealed”

vent. This deduction was made because of the attic space

moisture found near the vent and because of the frost accumulation within the outside bonnet covering the vent. This

moisture was observed even though the exhaust fan was never

turned on. It was also observed that moisture was condensing

on the inside walls of the vent stack and running back onto

the surface of the ceiling vapor barrier. Figure 51 shows
Figure 50 Roof test cut number 3 showing water and ice on bottom

surface of sheathing and water droplets on top surface

of roof insulation.

Figure 52 Location of water found on top of plastic film vapor

barrier of bathroom exhaust.

69
the point where water was observed on top of the vapor

barrier at the base of the exhaust vent.

Interior wall observations - The walls were inspected for

condensation by peeling back the aluminum siding. Since

exterior sheathing was not installed under the aluminum, this

revealed the outside surface of the wall insulation. See

figure 52 It was observed that considerable frost

had accumulated between the outside surface of the

wall insulation and the metal siding and on the inside

surface of the top fascia. This frost accumulation was

very pronounced on the upper half of the wall but not

on the lower half.

These observations indicated that interior moisture

was getting into the wall cavity either through a diffusion

process, or through leaks. The location of the frost

further supports previous observations concerning convective

air currents within the insulated walls. It appears that

air is moving up within the cavity carrying moisture to the

upper half of the wall and allowing it to escape under the

vented fascia. On this basis, it appears that the vented design

of the wall is functioning to remove moisture from the wall cavity.

Surface condensation - Moisture was also observed to be

accumulating on the inside surface of the walls. This

condensation occurred only at the base of the walls both

in open areas and within enclosed cupboard and closet areas.

Figure 53 shows a close-up photograph of this condensation

70
Figure 53 . Surface moisture condensation at base of wall.

Figure 52 # Fros t accumulation at top of wall and under fascia.

71
at the base of a wall. Note that the condensation pattern

was very distinct. Figure 55 is a picture taken of the

hallway looking from the kitchen area. The surface condensation locations were outlined with white tape to make

them visible in the photograph. Note that the condensation

did not occur in a uniform manner along the wall but at

specific areas only. By comparing the thermographs of the same

area (fig. 25) it was noted that condensation had occurred at

those locations where pronounced cold streaking had previously

been observed. It was concluded that cold outside air

which was convectively looping within the wall cavity was

lowering the temperature of the wall paneling below the dew

point (48 F) of the inside air (72 F, 42 percent RH),

resulting in this surface condensation.

Surface condensation also occurred at locations having

obvious thermal shorts. This was true especially for the

aluminum frame around the rear entrance door, which showed

heavy condensation and frost and ice buildup.

Window condensation - Surface condensation was also observed

on the windows. This condensation appeared to be excessive

due to the design of the exterior primary window and interior

storm window. Figure 55 shows a typical window with surface

condensation. It is important to note that almost all of

this condensation occurred on the inside surface of the outside window, not on the inside surface of the storm window.

It was concluded that the lack of seal between the storm

I

72
I

Figure 55. Typical window condensation.

73

*
window and the interior wall surface allowed moisture to

move freely to the outside, primary window.

It was hypothesized that if the inside window were well

sealed and the outside window sealed to a lesser extent (as

in typical residential site-built construction where the storm

window is on the outside) , the window condensation would not

have been severe. To test this theory, the inside storm window was sealed to the wall surface using duct tape as shown

in figure 56, and the outside window was cracked open approximately 1/16 inch. Under these conditions, condensation did

not occur on the inside surface of the outside window.

5. CONCLUSIONS AND RECOMMENDATIONS

5 . 1 Conclusions .

A. For laboratory tests without wind effects, it was found that the

original-equipment furnace was considerably oversized. Using this originalequipment furnace, the total energy supplied per unit temperature difference

2 based on a thermal envelope area of 1916 ft ranged from 0.172 to 0.158 Btu/

2

h. ft F at inside-to-outside temperature differences of 82.2 and 27.9 F,

respectively. Under these same inside-to-outside temperature differences,

the apparent cyclical efficiency (determined by comparison with assumed

100-percent-efficient electric resistance furnace) of the original-equipment

gas furnace ranged from 71,7 to 57.7 percent, respectively. After modifying

the furnace to reduce its input capacity by 47 percent, the values ranaed

from 0.160 to.0.143 Btu/h ft F at inside-to-outside temperature differences

of 70.5 and 28.7 F f respectiyely

74
75
Under these same ins ide- to-outs ide temperature differences, the apparent

cyclical efficiency of the smaller capacity furnace ranged from 72.8 to

63.7 percent, respectively. It is concluded that a greatly oversized furnace

will cause a significant increase in seasonal energy consumption,

From the calculation procedure in Appendix A, the modified gas

furnace configuration is estimated to meet the heating load at -22 F with

a 15-mile per hour wind; and so is somewhat oversized for most areas of

New York State. Generally, a certain amount of oversizing is required for

recovery due to nighttime setback of the thermostat, reduction of furnace

capacity for mobile homes located in high altitude areas, and a possible

reduction with time of the thermal insulating effect of the mobile home.

B. The comparison between measured and predicted heat loss was very close

especially under conditions where the outside temperature was relatively

high (45 and 30 F). It should be noted, however, that predicted heat-flow

calculations included allowances for effect of cupboard and closet areas,

furnishings, draperies, and modified surface air films (refer to Appendices

A and B). If the standard ASHRAE calculations were made ignoring these

aspects, the heat-flow predictions would have been higher than measured.

Thus, standard heat flow calculations would normally result in some degree

of furnace oversizing.

C. Although the comparison between predicted and measured heat loss using

the calculation procedure referred to in item B. was close where the approximate outdoor temperatures were 30 and 45 F, for lower outdoor temperatures

the measured values were from 5 to 17 percent greater than the predicted values

It should be noted that the predicted heat losses included increased infiltration rates caused by stack effect and longer furnace percent on-time. It

76
is concluded that this apparent loss of insulating efficiency at lower

temperatures (higher ins ide- to-outs ide temperature differences) is due at

least in part to thermosyphoning of air in and around the insulation

within wall stud spaces.

D. A thermographic survey using an infrared television camera was

useful in identifying locations of air leakage, thermal bridges and temperature differences on wall surfaces. Through this analysis, it was

determined that, under low outside temperature conditions, convective

air currents were found to exist within the insulated walls, reducing

their efficiency. The thermographic analysis indicated that this thermosiphoning was caused in part by the vented wall construction which was

used, and by the method of installing the insulation. To reduce this

thermosiphoning action, it is recommended that carefully fitted, fullthickness insulation be used, or some other mechanism be employed to

reduce the driving force, or to eliminate locations where convective air

currents can occur through gaps around the edges of the insulation.

E. Pressurization tests were used to identify air-flow paths as

sources for potential air leakage. These tests showed that 40 percent of

the total pressurized leakage occurred through the walls. The largest

portion of the wall loss was due to the specific wall-window construction used on this mobile home. Air leakage at this location was caused

by sealing the primary window to the vented outside siding. The interior

storm windows are attached to the inside paneling (the pressure envelope)

but are not sealed in any fashion. Other envelope penetrations such as

furnace flue and bathroom exhaust vents were found to be poorly sealed,

resulting in excess leakage.

77
F. In this study, it appeared that the combination of a vapor

barrier and the attic space vents would prevent excessive moisture buildup or condensation in the attic space. However, unsealed penetrations

through the ceiling of the mobile home will allow moisture-laden interior

air to rise into the attic space, resulting in excessive condensation

under high interior-moisture conditions.

G. Convective looping of cold air within the wall cavities will

cause interior surface wall condensation under high interior-moisture

conditions

H. Excessive surface window condensation was observed and was

found to be the result of putting a non-sealed storm window on the inside

surface with a well-sealed window on the exterior.

5 . 2 Recommendations

A. It is recommended that this study be continued to provide further

information in some areas which have been investigated and to allow work

in some new energy-related areas. The continued work should involve:

1) An analysis of energy consumption characteristics of this

mobile home under heat-gain (cooling) conditions;

2) A heat-loss analysis of a similar mobile home constructed to

eliminate thermosiphoning within walls—to assess the

magnitude of this heat loss;

3) An analysis of alternative wall constructions such as fullthickness insulation, insulating sheathing, and others, to

clarify their heat transfer and condensation characteristics.

78
4) An analysis of the relationship between pressurized leakage

\ and natural air infiltration. A standardized pressurized

leakage test should be developed and a maximum pressurized

leakage should be recommended for future construction standards.

B. It is recommended that the following findings from this study be

utilized in future modifications of construction and safety standards for

mobile homes; specifically, these standards should be modified in the

following areas:

1) Construction standards should limit furnace oversizing in

order to increase seasonal efficiency. This could be done

by providing furnaces adequate for the coldest areas within

the applicable market, along with a dealer-installed kit

designed to reduce the excessive capacity of the furnace in

warmer climates;

2) Also, in order to reduce oversizing of furnaces, calculations

to predict heat loss or gain under design conditions should

include the insulating effect of draperies, cupboards, closets,

and similar items which add to the thermal resistance of the

exterior envelope of the mobile home. The resistance of the

interior air films used in the calculations should recognize

that each exterior wall of a mobile home typically "sees" more

cold wall surfaces than for conventional residences, thus

reducing the radiation component of the film heat transfer

coefficient. It is recommended that these factors be included

in standard calculation procedures.

79
3) Installation methods for insulation should be specified to

reduce potential for thermosiphoning by convective air currents. This should include full-thickness insulation in walls,

smooth installation of mechanically attached wall insulation,

and careful installation of insulation at all locations to

eliminate locations for convective air movement.

4) Mobile home construction standards should include methods to

reduce air leakage paths and to reduce the potential for

condensation within attic and other structural cavities.

First of all, the primary window should be sealed continuously

to the pressure envelope of the mobile home.

Secondly, penetrations through the pressure envelope should

be made airtight with respect to the envelope, especially

those penetrations through the ceiling, such as plumbing, vent

stacks, ceiling exhaust vents, and furnace stacks.

Thirdly, connections between wall and floor and between floor

and ceiling should be specifically designed to eliminate air

leakage at these locations.

It is recommended that future construction standards include

these methods and enforce them through pressure-leakage tests

of completed mobile homes.

6. REFERENCES

1. G. T. Tamura, "Measurement of Air Leakage Characteristics of House

Enclosures," ASHRAE Transactions, Vol . 82, Part II, 1975.

2. C. M. Hunt, S. J. Treado, and B. A. Peavy, "Air Leakage Measurements

in a Mobile Home," Natl. Bureau of Standards report NBSIR 76-1063

(July 1976)

80
7. CONVERSION FACTORS TO METRIC (SI) UNITS

Phys ical

Quantity Symbol To convert from To Multiply by

Leng th foot me ter 3.048 x

r—A

1 o

T—

inch me ter 2.540 x io

“ 2

Area A ft

2 2 m 9.290 x 10' 2

Volume ft

3 3 m 2.832 x

10- 2

Temperature t F C U

II

CJ u -32)

F low Q

, 3, . ft /min m

3

/S 4.719 x

1 o

T^-

Density P lbm/f

3 kg/m3 1.602 x 10

Pressure P inch mercury Pa 3.377 x 10

3

(60F ) h inch water (60F) Pa 2.488 x 10

2

Power Btu/h W 2.931 x

10- 1

Heat Fl ux Btu/h ft

2 W/m2 3.154

Thermal o o Transmittance U Btu/h ft F W/m K 5.678

Thermal

Resistance R h ft

2 F/Btu Km

2 /W 1.761 x

10-'1

81
. * I
APPENDIX A

Calculations for Thermal Transmittance

The following calculations for thermal transmittance, U in

2

Btu/h ft F, are made for the calculation form (table A-l ) from the

2 numbered items using the resistances in h ft /Btu of individual components

2 and weighted area, A in ft .

l.a) Unobstructed roof area

At Insulation At Framing

Inside Air Film 0.99 0.99

3 / 4 " Fiberboard 1.89 1.89

2" x 2" Wood Truss — 1.88

R-l4 Insulation (thickness

constructed near edges) i4.oo

Partial Air Space — .89

2" x 2" Wood Truss — 1.88

Foam Sheathing, 1/4" 1. 04 —

Metal Roofing .00 .00

Outside Air Film .61 .61

18.1*3 9.18

446 -5Q + kfi T Weighted UA = = 29.52

u = 29.52A95.09 = .0596

1. b ) Partition contact area - Additional thermal resistance

occurs at partition contact areas.

Resistance of unobstructed roof area = l6.4l

Wood partition resistance = .94

Air film obstruction = . 50

17.85

U = .056

A-l
1. c) Bathroom vent - The bathroom vent pipe forms a

5

10

15

20

thermal bridge from the inside to the outside through the

metal of the duct pipe. From considerations of air films,

the thermal transmittance is estimated to be U = 0.5.

2. a) Unobstructed wall area

At Insulation At Framing

Inside Air Film 1.07 1.07

Wood Paneling, 1/8" .16 .16

Wood Framing, 3 1/2" — 4.38

Insulation, R-7 7.00 —

Air Space, 3/4" 1.01 —

Siding, Aluminum .00 .00

Outside Air Fiim .68 .68

9.89 6.29

Weighted UA = 467.3 77.10

9.89 6729 59.. 51

59.51

544 37 = .1093

2. b) Wall hrea covered by draperies and valance - the heavy

drapery material reduces the radiant and convective

components of the inside air film resistance in addition

to heat transfer through the drapery material. R = 0.99 +

9.15 = 10.14 or U = .099

2. c) Partition contact area - Refer discussion of 1. b).

Resistance of unobstructed wall area = 9.1^

Wood partition resistance = .94

Air film obstruction = . 50

10. 59

U = .094

A-2
5

10

15

20

2. d) Window area - Considerations for the window area include

exposed glass, drapery, and opaque and sheer curtains

calculated on a weighted area average basis. The thermal

transmittance of the exposed glass area is based on inside

and outside air film resistances of 1.46.

Area

Storm

Windows

No Storm

Windows

Exposed glass 5.22 .44 .73

Sheer curtains 24.26 .40 .64

Opaque curtains 4.69 .37 .56

Draperies plus

curtains 39.34 .31 .44

- 73.51

Totals UA = 25.93 39.27

Weighted U = .353 .534

The sheer curtains have patterned holes and add a

thermal resistance to the window area by a decrease in

the radiative transfer and a decrease in the convective

air flow. Assuming that the opaque area of the sheer

curtain reduces the radiative transfer by 1/3 and the

curtain reduces convective transfer by 10 percent* 'the

inside surface resistance is then 0.86 or an incremented

resistance of 0.18. This gives U = 0.4.

The opaque curtains are assumed to reduce radiative

transfer by 50 percent and the convective transfer by

25 percent, giving an inside surface resistance of 1.09

or an increase of 0.4l. This gives U = 0.37.

A-3
The combination of draperies and curtains are assumed to

give an incremented resistance of 0.48l, due to the

5

10

15

20

25

thermal resistance of the drapery material (k = 0 . 26 ,

1/8" thickness )

This gives U = 0.31.

The above calculations are for storm windows. A

similar procedure is followed for windows without storm

windows assuming U = 0.73 for exposed glass.

2. e) Front door with storm door

Inside surface 1.07

Door with storm door 2.18

Outside surface 0.68

3.93

or U = 0 .25

2. f) Rear door

Inside surface 1.07

Door 1.19

Outside surface 0.68

2.94

or U = .34

3. a) Unobstructed floor area

At Insulation At Framing

Inside air film 3.83 3.83

carpet/vinyl flooring

(see note)

1.20 1.20

subfloor, 3

A" • 98 .98

j oist , 5 1/2" — 6.88

air space, 4" 1.23 —

insulation R-4 4.00 2.00

simplex Board .10 .10

outside air film .92 .92

12.26 15.91

A-4
10

15

20

25

Weighted UA = ygf + fftfi= 2T ' 21

U = 27.21/341.34 = .0797

Note: Averaging individual resistance for carpeting

(192.88 ft^ and vinyl flooring ( 148.46 ft^) is

„ _ 2.08 x 192.88 + .05 x 148.46 , „„ R 35135 = 1 ' 20

3. b) Floor area obstructed by bed - The area under beds is

considered to have increased thermal resistance because of

the air space trapped by hanging bedspreads, and the resistance of the mattress. For the series and parallel heat—

flow paths, analysis shows that the equivalent U - value is

, (U a + U.a, ) U

jj.* _ mm h h

U + Umma + Uab b

where

U = U - value for mattress

m

05

= U - value for bedspread = .685

U = U - value for unobstructed floor = .0797

a = ratio of area of component to area of floor under beds

TT , (.05 x 1.0 + .685 x .43) .0797 u - nniT

.0797 + .05 V .~685_

x

_T43

" ’°6kl

3. c) Floor area under stove - The stove area is considered to

have increased thermal resistance , using the

rationale of 3.b, U = .072

3. d) Floor area under couch and stuffed chairs - using the

rationale of 3.b, U = . 068.

3. e) Partition contact areas - using the rationale of l.b, U = 0, 071.

A-5
4. Heating ductwork in floor - Heat loss from duct work occurs

through insulation (R-4) and bottom board downward into the

crawl space.

5

10

15

20

Insulation R-4 = 4.00

Simplex board = 0.10

or U = 0.20

5. Closets and Cupboards - Heat flow through closets and cupboards eventually flows through the walls, ceiling, and/or

floor. These areas are not equal to areas of closets and

cupboards exposed to interior environment of the mobile

home. In order to calculate the heat flow through these

areas, it was necessary to develop an equation based on a

heat balance into and out of the closet and cupboard areas

such that

Q

=- (t . - t ) + C (t -t) 1 o o c D

where

D =

and

C =

Vl + A

2

U

2 + A3

U

3 + A

4

U

4 + A

5

U

5 + A6°6 + V? + Vs

<Vl + A2

U

2 + A

3

U

3

> (A

4

U

4 + A

5

U

5 + A6

U

6 + *7U7 + W

A

3

+U3 A

J U1 + A2

U

2 + All

25

A-6
Subscripts 1, 2, and 3 refer to properties of the walls,

ceiling and floor, respectively. Subscripts U, 5, 6, 7, and

8 refer to the five possible sides of the enclosure (closet or

cupboard) exposed to the interior temperature, and

t^ = interior temperature

t = outside temperature

t ^ = crawl space temperature

For the l6 enclosures in the mobile home, values of D and C

were calculated. The sums are

= 20.2, — = 7.09

0 D

15

A-7
Table A-l

Calculation form for area thermal transmittance

5

10

15

U 0 Area UA

9 . Btu/h ft^ F ft? Btu/h F

Roof Areas (552 ft ) a. Net roof area .060 195-09 29.70

b. Partition contact area .056 13.72 .77

c

Bathroom vent .5 3.00 1.50

Total 31.97

Wall Areas (812 ft

2

) a. Net wall area .109 511.37 59.88

b. Wall with drape and valance .099 20.17 2.02

c

Partition contact area .094 9.33 .89

d. Window area (storm windows) -353 73.51 25.95

e. Front door with storm door .25 16.55 3.97

f. Rear door - no storm door .34 13.71 1.32

Total 96.96

Floor Areas ( 522 ft

2

) a. Net floor area -079 3ll.3l 25.60

b. Under bath tub .070 10.22 .72

cUnder beds .065 50.25 3.12

d. Under stove .072 5.00 .35

e. Under couch & stuffed chairs . 068 22.20 1.16

f. Partition contact area .071 13.72 .93

Total 33.79

4. Heating Duct Work In Floor .20 55-00 11.00

5. Closets & Cupboards

(t. - t ) 20.20

1 o

(t - t ) 7-09

o c Conduction Heat Loss

20

1. 31.97 (tic

2. 96.96 (

fc iw

3. 33.79 ( tpf

4. 11.0 (td

5. 20.2 (Uw

6. 7.09 < C o

- Q

c = Sum of lines 1-6.

to)

t Q ) 110.36 (t. - t c

) " *0)

- to)

t )

t ) (no storm windows)

o

'

A-8
Table A-l

Calculation form for area thermal transmittance (continued)

5

where t. = interior air temp near ceiling

t ^

= interior air temp near mid-height

= interior air temp near floor

= average heating duct air temp

t = air temperature in crawl space

to = outside air temp

Infiltration Heat Loss - See section 4.1.

10

a = 55.8 I (t. - t ) 1 1 o

I = infiltration rate, air changes per hour

15

A-9
'
I

APPENDIX B

Rationale for Determining Thermal Resistance of Interior Surfaces

Initial thermal analyses of the mobile home indicated that the resistance of the interior air film was greater than design values published in

the ASHRAE Handbook of Fundamentals. This is logical because large portions

of the interior wall, ceiling, and floor surfaces face other surfaces that

are nearly identical to the temperature of the surface in question. Since

conductance across a surface air film is composed of both convective and

radiative heat transfer, and since radiative transfer does not occur between

surfaces of equal temperature and emittance, the interior surface conductance is decreased under these conditions.

The ASHRAE design surface conductance value for vertical surfaces

2 is listed as 1.46 Btu/h ft F, and consists of 0.54 transferred by convection and conduction, and the remainder, 0.92, transferred by radiation.

Obviously, this is a conservative value for mobile homes where surfaces of

exterior walls, floor and ceiling face many similar surfaces of nearly

equal temperature. For example, the living room and kitchen and the rear

bedroom have five sides with surfaces of exterior walls, floor and ceiling.

Each of these five surfaces faces four surfaces with nearly the same temperature, with only one warmer surface, an interior partition wall. The

radiative transfer component of the film conductance is small under these

conditions

A paper by F.W. Hutchinson, "A Rational Reevaluation of Surface Conductances for Still Air," (ASHRAE Transac t ions , Vol . 70

1964, p.105) deals

with this subject, In this reference, the following surface conductances are

proposed based on the number of room surfaces where outside surfaces are

exposed to outdoor temperatures.

ASHRAE Handbook of Fundamentals , p. 357 (1972).

B-l
Position of Direction of Number of room surfaces exposed

Surface Heat flow 1 2 3 4 5 6

Horizontal Upward 1.43 1.17 1.01 .88 .78 .71

Vertical Horizontal 1.21 .96 .80 .68 .60 .59

Horizontal Downward .57 .37 .28 .22 .19 .16

5

10

15

20

These values were used as a guide in estimating the surface conductance

for different areas of the mobile home. Obviously, in a

furnished mobile home, some adjustments must be made for furnishings which

are considered to be at or near room temperature, and for the heating effect

on floor surfaces of the heating duct. The following surface

conductances were used to calculate predicted heat losses for the

mobile home:

A. Walls (vertical surfaces, heat flow horizontal)

1. Living Room and Kitchen.

Five room surfaces are exposed to the outside. Adjustment

was made for cupboards, furniture, heated floor duct areas.

2 Conductance estimated to be 0.90 Btu/h ft F.

2. Hallway.

Three sides exposed, but interior nonexposed wall is

large compared to exposed floor and ceiling areas.

Conductance estimated to be .96.

3. Rear Bedroom.

Five sides exposed. Adjustment was made for bed, closet

and heated floor duct areas. Conductance estimated to

be 0.90,

25

B-2
4. Bathroom.

Three sides exposed. Adjustment was made for tub alcove,

lavatory cabinet and furnishings. Conductance estimated to

be 1 . 08 .

5. Center Bedroom.

Three sides exposed. Adjustment was made because of bed area.

Conductance estimated to be 1.08.

In order to calculate total heat loss for the mobile home, it was

decided to average the surface resistances based on areas involved

so that one interior surface resistance could be used for all walls.

This was done as follows:

Location % of Total Surface

Wall Area Conductance

1 . Living room and

Kitchen 46 0.90 .41

2 . Hallway 19 .96 .18

3. Rear Bedroom 24 0.90 .22

4. Bathroom b 1.08 .04

5. Center Bedroom 7 1.08 .08

Weighted average = .93

20 R = 1.^7

B. Ceilings (horizontal, heat flow up)

1. Living Room and Kitchen.

Five surfaces exposed. Adjustment made for cupboard and

2

furniture area. Conductance estimated to be .95 Btu/h ft F.

25

B-3
2 . Hallway

Three surfaces exposed. No adjustments. Conductance

estimated to be 1.01,

3. Rear Bedroom.

Five surfaces exposes. Conductance estimated to be .95.

10

15

20

4. Bathroom.

Three surfaces exposed. Adjustments made for limited

exterior wall area and for furnishings. Conductance estimated

to be 1.17.

5. Center Bedroom.

Three sides exposed. Adjustment made for bed area. Conductance

estimated to be 1.17-

Average resistance of ceiling surface

Location

was calculated as follows

% of Total

Ceiling Area

Surface

Conductance

1 . Living room and

kitchen 49 .95 .466

2. Hallway 9 1.01 rH OON

3. Rear bedroom 17 .95 NO OJ

i

—

4. Bathroom 12 1.17 .i4o

5. Center bedroom 13 1.17 .152

Weighted average conductance .= 1.011

R = .99

B-4
5

10

15

20

Floors (horizontal, hdat flow down)

1. Living Room and Kitchen.

Five surfaces exposed. Adjustment made for furnishings

covering floor and for cupboard areas. Conductance estimated

2

to be .22 Btu/h ft F.

2 . Hallway

Three surfaces exposed. No adjustment made. Conductance

estimated to be .28

3. Rear Bedroom.

Five surfaces exposed. Adjustment made for closet area

on one exterior wall. Conductance estimated to be

.22

4. Bathroom.

Three surfaces exposed. Adjustments made for cupboard

area furnishings. Conductance estimated to be .37

5. Center Bedroom.

Three surfaces , Adjustments made for closet area

on one exterior wall. Conductance estimated to be .37-

resistance of floor surface . was calculated as follows:

B-5
5

10

15

20

25

Location % of Total Sur face

Floor Area Conductance

1. Living room and

kitchen 53 .22 .117

11 .28 .031

l4 .22 .031

ik .37 .052

8 .37 .030

.261

R = 3.83

Based on the above calculations , the surface resistances

used to calculate wall. ceiling and floor 'U' factors- were as follows

1. Wall area R = 1.07 h ft F/Btu

2. Ceiling area R = .99

3. Floor area R = 3.83

I

B-6
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 76-1132

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

THE THERMAL PERFORMANCE OF A TWO-BEDROOM MOBILE HOME

5. Publication Date January 1977

6. Performing Organization Code

7. AUTHOR(S)

G. J. Teitsma and B. A. Peavy

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

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

The Federal Energy Administration

1200 Pennsylvania Avenue, N.W.

Washington, D. C. 20461

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

Tests were conducted on a mobile home located in an Environmental Climatic Laboratory

for the purpose of evaluating its thermal performance. The heating demand greatly affected the part-load efficiency of a gas-fired, forced-air, sealed-combustion furnace

system. The practice of installing oversized heating plants was shown to result in

low seasonal operating efficiencies. Air leakage measurements were performed using a pressurization technique to quantify the amount of air leakage through the various parts

of the mobile home. Separate air infiltration tests using the SF^ tracer-gas technique

showed that somewhat higher air infiltration rates were induced by operation of the

mobile home heating plant. A thermographic survey of interior surfaces showed that the

technique used to install the wall insulation may allow wrinkles formed in the surface

of the insulation to form air paths running the height of the wall cavity. Convective

air flow through these paths may create heat leaks on the building surface which can have an impact on the overall heat-loss rate. Separate tests were also conducted to

identify places in the mobile home envelope having high condensation potential.

!

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; energy conservation; mobile home; part-load efficiency; thermography.

18. AVAILABILITY [3 Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

1 For Official Distribution. Do Not Release to NTIS UNCL ASSIFIED

101

1 | Order From Sup. of Doc., U.S. Government Printing Office Washington. D.C. 20402. SD Cat. No. C13

20. SECURITY CLASS

(THIS PAGE)

22. Price

[XI Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151 UNCLASSIFIED

$5.50

U S COMM- D C 29042-P74
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