NATL, INST. OF STAND & TECH R.I.C. NBS

PUBLICATIONS

NBSIR 80-2105

Air Leakage Measurements of an

Unpartitioned Mobile Home

Samuel Silberstein

Building Thermal Performance Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U S. Department of Commerce

Washington, D.C. 20234

August 1 980

-QC—

100

,1156

80-2105

1980

c. 2

Sponsored by

U.S. Department of Energy

1000 Independence Ave., S.W.

Washington, D.C. 20585

NBSIR 80-2105

AIR LEAKAGE MEASUREMENTS OF AN

UNPARTITIONED MOBILE HOME

NATIONAL BUENA l 07 STANDARDS

LIBEAST

OCT 1 0 1980

Db-L O-CC -Cure

Samuel Silberstein

Building Thermal Performance Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

August 1980

Sponsored by

U.S. Department of Energy

1000 Independence Ave., S.W.

Washington, D.C. 20585

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

> Luther H. Hodges, Jr.. Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technology, and Innovation

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Director
f.Q V Al ? t»*

' *
ABSTRACT

Air exchange rates, I(h ), of an unpartitioned mobile home were measured at

various indoor-outdoor temperature differences, aT(K), using SF^ tracer in an environmental chamber, and found to be lower than for conventional buildings but similar to other mobile homes. There was little scatter from the

regression equation I = 0.0182 + 0.0118 |AT|, with relative standard errors

of the first and second coefficients of 62 and 2.5 respectively.

A fan depressurization experiment was a coefficient of C = 1.64 x 10 m/s*Pa^*

of a previously measured mobile home.

Iso performed, and yielded a flow

” , which is also comparable to that

It was further found that:

(1)

For I = 0.24 h" f no SF^ could be ^etected In the environmental chamber

even after five hours, but when I = 9 h for more than five minutes, the

tracer gas method could not be used accurately ’ in the environmental chamber

even with exhaust fans operating;

(2) The standard error is useful for monitoring whether sufficient con- centration measurements were taken at each step;

(3) An air bag sampling technique appeared as good as the conventional

monitoring method for determining infiltration rate;

(4) Reported intercepts of regression equations vary greatly from building

to building, and it may be difficult to analyze the significance;

(5) The possibility that 1=0 h

_1

at AT = 0 K cannot be excluded.

Keywords: Air leakage measurements; environmental chamber; fan pressurization; mobile home; sulfur hexafluoride; tracer gas.

iii
TABLE OF CONTENTS

Page

ABSTRACT i i i

LIST OF TABLES AND FIGURES v

1. INTRODUCTION 1

2. TEST METHODS 1

2.1 Tracer Gas Methods I 2.2 Fan Depressurization 3

3. RESULTS 4

3.1 Infiltration Measurements 4

3.2 Uncertainty of the Air Exchange Rates 4

3.3 Fan Depressurization 5 3.4 The Presence of SFb in the Environmental Chamber 6

4. DISCUSSION 6

ACKNOWLEDGMENT 7

REFERENCES 7

iv
LIST OF TABLES AND FIGURES

Page

TABLES

Table 1. Summary of Infiltration Rate Measurements. 9

Table 2. Correlation Coefficient and Standard Error Monitoring

Corresponding to the Experiment in Figure 6. 10

Table 3. Fan Depressurization Measurements. 11

Table 4. Infiltration Rate Dependence on Temperature and Wind Speed. 12

FIGURES

Figure 1

.

Air Exchange Rate Dependence on Absolute Value of

Outdoor Temperature Difference.

Indoor13

Figure 2. Decay of Tracer Gas Concentration Over Time at an Indoor-Outdoor Temperature Difference of 25.4 K.

Average

14

Figure 3. Decay of Tracer Gas Concentration Over Time at Two Different

Average Indoor-Outdoor Temperature Differences. 15

Figure 4. Decay of Tracer Gas Concentration Over Time at an Indoor-Outdoor Temperature Difference of 19.0 K.

Average

16

Figure 5. Decay of Tracer Gas Concentration Over Time at an Indoor-Outdoor Temperature Difference of 29.1 K.

Average

17

Figure 6. Decay of Tracer Gas Concentration Over Time at an Indoor-Outdoor Temperature Difference of 0.56 K.

Average

18

Figure 7. Decay of Tracer Gas Concentration Over Time with an Open

Window. 19

Figure 8. Dependence of Air Exchange Rate on Outdoor-Indoor

Difference as Measured by Fan Depressurization.

Pressure

20

Figure 9. Decay of Tracer Gas Concentration During Fan Depressurization Test. 21

v
' ;
1 . INTRODUCTION

There are few existing measurements of air leakage characteristics of mobile

homes [1,2] even though such information is important for predicting energy

use, and indoor air pollutant concentrations and their health effects. As

part of an ongoing study of the thermal characteristics of a mobile home,

infiltration rate was measured by tracer gas, and envelope permeability by

fan depressurization. The absence of wind made it possible to accurately

measure the temperature dependence of the air exchange rate in isolation,

and to compare it with that of other structures.

2. TEST METHODS

2.1 TRACER GAS METHODS

Infiltration rates of an unpartitioned mobile home were measured in an environmental chamber at the Center for Building Technology, National Bureau

of Standards, Washington, using the sulfur hexafluoride (SF^) tracer gas technique described elsewhere [3]. The mobile home contains aluminum-backed fiberglass insulation with thermal resistance 1.9 m^*K/W (R-ll) in the walls and

floor and 3.3 m^-K/W (R-19) in the ceiling. The mobile home is 11.989 m long,

2.856 m wide and 2.438 m high, for a total volume of 83.48 nr and a total

surface area of 140.87 m

3 Four cm of SF^, calculated to give an initial concentration of about 50 ppb,

were injected into the mobile home. A fan was run in the mobile home throughout each experiment to mix tracer gas with air. To further ensure adequate

mixing, SF^ monitoring, using an electron capture detector [3]

,

was started

about one-half hour after injection. Sulfur hexafluoride concentration was monitored for at least one hour and infiltration rate was calculated from

the rate of tracer gas dilution:

I = ln(c/c 0 )

( 1 )

where:

I = infiltration rate (h-

*

)

t = time (min)

c = SF^ concentration at time t min

c = SF^ concentration at time 0 min

(c and c

Q are expressed in mutually consistent arbitrary units.)

A pocket calculator was programmed to linearly fit the natural logarithm of

concentration with time (min) by least squares analysis; the infiltration rate

is 60 times the negative of the slope of the regression line, as can be deduced

from equation (1).

Standard errors of the regression coefficients of an equation of the form:

y

= a + bx

1
were calculated [4] by the equations:

u 2 1/2

sa

= RMS (1 + X ) (2a)*

s b = RMS/d/ox)

(2b)*

where

:

s^, ^

= standard errors of a and b respectively

N = number of measurements

RMS =

1 (yjL “ a ~ bxi)

2

) 1 / 2

N

M x

= 1 f x

i

N 1

°x " Ci

J ^

’

»x> 1/2

N 1

The correlation, R

z

, is given by:

2 2 °

2

R

2 = b

2 x ^bms2

(3)

Instruments were located outside of the mobile home (and also outside the

chamber for low chamber temperatures). A small tube was passed out a window

to the detector and the window was sealed with tape to prevent any induced air

leakage. SF^ was injected through the tape and once the experiment began the

If equally spaced intervals are used, then:

s =

1 RMS (= 2N_1/2 RMS)

a h(N+l)

s

b ' (7FTMIm)~

)1/2 MS/4x ( “ (12/n3)1/2

where:

4x = length of each interval

x. = (i-l)Ax, i = 1,..., N

(2a ' )

(2b’)

2
doors remained closed. Lights were kept off during the entire experiment to

prevent heat build-up. An average of six mobile home and twelve chamber

thermocouple readings were monitored at approximately ten-minute intervals

during each experiment.

In addition, air bag samples of the mobile home and environmental chamber were taken for about five minutes, as described by Grot [5], in order to 1) compare

that technique of air exchange rate determination to direct SF^ monitoring, and

(2) detect any SF^ in the chamber.

2.2 FAN DEPRESSURIZATION

A depressurization test was conducted with the fan and duct apparatus as described by Teitsma and Peavy [7]. It consisted essentially of an inline

fan and duct. A commercial pitot-static assembly Was mounted midway in the

duct to monitor flow rate. The outlet end of the duct was sealed into the

doorway using a wooden board, polyethylene film and tape. Pressurization

was not done because of lack of space in the environmental chamber. A

magnehelic gage (range 0.25 in of ^0 (62 Pa)) was used to measure the pressure

drop across the assembly of pitot-static tubes in a duct of cross-sectional

area 0.929 m^ (1 ft^), and a magnehelic gage (range 0.50 in of 1^0 (124 Pa))

was used to measure the indoor-outdoor pressure difference. Each pressure

difference remained nearly constant during any experiment. The flow rate

through the duct was controlled by blocking selected fractions of the fan

outlet area. Fan flow rate was calculated [6] by the equation:

Q

= 1.29A*AP

1/2

g

(4)

where

:

O Q

= flow rate, m /s

A = cross-sectional area of the flow monitor, m^

APg = pitot-static gage pressure difference, Pa

o (When Q is measured in cfm, A in ft ^ and AP in inches of l^O, the constant 1.29

in equation (4) is replaced by 4005.)

An experiment was also done to compare flow rates determined by pressure

difference and tracer gas techniques; the indoor air temperature in the mobile

home remained nearly constant at 20.0°C and the chamber temperature at 17.3°C

during this experiment.

The best fit between Q and AP [6] was obtained for n = 0.48 in the equation:

Q

= CA(AP) n

(5)

where

:

C = flow coefficient (m/s*Pan

) A = surface area (m^)

3
AP = environmental chamber-mobile home pressure difference (Pa) n = flow exponent

C was calculated for n = 0.5, and also for n = 0.65 since n is often

near this value [8],

O A surface area of 138 m was used for the mobile home (after subtracting

3 m

z for the film and tape holding the fan apparatus in place).

3. RESULTS

3.1 INFILTRATION MEASUREMENTS

Measurements were done to relate infiltration rate and indoor-outdoor temperature difference. The data are summarized in Table 1 and displayed graphically

in Fig. 1. Results of detailed experiments done at various indoor-outdoor

temperature differences are shown in Fig. 2 to 6. The regression line in

Fig. 1 was determined by ignoring temperature difference standard deviations, and the data points corresponding to 2.14 and 2.16 K. The temperature

difference error bands of these last two points are much greater than for the

other point in the vicinity, 0.56 K, and the regression line passes through the

boxes containing these points in any case. The fit is excellent, with corre- lation R^ > 0.99. The equation describing the regression line is given by:

I = 0.0182 + 0.0118 | AT | (6)

s a = 0.011 h

-1

s b

= 0.0003 h

_1 /K

where

:

air exchange rate (h~*)

mobile home air temperature (°C)

environmental chamber air temperature (°C)

T in Tout

In the experiment shown in Fig. 2, Grot's air bag method [5] for determining

air exchange rate was compared with direct monitoring of tracer gas. During

this experiment a window was open and a fan operated in the interior of

the mobile home. Air bag samples were taken in the mobile home at about

23 and 89 min. The air exchange rate was calculated to be 0.26 h , or 15% lower than the air exchange rate of 0.306 + 0.014 h” calculated from

the regression line in Fig. 7.

3.2 UNCERTAINTY OF THE AIR EXCHANGE RATES

It was generally found that 4 or 5 concentration measurements at 10 min

intervals sufficed to stabilize the linear regression correlation coefficient

and calculated infiltration rate standard error, or to reduce the relative

error to 10%.

4
The calculated relative standard error and correlation coefficient can be

monitored after each concentration measurement. The former appeared to be a more sensitive measure of dispersion since it frequently continued to decrease

with additional data after the latter had stabilized. Since these measures

serve as predictors of future concentration measurements, the experiment can

be terminated after they reach desired levels or stabilize. Table 2 shows how

these parameters changed during the course of the experiment shown in Fig. 6.

The worst case was chosen for illustration; in another experiment (Fig. 7),

for example, a correlation of 0.99 was achieved by the third measurement.

When the time interval is small, four values should probably be taken

to assure accuracy. The reason the air bag method [5] is capable of yielding

accurate results with only two concentration measurements is probably that

they are taken a long time apart. Equation (2b' ) of the note in the test

methods section suggests that large time intervals can reduce the number

of concentration measurements required to achieve a specified degree of

accuracy.

3.3 FAN DEPRESSURIZATION

Fan depressurization data are listed in Table 3 and plotted in Fig. 8. The

best fit was obtained using either of the relationships:

Q

= 0.0432(AP) 0 * 5 (7a)

or:

I = 1 . 86( AP )°* 5 (7b)

However, if n = 0.65 is assumed, the fit is still excellent except for the

pressure difference measurement corresponding to the lowest flow rate. For

n = 0.65, the equations became:

Q

= 0.02265( AP) 0 * 65

(7a')

or:

1 = 0.9766(AP)0 - 65 (7b')

Thus there is no large disagreement with Shaw and Tamura's suggested flow

exponent of n = 0.65 [8], In order to facilitate comparison, flow coefficients

were calculated by fitting the data of the present paper and from Teitsma and

Peavy [7] to equation (5) with n = 0.65. (The best fit in the latter paper was obtained for n = 0.60.)

Flow coefficients of 1.64 x 10

-

^ and 2.26 x 10

-

^ m/s*Pa^*^ 3

, respectively, were

obtained. They are comparable with Tamura’s [9] calculated flow coefficients of

1.1 x 10 and 4.6 x 10 m/s’Pa^'^ 3 for two single-story houses.

5
3.4 THE PRESENCE OF SF^ IN THE ENVIRONMENTAL CHAMBER

In the experiment shown in Fig. 4 (I = 0.24 h

- ''- ), air bag samples were taken

from the chamber to detect any SF^, but even after 5 hours none was found.

In the experiment described in Fig. 8 and 9, the air exchange rate measured

by tracer gas declined from 28 to 12 h

-

'*' , compared to 16 h” when measured

by Pitot-static flow monitoring at AP = 81.9 Pa, suggesting SF^ accumulation

in the environmental chamber. In another experiment (data not shown) enough

SF^ accumulated after 5 min at an induced air exchange rate of 9 h at 19.7

Pa to make it impossible to use the environmental chamber for tracer gas

measurements

.

4. DISCUSSION

The unpartitioned mobile home appeared to be an extremely tight structure.

Air exchange rates ranged from 0.03 h~* for | AT | = 1 K to 0.4 h ^ for | AT | = 29 K with windows and doors closed, a temperature dependence comparable to

partitioned mobile homes [1,2], an experimental masonry block building [10]

and to other buildings with tightened envelopes [11-13] (Table 4). The mobile

home studied here seems to be typical of mobile homes in envelope tightness,

judging from the limited number of studies. This raises questions about occupant

exposure to air contaminants, most notably formaldehyde [14],

The flow coefficient of the mobile home surfaces of the present report was three quarters that measured by Teitsma and Peavy [7]. The flow exponent giving

the best fit was n = 0.5 but n = 0.65 also gives excellent fit.

Table 4 contains several anomalous results. The mobile home described here seems half as leaky as that described by Hunt et al.[l] at AT = 0 K while it

is twice as sensitive to changes in | AT | . The present mobile home is about as leaky as the experimental masonry building (also an unpartitioned single chamber)

at AT = 0 but about 10 times as sensitive to changes in | AT | [10]. A wooden

house retrofitted to conserve energy seemed to become more leaky at AT = 0 K

and about 17% more sensitive to wind-induced infiltration (which is easily

explainable by experimental error) while becoming half as sensitive to AT-induced

infiltration [11]. A caulked mobile home seemed to be less sensitive to windinduced infiltration and more sensitive to AT-induced infiltration than one

that was covered with continuous sheathing board [2]. While this seeming independence of I , b and c may have physical significance, the work described

here suggests another possible explanation, namely that estimates of I Q are highly uncertain while b is relatively certain. In this report, I and b were estimated to have relative calculated standard errors of 62 and 2.5%

respectively. This predicts that I might be substantially changed by further

data points while b would not.

Unfortunately, statements about uncertainty of the coefficients are rare in

the literature, but if the uncertainties are similar to those reported here,

the apparent anomalies in the relative sizes of I might disappear. The calculated standard errors used here do not depend on errors or variation in

temperature and infiltration rate during each experiment, but only on deviation

6
from linearity. This is because temperature can be precisely controlled and

measured. Wind speed, on the other hand, fluctuates so measurement error

may have to be considered.

The absence of wind in the environmental chamber eliminated much scatter, and

enables one to begin to answer the two related questions: 1) Does I "really"

depend linearly on | AT | ? and 2) Is I Q "really" greater than Oh ? Linearity

has been questioned on theoretical grounds, but rarely has inclusion into the

regression analysis of nonlinear terms improved fit for ordinary temperature

ranges [15]. Use of nonlinear models is summarized in reference 16. This

report suggests adequacy of the linearity assumption concerning | AT | at

least, since a correlation > 0.99 was obtained between the data and the

regression line. Since there was no wind in the environmental chamber,

there is no conflict with Sinden's argument that I is subadditive in | AT

|

and wind speed [17]. The second question cannot be answered conclusively

but I doesn't differ from 0 h~* at the 5% level of significance (calculation

not shown).

Another aspect of infiltration measurements studied was use of air bag sampling

[5]. Infiltration rate measured by that method [5] was in good agreement with

the usual tracer gas technique. The air bag method eliminates the need to

transport and set up heavy equipment and makes possible otherwise impractical

measurements and large numbers of air exchange measurements.

ACKNOWLEDGMENT

The author would like to thank D. A. Didion, D. T. Grimsrud, R. A. Grot,

C. M. Hunt, T. Kusuda, J. H. McAuley, C. Park, S. J. Treado, and D. K. Ward

for their useful technical assistance, discussion, review and support.

REFERENCES

1. C. M. Hunt, S. J. Treado and B. A. Peavy, Air leakage measurements in a mobile home, National Bureau of Standards (U. S.), NBSIR 76-1063 (1976).

2. V. W. Goldschmidt and D. R. Wilhelm, Summertime infiltration rates in

mobile homes, ASHRAE Trans. 85, Part 1, 840-849 (1979).

3. C. M. Hunt and D. M. Burch, Air infiltration measurements in a four-bedroom

townhouse using sulfur hexafluoride as a tracer gas, ASHRAE Trans. 81,

Part 1, 186-201 (1975).

4. P. G. Hoel, S. C. Port and C. J. Stone, Introduction to statistical theory

(Houghton Mifflin Co., Boston, 1971).

5. R. A. Grot, A low-cost method for measuring air infiltration rates in a large sample of dwellings, National Bureau of Standards. (U. S.), NBSIR

79-1728 (1979).

6. Infiltration and natural ventilation, ch. 1 in ASHRAE handbook and

product directory 1977 - fundamentals. (American Society of Heating,

Refrigerating and Air-Conditioning Engineers, Inc., New York, 1977).

7
7. G. J. Teitsma and B. A. Peavy, The thermal performance of a two-bedroom

mobile home, National Bureau of Standards (U. S.), Building Science Series

102 (1978).

8. C. Y. Shaw and G. T. Tamura, The calculation of air infiltration rates

caused by wind and stack action for tall buildings, ASHRAE Trans. 83,

Part 2, 145-158 (1977).

9. G. T. Tamura, The calculation of house infiltration rates, ASHRAE Trans.

85, Part 1, 58-71 (1979).

10. R. J. Clark, P. S. Gujral and D. M. Burch, An evaluation of thermal energy

conservation schemes for an experimental masonry building, in prep.

11. D. M. Burch and C. M. Hunt, Retrofitting an existing wood-frame residence

for energy conservation - an experimental study, National Bureau of Standards (U. S.) Building Science Series 105 (1978).

12. C. W. Coblentz and P. R. Achenbach, Field measurements of air infiltration

in ten electrically heated houses, ASHRAE Trans. 69, 358-365 (1963).

13. J. E. Peterson, Estimating air infiltration into houses, ASHRAE J. 21,

60-62 (1979).

14. I. Andersen, Formaldehyde in the indoor environment - health implications

and the setting of standards, pp. 65-88 in Indoor climate, P. 0. Fanger,

and 0 Valbj^rn, eds. (Danish Building Research Institute, Copenhagen,

1979).

15. C. Sepsy, M. F. McBride, R. S. Blancett and C. D. Jones, Air infiltration, ch. 9 in Fuel utilization in residences, EPR1 EA-894 (Electric

Power Research Institute, Palo Alto, 1978).

16. H. Ross and D. Grimsrud, Air infiltration in buildings: literature survey and proposed research agenda, LBL-W7822 (U. S. Department of Energy,

Washington, 1978).

17. F. W. Sinden, Wind, temperature and natural ventilation - theoretical

considerations, Energy and Buildings 1, 275-280 (1978).

8
Table 1. Summary of Infiltration Rate Measurements

Fig. T.in (a),°C Tout (a),°C AT (a), K I (Sj ), h" 1

b 19.3 (0.02) 18.9 (0.01) 0.56 (0.02) 0.0265 (0.0051)

3 13.8 (1.6) 15.9 (2.6) -2.14 (1.85) 0.0308 (0.0026)

2 25.4 (0.3) 23.3 (1.1) 2.16 (1.35) 0.0571 (0.0060)

3 26.2 (0.5) 13.7 (0.4) 12.56 (0.85) 0.164 (0.004)

4 18.0 (0.9) -1.0 (0.3) 19.03 (0.9) 0.241 (0.003)

5 17.7 (0.1) -11.4 (0.1) 29.14 (0.15) 0.363 (0.005)

9
Table 2 Correlation Coefficient and Standard Error Monitoring

Corresponding to the Experiment in Fig. 6

Measurement

Air exchange^ rate. Correlation

coefficient, R^

Relative calculated

standard error, S^/I

1

2 0.0153 ( ) — —

3 0.0126 (0.0136) 0.221 1.08

4 0.0159 (0.0058) 0.652 0.365

5 0.0334 (0.0073) 0.807 0.219

6 0.0233 (0.0072) 0.636 0.309

7 0.0219 (0.056) 0.690 0.254

8 0.0265 (0.0051) 0.768 0.194

f

10
Table 3. Fan Depressurization Measurements

Condition Q 1 AP|

m'Vs cfm Pa in H^i

fan totally covered 0.224 474 24.1 0.100

•• 3/4 0.378 800 81.9 0.329

•• 3/4 0.383 811 80.1 0.322

•• 1/2 0.447 948 107.5 0.432

•• uncovered 0.482 1021 123.2 0.495

11
Table 4. Infiltration Rate Dependence on Temperature and Wind Speed

I = I 0 + b | AT | + cV

where V = wind speed (m/s)

Building b(h~ 1 /K) c(h ^/m» s

^

) Reference

unpartitioned mobile home 0.018 0.012 * present

partitioned mobile home 0.036 0.006 * 1

partitioned mobile homes: 2

caulking** -0.00835** 0.0103 0.036

continuous sheathing board** 0.0159 0.0065 0.0172

experimental masonry block* 0.016 0.0009 * 10

wood frame: pre-retrofit 0.11 0.018 0.044 11

post-retrofit 0.22 0.009 0.051

10 electrically heated 0.25 0.015 0.048 12

.. •• ++ tightly constructed 0.10 0.011 0.027 13

it } ~f "loosely constructed" 0.10 0.022 0.067 13

* No wind in the NBS environmental chamber

** In the original paper the relation given was I = 0.0635 + 0.0103 | AT | + 0.018 + 1.53 x 10_^ AT*V for the first mobile home and I = 0.0503 + 0.0065 | AT | + 0.0086 V + 0.89 x 10 AT*V^ for the second. For comparability, the coefficients in the table were computed

by neglecting the AT*v terms and minimizing the difference between the expression in the

original paper and one linear in V for V = 2 m/s. The small negative value of I Q

for the

first home is an artifact of this procedure.

Winter only; in original paper the second order relationship, I = 0.017 + 0.0005 | AT

|

+ 0.00001 | AT

|

was derived, but a linear fit was recomputed here.

+

Typical values.

12
| A TEMPERATURE | (K)

Figure 1 . Air exchange rate dependence on absolute value of indoor-outdoor

temperature difference. (Data are summarized in Table 1.) The

width of the box around each point is two calculated standard deviation units (a^); the height is two calculated standard error units

(Sj). The dashed lines represent the solid regression line modified

by adding (top) and subtracting (bottom) one calculated error unit

to each coefficient of the regression equation.

13
SF$

CONCENTRATION

(arbitrary

units)

0 30 60 90 120 150 160 210

TIME (min)

Figure 2. Decay of tracer gas concentration over time at an average indooroutdoor temperature difference of 25.4 k.

14
SFg

CONCENTRATION

(arbitrary

units)

0 5 tO IS 20 2S 30

TIME |b)

Figure 3. Decay of tracer gas concentration over time. An electric heater in

the mobile home was on during the first 3.85 h and the doors between

the environmental chamber and outdoor buildings were open until 23.85

h had elapsed. Mobile home-environmental chamber temperature difference remained relatively constant during the time intervals indicated

by orackets.

15
SFg

CONCENTRATION

(arbitrary

units |

TIME (min)

figure 4. Decay of tracer gas concentration over time at an average indooroutdoor temperature difference of 19.0 K. Air bags taken in the

environmental chamber at the times indicated by arrows showed no

bt'k present.

16
SFg

CONCENTRATION

(arbitrary

units)

Figure j Decay of tracer gas concentration over time at an averag

outdoor temperature difference of 2y.l K.

indoor17
SFg

CONCENTRATION

(arbitrary

units)

90

1

1 1 1 1

89 -

70 -

60 1= 0.0265 ±0 .005b-

-

50

•

w -

Tin =1 9.46 ± 0.02°C

Tottrio.H± o.orc

40 AT=0.5S±0.020

'

30 l l i I l 0 15 30 45 60 75 90

TIMEImii)

Figure 6. Decay of tracer gas concentration over time at an average indooroutdoor temperature difference of 0.5b K.

18
SF

6

CONCENTRATIONIarbitrary

units)

igure 7. Decay of tracer gas concentration over time with an open window.

Air bag samples were taken in the mobile home at the times indicated by arrows

.

19
Figure 8

•UTDOOR-MDOOR PRESSURE DIFFERENCE (in H 20)

11 Il2 13 1.4 1.5

OUTDOOR MOOOR PRESSURE DIFFERENCE (Pa)

Dependence of air exchange rate on outdoor-indoor pressure difference as measured by fan depressurization. (Data are summarized in

Table 3.)

20
igure Decay of tracer gas concentration during fan depressurization test.

21
«b>l I4A (REV. B-781

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 80-21Q5

4. TITLE AND SUBTITLE

AIR LEAKAGE MEASUREMENTS OF AN UNPARTITIONED MOBILE HOME

5. Publication Date August 1980

7. AUTHOR(S)

Samuel Silberstein

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

8. Performing Organ. Report No. NBSIR 80-2105

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, state, ZIP)

U. S. Department of Energy

1000 Independence Ave., S. W.

Washington, D. C. 20585

13. Type of Report & Period Covered Final

15. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or leaa factual aummary of moat significant information. If document includes a aignificant bibliography or

literature survey, mention It here.) Air exchange rates, I(h

-

^), of an unpartitioned mobile home were measured at various

indoor-outdoor temperature differences, AT(K), using SF^ tracer in an environmental

chamber, and found to be lower than for conventional buildings but similar to other

mobile homes. There was little scatter from the regression equation I = 0.0182 +

0.0118 | AT |

,

with relative standard errors of the first and second coefficients of 62

and 2.5%, respectively.

A fan depressurization experiment was also performed, and yielded a flow coefficient

C = 1.64 x 10 m/s*Pa°* , which is also comparable to that of a previously measured

lie home. It was further found that:

T7 „ _ T O/. l-“ 1 nr, 1J . 1 1 -

of

mobile

(1) For I = 0.24 h

x

, no SF^ could be detected in the environmental chamber even after

five hours, but when I = 9 h" for more than five minutes, the tracer gas method could

not be used accurately in the environmental chamber even with exhaust fans operating;

(2) The standard error is useful for monitoring whether sufficient concentration measur ments were taken at each step;

(3) An air bag sampling technique appeared as good as the conventional monitoring method

for determining infiltration rate;

(4) Reported intercepts of regression equations vary greatly from building to building,

and it may be difficult to analyze the significance;

(5) The possibility that I = 0 h at AT = 0 K cannot be excluded.

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 leakage measurements; environmental chamber; fan depressurization; mobile home;

sulfur hexafluoride; tracer gas

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20402, SD Stock No. SN003-003-

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VA. 22161

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