NATIONAL BUREAU OF STANDARDS REPORT

23 36

VENTILATION MEASUREMENTS

(Project No. ME-14)

by

C r W. Coblentz

M. A. Barron

P. R. Achenbach

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

. /
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing of

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-20-1014 April 3, 1953 2336

VENTILATION MEASUREMENTS

(Project No. ME-14)

by

C. W. Coblentz

A. Barron

P. R. Achenbach

to

Office of the Administrator

Housing and Home Finance Agency

Washington, D. C.

The publication, reprii Approved for public release by the pa,t ' ,s P rohlbl,ed

unless permission not Director of the National Institute of iards ' Washln e'°" 25.D.C. Such pern,, Standards and Technology (NIST)

" h3S b68n Sp0Clfi ’

cally prepared If thal _ , _ _

' ,rt for Its own use, on October 9, 2015.

Ventilation Measurement

ABSTRACT

A study was made at the National Bureau of Standards

of the methods for measuring the infiltration of air

into buildings and the natural ventilation of cr&Wl

spaces and attics. This research was performed under

an agreement with the Office of the Administrator,

Housing and Home Finance Agency, authorized under

Title III of the Housing Act of 194$, as amended,

and was identified as Project No. 1950-ME-14 "Ventilation Measurement".

It was found that several tracer gas methods are available for infiltration measurement and that these methods

are probably more accurate and better adapted to field

use than calorimetric methods or direct air flow measurements. The more promising tracer gas methods are believed to be (a) helium gas with a katharometer , (b)

ethane gas with an interferometer, (c) methane gas with

an infrared gas analyzer. The use of either a radioactive gas with an electrometer or a halogenated hydrocarbon gas with a halide photometer is believed to be

potentially practical but these methods involve some

hazard to the personnel using them.

The heated thermocouple anemometer was found to be better

suited to the measurement of very low air velocities in

ducts and rooms such as those associated with natural

ventilation of crawl spaces and attics than any other

known instrument. A heated thermocouple anemometer and

a portable helium katharometer developed at the National

Bureau of Standards are described and their performance

illustrated. Studies were made to determine the accuracy

and lag of a commercially-made helium analyzer in measuring the absolute helium content in air and to determine

the effects of pressure and sampling rate on the performance of the instrument. Infiltration measurements made

simultaneously with the portable helium katharometer developed at the National Bureau of Standards and a commercially-made katharometer differed by amounts ranging

from 0 to 4 percent.
2

A detailed study of the air exchange between the various

parts of an experimental house and the outside as affected by temperature differences revealed that there was

two-way flow between the basement and outside and between

the living space and outside and one-way flow from attic

to outside. In addition there was air movement from basement to living space, from basement to attic, and from living space to attic. All of these air exchanges were interdependent and most of them tended to increase as the indoor

outdoor temperature difference increased. This experimental house fyas enclosed in a larger structure and was not exposed to natural wind.

Some data are reported on the natural ventilation of a

basement through foundation openings and by means of a

vertical stack reaching from the basement through the

roof.

This investigation reveals broad possibilities for further study of air movement into buildings and through

buildings which would probably lead to revised construction for the purpose of better control of the air flow,

vapor flow, and heat loss of dwellings and other structures .

I. INTRODUCTION

The computation of the heat loss of a building usually includes an item for the heat carried out of the building as a result of the infiltration of cold air. The computation of the infiltration heat loss is generally based on the length of crack

around windows and doors, an estimate of the workmanship involved,

and a design wind velocity or it is based on a more general estimate of the number of complete air changes that will occur in the

building per hour under design weather conditions. These methods

are known to be approximations, but they have received wide usage

because accurate measurements of the air leakage for different

kinds of structures are not available. Unknown heat losses such

as that for infiltration have caused engineers to resort to the

use of safety factors in the selection of heating plapt capacity.

Little is known about the actual infiltration rates in existing buildings or how well the actual values compare with the

values computed by the previously mentioned methods because there

has been no generally accepted method of proved accuracy for measuring the infiltration rate in buildings.
- 3 -

The ventilation of attics and crawl spaces has likewise been

based on empirical rules developed by trial and error and improved

by experience because the amount of ventilation provided by any

given arrangement could not readily be determined.

Attic and crawl space construction could be better protected

against condensation and deterioration if ventilation rates could

be more accurately evaluated for different arrangements of louvers,

openings, etc. Greater precision in selecting heating equipment

for houses could be attained if infiltration rates were accurately known and there would be a probable saving of materials and

fuels and a greater assurance of comfort for the owner.

— u The present project was established to investigate various

methods of measuring infiltration in buildings and to study methods

for measuring the natural ventilation occurring in attics and crawl

spaces with certain duct and louver arrangements. The course of

the investigation was guided by the availabilities of suitable instruments for the measurements that were to be made and by the results that were observed as the investigation progressed. The

kathometer used for the major portion of the infiltration measurements was loaned to the National Bureau of Standards by the American Society of Heating and Ventilating Engineers. Early investigation also showed that precise measurements of crawl space ventilation could not be made until an instrument for measurement of

very low air velocities was available so a heated thermocouple

anemometer was designed and constructed.

The work done under this project can be divided into five

parts as follows:

1. Survey of Infiltration Measurement Methods

2. Infiltration Measurements with a Cambridge Katharometer

and an Interferometer

3. Design of a Portable Katharometer

4. Measurements of Crawl Space Ventilation

5. Design and Calibration of a Heated-Thermocouple

Anemometer
- 4 -

II. SURVEY OF INFILTRATION MEASUREMENT METHODS

The following nine methods for measuring infiltration rates

were either tried or investigated sufficiently to evaluate their

practicability;

a. Helium or hydrogen gas with a katharometer

b. Ethane gas with an interferometer

c. Radioactive tracer gas (ethane) with an electrometer

d. Hydrogen gas with RCA Detector tube

4 e. Hydrocarbon gas with an infrared gas analyzer

f. Hydrocarbon gas with a sensitive hygrometer to

sense changes in the moisture content of samples

after combustion of the hydrocarbon gas.

g. Halogenated hydrocarbon gas with a photometer.

h. Calorimetric determination based on the amount of

additional heat required to heat the Test Bungalow

with infiltration as compared to that required with

no infiltration for equal temperature differences

between indoors and outdoors.

i. Determination on an equivalent crack or orifice

?irea by pressurizing the living space with an

auxiliary blower and measuring the air flow and

the pressure difference between indoors and outdoors .

The first two methods listed involving the use of a katharometer and an interferometer were tried and these methods will

be discussed in detail later.

The use of a radioactive tracer gas^ appeared to be practical,

at first. Radioactive carbon has such a long half-life that it

could be considered to be a constant source of electrons for the

duration of tests such as these. Ethane gas with radioactive

carbon molecules was obtainable through the Atomic Energy Commission; ethane having a' density and diffusion rate closely approximating that of air. An electrometer with sufficient sensi-

'tivity to measure electron flow rates equivalent to 10-^5

amperes was available as a recently-developed item of one manufacturer. However, calculation of the concentration of radioactive gas that would be required to produce a measurable current with this electrometer indicated that the radioactivity
- 5 -

level would be higher than could be tolerated safety by human

beings . Thus all of the observations would have to be made by

remote control and the test space would remain contaminated for

some time after any given test. This method might prove to be a

practical one, however, if an instrument were developed that would

measure lower current levels than presently available electrometers

are designed for so the test space could safely be occupied by the

observers.

A hydrogen detector tube with a paladium window for the detection of hydrogen gas in air was investigated for its usefulness

in infiltration studies. It was found, however, that this detector

apparatus was designed primarily to detect and locate leaks in

vacuum tubes using hydrogen gas, and does not provide a quantitative measurement of the tracer gas.

A commercially made gas analyzer is available for the detection and measurement of carbon dioxide, carbon monoxide, methane,

or other hydrocarbon gases in air based on the principle of the

absorption of energy in the infrared region by these gases. The

instrument uses a source of infrared energy, reflecting mirrors,

sampling cells, and two bolometers as two elements in a Wheatstone

bridge circuit. The amount of infrared energy absorbed from the

original beam is a measure of the concentration of the tracer gas

in the sample. The instrument is equipped with a recorder and is

used for control and recording of gas concentration in various

industrial processes.

It can be made sensitive to concentrations of less than one

percent for full scale deflection and provides a printed record

of the change in concentration of tracer gas with time. The

analyzer is a self-contained cabinet-type unit equipped with a

sampling system suited to the application. It appears to be wellsuited to the purpose of infiltration measurements except for its

high original cost; the selling price being approximately four

thousand dollars.

2

A film of phosphoric acid or sulfuric acid is sensitive to

small changes in the water vapor content of air or other gases.

The relative humidity of air can be measured by obtaining equal

indications of moisture content for a sample of air with unknown

moisture content and a sample of oxygen under pressure with

known moisture content by passing them over a phosphoric acid

film on a suitable electrode. This type of hygrometer could be

used in conjunction with hydrogen or a hydrocarbon tracer gas

for measuring infiltration rates. The mixture of air and tracer

gas would be sampled and the tracer gas burned by means of a hot

wire element after which the moisture content of the resulting

gases could be determined by means of the phosphoric acid hygrometer. The concentration of tracer gas could be computed
- 6 -

from the relative humidity data. Measurements of relative

humidity of the air in the building would also have to be made

without combustion of the tracer gas so corrections could be

made in the results obtained from the combustion of the tracer

gas. This method has some, but not all, of the disadvantages

of using water vapor directly as the tracer gas in that most

atmospheres have some water vapor in them; the exchange of

water vapor between the materials in a building' and the air

inside the building probably seldom attains a steady state,

and the presence of observers or other moisture-generating

sources might disturb the water vapor content of any building

under observation.

A portable instrument is commercially available to measure

low concentrations of halogenated hydrocarbons in air. The

principle of operation of this apparatus is as follows:

The intensity of the blue lines of the copper spectrum,

produced in an electric arc between two electrodes, is continuously measured with an electric photometer using a blue

sensitive phototube fitted with a blue glass color filter.

Halide vapor coming in contacts with the electrodes reacts to

form a copper halide, which is carried into the arc. The intensity of the blue spectrum is proportional to the concentration of halide vapor present.

Although a full scale deflection of the indicating meter

is said to be obtained at a concentration of less than 0.1$

of carbon tetrachloride in air, the accuracy of the instrument

is only ±10$. Because of its limited accuracy and the possible

hazards to personnel working continuously in an atmosphere with

halogenated compounds, this method of tracer gas detection was

considered impractical.

The possibility of making a calorimetric measurement of

the heat loss attributable to infiltration and from that a

derived value of the quantity of air leakage was investigated.

This method would involve the measurement of the heat required

by the Test Bungalow for a given temperature difference with

no infiltration and a comparative value of the heat loss under

identical conditions except that infiltration would be permitted.

It was proposed that the inside surface of the entire living

space would be sprayed with one or more coats of vinal chloride

acetate or polyethylene material that would reduce the air leakage and vapor transmission to a negligible value. These materials

could be peeled off readily when the tests were completed without permanent damage to the interior finish of the structure.
- 7 -

While evaluation of the heat loss due to infiltration

might be possible by this method the following practical difficulties indicated that it was not the most promising method:

(a) It would be difficult to seal all cracks and fissures in

the structure especially those in the hollow studs space

that permitted air leakage directly from the basement to

the attic, but which removed heat from the living space

by transmission through the wall surfaces.

(b) The method could not be applied to existing structures

in the field.

(c) Since more heat would be required when infiltration did

exist, it would be difficult, if not impossible, to attain the same temperature distribution in the building

for the two cases. Consequently, a comparison of heat

requirements for the two cases would probably not be devoid of all influences other than infiltration.

It had been postulated that an equivalent crack or orifice

area could be established for any room or building by pressurizing the space with an auxiliary blower that would assure leakage

in one direction through all the openings in the enclosing surfaces. By measuring the air delivery of the blower with a suitable orifice and determining the indoor-outdoor pressure difference with a sensitive micro-manometer an equivalent aggregate

area of leakage could be computed from the orifice formula,

«* uW

rate of air delivery by blower, cu ft/ min

indoor-outdoor pressure difference, in W.G.

density of air, lb/cu ft

equivalent area of all leaks, sq ft

combination of the orifice constant and several

conversion factors for the system of units employed

-"However, it appears that no practical use could be made of

the equivalent area A after evaluating it because the pressures

causing flow through a building are a combination of wind pressure

and chimney effects such that (a) the crack area serving as inlets

and outlets for leakage would often be unequal (b) the neutral

pressure zone in a building may shift up and down with outdoor

temperature, and (c) the wind pressure causes primarily horizontal air motion through a building whereas the chimney effect produces primarily vertical movement of air through tire- building.

where Q

= h =

d = A = K =
- a -

III. INFILTRATION MEASUREMENTS WITH A CAMBRIDGE

. KATHAROMETER AND AN INTERFEROMETER

A*. Description of Ethane - Interferometer Method

Ethane has favorable characteristics as a tracer gas for

air infiltration measurements because both its density and

diffusion rate are very nearly equal to that of air. An interferometer provides a simple way to determine low concentrations

of ethane in air 0 An interferometer divides a beam of light into two or

more parts that travel optical paths of different lengths and

which are later recombined to form interference fringes. The

optical length of path depends not only on the geometric length

of path but also the refracture index of the materials through

which the light beams pass. The dispersion of the interference

fringes produced by passing two light beams through gases with

different refractive indices can be measured by adjusting the

relative angularity of identical plane-parallel plates of optical glass placed in the paths of the two beams to compensate

for the dispersion. The changes in position of the optical

plates can be used to evaluate the difference in refractive

index of the two gases.

The instrument available at the National Bureau of Standards

for making decay measurements With ethane gas was a portable

interferometer ‘with two 10 cm. chambers through which the airethane mixture in the room and the outside air could be passed.

Because of the relatively short length of the chambers in this

instrument the displacement of the fringes was small when comparing the refractive index of air and an air-ethane mixture

containing Tes^ than 1 percent ethane. As a result only small

adjustments of the optical plates were necessary for realigning

the interference fringes and the accuracy was limited. A more

elaborate instrument with longer chambers would have provided

greater precision in measurement. The portable interferometer

was used as a check method for comparison with the katharometer

in studying infiltration of air in the north bedroom of the

Test Bungalow.

B. Description of Helium Katharometer

The measurement of low concentrations of hydrogen or helium

in air can be accomplished easily and with a high degree of accuracy by virtue of the difference in thermal conductivity3 of

these gases and that of air. The thermal conductivity of hydrogen is approximately 7 times that of air whereas the thermal
- 9 -

conductivity of heliugi is about six times that of air. A

tracer gas tecjinique^ > 5 for studying the infiltration of air

in buildings was first described by Marley using a katharom£

eter® (a thermal conductivity meter) to evaluate the concentration of the tracer gas in air. An instrument of this type

manufactured by the Cambridge Instrument Company for use with

helium as a tracer gas was purchased by the American Society

of Heating and Ventilating Engineers and loaned to the National Bureau' of Standards for studies of infiltration in the Test

Bungalow. This instrument was equipped with three separate

thermal conductivity cells so three samples of helium-air

mixture could be drawn simultaneously for concentration determinations. A photograph of the Cambridge helium analyzer

is shown in Fig. 1.

Each of these thermal conductivity cells contained two

platinum wires that were heated by a constant electric current.

The wires were installed in two cavities drilled in a single

brass block so that their wall temperatures would always be

equal. The wire temperature reaches a steady value when the

heat generated by the electric current is equal to that dissipated by the wire to its surroundings. One cavity was closed

at both ends and the tracer gas-air mixture to be analyzed

was passed through the other cavity. Since the thermal conductivity of helium is roughly six times that of air, the wire

in the sampler cavity was cooled more than the wire in the

reference cavity. This cooling lowered the electrical resistance of the platinum wire. The two wires formed two legs of

a Wheatstone bridge circuit and this change in resistance caused

a bridge unbalance. The unbalance was indicated on a galvanometer calibrated directly in percent of helium in air. The

instrument was equipped with a motor-driven vacuum pump to draw

the helium-air mixture through the sampling cavity and these

samples were bubbled through three inches of water. The samples

were bubbled through water because the amount of water vapor in

air has a considerable effect upon its thermal conductivity.

With this arrangement, the thermal conductivity of the air in

the sealed cavity serving as a reference cell was compared with

the thermal conductivity of the helium-air mixture drawn through

water and brought -1 to a constant relative humidity approximating

saturation

.

A selector switch allowed any one of the three units to be

connected to the galvanometer, which was calibrated from zero

to lo6% He and three samples could be measured in quick

succession.
10

C. Performance Characteristics of the Cambridge Katharometer

A calibration of the Cambridge helium analyzer was made to determine how accurately it indicated the absolute volumetric concentration of helium in a mixture with air. This was done by preparing known concentrations of helium in air in glass flasks with a water seal. Several samples of each concentration were made and

passed through the instrument for separate determinations. The

results of this calibration, plotted in Fig. 2, show the average

correction factor as a ratio of the actual concentration to the

instrument reading. Fig. 2 shows considerable scattering of the

individual observations for a given helium concentration. A correction factor curve has been drawn for each of the two cells

used although it is recognized that the plotted observations do

not define any precise line. The third cell of the instrument

had become inoperative and was returned to the factory for repair.

The effect of scattering upon the correction factors determined for actual concentrations of 1 . 50

4

% and 0 . 633 % is shown in

the following table which gives the number of measurements made

with each cell of the apparatus and the maximum, minimum, and mean

values for the correction factors.

Actual No. of Obser- Correction Factors Determined

Concen- vations Made Maximum Minimum Mean

tration Cell 1 Cell 2 Cell 1 Cell 2 Cell 1 Cell 2 Cell-1 C.ell 2

0.633 6 7 1.149 1.100 1.083 1.056 1.117 1.081

1.504 4 4 1.098 1.052 1.086 1.048 1.092 1.051

It will be noticed in this table that the maximum deviation of

the values determined for the correction factop at an actual concentration of 0 . 633 % was 0.066 for the first cell and 0.044 for the

second cell, whereas for an actual concentration of 1.504% the

corresponding deviations were only 0.012 and 0.004.

The scattering of the points in Fig. 2 for separate determinations at the same concentration is believed to have been caused

principally by the drift of the zero position of the indicator over

a period of time. The change in the zero position of the indicator

varied as much as 1-1/2 scale divisions, 0.030% helium, over a */:

‘ period of seven hours. One and a half scale divisions corresponds to an error of 2% at 1.5% meter reading, 5% at 0.6% meter

reading, and 15% at 0.2% meter reading. The drift of the zero

point appeared to depend in part on whether or not a steady state

of heat flow existed between the platinum wire heating elements

in the cells and the enclosing brass block although this did not

appear to be the only determining factor. When gas flow was initiated through the cells after having the heating elements ener-


ao^oe^ uot3.oa.iJOD

Actual

Goncentratlon

, %

He

11 -

gized without gas flow overnight, the zero position changed

about one scale division for each cell during the first hour

of operation,, During the next six hours the zero position on

cell Noo 2 changed an additional half scale division in the

same direction whereas the zero position on cell No. 1 changed

a half scale division in the opposite direction.

A horizontal correction factor curve such as that shown

in Fig. 2 for cell No. 1 would cause no error in infiltration

measurements based on changes in concentration of helium with

time assuming that the error due to scattering was not present.

A correction factor curve with the slope shown for cell No. 2

in Fig. 2 would cause infiltration computations to be about

4 percent too high if no corrections were made to the observed

values and there was no error due to scattering. However,

the data in Fig. 2 suggest that the error resulting from the

variations in indicated values at any given concentration could

be greater than that resulting from the average change in correction factor from one end of the scale to the other.

Errors in reading the curved indicator scale caused by

parallax are considered to be of the order of one-fourth scale

division or 0.005% helium. Thus, parallax could cause a 2-1/2

percent error in the reading for a concentration of 0.2% helium.

The lag of the Cambridge device was determined by alternately introducing a helium-air mixture from a 6-gallon can and

pure air into two of the test cells and averaging the readings

taken during five such cycles. The results of these tests with

only 3 ft of tubing between the can and apparatus are shown in

Fig. 3, whereas Fig. 4 shows the results for a similar test with

a sampling line consisting of 30 ft of l/4-in. copper tubing.

It will be noticed that a near balance is reached after 3*5

minutes with the 3 ft sampling line, whereas with a 30 ft line

a balance of the indicator required about 5 minutes.

Some measurements were made to determine the effect of the

sampling rate on the indication of the Cambridge instrument.

It was found that no appreciable change of the indicator reading was noticeable if the sampling rate remained within the

range from 100 to 170 cc/min. However, flow rates below

100 cc/min caused erroneous results. There was no quantitative flow rate indicator on the Cambridge instrument, but an

operator with some experience could determine from the bubbling

rate in the saturators when the flow rate was normal. The instrument was found to be practically insensitive to atmospheric

pressure fluctuations or pressure differences that may arise

from long sampling lines. A test showed that a change in pressure at the inlet of the instrument from 36 in. W. G. pressure

to 36 in. Wo Go vacuum increased the indicator reading by only

0.02% of helium at the middle of the scale.
- 12

The characteristics of the Cambridge katharometer described above indicate that the following precautions should

be taken during use to minimize errors in the results:

(1) Gas should be drawn through the cells for at least

an hour before any measurements are taken,

(2) Helium concentrations in the range from 0,4 to 1.4

percent should preferably be used to reduce the importance of

the error caused by drift in the lower end of the scale and

parallax at the two ends of the scale.

(3) The rate of gas flow through the bubblers should be

noted to ascertain that it is normal and constant.

(4) The shortest possible sampling lines should be used

and appropriate consideration given to the lag of the instrument at the beginning of a test.

(5) Numerous readings of concentration should be taken

during any test so the errors caused by drift and parallax for

a given observation would not be of such great significance.

D. Pilot Installation

A pilot installation was made in the north bedroom of the

Test Bungalow to study the possibility of stratification of the

tracer gas in the room and to furnish information on the best

.arrangement of the gas supply and sampling systems for the entire building.

Seven stations were chosen in the north bedroom to furnish

data on stratification of the helium gas. These stations were

near the ceiling, near the floor, midway between ceiling and

floor and in upper and lower corners of the room at locations

considered most likely to reveal stratification if it occurred.

One-quarter inch copper tubing was run from each of these stations through the wall of the room and into the south bedroom

where the helium analyzer was placed. Flexible tubing was used

at one statidn so that, in conjunction with a pulley arrangement, it could be made to scan the wall from floor to ceiling

choosing any point for sampling. An additional copper line

was installed in the north bedroom to introduce the helium into

the room. This line was also used as a sampling line during

the test. By returning the helium-air mixture to the test, room

after passing it through the analyzer it was not necessary to

compensate for this volume of air in the infiltration calculations. Later it was determined that the samplers only extracted about one cu. ft. of mixture per hour and this was below

the precision of the infiltration measurements. The tracer
PERCENT

HELIUM

TIME (MINUTES)

3

2

.1

0

9

8

7

6

5

.4

.3

,2

.1

TIME (MINUTES)
[f[
- 13 -

gas was taken from compressed-gas cylinders and metered through

an orifice meter 0 A 12 TT propeller type fan was operated in the

room for approximately one minute after the tracer gas had been

introduced to completely mix the air and helium gas. The compressed-gas cylinder and orifice meter are visible at the right

of Figo lo

Tests were made with this pilot installation using both the

helium-katharometer and the ethane-interferometer methods. In

each case an initial tracer-gas concentration of approximately

one percent was used. When internal and external conditions of

the test room remained constant during a test the rate of fresh

air leakage would be expected to remain constant with time. On

this premise the graph of the volume of air infiltration versus

time should be a straight line passing through the origin. Consequently, it should be possible to obtain a reasonably accurate value for the air change rate, from the slope of the line

with only a few measurements.

The following formula was used to calculate the air change

rate from the observed decay of the tracer gas.

c = concentration of the tracer gas at time t

c 0

= initial concentration of the tracer gas at t = o

R = K = number of air changes per unit of time

V

K = volume of air infiltration per unit of time

V = volume of room

Equation (1) is obtained by integrating the following expression for the rate of loss of tracer gas per unit of time:

Figures 5 and 6 show the results of infiltration tests in

the north bedroom with the room closed and with no indoor-outdoor

temperature difference using helium and ethane as the tracer gas,

respectively. The results obtained by the two methods during

separate tests under the same conditions agree quite closely

during the first five and a half hours when observations were

made at half-hour intervals. Based on the first 5 1/2 hours of

c = c 0 e -Rt

( 1 ) where

( 2 )
- 14 -

the test the infiltration rate was 0.129 air changes per hour

as measured with the katharometer and 0.125 air changes per

hour as measured with the interferometer. The - observations

taken with the two instruments on the day following the start

of the test after an elapsed time of 22 hours do not agree

satisfactorily. The results obtained with the katharometer

is that which would be expected if the rate of infiltration

remained constant throughout the test. The result obtained

with the interferometer after 22 hours was much lower. Since

a period of about 16 hours elapsed, during which the test

structure was unattended, between the first group of observations and the single observation taken on the next day, it is

not certain that cooling of the structure or entrance by some

other person did not change the infiltration into the test room.

The interferometer used for those tests had only 14 scale

divisions for maximum deflection whereas the scale on the

katharometer had $0 divisions for a full scale reading. Consequently, the precision of any observation with the interferometer was of a lower order than for the other instrument

and it was especially difficult to read correctly at low interference ratios. For example, if the observed deflection after

22 hours had been read as 3 scale divisions instead of 4 in

Fig. 6, the percent decay would have been 7$«6 and the air

changes 2.2 instead of 1.26. Under these conditions the agreement between the two methods after 22 hours would have been

reasonably good. However, for tests of shorter duration the

two instruments corroborated each other in the determination

of infiltration rates. Because of its greater sensitivity the

katharometer was used for all observations of infiltration after

this initial comparison. An interferometer with a longer light

path could be used to attain greater sensitivity than that of

the instrument used for this comparison.

Studies were made to determine whether or not stratification of the tracer gas occurred in the north bedroom as air infiltration progressed in order to assist in the design of an

adequate sampling system for the entire Test Bungalow. Fig. 7

shows the results of a test made with no difference in temperature between indoors and outdoors, no air circulation outdoors,

and with the door and windows of the room closed. A fan in the

attic was used to exchange air between the outdoors and the

Test Bungalow enclosure by means of the chimney to prevent buildup of the helium concentration in the enclosure. Observations

of the helium concentration were made -near the floor, near the

ceiling, and at the 3-foot level for 77 minutes without agitation of the air in the room. Fig. 7 shows that the tracer gas

concentrations corresponded to leakage rates of 1.#, 0.3$, and

0.5 air changes per hour for the first hour at the floor level,

3-foot level, and ceiling level, respectively. This stratification of helium in the room was attributed to the inward leak-


OT\ng®

i

«

<

c

« TIME (hours)

AIRCHANGES

AT

DIFFERENT

ELEVATIONS

DUE

TO

STRATIFICATION

OF

HELIUM.

S30NVHD HIV

CO

TIME

in

Minute

- 15

age of fresh air in the lower part of the room and outward leakage of contaminated air in the upper part of the room to the attic

The attic fan reduced the pressure in the attic about 0.01 in.

Wo G„ This pattern of air infiltration would result in more rapid

dilution of the helium gas in the lower part of the room than near

the ceiling. This conclusion was supported by a test which reveal

ed no stratification of helium in air in a closed vessel as a result of the lower density of helium after the air and helium were

initially well-mixed.

When a desk fan was turned on after 77 minutes of observations under still air conditions, the concentration at the ceiling decreased and that at the floor level increased until both

stations indicated concentrations equal to that at the three-foot

level after the fan had been operating about 15 minutes. The results. in Fig. 7 indicate that -for this particular. building the

concentration at the 3-foot level represented an average for the

entire room under conditions that produced stratification of the

tracer gas. The difference in infiltration rates shown in Figs.

and 6 as compared to Fig. 7 when there was no indoor-outdoor

temperature difference in either case, was accounted for by the

operation of the fan in the attic.

Subsequent tests revealed that no measurable stratification

occurred when heat was being supplied to the test room. This is

probably accounted for by the mixing action caused by the con**

vection from the heater and the downdrafts near the cold walls

of the room.

Preliminary tests in the north bedroom with indoor-outdoor

temperature differences of 1$°F and 20°F showed that the infiltration increased markedl}?- with increase in temperature difference. The results shown in Figs. $ and 9 can be compared with

those in Figs. 5 and 6 to indicate that the infiltration with a 20 degree temperature difference was about five times as great

as for the condition with no temperature difference between indoors and outdoors.

Figs. 10 and 11 show the infiltration observed in the north

bedroom with no temperature difference between indoors and outdoors when a window was opened 3/$-inch from the bottom and from

the top, respectively. In each case a desk fan was used to keep

the air and helium gas

1

' mixed during the test. The tests indicated an infiltration rate of 0.45 air change per hour with the

window opened from the bottom and 0.52 air change per hour with

the window opened from the top.

In comparing the -inf iltration indicated in Figs. 10 and 11

with partially open windows with that indicated in Figs. 5 and 6

for a closed room, it should be pointed out that a desk fan was

in steady operation in the north bedroom during the tests with
- 16 -

the open windows whereas the fan was not in operation during

the other tests. Investigation showed that the infiltration

rate was approximately doubled by the operation of the desk

fan inside the north bedroom for otherwise identical conditions.

If it is assumed that the observed infiltration rates in Figs.

5 and 6 would have been doubled by the operation of a desk fan,

it is concluded that the infiltration rate was about twice as

great with a window opened 3/$-inch from top or bottom as for a

closed room with no indoor-outdoor temperature difference.

E. Infiltration Measurements in a Whole House

After completing the preliminary investigation of infiltration in the north bedroom a series of tests was planned

using the entire house. Based on the results obtained in the

north bedroom a single sampling tube was installed in each room

to withdraw gas samples 3 feet above the floor. This precaution

may have been unnecessary inasmuch as it was found that no

measurable stratification occurred in the north bedroom when it

was heated.

Fig. 12 is a schematic drawing of the manifold installed in

the south bedroom, which remained the instrument center, so

samples could be taken from any part of the house. The sampling

tubes also served as a distribution system for introducing helium

into the five rooms of the house. The compressor shown in Fig. 12

purged the lines of helium after feeding was completed so the

katharometer would not be subjected to extremely high concentrations at the start of a test. Sufficient experience was obtained

during the first few tests to regulate the desired concentration

of tracer gas by controlling the length of time that the valve

on the helium cylinder was open. The use of the orifice flow

meter was then discontinued. The introduction of helium was done

with all interior doors open and four fans running at appropriate places to mix the helium with the air in all the rooms. In

this way all the rooms had approximately the same concentration

of helium at the beginning of the test.

The general procedure for a test was as follows: Signs

were placed outside the refrigerated enclosure requesting visitors not to enter because entrance, even into the enclosure,

caused pressure changes that would disrupt the steady state conditions. All windows in the house were closed and locked and ' the external doors closed. The fans inside the house were turned

on and operated throughout the feeding time and the time required

to purge the lines of helium. Then the inside doors were all

closed so the air change rate of each room could be measured individually. (It was later found that the overall air change rate

of the house was the same with the inside doors open or closed.)

The helium analyzer was turned on and readings commenced. Samples

of gas were drawn from any three stations for five minutes, then


AIR

CHANGES



HARO.MET.ER

A/INDOW 0

R. CHANGES

.05

ij

p

E 04

.03

FIG. I

NT OF. NOR'

UM TEST M

'RTH BED ROOM

THOD

3/8 FROM T 0

TIME (minutes)

ATTIC

SHELL K, LpN^R

SCHEMATIC

DIAGRAM

OF

HELIUM

ANALYSER

INSTALLATION

- 17 -

from three other stations „ The five-minute interval was used

because experiment had shown that it took that long for the

thermal conductivity cell to become responsive to the helium

concentration at a given station,, During the five minutes the

galvanometer needle was moving slowly up or down the scale adjusting itself to the new sample. The tests lasted, in general,

about one hour or until the concentrations were too low to give

accurate readings. A disadvantage of the analyzer was found to

be the curved face on the galvanometer and the absence of a parallax compensator, so readings below 0.2 % and above 1.4%

were considered to be less precise than those in the center of

the scale when the air change rate curves were drawn.

It was planned to determine the air change rate of the

Test Bungalow for a range of indoor-outdoor temperature differences so a test was made to find its infiltration with no temperature difference and no wind. Fig. 13 shows the results of this

test. Fig. 14 represents the air change rate with no temperature difference but with the refrigeration blowers running and

creating the equivalent of approximately a two mile per hour

wind. This was actually the average air motion around the house

in a circular pattern in a vertical plane and was constant for

all tests since the blowers were operated at constant speed.

All of the remaining tests were made with the blowers running.

In Figs. 13 and 14 the air change rate is reported as a

weighted average, which was arrived at in the following manner:

Since the rooms were of different sizes, it would not be correct

to merely calculate the air change rate of each room and average

the rates of the individual rooms because the small rooms would

affect the average air change rate of the entire house disproportionately under such a procedure. Therefore, the air change

rate of each room was multiplied by its fractional part of the

entire volume of the house. The sum of these products was called the "weighted air change rate" of the house and is indicated

by a dotted line in Fig. ]_3o

It will be noted in Figs. 13 and 14 that some of the curves

showing the relationship between air infiltration and time are not

straight lines whereas in Figs. 5, 6, 3, 9, 10, and 11 this relationship is best represented by a straight line. Later observations led to the conclusion that the curvature of the air leakage

lines obtained from these early tests using all rooms of the

house was probably caused by inadequate mixing of the helium and

air or inadequate purging of the sampling lines after using them

to introduce helium into the rooms.

Before additional infiltration measurements were made it was

found desirable to modify the basic air change rate formula (1)

discussed earlier in this report. It was observed during the tests

of the entire Test Bungalow that the concentration of helium in the

enclosure increased enough, due to leakage of the contaminated air
- id -

from the house, to affect the results in the house. Because

the air infiltrating into the house was not pure air, but air

with helium in it, formula (1) no longer described the conditions of the test. Since the enclosure surrounding the house

had a volume of only about 5 times that of the living quarters

of the house the concentrations of helium in the enclosure sometimes reached 0 . 25$. Bor this reason the following formula was

derived to represent the actual conditions that prevailed.

If C]_ = helium concentration in the house at time t]_, $

c 2 =

tt rr tr tt ft tr rt t2j j

C]. = " " " "enclosure" " t lf %

C 2 =

tt rt tr tt tt tt ” t 2 , $

v = volume of the living space, cu. ft.

V = volume of the enclosure, basement and attic, u.ft.

M = total helium in the system, cu. ft.

K = infiltration rate into house, cu. ft /hr

then V <*P- = -K (c - C) (3)

dt

M = v c + V C (4)

These formulae could have been combined and integrated, if

M were a constant, and then solved for K. However, the enclosure

had an air change rate with the outside atmosphere £s high as 0.15

air changes per hour. Thus M was not a constant and the equation

cannot be integrated.

Since the interval between readings of the helium concentration in the enclosure was expected to be ten minutes, the change

in helium concentration in the enclosure would be very small during that interval. If the concentration of helium in the enclo*-

sure is considered to be constant between consecutive readings

ten minutes apart eouation (3) can be integrated and the definite

integral used to evaluate K, the infiltration rate of the living

space, for any short interval with very little error.
S39NVH0 UIV

TIME

(minu

tes)

TIME

(minutes)

- 19

Integrating equation (3)

log (c - C) = “ Kt

V

or loS j gl ~ Cl =5 (t 2

- t x

) c; 2 - C 2

Where ~ (t 2 - t]_) = infiltration from time tq to time t

2

and ' C 1

" C 1 = e f

d2 - C 2

where t 2 and tq are the times corresponding to two consecutive

observations of the helium concentration,, Equation (5) can be

solved for values of K, which is the number of air changes per

V

hour based on observations taken at ten-minute intervals more

or less® By computing the logarithmic mean value of Cq and C 2 , the concentration in the enclosure, during the time interval

under consideration from katharometer measurements, the computed

values of K would be quite accurate for short time intervals

.

V

This method of calculation was used for all subsequent tests

.

At first, observations of helium concentration were taken

in all five rooms and the infiltration rate for each room computed individually as described previously for the weighted

average method „ However, it was noted that the average of the

concentrations in the north bedroom, living room and bathroom

was, in almost every case, very close to the average of the five

rooms so measurements were made only in these rooms and sampling

stations were added in the attic and bAsemeftt„ All the rooms

were still contaminated with helium so the exchange of air between rooms would result in representative concentrations in the

three sample rooms as before and give true indications of the

total air changes,, Under this procedure the actual concentrations, in percent helium, of the north bedroom, living room,

and bathroom at each time interval, were averaged and then computed for air change rate in the manner just described using

equation (5)» The results of this simple method checked well

with those of the more elaborate method,, For example, Fig„ 15

shows the .infiltration computed for each of the five rooms based

on a single sampling station in each room and also the weighted

average of the five rooms as a dotted line c The infiltration

rates for the north bedroom, living room,: and bath were 0„55,

0 o £6, and 0„69 air change per hour, respectively, resulting in

a three-room average of 0 o 70 o This three-room average is very

close to the weighted average of 0„71 for the five rooms.
20

The results of a number of infiltration tests in the Test

Bungalow for a range of indoor-outdoor temperature differences

are plotted in Fig. 16 to 13, inclusive. Duplicate tests are

plotted on Fig. lo, 17, and 13 for indoor-outdoor temperature

differences of 20°F, 55°F, and 70°F, respectively, in addition

to other test data. The observations for each test are quite

consistent and all lie very close to a straight line. A single

curve represents the infiltration for each test because the infiltration rates for the north bedroom, living room and bath

were averaged to obtain a weighted average in accordance with

the procedure described above. It will be noted in Figs. 16 to

13 that the infiltration rates during duplicate tests were very

consistent in some cases and deviated by as much as 10 percent

in other cases. Some of the inconsistencies can be traced directly to differences in the basement temperature during comparable tests. The effect of basement temperature on infiltration will be discussed in more detail later. The relation of

air change rate in the living quarters to indoor-outdoor temperature difference is also summarized in Table 1.

Table 1

AIR CHANGE RATES IN THE LIVING QUARTERS FOR

A RANGE OF INDOOR-OUTDOOR TEMPERATURE DIFFERENCE

INDOOR-OUTDOOR TEMPERATURE DIFFERENCE

0°F 20°F . 33°F\ 55*F 70°F 35°F 90°F

AIR CHANGES PER HOUR

.2 45 . 500 .792 1.15 1.31 1.60 1.64

.230 .540 ,730 1.05 1.19 1.62

F. Infiltration in Basement, Attic, and Living Space

It is generally accepted that the infiltration into a building caused by the difference of the indoor and outdoor temperak

tures is the result of the chimney effect. In a closed building

with the ordinary amount of air leaks suitably distributed, a

neutral zone exists at about midheight when the building is

heated above the outdoor temperature. At the neutral zone the

internal and external pressures are equal. Below the neutral

zone a negative pressure exists in the building and air will

leak inward whereas above the neutral zone the internal pressure

is positive and the air leakage will be outward. Pressure

measurements in the Test Bungalow with a sensitive differential
)

'

S39NVH0 yiV

TIME

(minutes)

!

TIME

(minutes)

S39NVH0 UIV

TIME

(minutes)

S39NVH0 dlV

TIME

(minutes)

21

manometer showed that this neutral zone existed somewhere between floor and ceiling of the living quarters for certain test

conditions. Based on these pressure measurements it was .as- sumed that air exchange took place in both directions between

the basement and the Bungalow enclosure and that there was no

infiltration from the enclosure to the attic when the attic

louvers were closed, but only exfiltration from the attic to

the enclosure.

With these assumptions the air movement between enclosure;,

basement, living space, and attic was determined by the following procedure:

(a) ' The basement was contaminated with helium and the rate

of air flow from the enclosure into the basement was

determined ,

(b) The attic was contaminated and its exfiltration to the

enclosure was determined,

(c) The living space was contaminated and its total exfiltration to attic and enclosure measured.

(d) The increasing concentration of helium in the attic during

step (c) was observed. The infiltration rate of the attic

from the living space was computed taking into account the

measured exfiltration from attic to enclosure.

(e) The difference between the attic exfiltration determined

from step (b) and its infiltration from the living space

is its infiltration from the basement.

(f) The decreasing concentration of helium in the living space

during step (c) was observed. The rate of air movement

from basement to living space was computed from the decrease in helium in the living space, the known total air

motion from living space to attic and enclosure and the

mean concentration of helium in the basement and enclosure

during the test.

(g) The difference between the total infiltration into the basement measured in step (a) and the sum of the air exchange

from basement to attic determined in step (e) and the air

exchange from basement to living space determined in step (f)

is the exfiltration from basement to enclosure.

(h) The difference between the infiltration from basement to

living space determined in step (f) and the total exfiltration from the living space measured in step (c) is the

infiltration from enclosure to living space.
22

(i) The difference between the total exfiltration from the living space determined in step (c) and the exfiltration from

the living space to the attic determined in step (d) is the

exfiltration from the living space t© the enclosure.

If BE = the air flow from the basement to enclosure i » BL = the air flow from the basement to living space

BA = the air flow from the basement to attic

EB = the air flow- from the enclosure to basement

LA = the air flow from the living space to attic

LE = the air flow from the living space to enclosure

EL = the air flow from the enclosure to living space

AE = the air flow from the attic to enclosure

Kp = log mean average of concentration in living space

during test

= log mean average of concentration in attic during test

= concentration in attic at start of test

= concentration in attic at end of test

Vj[ = volume of attic

KE = log mean average of concentration in enclosure during test

Kg = log mean average of concentration in basement during test

Kp = concentration in living space at start of test

Kp = concentration in living space at end of test

Vp = volume of living space

then 1. BL + BA + BE = EB

2. LA + LE = BL + EL

3 o BA + LA = AE

4. EL + EB = AE + LE + BE

5
- 23

Formula 5 is derived from the fact that the helium present in

the attic at the start of the test plus that 'flowing into the

attic during the test must equal the helium present in the attic at the end of the test plus that which leaked into the enclosure during the test. That is,

KAVA

+ Kl x LA = K>a

+ Ka x AE

Formula 6 is derived from the fact that the helium present in the

living space at the start of the test plus that flowing into it

from the basement and enclosure during the test must equal the

helium in the living ^pace at the end of the test plus that flowing from it to the enclosure and attic during the test. That is,

VlK^ + BL x Kb + EL x Ke

= V

lk£ + (LE + LA)KL

The quantities EB, AE, .and LA + LE can be determined by conducting infiltration tests of the basement, attic, and living

quarters, respectively and

kl , ka , ka , ka , kb , k

e , k", kI

will be known by observing concentrations inthe attic, basement,

enclosure, and living space during these tests. There will re«

main six unknowns in the above six equations which can readily

be determined by computation.

Infiltration tests were made of the attic, basement and living space at various indoor-outdoor temperature differences so

the patterns of air movement could be determined. These tests revealed the aforementioned inconsistency in the original tests of

the living space. It was found that small changes in the basement temperature, when the temperature difference between living

space and enclosure was constant, had considerable effect on the

air change rate of the basement which in turn affected the air

change rate of the living space. Since the basement temperatures

were not too carefully regulated during the original tests of the

living space there were some variations in results for duplicate

tests as shown in Figs. 16 to 1$.

Figs. 19, 20, and 21 show the air change rate vs. temperature

difference curves for the house, basement, and attic, respectively.

These curves are based on actual infiltration tests and form the

basis for the calculations of the air flow patterns in the entire

structure. It is noted that the variation of infiltration in the

living space and attic with temperature difference between indoors

and outdoors is linear whereas the basement infiltration is proportional to a power of the temperature difference greater than
- 24 -

one. The relation between infiltration and temperature difference

could not readily be predicted because the chimney effect of the

entire structure depends on the temperature differences between

enclosure and basement and between enclosure and attic as well as

that between the enclosure and living space.

Figs. 22, 23, and 24 are graphical representations of the

air flow to and from the living space, to and from the basement,

and to and from the attic, respectively, for a range of temperature difference between living space and enclosure from 20 to 90

degrees F. The upper curve in each figure r is plotted from direct

measurements made with the katharometer . The other curves in each

figure are derived from the relationships in the six simultaneous

equations shown earlier.

All of the infiltration curves show consistent trends with

variation of indoor-outdoor temperature difference except curves

F and H in Fig. 22 and curves F and © in Fig. 23 . All of these

four curves depend on the evaluation of equation 6 of the group

of simultaneous equations and involve several measurements of

helium concentration in the basement, living space, and enclosure

during a given test. It is believed that the results plotted for

these curves at a temperature difference of 55°F are in error and

that there -.should not be a radical change of curvature at this

temperature difference.

The air exchange rates that involved measurements in the basement are not considered as accurate as the other results because

considerable equipment was stored in the basement. This condition

made the basement volume somewhat indeterminate and hindered good

mixing of the helium and fresh air initially and during the progress of the tests. More reliable data could be obtained in the

basement, if it were empty.’

The leakage indicated from basement to attic presumably occurred through the hollow stud spaces in the walls without entering the living space. Filling the stud spaces with insulation

would close this path of air flow.

It is not knbwn whether or not the air movements between the

enclosure, basement, living space, and attic that are shown in

Figs. 22, 23, and 24 are typical for frame houses of similar construction. The Test Bungalow had a plastered ceiling and was

finished with gypsum wallboard with nailing strips at the joints

of the wall surfaces at the time of these tests. It is probable

that there were some cracks for air leakage between the stud

spaces and the living space. A number of openings had been made

through the double wood floor for tests of heating equipment

prior to the infiltration tests, but these were carefully rebuilt,

sealed with building paper between sub-flooring and finish flooring and caulked at the edges before starting the infiltration

tests

.
TEMP. DIFF. ( ° F ) LIVfNG SPACE TO ENCLOSURE

Pc

H Pg

e

tP>

e

rPo

P

u

NFILT SUREMENTS OF TEST BUNGALOW

D1FFELREN C£

T E M P. DIF F. (° F ) LIVING SPACE TO ENCLOSURE

8

.6

.4

2

.0

8

6

C

.4

2

0

TEMP. DIFF. (°F)

LIVING SPACE TO ENCLOSURE

TEMP.

DIFFERENCE

(°F)

LIVING

SPACE

TO

ENCLOSURE

TEMP.

DIFFERENCE

(

°F)

L

I

VING

SPACE

TO

ENCLOSURE

000! xHH/£ \.d 39NVH0X3 dIV

TEMP.

DIFFERENCE

(°F)

LIVING

SPACE

TO

ENCLOSURE

- 25 -

G. Effects of the Opening of the Attic Louvers

During all the tests previously discussed in this report the

louvers of the attic were packed with insulation to prevent air

circulation., The Test Bungalow was normally kept in this condition for tests of heating equipment. However, since attic ventilation is often recommended for winter conditions a short series

of tests was made, for comparison, with the attic louvers open.

Figs. 25 and 26 show the results for two of these tests. A comparison of these results with those summarized in Table 1 indicates that opening the attic louvers increased the infiltration

in the living space from 30 to 35 percent. The infiltration was

also increased in the basement, and of course, the ventilation in

the attic was very much higher when the louvers were open than

when they were closed.

H. Door Tests

Tests were also made to determine the amount of air infiltration when a person opens and closes an interior door to enter a room or an exterior door to enter a house. An opening time of 4

seconds and an opening width of 28 inches were found to be representative values, and these values were used in the following

tests. There was no temperature difference between the spaces

connected by the doors for these tests.

After mixing the room air with about 0.5$ of helium a series

of concentration measurements was made. The door was then opened

and closed as described above ten times at one minute intervals

to obtain a significant change of concentration in the room. Before continuing with the concentration measurements it was necessary to thorughly mix the infiltrated air in the room with the

helium-air mixture by operating a circulating fan in the room for

30 seconds, after which another series of concentration measurements was made. Previous tests had shown that the infiltration

rate of a room was appreciably increased by a forced air movement

in the room. Therefore, the fan was operated again for another

30 seconds with the door closed before taking a third series of

concentration measurements to evaluate the effect of the fan operation. The air changes were then calculated and plotted against

time. As the three groups of measurements were taken with the

doors and windows of the room in the same condition the air change

rate should have been constant, i.e., the air change curves should

be straight and parallel lines. The vertical distances between

pairs of curves were a measure of the air changes caused by the

door openings and fan operation. Fig. 27 shows the test results

obtained when opening the interior door between the north bedroom

and the hall of the Test Bungalow without heating or forced air

circulation around the building. Tests were made under the same
- 26 -

conditions with the outside doors of the living room and the

kitchen and the following values were obtained for the air infiltration for one opening of the door in each case.

Room Door Size, in. Infiltration, cu ft

North bedroom

Living room

Kitchen

30 x 73

36 x 73

30 x 73

17.4

36.5

32.4

It is probable that the observed value of air infiltration

for each door opening was a little lower than the actual value

because of rebreathing during every opening of the door after the

first. That is, with no forced air motion either inside or outside the room near the door, the air would be contaminated with

helium on the outside and the room air-helium mixture near the

door on the inside would have a helium concentration lower than

the room average after the first few door openings. Consequently,

the air entering the room would not be pure and the air leaving

the room would not be representative of the average in the room.

Although there was no temperature-difference between outdoors and

living space during these tests, it would be expected that the

basement caused some chimney effect and that this chimney effect

would cause greater infiltration through an outside door than was

observed for an interior door.

I. Effect of an Open but Unheated Fireplace

Two tests were made to determine the effect of an open; fireplace flue on the infiltration rate of the Test Bungalow. The

flue of the fireplace was generally kept closed with a steel plate

during all tests. When this plate was removed the air change rate

of the living space with all inside doors kept open and with an

outside temperature of 32°F increased from 0.73 to 1.99 per hour,

i.e. by 1.21 air changes per hour. With a house volume of 4,900

cu. ft, this means that the volume of air removed from the house

through the unheated fireplace flue every hour approximated 6,000

cu ft.

IV. DESIGN OF A PORTABLE KATHAR0METER

The Cambridge helium indicator appeared to be quite satisfactory for measurement of infiltration in the Test Bungalow. However,

the lag in response of the instrument was some disadvantage in attempting to observe the helium concentration at a number of stations. This lag was related to and dependent in part upon the

length of the sampling lines. It was also observed by trial that

the instrument was too cumbersome and heavy for field use.
EH

O0 Oj

S3SNVH0 HIV

IME

(MINUTES)

rh::.f

S3DNVH0 HIV

TIME

(MINUTES)
I
i4-

. o S30NVHD HIV

TIME

IN

MINUTES

- 27 -

Consideration of the operating principle of the helium katharometer led to the conclusion that a simpler portable instrument

could be designed using the same principle, but depending on

natural convection rather than a vacuum pump for sampling the airtracer-gas mixture. Such an instrument was designed, constructed,

and preliminary tests completed. A photograph of the pilot instrument is shown in Fig. 2&.

The helium indicator designed at the National Bureau of Standards was comprised of a portable amplifier the size of a small

table radio and a sensitive cell consisting of a metal block with

two cylindrical cavities in which thermistors were installed. The

thermistors were arranged in a Wheatstone bridge circuit with the

two reference resistors placed in the metering box which could be

connected to the cell by a cable of any desired length. For testing, the cell was placed in the room whose infiltration was to be

determined and the operator with the metering box could be in close

proximity or outside the building.

One thermistor cavity was continuously ventilated by a natural convection air movement resulting from the heated thermistor

and passing through small holes at the top and at the bottom of

the cavity. The other thermistor cavity was tightly sealed during the test after having been opened before the tracer gas was

introduced into the room to assure that the tracer gas itself was

the only difference between the air in the two cavities. The

equality of the air temperature in the cavities was assured by the

enclosing metal block.

The thermistors were heated with alternating current and the

bridge circuit was balanced before tracer gas was introduced into

the room. The off-balance potential, resulting from the presence

of tracer gas in only one cavity, was electronically amplified.

The output current of the amplifier was adjusted to be directly

proportional to the concentration of the tracer gas. An amplifier

gain control made it possible to read either the absolute tracer

gas concentration, to provide a full scale deflection for any

helium concentration between 0 . 1+% and 1 , 5 % or to observe the concentrations of any other tracer gas having similar thermal conductivity that is convenient for the particular study to be undertaken. By adding a selector switch to the metering box of the instrument, any number of test cells could be used thus permitting

as many observation' "stations during one test as desired.

Several comparison tests were made using the new instrument

and the Cambridge helium indicator in the Test Bungalow. Figs. 29

and 30 show comparisons between the airchanges calculated from

decay measurements made at the same time in the same space with

the two analyzers. These curves show substantial agreement

between the two instruments for infiltration rates of 1.1 and 2.

A

airchanges per hour. There was some small scattering of the

points for both instruments but the data indicate a straight line
- 28 -

infiltration rate for each. The same line best represents the

data for both instruments in Fig. 29 whereas in Fig. 30 the

best line for each set of points indicates a difference in infiltration rate of about 4 percent, the Cambridge instrument indicating the higher value. The low initial concentration of 0.24$

used for the test represented by Fig. 30 was probably disadvantageous to the Cambridge instrument because of parallax and drift

errors in reading the lower end of the scale.

When considering the results in Fig. 29 and 30 along with

the correction factors determined for the Cambridge instrument

and shown in Fig. 2, it is concluded that the NBS katharometer

indicated infiltration rates that were higher than the true

values by amounts ranging from 0 to 4 percent. FThe NBS instrument was not graduated in percent helium so a calibration of

this instrument in terms of absolute concentrations could not

be made.

In preparing for the comparison of the performance of the

two helium indicators the following test procedure was used.

Helium gas was fed into the North Bedroom of the Test Bungalow for a period of one minute during which the air and helium

were being mixed by means of a 16-inch desk fan. This mixing

continued for one pinute after ceasing to inject helium gas into

the room. Separate', -copper tubes were used for injecting the

helium gas into the room and for sampling the mixture, since

earlier tests revealed some difficulties in purging the helium

from such a line promptly after injection.

Following the one-minute injection period the gas mixture

was drawn through the sampling lines for 5 minutes before any

observations were taken. At the end of this 5-minute period

the indicator on the Cambridge instrument had reached the maximum, and it was at this time that the decay measurements commenced as shown in Figs. "29 and 30.

The thermal conductivity cell of the NBS instrument was in

the room to be investigated all during the above procedures with

the ports to the sampling cylinder’ open' 'to the atmosphere in the

room. The zero point on the time scale for the NBS instrument

was the same clock time as for the other instrument in Figs. 29

and 30. The concentrations observed at zero time on both instruments were considered 100$ concentration for comparison with

later readings on the same instrument. Thus, the curves shown

on the attached figures really represent rates of dilution relative to the concentration that existed at zero time. It is

probable that the absolute concentrations of helium in the thermal

conductivity cells of the two instruments were actually a little

different at the zero point on the time scale.
FIG.

23

COMPARISON

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8 83utfqo **TV

Time,

minutes

- 29 -

V. MEASUREMENTS OF CRAWL SPACE VENTILATION

A. Ventilation through Foundation Louvers

Prior to the investigation of infiltration by means of a tracer gas and the katharometer a study was made of several

methods of ventilating crawl spaces for dwellings. It is generally accepted that the crawl space of houses should be ventilated during the summer in most parts of the United States east

of the Mississippi River where high humidity occurs during the

summer to minimize condensation and rot of floor and foundation

constructions. The usual method used is to provide openings in

the foundation wall on all or several sides of a house so

natural convection and wind forces can ventilate the space

under the floor. However, very little is known about how much

air exchange occurs through such foundation louvers, probably

because instruments for measurement of very low air velocities

have not been available.

Tests were made to determine the amount of ventilation provided for a crawl space beneath a house by openings in the

foundation walls. The Test Bungalow was used for this purpose

and observations were made with still air surrounding the house

and with the blowers of the refrigerating units circulating approximately 20,000 cfok around the structure. Observations were

taken for outdoor temperatures of 0°F, 50°F :and #5°F with the

indoor temperature being maintained at about 70°F in the living

space. The area of the foundation ventilators was determined

by the following formula: Area = 2 sq ft per 100 linear feet

of perimeter plus 1/300 of the crawl space area. For the Test

Bungalow the formula indicated a total of 4.17 so ft of ventilator area.

For the tests six of the panes were removed from the basement windows; two each on the east and south exposures and one

each on the north and west exposures. The total area of the six

openings was 4. OS sq ft. Metal ducts about two feet in length

were installed in the openings to streamline the air flow somewhat and facilitate air velocity measurements. For these tests

all of the visible cracks and openings in the floor construction

were sealed and all visible cracks in the subfloor duct system

of the warm air heating plant were sealed to minimize air exchange between the basement and living space. Observations of

air velocity were made with a pitot tube and differential manometer when the blowers were in operation whereas the rate of air

motion was determined by timing the travel of visible smoke in

the metal ducts through the foundation for the still air condition around the house. ‘The latter method was not considered

to be very precise but was used because the delivery of the commercial thermocouple-anemometer ordered for this purpose was delayed several times. The results of these observations are

shbwn in Table 2.
- 30 -

The data in Table 2 show that air flowed into the basement

through a part of the openings and out through others when the

blowers were in operation, but the net flow was inward for all

three outdoor temperatures tried. The amount of air flowing

into the basement and out again ranged from 300 to 400 cfm whereas the amount that entered the basement through the foundation

ventilators and then passed upward through the floor ranged from

£6 to 244 cfm. The results indicate that the natural chimney

effect of the house assisted the flow of air upward through the

house construction because the net inward flow increased as the

outdoor temperature decreased. Test 3 indicates that the blowers

used for circulating air around the Test Bungalow created a lower

pressure at the roof than at the basement level. With the outdoor temperature higher than the temperature of either the living space or the basement as in Test 3 the chimney effect of the

house should have been reversed and the net flow of ventilating

air should have been from basement to enclosure instead of vice

versa. This result was observed in Tests 9-11 when the blowers

were not running. It is apparent that the blowers counteracted

the chimney effect and produced an upward flow through the floor

of 36 cfm. A comparison between Test 1 in Table 2 and tests with

the katharometer for the same indoor-outdoor temperature difference shows that the net air leakage into the basement and up

through the house was about twice as great with the foundation

ventilators open as when they were closed.

For still air conditions around the house as in Tests 4-11

of Table 2 the chimney effect of the house predominated and the

direction of flow of air between basement and outdoors was determined by 'the relation between the temperature indoors and the

outside temperature. As the outside' temperature was lowered from' 5CPF

to 0°F the net inward flow of outside air to the basement increased from 111 cfm to 366 cfm. For three tests with the outside air 10 to 15 degrees F warmer than the living space the net

flow of air from the basement to outside ranged from 119 cfm to

152 cfm. If the Test Bungalow were assumed to have a crawl space

two feet high the rates of air exchange reported for still air

conditions would range from one air change in eleven minutes for

Test 3 to one air change in 3.4 minutes for' Test 5.

An apparent inconsistency is indicated by a comparison of

the net flow of air into the basement in Test 1 with that observed for Tests 4 and 5. This comparison shows greater ventilation with still air than with forced air circulation around

the bungalow for the same outdoor temperature. This would appear to contradict the indication in Test 3 that the blower opertion provided an upward air movement through the structure in opposition to the chimney effect. It is quite probable that air
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- 31 -

entered the basement from the enclosure through cracks and

fissures as well as through the foundation ventilators and

that the effective area of such cracks and fissures was not

the same for the conditions of natural and forced circulation.

The measurements in still air are not considered precise

within ±20 percent because of the extremely low air velocities

and because flow occurred in both directions simultaneously in

the same duct in some cases. Ventilation measurements made'

with a katharometer would probably be more accurate provided

the tracer gas could be kept adeouately mixed and the response

of the cell were fast enough.

In a typical occupied house under still air conditions

the air entering the crawl space would come predominantly from

the living space when the outside air was warmer than the living space and it would come predominantly from outside when the

outside air was colder than the living space. In an actual

house in the summer time the direction of air movement would

probably reverse at least twice in twenty-four hours under still

air conditions due to the change in relation of indoor and outdoor temperatures. During the late hours of darkness and the

early forenoon the outside air would often be cooler than the

indoor air so the air motion would be upward through the house

and the outdoor air would enter the crawl space. The air at

this time would have the lowest moisture content and would have

a drying effect in the crawl space. During the afternoon and

evening hours the outside air would often be warmer than the

indoor air so the air motion would be downward through the house

and air from the living space would leak into the crawl space.

The air at this time would probably have its highest moisture

content which would tend to add moisture to the crawl space.

B. Ventilation by an Unheated 6-in. Vertical Duct

The ventilation of the basement achieved by a 6-in. vertical duct extending from the basement to a level about one foot

above the roof was measured for several different conditions.

The vertical duct had a cross section area of 0.196 sq ft and a

total length of 17.54 ft. It had been suggested that such a ver

tical stack in a house might be used to ventilate a crawl space

through openings in the floor and thus avoid the need for founda

tion ventilators. Advantages claimed for such an arrangement

were that the annoyance of closing the foundation louvers in the

winter time and opening them in the summer time would be avoided

or the chilling effect on the floor in the winter that resulted

from leaving the foundation louvers open all the year around

would be avoided.
- 32 -

For this test the basement windows and basement door were

sealed and all visible cracks at the sill of the house were caulked. A 6 by 14 inch register that connected the basement and living space in each room was left open. For some of the tests the

attic was heated to simulate solar effects on the roof.

The results observed with no heat in the 6-in. vertical duct

are summarized in Table 3. Tests 1-3 show that the air flow rate

up the duct ranged from $ to 14 cfm when the temperature in the

living space was from 12 to 16 degrees warmer than the outdoors.

The higher rate was observed when the attic was heated to a tem-

'perature 40 to 45 degrees F higher than the outdoors to simulate

solar effects. When the indoor and outdoor temperatures were

about equal as for Tests 4 and 7, the quantity of air flowing in

the vertical stack was very small, sometimes changed direction,

and sometimes was too small to be measured. Heating the attic to

temperatures ranging from 11$°F to 12£°F as in Tests 5 and 6

created enough chimney effect in the duct to cause an air flow

rate of about 5 cfm with no temperature difference between living

space and outdoors. Table 3 shows that the movement of air"

through the floor registers was predominantly upward even though

the basement was sealed at all noticeable cracks.

C. Ventilation by a Heated 6-in. Vertical Stack

The ventilation provided in the basement of the Test Bungalow by a 6-in. vertical stack, heated in a manner simulating

that which might occur when the flue gases from a gas water heater were discharged into the stack, is summarized in Table 4. For

these observations an electric cone heater was inserted into the

6-in. stack about 6 feet above the floor level through the side

outlet of a tee and the side outlet covered to prevent entry of

air at that place. The voltage on the electric heater was adjusted to heat the air to a temperature ranging from 150°F to 200°F

simulating the flue gas temperature of a gas water heater beyond

the draft diverter.

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were measured for the following two test conditions:

(a) Basement sealed insofar as possible and with the floor

registers that connected the basement and living space

open. The attic was heated to simulate solar effects and

the vertical duct was heated to simulate the heat provided

by the flue gases from a gas water heater.

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- 33 -

The air flow in the 6-in. duct ranged from 17 to 26 cfm

for the first four tests summarized in Table 4 when the foundation ducts were sealed and the basement was sealed up at all

visible cracks. However, the air flow through the open floor

registers was also upward indicating that more air was entering

the basement from outside than was flowing up the 6-in. stack.

The stack reduced the pressure in the basement from 0.007 to

0.00$ in W.G. below the outdoor pressure and the living quarters

near the floor were at a pressure just slightly below the basement pressure in Tests 1 to 4. The flow of air up the 6-in.

stack was from 50% to 100% greater with the stack heated as in

Tests 1 to 4 of Table 4 than was observed with the stack unheated as in Tests 2 and 3 of Table 3» Operating the blowers in the

space between the Test Bungalow and its enclosure appeared to

increase the flow up the stack slightly.

When the foundation ventilators were open as in Test 5-10

of Table 4, the flow of air up the 6-in. stack increased from

20 to 40 percent. The flow up the stack was not much different

when four ventilators were open than that observed when only two

were open, but the total air flow into the basement was increased

significantly. More air entered the foundation ventilators than

traversed the stack by a ratio of 4 to 1 in some cases and as

high as 6 to 1 in other cases indicating that more air was passing upward through the floor construction than was moving up the

stack. Comparing the air movement through the foundation ventilators in Tests 5 and 6 with that in Tests 7 and $ of Table 4,

it will be noted that sealing the floor registers reduced the

basement ventilation appreciably. However, opening all of the

foundation ducts as for Tests 9 and 10 more than offset the effect of sealing the floor registers.

The air flows up the vertical stack for Tests 1 to 4 in

Table 4 ranged from l/2 to l/3 that observed as total basement

infiltration for the same indoor-outdoor temperature difference

with the katharometer . This indicates that the vertical duct

was only conveying a part of the total air through the house construction . The infiltration in the basement with the foundation louvers

open and with the blowers outside running as in Tests $ and 10

of Table 4 ranged from nearly twice to about 5 times that observed

with the katharometer for the same indoor-outdoor temperature difference, but without the louvers open in the basement. However,

the attic was not heated and there was no heated vertical duct extending up through the structure for the tests using the katharometer.
- 34 -

In no case did the 6-in. stack cause air to move from the

living space through the floor registers into the basement even

though the windows and the door in the basement were caulked

and the sill plate was sealed. Of course, a full basement wall

presents more area and more joints for air leakage than would

crawl space foundation walls, but it is concluded from these

tests that special measures would have to be taken to seal such

a wall sufficiently to ventilate the cr^wl space through floor

registers from the living space above by the use of a vertical

stack such as that tried for these experiments.

VI* THE DESIGN AND CALIBRATION

OF A HEATED THERMOCOUPLE ANEMOMETER

A. Introduction

. j , For investigating the ventilation of house attics, basements -and crawl spaces as well as for measuring air motion in

the proximity of heated and cooled walls, windows, grilles,

etc., a device was required that would measure air velocities

as low as 5 ft/min non-directionally and omni-directionally

with reasonable precision and which was easy to operate and

was portable. Since all known commercial apparatus was either

inaccurate or of too low sensitivity at the desired air flow

rate, the design and construction of a suitable instrument was

undertaken.

A study of the literature 9, 10, 11 on this subject indicated that the required results were most likely to be achieved

with a heated thermocouple anemometer if reproducible measurements could be obtained at temperature differences between the

hot thermo- junction and the ambient air low enough to prevent

self-generated natural convection currents from distorting the

readings at very low air velocities.

The differential electromotive force in a thermocouple

anemometer is provided by one or more electrically-heated

thermo junctions and an equal number of unheated junctions connected in series and placed in the same air stream. The magnitude of this electromotive force can be related to the air

velocity by calibration. It! was found that the heat loss by

free convection, radiation, and conduction from a horizontal

wire of 0.004 in. to 0.005 in. diameter heated 3°F above

room temperature was about equal in magnitude to the additional increment of heat loss caused by a superimposed forced convection of 5 ft/min for the same temperature difference.

Therefore, to prevent the effects of free convection from

being predominant or equal to the effect of a forced convection of the order of 5 ft/min it was necessary to design the

heated thermo junctions for a temperature rise of less than 3°F#
- 35 -

B. Design of the Instrument

The thermocouple anemometer was built in the form of a probe for portable application in ducts and rooms. The probe

was designed with two pairs of thermo junctions in series to

double the differential electromotive force ( EMF ) and also to

obtain a symmetrical design pattern. Chromel-P and constantan

junctions were selected for their high electric resistance and

also for their relatively high EMF output of 33 microvolts per

degree Fahrenheit. Availability determined the use of 0.004 in.

chromel and 0.005 in. constantan wires for the heated junctions

and 0.040 in. wires for the cold junctions which were arranged

as shown in Fig. 31. It seems obvious that the electric current which heated the smaller wires a maximum of 3 °F would not

cause a significant temperature increase of the larger wires

having a cross section area one hundred times as great. It

will be noticed that the potential of the two hot junctions is

opposed by the cold junction potential so that the total EMF

at the ends equals twice the potential difference between one

pair of junctions.

The schematic diagram in Fig. 31 shows the alternating current heating circuit divided into two parts with one side of the

line connected to the center of the thermocouple circuit and with

the other side of the line connected to its extreme ends so that

a zero A.C. potential could be made to exist across the entire

thermocouple circuit. A variable resistor, Rq , between lines 1

and 3 in the diagram was provided to compensate for differences

in the resistances of the two parts of the thermocouple circuit

and for differences in the series resistances, R^ , in lines 1 and 3.

A zero A. C. potential difference between terminals 1 and 3

was obtained by adjusting resistance Rq until there was no noticeable vibration of the D.C. microammeter needle. Resistors, R£

,

each contained 1500 ohms resistance as compared to a resistance

of 3.5 ohms for the D.C. microammeter. Thus, only about one

tenth of one percent of the thermoelectric current generated by

the thermocouple circuit was not registered on the D.C. microammeter . Fig. 32 is a photograph of the thermocouples at the end of

the probe showing the symmetrical arrangement of the two pairs

of thermocouple junctions which resulted in essentially an omnidirectional design for air-velocitv measurements. Fig. 33 is a

photograph of the entire prototype thermocouple anemometer.

C. Calibration of Thermocouple Anemometer

The thermocouple anemometer was calibrated in a small wind

tunnel designed for isothermal conditions and using a compressed

air supply. The compressed air was brought to the tunnel through

a 100 gallon surge tank to reduce pressure variations. The air
- 36 -

flow rate was measured with an orifice flow meter constructed

in accordance with the ASME Research Publication entitled "Fluid

Meters, Their Theory and Application" Fourth edition and calibrated with a gas meter for rates below the range covered by

this publication. The pressure drop across the orifice was observed on two U-tube manometers, one filled with water and the

other with mercury, which permitted the use of the same orifice

plate for pressure drops ranging from 1 cm of water to 60 cm of

mercury, corresponding to average air velocities in the wind

tunnel from 4.# ft/min to 129.? ft /min. A cone-shaped adapter

connected the pipe downstream from the orifice meter and the

wind tunnel. A cloth screen was installed at the entrance of

the wind tunnel to equalize and streamline the air flow over

the full area of the wind tunnel. The probe was attached to the

end of a piece of 5/$-inch steel tube and placed in the center

of the tunnel, 12 inches above the cloth screen. The wind tunnel

consisted of an $-inch stainless steel tube, 4 feet long installed in a vertical positioij.

During the initial calibration of the prototype instrument

a semi-precision portable potentiometer was used to measure the

EMF produced by the thermocouple circuit. The relation between

the terminal EMF of the thermocouple circuit and the air flow

rate in the wind tunnel is shown in Fig. 34. A heater current

of 75 milliamperes was used for the air velocity range from 0 to

35 ft/min and a heater current of 120 milliamperes was used for

the air velocity range from 20 to 130 ft/min. The use of two different heater currents- provided greater sensitivity over the entire range of air flow rates. The upper part of the curve for

a heater current of 75 milliamperes shows a change of only 10

microvolts in EMF for the range of flow rates from 21.5 to 33.4

ft/min whereas the other curve shows a change of 22 microvolts ' . in EMF for the same range of flow rates when a heater current

of 120 milliamperes was used. The change in curvature of the

curve for the lower heater current for flow rates below 5 ft/min

is believed to have been caused by the increasing effect of free

convection around the heated thermocouple junctions.

The curves in Fig. 34 apply to air at a temperature of 70°F

and at approximately standard barometric pressure. Tests at high

and low values of relative humidity showed that the effect of

humidity on the electromotive force developed by the heated thermo

couple probe could not be detected. The difference in density between dry air and saturated air at 70°F is slightly over 2 percent

so the difference in EMF caused by a chanve of relative humidity

less than 100 percent could hardly be measured reliably with a

semi-precision potentiometer.
cr

LU

LlI o

UJZ<

LlI

CL

Z>Ooo

or

LUX

I-Q

LU

I—<

LUXo<X

CD<QO

LUXo

U1

rO -o

OJ -o Z o

in

PQZ

FIG.

32
I
FIG.

33

O LfNh-TjQ o p-ririO f^KM^OVQ tT\tt LTi rt rftr+CvnM

q.WOJ.JITLQ J9^9H £/ iOJ upD/^j ao^TV

. _ .T I

UTGi/4-J r 9^eH ^ou«xty

- 37 -

The heat transfer from a heated wire by convection is approximately proportional to the density of the fluid circulated

over it. That is, for a given total heat transfer rate from

the wire to ambient air the temperature difference would be inversely proportional to the density of the air. Thus, for small

variations in air temperature, the EMF produced by the heated

thermocouple anemometer would be inversely proportional to the

air density.

The use of a semi-precision potentiometer for observations

of the EMF of the heated-thermocouple anemometer greatly reduced its portability so the apparatus was modified to use a

microammeter to observe the thermoelectric current of the probe.

A microammeter with a resistance of 3*5 ohms, and a full scale

of 100 microamperes was found to give suitable readings.

The heated-thermocouple anemometer was recalibrated using

this microammeter and the results are plotted in Fig. 35. Two

values of heater current were again used to obtain suitable

values of thermoelectric current for a range of air flow rates.

The results in the wind tunnel were checked by installing

the anemometer on the carriage of the Current Meter Rating tank

at this Bureau. By adjusting the velocity of the carriage, the

desired values of air velocity were obtained. These results

verified those obtained in the wind tunnel.

A computation can be made of the probable thermoelectric

current that would flow through the microammeter circuit for any

given heater current and air flow rate by computing the electric

energy dissipated in the thermocouple wires and the probable

temperature difference required between the hot junctions and

the air to transfer this heat to the air stream.

The total heat dissipated by the heated wires equals the

heat input after reaching a steady state condition. The overall

resistance of the probe was 2.4 ohms. As the resistance of the

smaller wires was one hundred times that of heavier ones, the

resistance of the entire probe was used to compute the heat input. The electric energy converted into heat in the thermocouple wires would be

Qj = I

2 R x 3.415 Btu/hr (1)

Since the heater current was divided equally between the two

halves of the thermocouple circuit the total heat input would

be as follows:

Qj, = 0.01152 Btu/hr

Qj^

= 0.0461 Btu/hr

For Ip = 0.075 amp

For Iq = 0.150 amp
- 33 -

The heat loss by radiation would be almost negligible since

the temperature difference between the hot wires and the surround

ings was small and the emissivity of the constantanand chromel

wires was of the order of 0.05. Using the radiation equation

with a 2°F temperature difference and an emissivity of 0.05 the

heat loss by radiation was as follows:

Qr

= 0.0000153 Btu/hr

By comparison with the total heat dissipation QR was negligible.

The conduction of heat from the thermocouples was unknown,

but was small because the three leads connecting the probe to the

power supply was brought through a hard rubber mounting about

5/3 inch in diameter and 3/4 inch long.

The heat transfer due to forced convection can be expressed

by equation ( 3 )

Qc = f c x A x At, Btu/hr (3)

where A = surface area of the wire, sq ft

At = temperature difference between wire and air, °F

f c = surface film coefficient, Btu/(hr)(sq ft)(°F')

k

' fc = x d

where Nnu = Nusselt Number

k = thermal conductivity of air, Btu/(hr)(sq ft)(°F/ft)

d = diameter of wire, ft

12 Hilpert gives the following relationship between the

Nusselt number, Nnu , and the Reynolds number, R e , for forced

convection around heated wires and cylinders.

Qr = 1723 Ae

(1000) ( 1000 ) (1000)

( Tw ) 4

- (. Tf

)>*

( 2 )

( 1000 ) ( 1000 )
S3d3dlNV0d3IW ‘_LN3dUnO Oldl03130lNd3Hl

- 39 -

Nnu B Re (4)

where the values of B and n are selected from the following

for the appropriate Reynolds number

„

Re n B

1-4 0.330 0 c $91

4“40 0.3$5 0 o $21

40-4000 0„466 0 o 6l5

4000-40,000 0.61$ 0o 179

40 , 000-250 9 000 0.$05 0.0239

The Reynolds Number for the air flow was

= V x d x 0 (5)

A

"

where: V = air flow rate, ft/sec

d = diameter of wire, ft

^

= density of air, lb/ft^

yM = absolute viscosity of air, Ib/ft sec

The thermoelectric current flowing in a circuit of 5»9 ohms

total resistance (

0 4 ohms probe resistance plus 3° 5 ohms meter

resistance) with 2 x 33 = 66 microvolts EMF per degree temperature

difference would be

I0= _^6 x At = ll o 20 x At, microamperes (6)

By solving for At in equation (3) and inserting its value

in equation (6)

o

cy

o

cv o X

11— 11— II Mc (7)

A x f c

I0 = 76,100 x 0

c

1 c ($)
- 40 -

Neglecting the heat transfer from the thermocouple wire

by radiation and conduction the heat input calculated from

equaltion (1) equals the heat dissipated by the forced convection.

Ql = Qc

Therefore, for

Ip = 0.075 amp, I 0 = 76,100 x 0.001152 = 375

f c ^c I? = 0.150 amp, I n - 76,100 x 0.0461 - 3500

f c " fc

Table 5 shows the calculated values of the Reynolds and

Nusselt numbers for a range of air flow rates from 5 ft/min

to 130 ft/min and also the resulting values for the coefficient

f c

. The calculated and the observed values of the thermoelectric

current I 0 in microamperes for heater currents of 75 and 150

milliamperes are also sliown in Table 5.

Table 5

Airflow

Rate, f

ft/min

. R

e V

Nnu fc

c.

M O 0 75 MA I0 for 150 MA

calcu-

' lated observed

calculated observed

5 0.189 0.513 20.1 43.5 35

10 0.373 O .646 25.4 34.4 23

, 20 0.756 0.313 31.3 27.6 22

30 1.134 0.930 36.4 24.1 19 96.2 76

50 1.390 1.101 43.2 31.1 62

70 2.646 1.229 43.2 72.6 56

130 4.914 1.513 59.6 53.3 45

A comparison of the observed and calculated values of the

thermo-electric - current of the heated thermocouple anemometer

is shown in Fig. - 35 for air flow rates from 5 ft/min to 130

ft/min. This figure shows that the slopes of the curves for

the observed and calculated currents were very nearly equal for

the same flow rate, but the calculated values were from 23 to

31 percent higher than the observed values. This discrepancy

is accounted for in part by the radiation and conduction of

heat from the smaller thermocouple wires and by the convection

heat transfer that occurred from the larger wires where they

joined the smaller wires. That is, the effective area for convective heat transfer was somewhat greater than the area of the

smaller wires and this effective area, if it could be evaluated,

should have been used in equation (7) for computing the thermoelectric current.
- 41 -

In addition, the values of B and n selected for use in

equation (4) may not have been entirely suited to the conditions of heat transfer that existed, but appeared to be the

best available in the literature.,

It is expected that the sensitivity of the heated thermocouple anemometer could be increased by adding a small electronic amplifier to the output „ Operating on the EMF output

of the anemometer, only a small rate of amplification would

be required and a less delicate indicator could be usedo

Another advantage of amplification would be that a suitable

gain control could be used to obtain a full scale measurement

for both air velocity ranges.

VII. DISCUSSIONS AND CONCLUSIONS

This investigation of the infiltration in the Test Bungalow

and of various methods for the measurement of infiltration reveals first, that the air movement through the various parts of

a frame building are quite complicated and second, that instruments are now available for reasonably precise measurement of

air infiltration rates. The present study is considered to be

only a preliminary exploration of the subject of infiltration

but it reveals broad possibilities for the development of new

and reliable information on the air leakage into buildings

under the influence of wind and temperature difference and how

it is affected by building design and construction practices.

The results of the measurements in the Test Bungalow show

that the rate of infiltration increased as the indoor-outdoor

temperature difference increased and that under this influence

alone a number of interdependent air flows took place between

attic, living space, and basement and between these spaces and

the outside air. The large amount of basement infiltration in

the Test Bungalow suggests that houses without basements or

crawl spaces would probably have appreciably less infiltration.

The air movement through the stud spaces in the Test Bungalow

would not be present in a building with solid walls or one in

which the stud spaces were filled with granular or fibrous insulation. The measurements in the Test Bungalow showed that

opening louvers in the attic increased the ventilation through

the entire structure and that considerable air leaked into the

basement through the concrete block foundation walls even when

the basement door and windows and the sill were caulked. These

observations indicate that considerable variation in air leakage' values are to be expected in houses of different construction.
- 1+2 -

Before any reliable estimates could be made of the absolute values of the infiltration for particular types of construction, field surveys of a number of houses of each construction would be necessary. Field surveys of this type might

suggest how building construction could be changed and improved

to provide better control of air movement, vapor movement, and

heat loss than is now possible. The exact effects of weather

stripping and storm windows on air leakage could be evaluated

by tracer gas methods of infiltration measurement. A study of

exposure factors and the effect of house orientation on air

leakage is also possible.

The use of the heated-thermocouple anemometer and the

helium katharometer or other tracer gas technique together

could provide valuable information on attic and crawl space

ventilation for condensation control which might result in the

development of construction criteria for the ventilation of

these spaces.

The investigation of methods of infiltration measurement

described in this report indicated that a number of tracer gas

methods are available and that these methods are probably more

accurate and better adapted to field use than calorimetric

methods or direct air flow measurements. The more promising

tracer gas methods are believed to be (a) helium gas with a

katharometer (b) ethane gas with an interferometer, (c) methane

gas with an infrared gas analyzer. Suitable measuring techniques are possible using either a radioactive gas with an

electrometer or a halogenated hydrocarbon gas with a halide

photometer. However, these latter two methods present some

hazard to the personnel using them or to the occupants of the

building being tested.

The Cambridge katharometer loaned to the National Bureau

of Standards by the American Society of Heating and Ventilating

Engineers for this investigation appeared to provide a better

means for measuring infiltration rates than other methods previously used for this purpose. A calibration of the instrument

showed that the indicated values of concentration were subject

to some errors caused by parallax and drift at the zero setting,

but that on the average the error in infiltration measurements

would not exceed 4 percent if some precautions were taken in

operating the instrument. The instrument was not sufficiently

portable for field use and it had a lag in response ranging from

3.5 minutes with no sampling line to about 5 minutes with a

sampling line 30 ft long.
43 -

A katharometer based on the same principle as the Cambridge

instrument was designed and built by the National Bureau of

Standards., It was portable and employed natural convection

rather than a pump for circulating the tracer-gas-air mixture

through its thermal conductivity cells „ It was shown to have

an accuracy equal or slightly better than the Cambridge instrument o The heated thermocouple anemometer appeared to be the type

of instrument best suited to measuring air velocities below

100 ft/min, It can be made with sufficient sensitivity and

accuracy to measure streamlined air flow rates as low as 5

ft/min, Turbulence in an air stream would probably alter its

accuracy at the lower end of the velocity range. Such an instrument seems to be well-suited to measurements of the air flow

rates associated with natural ventilation of attics and crawl

spaces through Louvered openings.
VIII. References

1. Le Mesure de Ventilation par Traceurs Radioactifs, by

R. Cardiergues et P. Leveque, ( chaleur & Industrie,

Jan. 1952, pp 21-25)

2. Electrical Measurement of Water Vapor with a Hygroscopic

Film, by E. R. Weaver ( Analytical Chemistry, Vol. 23,

No. 8 , August 1951)

3. Gas Analysis by Measurement of Thermal Conductivity,

by H. A. Daynes (Cambridge University Press, 1933)

4. The Measurement of the Rate of Air Change, by W. G. Marley

(Journal, The Institution of Heating and Ventilating

Engineers, Vol. 2, 1935)

5. Measurement of Ventilation Using Tracer Gas Technique,

by J. B. Dick (Heating, Piping, and Air Conditioning, May 1950)

6. The Theory of the Katharomet er . by H. A. Daynes (Proceedings,

Royal Society, Vol. 97, 1920 A)

7. Can We Locate the Neutral Zone in Heated Buildings, by

J. J. Blackmore (ASHVE Transactions 1915 p. 501)

8 . The Neutral Zone in Ventilating, by J. E. Emsweiler,

(ASHVE Transactions, 1926, p. 59)

9. The Heated Thermocouple Anemometer, by C. P. Yaglou

(Journal Industrial Hygiene and Toxicology, Vol. 20,

Oct. 193 S, No. 8)

10. A Simple Heated-Thermocouple Anemometer, by H. B. Nottage

(ASHVE Journal Section, Heating, Piping, and Air Conditioning,

Vol. 22, Sept. 1950)

11. An Ionization Anemometer, by J. E. Lovelock and E. M. Wasilewska,

Journal of Scientific Instruments, Vol. 26, 1949, p. 367)

Forsch. Gebiete Ineenieurw, R. Hiloert, Vol. 4, 1933,

pp 215-224).

12
THE NATIONAL BUREAU OF STANDARDS

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3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

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