NBS TECHNICAL NOTE 710-6

BUILDING

RESEARCH TRANSLATION

Ventilation Air Inlets

For Dwellings
NATIONAL BUREAU OF STANDARDS

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ML BISSAU uS" SiiuiWiHUa

JAN 2 1 1973

BUILDING RESEARCH TRANSLATION

Ventilation Air Inlets for Dwellings

M. Croiset and H. Bizebard

Centre Scientifique et Technique du Batiment

Paris, France

Translated by the Joint Publication Research Service, U.S. Department of Commerce,

Washington, D.C. 20234

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of

transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

.' • •

ftjLi^<L.aJl -vu*-5d£_ no. 7/0 ~£

"V^

V **

**«Ui of

U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secrefary

^•<U NATIONAL BUREAU OF STANDARDS, Lawrence M. Kushner, Acting Director,

Issued January 1973
National Bureau of Standards Technical Note 710-6

Nat. Bur. Stand. (U.S.), Tech. Note 710-6, 62 pages (Jan. 1973) CODEN: NBTNAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 013.46:710-6). Price $1.00 .
FOREWORD

The United States/French Cooperative Program on Building

Technology entails an exchange of personnel between the

National Bureau of Standards (Center for Building Technology)

and the Centre Scientifique et Technique du Batiment

(CSTB) of France. The program also involves the exchange

of information between the two research organizations.

It is felt that some of the documented information can

be usefully shared with the U.S. building industry; and,

therefore, certain papers were selected for reproduction

in media on sale to the public by the Government Printing

Office. It should be understood that the CSTB documents

made public through such media as this TECHNICAL NOTE

do not necessarily represent the views of the National

Bureau of Standards on either policy or technical levels.

At the same time, building researchers at the National

Bureau of Standards consider it a public service to share

with the U.S. building industry certain insights into

French building technology.

(/James R. Wright, Director

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

III

VENTILATION AIR INLETS FOR DWELLINGS

Recommendations for the Elimination of Discomforting

Drafts in the Case of Outside-Wall Air Inlets

Designed for Dwelling Ventilation-'

by

M. Croiset and H. Bizebard

Preliminary tests have shown the existence of a "discomfort

index", a function firstly of the difference between the temperature in the room and the temperature of the air current and,

secondly of the speed of the air stream. The permissible limit

for this index has been fixed at two degrees C- , at least in

that part of the room situated more than 20 cm. from the outside

walls and less than two meters in height.

Systematic artificial tests have resulted in satisfactory

solutions being found for the air inlets into the outside walls. —An elongated aperture placed above a radiator and fitted

with a deflector so that cold air entering the room mingles

with the ascending warm air current. —An aperture located behind a convector heater so that the same result is achieved as in the case of the radiator. —A row of apertures located along the heated ceiling placed so that entering air is diffueed into the warm air before reaching the occupied zone.

Some calculations aimed at determining the orders of magnitude

of the necessary sections and the possible force of the air current

in a high wind, have revealed the need for a manual or an automatic

regulator where a wall is exposed to wind.

Key words: Air inlet; discomfort index; draft; outside wall;

ventilation; wind.

1/

-'This paper is translated from the French original and is published

under the Building Research Division/Centre Scientifique et Technique du Batiment information exchange program.

2/-Centigrade thermometer readings will be used in temperature

measurements unless otherwise stated.

1
RECOMMENDATIONS

1. GENERAL

Statutory requirements for air inlets or intakes supplying ventilation

in dwellings are contained in the lU November 1958 governmental decree on

ventilation of residences and in the memorandum of the same date prescribin

Sanitary Regulations for Lavatories, Bathrooms, and Toilets in Central

Position (i.e. not along outside walls). Among the measures commonly

adopted in compliance with this decree and its associated regulations is

the provision of air-inlet openings in external walls. Generally these

2 air inlets are simple 150 cm rectangular holes covered with protective

grilles.

Following our research—a report of which is contained in the enclosed

supporting study—we are now in a position to make recommendations on air

inlets in external walls. These recommendations do conflict with the

regulations on some points. But the CSTB will shortly submit proposals

for the amendments needed to obtain maximum benefit from the findings of

its research.

The subject recommendations concern solely direct air-inlet openings

in external walls. They do not cover any other air-inlet principles, such

as horizontal air ducts, vertical air ducts, etc., a fact which does not

per se constitute disapproval of these other principles or systems.

1.1 Guidelines

The guidelines from which these recommendations stem, are as follows:
First, relate the cross section of air inlets, or more correctly,

their pressure-loss characteristics, to the desired air changes within

the different rooms of the dwelling. This relationship is expressed by

the concept of "basic air flow".

Second, establish cross-section limits not only with a view to

obtaining a minimum degree of ventilation, but also to precluding excessive

flow of air under high wind conditions. Authorize, as and if required, air

inlet devices with adjustable openings.

Third, provide a means for numerically expressing the degree of

protection against cold air drafts by employing the concept of a discomfort

index

Fourth, distribute air inlets as much as possible throughout the

dwelling by authorizing indirect ventilation in kitchens, bathrooms, and

toilets, whether these rooms be in a central position (i.e. along an

outside wall) or not. Air would enter into living rooms and bedrooms and

leave from service rooms, (i.e. kitchens, bathrooms, toilets) where the air

is most polluted. Such an arrangement allows the air flow from the air

inlets to be more widely distributed and consequently facilitates efforts

to control drafts. In addition, it provides better ventilation for the

dwelling unit as a whole

1.2 Basic Air Flow

The basic air flow of an air inlet is defined as that amount of air

that must be delivered by the inlet to provide the desired air change

throughout the various rooms in a dwelling. No regulations presently

prescribes the desired air change. We recommend the following values:
Bedrooms and living rooms

2 3 less than 15 m 30 m /h

P 3 more than 15 m U5 m /h

Service rooms

kitchens for dwellings of less

than three rooms U5 m-^/h

kitchens for dwellings of three

or more rooms 60 m /h

3 bathrooms 30 m /h

toilets 30 m

3 /h

3 combined bathroom-toilet 30 m /h

When each room is ventilated independently of the others, the basic

air flow of each air inlet must be equal to the desired air change in the

room serviced by that inlet. If we adopt the principle of placing air

inlets in living areas (bedrooms, living rooms) and air outlets (or

exhausts) in service rooms, the basic air flow of each inlet must be at

least equal to the desired air change in the room in which that inlet

is located, and also be such that the outlet air flow in the service

rooms is at least equal to the desired air changes for those rooms.

First example: air inlets are located in two bedrooms of less than

o 15 m and the outlet is in a combined bathroom-toilet. The basic air

3 flow of each air inlet will be 30 m /h.

Second example: the air inlet is located in a living room, the outlet

3 in a kitchen. The basic air flow will be U5 m /h in small dwellings and

3 60 m /h in the others. Air inlets may also be divided between the kitchen

and living room, thus limiting the basic air flow for each room to

30 m3/h.
Provision should therefore be made for air inlets with basic air

flows equal to 30 m /h, U5 nrVh, or 60 m /h, depending on the case

involved. But an efficient distribution of the inlets among the various

rooms will often permit limiting needs to basic air flows of 30 Er/h.

1.3 Practical Air-Flow Limit

As we said above, the cross sections of air inlets must be such as

to meet two contradictory requirements. The first is to obtain

approximately the basic air flow under average thermal draft conditions,

the second is not to have excessive air flow under high wind conditions.

The compromise which can be made thus leads to "a practical limit" to

air flow, a limit corresponding to wind pressures that are rarely exceeded.

Shielding or protection against cold air drafts must be provided up to

this air flow limit.

1. In natural ventilation conditions, the practical limit can be

set at a value equal to the basic air flow or four times as great. On

those outside walls that are particularly exposed, because of the site of

the dwelling, its orientation, or height, this requires using air inlets

with openings that are manually or automically adjustable. Obviously

these openings cannot be completely closed. When shut and under average

thermal draft conditions, air flow should be equal to at least half of

the basic flow.

In certain cases of exceptionally unfavorable exposure to wind where

we would be required to set a higher practical limit, it appears advisable

to consider solutions other than direct inlets in outside walls, for

example, vertical or horizontal ducts that are not covered by the

recommendations herein.
The practical limit indicated above can be reduced in the following

two special cases: —when through automatic control and adjustment the air-inlet air

flow remains clearly below the quadruple of the basic air flow.

In such cases the practical limit employed will be the flow

actually obtained under the limiting wind-pressure conditions

employed in the general case; —in the case of exceptionally sheltered situations.

However, in no case will the practical limit ever drop below double

the basic air flow.

2. In mechanical ventilation conditions it is generally possible to

provide air inlets having a smaller cross section than those used with

natural ventilation, and thus reduce wind effect. Consequently the

practical limit will generally be less than the quadruple of the basic

air flow. The flow actually obtained under the limiting wind-pressure

conditions of the general case will be used.

When the present regulation is amended it will be possible to define

more exactly therein the rules on the pressure-loss characteristics of

air inlets. However, as of now, we consider that the orders of magnitude

of the values that it would be advisable to adopt for natural ventilation

are as follows

—0.3 to 0.8 mm of water for pressure loss corresponding to basic

air flow; —k to l6mm—depending upon exposure conditions and exclusive of

of exceptional situations —for the pressure corresponding to the

practical limit of air flow.

6
Air inlet cross sections with which these two specifications can be

p met, are of the order of 30 to 70 cm for fixed inlet devices.

Cross sections of adjustable devices would be the same in the open

position but could be reduced by one-half in the closed position.

l.k Definition of the Discomfort Index

The discomfort which a cold draft of air produces at a particular

point inside a room is expressed numerically by the value of the

"discomfort index" equal to the sum of the difference between the mean

air temperature of the room at the same level and the temperature of the

air stream at that point , affected by the drop in temperature equivalent

to the velocity of the air stream at that point given by the graph in

figure 1 , p . 9

2. RULE

The value of the discomfort index determined for an outside

temperature of 0° , an inside temperature of 20° and an air-inlet air

flow equal to the practical limit defined in paragraph 1.3 , must not

exceed two degrees throughout the entire zone situated at a height of less

than two meters and at a distance of more than 20 cm from the outside

walls

When the air inlet is combined with the heating system, the above

rule must be complied with under normal heating conditions. Furthermore,

in the absence of any heating and with outside and inside air temperatures

equal to 20°, the rule must also be followed.
When the air inlet has a manually adjustable aperture, the recommendation should be followed with the aperture in its minimum open position.

3. PRINCIPLES OF VARIOUS SOLUTIONS

The air inlets whose principles are described below permit carrying

out the recommendation pertaining to the discomfort caused by drafts in

the general case of an air flow which is four times greater than the basic

air flow. Only the principles are outlined below. Working details for

implementing the recommendation on pressure losses, plus the customary

rules for safeguards against intruding animals, rain and snow, can be

presented in detail within subsequent documents (agreements or standards)

.

These solutions do not exclude other solutions, especially if the

control and adjustment provisions, or use in sheltered situations, allow

the requirement for protection against cold air drafts to be limited to

double the basic air flow.

The air inlets of standard design recommended below all require

combination with a heating system.

3.1 Air Inlet Combined with Radiator Heating (Figure 2a, p. 9)

The principle of this device calls for an elongated opening in the

wall behind or above a radiator. The opening has a deflector which directs

the air upward in such a way that the supply cold air mixes with the

ascending warm air current produced by the radiator. The elongated opening

must not extend more than 10 cm beyond each side of the radiator.
Fig. 1. Drop in temperature equivalent to the velocity of the air stream. Temperature differential between

still air and air stream

-5°"

* ^~

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s y 7"

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0,10 0,15 0,20 0,30 0,40 0,50 0,60 0,70 0.60 0,90 1,00 (Still air) Air-stream velocity

(a)

(c)

Fig. 2.

9
3.2 Air Inlet Combined with Shlelded-Convector Heating (Figure 2b, p. 9)

The principle here calls for positioning the opening behind the

heater section with the supply cold air being directed so that it mixes

with the naturally recirculating air in passing over the heating tubes.

3.3 Air Inlet Combined with Ceiling Radiant (Panel) Heating (Fig. 2c, p. 9)

The principle involved here calls for a series of point openings

distributed alongside the ceiling over the maximum possible length of the

outside wall in such a manner as to diffuse the supply cold air within the

layer of warm air lying under the ceiling above the occupied zone.

3.4 In the case of warm-air heating, there is no need to conduct research

for adequate air inlets in the outside wall since the warm-air registers

or grilles constitute such air inlets.

SUPPORTING STUDY

Introduction

In France at the present time ventilation design almost generally

calls for 150 cm^ air inlet openings in the lower part of walls within

kitchens and bathrooms along outside walls. During the cold season the

drafts created by these inlets become intolerable. Occupants unable to

stand the strong cold blast of air usually aimed at their ankles or feet,

block the air inlets. We decided to study ways and means capable of

eliminating or reducing the discomfort caused by such drafts so as to

10
make air inlets on outside walls acceptable.

The study was conducted in two phases: —preliminary natural tests that led to the definition of

a numerically expressed "discomfort index," and also to

the selection of classification criteria for air inlets; —systematic artificial tests of the various possible

types of air inlets combined or not combined with the

heating system.

A survey made in occupied dwellings partially confirmed the results

obtained

PART 1: DEFINITION OF A QUALITY CRITERION

AND DETERMINATION OF ADMISSIBLE LIMITS

1. TESTS COMPLETED AND DEFINITION OF A DISCOMFORT INDEX

Tests were undertaken with a view to relating the sensation of

discomfort experienced upon contact with a draft to the latter 's velocity

and temperature characteristics, and to deduce therefrom admissible

limiting values for these drafts.

These tests were conducted in situ within a bathroom located on the

second floor of a seven-story building. The bathroom had a conventional

air inlet on the outside wall and a vertical duct that provided rather

good ventilation in the wintertime since the air flow (measured by the

"tracer-gas" method) varied from 45 to 60 m->/h. To obtain various

11
combinations of draft velocity and temperature, a deflector was mounted on

the opening in some cases, in other cases the entering air was more or

less heated by a portable radiator.

Air temperature and velocity were measured at points located at

varying distances from the inlet opening along the air stream direction of

flow, by means of an electrical anemometer or a resistance thermometer.

By means of these two characteristics and by making use of the concept of

"resulting" temperature it is possible to compute a single index which we

have called the "discomfort index." It is computed in the following

manner

The discomfort caused by a draft results from the local cooling

of the human body. This cooling is due simultaneously to the temperature

differential of the draft and the air, and to the velocity of the draft,

phenomena that cumulatively produce an overall drop in the resulting

temperature. An equal drop in temperature, that is to say, an equal

sensation of cold, could be brought about by a greater drop in air

temperature without velocity. Consequently it can be stated that the

velocity is equivalent to an additional deviation in temperature. The

latter is given by the chart in Figure 1, p. 33. These curves were deduced

from curves plotted by the American Society of Heating and Air Conditioning

Engineers, and by A. Missenard (Bibliograph 1) for the case of an undressed

person at rest. In fact, drafts are most disagreeable to those parts of

a person at rest (immobile) that are covered by little or no clothing, such

as the ankles, and the nape of the neck.

If A6 is the true air temperature deviation and A0' the temperature

equivalent to the increase in velocity, then the discomfort index is

12
equal to their sum. This index is thus expressed in degrees and is

represented by the letter g.

The accompanying table presents an example of the values obtained in

the case of a 150 cm2 inlet opening with and without a deflector, for an

air flow of 60 m

3 /h, an outside temperature of +1°, and an inside

temperature of +18°.

Distance to opening

(cm)

Air-stream

.'temperature

(°)

A9

(°)

Air-stream velocity

(m/s)

A 6'

(°)

g

(°)

Opening without deflector

10 cm

30

60

100 150

2

4,5

9,5 12

13,5

16

13,5

8,5 6

4,5

1 / 1,40 0,80/0,90 0,30/0,50

0,30/0,45

0,30

> 10

115,5 4

3

> 26

24,5 14

10

7,5

Opening with deflector

10 30

60

100

13

14,5 J5.5

17

5

3,5 2,5

1

0,20/0,30

0,25

0,15 0,10

3,5

2,5 0,5

8,5 63

1

Sensations experienced by the human subjects in the various

experiments were classified as follows: —"unbearable" if the immediate sensation was extremely

disagreeable; —"very disagreeable" if the sensation was immediately

disagreeable; —"disagreeable" if the sensation was disagreeable after

being at rest ("stationary") for a certain time; —"slightly disagreeable" if the cool-air movement was felt

without being disagreeable after being at rest for an

13
extended period

;

—"bearable" if no disagreeable sensation was experienced

even after an extended period at rest.

TEST RESULTS. VALUE OF DISCOMFORT INDEX

Test results grouped on the accompanying table proved that there was

satisfactory agreement between the values of the discomfort index and the

sensations experienced.

Temperature (°) A'l Velocity of air-stream A U' g = A 6 - A 6'

of still air of air stream

t°) (m/s) (°) (°)

Measurements corresponding to an intolerable sensation.

21,5 16 5.5 0.60 4,3 9.8 23.5 17 6,5 0.40 2.8 9,3 22 14.5 7.5 0.70 5,5 13 22 14.5 7.5 0.80 6 13.5 21 13,5 7.5 0,50 4,8 12.3 22 15 7 0.40 3.5 10.2

Measurements corresponding to a very disagreeable sensation

20 16,5 3.5 0.40 3 6.5 22 16.5 5.5 0,25 1.8 7.3 21 15 6 0.25 2 8

21.2 17.5 4 0.50 3 7 20 16.5 3.3 0,40

0,50

3.3 6,8

Measurements corresponding to a disagreeable sensation.

22 20,5 1,5 0,8 3.8 5.3 21 17.5 3.5 0,30 2 5.5

21 16.5 4.5 0,20 1.3 5,8 21,5 18,5 3 0,40 2.5 5,5 21.2 17,5 3,7 0.20 1,1 4.5 21 17,5 3.5 0,30 2 5,5 21,5 18,5 3 0,25 1.3 4,2 21 16.5 4.5 0.20 1.3 5.8

Measurements corresponding to a slightly disagreeable sensation.

20 18 2 0.35 2 4 20 17.3 2.7 0,15 0.5 3.2 23.S 22 1.5 0.20 0,7 2.2 21.5 18.5 3 0,20 0,8 3.8

14
For those discomfort index values under two degrees, the sensation

was bearable. We do not give the corresponding values for temperature

and velocity deviations, because their measurement thus becomes quite

inaccurate and does not have much significance. The correspondence is

as follows:

Discomfort under value Sensation experienced

Above 10° Intolerable

From 6 to 1 Very disagreeable

From 4 to 6 Disagreeable

From 2 to 4 Slightly disagreeable Below 2° Bearable

The limiting value of two degrees may seem to be quite low. However,

that same value is also found in the conclusions of studies made in allied

subject areas.

Figure 2, p. 33, gives curves established by Houghten (Bibliography 2)

for air-conditioning problems. On the same graph we have plotted those

curves of equal value for the discomfort index. It is noted that: —for low values of g —the most important —the paths of

the two curves are about parallel; —considering the divergence between the two definitions of

still air (0 m/s on the one hand, and 0.10 m/s on the other),

the value g = 2° corresponds to a percentage of "dissatisfied

or discontented individuals" of the order of 10 per cent.

Recommendations submitted by COSTIC [Comite Scientifique et Technique

de l

1 Industrie du Chauffage, de la Ventilation et du Conditionnement d'Air;

15
Scientific and Technical Committee of the Heating, Ventilation and

Air-Conditioning Industry] (Bibliography 3) are based on the Houghten

curve for 10 per cent "dissatisfied individuals."

COSTIC bases its recommendations for floor or ceiling heating

(Bibliography 4) on the need not to exceed a 2° radiant temperature

differential between head and feet. With respect to floor heating this

rule would correspond to only 5 per cent "dissatisfied persons."

3. OCCUPIED ZONE AND CLASSIFICATION CRITERIA FOR AN AIR INLET

There is no need to consider any discomfort caused by cold drafts in

the zone adjacent to the ceiling, a zone that is inaccessible unless a

person raises his arms. The same may be admitted for the zone close to

walls and mainly to outside walls which, colder than the other walls, are

in any event a cooling sources.

We will allow that an air inlet, under given temperature and air flow

conditions, is acceptable if the discomfort index is below 2° throughout

the zone located at a height of less than 2 meters and at a distance of

more than 20 cm from the outside walls. We will call this the "occupied

zone.

In a more qualified manner, and for the purpose of making some system

of classification possible, we will adopt the following criteria: —g below 2° throughout the occupied zone GOOD. —g below 4° in the occupied zone and below 2° in the zone limited

to a height of 2 meters and a distance of 40 cm from outside

walls (zone where individuals remain for a prolonged period of

time) ;

.- UNSATISFACTORY

16
—other cases POOR.

It may also be necessary to give consideration to relative position

with respect to "hot spots" in the zone (e.g. proximity of a radiator),

since the contrast in such cases accentuates the cold sensation from a

draft.

PART 2: SYSTEMATIC ARTIFICIAL TESTS

1. EXPERIMENTAL METHOD

1.1 . Apparatus and Facilities

The experimental facilities and apparatus are illustrated in Figure 3,

p. 34. The specific air inlet unit to be examined and tested was set

within the wall separating the two rooms. One of these rooms represents

a room in a house, the other the outside ambient medium. Air was exhausted

by means of a duct with its outlet generally in the ceiling However, this

outlet could be moved if desired, for example to cause the air to leave

from a low part of the room. This duct was equipped with a controlled

(variable) blow fan.

The inside room was heated by radiator, ceiling or floor panel

heating, which made various heating and ventilation combinations possible.

1.2 Test Conditions

Inside temperature was maintained at 20°C, outside temperature at 0°C.

When this was not strictly possible, the two temperatures were

simultaneously raised or lowered so that their differential would remain

equal to 20°

17
In an initial test series the air flow used was uniformly equal to

60 m-'/h. As indicated in the recommendations outlined in the beginning

of this "Cahier", this air flow is, for an air inlet situated in a

standard size room in a dwelling, that minimum flow for which the

requirement for protection against cold drafts must be met.

Those air inlets having given satisfactory results during the initial

test series were subjected to an additional test with an air flow of

120 m /h. The latter is the maximum flow called for by the Recommendations

for air inlets with a basic flow equal to 30 m /h.

After calculating the values of index g the following were plotted: —the curve of maximum discomfort as a function of the distance

to the wall, obtained by determining the point where g is

maximum in each vertical plane considered; —the vertical projection of the volume in which g is equal

to or greater than 2°, called the discomfort zone. We

generally prefer the second of the above representations.

With it the draft can be located and pinpointed in relation

to the room's hot spots.

This testing facility can also be used, if desired, to measure the

air inlet's pressure loss.

1.3 Conduct of a Test

By means of a preliminary test in which smoke was used, the air

stream's trajectory could be located and the zone in which measurements

were to be made could thus be limited. Then air-stream velocity and

temperature were measured successively at different points located at an

18
increasing distance from the air inlet, generally at 10, 30, 60 and 100 cm.

The drop in air temperature was thus measured by taking the temperature

gradient within the room into account.

The resistance temperature detectors were not shielded from cold or

hot radiations.

1 .4 Accuracy

There were two kinds of error sources.

1. Errors in Test Conditions

Inside temperatures (Ti) and outside temperatures (Te) were not

always 20° and 0° . They were frequently several degrees higher than that

but the Ti - Te temperature differential remained equal to 20° +1°. This

resulted in a relative error of 5 per cent in the A8 , which in the zone of

interest to us (A9 # 2°) amounted to an absolute error of one-tenth of a

degree.

The air flow had to be corrected to take account of air leakage from

the room. This correction was made by adding the leakage flow corresponding

to air-inlet pressure loss to the desired flow through the air inlet

(60 or 120 m /h) . This implied a prior calibration with the air inlet

absent, but unfortunately it was a rather rough measurement for the leaks

were not uniform, especially those at right angles to the door. The

higher the air inlet's pressure loss, the higher the correction required.

Numerous tests were performed on inlet openings of the order of

200 cm ; this is always the case with floor heating. Pressure losses

remained low and the correction made to the air flow scarcely exceeded

five per cent. This correction was not always made. If it is deemed that

19
there was the same resultant relative error in air stream velocity, the

absolute error in that velocity was at the most equal to 0.015 m/s for

the velocities of interest to us (0.30 m/s). This corresponds to an

equivalent temperature drop of one-tenth of a degree.

With smaller cross sections of the inlet opening, the correction

increased rapidly. For 50 cm^ it was of the order of 30 per cent. Some

tests were made without this correction having been rigorously estimated,

and it now seems that it would have been clearly underestimated. The

error by default in the air flows amounted to 20 per cent. There was a

resulting error of one-half of a degree in the equivalent drop in

temperature. The corresponding tests will be conducted anew. As we shall

see in paragraph 3, these tests are part of the supplementary research

program aimed at obtaining more specific and detailed information on the

ejection velocity of the air. The fact that the first tests at high

velocity were carried out under favorable conditions (air flow was too

weak) foreshadows less favorable new results.

2. Errors in Measurements.

Temperatures were continuously recorded. The magnitude of the cyclic

variation due to automatic regulation and control was of the order of a

degree. But owing to the lengthy period of this variation, the error in

the difference of the two temperatures of the air stream and the still air

was reduced by making both readings at two equivalent instants of the

cycle. The error under these conditions could be estimated to be less

than three-tenths of a degree.

Velocity was measured within 5 cm/s. The resultant error in the

equivalent drop in temperature in the zone of interest (30 cm/s) was of

20
the order of four-tenths of a degree.

In conclusion, except for the case of the inlet openings with small

cross sections, the two errors in tests conditions were of the order of

one-tenth of a degree. The errors in measurements were larger. We feel,

however, that we did considerably reduce the overall error by multiplying

the number of tests. Only the average results obtained are given herein,

since the deviations between various results were clearly below the sum

of the errors evaluated above.

3,

2. RESULTS OF A SYSTEMATIC TESTS WITH A 60 m /h AIR FLOW

Results presented in the form of a vertical projection of the discomfort zone are grouped within Figure 4, p. 35. Also shown in that

figure are the points of maximum discomfort at fixed distances from the

outside wall, i.e. at 10, 30, 60 and 100 cm. The values of g, A9 , and

A6 ' at each of these points is also indicated. The limit of the occupied

zone is marked on each diagram. We will first comment on the results in

the order presented in Figure 4, p. 35, then we will synthesize them.

2 .1 Compact Opening in the Lower Part of Wall

2.11 Without Deflector (Figure 4A, p. 35)

2 This was a 150 cm opening installed 20 cm from the floor. It is the

most common type of air inlet in current use (Figure 5, p. 34). The result

obtained was very poor. As it left the opening, the cold, and thus heavy,

air stream dropped toward the floor and travelled along it for a distance

of more than two meters from the wall, without spreading out. At 1.50

meters the sensation was still uncomfortable and g was above 6°.

21
2.12 With Deflector (Figures 4B, 4C, and 4D, p. 3"5)

The opening was left unchanged and three deflectors were tried. The

first deflector was a single plain plate set 3 cm out from the opening and

projecting beyond it for 5 cm on all four sides. The draft was divided,

checked, and perceptible only as far as 0.80 meters from the wall.

However, the result was still poor.

A better result was obtained by closing off the bottom and one side

of the deflector. This arrangement prevented the air stream from being

forced down to the floor where it could be deflected and then spread

throughout the room. Although the result was unsatisfactory, this

arrangement may at times prove worthwhile in cases where the use of a room

is such that there is little probability that occupants will remain on

the open side of the deflector for any length of time.

The same deflector with only its upper part left open produced

slightly better but still unsatisfactory results.

The curves of maximum discomfort as a function of distance from the

air inlet (Figure 6, p. 36), highlight the various successive improvements.

2.2 Elongated Opening at Window Sill Height (Figures 4E, 4F, and_4G^

p. 35 and Figure 7, p. 36)

In comparison with the preceding arrangement, an attempt was made in

this case to spread out the air stream by increasing the width of the

opening from 15 to 100 cm, and also to move the air stream away from the

floor where it can only penetrate into the occupied zone.

We will only describe the results obtained with a deflector, since

results without a deflector remained poor and are of little value. With

22
the length of the inlet opening fixed and equal to 1 meter, we studied

the effect of its aperture (dimension "e" on Figure 8, p. 37). The smaller that aperture, the better the result obtained. The explanation for

this most probably lies in the fact that the velocity of the air as it

leaves the opening facilitates the diffusion of the air against or close

to the wall, outside of the occupied zone. We further ascertained that a

reduction of one-half in the length through modification of the aperture

led to about the same result, since the increase in velocity compensated

for the decrease in spread. None of the results obtained were, however,

completely satisfactory.

For the present, no study has been made with inlet openings of

greater length, at least in the case of openings with deflectors. One

test was made with a 1.50 m by 1.50 m window whose joints (cracks) had a

total crack length of 7.50 m (Figure 4H, p. 35). But the disparities in

the thickness of these joints caused the air to enter essentially via the

horizontal joints and mainly in the lower part of the window. The result

was unsatisfactory. The cold air stream dropped rapidly toward the floor

near which it penetrated into the occupied zone.

2 .3 Air Inlet Combined with Radiator Heating

Tests proved that to have an efficient combination of air inlet and

radiator

—the air must be delivered into the top part of the

radiator or above the radiator in order to take

advantage of the ascending warm air;

23
—a deflector must be provided to direct the air upward so as

to preclude having the velocity of the cold air stream drive

the stream through the ascending warm current without having .

time to become sufficiently heated. This is true even if the

air is delivered behind the radiator.

In figure 4 I-4L, p. 35, we show results obtained with an elongated

opening set above the radiator. This is the most practical solution

(Figure 9, p. 3?)

.

Without a deflector (Figure 41, p. 35) —length of radiator and inlet

opening = 1 meter —the cold air stream was still discomforting 30 cm from

the wall, although it was being carried upward by the current of warm air.

This discomfort was accentuated by the contrast with the radiator's warm

radiation.

With a deflector (Figure 4J, 4K, and 4L, p. 35), and with the length

of the radiator and inlet opening still at one meter, good results were

obtained. The discomfort zone was extremely limited. However, it is

important to insure that the air inlet does not extend up beyond the top

level of the radiator. On the other hand, the inlet opening can be extended laterally to each side of the radiator providing this lateral extension

is for no more than 20 centimeters. Good results obtained with a 10 cm

extension were still observed at possibly 30 cm but with definitely no

more than that. Results became clearly unsatisfactory with a 50 cm

extension.

2.4 Air Inlet Combined with Floor Panel Heating (Figures 4M and 4N, p. 35)

The same one-meter long opening with a deflector that had proved

satisfactory with radiator heating, was no longer so with floor heating.

24
Results were even very poor. The floor temperature (26°) is obviously

much lower than that of the radiator and there is no ascending warm air

current of the same large volume as that produced by the radiator.

Spreading the delivery of air over a length of 4 meters by means of a

o row of 4 cm openings 8 cm apart scarcely improved results.

Additional improvement might perhaps be obtained by reducing the

total cross section of the inlet in order to increase the ascending

velocity. In that case the favorable elements would undoubtedly be the

velocity and distribution of air more than the presence of a heated

floor. The proximity of the floor may even be a disadvantage.

2.5 Air Inlet at the Ceiling. Combined with Ceiling Panel Heating .

2.51 Without Ceiling Heating (Figures 40 and 4P, p. 35)

Two arrangements were tested. The first consisted of a two-meter

2 long and two-centimeter wide opening. The second was a row of 4 cm

openings, with an opening every 8 cm over a distance of 4 meters (Figure

10, p. 37). First result was poor, the second unsatisfactory. In the

second instance, as the air streams spread out, they lost their velocity

more quickly and the mass of cold air dropped down closer to the wall.

In both cases the air stream accelerated the convection current flowing

down along the outside wall. Heating was provided from the floor.

No study was made of the effect of an increase in the ejection

velocity obtained by reducing the cross section of the air inlet.

2.52 With Ceiling Heating

The two preceding tests were repeated with ceiling heating and a

ceiling surface temperature of close to 30° . With the one-meter long

opening, the heated air stream dropped down less rapidly than previously

25
and penetrated into the occupied zone only 80 cm from the wall. The

result was unsatisfactory. The draft was discomforting up to 1.50 cm

above the floor.

With the openings spread out, the cold air was able to become widely

diffused in the warm air and also became quickly heated. On the other

hand, its velocity decreased rapidly and was only 0.25 m/s at 10 cm from

the wall whereas with the one-meter long inlet opening and the same

cross section, the velocity was still 0.30 m/s at 60 cm from the wall.

The discomfort zone was localized within the 20 cm surrounding the air

inlet. The result was excellent.

2 . 6 Summary Analysis of Results

Those arrangements and devices (designed to protect occupants

against cold drafts) that have just been tested and examined are based

on two principles.

When the air inlet is located in the upper part of the occupied zone,

that is to say less than two meters high, the objective is to reduce the

velocity of the air and to heat it within the 20 cm-thick layer alongside

the wall.

When the air inlet is located above the occupied zone, the objective

is to obtain similar results, but in this case within the 50 cm layer

under the ceiling.

2.61 Air Inlets in the Upper Part of the Occupied Zone

When the inlet is not combined with a heating system, a deflector

directing the air upwards constitutes the first and most effective means

of protection. The purpose of the deflector is to halt the air stream and

26
above all to prevent the cold, and thus heavy, air from falling too

rapidly to the floor where it cannot help from penetrating into the

occupied zone. A table placed against the wall produces the same result

with respect to the floor; and, in particular, it should change the

unsatisfactory results obtained with a window into poor results.

The efficiency of an opening with a deflector appears to depend on

two elements capable of accelerating diffusion of the cold air within the

warm air before penetration into the occupied zone. These elements are

the ejection velocity of the air and its spreading. Tests in this subject

area have not yet been completed. But the only air-inlet devices which

could most likely produce satisfactory results (opening of great length

or divided opening spread over a great length, and a small cross section)

present practical development problems of a probably critical nature,

such as homogeneous distribution of the opening over a distance of several

meters, and constriction on the order of a millimeter.

The combination of inlet and radiator heating gives satisfactory

results provided certain rules are followed relative to the level and

extension of the opening with respect to the radiator.

Floor heating produced only poor results. It does not seem apt to

lead to a satisfactory solution, at least in the case of direct air inlets

in outside walls. In this report, we do not take up the problem of ducts

laid within the floor or in contact with it.

2.62 Air Inlets at the Ceiling

To take maximum advantage of the free 50 centimeters below the

ceiling, the air must penetrate or at least be directed as close as

possible to the ceiling. Distribution of the air over a great length is

27
of prime importance, at least with cross sections of the order of 200 cm^.

Small cross sections producing great ejection velocity were not studied.

As our tests now stand, only the combination of air inlet and ceiling

heating is conducive to satisfactory results.

3. RESULTS OF A FEW TESTS WITH AN AIR FLOW OF 120 m

3 /h.

These tests were limited to the two arrangements that had produced

satisfactory results with a 60 m /h air flow—opening with deflectors above

a radiator, and divided opening spread alongside a ceiling with panel

heating—and to the "traditional" air inlet constituted by the window

already tested at 60 m /h.

Results are assembled in Figure 11, p. 38.

Opening with deflector above a radiator

The results were still good. The test was made with the opening

extending laterally 10 cm beyond each side of the radiator.

Opening spread alongside a ceiling with panel heating

Here also results remained good. The air became heated more slowly

but the discomfort area did not extend down more than 40 cm from the

ceiling.

Window

The previous unsatisfactory results became poor in this case. The

air stream emanating from the top joint of the window penetrated slightly

into the occupied zone. The much larger air stream entering from the

bottom joint was still discomforting 60 cm from the wall.

28
SURVEY IN OCCUPIED DWELLINGS

PARTIAL CONFIRMATION OF RESULTS

A short survey was conducted in occupied dwellings equipped with the

2 only type of air inlet in current use, namely the 150 cm inlet set in

the lower part of the wall. This device had been improved by the

installation of deflectors.

The survey was made in the kitchens of HLM [Habitations a Layer

Moderee; Low-Cost Housing Program) apartment buildings within the Paris

area. The following deflectors were installed in various floors and at

different exposures: —a single plate or panel set 3 cm away from the opening; —the same arrangement, but with the bottom and one side

closed; the closed side faced the most utilized part of

the kitchen; —the same arrangement with only the top open.

The deflectors were installed during February 1960. Occupants were

questioned in March and April, 1960, and at the end of the winter of

1960-1961. A summary of answers obtained follows:

1. Deflector open on all four sides.

The occupants acknowledged that this was an improvement over the

opening without a deflector. But they complained of gusts of wind. They

thought that the current of cold air passing under the deflector was

especially disagreeable. Replacement of this deflector by another type

closed at the bottom was appreciated.

29
2. Deflector with bottom and one side closed.

Ten deflectors were installed on the first five floors of the building

A pronounced improvement was noticed and occupants on the whole appeared

satisfied. Some, however, did complain of gusts of wind. It would seem

that the small size of the kitchen renders the cold current that rises

along the wall, discomforting.

3. Deflector with only the top open.

Nine deflectors were installed. We then received additional requests

for these from other tenants. Yet several persons did object to the

gusts of wind and the very swift current of cold air along the wall.

In our opinion, these results demonstrate: —the substantial improvement brought about by a deflector; —the need to eliminate, however, all air currents directed

toward the floor; —the satisfaction, although not total, resulting from the

third arrangement or device; —the need to reduce the discomfort zone to an extemely

limited layer of air along the wall.

CONCLUSION

The recommendations presented at the beginning of this "Cahier"

constitute this study's conclusions. We shall add but a brief comment.

Our standards for satisfactory air inlets, namely, a discomfort

index value limited to two degrees, and a maximum distance of 20 cm from

the wall, may appear severe. With respect to the first standard, we have

30
seen, however, that we also find similar values for problems in allied

fields. As for the second criterion, the results of the survey outlined

above seem to confirm the need to be rather strict.

Up to now tests have been conducted with only a 20° temperature

differential, one that is often exceeded in cold regions. Tests will be

undertaken with greater differentials which can but lead to stricter

conclusions

Certain tests are not yet finished, particularly those in connection

with the combined effect of air inlet velocity (openings with small cross

sections) and distribution (openings of great length) . Even though we

can, if necessary, hope to obtain worthwhile results for an air flow of

60 m /h without combing the air inlet with the heating system, it does

not seem that such would be possible for double that flow. Yet only

adjustable openings —for which there is no guaranty of success —in

relatively unexposed sites, permit obtaining valid protection with an

o air flow of 60 m /h.

For all these reasons, we have presently defined as standard air

inlets only those devices combined with a heating system, devices whose

effectiveness with a strong air flow is certain.

31
BIBLIOGRAPHY

1. Missenard, A., Cours superior de chauffage, ventilation,

conditionnement de l'air (Advanced Course in Heating, Ventilation

and Air Conditioning)

.

2. Houghten, ASHVE (American Society of Heating and Ventilation Engineers)

Transactions , Vol. 44, 1955, p. 533, and HPAC [expansion unknown],

December 1958

.

COSTIC, Cours d'aeraulique du stage du perfectionnement des cadres

("Aeraulics" Course in Cadre Refresher Training Program)

.

COSTIC, Manuel des Industries Thermiques (Thermal Industries Handbook),

Vol. 1, Chapter 6.

32
V // 4. 4 4,

5°/? J,fy

V

•A

XS3C

° //

0,10 Q200,X0JO O.iO 0,50 0,60 0,70 0,60 Q901.00 1,20 1.50 (Sti 1 1 a ir) a ir-stream velocity' in M/S

Drop in temperature equivalent to an

increase in the volocity of the air for different air-stream temperatures.

Figure 1.

Figure 2. HOUGHTEN: percentage of "dissatisfied persons" in air conditioning as a function of velocity and temperature

differential with comfort conditions. -----Line of equal value of discomfort index.

g,e g.s g*4 9-3

Still air HOUGHTEN oL

/ / y

sf y

,',

ffl° 1> / ^

">,3 ^

4'

£?

*' 'olo

. ' /'

, 1$& ',

' •' ^J 'h * >^> ,.- & ** ^5 %

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,, .-- *\ ,- ^t!"*' -'

I'A'^, w, (<«*,. - *^L

^Hp9*2

Still a ir C.S.T.B.

-2 -I Temperature drop

33
Fig. 3. Experimental apparatus Layout diagram

Air exhaust fan Sectional drawing from A-B

Test partition for air inlet devices; Heating panel

Air-outlet duct ~B variable flow

Removable partition

Heating panel or slab.

Fig. 5. The 150 cm opening installed 20 cm from the

floor (shown are resistance temperature detectors

for measuring air-stream temperatures)

34
Fig. 4 Test Result: -f 60 Cubic Meiers Per Hour

o a 2030 * B»f, tmj

- L

p, •*,. i

„*

_=_ X-J- 1- bBT,.,».,=„>_ ITtt

Elongated opening at win

o a 2 0JD < T

( >_ j£"J

i*

vm^5

'JO 150

- Hhp

MJ

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IL §* ^.j .' »

1

.

r

t

-i

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» 20 JO 40 50 f, cmj

Elongated opening above a radiator

(Ft,. I) |R«. J) (Fit. K)

i 2010 <0(„mj -, • » *"""•' » » »r>""J —nTM

|-|"»

I J

i

t20X(.<m)

^

Opening near (looi panel heating

is. -L

w 20 i

|

' m- 2

,2 Mkh^Vfl BBiTWLi'i>.i...

loo. c.n.1 Unrng »•£

Opening near ceiling

? 20 30 iO 50

Opening near ceiling panel h

~^_ i _.i__nH|

-\——

i

35
Figure 6.

,,,' \

1

1 LEGEND

: 20

i )lane deflector h

ft set 3 cm behind grille Q

ill —•: Plane deflector with

li

1 II air upward h

g.t .7° x:< '10an

[

'U

!l!

i

i>n

15

i !

:i

i

1

• i \

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1 \

1 \

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i \

i >,\

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r. \

'

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\ s

^, 5 ?\

\ \ \ \ \ \

X v

\ x

\ \, X

2'- — -V

s

' ^*

**«- vs

w - *« nssrT'm_»__

( ) 1791 5 ic x ( ml

9,,j

Fig. 7. Elongated opening with de directing air upward.

Comparative discomfort bless

' as function of distance t air inlet cases of aperature e.

'flector

ad by drafts

for different

1 LEGEND

i e - 2cm

20 e = 1 cm

T

I

!r —.—._

: e -0,bcm ——— e ?02cm

X: > 1 10cm

i

!

v

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15 BUId

III

1

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i

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\

V\

P ! _ \ V * N jSl s^ "s , ^.

-*.„

C [? o\ 5 1C x m) 36
Cold surrounding

medium

e Variab le

Test room

Adjustable deflector

Fig. 9. Opening with deflector above a radiator. Fig. 10. Orifice spread alongside ceiling.

37
Fig. 11. Test results with a 120 mr/h air flow

10 20 30 iO(xcm)

Verticle projection

140

130 120

110

100 90

SO

70

60

5040

3020

10

s l

< m

30

\ 1

1.2'

3

ww°~ im = ;

: ft 1> 1>

Cold air inlet Horizontal projection

Small slit with deflector and inlet above top of a

radiator

10 20 30 40 fX cm J

c eiling pane heati ng 30" C.

\*2°- 35,07

', \

i.

250

240

230 220

210 200

190

10 20 30 40 (xcm)

Elongated divided opening close to ceiling with panel heating

10 20 30 40 50 60 70 SO 120 [x cm)

Horizontal joints (slits) in a window

38
ANNEX

DETERMINATION OF THE PRACTICAL AIR FLOW LIMIT

1. INTRODUCTION

Air inlets must be neither too closed nor too open. Not too closed,

so as to preclude their blocking ventilation under the most frequent draft

(draw) conditions (average thermal draft, light winds). Not too open, in

order to avoid excessive air flow during a strong draft, in other words,

during high winds. This is the old argument as to whether windows should

or should not be airtight.

Even if those measures outlined in the preceding study are taken to

control discomfort resulting from cold air drafts, the drawbacks of strong

air flows continue to exist. First of all the latter needlessly increases

heat losses. Then they can also cause discomfort outside the normal

heating period since most facilities used to eliminate discomfort caused

by cold air drafts involve combining the heating and ventilation systems.

And lastly, even during a heating period, a strong air flow reduces the

effectiveness of these facilities.

The calculations which follow are designed to determine the order of

magnitude of pressure losses reconciling at best the contradictory

requirements we have just mentioned. Rigorous calculations should take

a very large number of variables into consideration, inter alia, those

pertaining to exposure to winds, construction of air-outlet ducts, part

played by static exhaust fans, etc. The CSTB is currently studying these

complex problems. These studies have not been completed. To obtain some

39
orders of magnitude and grasp the meaning of the phenomena involved, we

shall limit ourselves in this report to simple values, but, in our view,

these values are sufficient.

2. FACTS SURROUNDING THE PROBLEM . THERMAL DRAFT AND FORCE OF WIND

We have chosen to study the following ventilation plan in which air

inlets placed along outside walls are fully brought into play. The air

inlets are located in the "non-service" rooms of the dwelling, such as

the living room and bedrooms, and the air exhaust outlets consisting of

vertical ducts are in the service rooms, i.e. kitchen, bathroom and

toilet. To be more specific we shall limit our study to an apartment

depicted in Figure 1, p. 51. It comprises two non-service rooms

along the west outside wall and two along the east outside wall. One

exhaust duct outlet is in the kitchen, the other in the combination

bathroom-toilet. If we assume that the windows in the service rooms are

airtight, then it makes little difference ventilation-wise whether these

rooms are along outside walls or in the central part of the dwelling, that

is not along an outside wall.

During the winter, in the absence of any wind, solely thermal draft

(chimney effect) is active. The air enters almost uniformly through the

four non-service rooms and leaves by the service rooms where it is the

most polluted. When there is a light wind, the ventilation flow diagram

remains unchanged , however , the rooms on the west are more ventilated

than those on the east.

40
Under strong-wind conditions, ventilation through the ducts is

supplemented by cross-ventilation, with a great volume of air entering by

the west rooms and leaving partially through the ducts and partially

through the east rooms. Outside of the heating season, cross-ventilation

is dominant and vertical ventilation is almost nonexistent.

What is the relative importance of the forces involved?

Thermal draft is proportional to height of the duct and temperature

differential At between the outside and inside temperatures. Its value.

in millimeters of water, is:

0.0045hAt

where h is expressed in meters, and At in degrees centigrade.

The influence of the duct's height is obviously important. However,

for our purposes we shall limit ourselves to the average height of ducts

in five-story buildings, that is 8.50 meters, and defer until later any

study of the influence of the height.

For At, we shall use as average value, the average value for six

winter months in Paris, that is the inside temperature of 22° (temperature

in the ducts is always slightly higher than the average temperature of

the rooms) minus the outside temperature of 6°, consequently a At of 17°.

Under severe weather conditions (-15°) , thermal draft is double. In mild

weather (+15°), it is reduced by one half. Since air flow varies almost

like the square root of the draft, the result is that air-flow variations

are only around the average value of approximately + 40 per cent.

Moreover, the importance attached to natural ventilation by thermal draft

lies in this phenomenon

41
When the wind is perpendicular to the building, it creates pressure

on one facade and reduces pressure on the other.

The relation linking pressure and reduced pressure to wind velocity

is a function of many factors: height and shape of the building,

neighboring obstacles .... With V as the wind velocity in an open site

at a given height, it is assumed that pressure and reduced pressure on a

building at that height and in the absence of obstacles, are equal

respectively to

:

2 2 +0.8 — and -0.5 L

16 16

2 where — = dynamic pressure of the wind in millimeters of water, with V

16

expressed in meters per second.

Wind-velocity rates vary considerably with site, exposure and height.

We consider as: —light, a 2 m/s wind with dynamic pressure equal to 0.25 mm

of water;

o —moderate, a 4 m/s wind (V /16 = 1 mm);

n —strong, an 8 m/s wind (V /16 = 4 mm);

2 —very strong, a 16 m/s wind (V /16 = 16 mm).

On the average site, 2 m/s represents the most frequent velocity.

Hence it can be seen that in a very strong wind, pressures and reduced

pressures will be 64 times what they are on the average, and air flow

will be 8 times the average air flow.

In concluding, under average winter conditions, thermal draft is

approximately three times greater than the force of the wind. On the

other hand, in exceptional conditions, thermal draft can increase air flow

42
by merely 40 per cent, whereas the wind can multiply it by eight. The

solution to the problem is to facilitate vertical ventilation to the

maximum by employing large ducts, and, contrariwise, to reduce crossventilation by using rather constricted air inlets.

3. CALCULATION OF AIR FLOW IN THE CASE OF AN AIR INLET CONSISTING OF

2 MORE OR LESS AIRTIGHT WINDOWS OR 150 cm OPENINGS .

To simplify computations we can assume—with little error-that all

air leaving via the kitchen duct comes from the living room and first

bedroom, and that all air exhausted through the bathroom duct comes from

the other two bedrooms. Both halves of the dwelling may then be considered

separately. By deeming both halves to be identical from our point of view,

we may even make our computations for only one half.

We shall make those computations with three types of air inlets

characterized by pressure-loss curves E]_, E~ , and E plotted in Figure 2,

p. 51. Curve E is for a highly airtight window, one that frankly is

not very common in France. Curve E is for a very ordinary wooden window. ' 2

2 Curve Eo is for a 150 cm opening covered with a fine-mesh grille.

We chose pressure losses in the ducts that are clearly below the

losses experienced in ducts generally constructed. As we indicated above,

we did this in order to favor vertical ventilation as much as possible.

Such a pressure-loss curve can be realized providing the cross section of

the ducts is increased, and, above all providing any constriction at the

inlet grille duct fittings, and exhaust fan, is avoided. But that is not

the purpose of this study.

43
In our computations all the dwelling's inside doors were assumed open

and then closed. Rather airtight doors were chosen (curve P]_, Figure 2,

p. 51) in order to better highlight their effect.

Compiled results are given in Table 1, p. 53. To simplify matters,

it was assumed that there was no air flow within the vertical duct in the

absence of any thermal draft. In using a desired hourly air change equal

o to one, or a total air flow by duct of the order of 60 m /h, it was ascertained that, in the absence of wind and with average thermal draft, only

the combination of 150 cm openings and open doors was satisfactory.

Unfortunately, with a very strong wind this leads to an air flow five times

greater than the one desired. Furthermore, with all air entering the

west bedroom in this case, the flow in that bedroom is ten times greater

than desired. It seems, therefore, that it is difficult to find a compromise. But very strong winds only occur frequently in exposed sites.

If we disregard them it would be possible perhaps to arrive at an

acceptable solution by using pressure losses ranging from those experienced

with ordinary windows to those with 150 cm^ openings. Such pressure

losses can be obtained for example, with elongated and thin openings (of

the order of one-meter long and 5 mm thick) which correspond to those

measures advocated for control of cold air drafts in the case of radiator

heating.

Closing the doors reduced air flow in a strong wind to a rather

appreciable extent. Such closing also reduces air flow under thermal

draft conditions. A good solution is to reduce pressure losses in the

air entering the bathroom (or kitchen). As a matter of fact, under

thermal draft conditions the air flow there is double the flow passing

44
by the bedroom doors, and consequently pressure loss is approximately

four times as great. Pressure losses can be rather easily reduced, and

moreover with little inconvenience, by, for example, providing a

permanent staggered air passage, approximately one-centimeter wide, above

the door (Figure 3, p. 52).

We shall resume our computations in more detail with this new data.

4. COMPUTATION OF AIR FLOW IN THE CASE OF CONSTRICTED OPENINGS AND

PERMANENT AIR PASSAGES INTO SERVICE ROOMS .

Computations were made as before by using as pressure-loss curves: —curve E / , for air inlets; —curve P-. , for bedroom doors, —curve P2 , for kitchen and bathroom doors.

Results are compiled in Table II.

With doors open, the values are between those in the second and third

columns of Table I, and there is nothing special to report.

With the doors closed, and with only thermal draft, air flow is

reduced by merely 15 per cent, whereas without air passages at the entrance

to service rooms it would be reduced by 25 per cent. With wind only, the

reduction is of the order of 20 per cent.

Computations were carried further than previously with a view to

determining the combined action of wind and thermal draft, at least under

average thermal draft conditions. The effect of wind on the static

exhaust fan, pressure loss included, was assimilated to a reduced pressure

V

2 equal to 0.25 —

16.

45
Overall results are in Table III, p. 54. Following are the results

o expressed as ratios of the desired values (air change of 60 m /h for half

o of the dwelling, entering air flow of 30 m /h per room):

Dwelling

air changes

Entering

air flow West facade

No wind

Light wind

Moderate wind

Strong wind

Very strong wind

0.8 — 0.7

0.85 — 0.7S

0.9 — 0.8

1.7 — 1.4

3.7 — 2.9

1 1 — 0.9

1.1 — 0.9

1.8 — 1.4

3.5 — 2 8

7.4 — 5.8

For no wind, light wind, or moderate wind, air change in the dwelling

almost reaches the desired value without the entering air flow on the

west facade attaining more than twice the desired value.

For a strong wind, air change in the dwelling exceed the desired

value by fifty per cent, and entering air flow on the west facade is

triple the desired value. Given the rather infrequent occurrence of such

winds, whose velocity is exceeded not anymore than one to five times out

of a hundred on the average site, the excess in air change is acceptable.

As for the discomfort caused by drafts, we have seen in the preceding

study that certain steps can be taken to alleviate that discomfort in

situations where air flows are equal to four times the desired value.

For a very strong wind, the overall air change is more than triple

the desired value, and the air-inlet air flow on the west facade can be

seven times greater than the desired value. These values are unacceptable.

46
But there is no fear of encountering such winds with appreciable

frequency except on an exposed site. In such instances, special precautions

are necessary. Two such precautionary measures were studied.

Dyssymmetrical Openings

With a profile such as the one depicted in Figure 4, p. 52, it is

possible to obtain an outlet pressure loss triple that of the inlet loss.

With average thermal draft and a very strong wind, air change in a

dwelling and air-inlet air flows on a west facade decrease very little:

3 3 210 m /h instead of 220 m /h, with doors open, or a reduction of only

five per cent.

This solution consequently seems to be of little value.

Adjustable Openings

If the inlet opening has a hand-lever with which the aperture can be

adjusted at will, all settings are possible. However, we believe it

desirable to limit the possibility of closing the opening, in such a way

that the air flow for a given pressure loss does not decrease more than

one-half.

Under these conditions and with average thermal draft, the following

results are obtained:

Air change in half of dwelling

Air inlet air flow

per room on west facade

No wind

Light wind

Moderate wind

32 m

3/h instead of 44,

or 27 percent reduction

34 m

3/h instead of 51,

or 33 percent reduction

38 m

3/h instead of 53,

or 30 percent reduction

16 instead of 32

20 instead of 32

28 instead of 53

Strong wind

Very strong wind

55 m

3 /h instead of 104,

or 47 percent reduction

115 m

3 /h instead of 220

or 48 percent reduction

55 m

3 /h instead of 104.

or 47 percent reduction

115 m

3 /h instead of 220,

or 48 percent reduction

47
With no wind, light wind, or moderate wind, air change in the dwelling

is reduced only approximately 30 per cent. On the other hand, with a

strong or very strong wind, air change, like the air flow from the air

inlet on the west facade, is cut nearly in half.

It appears, therefore, that this solution should be retained.

Automatically adjustable openings can also be devised.

5. INFLUENCE OF HEIGHT

All preceding computations were made in the case of a uniform height

of 8.50 meters.

With greater heights, thermal draft increases. To retain the same

air flows, pressure losses should be increased, and preferably air-inlet

losses rather than duct losses. Wind effect can be reduced by such action.

An approximate calculation shows that for a draft height, double the

height previously used of 8.50 m, the same air flow can be obtained, with

no wind, by multiplying air-inlet pressure losses by 2.5 and duct pressure

losses by 1.5. With a strong wind, there will be a resultant decrease in

air flow, on the west facade, of the order of 35 per cent compared with

previous computations

.

For lesser heights, pressure losses should contrariwise be decreased

and preferably those within the ducts.

For a draft height that is one-half of the 8.50 m height previously

used, the same air flow can be obtained, with no wind, by reducing the

pressure losses of the duct by two-thirds and those of the air inlets by

one-third. With a strong wind, there will be a resultant increase in air

flow of the order of 30 per cent.

48
The most difficult case to resolve is that of the last few floors of

high buildings subjected to the most violent winds, and having only a

limited thermal draft height. Perhaps some common or collective duct

arrangements would allow equilibration of thermal drafts at the different

floors of buildings. And lastly, air inlets in outside walls are not the

only possible inlets. In extreme cases, air inlets by means of ducts are

perhaps desirable.

6. CONCLUSION

The Recommendations given in the first few pages of this "Cahier"

contain the conclusions of this report. These conclusions amount to distinguishing four natural ventilation situations with respect to exposure

to wind.

1. Minimum exposure situation, that is to say a situation in which

velocities greater than 8 m/s can be disregarded from our viewpoint.

Inlet openings with fixed apertures seem suitable. The exact value of

pressure loss characteristics cannot be given, since, strictly speaking,

that value is a function of the other parameters upon which ventilation

depends (cross section and height of ducts...). These characteristics

must be such, however, that for a 4 mm pressure loss —corresponding to

the pressure difference obtained on a west facade with a "strong" wind

air flow must not be more than four times the basic air flow. Protection

against cold air drafts will be provided for this air flow.

2. In an exposed situation, adjustable inlet openings are practically necessary. We recommend that they be accepted on condition that the

air flow in closed position remain equal to half of the air flow in open

49
position. Pressure-loss characteristics will be such that air flow does

not exceed the quadruple of the basic air flow in closed position and for

a 16 mm pressure loss corresponding to the pressure difference obtained

on the west facade under a "very strong" wind.

3. In an exceptionally exposed situation, which can be the case of

a very high building or one situated on an extremely open site, it will be

difficult to obtain satisfactory results with air inlets in outside

walls, except perhaps when automatically adjustable or controlled devices

permit limiting the air flow regardless of the wind pressure.

4. In an exceptionally sheltered situation, which can be the case

inside a city, we could tolerate having protection against cold air drafts

provided only for double the basic air flow.

In artificial ventilation, the problem is different. A permanent

draft of several millimeters is actually available and it is much superior

to thermal draft. Consequently, air-inlet pressure losses can be increased

and wind effect decreased. This can be a worthwhile solution for high

buildings exposed to wind.

50
Fig. 1. Ventilation flow diagram for an

apartment with two exposed walls

0.05 0.1 0,2 0.<05 I 2 3 | 5 10 1 s H m

Pressure losses in mm water

Fig. 2. Pressure-loss graph

51
Fig. 3 Permanent air passages at top of floor

Outside Inside

Fig. 4. Dyssymmetrical opening

52
Table I

Air Inlets in More or Less Airtight Windows or in 150 cm Openings

All Doors are Rather Airtight

a) Thermal draft only

b) Wind only i

Mild weather

Winter average

Exceptional cold

Light

Moderate

Strong

Very strong

Ventilation air flow for half of dwelling, doors open and doors closed.

Rather airtight windows

6—6

9—9

15 — 14

2—2

4—4

12 — 11

32 — 31

Very ordinary windows

25 — 19

37 — 28

55 — 42

10—9

23 — 20

55 — 48

132 — 112

150 crn^ openings

40

59

25

37

54

34 — 20

71 — 43

238 — 90

310 — 190

Table II

Entering air through constricted openings, rather airtight bedroom doors, permanent air passages into kitchen and bathrooms

Ventilation air flow for half of dwelling, doors open and doors closed

a) Therm

i

al draft only

Mild weather

Winter average

Exceptional cold

In parentheses the air flow that would be obtained

if all doors were sufficiently airtight

32 — 28

47 — 41 (35)

69 — 60

D4

b) Wind o nly

Light

Moderate

Strong

Very strong

15 — 12

35 — 28

78 — 63

178 — 137

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54
iform NBS-114A (1-711 2. Gov't Accession No.

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-710-63. Recipient's Accession No.

4. TITLE AND SUBTITLE

BUILDING RESEARCH TRANSLATION Ventilation Air Inlets for Dwellings

5. Publication Date January 1973

6. Performing Organization Code

7. AUTHOR(S) M. Croiset and H. Bizebard

8. Performing Organization

10. Project/Task/Work Unit No. 4603104

9. PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Same as item 9

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES Translated by the Joint Publication Research Service

U.S. Department of Commerce Washington, D.C. 20234

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) Preliminary tests have shown the existence of a "discomfort index", a function

firstly of the difference between the temperature in the room and the temperature

of the air current and, secondly of the speed of the air stream. The permissible

limit for this index has been fixed at two degrees C, at least in that part of the room situated more than 20 cm. from the outside walls and less than two meters

in height.

Systematic artificial tests have resulted in satisfactory solutions being found

for the air inlets into the outside walls. —An elongated aperture placed above a radiator and fitted with a deflector so that cold air entering the room mingles with the ascending warm air current. —An aperture located behind a convector heater so that the same result is achieved as in the case of the radiator. —A row of apertures located along the heated ceiling placed so that entering

air is diffused into the warm air before reaching the occupied zone. Some calculations aimed at determining the orders of magnitude of the necessary

sections and the possible force of the air current in a high wind, have revealed the need for a manual or an automatic regulator where a wall is exposed to wind.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Air inlet; discomfort index; draft; outside wall; ventilation; wind.

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