• j^-f '^yj Crops Protection Research Brancíi

V(>, %dj Crop3 Research D:r' sion, ARS

U, S, Department of A-riculture

Beltsville, Mary].and

Farmhouse Design

and Equipment for

SUMMER COMFORT

AGRICULTURE HANDI

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Agricultural Research Service

U.S. DEPARTMENT OF AGRICULTURE
Contents

Page

Solar control for house-temperature reduction 1

Shading 2

Overhangs — 2

Light colors -- 4

Roof spray 5

Insulation 5

Vapor barriers 7

Air movement 7

Night air cooling with attic and window fans 7

Cooling with well water 9

Evaporative cooling 10

Mechanical refrigeration air conditioning 12

Operation and size 12

Types and requirements 12

Electrical characteristics 13

Power requirements , 13

Controls 15

Water-cooled condensers 15

Heat pumps 16

Literature cited 16

Appendix _ 16

Cooling-load estimate form for room air conditioners 16

Cooling-load estimate form for central air conditioners ^ 20

Washington, D.C. Issued April 1963

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington 25, D.C. - Price 15 cents
Farmhouse Design and Equipment

for Summer Comfort

BY CHESTEB P. DAVIS, JB./ and JOSEPH W. SIMONS, Agricultural Engineering Research Division, Agricultural

Research Service^

Comfort in the home during hot, summer

periods is desirable so that work, recreation, and

restful sleep may be enjoyed.

Effective cooling equipment in summer is as

important for the modern home as a dependable

system for supplying uniform heat in winter.

Depending on location, most farm families

spend substantial amounts for heating their homes

during the 4 to 8 months of cold weather. In the

farm home of today comfortable living can be

provided at reasonable cost in the remaining

months of moderate to hot weather. In some

cases the lower cost cooling methods such as the

use of window or attic fans, well water, and evaporative coolers will provide relief from the heat.

The most ideal and positive method of cooling is

the mechanical refrigeration system. Costs of

these systems have come within the financial reach

of many farm families.

Eegardless of the method used to improve comfort, consideration must be given to temperature,

relative humidity, air movement, and cleanliness.

High temperatures become almost unbearable

when relative humidity is high and there is little

air movement. Heat prostration or other illness

may occur. However, if temperatures are moderate, liigher humidities can be tolerated.

To maintain comfortable temperatures inside a

building when it is hot outside, prevent as much

heat as possible from reaching the interior and

remove the heat that does enter if undesirably high

temperatures result. Methods of attaining these

requirements include (1) exclusion or reflection of

direct radiation from the sun; (2) insulation of

the house to reduce heat transfer through walls

and ceiling; (3) movement of air within the

rooms; (4) ventilating with cooler outside night

air; and (5) cooling room air or incoming air by

using water, evaporative cooling, or mechanical

refrigeration.

SOLAR CONTROL FOR HOUSE-TEMPERATURE REDUCTION

Protection from direct rays of the sun or reflection of the solar heat can do much to reduce temperatures in the house. In houses cooled by mechanical air conditioning or other methods this

protection serves to lower the initial investment

because of the smaller capacity of equipment required. Operational costs are also reduced.

There are three major methods of obtaining this

protection: (1) Orientation of the farmhouse so

that the principal glass areas receive maximum

protection from the direct rays of the sun; (2)

provision for shading the house, particularly glass

areas, with roof overhangs, awnings, shutters,

louver-type screens, vegetation, or other devices;

and (3) utilization of light-colored roofs, exterior

'Died July 1962. ^ ..^.

^The copyright iUustrations are used with permission.

Italic numbers in parentheses refer to Literature Cited,

p. 16.

walls, and window hangings to reflect solar

radiation.

In the United States the sun shines on the

roof and south wall of the house most of the day.

Glass areas in south walls can be more easily

shaded with roof overhangs and similar devices

than those in east or west walls on which the sun

also shines during part of the day. For this reason, protection against solar heat is easier if the

long dimension of the house runs east and west

and minimum glass areas are used in east and west

walls. Tliis orientation may not be best to utilize

prevailing breezes if natural ventilation is used,

but it does have the added advantage of best exposure for solar heatin winter.

Ground surfaces around the house affect the

amount of radiated and reflected heat (fig. 1).

Large concrete or bituminous-covered areas ad-
LAWN 80° F. BLACKTOP 120* F.

FIGURE 1.—Radiated and reflected heat from lawn and

blacktop adjacent to exposed wall of house. (From

Fitch (6).)

jacent to the house and exposed to the SITII should

be avoided.

Shading

Plantings of deciduous trees can shade the house

in summer and yet permit the sun to penetrate during winter for indoor light and heat. Trees and

shrubs should not be planted so close to the house

as to shut off breezes if natural ventilation througli

doors and windows is depended on for cooling.

Metal or canvas awnings reduce by 70 to 75

percent the heat coming through windows. Awnings with open sides are about 15 percent more

effective than those with closed sides during

periods of maximum solar radiation. Open awnings must be wider than the window to keep the

sun from shining in at the sides. Light-colored

awnings are more effective than dark ones.

Louver or bar screens are about 90 percent

effective in reducing heat through south windows

not otherwise shaded, and they are from 55 to 75

percent effective for east and west windows. Inside Venetian blinds are from 25 to 50 percent

effective, depending on the color, whereas fully

drawn inside roller shades are not quite so effective.

Overhangs

Overhangs, or extensions, of the roof over the

south wall (fig. 2) are essential and are usually

simple to incorporate into the house design. The

following guide may be used :

Width of overhang = factor X shadow height

(distance below eave of roof)

To determine the roof overhang needed to cast

the desired shadow height on a south wall or window, (1) check the latitude (fig. 3) in which you

live, (2) select the factor for your latitude from

the following tabular data, (3) choose the shadow

height desired on the glass area or wall, and (4)

multiply the factor by the shadow height selected.

The following factors are used for calculating

the width of an overhang for properly shading a

Id, »ill.,

FIGURE 2.—Relationship between width of overhang and

shadow height.

south wall or window in various latitudes from

April 1 to September 11 :

Latitude (°) Factor

25 0. 37

30 .48

35 .59

40 .71

45 . 85

50 1. 02

For example, in a latitude of 35° to shade a

glass area extending 5 feet below the eave of the

roof, or a horizontal overhang, multiply 5 by the

factor 0.59, and the width of the overhang should

be approximately 3 feet.

West windows can be effectively shaded by awnings or metal louver screening over the windows

for early-afternoon protection and by vertical

shading devices opposite the windows for lateafternoon protection. However, if an overhang

is preferred (fig. 4) rather than awnings or louver

screening, follow the same procedure as for south

windows, using the factors for west windows as

given in table 1.

TABLE 1.—Factors for calculating width of overhang ove?' loest windows for voHoits times and

latitudes from April 1 to Septemher 11

Time

Factors at latitudes (°) of—

(p.m.)

25 30 35 40 45 50

1 0. 27

.62

1.07

1.80

0.29

.64

1.10

1.88

0.31

.67

1. 15

1.96

0.33

.71

1.21

2.05

0.35

.76

1.28

2. 14

0.38

.81

1.36

2.34

2

3

4
FIGURE 3.—^lap of the United States showing latitudes.

FIGURE 4 Overhang and vertical shading device for west wall or window. A, Shadow height desired; B, width of

overhang ; C and D, distances overhang must extend south and north, respectively, of window edges.
Using the same example as given for a south

wall, 5 feet multiplied by the factor 0.31 for 1 p.m.

will give an overhang of li^ feet. For 2 p.m., 5

multiplied by 0.67 equals 3% feet, and for 3 p.m.,

5 multiplied by 1.15 equals 5% feet.

It is generally impracticable to build an overhang wide enough to provide proper shading at

4 p.m. unless a patio or porch roof is planned.

Therefore, calculate the overhang for 1, 2, or 3

p.m., selecting the one that fits your situation best.

Eemember that a vertical shading device (fig. 4)

must be used in combination with the horizontal

overhang when it is desired to limit the width of

the overhang. If a walkway is planned between

the house and the vertical shading device, the

overhang should be sufficiently wide to provide

passage for one or two persons or perhaps for

lawn equipment such as a wheelbarrow.

The vertical shading device must be placed opposite and run parallel to the window and extend

to the edge of the overhang, as shown in figure 4.

Vertical shading devices may include shrubs, a

lattice covered with vines, a decorative block wall,

or a wooden screen. A louvered wooden screen

or wall cuts off less light than a solid one, but all

the vertical shading devices that are affective in

late afternoon will cut off the view to a great extent. Shrubs or vines that lose their leaves in

winter permit sunlight in cold weather. Removable screens provide the same advantage.

The length of both the overhang and the

vertical shading device must be calculated as well

as the overhang of a horizontal shading device.

Generally the overhang and the vertical shading

device are made the same length. Figure 4 illustrates the distances that the shading device must

extend both southward and northward from the

edges of the window. To calculate these distances

proceed as follows :

1. Use the overhang calculated for 1 p.m. for

your particular latitude.

2. Select the proper latitude factor from the

following data :

Latitude (°) Factor

25 1.26

30 1.60

35 1.87

40 2.12

4{> 2.41

50 2. 67

3. Multiply the width of the overhang (5),

which has been calculated in step 1 (above), by

the factor selected in step 2. This is the practical

distance (C) that the overhang and vertical shading device must extend south of the edge of the

window.

4. To calculate the distance (D) that the shading device must extend north of the edge of the

window, multiply the width of the overhang by

0.30. This extra northward extension of the shading device provides late-afternoon protection in

early summer.

4

^ A SUMMER \ Js ,1

FIGURE 5.—Louvered overhang. (From Ramsey and

Sleeper (8).)

©

©

FIGURE 6.—Egg-crate overhang. (From Ramsey and

Sleeper (8).)

In the preceding example the width (B) for 1

p.m. was 1^ feet. This width multiplied by 1.87

for 35° latitude gives 2% feet, which is the distance the shading device must extend southward

from the edge of the window. This width also

multiplied by 0.30 equals about 6 inches, which

is the distance the device should extend northward

from the window edge.

Similar calculations can be made for shading

east windows. The time factors are interchangeable as follows :

West loindows East windows

{p.m.) {a.m.)

1 11

2 10

3 9

4 8

Horizontal louvers (fig. 5) allow movement of

air and entry of diffused light. An egg-crate

shading device (fig. 6) although more expensive

is more effective as it eliminates oblique rays of

the sun.

Light Colors

A light-colored roof covering such as composition shingles absorbs only about one-half as much

radiated solar heat as a black or dark roof. White

marble chips absorb about one-third as much solar

heat as dark ones. These figures are generally

true in clean atmospheres and where the light

color does not darken with age. Light-colored

shades, draperies, blinds, other window hangings,

and exterior-wall paints also reflect solar heat

better than dark ones. Thus, light colors should

be used wherever possible for most effective protection against solar heat.
Roof Spray

Koor.^^ ^^^ surface temperatures in the house have

Deen reduced by spraying the roof with water (9).

JLííL^^Í ^"^ temperature reduction resulted

wnen water was sprayed on a black composition

root ana the ceilmg was uninsulated, the windows

and doors were closed, and the windows were

shadecl. Benefits were less with the insulated

celling commonly provided for economical heating in winter. A good water supply, pumped at

the rate of from one-fourth to one-half gallon per

hour per square foot of roof surface, will likely

be required depending on climate, type of roof

surface, and method of application. Other means

of cooling the interior of the house are probably

more satisfactory and economical considering the

costs of the installation and operation of the pump

and the amount of water required.

INSULATION

Insulation of the walls and ceiling of the house

helps to retard entrance of heat from the outside.

It has been customary to specify insulation in

terms of inches of thickness. A tetter method is

to specify it in terms of resistance (B) to heat

flow that will be provided when the insulation is

installed. The higher the R value, the greater

will be the resistance to heat flow ; consequently,

the rate of heat flow is less. Some manufacturers

are now specifying the R ^^alue of their insulation.

To the R value of insulation should be added

the R value of construction, which is usually small

in comparison with the former. This has been

done in tables 2-4 for typical wall, ceiling, and

roof construction. For hot-weather comfort and

economy in air conditioning it is suggested that

the total R value of construction and insulation

be not less than 11 for the walls and 17 for the

ceiling. If the attic is unoccupied, insulation will

normally be installed in the ceiling. In this case

and with good natural ventilation in the attic,

an R value for the ceiling may be increased by

adding 3.0 for the insulation of the roof. Even

though the construction of a particular house may

be somewhat different from that specified in the

tables, an estimate can be made with sufficient accuracy as to whether or not the construction meets

the suggested insulation value.

Insulation for residences generally is obtainable

in several types, including loose fill, bat, blanket,

board, slab, and reflective. Foamed plastic is a

new insulation that may become economical for

residences. Walls and ceilings of houses already

built are often insulated by blowing in loose-fill

insulation. Stud spaces should be completely

filled by blowing in the insulation from both top

and bottom by means of pneumatic equipment.

If this is not done, the density of the insulation

will not be uniform. Wind or heavy traffic on a

nearby road that causes vibration of the structure

may result in eventual settling of the insulation

and thus some space at the top will be left uninsulated. Loose-fill insulation includes mineral

wool (glass, slag, or rock), macerated wood pulp,

or treated shredded wood fiber. Sawdust or shavings, although sometimes used, are not generally

TABLE 2.—R values for typical walls

Exterior wall finish Interior wall finish

Total R value of

construction and—

Type of wall

No

insulation

Fibrous

insulation

(2

inches)

Fibrous

insulation

(3

inches)

Wood frame Drop siding (1 by 8), wood

sheathing (2^2).

Drop Biding (H by 8), insulation-board sheathing

Brick veneer, wood sheathing

Concrete block (8)

Gypsum board (^) 4.0

5.2

3.8

2.9

4. 1

3.6

2.6

11.4

12.5

11.2

15 4

Do Plywood (%) 16. 2

Brick veneer, wood frameConcrete block, lightweight aggregate.

Brick III' ---

Gypsum board (H), plaster

None -

14. 9

do

Face brick (4), common brick

(4).

Concrete (6) (140 Ibs./cu. ft.)-

Gypsum board (%) on furring.

Plywood (H) on furring

Gypsum board (%) on furring.

11.5

11.0

10.0

15.2

14.7

PoiirpH pnn ffpfiP — 13. 7

1 R values computed from American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (^). All

measurements in parentheses in inches unless otherwise specified.
TABLE 3.—E values for typical ceilings

Ceiling finish

Gypsum board {}/%)

Do

Gypsum lath {}/%), plaster (>i) --

Gypsum board (%), acoustical tile (,^)-

Woodlath, plaster (H)

Type of floor above ceiling

None

Wood subfloor (2^2)-

None

.do_

Wood subñoor (2^2)-

Total E value :/-

construction and—

No

insulation

2. 2

4.3

2.3

3.3

4. 6

Fibrous

insulation

(2 inches)

9.6

11.7

9.7

10.7

12.0

Fibrous

insulation

(4 inches)

17.0

19. 1

17.1

18.1

19.4

1 See footnote 1, table 2.

recommended as they absorb moisture readily,

provide a nesting place for rodents, and require

treatment against fire and insects.

Vermiculite ^^ (expanded mica) is used most

commonly to fill the cores of concrete block and

thereby reduces heat loss or gain. It is less than

two-thirds as good an insulator as mineral wool.

A vermiculite that does not absorb moisture as

readily as the old type is now available. It insulates only the core space and does not reduce heat

gain or loss through the web sections of the block.

A more effective method of insulating concreteblock or other masonry walls is to fasten furring

strips on the inside and apply one of the other

types of insulation to the strips. Walls below

ground need not be insulated as well as those above

ground because of the lower heat gain from the

cooler ground.

Concrete-block or masonry walls must be waterproofed to prevent moisture from reaching the

insulation. Moisture reduces the effectiveness of

the insulation and may shorten its life. Waterproofing the exterior of such walls is best. Mate-

^The mention of a trade product does not imply its

endorsement by the U.S. Department of Agriculture over

similar products not named.

rials for waterproofing the interior of existing

walls may or may not be effective.

Bat and blanket types of insulation are most

commonly used in new construction and sometimes in remodeling. They are generallv composed of fibrous mineral wool, wood fiber, or

cotton fiber, backed or covered with a treated kraft

paper. The backing forms lips that permit easy

attachment to studs or joists with the use of a

hand stapler.

Board-type insulation, in the form of large

sheets, planks, or ceiling tile, usually one-half

inch thick, is often used in remodeling because it

provides some insulation as well as a finished interior in covering existing surfaces. This type of

insulation is about two-thirds to three-fourths as

effective an insulator as mineral wool of equal

thickness.

Slabs and planks for roof decking or above the

deck can be obtained in thicknesses up to 3 inches.

Some of these are about three-fourths as good an

insulator as mineral wool.

Aluminum foil is the most commonly used reflective-type insulation in house construction. It

is light weight and easy to install, but it provides

little fire resistance. Its effectiveness depends on

the reflectivity of its surfaces and the formation

TABLE 4.—R values for typical pitched roofs ^

Ceiling finish applied directly to

rafters

Total R value of construction 2

and—

Type of roof covering

No

insulation

Fibrous

insulation

(2 inches)

Fibrous

insulation

(3 inches)

Asphalt shingles, building paper, wood sheathing

Asphalt shingles, roof-insulation board (2),

Gypsum board (H), acoustical

tile (H).

Rafters exposed

5.0

8.7

3.5

3.6

10.8 18.2

tongue-and-groove wood (1^).

Asbestos-cement shingles, building paper, wood Gypsum board (H) 9.5

9.6

17.0

sheathing (2^2).

Tile shingles, building paper, wood sheathing Wood lath plaster (H) 17.0

(^32).

See footnote 1, table 2. 2 Rafter spaces ventilated above insulation.
fh f^^^ ^^^ spaces. Conditions in the atmosphere

tnat tend to promote chemical action, deposit dust,

or soil the surface will reduce the effectiveness of

any exposed reflective surface. To be effective,

renective insulation must face an air space. Eeflective insulation may be installed in single sheets

between framing members, but to be adequate

several sheets with air spaces between are necessary. Installation of individual sheets in this

manner is impractical. However, accordionpleated alummum-foil insulation with several

sheets fastened together is available. When

this type is stretched to full width by pulling

on the fastening lips, air spaces are formed between the sheets.

Double glazed windows, called insulating glass,

also aid in reducing heat from the outside, although if exposed to direct sunlight, they will

transmit almost as much solar heat as single glazed

windows. Consequently, shading should be provided to reduce solar heat gain.

In the summer some provision must be made

for removing the heat that eventually builds up

within the house. Fan ventilators, evaporative

coolers, or mechanical air conditioners are generally used. If they are not provided, inside conditions during the late afternoon and at night in an

insulated house may be far less comfortable than

in an uninsulated house.

VAPOR BARRIERS

Summer air cooling for comfort does not normally create serious vapor problems in exterior

walls and ceilings. However, serious problems

can occur in winter. Moisture passing through

the construction from the inside to the outside

may condense and cause loss of insulative value

and deterioration of the insulation and structure.

Therefore the walls of every well-constructed

modem dwelling in most areas should have a vapor

barrier.

The vapor barrier should be placed between the

inside finish and the insulation. Polyethylene,

metal sheet or foil, duplex kraft paper with aluminum foil on one side, or duplex kraft paper with

asphalt between the laminations may be used. The

ordinary asphalt-saturated building paper or felt

(15 to 30 pounds) is not satisfactory. Some insulations and building boards are foil backed and

this backing provides a vapor barrier if properly

applied. Joints in the barrier should be held to

a minimum and made by lapping over framing

members. Vapor-barrier sealing tape is available

to seal joints around pipes and wiring outlet boxes

and to repair any holes in the barrier caused by

installation. If polyethylene film is used, it

should be not less than 0.002 inch (2 mils) thick.

Water-vapor transmission of a barrier is measured in perms, the unit of permeance. A perm

equals 1 grain (7,000 grains = 1 pound) of moisture per square foot per hour per inch of mercury

vapor-pressure difference. The permeance of a

vapor barrier used to protect insulation should not

exceed 1 perm.

Paints on the inside surfaces of a house have

some value as vapor-barrier materials. Alkyd

gloss, semigloss primer-sealer plus enamel, or

rubber-resin lacquer paints have low vapor permeance. Two or three coats are necessary to reduce permeance to 1.

Sheathing papers under the outside finish should

not be of the vapor-barrier type, so that any moisture entering the wall can escape. Ordinary

building papers and felts commonly used are satisfactory for this purpose.

AIR MOVEMENT

Although the temperature may be several degrees cooler inside a house than outside, the house

may seem warmer because of lack of air movement.

A room fan will create air movement and improve

man's comfort, but its cooling effects are reduced

when the temperature and humidity are high.

There are many types of fans. They vary in

construction, safety, and design. Adjustable floor

stands, wall-bracket mounting, oscillation, mechanical shields against accidental contact, and

other features should be considered.

Generally, low-cost fans have high speed with

fairly low air-moving capacity and no oscillating

features, whereas more costly fans are slower, yet

have larger blades, which move more air with

less noise, and they usually have speed-adjustment

and oscillating features.

The fan incorporated as part of the forced-air

heating system may be used to provide movement

of house air during the summer. Basement air

surrounding the furnace may be circulated

through the house by operating the furnace fan

with the fan chamber open.

NIGHT AIR COOLING WITH ATTIC AND WINDOW FANS

In some sections of the country night temperatures drop rapidly, even though heat records are

established during the day. Eapid movement of

this cooler night air accomplishes the twofold purpose of displacing warmer inside air and providing air circulation to afford relief to house occupants. With a well-insulated house and sufficiently cool nights, the temperature of the interior

air, wall surfaces, and furnishings may be lowered

appreciably. By keeping the windows closed.

663900 0—63 2
FIGURE 7.- -Nigiit air cooling v/ith an attic fan.

Stover (11),)

(From

reasonably comfortable conditions may result during the heat of the following day.

An attic fan (fig. 7) pro" ides a method for

utilizing the cooler night air. Forty air changes

per hour for the average three-bedrconi house can

normally be provided by a 30- to 36-inch fan

operated by a one-third horsepower electric motor.

(See table 5.)

The attic fan, wluch provides air movement for

rooms in the house, could also serve to remove the

daytime accumulation of attic hsat. Often the

unventilated attic air is 25 degrees or more ?rarmer

than the outside air. This hiffh temperature is

thus responsible" for liîativëîy rapid lieat flow

through the ceiling to the interior of the. house,

particularly if ceiling insulation has not been used.

If an attic fan is not available for ventilating

the house, a small fan may be used to ventilate

only the attic space during the day. The fan

should be capable of changing the air in the attic

at least once each minute and should operate continuously when the temperature of the attic is

higher than that of the outside air (7).

The air is usually exhausted from the attic to

the outside through large louvers at the gable ends

of the house, openings in the eaves, or vents in

hip roofs.

Window exhaust fans are relatively inexpensive

and reasonably effective in providing good air

movement. Generally they do not have the capacity of an attic fan. No construction is normally

required, as the mounting panel is usually adjustable for the size of installation required. Window fans do not remove accumulated attic heat.

They are likely to be noisier because of higher

operation speed and close proximity to the occupants and thus more objectionable than attic fans.

Night air cooling does have some serious disadvantages. Chief among these are the dust and

pollen, which are likely to be brought into the

One change every

1 1/2 minutes.

One change every minsjfe

FIGURE 8.—Minimum air changes recommended for attic ventUation systems.
IABLE 5.—Approximate capacities of attic fans and recommended sizes of inlet and outlet openings

40 AIR CHANOBB PER HOUR

Habitable Fan

diameter

Air discharge »

Normal

horsepower

Recommended

fan speed

Inlet opening to attic Outlet opening from

attic

house

volume

(eu. ft.) 2

Free air

opening

Wood

grille (60

percent)

Metal

grille (80

percent)

Wood

louver (50

percent)

Metal

louver (80

percent)

7,400

Inches

30

36

42

Cubic feet

per minute

4,950

7,350

10, 700 /2

R.p.m.

600

410

360

Square

feet

8.25

12.25

17.85

Square

feet

13.75

20.4

29.75

Square

feet

10.3

15.3

22.3

Square

feet

16.5

24.5

35. 7

Square

feet

10. 3

11,000 15 3

16,000 -- -- 22 3

AIR CHANCES PER HOUR

7,400-

11,000-

16,000-

36

42

48

7,400 %

1,000 H

6,000 %

410

360

375

12.3

18.3

26.7

20.5

30.5

44.5

15.4

22.9

33.4

24. 6

36. 6

53.4

15.4

22. Ô

33.4

1 Fan manufacturers and heating, ventilating, and airconditioning dealers should be consulted as to plans and

instructions for installation.

2 Basement and attic volumes not usually included.

3 At Ko-inch static pressure.

house, and the noise. The latter can be minimized

by using attic rather than window fans. In some

areas nighttime humidity may be sufficiently high

to be objectionable if drawn into the house.

The size of the attic or window fan required

for night cooling depends largely on the location,

volume of the house in cubic feet, and number of

air changes needed per hour (fig. 8). Approximate fan capacities and recommended inlet and

outlet opening sizes are given in tabk 5 as a ^uide

for selecting an attic fan.

Costs of the fan and construction incident to

installation may approach the cost of a mechanical

refrigeration unit. However, operational costs

will no doubt be smaller for exhaust cooling with

night air. The disadvantages previously given

should be considered before selecting a method of

cooling the house.

COOLING WITH WELL WATER

Air cooling with well water is another method

of low-cost cooling {10^ 11). This method is inexpensive if good usage, such as in rural areas,

can be made of the water for lawn or garden irrigation or stock watering and if an adequate supply of water at 60° F. or cooler is available near

the surface. Pumping costs should not be excessive.

Surveys of ground-water sources indicate suitable well-water temperatures exist in many areas

of the United States. However, ground water m

the Southern States, especially southern Arizona,

New Mexico, and the Central Valley area of California, is generally too warm to be depended on

for this type of cooling.

Approximately 1,300 cubic feet of space may be

cooled when 1 gallon of water per mmute at 60

F. is used. Thus an ordinary-size house will require 6 to 9 gallons of water per minute for conditioning the entire house and proportionately

less for individual rooms. Table 6 presents data

on approximate cooling capacities and quantities

TABLE 6.—Cooling capacities and water required at

two temperaturesjor cooling various-size house areas

Room or house

volume (cu. ft.)

Approximate

cooling capacity required 1

Approximate wac r

required 2 when

temperature of water

is—

60° F. 55° F.

2,000

B.t.u. per hour

6,000

11, 750

17, 000

21, 000

25, 000

30, 000

Gallons per

minute

1. 6

3.25

4.5

5.6

6. 75

8.1

Gallons per

minute

1 0

4,000 2 0

6,000 2 75

8,000 3 4

10,000 4 0

12,000 -- -__ - 4 8

1 Dependent on wall and roof exposure, window areas,

kind and quantity of insulation, and location in the

United States.

2 Assumed that water temperature in heat-exchange

coil will reach 67.5° F.
•ANTI-SIPHON VALVE

COOLED

AIR

_ _ ^>.

WELL I T

FIGURE 9.—Room cooler using well water to remove heat.

of water required to produce partial summer comfort in a house.

The cooling system provides circulation of

water by a pump through a radiator or similar

heat-transfer coil (fig. 9). A fan or blower moves

the air directly from a room or through ducts from

the various rooms of the house through the radiator and back to the space being conditioned. Heat

from the warmer air is picked up by the cooling

coil, and the cooled air is returned to the room or

rooms. Although the equipment is not available

as a commercial packaged unit, the components

can be obtained and the unit can be assembled

locallv.

EVAPORATIVE COOLING

In some localities (fig. 10) evaporative cooling

may provide satisfactory comfort except during

limited periods of high humidity. This type of

cooling is used rather extensively in hot, dry

areas of the United States, and if properly utilized and maintained, it can provide comfort

under some conditions in other areas of the country. However, in many localities only partial

relief is obtained {S, pp. U7-H9).

Although the conditioned air in passing

through a material such as excelsior or other good

water-absorptive material may not always be in

the comfort zone, it may provide partial comfort

10

by reducing interior surface temperatures (fiff.

11).

Since evaporative cooling increases the humidity of the air, relatively large quantities of air

should be used so that the air does not become

fully saturated. An air velocity of 200 to 300

feet per minute through the absorptive material

is adequate.

Water usage in evaporative cooling is low compared to cooling with well water. Studies have

shown that from 5 to 10 gallons of water per hour

are used for the average-size house.

Manufacturers of packaged units recommend

as much as 20 to 40 room air changes per hour.
FIGURE lO.-Map of the United States showing general areas most suitable for evaporative cooling. (From Literature Cited (2).)
Table 7 gives some data on evaporative coolers.

The resultant positive air movement aids in

achieving comfort.

An outlet must be provided of suiScient size to

discharge air from the house or rooms to be conditioned. The approximate size of the discharge

opening or openings should roughly parallel that

of the free air opening for comparable airdischarge rates, as given in table 5.

TABLE 7.—Evaporative cooler data ^

40 AIR CHANGES PER HOUR ^

TABLE ï.—^Contmued

Fan capacity (cu. ft.

per minute)

Space cooled Horsepower

required

2,500

Cubic feet

3,750

5,250

7,500

11, 250

15, 000

}i

3,500 Vz

5,000 K

7,500 K

10,000 1

I AIR CHANCES PER HOUR ^

1,875.

2,625.

3,750-

5,625.

7,500.

Ye

20 AIR CHANGES PER HOUR «

Fan capacity (ou. ft.

per minute)

Space cooled Horsepower

required

1,250 _ . _

Cubic feet

3,750

5,250

7,500

11, 250

15, 000

v%

1,650 %

2,500 k

3,450 . .. %

5,000 .- . .-- %

1 Based on data from Stover (10).

2 Humid eastern Great Plains and Eastern and Southern

United States.

3 Central Great Plains.

^ Arid Western United States and western Great Plains.

FLY SCHEEN

COOLED AIR

TO ROOMS

TO WATER

SYSTEM

FIGURE 11.—Cooling by evaporation. (From Stover (11).)

MECHANICAL REFRIGERATION AIR CONDITIONING

Mechanical refrigeration air conditioning provides the most consistent means of cooling for insured comfort. In uniform environments with

air movements of 25 feet per minute, sedentary

or slightly active healthy men and women normally clothed are comfortable the year round

when the dry-bulb air temperature is within 73°

to 77° F. and the relative humidity is 25 to 60

percent (5).

Mechanical air conditioners may be window (fig.

12) or portable units or central systems (fig,

13). Air-conditioning units have either aircooled or water-cooled condensers. Units with

air-cooled condensers should be located so that the

condensers are shaded from the sun and have unrestricted air circulation over the outdoor coil.

Heat removed from the house is rejected either to

water by a water-cooled condenser or to outside

air by an air-cooled condenser. With either type

of condenser the heat must be rejected outside'the

air-conditioned space.

Operation and Size

In mechanical air conditioners air is passed

through electrostatic or mechanical-type filters or

both and over a series of refrigerant-cooled coils,

where the air is cooled and generally dehumidified.

12

A fan then forces the cooled air into the airconditioned space either directly or through

ducts as in a central system.

Size is measured in terms of British thermal

units of cooling or total heat-removal capacity.

Careful attention should be paid to matching the

capacity of the unit with the requirements of the

cooling load. Typical heat-removal or cooling

estimate forms for room and central air conditioning are included in the Appendix. You may wish

to consult with local equipment or electric-power

suppliers relative to using these forms.

Types and Requirements

Window or portable units for room cooling are

available in capacities ranging from about 6,000

B.t.u. per hour to 24,000 or more. Although most

are designed for conventional window mounting,

many are made for mounting in casement windows, walls, or as console units in front of windows. The lightweight portable air conditioner

is a recent innovation. Most of the room units

have air-cooled condensers.

Central air-conditioning systems are becoming

more popular. Major components may be obtained in factory-made assemblies, which can be

matching components for winter heating, or they
FiGUKE 12.—Window air-conditioning unit for individual room.

may be obtained in separate parts and combined

on the job into an integrated system. The summer conditioning equipment may be obtained separately and added to existing heating systems.

Chillers may be combined with hot-water heating

systems to provide cold water for circulation to

rooms (fig. 14). Other changes must be made

simultaneously in the hot-water system, such as

the addition of suitable valves, provision for removal of condensate drip, insulation of piping to

prevent sweating, and change of room radiators

to convectors.

Year-round air conditioners require less space

than a separate heating plant plus a separate summer air conditioner. Usually the heating and

cooling units of the year-round system operate independently of each other. The air circulated by

a fan shifts from the cooling to the heating unit

of the equipment or passes through both. Only

one of these units is active at any one time, and

both are interlocked to prevent simultaneous

operation.

Electrical Characteristics

Room air conditioners are normally designed

for 115- 208-, or 230-volt operation. The National Electric Code effectively limits ratings of

115-volt circuits to 7.5 amperes for coolers on a

multiple-outlet branch and to 12 amperes for

single-outlet branch circuits regardless of nominal

compressor horsepower. Conditioners requiring

above 12 amperes will normally be wired for 208-

or 230-volt operation.

Power Requirements

Power requirements for operation of air- and

water-cooled air conditioners vary in proportion

to the required cooling capacity. Table 8 relates

this requirement to approximate room size. The

upper range of floor area should be associated with

moderate outdoor summer temperatures, good insulation, and good construction practices, particularly with regard to orientation and shaded glass

areas.

In using table 8 the following information and

instructions should be noted. The cool floors are

assumed to be over cool basements, air-conditioned

rooms, sealed crawl spaces, or on slabs. The warm

floors are over unconditioned spaces or well-ventilated crawl spaces. Blinds, shades, or curtains

must be used to prevent direct sunlight from entering the rooms. Rooms connected by archways

or open doorways should be treated as single

rooms.

To select an air conditioner for residential living areas, calculate the room floor area and check

13
FIGURE 13.—Packaged unit for central air conditioning.

on such items as insulation and room exposure,

and then locate in table 8 the corresponding required cooling capacity (B.t.u.) for the floor area.

The selection made applies to single rooms of

average construction with average glass areas and

receiving average sunshine. To select a central

air conditioner for multiple rooms or an entire

house, determine the average floor area and select

the corresponding required cooling capacity

(B.t.u.) from this table. These capacities are

based on areas that are to be comfort conditioned

in localities where temperatures do not usually

exceed 95° F. In those areas where air-conditioning estimates are based on 100°, a unit with

about 15 percent greater capacity should be

selected.

In general, air-cooled units have slightly larger

power requirements than water-cooled units.

This disadvantage may be offset in the latter type

unit by lower water-supply and disposal costs or

use of cooling towers as additional equipment.

It is desirable to check with your local utility

company concerning their rates and regulations,

local codes and ordinances relative to the capacity

of your electrical system, and regulations concerning air conditioners. It is often necessary to

14
install larger service drop and entrance wiring

as well as switches to enlarge distribution panel

equipment.

Controls

Generally air conditioners come with built-in

thermostats or provision is made for wiring to

a remotely located temperature control. Some

of the small window or portable units are not

thermostat equipped, but a thermostat may be

available as optional equipment.

Water-Cooled Condensers

The water-cooled condenser requires large quantities of water to which heat is rejected. Approximately 75 to 150 gallons of water per hour for each

12,000 B.t.u. of cooling capacity must be supplied.

Often this water can be used effectively in yard

and garden irrigation. Where plentiful supplies

are not present, a water-conserving cooling tower

may be installed to cool the circulating water so

that it can be reused. This tower is commonly

located out of doors. It should be away from

TABLE 8.—Roorn air-conditioner selection guide

FLOORS COOL AND ADJOINING ROOMS AIR CONDITIONED

Floor area of rooms with following exposures and with—

Required

cooling

capacity

Ceiling under warm living space or insulated

ceiling under attic

Uninsulated ceiling under attic Typical

power

required

(B.t.u.)

North

and

east

East

and

south

South

and

west

West

and

north

Average

North

and

east

East

and

south

South

and

west

West

and

north

Average

28,000

23,000___

18,000

16,000

14,000

12,000

9,800

8,800

7,700

6,000

Square

feet

1,870

1,430

1, 110

980

830

670

480

410

340

230

Square

feet

1,790

1,360

1,050

930

790

630

450

380

320

210

Square

feet

1, 650

1,250

950

840

710

560

390

330

270

180

Square

feet

1,730

1,320

1,010

890

750

600

420

360

300

200

Square

feet

1,760

1,340

1,030

910

770

615

435

370

310

205

Square

feet

1,030

790

610

540

460

370

270

240

200

140

Square

feet

990

760

580

520

440

350

250

220

190

130

Square

feet

940

720

550

490

410

330

230

200

170

120

Square

feet

970

740

570

510

430

340

240

210

180

120

Square

feet

985

755

580

515

435

350

250

220

185

130

Kilowatts

4.0

3.4

2.75

2.45

2.20

1.95

1. 75

1.4

1. 25

.9

FLOORS COOL AND ADJOINING ROOMS NOT AIR CONDITIONED

28,000

23,000

18,000

16,000

14,000

12,000

9,800

8,800

7,700

6,000

1,680

1,270

970

860

720

580

400

340

280

190

1,600

1,210

920

820

680

540

370

310

250

170

1,520

1, 140

860

750

620

480

330

280

220

150

1,590

1, 190

900

790

660

520

360

300

240

160

950

730

560

490

410

330

240

210

170

120

920

710

540

470

390

310

230

200

160

110

880

670

510

440

370

290

210

180

150

100

910

690

530

460

385

305

220

190

155

105

FLOORS WARM AND ADJOINING ROOMS NOT AIR CONDITIONED

28,000

23,000

18,000

16,000

14,000

12,000

9,-800

8,800

7,700

6,000

1,230 1,170

930 880

720 680

630 590

530 500

420 400

300 280

250 230

210 200

140 130

1, 100

830

630

560

460

360

250

210

180

120

1, 140

870

660

580

480

390

270

220

190

130

790

600

460

410

350

280

200

180

150

105

770

580

440

390

330

270

190

170

140

105

750

560

420

370

310

250

180

150

130

100

760

570

430

380

320

260

190

160

140

100

4.0

3.4

2.75

2.45

2. 20

1. 95

1.75

1.4

1. 25

.9

4.0

3.4

2.75

2.45

2.20

1. 95

1.75

1. 4

1. 25

.9

1 Based on data in Chrysler Airtemp Room Air Conditioners {1).

15
living and bedroom areas because of some noise

inherent in its operation.

Heat Pumps

Another system of mechanical refrigeration air

conditioning is the electrically powered heat

pump. In addition to removing heat from the

house in summer, the equipment is capable of supplying heat in winter to provide year-round comfort. This heat may be taken from or rejected

to the water or outside air. Ordinarily the heat

pump is sized to handle the summer cooling load

and is supplemented with an electrical resistancetype heater to handle the winter heat load.

Operating costs for cooling are comparable to

those for other mechanical refrigeration air-conditioning systems. For heating, comparative costs

with combustion-type fuels should be considered.

COMBtNATIOM HCATtNG

ANDCOOUNG UNITS .

HOT OR CHtLLED WATER

FIGURE 14.—Combination summer air-conditioning and hotwater heating system. ChiUed water is circulated in

summer through the same pipes used in winter for circulating hot water. (From American Society of Heating, Refrigerating and Air-Conditioning Engineers,

Inc. (^),)

LITERATURE CITED

(1)

(2)

(3)

(4)

(5)

(6)

ANONYMOUS,

(N.D.) CHRYSLER AIRTEMP ROOM AIR CONDITIONERS.

Form LL-476, 12 pp. Airtemp Div.,

Chrysler Corp., Dayton, Ohio.

1941. EVAPORATIVE COOLING MAP. Heating, Piping

and Air Conditioning 13(1) : 43-44.

1960. EVAPORATIVE COOLING WHEN AND HOW TO

USE IT. HPAC Engineering Data File.

Heating, Piping and Air Conditioning 32

(3) : 141-158.

AMERICAN SOCIETY OF HEATING, REFRIGERATING AND

AlR-CONDITrONING ENGINEERS, INC.

1960. HEATING VENTILATING AIR CONDITIONING

GUIDE 1960. Ed. 38, 792 pp. New York.

FAHNESTOCK, M. K., and WERDEN, J. E.

1956. ENVIRONMENT, COMFORT, HEALTH AND PEOPLE. Refrig. Engin. 64(2) : 43-49.

FITCH, J. M.

1950. BUILDINGS DESIGNED FOR CLIMATE CONTROL.

In National Academy of Sciences, Weather

and the Building Industry. 158 pp. Washington, D.C.

(7) GRUB, WALTER.

1959. COOLER HOMES FROM ATTIC VENTILATION.

Ala. Polytech. Inst., Agr. Expt. Sta., Leaflet

63, 3 pp.

(8) RAMSEY, C. G., and SLEEPER, H. R.

1956. ARCHITECTURAL GRAPHIC STANDARDS. Ed. 5,

758 pp. New York.

(9) SIMONS, J. W., and LANHAM, F. B.

1942. FACTORS AFFECTING TEMPERATURES IN SOUTHERN FARMHOUSES. U.S. Dept. Agr. Tech.

Bui. 822, 91 pp. (Revised 1951.)

(10) STOVER, H. E.

1949. THE ATTIC FAN FOR HOME COOLING. Rural

Electrif. 8, 4 pp. Engin. Eit. Dept., Kans.

State Col., Manhattan.

(11)

(n.d.) SUMMER COMFORT FOR THE HOME. Rural

Electrif. 14, 8 pp. Engin. Ext. Dept., Kans.

State Col., Manhattan.

(12) STROCK, CLIFFORD, ed.

1959. HANDBOOK OF AIR CONDITIONING, HEATING

AND VENTILATING. 1112 pp. New York.

APPENDIX

Cooling-Load Estimate Form for Room

Air Conditioners

Cooling-load estimate form for room air conditioners (form I) represents recommended practice

tor members of the Eoom Air-Conditioner Section

ot the Air-Conditioning and Eefrigeration Institute. This estimate is suitable for comfort airconditionmg jobs not requiring specific conditions

oí temperature and humidity. It may be used

tor all areas of the United States except where the

outside design temperatures {12) are above 95°

i^. dry bulb and 78° wet bulb, as indicated in fií?-

ures 15 and 16 For the few exceptional localities

this form should be modified or other forms should

be used.

16

On graph paper with about i/4-inch squares,

sketch the room, showing the location and size of

windows, doors, and other openings. Carefully

determine the directions and indicate north on the

sketch by an arrow. For most air-conditioning

jobs each square of the graph paper could represent 1 foot of room measurement.

The following directions apply to the nine items

on form I. The quantity entered each time should

be multiplied by the factor given and the product

should be entered in the last column.

1. Windows exposed to sun,—^Under quantity

insert the total square feet of window area for

the unshaded exposure having the largest cooling

load. For windows shaded by inside shades or

Venetian blinds, multiply the quantity by the fac-
-r OKM: I.—Gooling-load estimate for room air conditioners

^^' Item Quantity

1. Windows exposed to sun, facing—

a. East, southeast, or south sq. ft. X

b. Southwest sq. ft. X

c. West sq. ft. X

d. Northwest sq. ft. X

(Use only exposure with largest cooling load.)

2. Windows facing north or in shade sq. ft. X

(Use all windows not included in item 1.)

3. Walls (based on lineal feet of wall) :

a. Light construction, exposed to sun ft. X

b. Heavy construction, exposed to sun ft. X

c. Shaded walls or partitions ft. X

(Include all walls not used in 3a or 3b.)

(In 3a and 3b use for only that exposure given in

item 1.)

4. Eoof or ceiling (use one only) :

a. Eoof uninsulated sq. ft. X

b. Eoof with 1 inch or more of insulation sq. ft. X

c. Ceiling with occupied space above sq. ft. X

d. Ceiling with attic space above sq. ft. X

5. Floor:

(Disregard item 5 if floor directly on ground or sq. ft. X

over unheated basement.)

6. People and ventilation (number of people) X

7. Lights and electrical equipment in use watts x

8. Doors and arches continuously open to unconditioned space (lineal feet of width) — ft. X

9. Total cooling load to be used for selection of room

air conditioner(s) —

Factor

Inside Outside

shades awnings

45 25

65 40

100 60

35 25

14

Cooling

load

B,tM.

fer hour

90

50

30

16

7

3

10

900

3

300

tor for inside shades. For windows shaded by

outside a^\Tiings or by both outside awnings and

inside shades or Venetian blinds, use the factor for

outside awnings. Only one number should be

entered in the last column for item 1.

2. Windoios facing north or in shade.—Insert

the total square feet of window area of all windows not included in item 1.

3. Walls,—For 3a or 3b insert the length of the

wall that had the/'largest cooling load in item 1.

The total length of all walls and partitions not

included for 3a or 3b should be inserted for 3c.

The factors are based on a wall 9 feet high and

are applicable to walls of usual heights and average construction. An uninsulated frame wall or

a masonry wall 8 inches or less in thickness is considered light construction. An insulated frame

wall or a masonry wall 12 inches or more in thickness is considered heavy construction.

4. Roof or ceiling.—Insert the total square feet

of roof or ceiling area for 4a, 4b, 4c, or 4d. Use

one only.

5. Floor.—This item can be ignored if the floor

is on the ground or over an unheated basement.

Otherwise, insert the total square feet of floor area.

6. People and ventilation.—Estimate the number of people who normally occupy the space to

be air conditioned and enter this number under

quantity. The factor includes the normal cooling load per person and approximately 15 c.f.m.

of ventilation air per person.

17
This map is reasonably accurate for most parts

of the United States but is necessarily highly

generalized, and consequently not too accurate in

mountainous regions, particularly in the Rockies.

FIGURE 15.—Map of the United States showing outside dry-bulb design temperatures (°F.) in summer based on standards of Air-Conditionins and

Refrigeration Institute. (From Strock (12).)

©
^

^^xe.-„.p. ^ „„« ,u^ .,^"SiÄÄÄrTsriÄ' ,i5n°"" -- «« «"-«• «' *—«.ni« »-'
7. Lights and electrical equipment,—Insert the

total number of watts for lights and electrical

equipment that will be in use when the room air

conditioner is turned on and the sun is shining.

8. Doors and arches.—Insert the width of any

door or arch that is continuously open to an unconditioned space.

9. Total cooling load,—KM the cooling loads

(B.t.u.) of items 1 through 8. One or more room

air conditioners with capacities equal to or greater

than this total cooling load should be selected.

Cooling-Load Estimate Fori^i for Central

Air Conditioners

The cooling-load estimate form for central air

conditioners (form II) represents recommended

practice for members of the Self-Contained AirConditioner Section of the Air-Conditioning and

Refrigeration Institute, l'hîs estimate is suitable

for comfort air-conditioning jobs not requiring

specific conditions of temperature and humidity.

The following directions refer to the 12 items

on form II. The quantity entered each time

should be multiplied by the factor given or indicated and the product should be entered in the

last column.

1. People.—Insert the number of people normally occupying the space after the air conditioner

is installed. If all are engaged in the same activity, the number should be inserted for la or lb.

If some are more actively engaged than others,

the total number should be properly divided for

la and lb. If it is a space that would be occupied

by a large number of people for only a few

minutes and then a smaller number for the

remaining time, use the largest number of people

FORM II.—Cooling-load estimate for central air conditioners

No. Item Quantity Factor Cooling load

B.t.u. per

1. People: _ ^^^

a. Number sitting or moving slowly—^ . X 400 —

b. Number working, dancing, or similar activity X 660 =

2. Window^s exposed to sun sq. ft. X —^ =

(Use exposure with largest window area.)

8. Lights and electrical appliances watts X 3.4 =

(Include only those appliances not listed under other

heat sources on p. 21.)

4. Other heat sources ^ =

5. Subtotal (sum of items 1 through 4) — —

6. Windows not included in item 2 sq. ft. X —^ =

7. Walls and partitions less windows sq. ft. X —^ =

Walls and partitions less windows sq. ft, X —^ =

Walls and partitions less windows sq. ft. X —^ =

8. Floor sq. ft. X ^ =

9. Ceiling sq. ft. X ^ =

10. Ventilation or infiltration c.f.m.* X * =

11. Subtotal (sum of items 6 through 10)

12. Total cooling load to be used for selection of central

air conditioner (items 5 and 11)

' See table 9.

^ See directions for item 4.

' See table 10.

* See directions for item 10.

20
TABLE ^,—Cooling-load factors for windows exposed to sun ^

^ Data to be used in completing form II for central air conditioners.

Description of windows

Factors for windows withI exposures of—

NE. E. SE. S. SW. W. NW.

Clear glass (single or double), no protection

Completely shaded by awnings

110

30

65

44

180

50

110

72

160

45

95

64

105

30

60

42

160

45

95

64

180

50

110

72

110

30

With light-colored inside shades or Venetian blinds. _

Glass brick, no protection --

65

44

that would be present for approximately 15

minutes.

2. Windows exposed to sun.—Insert the maximum total square feet of window area on any one

wall of the space exposed to direct sunshine.

Refer to table 9 for the proper factor, and insert

it on the line indicated. If all the windows are

on the north wall or on a wall shaded completely

from the sun by an adjacent building, no entry

should be made for this item.

3. Lights and electrical appliances.—Insert the

total number of watts in use, not including the

watts consumed by appliances listed under

item 4.

4. Other heat sources.—To calculate the cooling

load due to gas and electrical appliances and

motor-driven apparatus, complete the following

computation and insert the total on the line indicated in item 4.

Heat source

Electric motors total name-plate horsepower __

Gas burners number

Glass coffee makers do __

uantity Factor

X 9.800 =

Cooling

load

B.t.u.

per hour

X ßOOO =

X 900 =

5. Subtotal.—^After checking the products of

the first four items, add them and cany this subtotalto the line atthe right.

6. Windoios not included in item 2.—Insert the

total square feet of windows not included in item

2. In table 10 select the factor for these windows

under the outside dry-bulb design temperature for

the given locality (see fig. 15). Insert this factor

on the line indicated in it^m 6.

7. Walls and partitions.—Three lines are provided for this item, as it is quite possible that

several wall constructions may be used on a particular space. Each time subtract the area of the

windows from the total wall or partition area and

insert the total net wall or partition area. In table

10 select the proper wall or partition factors

shown under the design temperature already

established. Insert these factors on the proper

lines indicated in item 7.

8. Floor.—Insert the total square feet of floor

area. Refer to table 10 for the factor to be inserted on the line indicated.

9. Ceiling.—Insert the total square feet of ceiling area. Refer to table 10 for the factor that

fits the conditions of the building. Adjust this

factor if the ceiling is insulated. For example,

to obtain the adjusted factor for a 4-, 2-, or 1-inch

insulation, multiply the factor in the table by 0.2,

0.3, or 0.4, respectively. Insert the factor or adjusted factor on the line indicated.

10. Ventilation or infiltration.—To calculate the

requirements for both ventilation and infiltration,

use the largest quantity in cubic feet per minute.

Use no less than the amount required by local

ordinance and no less than the amount drawn

from the space if exhaust fans are used.

To determine the quantity for ventilation in

item 10, complete the following computation :

Smoking

None

Light

Heavy

1 Must equal number used in item 1, form II,

Numher of

occupants ^

X

X

X

Factor

71/2

15

40

Cubic feet

per minute

21
TABLE 10.—Cooling-load factors for windows^ walls^ floors^ and ceiling at various outside dry-hulb

design temperatures ^

Factors at temperatures ( ° F.) of—

Part of building

86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 1Ö1 102 103 104

Windows (no sun) 8 9 10 11 12 13 14 15 16 17 18 19 20 21. 22 23 24 25 26

Walls:

Heavy masonry 2 3 . 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6 6 1

Average masonry 3 3 3 3 4 4 4 4 5 5 5 6 6 6 6 V V V V

Insulated masonry or

frame 1

2

2

3

2

3

2

3

2

4

2

4

3

4

3

4

3

5

3

5

3

5

3

5

4

6

4

6

4

6

4

6

4

7

4

7

5

Average frame 7

Partition,^ inside:

Single thickness 5 5 6 7 7 8 8 8 9 10 10 11 11 12 12 13 14 14 15

Double thickness 3 3 3 4 4 4 4 5 5 5 6 6 6 6 7 7 7 8 8

Glass brick (no sun exposure) _ _ _ _ 4

2

4

2

5

2

5

2

5

3

6

3

6

3

7

3

7

3

8

4

8

4

8

4

9

4

9

4

10

5

10

5

10

5

11

5

11

Floor _ 5

Ceiling under—

Unventilated attic 11 11 11 12 12 12 12 13 13 13 13 14 14 14 15 15 15 15 16

Ventilated attic 7 7 8 8 9 9 10 10 10 11 11 12 12 13 13 14 14 14 15

Flat roof 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19

1 Data to be used in completing form IT for central air conditioners.

2 Only used if house is partially air conditioned.

To determine the quantity for infiltration in

item 10, compute the following equation :

Cubic feet per minute=

room height X length X width X wall factor

60

The wall factors for a room with one, two, or tliree

or more outside walls are 1,1.5, and 2, respectively.

The infiltration does not include the amount that

will enter the space if doors or windows remain

open.

Insert the number of cubic feet per minute for

ventilation or infiltration on the line provided in

item 10. Select the ventilation or infiltration factor for the outside wet-bulb design temperature

of the specified locality (see fig. 16) from the following data :

°^- Factor

64 0

65 1

66 :::::_:::: 3

°F. Factor

67 5

68 8

69 11

70 14

71 17

72 20

73 23

74 27

75 30

76 33

77 37

78 41

79 45

80 49

11. Subtotal.—^After checking the products of

items 6 through 10, add them and carry this subtotal to the line atthe right.

12. Total cooling load.—Add the subtotals of

items 5 and 11. A central air conditioner with a

capacity equal to or greater than this total cooling

load must be selected to obtain comfort conditions

within the specified space.

22

U.S. GOVERNMENT PRINTING OFFICE : 1961 O—663900