NATIONAL BUREAU OF STANDARDS REPORT

THE EFFECT OF A WEATHER-BAN SUN SHIELD

ON THE PERFORMANCE OF A WINDOW AIR CONDITIONER

by

C« Wo Phillips

Po R. Achenbach

Report to

Buildings Management Division

Public Buildings Service

General Services Administration

Washington^;?,: Do C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

5331
THE national bureau of standards

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

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

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

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the back cover.

Reports and Publications

The results of -the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project

or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly peri*

odicats, available from the Government Printing Office: The Journal of Research, which present)*

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basie Radio Propagation Piedictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications The Applied Mathematics

Series, Circulars. Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications

Information on the Bureau’s public ations c an be found in \ BS Circular KiO, Publications of

the National Bureau of Standards {$1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office-. Washington 25, D. C.

Inquiries regarding the Bureau’s i e-ports should be .addressed to the Office of Technical Information. National Bureau of Standards, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-4830 June 13, 1957 5331

THE EFFECT OF A WEATHER-BAN SUN SHIELD

QN THE PERFORMANCE OF A WINDOW AIR CONDITIONER

by

C. Wo Phillips

Po Ro Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

To

Buildings Management Division

Public Buildings Service

General Services Administration

Washington 25, D 0 Co

IMPORTANT NOTICE

NATIONAL BUREAU OF STANDARDS REPORTS are usually preliminary or progress accounting documents

intended for use within the Government. Before material in the reports is formally published it is subjected

to additional evaluation and review. For this reason, the publication, reprinting, reproduction, or open-literature

listing of this Report, either in whole or in part, is not authorized unless permission is obtained in writing from

the Office of the Director, National Bureau of Standards, Washington 25, D. C. Such permission is not needed,

however, by the Government agency for which the Report has been specifically prepared if that agency wishes

to reproduce additional copies for its own use.<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

THE EFFECT OF A WEATHER-BAN SUN SHIELD

ON THE PERFORMANCE OF A WINDOW AIR CONDITIONER

by

Co Wo Phillips and P. R. Achenbach

Abstract

A device for partially shielding a window air

conditioning unit from direct rays of the sun,

known as "Weather-Ban”, was tested to determine

its effect on the performance of a 3/4 horsepower Fedders window air conditioner . The

tests showed that the shield did not produce

measurable effects on the capacity of the unit,

the inlet and outlet air temperatures of the

evaporator and condenser, nor in the suction

and discharge pressures of the compressor, but

it did reduce the surface temperature of the

top of the condenser housing about 19 deg F.

Analysis indicates that a sun shield would be

of greater benefit on an air conditioner with

an exposed condenser coil than on the Fedders

unit which provided a housing over the entire

condenser section,, However, computations of

the probable solar heat transfer at the time of

day and for the direction of orientation that

caused the greatest absorption of solar energy

on an unhoused condenser, indicate that the

capacity of a window air conditioner would

probably be increased on the order of one

percent by a shield like the specimen tested.

I. INTRODUCTION

At the request of the General Services Administration

in a letter dated July 19, 1956, tests were made of a "Weather-Ban" protective shield for window-type air

conditioners manufactured by Weather-Ban Products, Inc.

The purpose of these tests was to determine whether or

not this shield increased the cooling capacity of a window-type air conditioning unit by shading the unit

from the sun’s rays thus reducing the entry of solar

heat into the condenser section of the unit.
*
- 2 -

II. TEST SPECIMEN AND TEST APPARATUS

The Weather-Ban shield was constructed of 0.05-in.

thick aluminum, which was coated with a white enamel

paint o It was 28" long, 22 1/4" wide, and 10" deep at the

back. Figo 1 shows the shield in place on the air conditioner used for the tests . The top surface of the shield

was lined with a 2"xl8"x28" piece of glass fiber insulation.

A five inch lip was formed on the front part of the top.

This shield was installed on the condenser portion of the

air conditioning unit according to the manufacturer's

directions

.

The air conditioning unit used was a Fedders model

NW7A5 which was supplied for the test by the General

Services Administration. It was an open-type unit and

had the following motor characteristics:

Evaporator fan motor 1/150 H.P. 0.3 Amps. 208 Volts

Condenser fan motor 1/25 H.P. 0.9 Amps. 208 Volts

Compressor motor 3/4 H.P. 6.6 Amps. 208 Volts

It should be noted that the air conditioning unit used

had certain features which directly affected the extent to

which some of the observations could be considered conclusive. This unit was equipped with a thermostatic

expansion valve to. 'control the flow of liquid refrigerant

to the evaporator. This valve caused a modulating suction

pressure at the compressor which would make it difficult

to observe small variations in the suction pressure

resulting from the presence or absence of the Weather-Ban

shield. A capillary tube feed such as is common with many

units, might have permitted more precise data on the

possible effectiveness of the shield.

Also, the unit furnished for the tests was of such a design that the condenser coil itself was protected to a degree from direct sun rays by the louvred construction of

the 0.053 inch steel condenser housing, as contrasted with

the type of construction in which the condenser tubes and

fins are directly exposed.

For the first of two major tests, indicating pressure

gauges were installed to measure discharge and suction

pressures of the air conditioning unit. For the second

test recording pressure gauges were installed.
*

*
Figure 1

-3-

Thermocouples were installed at the following points

to measure temperature:

1. Condenser air outlet

2. Condenser housing surface

3. Condenser air inlet

bo Evaporator air inlet

5 o Evaporator air outlet

Ambient temperature was considered to be the same as the

condenser air inlet temperature <= For the first test,

temperatures were measured with a hand potentiometer,

and for the second, with a recording electronic potentiometer o For the second test a pyrheliometer was used to

measure the solar radiation on a horizontal surface.

Fig, 1 shows the enclosure and the general setup for

the second test. The pyrheliometer can be seen directly

in front of the louvred grille of the condenser section

of the air conditioning unit. Other instruments shown are

the two indicating pressure gauges and the temperature

recorder on the left and the two pressure recorders on

the froht and right.

Fig, 2 shows the evaporator side of the test setup.

The small fan on the lower left corner of the enclosure

over the evaporator portion of the air conditioning unit

was used to create a constant evaporator load. The

potentiometer used to check the recorder values for

temperature and pyrheliometer output is located below

the evaporator enclosure,

III. TEST PROCEDURE AND TEST RESULTS

Two major tests were made on the Weather-Ban shield,

one on July 12, 1956, and the other on September 13, 195o.

Both tests were made in Washington, D» C. , during the

afternoon under bright summer sun.

The July test was run with the air conditioning unit

in an exposed test setup with no enclosure to eliminate or

minimize wind currents. The purpose of this exposed setup

was to simulate conditions similar to the installation of

the conditioner in the window of a building. Pressure and

temperature observations were recorded by an operator.

mra O

-4-

The July 12 test was run from 1:30 P.M. to 4:15 P.M.

,

with readings taken at 3 -minute intervals during various

periods throughout the afternoon- Table I shows the

maximum and minimum values observed with the shield on

and off during this period.

TABLE I Range of Temperatures and Pressures Observed on Fedders Air

Conditioner With and Without Weather-Ban Shield During Test 1.

1:30 P.M. to 4:15 P.M. , July 12, 1956

Shield On Shield Off

Min- Max. Min. Max

.

Condenser Air

Outlet-Temp. °F 92.4 111.7 108.9 112.1

Condenser Housing

Surface-Temp. °F 96 .5 107.2 120.4 126.2

Condenser Air Inlet

Temp. °F 85.4 95-3 86.9 90.2

Evaporator Air Inlet

Temp. °F 86.3 93-8 88.4 91.3

Evaporator Air

Outlet-Temp. °F 68.1 73.3 69 .

6

73.3

Discharge Pressure

psig 164. 189 . e CO 0- 1

—

1 184.

Suction Pressure

psig 30. 35. 32 . 36 . Table II shows the average of the values observed at

3 -minute intervals during typical periods with the

shield on and off between 1:30 P.M. and 4:15 P.M. on

July 12 .

i 95b

.

-5-

TABLE II

Average Temperatures and Pressures Observed on Fedders Air

Conditioner With and Without Weather-Ban Shield During Test 1,

1:30 P.M. to 4:15 P.M. , July 12, 1956

Shield On Shield Off

Condenser Air

Outlet-Temp. °F 111.0 110.9

Condenser Housing

Surface-Temp. °F 106.7 124.5

Condenser Air Inlet

Temp. °F 92.1 88.4

Evaporator Air Inlet

Temp. °F 92.4 99066

Evaporator Air

Outlet-Temp. °F 70.5 0 0

r~\ uDischarge Pressure

psig 185c 182.

Suction Pressure

psig 33 ° 35*

It will be noted that in a number of instances the maximum

and minimum values vary widely from the average values.

In many cases the difference between the maximum or minimum reading and the average is far greater than the

difference between the values observed with the shield

on and with the shield off. For example, the minimum

Condenser Air outlet reading with the shield- on is

l8.6°F lower than the average condenser Air Outlet reading

with the shield on, and yet the difference between the

averages for the condenser air outlet with the shield on

and off was only 0.1°F. This serves to point out the

big effect of changing conditions, primarily wind velocity

and direction. The only reading which showed a significant

change when the shield was removed or replaced during this

test was the condenser housing surface temperature. The

average values of the condenser housing temperature shown

in Table II with and without the sun shield differed by

17.8°F.
>
- 6 -

The September test was run with the conditioner

supported in a plywood structure designed to provide

more stable testing conditions . All thermocouple readings

taken in the previous test, plus an ambient temperature

and a sun intensity observation were taken onm sixteenpoint electronic constant-balance recorder. The suction

pressure and discharge pressure readings were recorded.

The sun intensity figures were obtained by attaching a pyrheliometer to one point on the sixteen-point recorder.

The values which were recorded were not absolute values

of solar intensity, but were relative. Two tests were

made on the afternoon of September 13, running from

2:00 P.M. to 3:00 P.M. and from 3 ° 00 P.M. to H-:O0 P.M.

Since the tests were of similar nature and the results

were in agreement, only the first test has been reported

here. From 2:00 P.M. to 2:30 P.M. the air conditioner

was operated without the Weather-Ban shield, and from

2:30 P.M. to 3«00 P.M. it was in place. The maximum

and minimum readings shown in Table III are for this

entire period of time. The average values shown in

Table IV cover a representative span of ten minutes with

the shield off and ten minutes with it on.

TABLE III

Range of Temperatures and Pressures Observed on Fedders Air

Conditioner With and Without Weather-Ban Shield During Test 2,

2:00 P.M. to 3:00 P.M. September 13, 1956

Shield. On Shield. Off

Min. Max. Mini i. . Max.

Evaporator Air Inlet

Temp. °F 85oO 86 .

5

86 .

0

88.0

Evaporator Air

Outlet-Temp. °F 66 .

0

67.0 66 .

0

68.0

Condenser Air Inlet

Temp. °F 88.0 92.0 87 .O 93.0

Condenser Air

Ohtlet-Temp. °F 109.0 111.0 109.5 111.5

Condenser Housing

Surface-Temp. °F 103.0 106.0 120.0 126.0
•'

.
-7-

TABLE III (continued)

Shield On

Min. Max.

Shield Off

Min. Max.

Sun Intensity 178. 216 . 130 . 214.

Ambient -Tempo °F 87 = 0 93 oO 87*0 97 .

0

Discharge Pressure

psig 172. l 85 o 175 ° 186 . Suction Pressure

psig 29. 35° 29 34.

TABI^E IV

Average Temperatures

Conditioner With and

2:00 P.M.

and Pressures Observed on Fedder:

Without Weather-Ban Shield During

to 3:00 P.M. September 13, 1958

Shield On Shield Off

Evaporator Air Inlet

Temp. °F 86.3 87*0

Evaporator Air

Outlet-Temp. °F 660 9 67.4

Condenser Air Inlet

Temp. °F i 90.1 190.4

Condenser Air

Outlet-Temp. °F 110.1 110.7

Condenser Housing

Surface-Temp. °F 106.0 125.1

Sun Intensity 204. 204.

Ambient-Temp. °F 89.9 91.2

Discharge Pressure

psig 180 . 180 . Suction Pressure

psig 32. J32.

- 8 -

The differences between the maximum and minimum

readings in the September test were considerably smaller

than in the July test. These smaller differences between

maximum and minimum readings still exceeded any differences

in the readings produced by removing or installing the

Weather-Ban shield. As in the July test, no significant

change, other than in the temperature of the condenser

housing surface, was observed in the September test

with the Weather-Ban shield in place or removed.

Table IV shows a difference in temperature of the

air between evaporator inlet and outlet of 19 A deg F

with the sun shield on and 19.6 deg F with the sun shield

off. The corresponding temperature rises of the condenser

air were 20.0 degrees F and 20.3 degrees F respectively.

If the sun shield had been beneficial to the capacity of

the unit, the decrease in air temperature as it passed

through the evaporator should have been greater with the

shield on than with it off whereas the results show the

reverse occurred. The differences in the cooling and

heating effects of the evaporator and condenser with and

without the shield are of the order of one percent, and

are considered to be well within the variability of

operating conditions during the tests.

During the summer when the two reported tests were

made, many other test runs were also made, but were not

reported because of excessive changes in ambient conditions

such as wind, solar radiation, etc. Thao re suits of one

of these additional tests, made on September 20, 1966

are shown in Graph I. Although the solar radiation varied

considerably, no noticeable change, other than in the

condenser surface temperature, occurred when the solar

radiation changed, or when the shield was installed or

removed

.

IV. DISCUSSION AND C0NCEUSI0NS

On the basis of the observations made during the

tests reported, the installation of the Weather-Ban

shield produced no measurable change in the operating

characteristics or the capacity nof the Fedders air

conditioner furnished for the tests during operation of

the air conditioning unit in bright sunlight.

It can be shown from the computed incident solar

radiation and solar heat transmission that a very small

changein operating conditions would be expected as a result

of applying the Weather-Ban sun shield.
.

.

.
Graph

1
> .


-9-

Assuming that the air conditioner used for these

tests had an air Circulation rate of 400 cubic feet per

minute through the condenser, and that the unit was

rejecting a total of 9? 000 Btu per hour, the temperature

rise of the condenser air would be about 21 degrees F.

From Table IV the temperature rise was observed to be

20 and 20,3 degrees F, respectively, for the two cone-'

ditions of operation reported. The top surface area of

the air conditioner housing was approximately four

square feet, and assuming that the thermal conductance

of the top was 0.6 Btu/sq . ft 1

( °F ) , the observed rise

of 19ol°F in the temperature of the top surface when

the shield was removed would cause an additional transfer

of about 46 Btu per hour, and a temperature rise in the

condenser air of about 0.1°F.

Air entered the condenser section through one third

of the vertical front facfe of the housing and was

discharged throughrthe remaining two thirds of the front

face. The front face was oriented due south during the

tests and approximately 100 Btu/hr of direct and diffuse

solar radiation would be absorbed by the one square foot

of inlet grille at 2:30 P»M. eastern daylight time. If

all of this heat were transferred to the ingoing condenser

air the average air temperature would be increased an

additional 0.23°F when the shield was not in use. Since

the Weather-Ban shield did not shade the ends of the

condenser section, its presence would not affect the

transfer of solar radiation through these surfaces.

Thus it is expected that the solar shield would not

have decreased the rise in condenser air temperature by

more than about 0.33°F* Such a small change would be

difficult to measure with certainty in this type of test.

Published information on the performance of Refrigerant-12

compressors indicates that the decrease in capacity of

such compressors is less than one percent for one degree

rise in condensing temperature for the compression ratio

involved in these tests. I

The use of an air conditioner without a housing over

the face of the condenser would have possibly been more

favorable to the sun shield in that solar radiation falling

on the condenser tubes and fins would have been absorbed

to a large degree when the shield was not in use. This

would have increased the amount of heat to be absorbed by

the condenser air by a larger* increment than for the Fedders
> 
- 10-

unit used for these tests. However, evenmthis type air

conditioner would probably increase the heat rejection of

the condenser by only about b percent when operating

unshaded at the time of day when the solar absorption

would be the greatest. It is probable that this unfavorable set of conditions would not have decreased the cooling

capacity more than one percent and, therefore, could not

haVe been measured with certainty by the methods usually

employed for rating air conditioners.

No determinations were made during these tests on

any other claims of the manufacturer for the Weather- Ban

shield

.

U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

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

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C., and its major field laboratories in Boulder, Colorado, is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section carries out spe- cialized research, development, and engineering in the field indicated by its title. A brief

description of the activities, and of the resultant reports and publications, appears on the

inside front cover of this report.

WASHINGTON, D. C.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation,

Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology

and Lubrication. Engine Fuels.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Nuclear Physics. Radioactivity. X-rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. AEC Radiation Instruments. Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics.

Mass and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Concreting

Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital

Circuitry. Digital Systems. Analogue Systems. Application Engineering.

• Office of Basic Instrumentation • Office of Weights and Measures

BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials.

Gas Liquefaction.

Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular

Propagation Services. Sun-Earth Relationships.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

Navigation Systems. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Radio

Systems Application Engineering.

Radio Standards. Radio Frequencies. Microwave Frequencies. High Frequency Electrical

Standards. Radio Broadcast Service. High Frequency Impedance Standards. Calibration

Center. Microwave Physics. Microwave Circuit Standards.