NATIONAL BUREAU OF STANDARDS REPORT

2296

PERFORMANCE OF A DEVELOPMENT MODEL 3HP YORK CONSOLE

AIR CONDITIONER FOR VANS AND PREFABRICATED BUILDINGS

by

Henry Karger

C. W. Phillips

P. R. Achenbach

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

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0

NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT MBS REPORT

1000-30=4700 February 20, 1953 2296

PERFORMANCE OF A DEVELOPMENT MODEL 3HP CONSOLE

AIR CONDITIONER FOR VANS AND PREFABRICATED BUILDINGS

manufactured by

York Corporation

by

Henry Karger

C„ Wo Phillips

Po Ro Achenbach

Heating and Air Conditioning Section

Building Technology Division

To

Engineer Research and Development Laboratories

Fort Belvoir, Virginia,,

The publication, repi

unless permission Iso

25, D, C, Such perm

cal ly prepared If tha

Approved for public release by the > p«*. '• prohibited

Director of the National Institute of ^d,, Washington

Standards and Technology (NIST)

on October 9, 2015.

Performance of a Development Model 3HP York Console

Air Conditioner for Vans and Prefabricated Buildings

Abstract

Performance tests were made of a development model of a 3HP sectional console air conditioner, for vans and prefabricated buildings, manufactured by York Corporation of

York, Pa 0 As received, the total net cooling capacity

of the specimen was about 9000 Btu/hr at ACRE standard

rating conditions.) The capacity was unnecessarily low

because misadjustment of the expansion valve caused liquid

refrigerant to pass through the evaporator into the compressor, because of a number of serious air leaks into the

cabinet and between cabinet sections, because there was no

insulation between evaporator and condenser sections, and

because conditioned air was short circuited between outlet and inlet of the evaporator section,, After correcting

these and other faults, comparisons were made of the

capacity of the unit when mounted inside the conditioned

space, when mounted outside the conditioned space, and

when divided into two parts with the condenser section outside and the evaporator section inside the conditioned space D Under ASRE standard rating conditions the total net cooling

capacity ranged from 13,040 Btu/hr for the inside installation to 15,600 Btu/hr for the divided installation., The

outside mounting produced 9 percent higher capacity than

the inside mounting primarily because of air leakage into

the condenser section of the cabinet from the conditioned

space for the inside installation., The divided installation produced 10 percent higher capacity than the outside

mounting chiefly because non-useful heat transmission through

the cabinet of the evaporator section was eliminated. The

performance factor of the unit in Btu/hr per watt was lower

than required by the Federal Specification for self-contained

air conditioners whereas the net sensible heat ratio was

higher than required by this Federal Specification,

I. INTRODUCTION

In accordance with a request from the Engineer Research and

Development Laboratories, Fort Belvoir, Virginia, dated September 23,

1951, tests of development models of two multi-section, package-type

air conditioning units were made to determine their performance as

a basis for developing air conditioning equipment for vans and prefabricated buildings for Theater-of-Operation use. The two units

were designed, for capacities in the range from 13,000 to 22,000

Btu/hr, This report presents the results obtained on a specimen

manufactured by York Corporation of York, Pennsylvania, Tests were

made to determine net cooling capacities, the quantity of conditioned

air circulated, the quantity of air circulated through the condenser,

and the starting current of the unit.
.
- 2 - Capacity tests were requested at standard rating conditions of

the American Society of Refrigerating Engineers with outdoor temperatures of 95°E dry bulb, 75°F wet bulb, and indoor temperatures of

$0°F dry bulb, 67°F wet bulb, and also at high outdoor ambient temper

ature conditions of 125°F dry bulb, $5°F wet bulb with indoor tempera

tures of 90°F dry bulb, $0°F wet bulbo

II o DESCRIPTION OF TEST SPECIMEN

The specimen air conditioning unit was identified as follows:

(NBS Test Specimen $2-52)

York Corporation, York, Pa.

Model V-$0 SC

PoOo No. 1R 7$1

The air conditioning unit was built for operation on alternating current, 20$ volts, 3-phase, 60 cycle. The sectional construction of

the unit permitted operation in three different ways: the entire

unit within the space to be cooled, with ducts to the condenser section; the entire unit on the outside of the space to be cooled, with

ducts to the evaporator section; or the unit divided into two parts

with the evaporator section placed inside the cooled space and the

condenser section placed outside the cooled space. The sectional

construction is evident in Figures 1 to 4° The bottom section contained the condenser and the condenser fan; the second section contained the hermetic motor-compressor assembly; the third section contained. the evaporator coil and the evaporator fan, while the fourth

or top section acted as a plenum chamber for the air discharged into

the space to be cooled. The two lower sections were not built for

ready separation, and the condenser air entered the unit through the

second section and was blown out through two outlets in the bottom

section of the unit. The second and third sections were separated

from each other by a piece of sheet aluminum approximately 3/16 inch

thick. The evaporator air entered the unit through the third section

and was blown out through the top section. Figure 4 is a view of the

air conditioning unit with all the face panels removed, and the four

different sections of the unit can be seen very clearly.

The electrical controls for operation of the air conditioning

unit were mounted on the right side of the third section, as viewed

in Figures 1 and 3, underneath a small face plate, which could be removed by unscrewing two wing bolts. The controls consisted of a three-position selector switch, which was marked "Fan", "Off", and

"Cool". When the selector switch was turned, to the "Fan" position,

only the evaporator fan would operate: if turned to the "Cool" position, both of the fans and compressor would operate, with the thermo

stat regulating the operation of the compressor according to the

temperature at the inlet of the evaporator. The thermostat adjusting knob was located directly below the selector switch. The unit

was not equipped with any means such as dampers, etc. for introducing outside air into the cooled space.

3

Two centrifugal fans were used to circulate air through the

condenser, the fan wheels being mounted on opposite ends of the

shaft of the driving motor 0 A similar arrangement was employed

for air circulation through the evaporator,, These assemblies can

be seen in Figure 4« A thermostatic expansion valve was used as

the refrigerant flow control,.

Figure 1 is a front view of the unit from the room side.

Figure 2, a rear view of the unit, shows the condenser air inlet in

the second section and the two outlets in the bottom section of the

unit 0 A front view with all panels removed is shown in Figure 3?

whereas Figure 4 shows a rear view with all panels removed.

The

the unit

physical dimensions,

were as follows:

weight and the electrical data for

Height, inch

Width, inch

Depth, inch

Weight, lbs.

55

42

15-1/2

500

Compressor Motor, HP

Condenser Fan Motor, HP

Evaporator Fan Motor, HP

Refrigerant Charge, lbs. Freon-12

The unit was equipped with an air filter made of expanded aluminum

mesh at the evaporator inlet. All framing and panels of the unit

were made of aluminum.

III. TEST PROCEDURE

Circular No. 16-R, published by the American Society of Refrigerating Engineers, entitled Tt Methods of Rating and Testing Air Conditioners", was used as a general guide for the procedure to be used in determining the capacity of the air conditioning unit. This ASRE circular states that the capacity rating of self-contained air conditioning units shall be the net total room cooling effect in British Thermal

Units per hour. The following apparatus was used to determine this

net room cooling capacity.

A portable, 600 cu. ft. warehouse normally used for the refrigerated storage of various materials was used as a calorimeter for the

first series of tests, The air conditioning unit was mounted in the

opening normally used for the refrigerating unit for the warehouse.

It was placed on the inside of the warehouse-calorimeter flush with

the outside wall. The calorimeter was then sealed in such a manner

that only the openings for the condenser air circuit communicated with

- 4 -

the outside space,, For the second series of tests the air conditioning unit was placed entirely on the outside of the calorimeter and

short ducts were used on the evaporator air circuit into the calorimeter,, For the third series of tests, the evaporator section of the

air conditioning unit was separated from the condenser section and

was placed on the inside of the calorimeter whereas the condenser section was placed on the outside of the .calorimeter „ The calorimeter

was sealed so that there was no communication other than the refrigerant lines between inside and outside,.

For each series of tests, the warehouse, with the air conditioning unit in place, was calibrated to determine the heat transmission

per degree of temperature difference between the inside and outside,

since this heat constituted part of the sensible heat load. Electric

heaters were placed on the inside of the calorimeter to provide the

remainder of the sensible heat load for the air conditioning unite A

humidifier consisting of an electric heating element immersed in water

was also placed inside the calorimeter to provide the necessary humidity, and provision was made to weigh the amount of water evaporated 0 The calorimeter was made as airtight as was considered necessary, and

provisions were made to measure the amount of air which was introduced

into or exhausted from the calorimeter by the air conditioning unit

during operation,, This was done by removing air from or introducing

air into the calorimeter through a pipe by means of a blower,, The air

quantities were measured by a pitot tube placed inside of the pipe,,

The amount of air flowing through the pipe was regulated by a throttling

valve so that the pressure difference between the inside and the outside

of the calorimeter was zero ± 0„002 in. W.G„ Calibrated watthour

meters were used to measure all electric energy consumption,, Temperatures were measured by means of calibrated thermocouples using an

electronic, constant-balance type potentiometer. Humidity measurements were made utilizing calibrated lithium-chloride-coated elements

in conjunction with a micro-ammeter. Humidity measurements observed

with the electric hygrometer were checked regularly with a 24” mechanical psychrometer . The condensate drained from the evaporator coil was

collected as a. check against the amount of water evaporated by the

humidifier

Measurements of the quantities of air circulated by the evaporator and condenser fans were made by means of a pitot tube located inside a smooth, round duct during separate tests with the air conditioning unit removed from the calorimeter. This duct was connected to the

outlet of the evaporator or condenser air circuit by means of a plenum

chamber and an exhaust blower was attached to the other end of the duct.

The air flow through the duct was regulated by a throttling device so

that the static pressure at the evaporator or condenser outlet opening

in the cabinet was zero ±0.002 in. W.G. with respect to the pressure

in the test room to determine the free-air delivery of the fans.
,
IV „ TEST RESULTS

A 0 Cooling Capacity

The unit, as received for tests, produced a total net cooling

capacity of 9000 Btu/hr under conditions of 95°F LB, 75°F WB condenser ambient and &0°F DB 67°F WB evaporator ambient with the assembled unit within the conditioned space,, The capacity was found

to be unnecessarily low because certain features of design, workmanship, and control adjustment needed improvement . These features

were modified during the course of several preliminary tests in cooperation with representatives of the manufacturer after which the

test results hereinafter reported were obtained. The defects in the

unit and the modifications made are described in the section entitled

"Design and Workmanship".

Determinations of the total net cooling capacity of the unit were

made for two different sets of indoor and outdoor temperature and

humidity conditions, for each of three different positions of the unit

with respect to the calorimeter. Tests numbered la and lb were made

with the unit entirely within the calorimeter, tests numbered 2a and

2b were made with the unit on the outside of the calorimeter, and

tests numbered 3a and 3b were made with the unit divided as described

previously. The enthalpy difference between outdoor and indoor temperature conditions for any air that leaked through the air conditioner

into or out of the conditioned space was not credited to the total net

cooling capacity of the unit. The desired test conditions, the average temperatures maintained during the tests, and the results are summarized in Table 1.

A comparison of capacities observed for the three methods of mounting the air conditioner shows that the lowest capacity/- can be expected

when the unit is mounted wholly within the cooled space. Using the indoor location as a base for comparison, the capacity was increased 9°1

and 15 .# percent with the unit mounted on the outside of the cooled

space, and was increased 20.3 and 36.6 percent with the unit divided,

for the lower and higher ambient temperatures, respectively. The difference in capacity between inside and outside mounting was probably

due chiefly to the fact that the unit exhausted some air from the

calorimeter when mounted entirely inside and this air was replaced with

ambient air, whereas there was no air movement into or out of the calorim

eter when the unit was mounted on the outside of the calorimeter.

The differences in capacity between Tests 2a and 3a and between

Tests 2b and 3b represent with reasonable precision the non-useful heat

gain of the evaporator section (through the frame, panels, etc.) from

the ambient air in the two cases since the evaporator section was outside the calorimeter for tests 2a and 2b and inside for tests 3a and 3b

and there was no measurable air leakage to or from the calorimeter in

either case. These capacity differences amounted to 14-50 Btu/hr for an

ambient temperature of 95°F (Tests 2a and 3a) and 2490 Btu/hr for an

ambient of 125°F (Tests 2b and 3b).

- 6 - Table 1

Performance of York Corporation Air Conditioner

Model V-$OSC, NBS Specimen $2-52

Desired Test Conditions

Ambient Air Conditions : Dry Bulb Temp., °F 95 • 125

Wet Bulb Temp. , °F 75 : $5

Relative Humidity, % 40 : 20

Air Conditions at Evaporator Inlet

Dry Bulb Temp. , °F $0 : 90

Wet Bulb Temp. , °F 67 : $0

Relative Humidity, % 51-65

Observed Test

Test No. la

Conditions

2a 3a lb 2b 3b

Ambient Air Conditions

Dry Bulb Temp. , °F 96.4 94 .$ 95.9 126.1 124.6 126.0

Wet Bulb Temp., °F 76.3 74.6 76.$ $6.9 $6.0 $7.5

Relative Humidity, % 40.5 39.0 43.0 22.0 22.0 22.5

Air Conditions at Condenser

Dry Bulb Temp., °F

Inlet

99.$ 95.3 9$.

12$.125.5 12$.

Wet Bulb Temp., °F

Relative Humidity, %

77.3 74.$ 77.4 $7.4 $6.2 $$.3

37.3 3$. $ 39.5 20.4 21.5 21.0

Air Conditions at Condenser

Dry Bulb Temp., °F

Outlet

109.7 106.4 110.2 140.0 139.1 142.0

Air Conditions at Evaporator

Dry Bulb Temp. , °F

Inlet

$1.7 79.9 79.7 90.2 90.0 91.0

Wet Bulb Temp., °F 6$.

66.9 66.9 $0.1 $0.0 $0.7

Relative Humidity, % 51.0 50.$ 51.0 65.2 65.0 65.2

Air Conditions at Evaporator

Dry Bulb Temp., °F

Outlet

6$.0 66.1 67.4 $0.6 $1.4 $1.5

Wet Bulb Temp., °F 62.0 63.2 64 0 4 76.5 77.4 77.5

Electrical Data

Power Consumption, watts

Compressor Motor 2206 2135 2166 2$6$ 2 $3 5 2$$6

Evap. Fan Motor 206 230 231 201 223 221

Cond . Fan Motor 541 622 612 521 5 $6 573

Total 2953 29$7 3009 3590 3644 36$0

Current Used, amps

Compressor Motor, rated (?.3amps 6. 5 6.3 6.3 7.9 7.$ 7.9

Evap .Fan Motor, rated 1.5 amps 1. 6 1.5 1.6 1.6 1.5 1.5

Cond. Fan Motor, rated 4°

Terminal Voltage

9 amps 3. 6 3.4 3.4 3.5 3.3 3.3

209 209 20$ 209 20$ 20$

Table 1

7 -

- continued

Test Noo la 2a 3 a lb 2b 3b

Moisture Load, lbs/hr

Evaporated at humidifer 1.13 1.33 2.13 5 0 5 5.44 5.75

Collected off evaporator 2.25 1.15 2.33 5o75 5.47 6.0

Head Pressure, psig 135 173 133 275 272 236

Suction Presure, psig 33.7 36.0 36.0 55 ol 53.3 53.5

Net Sensible Cooling

Capacity, Btu/hr 11,340 12,760 13,410 6150 3120 10,270

Net Dehumidifying

Capacity, Btu/hr 1200 1460 2260 5330 5760 6100

Total Net Cooling

Capacity, Btu/hr 13,040 14,220 15,670 11,930 13,830 16,370

Sensible Heat Ratio, % 90.9 39 0 3 35.6 51o6 58.5 62.7

Performance Factor,

Btu/hr/watt 4 0 4 4o 3 5 o2 3.3 3.3 4 . 4

Computations of the net sensible heat removal from the conditioned

space based on the air circulation rate of the evaporator fan and the increase in dry-bulb temperature between the evaporator section outlet and

inlet openings do not agree well for every test with the values of net

sensible cooling capacity reported in Table 1. A part of this discrepancy is accounted for in tests la and lb by the sensible heat of the air

forced into the calorimeter by the auxiliary blower to replace that exhausted by the air conditioner. Some error is probable in all tests because it is impossible to obtain a true weighted average temperature of

a stream of air when discharged in confined conditions with several sudden changes of direction as was the case for the test specimen. Furthermore, the air circulation rate of the evaporator fan was not determined

during each capacity test, but was measured in a separate test with the

unit outside the calorimeter.

The electric power consumption of the test specimen was rather high

for the total net cooling capacity observed, as shown in Table 1 by the

low performance factor in Btu/hr/watt. For tests made at ASRE standard

rating conditions (ambient conditions 95 LB, 75 WB; room air inlet SO DB,

67 WB) , Federal Specification OO-A-372, covering self-contained air conditioning units requires a minimum performance factor of 6.0 Btu/hr/watt

for console-type air conditioners with air-cooled condensers such as

this one. The performance factor for the test specimen ranged from 4.4

to 5.2 Btu/hr/watt for tests la, 2a, and 3a.

Table 1 shows that the sensible heat ratio was from $5 to 90 percent for the tests at ASRE standard rating conditions with 51 percent

relative humidity in the conditioned space (Tests la, 2a and 3a).

This result indicates that this unit could only remove a limited amount

of moisture from a space at a humidity level of 51 percent. The Federal

Specification for self-contained air conditioning units requires that

the sensible heat ratio be within the range from 70 to $0 percent for

these room conditions.

- 3 -

By contrast, the sensible heat ratio was reduced to the range from

52 to o3 percent for tests lb, 2b, and 3b in higher ambient temperatures for which the relative humidity of the room was maintained at 65

percent. For these tests the dehumidification load seriously reduced

the sensible cooling capacity of the unit. For the conditions prevailing during tests lb, 2b, and 3b the dew point temperature of the outdoor air was 72°F whereas it was 76„5°F for the indoor air. Thus an

exchange of air between indoors and outdoors would remove moisture

from the conditioned space. During actual use in ambient conditions

of 125 DB and $5 WB, this air conditioning unit would probably reduce

the indoor relative humidity below the 65 percent level in all applications except those where an unusually large amount of moisture

( 5 or 6 pounds per hour) was released in the conditioned space.

Bo Air Circulating Capacity

Determinations of the air circulating capacity were made for both

the evaporator and condenser fans. The results of these measurements

are summarized in Table 2, The Federal Specification OO-A-372 for

self-contained air conditioners requires a minimum air circulation

rate of 30 cfm per thousand Btu/hr of rated capacity for this type

unit. The observed air circulation rates of the test specimen exceeded this value considerably for both the evaporator and condenser

fans based on the observed capacities.

Table 2

Air Circulating Capacity of York Unit

Air Capacity

Temp, of Air, °F

During Test

cfm DB WB

Evaporated Fan 340 37 66

Condenser Fan 1597 96 66

As pointed out earlier in the report, some air was exhausted from

the calorimeter by the unit during tests la and lb when the condenser

section was mounted inside the calorimeter. This leakage amounted to

23 to 30 cfm, respectively, for tests la and lb, and probably occurred

around some of the removable panels of the condenser section of the

cabinet in such manner that the condenser fans exhausted air from the

calorimeter. The evaporator section of the cabinet was apparently

leak-tight because no leakage occurred during the tests with only

the evaporator section in the calorimeter. It should be noted that

some of the modifications described in Section D of Test Results of

this report directly affected the amount of air leaking through the

cabinet sections.

- 9

-

C 6 Electrical Tests

A Brush oscillograph was used to measure the starting current

of the complete unit and of the two fans. The highest instantaneous

starting current observed for the complete unit was 66. 3 amperes,

and for the two fans, 46 amperes. The time of starting was 0.117

seconds for the compressor and 0,51 seconds for the fans.

The unit was equipped with a timer which prevented the fans

and compressor from starting simultaneously.

Do Design and Workmanship

As a result of attempts to determine reasons for the low capacity

observed for the unit as received, certain construction features were

noted which required modification or adjustment.

It was noted that if the assembled unit was set on an uneven

floor the frame could be distorted sufficiently to cause the condenser blower wheels to rub against the scroll sides. Apparently

this was caused by the softness of the particular aluminum used

for framing and by the further weakening of the angle base framing

(see Figure 4) resulting from relief notching of this angle at the

condenser fan discharge openings, A representative of the manufacturer stated that 3S-1/2 H or 3S-H-14 aluminum was used for the

prototype under test and that in production of this item 52-S-H-14

aluminum, more suitable for the purpose, would be used.

Figure 3 shows that the base angle of the second section, to

which the compressor base rails are attached is bent outward. The

opposite angle, as can be seen in Figure 4 was bent inward. Representatives of the manufacturer stated that this could have occurred

in transit and was aggravated by the softness of the aluminum used.

As delivered for tests, a very poor fit between cover panels

and the frames of the sections was noted. The panels were of sheet

aluminum, were not equipped with gaskets, and were each attached by

means of 4 threaded aluminum fasteners. The resulting poor fit permitted considerable air exchange between the unit sections and- the

surrounding ambient. These openings were sealed before the tests

were made since the representative of the manufacturer stated that

in production gaskets woulS be provided between sections and cover- panels and between sections.

Some of the threaded aluminum fasteners used to fasten the panels to the section frames were stripped at the time of receipt of

the unit and others became stripped during the removal and replacement of panels during the tests.

10

The bottom and end portions of each section were welded. Cracks

were observed on some of these welds and in Figure 4 two of the cracked welds can be clearly seen, one in the lower right corner of the top

section, the other in the lower left corner of the compressor section.

At least three other such welds were also cracked.

No evaporator or discharge air louver or grill was supplied with

the unit. As can be seen in Figure 1 the return air opening to the

evaporator is directly beneath the evaporator discharge opening. In

order to prevent serious short-circuiting of the evaporator air during tests it was necessary to install a baffle projecting from between

the two top sections.

Preliminary runs made prior to testing indicated serious flooding

of refrigerant from the evaporator to the compressor. A representative

of the manufacturer made several adjustments to the expansion valve

and shifted the position of the bulb for the thermostatic expansion

valve before correcting the flooding condition. He cut an access opening in the end of the evaporator fan section (see Figure 4, right hand

side of the third section)' to permit adjustment of the expansion valve

while the unit was operating and ip position for test. The manufacturer’s representative discharged, evacuated and recharged the S3^stem

with 6 lbs. of dichlorodifluoromethane , after correcting the flooding

condition, in an attempt to lower the head pressure observed during

the preliminary runs.

Various openings between sections for electric lines, refrigerant tubing, etc., were not sealed when the unit was received. A representative of the manufacturer stated that these openings, which would

permit exchange of air between evaporator and condenser, would be

sealed in production. These openings in the unit under test were then

sealed with a mastic-type material before testing.

V. DISCUSSION AND CONCLUSIONS

The tests of this development model air conditioner showed that

a considerable gain in capacity was obtained by separating the evaporator and condenser sections of the unit, installing the former in the

cooled space and the latter outside the space to be cooled, as compared to mounting the entire unit either inside or outside the space.

This increase in capacity amounted to 20 percent as compared to the

inside installation and 9 percent as compared to the outside installation for ASRE standard rating conditions indoors and outdoors. The advantage of dividing the unit was even greater for higher outdoor

temperatures

.

11 -

The performance factor of the unit in Btu/hr of total net cooling capacity per watt of electrical energy input was considerably

below the value of 6.0 required by Federal Specification, OO-A-372,

for self-contained air conditioners. The unit was shown to have a limited capacity for dehumidification at relative humidities near

50 percent by the relatively high sensible heat ratio observed under

ASRE standard rating conditions.

As received the capacity of the unit was seriously reduced by

air leaks around the cabinet panels, recirculation of conditioned

air from evaporator outlet to inlet and improper adjustment of the

refrigerant control device. Attention should be given to improving these features in any future development.

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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 by Congress in Public Law 619, 1950.

These include the development and maintenance of the national standards of

measurement and the provision of means and methods for making measurements

consistent with these standards; the determination of physical constants and

properties of materials; the development of methods and instruments for testing

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front 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 periodicals, available from

the Government Printing Office: The Journal of Research, which presents complete papers reporting technical investigations; the Technical News Bulletin, which

presents summary and preliminary reports on work in progress; and Basic Radio

Propagation Predictions, 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 publications can be found in NBS Circular 460,

Publications of the National Bureau of Standards ($1.00). Information on cali- bration services and fees can be found in NBS Circular 483, Testing by the National

Bureau of Standards (25 cents). Both are available from the Government Printing Office. Inquiries regarding the Bureau’s reports and publications should be

addressed to the Office of Scientific Publications, National Bureau of Standards,

Washington 25, D. C.