NATIONAL BUREAU OF STANDARDS REPORT

5885

CAPACITY TESTS OF A MATHES HEAT PUMP

MODEL 27HAR-REB-HP

by

Joseph Co Davis

Paul R, Achenbach

Report to

Seymour Johnson Air Force Base

Goldsboro, North Carolina

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-4830 May 2, 1958 5885

CAPACITY TESTS OF A MATHES HEAT PUMP

MODEL 27HAR- REB-HP

by

Joseph Co Davis

Paul R 0 Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Seymour Johnson Air Force Base

Goldsboro, North Carolina

IMPORTANT NOTICE

NATIONAL BUREAU OF

Intended for use within

to additional evaluation < listing of this Report, elt the Office of the Directoi however, by the Governn

to reproduce additional v

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

' or progress accounting documents

is formally published it is subjected

ntlng, reproduction, or open-literature ermission Is obtained in writing from

I, C, Such permission Is not needed,

Ically prepared if that agency wlshei

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
v • - V ‘1 JA**S0tTAi«
CAPACITY TESTS OF A MATHES HEAT PUMP,

MODEL 27HAR- REB-HP

by

Joseph C 0 Davis and Paul R 0 Achenbach

ABSTRACT

At the request of the Contracting Officer, Seymour

Johnson Air Force Base, cooling and heating capacity tests were made of a Mathes air-to-air heat

pump. Model 27HAR-REB-HP„ These tests were made

at the indoor and outdoor conditions stated in the

contract specifications, except that the air

circulation rate and static pressure at the outlet

of the indoor coil was set at 1100 cfm and 0.24 in.

W.G. respectively in accordance with an agreement

between the U 0 S. Air Force and the Mathes Company.

These tests, except for minor deviations, were made

under the procedures and conditions specified by

the American Society of Refrigerating Engineers

Standard No 0 16-56 „ The observed cooling capacity

was 23*700 Btu/hr at the specified test conditions

whereas the minimum required was 27*000 Btu/hr.

The observed heating capacity, without auxiliary

strip heaters was 14,300 Btu/hr, whereas the minimum required was 22,800 Btu/hr. At rated voltage

the strip heaters had a capacity of 3° 2 KW as

compared to the requirement of 3°6 KW. One modification was made in the indoor unit by the Mathes

Company due to malfunctioning of a check valve.

To improve heating performance the Company changed

capillary tubes in the outdoor unit until they

found one that gave the best performance.

1. INTRODUCTION

In accordance with a request from Captain W.A. Schrontz,

Contracting Officer, Seymour Johnson Air Force Base, United

States Air Force, by letter dated August 22, 1957 , tests

were made to determine the cooling and heating capacity of

a Mathes Heat Pump, Model 27HAR-REB-HP 0 These tests represented the second phase of a series of tests on three models

of heat pumps that will be used at this site. Results of

tests of the first model are covered in National Bureau of

Standards Report No a 5818, "Capacity Tests of Mathes Heat

Pump Model 38HAR-LEB-HP,

Specifications supplied by Captain Schrontz, Section 27AHeat Pumps (Alternate) of the contract specifications and

drawings for homes under construction at Seymour Johnson

Air Force Base, require a total heating capacity for the

27HAR-REB-HP of 27,000 Btu/hr and a total heating capacity

of 35, 086 Btu/hr. A breakdown of the capacity requirements

for these two conditions follows:

COOLING CAPACITY (Btu/hr)

Sensible Lat ent Total

18,900 8,100 27,000

HEATING CAPACITY (Btu/hr)

Condenser Heat

Transfer

From Auxiliary

Strip Heater Total

22,800 12,286 35,086

The specifications also require that the minimum air

circulation rate be 1000 cfm against an external static

resistance of 0 o 2 inch- of water. However, by agreement

between USAF and the Mathes Company before the tests

began, both cooling and heating tests were performed at a

minimum air circulation rate of 1100 cfm against an external static resistance of 0„24 inch* of water. This

change in the test conditions was confirmed in a letter

from Captain W. A. Schrontz, dated April 3, 1958.
»
-3-

2 . DESCRIPTION OF TEST SPECIMEN

The Model 27HAR-REB-HP, similar to the model previously tested, is known as a ’'split-type” unit in which

one section is placed outdoors and the other inside the

home at a suitable place for delivering conditioned air.

The two sections involved will be designated hereinafter

as the inside unit and the outdoor unit . The indoor unit,

similar to that tested previously, is known as a horizontal unit because the chilled air is discharged in a

horizontal direction from the unit.

During the cooling cycle, the coil of the indoor

unit served as an evaporator, absorbing heat; and during

the heating cycle, as a condenser, rejecting heat. This

operational change was accomplished by means of a change

in direction of circulation of the refrigerant through the

system, using a thermostatically-controlled solenoid in a

four-way valve. During the test the solenoid was controlled

by a manually operated switch to preclude shifting from

cooling to heating or vice versa. Capillary tubes were

used as the liquid refrigerant flow control device in both

the indoor and outdoor units with check-valves to by-pass

each when not needed„ Following the new ASRE refrigerant

designations, the refrigerant was R- 22 , The indoor unit, except for the capillary tube, is

the same as that for the 38 HAR-LEBo It consisted of a

coil (used as an evaporator during cooling), a blower for

circulating conditioned air through the duct system of the

home, and a capillary tube-check valve assembly. The coil

was a three-row coil, 30 in. wide and 20 in. high, with

13 fins per in. of tube length. A Torrington blower with

a 13 “in 0 diameter wheel was used and it was powered by a

1/3 HP single phase motor. Nameplate rating of the motor

was 230 volts, 2.7 amperes, with a service factor of 1 . 35 ° A speed of rotation of 1725 npm was also specified on the

nameplate and measurements after testing showed an rpm of

1660 „ The capillary tube had an ID of 0.1005 in. and a

length of 60.2 in. The housing of the indoor unit was 3^-°

3

in. wide, 33.2 in. deep, and 28.5 in. high. Wall thickness

0.053 in.
-

-
-4-

With the indoor motor pulley adjusted after the test

for 1100 cfm air delivery on coolings and with the temperature at about 75 °Fj the fan speed of rotation was 705 rpm.

The outdoor unit consisted essentially of a coil (used

as an evaporator during heating); a propeller fan; a hermetically- sealed Tecumseh No c H200TA-2-A1566 motor compressor

230 volts, 60 cycles, single phase, full load amperage 9 * 3 ; a capillary tube-check valve assembly; and a four-way valve.

The coil had rows, was 46 in, wide and 28 in, high, and

had 13 fins per in, of tube length. The fan blade assembly,

24 in, in diameter with a 40° pitch for each blade, was

powered by a 1/3 HP motor, single phase, 2,7 amperes, with

a service factor of 1.36, and with a rotational speed of

1725 rpm. The capillary tube had an ID of 0,0745 in, and

a length of 84 in. The housing of the outdoor unit was 51

in, wide, 27 in, deep, and 31 in. high. Wall thickness was

0,061 in. The 38 HAR-HP outdoor unit, which is the same as

the 27 HAR-REB-HP except for the compressor and capillary tube

check valve assembly, is shown in figure 2 with grilled

panel removed.

Measurements of the outdoor fan speed at an outdoor

temperature of about 75 °F showed 835 rpm.

Figure 3 shows the opposite side of the outdoor unit

facing the coil. Note the five-in-one thermocouple system

and the thermostat used for controlling outdoor conditions

during the test.

A schematic diagram of the heat pump system and

auxiliary equipment is shown in figure. 1.

A list of line sizes for this system and its auxiliary

equipment is shown below:

Size OD in.

1. Discharge line from outside of unit to

oil separator 1/2

2. Oil separator to 4-way valve 1/2

3 0 Oil return lines 1/4

4. Compressor suction to 4-way valve 5/8

5« Four-way valve to coil of outdoor unit 5/8

6

.

Liquid line to flowmeter manifold 3/8

7» Lines in manifold 1/2

8. Vapor line 3/4

-5

Some modifications of the heat pump were made by the

manufacturer during the test to improve its performance

„

These modifications are described in a later section of

the report.

3. METHODS OF TESTING

Except for minor deviations, the heat pump was tested

under the conditions described in ASHE Testing and Rating

Standard No. 16-56, as required by the specification.

Figure 4 shows the enclosure housing the indoor unit and

the 33-in. square test duct attached to the outlet side of

the unit. This duct housed the nozzle used for measuring

air circulation rate and the instruments for measuring

temperature and humidity of the outlet air, Because the

nozzle, mixing baffles, and screen introduced considerable

resistance in the outlet duct, an auxiliary blower powered

by a one-HP motor was provided at the downstream end of

the 33“in. duct, By adjustment of a wooden slide-type

damper at the outlet of the auxiliary blower, the static

resistance imposed upon the indoor unit blower was adjusted

to 0 o 24 inch of water. The auxiliary blower, return air

heaters, and humidifier are shown in figure 5.

ASRE Standard 16-56 requires that two independent

measuring methods be used during the test, each as a check

on the other. One method, known as the psychrometric

method, involved measuring the mass-flow of air through

the indoor unit and the change in enthalpy of the air

across the unit. The other method involved determination

of the flow of refrigerant through the indoor coil and

the change in enthalpy of the refrigerant across the

indoor coil. A correction to the total enthalpy change of

the refrigerant is necessary, either by adding or subtracting the heat equivalent of the electrical energy

supplied to the indoor blower motor depending on whether

the heating or cooling cycle is in use before comparing

it with the result of the psychrometric method. Values

obtained by the two methods must not differ by more than

six percent in order for a test to be valid.

- 6 -

Mass flow of air in the psychrometric method was

obtained by measuring humidity and temperature conditions

of the air entering the long-radius nozzle and the static

pressure drop across the nozzle. Enthalpy change of the

air was determined by measuring temperature, humidity, and

barometric pressure of the air entering the indoor unit,

and in the duct immediately after it left the unit.

In order to maintain 1100 cfm for both heating and

cooling, it was necessary to set the speed of the indoor

blower lower during heating than cooling. If the same

blower speed pulley adjustment is used in the homes at

Seymour Johnson Air Force Base, the flow of supply air

will be slightly greater for heating than cooling. The

pulley adjustment on the outdoor fan was the same for

heating and cooling.

Flow of refrigerant was measured by means of a

flowmeter in the liquid line of the syste.m--a Potter

Electronic type with an impeller which generated an electrical pulse on each revolution. A Potter counter

coupled to the flowmeter served to translate the pulses

into gal/unit time. By knowing temperature of the liquid

in the line, the flow was converted to mass flow 0 Enthalpy change was determined by temperature and pressure measurements at the inlet and outlet of the indoor

coil. For accurate measurement of capacity by the

refrigerant flow method it was imperative that there be

no gas bubbles in the liquid refrigerant as it passed

through the meter, and that the liquid refrigerant all

be evaporated in the coil.

To assure substantially oil-free refrigerant at the

flowmeter, an oil separator was provided in the hot gas

line between the compressor and four-way valve to separate

the oil. The oil was returned to the refrigerant at the

inlet to the indoor coil during the cooling cycle test

and to the inlet of the coil in the outdoor unit during

the heating cycle test.
.

.
-7-

During the test, power consumed by the indoor blower,

outdoor fan, and compressor was read from separate watthour meters. Simultaneous readings were made of currents

and voltages. The various meters, together with the other

instruments for measuring temperature and humidity, are

shown in figure 6.

The following ’’state" conditions for the indoor and

outdoor air were maintained during the cooling cycle in

accordance with contract specifications:

95 °F DB outdoors

80°F DB inside

67°F WB inside (50 percent relative humidity)

Refrigerant charge was the same for the cooling test

as for the heating test. The representatives of the Mathes

Company elected to set this charge at optimum on the

heating cycle such that on the cooling test following,

there was some flooding at the outlet of the indoor unit.

Steady state conditions were maintained for more than an

hour before the test Q During the test, readings were

taken every ten minutes for two to three hours, and the

hour representing the steadiest conditions was used for

evaluating the performance of the unit.

For the heating test, the following "state” conditions

for the indoor and outdoor air were maintained in accordance

with the contract specifications:

20°F DB outdoors

70°F DB indoors

It was possible to maintain "state” conditions for

both cooling and heating with the use of a test structure

having two controlled temperatures.

To make certain that no refrigerant was lost between

the heating test and the cooling test, immediately following the latter test, the temperature of the space

representing the outdoors was lowered to 20°F and the more

pertinent readings of the heating test observed. Values

for head pressure, suction pressure, and temperature were

essentially the same as during the heating test.
.

.
-8 -

4. TEST RESULTS

A. Cooling Test

ASRE Standard 16-56 requires that values obtained by

the psychrometric and flowmeter methods be averaged to

obtain the rated capacity of the unit. Since the representatives of the Mathes Company chose to set the refrigerant

charge so that there was some flooding at the outlet of the

indoor unit during cooling operation, the flowmeter did not

measure the amount of liquid evaporated in the indoor coil,

so it would not have been proper to use the flowmeter data

to obtain an average. However, ASRE 16-56 allows a maximum deviation of six percent between the two methods, and

since the flowmeter method has usually given higher values

on the cooling cycle than the psychrometric method, an

increase of one half of this six percent, or three percent,

was allowed,.

Test results for the cooling test follow:

Summary of Cooling Capacity Values (Btu/hr)

Test Rounded

Value Value

22,880

690

23,570

100

23,670 23,700

Following is a summary of the averages of the more

significant data observed during the cooling test,

Psychrometric Method

Temperatures ( °F)

At inlet to enclosure around indoor unit 80.0 DB

At outlet of indoor unit in duct 63 . 6 DB

Temperature difference across indoor coil 16.4 DB

At inlet to outdoor unit 94.6 DB

By psychrometric method

Flowmeter allowance

Correction for deviation of

barometric pressure from

standard barometric pressure

-9-

Relative Humidities {%)

At inlet to enclosure around indoor unit 49.8

At outlet of indoor unit in duct 83,7

Static Pressure across Nozzle (in. of H^O) 1<>12

Volume Air Flow at Nozzle (cfm) 1135

Mass Air Flow at Nozzle (lb dry air/hr) 507S

Barometric Pressure (ln 0 of Hg) 29 , 73

Diameter of Nozzle (in.) 7„03

Nozzle Coefficient # 99

Static Resistance (in. of H2 O) 0.24

Pressures (psig)

Compressor discharge 257,

In liquid line entering coil of indoor unit 241.

In vapor line leaving coil of indoor unit 84]

Difference in pressure across the oil separator was

less than 2 psi.

Difference in pressure across the flowmeter was about

3 psi.

Other Temperatures ( °P)

In liquid line entering coil of indoor unit 98 .

0

In vapor line leaving coil of indoor unit 50^8

In suction line of compressor 49.9

Motor Power Consumption (Watts)

Indoor blower 403

Outdoor fan 524

Compressor r?f) h

r?

Total 3559

- 10-

Coefflcient of Performance

Motor Voltages (Volts)

1°95

Indoor blower

Outdoor fan

Compressor

230.0

230.0

230.0

Motor Currents (Amperes)

Indoor blower

Outdoor fan

Compressor

2.7 4

3.10

12.00

It will be noted that the compressor current was 12

amp

s

0 whereas the 9.3 amperes appeared on the nameplate

as the full-load ampere rating.

Bo Heating Test

The heating test, performed in accordance with the

procedures described in ASRE Standard 16-56, except for

minor deviations, gave the following results:

Summary of Heating Capacity Values (Btu/hr)

Test Rounded

Value Values

By psychrometric method

By flowmeter method

Average

14,300

14,180

14,240

Correction for deviation of

barometric pressure during

test from standard barometric pressure 50

14,290 14,300

Following is a summary of the averages of the more

significant data observed during the heating test.

- 11 -

Psychromet rlc Method

Temperatures (°P)

At Inlet to enclosure around indoor unit

At outlet of indoor unit in duct

Temperature difference across indoor coil

At inlet to outdoor unit

69.7 DB

81.6 DB

TT79 DB

19.6 DB

Relative Humidity of Indoor Air in Duct (%) 14.5

Static Pressure across Nozzle (in. of HpO) 1.11

Volume Air Flow at Nozzle (cfm) 1140

Mass Air Flow at Nozzle (lb dry air/hr) 5006

Barometric Pressure (in. of Hg) 29.68

Diameter of Nozzle (in.) 7.03

Nozzle Coefficient • 99

Static Resistance (in. of H2 0) 0 236

Flowmeter (Refrigerant Method)

Temperatures (°F)

In vapor line entering coil of indoor unit 94. 2

In liquid line leaving coil of indoor unit 73. 5

Pressures (psig)

In vapor line entering coil of indoor unit 182

In liquid line leaving coil of indoor unit 182

Potter Meter Count for 10 Minutes 477. 8*

Other Pressures (psig)

Compressor discharge pressure

Suction pressure

183.

34.

Difference in pressure across the oil separator was less

than 2 psi„

Difference in pressure across the flowmeter was about

5.5 psi. This difference caused less than 4 psi change

in head pressure.

* Re frigerant flow, gal/min = Meter Count for 10 min, x 100

18133.8

- 12 -

Other Temperatures ( °P)

Compressor discharge 119-9

Suction line at compressor 9.0

Motor Power Consumption (Watts)

Indoor blower 385

Outdoor fan 684

Compressor 1677

Total 274^

Coefficient of Performance ( Exclusive of strip

heater) 1.52

Motor Voltages (Volts)

Indoor blower 229.9

Outdoor fan 230.6

Compressor 230.6

Motor Current (Amperes)

Indoor blower 2.67

Outdoor fan 3.73

Compressor 7*94

Power Consumption of Strip Heaters

Readings of the energy dissipated by the strip heaters

in the indoor unit were made every ten minutes for a period

of one hour with the following results:

Watthour meter value (Watts) 3211.0

Average terminal voltage (Volts) 227.8

Average current (Amperes) 13.94

Voltage times current (Watts) 3175.5

During the period in which the unit was being charged

with refrigerant prior to the heating test, the oil separator was closed off from the rest of the system. The temperature around the outdoor unit was about 28 °F. Then when
--
-13-

the separator was introduced into the system a decrease in

head pressure of about 17 psi occurred. A part of this

decrease was temporary, but the head pressure remained

below the value observed when the oil separator was out of

the system. By agreement enough refrigerant was added to

raise the head pressure to its original value. All tests

subsequent to this were performed with the oil separator

in the system and with the added charge.

The oil separator, to limit length of lines exposed

to the cold., was placed relatively close to the outdoor

unit. In addition to the normal felt insulation furnished

with the oil separator when purchased, it was insulated

with a 1-in. layer of glass fiber and a 3/4-in. layer of

hair felt; and the lines, except for a small section of

each near the outdoor unit, were insulated with a sponge

rubber type of material. With this insulation, it was

expected that the separator would cause little heat loss in

the vapor line to the indoor unit.

After the heating test, in order to determine the

extent of the loss, a test was performed with the oil

separator in the system, followed immediately by a period

with the oil separator by-passed and with only vapor

trapped in the separator. The data particularly noted

during these comparative periods were change in head pressure, pressure at the inlet to the indoor coil in the

vapor line, suction pressure, change in the count of the

refrigerant flowmeter (due to oil in the refrigerant),

change in the temperature rise of the air over the indoor

coil, and change in temperature at vapor line entering

coil of indoor unit. These data are presented below:

With the Without the

separator separator

Head Pressure (psig) l8l 185

Pressure at Inlet to Indoor Coil

(psig) 177 181

Suction Pressure (psig) 35 34

Flowmeter Counter (counts per min.) 50.8 51„2

Temperature Rise of Air through the

Indoor Coil (°F) 11.8 12 o 0

Temperature in Vapor Line Entering

Indoor Coil ( °F ) 94.5 96.5

-14-

The small difference in temperature rise across the

indoor coil indicates an increase in heat transfer of the

coil of only about 250 Btu/hr without the separator. The

increase in flowmeter indication was less than one percent.,

showing that little oil was being circulated with the

refrigerant

.

5. SYSTEM MODIFICATIONS

A. Replaced capillary tube-check valve assembly in

the indoor unit because of malfunction.

B. Three capillary tube and check valve assemblies

were tried in the outdoor unit while seeking to obtain an

optimum capacity in the heating cycle. The dimensions of

the three capillary tubes are listed below. The last of

the three assemblie's was used for the test reported in

part B of section 4 of this report.

Initial 1st Change 2nd Change

0.0795 in., ID 0.0745 in., ID 0.0745 in. ID

59.375 in.. Length 70.75 in.. Length 84 in. Length

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U. S. DEPARTMENT OK COMMERCE

Sinclair Weeks. Secretory

NATIONAL ItllREAU OF STANDARDS

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

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