NATIONAL BUREAU OF STANDARDS REPORT

5818

CAPACITY TESTS OP A MATHES HEAT PUMP

MODEL 38HAR-LEB-HP

by

Joseph C. Davis

Clinton W. Phillips

Paul R. Achenbach

Report to

Seymour Johnson Air Force Base

Goldsboro, North Carolina

<JJbS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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JtSll

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT MBS REPORT

1000-30-4830 March 20, 1958 5818

CAPACITY TESTS OP A MATHES HEAT PUMP

MODEL 38HAR-LEB-HP

by

Joseph C. Davis

Clinton W. Phillips

Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Seymour Johnson Air Force Base

Goldsboro, North Carolina

NATIONAL Sy&EAU 01? STAI

Intended for use within the Si 80 additional evaluation and ret lilting of title Report, either In the Office of the Director, Natii however, by the Government sj to reproduce additional copies

IMPORTANT NOTICE

ogress accounting documents

Approved for public release by the nelly published It Is subjected

Director of the National Institute of 0 „ „ o5ulned ffO0) Standards and Technology (NIST) iuch permission Is not needed, on October 9, 201 5.

reP,r«d lf that NP««y wishes

0. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FOR 01 it lUiai

CAPACITY TESTS OF A MATHES HEAT PUMP MODEL 38HAR-LEB-HP

by

Joseph C. Davis,, Clinton W. Phillips,, and Paul R. 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 38HAR-LEB-HP, at the indoor and outdoor conditions stated in the contract specifications.

The tests were made in accordance with American

Society of Refrigerating Engineers Standard

No. 16-56, entitled Methods of Rating and Testing

Air Conditioners. Certain modifications of the

unit were made during the test, and a second

outdoor unit was tested after it was found that

the original specimen did not have adequate

cooling capacity. The Tecumseh motor-compressors

in the two outdoor units bore the same model

numbers, but had different full-load current

ratings stamped on the nameplates. It was unknown whether the displacements of the two compressors were identical or not. The observed

cooling capacity of the system with the second

outdoor unit was 35.? 100 Btu/hr at the specified

test conditions whereas the minimum required

cooling capacity was 36,000 Btu/hr. The specimen

did not perform satisfactorily on heating

operation in that the discharge pressure of the

compressor was so low that the interlocking

pressure control on the indoor blower would not

permit it to continue running, and the temperature

rise produced by the indoor coil was inadequate,

There were gas bubbles in the liquid refrigerant

line between the condenser and capillary tube to

the outdoor unit and the refrigerant liquid was

flooding through the outdoor coil into the

compressor. The indication was that the capillary tube was not restricting the refrigerant flow

sufficiently. Upon arbitrarily restricting the

liquid refrigerant line a maximum heating

capacity of about 22,000 Btu/hr was observed

exclusive of the strip heaters. The adjustment that produced the maximum heating resulted

in a slight flooding of liquid into the compressor. At rated voltage the strip heaters

consumed 3.3 KW as compared to a requirement of

3.6 KW.

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 38 HAR-LEB-HP . These tests represented

the first phase of a series of tests on several models of

heat pumps that will be used at this site.

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

drawings for homes under construction at Seymour Johnson Air

Force Base require a total cooling capacity for this model

of 36,000 Btu/hr and a total heating capacity of 42,786

Btu/hr. A breakdown of the capacity requirements for these

two conditions follows:

COOLING CAPACITY (Btu/hr)

Sensible Latent Total

25,200 10,800 36,000

HEATING CAPACITY (Btu/hr)

Condenser Heat Transfer From Auxiliary Strip Heaters Total

35,500 12,286 42,786

The specifications also require that the minimum air

circulation rate be 1,300 CFM against an external static resistance of 0.2 inches of water.

OR OFFEO

2. DESCRIPTION OF TEST SPECIMEN

The Model 38 HAR-LEB-HP heat pump is known as a "splittype'' 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 . 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. Tests of the heat pump system were made with two

outdoor units. The second specimen was submitted when the

tests showed the first had inadequate capacity. The results

reported are those obtained using the second outdoor 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 consisted essentially of a coil (used as

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 threerow coil, 30 in. wide and 20 in. high, with 13 fins per in.

of tube length. A Torrington blower with a 13-in. 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. The capillary

tube had an ID of 0.117 inch. The housing of the indoor unit

was 33 13/16 in. wide, 32 7/8 in. deep, and 27 7/8 in. high.

-4-

The outdoor unit consisted essentially of a coil (used

as an evaporator during heating), a propeller fan, a

hermetically-sealed Tecumseh No. PJE-300 motor-compressor, a

capillary tube-check valve assembly., and a four-way valve.

The fan blade assembly., 24 inches in diameter with a 40°

pitch for each blade, was powered by a 1/3 HP, single phase

motor. Nameplate rating of the motor was 208 - 230 volts,

2.7 amperes, with a service factor of 1.35. The capillary

tube had an ID of 0.109 in. This unit with grilled panel

removed is shown in Fig. 1.

Fig. 2 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. The housing of the outdoor unit was 51 in.

wide, 27 in. deep, and 31 in. high.

3, METHODS OF TESTING

The heat pump was tested under the conditions described

in ASRE Testing and Rating Standard No. 16-56, as required by

the specification. Fig. 3 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 th.e outlet air. Because

the nozzle, mixing baffles, and screen introduced excessive

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 0.20

inches of water. The auxiliary blower, return air heaters, and

humidifier are shown in Fig. 4

ASHE 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 psychromet ric method,

involves 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
,

*
-5

-

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 which cycle is under operation 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.

Mass flow of air in the psychrometric method was obtained

by measuring humidity and temperature conditions of the air

entering the 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.

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. 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.

The following "state" conditions for the indoor and

outdoor air were maintained during the cooling cycle in

accordance with contract specifications:
,

•
6 -

95°F DB outdoors

80°P DB inside

67°F WB inside (50 percent relative humidity)

Before performing the cooling test* the refrigerant

charge in the system was adjusted in accordance with instructions from the Mathes Company, to produce approximately 3°

of superheat at the outlet of the indoor coil under the "state”

conditions specified above. Steady state conditions were

maintained for more than an hour before the test. During the

test, readings were taken every ten minutes for a full hour.

Averages of the readings were used for determining capacity

values

.

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 temperature spaces.

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 there was an 11 PSIG pressure drop across the oil separator during the test that would

not normally be imposed on the compressor, an adjustment was

made on the basis of a capacity vs. head pressure curve for

the PJE-300 compressor furnished by the Tecumseh Products

Company. This method of adjustment met with agreement from

the manufacturer. The adjustment amounted to an increase of

550 Btu/hr for the observed operating conditions. The results
.
-7-

of the two measuring methods applied during the cooling test,

and the total rated cooling capacity of the Model 38HAR-LEBHP heat pump are summarized below.

Summary of Cooling Capacity Values (Btu/hr)

By psychrometric method 35*000

By flowmeter method 34, 100

Average 34,550

Adjustment for 11 lb pressure drop

across oil separator 550

Total rated cooling capacity 35*100

ASRE Standard 16-56 allovrs an increase of 0.8 percent for

the psychrometric value of capacity for each inch of barometer

reading below 29.92 in. Kg during the test. Barometric

pressure in this case was 29.60 in. Hg. The correction

amounted to 91 Btu/hr for this test and is included in the

figures shown in the table.

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 61.2 OB

At inlet to outdoor unit 95.4 DB

Relative Humidities {% ) At inlet to enclosure around indoor unit 50.3

At outlet of indoor unit in duct 85.2

Static Pressure Across Nozzle (in. of Water ) 1.45

Volume Air Flow at Nozzle (cfm ) 1280

Mass Air Flow at Nozzle (lb dry air/hr ) 5:720

Barometric Pressure (in. of Hg ) 29.60

Diameter of Nozzle (in .) 7.03

Nozzle Coefficient . 99

Static Resistance (in. of water) . 20

-8 -

Flowmeter Method (Refrigerant Method)

Temperatures (°F)

In liquid line entering coil of indoor unit

In vapor line leaving coil of indoor unit

Pressures (PSIG)

In liquid line entering coil of indoor unit

In vapor line leaving coil of indoor unit

Potter-Meter Count for 10 Minutes

Other Pressures (PSIG)

Compressor discharge pressure

Pressure downstream of oil separator

Difference in pressure across oil

separator

Motor Power Consumption (Watts)

Indoor blower

Outdoor fan

Compressor

Motor Voltages (Volts)

Indoor blower

Outdoor fan

Compressor

Motor Current (Amperes)

Indoor blower

Outdoor fan

Compressor

*Refrigerant flow, gal/min ** Meter count (10 min)

3365 .

5

106.5

47.7

257.

45.7

319.5*

285

274

11.0

499

593

3998

230.1

230.4

230.3

3.15

3.25

18.50

x 100

-9-

B. Heating Test

No adjustment was made on the heat pump before performance

of the heating test. To make certain that no refrigerant had

leaked from the system during preliminary runs on the heating

cycle., the "state" conditions for cooling were established

prior to the heating test and it was found that refrigerant

superheat at the outlet of the indoor unit was still present

and less than 3°F* Thereafter, the "state" conditions for

heating were established as quickly as the test apparatus permitted . After the "state" conditions of 20° DB outdoors and 70°

DB indoors had again been reached and maintained for over two

hours, the heat pump was turned on for heating. Voltages and

currents for the indoor blower, outdoor fan, and compressor

were observed. These are shown below:

Voltages (Volts)

At indoor blower

At outdoor fan

At compressor

Currents (Amperes)

Indoor blower

Outdoor fan

Compressor

229 to 231

3.00

Offscale, over 5

11.00

Despite the large current drawn by the outdoor fan,

the system was allowed to run. From observations made at

the watthour meter, this fan alternately ran and stopped,

apparently cycling on its motor-protective device, repeating

the operation five to ten times. Finally, it ran continuously,

drawing about 4 amperes.

The head pressures and those at the inlet and outlet of the

indoor coil were low. Before ten minutes had elapsed , they

decreased to such a point that the indoor blower cut off. The

heat pump was turned off. After a short period it was turned

i * a. ONLY
1
-10

on again,, but within a few minutes the indoor blower again cut

off. It was impossible to obtain capacity data under these

conditions because of the intermittent operation of the indoor

blower. The Mathes heat pump was designed to cut off the

indoor blower at low condenser pressure to preclude blowing

cool air into the home after a change from the cooling to

heating. The condenser inlet pressure was about 165 psig when

the indoor blower stopped.

When it was obvious that the indoor blower would not

operate continuously,, the auxiliary blower was speeded up to

obtain about the rated air flow through the indoor unit.

Under these conditions a heating capacity of about 13,000 Btu/

hr was observed, exclusive of the strip heaters. During this

period, gas bubbles appeared in the refrigerant liquid line,

and no superheat was observed at the compressor suction,

the compressor discharge, or the condenser inlet.

The above data and the high and low side pressures

observed suggested the need for a capillary tube with greater

restriction. It was possible that the check valve in the outdoor unit leaked, but this could not be established from the

observations taken.

A capillary tube with greater restriction was simulated

by partially restricting a valve at a point in the liquid line

downstream from the indoor unit. At first, the valve was

adjusted so there was some superheat at the Inlet to the

compressor. Capacity values obtained under these conditions

were as follows:

The valve was then readjusted so there was no superheat

at the inlet to the compressor. The capacity obtained under

these conditions was as follows:

Heating Capacity

(Btu/hr

)

Psychrometric method

Flowmeter method

Average

20,400

20,000

20, 200

- 11 -

Heating Capacity

(Btu/hr

)

Psychrometric method 22,000

In this case the value obtained by the flowmeter method,

although not far different from 22,000 Btu/hr, is not reported

since it was certain that the vapor at the inlet to the

indoor coil was saturated and might have contained some

liquid refrigerant.

Following the heating tests at an outdoor temperature of

20°F .and an indoor temperature of 70°F, temperatures were

raised to 75°F DB and 35°F OB outdoors to duplicate those used

in a test made previously with another specimen by the manufacturer. Under these temperature conditions a heating

capacity of about 20,000 Btu/hr was observed with no restriction

in the liquid refrigerant line, and about 26,000 Btu/hr after

careful adjustment of the valve in the liquid line.

Power Consumption of Strip Heaters

Readings of the energy dissipated by the strip heaters in

the indoor unit was made every ten minutes for a period of

30 minutes with the following results:

Watthour meter value (Watts) 3312

Average terminal voltage (Volts) 230.2

Average current (Amperes) 14.22

Voltage times current (Watts) 3273

The contract specification requires a strip heater capacity

of 3*6 KW whereas the observed power consumption averaged

3.3 KW at rated voltage.

5. SYSTEM MODIFICATIONS

Cooling tests were made using two outdoor units. With

the combination of the first outdoor unit and the indoor unit

used throughout, some 20 tests, including some informal determinations, were made. During the tests of the first outdoor

unit, numerous adjustments were made by the manufacturer to
t

.

.
- 12 -

replace defective parts or to Improve the performance of the

system. The cooling capacity of the system with the first

outdoor unit using ASRE Standard testing methods was

32,500 Btu/hr after all modifications were made.

The principal modifications made on the system during the

tests made with both outdoor units are summarized below:

1. The capillary tube system of the indoor unit changed

from multiple tube assembly to single tube system of

0.120 in. ID, nominal.

2. During the process of installing a thermocouple well

in the outlet of the indoor coil, a partial restriction was found in the header common to the distribution lines from the coil. This was rectified by

the Mathes representative.

3. The outdoor fan motor was changed from 1/4 to 1/3 HP

on the first outdoor unit.

4. The capillary tube in the first outdoor unit was found

to be made of two sections of tubing, joined, both

having an ID of 0.100 In. It was replaced by a tube

having ID of 0.110 in., the nominal ID finally used.

5. NBS data having shown that the indoor blower was not

supplying an air flow of 1300 cfm against a static

pressure of 0.20 in. WG, the Mathes Company replaced

the 1/4 HP motor with a 1/3 HP motor.

6. A two-foot piece of the hot gas line between the compressor and four-way valve was changed from 3/8 to

1/2 in. in the first outdoor unit.

7. A new dryer was placed in the liquid line as one of

several steps taken to reduce the pressure drop

between the compressor and the indoor coil.

8. The outdoor fan motor pulley on the first outdoor unit

was adjusted by the manufacturer to give greater fan

speed prior to the final test of this unit. Stroboscopic readings showed a rotational speed of 890 rpm.

This test resulted in a cooling capacity of 32,500

Btu/hr.

-13-

9. The manufacturer replaced the first outdoor unit

with a complete,, new unit because of the low cooling

capacity of the first unit. The nameplate amperage

of the second compressor was 21.0, whereas that on

the first compressor was 19.5 The model numbers of

the two Tecumseh motor-compressor units were the same.

10. After installing the new outdoor unit, a refrigerant

leak was found in the four-way valve. The four-way

valve was replaced and the capillary tube-check valve

assembly, and liquid line dryer were replaced at the

same time.

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U. S. DEPARTMENT OF COMMERCE

Sincliiir Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

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

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