Cfe^Lu Yj b K

NATIONAL BUREAU OF STANDARDS REPORT

CAPACITY TESTS OF A MATHES HEAT PUMP

MODEL 38HAR-VEB-HP

by

Joseph C. Davis

Paul R. Achenbach

Report to

Seymour Johnson Air Force Base

Goldsboro, North Carolina

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

5908

FOR OFFICIAL USE OFILY
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT MBS REPORT

1000-30-4830 May 27, 1958 5908

CAPACITY TESTS OF A MATHES HEAT PUMP

MODEL 38HAR-VEB-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 Tor use within

to additional evaluation s listing of this Report, eit the OlHce of the Director however, by the Governm

to reproduce additional c

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

or progress accounting documents

is formally published It is subjected

iting, reproduction, or open-literature

emission Is obtained In writing from

. C. Such permission Is not needed,

catty prepared If that agency wlshe*

<NBS>

U. $. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

CAPACITY TESTS OF A MATHES HEAT PIMP

,

MODEL 38HAR-FEB-HP

by

Joseph C. Davis 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-VEB-HP . These tests were made at the

indoor and outdoor conditions stated in the contract

specifications and, except for minor deviations,

in accordance with the procedures and conditions

specified by the American Society of Refrigerating

Engineers Standard No. 16-56. The observed cooling

capacity was 34>500 Btu/hr at the specified test

conditions whereas the minimum required was 36,000

Btu/hr. The observed heating capacity, without

supplementary strip heaters was 2]q ,000 Btu/hr at

an outdoor temperature of 20°F, whereas the minimum

required was 30,500 Btu/hr. At rated voltage the

two strip heaters furnished with the unit had a capacity of 3*3 KW as compared to the requirement

of 3*6 Kw. At the request of the Mathes Company

a test was made with the outdoor temperature at

30°F. Capacity for this outdoor temperature was

27 , 1+00 Btu/hr.

for OFFICIAL use Duty

- 2 -

1 . INTRODUCTION

in accordance with a request from Captain ^ . 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-VEB-HP. These tests represented the

third phase of a series of tests on several models of heat

pumps that will be used at this site. Results of the tests

for the first two models are covered in National Bureau of

Standards Report No. 58 l8 , "Capacity Tests of Mathes Heat Pump

Model 38HAR-LEB-HP ," and No. 5885 , "Capacity Tests of Mathes

Heat Pump Model 2

7

HAR -REB -HP .

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

for homes under construction at Seymour Johnson Ai r Force Base,

require a total cooling capacity for this model of 38,000 Btu/hr

and a totaL heating capacity of Lj.2,786 Btu/hr. A breakdown of

the capacity requirements for these two conditions follows:

CO OLING CAPACITY (Btu/hr)

Sensible Latent Total

25,200 10,800 36,000

HEATING CAPACITY (Btu/hr)

Condenser Heat From Supplementary

Transfer Strip Heaters Total

30,500 12,286 1|2,786

In a letter Brom Captain Schrontz dated April 3 , 1958 , four

1.8 KW supplementary resistance heaters were specified as conditions of testing the Model 38HAR-VEB-HP Mathes heat pump.

With these heaters, the total required supplementary heating

capacity would be 24,572 Btu/hr.

FOR OFFICIAL
. >
- 3 -

The specifications also require that the minimum air circulation rate be 1,300 cfm against an external static resistance

of 0.2 in. of water.

2.

DESCRIPTION OF TEST SPECIMEN

The model 38HAR-VEB-Hp heat pump 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. This heat pump is essentially the same as the 38HAR-LEB-HP

recently tested except for capillary tube size in the outdoor

unit and the fact that the conditioned air is discharged in a vertical direction from the indoor unit instead of in a horizontal

direction.

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 thermostaticallycontrolled 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.

A schematic} diagram of the heat pump system and auxiliary

test instrumentation is shown in figure 1. The oil separator

was shown in this figure for purposes of explanation, but was

not used during the tests. A list of line sizes for this system

without the separator is shown below:

1. Compressor discharge to 4~wa7 valve

2. Compressor suction to li -way valve

3 . Pour-way valve to coil of outdoor unit

4* Liquid line to flowmeter manifold

4. Lines in manifold

6 . Vapor line

Size Qp (in.)

FDR OFFICIAL USE ONLY
«
-4-

The indoor unit consisted essentially 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 threerow coil, 30 in. wide and 2d . 25 in. high, with 13 fins per in.

of tube length. Because of the vertical discharge of conditioned air this coil was positioned at an angle of 45° from

vertical, rather than in a vertical position as in the case

of units discharging air horizontally. A Torrington blower

with a 13 -in. diameter wheel was used and it was powered by

an Emerson 1/3 HP single phase motor. Model No. S60CXBRT.

Nameplate rating of the motor was 230 volts, 60 cycle, 2.7

amperes, with a service factor of 1.35. Speed of rotation of

the motor was designated as 1725 rpm. The capillary tube had

an ID of 0.1195 in. and was 60 in. long. The housing of the

indoor unit was 28.25 in. wide, 30 in. deep and 50 in. high.

Wall thickness was 0.05 in. Differing from the horizontal

38HAR-LEB-HP model, the intake filter of this unit was

covered with a louvered door.

With the indoor pulley adjusted after the test for about

1300 cfm air delivery, and with the temperature about 75

the blower speed of rotation was 76 O rpm.

The outdoor unit, with the exception of a smaller capillary tube for heating, was the identical unit used for the first

heat pump tested. Model 38HAR-LEB-HP. It consisted essentially

of a coil (used as an evaporator during heating); a propeller

fan; a hermetically-sealed Tecumseh motor compressor. No. PJE300 , 230 volts, 50/60 cycles, single phase, full load amperage

of 21 . 0 ; a capillary tube - check valve assembly; and a fourway valve. The coil had 2 rows, 13 fins per in. and was 28 in.

high and 49 1/2 in. wide. 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 . 36 , and

rotational speed rating of 1725 rpm. The capillary tube had

an ID of 0.0895 in. and a length of 82 in. The housing of the

outdoor unit was 51 in. wide, 27 in. deep, and 31 in. high.

Wall thickness was 0.090 in. This unit with grilled panel

removed is shown in figure 2 .

FOR OFFICIAL USE ONLY
.
-5-

Measurements of the outdoor fan speed at an outdoor temperature of about 75 °F showed 800 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.

No modifications of the heat pump were made by the manufacturer during the test.

3. METHODS OF TESTING

Except for minor modifications, the heat pump was tested

under the conditions described in ASRE Testing and Rating

Standard No. 16 - 56 , as required by the specification. Fig. 4

shows the enclosure housing the indoor unit and the 33 -in.

square test duct attached to the outlet side of the unit. The

indoor unit was tested with the strip heater and electrical

assembly removed. This assembly is shown underneath the duct

in the figure. Note the two strip heaters, the number standard

with this model. 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 excessive resistance in the outlet duct, an auxiliary blower powered by a oneHP 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

unit blower was adjusted to 0.20 in. of water. The system

including the auxiliary blower, return air haters, and humidifier used for the tests on the 38HAR-LEB-HP and the

27HAR-REB-HP is shown in figure 5* The same system wasr used

for this test except that the 33 -in. duct and auxiliary motor

were raised to a level of about six feet to accommodate the

comparatively tall vertical type indoor unit.

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, involves measuring the mass-flow of air through the indoor unit

FOR OFFICIAL USE W
.

,*
-6-

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

which cycle is under operation, before comparing it with the

result of the psychrome trie 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 th« system—a Potter Electronic type with

and 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.

In all tests it was necessary that substantially oil-free

refrigerant be supplied to the flowmeter or that the rate of

oil circulation be determined. Pn the tests for the 38HARLeb-HP and 27HAR-REB-HP , this was accomplished by placing an

oil separator in the hot gas line betwehn 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 test and at the inlet of the outdoor coil during the

heating test. Note this equipment in figure 1.

FOR OFFICIAL USE ONLY
i ;: ?? : :.1
-7-

In the test of the Model 38HAR-VEB-HP , however, at the

request of the Mathes Company, the oil separator was left out

of the system, the oil return lines pinched off, and the oil

was allowed to pass with the refrigerant through the flowmeter. The amount of oil circulated and the necessary correction to be made were determined by sampling the refrigerant

immediately following the cooling test. The refrigerant taken

from the line while the heat pump was operating was discharged

into special flasks pre-cooled by dry ice, and then allowed

to evaporate slowly as the ice melted, leaving a residue of

oil.

Each of two samples showed less than 0.2 percent of oil

by volume which was insignificant. The oil-refrigerant

sampling method of correcting for oil circulation is the

method specified in ASRE Standard 16-56, and is considered

satisfactory by the National Bureau of Standards. Tt does

require replacement of the refrigerant taken for the oil

determination.

It was possible to maintain "state" conditions for both

cooling and heating with the use of a test structure having

two controlled-temperature spaces.

The following "state" conditions for the indoor and outdoor air were maintained during the cooling cycle in accordance

with contract specif ications:

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 Mathes Company, having chosen to

make the cooling test first, adjusted the refrigerant so that

about 1° superheat was obtained at the indoor coil under the

"state" conditions specified above.

FOR OFFICIAL USE Oil
’

. ' Hf-1
-8-

The heating test was performed on the day following.

Because refrigerant was removed from the system to determine

oil content as described above, the ’’state” conditions of

95°DB, 80°DB, and 50 percent relative humidity, were established

and refrigerant restored so that temperatures and pressures

were substantially the same as those on the cooling test.

The heating test was performed within five hours thereafter.

The following ’’state” conditions for heating were maintained in accordance with the contract specifications:

20°F DB outdoors

70°P DB indoors.

On the day following the heating test, the 95°DB, 80°DB

and 50 percent RH conditions were reestablished to test

again for charge. A small loss was noted, but because a

number of hours had elapsed since the heating test and since

there was no indication of loss of charge during the test

itself, the refrigerant charge during heating was considered

essentially the same as that used for the cooling test.

Steady state conditions were maintained for more than

an hour before each test. During the cooling test, readings

were taken every ten minutes for three hours and 40 minutes

and during the heating test, every ten minutes for two hours

and 40 minutes. In each case, the hour representing the

steadiest conditions was used for evaluating performance.

The same motor pulley setting for the indoor blower

was used for both the cooling and heating tests. In the

cooling test this setting resulted in a cfm of 1256 and in the

heating test a cfm of 1345. Thus a heat pump in a home at the

Seymour Johnson Air Force Base will have a somewhat higher air

circulation rate on the heating cycle than on the cooling

cycle for the same static pressure at the unit outlet.

Throughout the test a pressure difference of 20 psi

existed between the compressor discharge and the liquid line

entering the coil of the indoor unit as measured by calibrated

pressure gages. This difference was estimated to be 10 psi

greater than would normally be caused by the elements of the

heat pump system such as the dryer, four-way valve, etc. The

FOR OFFICIAL USE ONLY

-9-

oil separator was not in the line and the pressure drop as

measured by gages across the flowmeter was negligible.

Representatives of the Mathes Company were aware of this

condition, but in the interest of saving time and realizing

the loss of capacity would not be great, chose to go ahead

with the test without alterations.

The length of both the liquid line and the vapor line

during the tests was approximately the same as in the

installations at Seymour Johnson Air Force Base, or about

35 ft from outdoor unit to indoor unit.

Because of interference with thermocouple arrangement,

the louvered door covering the intake filter of the indoor

unit was left off the unit during the tests. The change in

performance due to this deviation from normal installation

procedures was negligible.

During the tests, 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 other instruments

for measuring temperature, humidity and pressure are shown

in figure 6 .

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. The results obtained by the two

measuring methods during the cooling test, and the total rated

cooling capacity of the Model 38HAR-VEB-HP are shown below.

This capacity, it will be noted, includes a correction for

deviation of barometric pressure from standard barometric

pressure. This is in accordance with ASRE 16-56 which allows

an increase of 0.8 percent of capacity for each inch of barometer reading below 29.92 in. of Hg during the cooling test.
..

.
- 10 -

Summary of Cooling Capacity Values (Btu/hr)

Test

Value

Rounded

Value

By psychrome tri c method

By flowmeter method

34,1*40

34,200

Average 34,320

Correction for deviation of barometric

pressure from standard barometric

pressure l8o

34,Soo 34,5oo

Following is a summary of the averages of the

nificant data observed during the cooling test.

more sigPsychrome tri c Method

Temperatures (°F)

At inlet to enclosure around indoor unit

At outlet of indoor unit in duct

Temperature difference across indoor coil

At inlet to outdoor unit

79.9 DB

61.3 DB

18.6 DB

95.il DB

Relative Humidities [%)

At inlet to enclosure around indoor

At outlet of indoor unit in duct

unit 5o.i

83.7

Static Pressure across Nozzle (In. of HI C\J o 1.36

Volume Air Flow at Nozzle (cfm) 1256

Mass Air Flow at Nozzle (lb of drv air/hr) 5519

Barometric Pressure (In. of He) 29.25

FOR OFFICIAL USE OMLY
•

'
- 11-

Diameter of Nozzle (In.) 7.03

Nozzle Coefficient . 99

Static Resistance (In. of H^Q ) 0.20

Flowmeter Method (Refrigerant Method)

Temperatures ( °F

)

In liquid line entering coil of indoor unit 108.8

In vapor line leaving coil of indoor unit 47.1

Pressures (psig)

In liquid line entering coil of indoor unit 268.5

In vapor line leaving coil of indoor unit 78.5

Potter Meter Count for 10 Minutes 323*5*

Other Temperatures (°F)

In vapor line halfway to outdoor unit 51.2

In suction line at compressor 61.1

Other Pressures (psig)

Compressor discharge 288.5

Difference in pressure across flowmeter

was negligible.

Motor Power Consumption (Watts)

Indoor blower 491

Outdoor fan 436

Compressor 3983

Total 4910

Coefficient of Performance 2.06

* Refrigerant flow., gal/min = Meter count (1 min, x 100)

3365-5

FOR OFFICIAL USE Off y

- 12 -

Motor Voltages (Volts)

Indoor blower 231.5

Outdoor fan 231.0

Compressor 230.7

Motor Current (Amperes)

Indoor blower 2.99

Outdoor fan 2.63

Compressor 18.11

B. Heating Test

The heating test gave the following results. The correction shown for deviation of barometric pressure from

standard barometric pressure is in accordance with ASRE

16-56, which allows an increase of 2.0 percent of capacity

for each inch of deviation below standard barometric

pressure for the heating condition. It will be noted that

this allowance is proportionately higher than that for the

cooling condition.

Summary of Heating Capacity Values (Btu/hr)

Test

Value

Rounded

Value

By psychrometric method

By flowmeter method

24,000

23,440

Average 23.720

Correction for deviation of

pressure during test from

barometric pressure

barometric

standard

320

24, 040 24,000

Following is a summary of the averages of the more

significant data observed during the heating test.
r-

.

»
-13-

Psychrometric 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

70.1 DB

87.5 DB

17.4 DB

19.9 DB

Relative Humidity of Indoor Air in Duct {$>) 12.0

Static Pressure across Nozzle (in. of Ho 0) 1.50

Volume Air Plow at Nozzle (cfm) 1345

Mass Air Flow at Nozzle (lb of dry air/hr) 5725

Barometric Pressure (in. of Hg) 29.40

Diameter of Nozzle (in.) 7.03

Nozzle Coefficient .99

Static Resistance (in. of HpO)

Flowmeter Method (Refrigerant Method)

Temperatures ( °P)

.20

In vapor line entering coil of indoor unit

In liquid line leaving coil of indoor unit

Pressures (psig)

114.4

81.5

In vapor line entering coil of indoor unit

In liquid line leaving coil of indoor unit

195.0

194.0

Potter Meter Count for 10 Minutes 151 . 8*

* Refrigerant flow, gal/min = Meter count for 1 min x 100

3365.5

-14-

Other Pressures (psig)

Compressor discharge pressure 197*5

Suction pressure 30*5

Difference in pressure across the flowmeter

was negligible.

Other Temperatures ( °P)

Compressor discharge 141.5

Suction line at compressor 5.9

Motor Power Consumption (Watts)

Indoor blower 479

Outdoor fan 589

Compressor 2587

Total 3655

Coefficient of Performance (Exclusive of

Strip Heater) 1 . 91

Motor Voltages (Volts)

Indoor blower 230 *1

Outdoor fan 231*1

Compressor 230.0

Motor Current (Amperes)

Indoor blower 2.92

Outdoor fan 3*30

Compressor 12.00

Power Consumption of Strip Heaters

Readings of the energy dissipated by the two strip

heaters which came with the indoor unit were made every

fifteen minutes for a period of one hour with the following results:

FOR OFFICIAL USE ONLY
.

i:
-15-

Watthour meter value (Watts)

Average terminal voltage (Volts)

Average current (Amperes)

Voltage times current (Watts)

3339

229.8

14.36

3300

The specified capacity for these two heaters given in

heat equivalent values is 12,286 Btu/hr. The observed capacity shown above is equivalent to 11,396 Btu/hr. Pour

heaters, of course, each having the same power consumption

would dissipate twice this amount or 22,792 Btu as compared

with the specification heat equivalent value of 24,572 Btu/hr

noted in Section I, Introduction.

C. Heating Test at 30°F

At the request of the Mathes Company, data were taken

at 30 ° during the lowering of the outdoor temperature for

the heating test. Readings were made wery ten minutes for

a full hour, preceded by a steady-state period of about

20 minutes.

Results of the test at this condition are given below.

Test Rounded

Value Value

Psychrometric method

Flowmeter method

27,430

26,640

Average 27,035

Correction for deviation of barometric

pressure during test from standard

barometric pressure 410

27,445 27,400

FOR OFFICIAL USE ONLY

INPOOR

UNIT

OUTDOOR

UN

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(ro/f

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Figure

igure

Figure 4

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Pieure
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Standa nli?.

U. S. DEPARTMENT OF COMMERCE

.Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

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

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