All 102630940

Kao, James Y/Field performance of three QC100 .U56 NO.87-3528 1987 V19 C.1 NBS-P Field Performance of Three

Residential Heat Pumps in the

Heating Mode

James Y. Kao

William J. Mulroy

David A. Didion

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Environment Division

Gaithersburg, Maryland 20899

February 1987

Sponsored by:

of Building Energy Research and Development

)epartment of Energy

ngton, DC 20585

research

information

FIELD PERFORMANCE OF THREE

RESIDENTIAL HEAT PUMPS IN THE

HEATING MODE

NBSIR 87-3528

mi

t

James Y. Kao

William J. Mulroy

David A. Didion

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Environment Division

Gaithersburg, Maryland 20899

February 1987

Sponsored by:

Office of Building Energy Research and Development

U.S. Department of Energy

Washington, DC 20585

X>

0

0**

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
*
AB STRACT

This report presents the results of a field performance study of

three heat pumps operating in the heating mode. The objective of

this study was to evaluate the thermal, energy, defrosting,

cycling, and other related performance under in-situ conditions

and to confirm the validity of Department of Energy (DoE) test

procedures by comparing these field results with those obtained

in the laboratories. The seasonal COPs without auxiliary heat

were 1.83, 2.31, and 1.92. The seasonal COPs with auxiliary heat

were 1.71, 1.95, and 1.60. General agreement was found in two

houses for cycling rates and building load estimation. Defrost

penalty was found to be light above 40°F. One house was analyzed

for cyclic performances. The cyclic degradation factor (C D

) was

found to be worse than the optional factor (0.25) of the DoE

procedure

Key Words: Defrosting; field performance; field performance of

heat pumps; heat pumps; heat pump test methods;

heating seasonal performance

in
ACKNOWLEDGEMENTS

This study was sponsored by the U.S. Department of Energy, Office

of Building Energy Research and Development. The authors wish to

express their appreciation to Charles W. Hurley for his

assistance in gathering technical information during this study.

IV
TABLE OF CONTENTS

Pa^e

ABSTRACT iii

ACKNOWLEDGEMENTS iv

LIST OF TABLES vi

LIST OF FIGURES . ... vii

SI CONVERSION FACTORS ix

1. INTRODUCTION 1

2. HOUSE AND HEAT PUMP SYSTEM DESCRIPTION . 3

3. FIELD DATA ACQUISITION SYSTEM 4

3.1 System Description 4

3.2 Measurements and Instrumentation 4

3.3 Data Format and Scanning Requirements 6

4. FIELD TEST RESULTS OF THREE UNITS 8

4.1 "Cycle" Data Analysis 10

4.1.1 Indoor and Outdoor Conditions 10

4.1.2 Defrost 11

4.1.3 Heating Load and Unit Sizing 13

4.1.4 Cyclic Coefficient of Performance.... 17

4.1.5 Thermostat Cycling Rate 18

4.1.6 Heating Capacity of Defrost Cycles... 20

4.2 "Scan" Data Analysis 21

4.2.1 Steady-State Performance 22

4.2.2 Part Load Performance 23

4.2.3 Thermostat Cycling Rate 25

4.2.4 Seasonal Capacity Profile 26

5. DISCUSSION AND CONCLUSION 28

6. REFERENCES 32

7. APPENDIX A Cyclic Degradation Factor 33

v
LIST OF TABLES

Pa^e

Table 2.1 House and Heat Pump Description. , 3

Table 3.1 Description of Field Data Points 5

Table 4.1 Comparison of Three Field Units 9

Table 4.2 Comparison of DoE and Field Design

Heating Requirements 16

Table 4.3 Comparison of Field and Laboratory

Test Results 22

v a.
LIST OF FIGURES

Pa ge

Figure 3.1 Schematic of instrumentation for typical field

unit showing location of 12 sensing elements... 35

Figure 4.1 Heat output of a typical cycle. 36

Figure 4.2 Energy input to outdoor unit of a typical cycle 37

Figure 4.3 Outdoor temperature vs. indoor temperature..... 38

Figure 4.4 Outdoor temperature distribution. .............. 39

Figure 4.5 Defrost time — Unit 1 40

Figure 4.6 Defrost time — Unit 2..... 41

Figure 4.7 Defrost time — Unit 3 42

Figure 4.8 Defrost time of three units (in hours) 43

Figure 4.9 Defrost time of three units (in fraction of

compressor-run time) 44

Figure 4.10 Building load 45

Figure 4.11 Heat output vs. outdoor temperature — Unit 1.. 46

Figure 4.12 Heat output vs. outdoor temperature — Unit 2.. 47

Figure 4.13 Heat output vs. outdoor temperature — Unit 3.. 48

Figure 4.14 Percent heat output vs. outdoor temperature — Unit 1 49

Figure 4.15 Percent heat output vs. outdoor temperature — Unit 2 50

Figure 4.16 Percent heat output vs. outdoor temperature — Unit 3 51

Figure 4.17 Cyclic COP vs. outdoor temperature — Unit 1... 52

Figure 4.18 Cyclic COP vs. outdoor temperature — Unit 2... 53

Figure 4.19 Cyclic COP vs. outdoor temperature — Unit 3... 54

Figure 4.20 Compressor cycling rate — Unit 1 55

Figure 4.21 Compressor cycling rate — Unit 2 56

V 1 1
P ag e Figure 4.22 Compressor cycling rate Unit 3 57

Figure 4.23 Capacity of defrost cycles -- Unit 3 58

Figure 4.24 Power input of defrost cycles — Unit 3 59

Figure 4.25 COP of defrost cycles — Unit 3 60

Figure 4.26 Steady state capacity — Unit 3 61

Figure 4.27 Steady state power input -- Unit 3.. 62

Figure 4.28 Steady state COP -- Unit 3 .63

Figure 4.29 Heating load factor vs. fractional on-time -- Unit 3 (all data available).... 64

Figure 4.30 Heating load factor vs. fractional on-time —

Unit 3 (data omitted below 42°F outdoor

temperature) 65

Figure 4.31 Part load factor vs. fractional on-time —

Unit 3 66

Figure 4.32 Part load factor vs. heating load factor —

Unit 3 67

Figure 4.33 Cycling rate (excluding defrost cycles) —

Unit 3 68

Figure 4.34 Comparison of laboratory and field test

results — Unit 3 69

v i i i
SI CONVERSION FACTORS

MULTIPLY BY TO OBTAIN

Btu 1.055 kj

B tu/ h 0.293 W

Btu/min 0.0488 W

° F °C = ( ° F - 3 2) / 1 .8

ft 2 0.0929 m2

O ft/ min, cf

0 .47 2 L / S inch 25.4 mm

inch of water 249 Pa

ton of refrigeration 3.52 kW
.
1 . INTRODUCTION

During 1980 and 1981, the National Bureau of Standards (MBS)

instrumented and collected data from three air-source,

residential heat pumps to evaluate the field performance of these

units. The three heat pumps were already in operation and were

selected from the homes of volunteers of NB S employees in the

Washington, D.C. area. Microprocessor-based data acqusition

systems were used to gather and reduce the energy, weather and

other related information. A previous report describes the

selection criteria of the house/heat-pump sets, the

instrumentation details, the hardware and software of the data

acqusition systems, and the preliminary data reduction procedures

[13 .

Test procedures for heat pumps were issued by the United States

Department of Energy (DoE) in 1979 [2] and require heat pump

manufacturers to perform certain laboratory tests to determine

the heat pump's thermal and energy performance. These test

procedures were based on research results performed earlier at

NB S [3,4]. A heat pump of the same model as one of the three

field units was subsequently tested in accordance with the DoE

procedures

The purposes of this field studyare two-fold:

(1) To give a comprehensive evaluation of the thermal,

energy, defrosting, cycling, and related performance of heat

pumps operating under in-situ conditions; and

1
(2) To compare the results of the field performance with

those obtained previously in the laboratory and, thus, to verify

the heat pump test procedures.

The analysis of the cooling data obtained in the 1980 cooling

season for the three field units was published in a previous

report [5]. In this report the field performance of these heat

pumps for the 1980-1981 heating season is analyzed and presented.

2
2 . HOUSE AND HEAT PUMP SYSTEM DESCRIPTION

The heat pumps monitored in this study were split systems. A

brief description of the three houses and some elements which may

affect the heating performance of the heat pumps are shown in

t ab 1 e 2.1.

Table 2.1 House and Heat Pump Description

Item HOUSE 1 HOUSE 2 HOUSE 3

1 House style 1 story 1 story 1 1/2 story

2 House wall brick frame frame

construction

3 Approx, living

area, sq. ft

2900 1800 1600 (1000 s.f.

bsmt unused)

4 Occupancy during vacant occupied vacant

working hours

5 System nominal 21/2 tons 3 tons 3 tons

cool, capacity

6 HP expansion non-bleed exp. constant area constant area

device valve device device

7 Auxiliary heater 15 kW electric 15 kW electric 15 kW electric

8 Defrost diff. air pressure timer (90 min of diff. air pressure

initiation across outdoor

coil reaches

0.5 in. of water

comp, on-time)

and t emp . in

outdoor coil

reaches 27 °F

across outdoor

coil reaches

setting for 12

seconds and

refrig. temp, in

outdoor coil

reaches 39°F

9 During defrost in cooling mode

and outdoor fan

off

in cooling mode,

outdoor fan off,

and one aux. heater on

in cooling mode,

outdoor fan off,

and one aux. heater on

10 Defrost outdoor refrig. outdoor coil outdoor refrig.

termination temp, reaches

65°F

temp, reaches

80°F or defrost

for 10 minutes

temp, reaches 75°F

or reaches 45 °F

for 5 minutes

11 Fins per inch 14 17 13

of outdoor coil

3
3. FIELD DATA ACQUISITION SYSTEM

3.1 System Description

The field data acquisition system and instrumentation of the heat

pumps are described in detail in the previous reports [1,5]. An

on-line microcomputer at each field site performed the following

functions; (1) controlling of the data monitoring strategy; (2)

processing of data obtained from the various analog and digital

points to engineering units; (3) performing computations for

preliminary data reduction; and (4) recording the results on

magnetic disks for further processing. The disks in the field

were replaced as necessary. Each time a disk was replaced, the

operation of the system was manually checked. The sensors and

instrumentation were calibrated periodically. A central

microcomputer located in the NB S laboratory was used to further

process the field disks for data analysis. This Z-80 based

central computer had 64K static memory and two disk drives.

3.2 Measurements and Instrumentation

Twelve analog and digital input points plus two on/off mode

conditions were measured and recorded at each field location. A

schematic illustration of the measured data locations is given in

figure 3.1. The measured and recorded quantities, and the sensing

element types are listed in table 3.1. A complete description of

the signal conditioning, computer interface system, and the

preliminary data reduction equations is given in reference 1.

4
Table 3.1 Description of Field Data Points

Data Acquisition —

Measured Quantity and Units Symbol Sensing Elaaent (or Calculated) Sean Cyclic Dally Half Hour

1 Pitot tube differential pressure

(Inches HjO) DP Pitot tube with variable

capacitance &P eell

TV*'

2 Return air dev point reap. (F) TDPR L1C1/RTD dev point cell XV CTXA CTIA IV

3 Outdoor air dev point top. (F) TDPO LICi/RTD dev point cell IV BSA

4 Baroaetrlc pressure (inches H^O) PATH Pressure cell with diaphragm

potentiometer

IV IV

5 Return air dry bulb taap. (F) TRET Linear thermistor IV GT1A CTIA IV

6 Outdoor air dry bulb temp. (F) TOUT Linear thermistor TV eoc HSA IV

7 Differential teap. across Indoor

coil DT Type-T thermocouple TV IV

8 Supply air dry bulb teap. (F) TSUP Linear thermistor IV IV

9 Compressor and outdoor fan energy

(pulse) DIC1 Watt-hour aeter with magnetic

latch pulse initiator IT RT

10 Indoor fan and 1st stage heater

energy (pulse) DIC2 Watt-hour aeter with magneticlatch pulse initiator

CIT RT

11 2nd stage heater energy (pulse) DIC3 Watt-hour metar with magnetic

latch pulse initiator

CIT RT

12 Condensate aetering punp (pulse) DIC4 Positive displacement solenoid

aetering piap with optical

coupler

RT

13 Compressor ON-OFF MODE O-ON Opto-coupler IV IV

14 Outdoor Fan ON-OFF MODE 3-OFF Opto-coupler IV IV

IS Coapressor on tlae for a cycle

(aec) CTXM Clock card CIT CIT

16 Defrost tlae for cycle (see) DTXM Clock card CIT CIT

17 Voluaetrlc flow rate in return

duct (ft J /nln) FLOW Calculated IV rv

18 Sensible heat (Btu) QS Calculated TI CIT DIT

19 Latent Heat (Btu) QL Calculated CIT DIT

20 Coapressor, outdoor fan and c.c. heater energy (Vh) ECXP Calculated CIT DIT

21 Indoor fan energy (Wh) EFAN Calculated CIT DIT

22 Auxiliary heaters (Wh) EHET Calculated CIT DIT

23 Coefficient of performance COP Calculated CIT DIT -7 Re far to text - TV: instantaneous value HSA:

CIT: cycle Integrated total RT:

CTIA: coapressor tlae Integrated average TI:

DIT: dally integrated total

EOC: end-of-cycle value

average of the 48 half hour acaaa for the day

running total for a cycle value for the last tine Inc resent

5
3.3 Data Format and Scanning Requirements

During the data collection, a cycle was defined as either a heating plus an off period, or a heating plus a defrost period.

The data acquisition software was designed to record four types

of data format:

(1) Scan data. Data recorded, among others, were the

instantaneous scans of the indoor and the outdoor temperatures,

the sensible heat output of the indoor coil between consecutive

scans, the accumulated heat output of the indoor coil, and the

accumulated energy input to the outdoor unit. The accumulated

data were the totals from the start of each heating cycle. There

were no auxiliary heat data in these files. High data

acquisition rates were desirable at the beginning of the on-cycle

and during the defrost. These data were recorded at intervals of

10 seconds for the first 2 minutes, 30 seconds for the next 4

minutes, 60 seconds for the next 6 minutes, and 5 minutes until

the compressor stopped or defrost started. These data were used

subsequently to calculate and record the integrated cycle data.

Since they occupied a great deal of storage space, the scan data

were recorded every eleventh cycle.

(2) Cycle data. Data included, among others for each cycle,

were the heat output of the indoor coil, the energy input of the

outdoor unit, the energy input of the indoor fan, the energy

input of the auxiliary heaters, the total compressor run-time

(including defrost), and the defrost time. Also recorded were

the indoor and the outdoor temperature averaged over the cycles.

6
(3) Daily data. Data were accumulated or averaged for each

day and recorded on the disks at midnight.

(4) Half-hour data. Instantaneous readings of certain data at

every half hour were recorded on the disks.

Thirteen data items, measured and computed, were recorded for

each of the above four types of data format. These thirteen

items together with the day and time of the moment of recording,

and the status of the heat pump (in heating, defrosting, off, or

malfunction) formed a "record". These "records" were used for

further reduction and analysis of the heat pump performance.

7
4. FIELD TEST RESULTS OF THREE UNITS

Table 4.1 summarizes the test results of the three heat pumps.

Although the heating data collection period was about half a year

(line 2), the data available for analysis covered 3828, 2427, and

3278 hours (line 6) for the three units which indicated that

about 25.5%, 40.2%, and 26.6% of the time (line 7) data were lost

or useless, or the systems were turned off. Since the available

data are not distributed equally during the data gathering period

for the three units, caution should be exercised in comparing the

performances of the units.

In data analysis, data stored under "cycle" data file for all

three units were used to calculate the cyclic heat output, cyclic

energy input, cycling rate, cyclic coefficient of performance

(COP), heating seasonal performance, and the defrost

characteristics. Since calculation for steady state performance

required only certain segments of the cycles, data stored under

"scan" data file were used to compute the steady state

performance, the part load factor (PLF), heating load factor

(HLF), and the degradation factor (C^). Steady state and

associate performance were analyzed for unit 3 only.

Figure 4.1 shows the capacity variations of a typical compressor

on-cycle. The outdoor temperature during this particular cycle

was about 33°F and the unit required frequent defrosting. The

negative capacity at the beginning of the cycle indicated that

this cycle started right after a defrost period. The capacity

increased rapidly until it reached a peak in about 6 to 8 minutes

8
Table 4.1 Comparison of Three Field Units

ITEM UNIT 1 UNIT 2 UNIT 3

1 Nominal cooling

capacity, refrig. tons

2 1/2 3 3

2 Heating season data

collection period

10/3/80-

5/4/81

(5136 h)

10/3/80-

3/20/81

(4056 h)

11/16/80-

5/20/81

(4464 h)

3 No. of total cycles 4428 3692 373 7 4 Total compressor-on

time, hour

1427 1450 1923

5 Avg. c omp r e s s or- on

time per cycle,

min / cycle

19.3 23.6 30.9

6 Total cycle time

avail. for analysis,

hour

3 828 2427 3 27 8

7 Percent of time data

not avail., %

25 .5 40.2 26.6

8 Avg. cycle time,

minute

51.9 39.4 52.6

9 avg. percent

compressor-on in

a cycle, %

37.3 59.9 5 8.7

10 No. of defrost cycles 141 916 46 5

11 Total defrost time,

hours

4.82 65.10 32.09

12 Avg. defrost time per

defrost cycle, min

2.05 4.26 4.14

13 Defrost time/

c omp r e s s o r- on time, %

0.34 4.49 1 .67

14 Tot. seasonal output,

incl . aux . heat

,

Btu x 10 6

30.536 47 .608 54.279

15 Tot. seasonal output,

ex cl . aux . heat,

Btu x 10 6

27 .898 40.897 42.665

16 Percent of aux. heat

used during season, %

8.6 14.1 21.4

17 Avg. heat output,

excl . aux . heat , Btu/h

19550 28200 22190

18 Avg. heat output/

cycle, ex cl . aux . he a t

,

Btu/ cycle

6300 11080 11420

19 Avg. heating load,

Btu/h

7980 196 20 16560

20 Seasonal COP without

aux. heat

1 .83 2.31 1.92

21 Seasonal COP with

aux. heat

1.71 1 .95 1.60

22 Max. cycle rate, cph 2.31 2.95 2.74

9
and started to decrease gradually after about 20 minutes

due to frost formation on the outdoor coil. The system then

started the defrost at about 44 minutes from the beginning of the

cycle. During the defrost period, the capacity dropped to

negative values even with some auxiliary heat on. This

particular defrost lasted for almost 5 minutes. Figure 4.2 is

the corresponding chart of the energy input to the outdoor unit.

After the initial surge, the energy input was quite constant

during the entire heating cycle. A decrease of less than 3% was

recorded when ice was formed on the outdoor coil. Then the

energy input dropped sharply and stayed low during the first 2

minutes of the defrost because of the switching of the

refrigerant path and the stopping of the outdoor fan. Finally,

the power input surged to a level even higher than that measured

during the heating cycle. This was caused by the loss of

condensing capacity and the high discharge pressure of the system

which helped to finish the cycle.

4.1 "Cycle" Data Analysis

4.1.1 Indoor and Outdoor Conditions

The three houses were equipped with electro-mechanical wall

thermostats. Thus, the indoor temperature and the system cycling

patterns were strongly influenced by the anticipator settings of

these thermostats. The average indoor temperatures over the

entire heating season, based on the available data and as

measured by the sensors located in the return air ducts, were

7 0 .7 °F, 70.2°F, and 69.5 °F, respectively for the three units.

Figure 4.3 shows the temperature distribution of the average

10
indoor air with respect to 5°F temperature bins of the outdoor

temperature. All three houses generally had higher indoor

temperature when the weather was warm. The indoor temperature

dropped at various rates when the outdoor became cooler. These

curves demonstrate clearly the droop charact e risic s of the room

thermostats. The exceptions were the 7°F bin and the 57 °F or

62°F bin of unit 2 and the 7 to 22°F bins of unit 3 where the

trend was reversed. These exceptions were probably caused by

manual resetting of the thermostats by the occupants. The total

indoor temperature differences caused by thermostat droop and

manual reset were approximately 9°F, 1 1°F, and 2°F for the three

houses respectively for the entire heating season.

Figure 4.4 shows the outdoor temperature distribution of the

three houses. Data were derived from the available good data

periods, excluding weather records when the heat pump monitoring

systems were receiving bad data. Because of the house location

difference and the time difference of available data,

considerable variations appear in the figure.

4.1.2 Defrost

Figures 4.5 to 4.7 depict both absolute defrost time and

percentage of compressor run-time of defrost in terms of outside

air temperature bins. Unit 1 (figure 4.5) had its highest defrost

time in the 30-35°F bin and it defrosted in all temperature bins

below 3 7 °F (Data were not available for the 5°F-10°F bin). The

pattern of defrost time was not clearly shown except that most

defrost was done between the outside temperature of 25°F to 40°F.
Unit 2 (figure 4.6) also had the highest defrost time in the 3 0-

35°F bin. It decreased toward the 5°F-10°F and 50°F-55°F bin. As

a percentage of compressor run-time, the defrost occurred more (8

to 9%) in the 5°F-15°F bins than the other bins. Therefore, the

effect of defrost was more important for the low outdoor

temperature range than for the overall heating season. Unit 3

(figure 4.7) had about the same defrost pattern as Unit 2 except

that Unit 3 did not have any defrost above 40 ° F. The large

amount of low temperature defrosting done by Unit 3 was not

expected since this unit had a demand defrost initiation system

whereas Unit 2 used only a simple timer to initiate defrost (see

table 2.1). The conclusion to be drawn from this is that all

demand defrost systems are not equally effective in avoiding

unnecessary defrosts. The shape of the Unit 2 t im e r- i n i t i a t e

defrost is reasonable. Below the balance point the unit will run

continuously resulting in a constant number of defrost

initiations. Defrost time for each defrost cycle will be high at

high temperatures because of the need to melt frost, and at low

temperatures because of the lower temperature of the mass of the

coil with respect t o the termination temperature. Th e s e test

results differ f r o m the assumption of the heat pump test

procedures which assume that def ros t is negligible below 17 ° F of

outdoor temperature and is occurring up to 45°F.

There were large differences in the total defrost time between

the three units. This can be seen from lines 10, 11, and 12 in

table 4.1, and figures 4.8 and 4.9. The total defrost time for

1 2
the heating season were 4.82, 65.10, and 32.09 hours,

respectively for the three units. Even considering the unequal

distribution of the available data, as mentioned previously, the

difference of the ratios of defrost time to total compressor runtime is significant. The three units had 0.3 4, 4.49, and 1.67% of

defrost time over compressor run-time. Unit 1 had a simple demand

defrost initiation criteria and did not initiate defrost as often

as the other two units (see table 2.1). A timer in unit 2 made

defrost available after every 90 minutes of compressor run-time

(together with temperature sensing of outdoor coil temperature).

Evidently this arrangement enabled this unit to go on defrost

more often than the other two units. The number of defrost

cycles during the heating season were 141, 916, and 465,

respectively for the three units. Figures 4.8 and 4.9 show

comparisons of the defrost time by outside temperature bins of

the three units in absolute time and percentage of compressor

run-time. Unit 2 had higher fin density (thus less space between

fins) on the outdoor coil than the other two units (table 2.1).

Presumably it would require more frequent defrost. However, these

units were not instrumented to yield data for more detailed study

on the process of frost and defrost.

4.1.3 Heating Load and Unit Sizing

The cyclic records of total energy output delivered to the houses

and the compressor on and off time were used to derive the

building load. The building load profiles of the three houses

are shown in figure 4.10. They had a generally linear

relationship to the outdoor temperature, except for the coldest

13
bins of units 2 and 3. This is consistent with what was shown in

figure 4.3 and discussed in paragraph 4.1, i.e., the indoor

temperature of units 2 and 3 were manually reset upward during

the cold period. The slope of these lines, of course, were

basically reflections of the house characteristics, such as the

thermal insulation, construction, house geometries, and internal

loads. The linear regression equations for the building loads

as functions of outdoor temperature bins are:

Y = 22.85 - 0.3569 X for house 1,

Y = 48.67 - 0.7934 X for house 2, and

Y = 56.40 - 1.015 X for house 3.

The DoE procedure assumes heating load to be zero at outside

temperature of 65°F. The above three equations yield zero

building loads when outside temperature are 64.0°F, 6 1 .3 °F, and

55.6°F, respectively for the three houses.

Figures 4.11 to 4.13 show the heat output at various temperature

bins during the heating season. The lower portions of the

stacked bars are for the heat output without auxiliary heat and

the top portions are for the auxiliary heat only. The numbers

above the bars are the percentage of auxiliary heat used in that

bin. Figures 4.14 to 4.16 show the heat output without auxiliary

heat, the auxiliary heat, and the total of these two in

percentage of the yearly total. Some conclusions may be drawn

from these charts:

(1) Manual thermostat reset may be seen for all three units

during the entire heating season. When a thermostat was adjusted

14
upward during the heating season and the amount of adjustment was

over the differential of the first stage (for the compressor) of

the thermostat, the auxiliary heater would respond even when the

weather was warm (the balance points of these units will be

discussed later). This can be seen for all three units. Unit 1 had considerable amount of auxiliary heat use even above the 37°F

outdoor temperature bin (figures 4.11 and 4.14). Units 2 and 3

had very high auxiliary heat use at low outdoor temperature.

Since these data were derived from the "cycle" data file, it is

impossible to determine the causes of the auxiliary heat —by the

thermostat adjustment or by the load demand.

(2) Sizing of heat pumps are usually determined by matching the

peak cooling load of a building and the cooling capacity of a heat pump system. The deficiency of the heating capacity of the

heat pump is made up by the auxiliary heaters. These charts show

that the heat output from the auxiliary heat for unit 1 during

the cold bins was relatively smaller than those for units 2 and

3. Excluding the 7° F bin for unit 2 and the 7 through 22°F bins

for unit 3, where the manual thermostat resetting was quite

evident, units 2 and 3 used larger portion of auxiliary heat

during the rest of the cold season. That indicates that unit 1 was more adequately sized than units 2 and 3 in relation to the

heating load of the houses.

(3) The DoE rating procedure assumes that a heat pump be sized

according to the following equations:

15
(65 - T od )

( Q s s

( 47 ) s for regions I,

minimum design ( 60 II, III, IV,

heating requirement = ( and VI

( .

( Q ss (47), for region V

and

• “ T 0D^

( 2 Q s s

( 47 )

, for regions

maximum design ( 60 I, II, III,

heating requirement = ( and IV

(

( 2.2 Q ss (47), for region V

• where Q ss (47) is the steady state capacity at 47°F and Tq D

is the outdoor design temperature for the DoE region. The test

houses were located in DoE region IV which had a T QD of 5°F. The

actual winter design temperature for the area in which the test

homes were located was around 10 °F. The DoE assumed design

heating requirements (DHR) at T 0D are compared to the actual

design heating requirements (figure 4.10) at the local design

temperature in table 4.2.

Table 4.2 Comparison of DoE and Field Design Heating Requirements

DoE minimum

DHR, kBtu/h

DoE maximum

DHR, kBtu/h

Field

DHR, kBtu/h

Unit 1 3 2.1 # 64.2 19.3 ##

Unit 2 36.2 # 72.4 40.7 ##

Unit 3 32.4 ### 64.8 46 .3 ##

Av e r a g e 33 .6 67 . 1 35.4

From a 1 ab o r a t o ry test [ 6 ]

## From building load regression equations given previously.

### From field test, see paragraph 4.2.1.

16
The field data indicate that the design heating requirements of

procedure. Unit 1 was oversized beyond the expectations of the

procedure. The sizing, and selection of this unit was done by the

home owner who was particularly concerned with energy

conservation. Unit 2 was 12% above the DoE minimum DHR and Unit 3

was close to the midway between the minimum and maximum DoE DHRs.

The single heating seasonal performance factor (HSPF) number used

for Air Conditioning and Refrigeration Institute (ARI) listing

and general advertising is that calculated at the minimum DHR for

region IV. This data suggests that because of consumer concern

with energy conservation it may be desirable for manufacturers to

provide HSPF listings 50% below the DoE maximum DHR. For the same

reason, the choice of the minimum DHR for advertising purposes

appears reasonable as it is the average of this limited sample.

(4) The balance point of units 2 and 3 was somewhere between

37 °F and 42°F bins when the auxiliary heat consumption changed

markedly. No conclusion may be made about unit 1 because of the

thermostat resetting.

4.1.4 Cyclic Coefficient of Performance

The "cycle" data were used to calculate the cyclic COP of the

units at all outdoor temperature bins. Figures 4.17 to 4.19 show

the cyclic COP of these units for the entire heating season. The

right-most columns are the seasonal COP and the other columns are

for the individual temperature bins. Both COP, with auxiliary

heat and without auxiliary heat, are shown side by side. The

Units 2 and 3 fall within the range of the DoE

17
seasonal COP's without auxiliary heat were 1.83, 2.31, and 1.92

respectively for the three units. When the auxiliary heat was

added, they dropped down to 1.71, 1.95, and 1.60. The balance

points can also be estimated from these figures. Above the

balance points, the COP of the two (with and without auxiliary

heat) should be equal. Below these points, the COP of the period

without auxiliary heat should be higher than that with electric

heat. The result of unit 1 (figure 4.17) is again confused by

the thermostat resetting. Unit 2 (figure 4.18) indicates a balance point of just above 42.5°F and unit 3 (figure 4.19) shows

somewhere between 37 °F and 42°F bins. The seasonal COP ratios

(without and with electric heat) were 1.07, 1.18, and 1.20 for

the three units. These numbers may also be interpreted to give a similar conclusion as stated in paragraph 4.3, that the heating

capacity of unit 1 was larger than those of the other two units

in relation to the house heating load. In fact, when comparing

units 1 and 3, a higher COP of unit 3 (1.83 for unit 1 vs. 1.92

for unit 3) was reduced to a lower one (1.71 for unit 1 vs. 1.60

for unit 3) when auxiliary heat was also counted. These figures

also show the cycling and the thermodynamic effects on the heat

pump performance. When the outdoor temperature was above the

balance point, the cycling dominated the performance. Below the

balance point, the lower outdoor temperature caused the heat

pumps to perform poorly.

4.1.5 Thermostat Cycling Rate

The heat pump cycling patterns are shown in figures 4.20 to 4.22.

The data points shown in these figures are the average cycling

18
rates of the cycles falling within the 1/10 load ranges and the

numbers below the data points are the number of cycles in that

range. These data were derived from "cycle" data file after the

elimination of defrost cycles and cycles where the thermostat

settings were manually adjusted upward. Since defrost caused the

systems to reverse the process regardless of the thermostatic

status, all the defrost cycles were excluded in the cycling

analysis. When a thermostat was adjusted manually upward, it

always shortened the off-period of the same cycle causing the

cycle to fall in the last ( o n- t im e / t o t a 1 cycle time = 0.9 to 1.0)

fractional on-time bin. It also caused the next on-period to be

extraordinarily long with notably higher return air temperature

and large auxiliary heat consumption. By examining all the

cycles in the last fractional on-time bins and applying these

criteria, these cycles were eliminated.

The peak cycling rates, N__„, were 2.31, 2.95, and 2.74 cycles

per hour for the three units. These cycling rates are in

agreement with the patterns of the indoor air temperature

discussed in paragraph 4.1 and shown in figure 4.3 where the

temperature droop of unit 1 is smaller than the other two units.

The peak cycling rates of units 2 and 3 (2.95 and 2.74), occurred

at approximately 50% of the heating load, are very close to the

cycling-rate requirement of approximately 3 cycles per hour

specified in the DoE heat pump test procedures. These figures

also show the parabolic curves of the thermostat model developed

in the cooling mode study [5]. The equation of the model is:

19
N 4 N G ( 1 - G) m ax

where N is the cycling rate, N max

^ s t *ie cycling rate at 50

percent on-time, and G is the fractional on-time corresponding to

Nc The values of the cycling rates in the .4 to .5 fractional

on-time bins were used to plot the curves, These figures show

that the model and the test data follow closely.

4.1.6 Heating Capacity of Defrost Cycles

The DoE test procedures require a "frost accumulation test" to

determine the heating performance of a heat pump between two

defrost periods and is used to indicate the effect of defrost on

the heat pump performance. Briefly, the test requires that the

performance of a complete cycle be recorded from the termination

of a defrost cycle to the next automatically terminated defrost

cycle. The results of the frost test is combined with those of

the steady-state tests to establish the heat pump's capacity

curve for estimating the heating seasonal performance factor

(HSPF) and seasonal operation cost. Since the steady-state

performance can only be derived from the "scan" file (will be

discussed in section 4.2) and the "scan" file had only a very

limited number of defrost cycles, "cycle" file data were used in

this investigation to analyze the defrost cycle performance of

unit 3 .

For the field study, all defrost cycles (a cycle having a defrost

period) which were preceded by defrost cycles were extracted from

the file and analyzed. Figures 4.23, 4.24, and 4.25 show the

20
heating capacity, the power input, and the COP of these cycles.

The total number of such cycles were 33 0 and the numbers shown

below the data points in figure 4.23 were such cycles in the 5°F

outdoor temperature bins. The regression lines in these three

figures were weighted by these cycles and they will be discussed

further in section 4.2.4.

4.2 "Scan” Data Analysis

As stated previously, the "cycle" file gives only the summed-up

data of the cycles, it can not be used to extract information

requiring only segments of cycles. Therefore, the "scan" file

was used to investigate the steady-state performance. The

steady-state results were then combined with the cyclic results

of the same cycles to calculate the heating load factors and

other part load performance (discussed later). This was analyzed

for unit 3 only.

Representative cycles at different outdoor temperatures of unit 3

were examined and it was found that the heat output reached

steady-state conditions at about 6 to 8 minutes after the cycles

were started. However, it took less than a minute for the power

input to reach s t eady- s t at e. Although over 3700 cycles were

recorded in the "cycle" file for this unit, some cycles were not

available for analysis because either the "cycle" or the "scan"

file of the same cycles contained bad data. Many cycles during

mild weather were also eliminated, because they never reached

steady-state conditions. The total number of cycles analyzed for

steady-state performance were 204.

21
4.2.1 Steady-State Performance

The heat output, power input, and COP of heat pump 3 are plotted

against the outdoor temperature in figures 4.26 , 4.27 and 4.28.

The equations of the regression lines are:

Y = 205 + 7.11 X for heat output,

Y =153+ 1.42 X for power input, and

Y = 1.57 + 0.01 9 0 X for COP.

These equations are used to calculate the capacity and COP at

47°F and 17 °F. Table 4.3 compares these results with those

obtained in laboratory tests on an identical unit [6].

Table 4.3 Comparison of Field and Laboratory Test Results

Field r esul t s Lab test Difference

Capacity at 47 ° F , Btu/h 3 2350 36200 + 11.9%

COP at 47 °

2.46 2.79 + 4.9%

Capacity at 1 7 ° F , Btu/h 19550 20510 + 4.9%

COP at 1 7 °

1 .89 1 .92 + 1 . 2%

It should be noted that the field data contained all cycles,

including defrost cycles, whereas the laboratory tests under the

DoE test procedure had relatively clean outdoor coils. The DoE

tests require a defrost cycle preceding the tests and the minimum

duration of the test to be half an hour. The frosting and

defrosting action of the field unit may have contributed to the

lower capacity and the COP.

Taking this into account would reduce the discrepancy at 17°F but

would not explain the performance difference above the defrosting

regime at 47°F. One possible cause for such observed data would

22
be a lower refrigerant charge in the field test unit. This would

reduce performance at high temperatures where superheat would

occur in the evaporator but would have little effect at low

temperatures where the unit would be flooding through the

evaporator and storing excess refrigerant in the accumulator.

4.2.2 Part Load Performance

Heating load factor (HLF) is defined [2] by the equation

Q C y c HLF = - Q s s

' where the quantity Q is the heating done for an entire cycle, cy c including an on-period and a subsequent off-period and Q is the s s amount of heating that would have been done for the entire cycle

at the steady-state output rate. It is an indication of the

combined effect of the building load and the capacity of the heat

pump system at a given time of the season. Figure 4.29 is a plot

of the fractional on-time against the HLF. The deviations of the

values between the HLF and the 45 degree line represent the loss

caused by cycling. The degree of frosting on the outdoor coil

resulted in much scattering between the fractional on-time of 0.6

and 0.85 (all cycles having defrost were deleted in fractional

on-time analysis, since their fractional on-time is always one).

When the data points below 4 2 ° F outdoor temperature are

eliminated as shown in figure 4.30, the scattering of the rest of

the data is much reduced. The data also show that below the

outdoor temperature of 42°F all cycles had fractional on-time

above 0.6. The DoE test procedure requires the frosting effect to

23
be neglected above 45°F.

The cyclic performance test of the DoE procedures specify that

the test be performed at 47°F outdoor temperature and at a 20%

building load (6 minutes on and 24 minutes off). By fitting all

data points above 45°F (numbered 30) with a straight line, the

equation is

Y = -0.0 80 + 0.93 9 X.

At 0.2 fractional on-time the HLF is 0.108. This HLF value and

the corresponding value of part load factor (PLF) will be used

later to compare the cyclic degradation factor.

Part load factor is defined L 2 ] as:

COP

PLF = cy c COP s s The part load factor represents the COP change effected by part

load cycling of the unit. The PLF and the fractional on-time

relationship is shown in figure 4.31. The regression line

equation is

Y = 0.6 63 + 0.33 2 X . At a fractional on-time of 0.2, the PLF is 0.729.

Figure 4.32 plots HLF against PLF. This figure gives the cyclic

effect taking account of off-cycle and cycle starting losses.

Therefore it is the loss caused by the cycling alone and is

called the cyclic degradation factor, C^.

[ 2 ] :

2 4

Its equation form is
1-PLF

1-HLF

Using this equation and the previously derived values of HLF

laboratory test value for the cyclic degradation factor was 0.375

[7], For comparison to field data this laboratory measured C D

should be multiplied by the ratio of field maximum cycling rate,

N „ „ = 2.74, to that of the laboratory test, N Q __ = 3, giving

Cq = 0.3 42 (see appendix A). The DoE test procedures allow the

heat pump manufacturers the option of assuming a of 0.25 in

calculating a heat pump's seasonal performance. The cyclic

degradation factor may be expressed on the HLF vs PLF figure by a straight line having the slope of C^. The area above this line

represents the cyclic inefficiency. In figure 4.32 three lines

are shown for the C^s of field result (0.3 04), laboratory test

(0.342), and the DoE option (0.25). For this particular house and

heat pump, the DoE optional degradation factor is more lenient

than degradation factors found from both laboratory test and

field measurements.

4.2.3 Thermostat Cycling Rate

The cycling rates of the 187 cycles are shown in figure 4.33.

These points do not include the cycles having defrost, as was

explained before. Averaging the cycling rates of the data points

between .48 and .52 fractional on-time yielded a maximum cycling

rate, N max » of 2.75 which is very close to 2.74 as derived from

all cycles of the "cycle" file (paragraph 4.1.5).

(0.108) and PLF (0 .7 29), C D is to be 0.3 04. The

25
4.2.4 Seasonal Capacity Profile

As stated previously in section 4.1.6, the DoE procedure combines

the steady-state capacity with the frost accumulation capacity to

give the heat pump's seasonal capacity profile. To construct a similar profile from the field data, figures 4.23, 4.24, and 4.25

of the defrost cycles and figures 4.26, 4.27, and 4.28 of the

steady-state data may be used. The power input of the defrost

cycles were very close to the steady-state cases (Y = 150 +1.41 X

in figure 4.24 vs Y = 153 + 1.42 X in figure 4.27). Yet, the

capacity of the defrost cycles was much lower than the steadystate capacity at lower outdoor temperature (Y = 9 8 + 9.04 X in

figure 4.23 vs Y = 205 + 7.1 1 X in figure 4.26). The slope of

the defrost cycles is steeper than that of the steady-state line.

This is contrary to the DoE assumption that between 17°F and 45°F

the slope of the capacity curve is relatively flat. Figure 4.34

shows the capacity profiles. The broken line is constructed by

using DoE procedure and laboratory test data points.

Using the laboratory test results in accordance with the DoE

procedures and the building load data of 36000 Btu/h (at 17.5 F)

obtained from the field for unit 3 (figure 4.10), the calculated

heating seasonal performance factor (HSPF) is 1.89. Using the

total energy output and input for the entire heating season of

unit 3 from the field, the HSPF was 1.60. The DoE test procedure

yields a +18.1% difference. A substantial portion of the

increased performance indicated by the DoE procedure is the

result of the higher value measured in the laboratory at the 4 7° F

steady state rating point. Performance under steady state

26
operation should be substantially the same in both laboratory and

field and it is therefore suspected that the field unit may have

had its performance reduced by some problems such as

undercharging. Discounting this the DoE procedure would still

have predicted high for this unit because of the high defrost

penalty it exhibited.

27
5, DISCUSSION AND CONCLUSION

Field data were collected and the heating performance of

three heat pump units evaluated. Two major types of data were

collected and used to evaluate the cyclic performance parameters

and seasonal performance. The first type consisted of scan data

collected at various intervals during the on portion of a cycle.

The second type consisted of cycle data in which data were

averaged or summed, as appropriate, for an entire on-off cycle.

Cycle data were collected for every cycle throughout the test

period.

Cycle data were analyzed for all three heat pumps. The

conclusions drawn from cycle data analysis were:

* The parabolic thermostat profile assumed by the DoE test

procedure was confirmed. This profile was also confirmed by the

cooling mode tests analyzed in [5] where derivation of the

parabolic thermostat model is also presented.

* The DoE test procedure assumes a maximum cycling rate at

5 0% run time of 3 cph. The test units had maximum cycling rates

of 2.31, 2.95, and 2.74 cph. Unit 1 (2.31 cph) was felt to be

nontypical because of thermostat setpoint changes by the

occupants, hence the assumption of 3 cph for the maximum cycling

rate is validated as typical for heating mode operation. The

maximum cycling rates in the cooling mode (1.64, 2.13, and 2.28

cph) were considerably lower [5].

28
* The degree day bases for the three houses were 6 4.0 °F,

61 .3 °F, and 55 .6 °F (average 60.3 °F) suggesting that the

traditional degree day base of 6 5 °F which is used in the DoE

rating procedure may be somewhat high, particularly in view of

trends toward better insulation, reduced infiltration, and

heavier use of indoor appliances in modern homes,

* On average the units were sized to meet the DoE minimum

design heating requirement confirming use of this point for

single point listing and advertising purposes.

* One unit was sized for the house heating load

substantially below the DoE minimum design heating requirement as

a result of energy conservation concerns on the part of the

owner. It may be desirable, to promote energy conservation, for

manufacturers to extend their HSPF tables to reflect lower

minimum design heating requirements.

* The DoE procedure assumes a substantial defrost penalty up

to 45 °F. The field tested units did not show a substantial

penalty over 40°F.

* The DoE procedure assumes that the defrost penalty reduces

to 0 at 17°F as result of the air holding little humidity. This

was substantially true for unit 1 which had demand defrost. On

the other hand the defrost penalty stayed approximately constant

for unit 2 which had timer (90 minute interval) initiated

defrost. This is reasonable since a substantial amount of energy

is necessary to warm the metal mass of a coil up to the cutoff

29
temperature for an unnecessary timer initiated defrost.

Surprisingly, unit 3 which had demand defrost behaved in much the

same way as unit 2 but at a lower energy consumption level

indicating overly easy defrost initiation. The current DoE test

procedure seems to characterize demand defrost best. As an

improvement, either a penalty could be subtracted from timed

defrost units or the length of the 17°F test period extended to

allow the inclusion of defrost penalty at this rating point.

Neither of these suggested solutions would account for the

possibility of wind initiation of overly sensitive demand defrost

systems.

Scan data were only analyzed for

primarily to analyze cyclic performance,

and model to this unit was tested in the

laboratory results are compared to the

the following conclusions:

unit 3. These were used

A unit identical in make

NB S laboratories and the

field test results with

* The cyclic degradation factor, C^, used to characterize

unit cyclic performance includes an assumption about thermostat

performance. A derivation is presented in Appendix A to show that

is proportional to the maximum cycling rate, N max , which

occurs at 50% on time. Hence for comparison between laboratory

and field results the cyclic degradation factor should be

multiplied by the ratio of the respective N max values. Analysis

of the cooling mode data reported in 15] on this unit confirms

this point. The laboratory measured value of 0.36 is multiplied

by an N max ratio of 1.64 cph to 3 cph. Therefore, the field

30
measured of 0.18 compares closely to the adjusted laboratory

measured value of 0.20.

* The cyclic test procedure of measuring was validated

for heating mode operation by comparing laboratory tests to the

field results. The field measured C D was 0.3 04. The laboratory

measured value after adjusting for cycling rates was 0.342.

* The DoE test procedure allows use of a default value of

0.25 for CD in lieu of a tested value. Both the field (C^ = 0.30)

and laboratory ( C ^ = 0.38 before adjusting and 0.34 after

adjusting) results indicating that the manufacturer would be

likely to use the default instead of the test values for rating

calculations. This was also true for the laboratory measured

cooling (0.36).

* The approach to cyclic loss calculation is based upon

the assumption that the part load factor, PLF, is a linear

function of the heating load factor, HLF, when the HLF is greater

than 0.2. This was verified by presentation of a plot of PLF vs

HLF based on field test data. Characterization of this curve for

HLF less than 0.2 is difficult because of insufficient data. It

would be expected to have a shape similar to those of the cooling

mode curves as shown in [5] which decrease rapidly below cooling

load factor of 0.2 and pass through the point 0,0 because of offcycle parasitic losses (control circuit and crankcase heater

powe rs) .
6 . REFERENCES

1. Hurley, C.W., Kelly, G.E., and Kopetka, P.A., "Using Microcomputers to Monitor the Field Performance of Residential Heat

Pumps," National Bureau of Standards, NBSIR 81-2285 (June 1981).

2. Federal Register, Part III, Department of En e r g y , 0 f f i c e of

Conservation and Solar Energy, Test Procedures for Central Air

Conditioners, Including Heat Pump, Thursday, December 27, 19/9.

3. Kelly, G.E., and Parken, W.H., "Method of Testing, Rating

and Estimating the Seasonal Performance of Central AirConditioners and Heat Pumps Operating in the Cooling Mood,"

National Bureau of Standards, NBSIR 77-1271 (April 1978).

4. Parken, W.H., Kelly, G.E., and Didion, D.A., "Method of

Testing, Rating and Estimating the Heating Seasonal Performance

of Heat Pumps," National Bureau of Standards, NBSIR 80-2002

(April 1980)

5. Parken, W.H., Didion, D.A., Woj ciechowski, P.H., and Chern,

L., "Field Performance of Three Residential Heat Pumps in the

Cooling Mode," National Bureau of Standards, NBSIR 85-3107 (March

1985) .

6. Mulroy, W.J., and Didion, D.A., "The Performance of a Conventional Residential Sized Heat Pump Operating with a NonAzeotropic Binary Refrigerant Mixture," National Bureau of

Standards, NBSIR 86-3422 (October 1986).

7. Mulroy, W.J., "The Effect of Short Cycling and Fan Delay on

the Efficiency of a Modified Residential Heat Pump," ASHRAE

Transactions, v.92, p t . 1, American Society of Heating

Refrigerating and Air-Conditioning Engineers, Inc. (1986).
7. APPENDIX A. Cyclic Degradation Factor

The cyclic degradation factor, C^, can be derived from the

parabolic model for thermostat performance and the effective time

constant method for characterizing unit performance.

The parabolic thermostat model [5] assumes that the heating

load factor is equal to the fractional on-time. This model

predicts the length of an on-cycle as:

whe re

‘on

= (1)

4 \8I (1 - hlf)

t = length of on-cycle, h

Nmax

= cycling rate at CLF = 0.5, cph

HLF = heating load factor.

The effective time constant approach to characterizing unit

capacity represents loss of unit efficiency as a short amount of

running time at the steady-state power level but with no

capacity

,

, That i s

whe re

t _ _ - t _ on e PLF = (2)

ton

PLF = part load factor

t = length of on-cycle, h

t = effective time constant, h

Substituting (1) into (2) gives:

The

PLF = (1 - 4 Nm t ) + (4 NmQV t ) HLF max e max e

slope of the HLF vs PLF line is C^, hence:

C D

= 4 Nmax t e

33
If a unit is tested at a cycling condition consistant with

one value of and is then operated in the field by a thermostat providing a different value for N max the field value

of C D would be related to the laboratory value by the Nmax ratio.

34
Outdoor ambient

•-—Dry bulb temperature

Figure 3.1 Schematic of Instrumentation for Typical Field

Unit Showing Location of 12 Sensing Elements

35
HEAT

OUTPUT,

Btu/hr

x

1000

UNIT NO. 3, DAY 32 1 22:3 1 : 1 2 — 23:26: 1 8

Figure 4.1 Heat Output of a Typical Cycle

36
ENERGY

INPUT,

Btu/hr

x

100C

ij I'J i i f'-j C_j t .j . |_) AY jV i jS i ,_j i I £_ — j/ ,_3 V t_i \ ! ri

Figure 4.2 Energy Input to Outdoor Unit of a Typical Cycle

37
INDOOR

TEMPERATURE,

AV.TEMP. 70.7F(U1 )*70.2F(U2),Q9.5F(U3)

Figure 4.3 Outdoor Temperature vs. Indoor Temperature

38
PERCENT

OF

TOTAL

TIME

Figure 4.4 Outdoor Temperature Distribution

39
DEFROST

TIME,

SEE

LEGEND

UNIT #1 TOTAL DEFROST TIME 4.6 HOURS

Figure 4.5 Defrost Time - Unit 1

40
DEFROST

TIME,

SEE

LEGEND

UNIT #2 TOTAL DEFROST TIME 65.1 HOURS

OUTDOOR TEMPERATURE BINS, F

\/ /

TIME IN HOURS % OF COMP. RUN TIME

Figure 4.6 Defrost Time - Unit 2

41
DEFROST

TIME,

SEE

LEGEND

UNIT #3- -TOTAL DEFROST TIME 32*1 HOURS

Figure 4.7 Defrost Time - Unit 3

42
DEFROST

TIME,

HOURS

ALL 3 UNITS

IZ71 UNIT NO. 1 OUTDOOR TEMPERATURE BINS, F

FTTI UNIT NO. 2 UNIT NO. 3

Figure 4.8 Defrost Time of Three Units (in hours)

43
OF

COMPRESSOR

RUN

TIME

ALL 3 UNITS

10

Q

5 -

1 -

[/ 7| UNIT NO. 1 OUTDOOR TEMPERATURE BINS, F

|'\ \,| UNIT NO. 2 UNIT NO. 3

Figure 4.9 Defrost Time of Three Units (in % compressor run)

44
BUILDING

LOAD,

1000

Btu/h

Figure 4.10 Building Loads

45
HEAT

OUTPUT,

Million

Btu

12

UNIT NO* 1

1 1 -

10 -

9 -

OUTDOOR TEMPERATURE E5INB. F

E

7 Zi COMP HEAT \\ \| ELCT HEAT

figure 4.11 Heat Output vs. Outdoor Temperature - Unit 1

46
HEAT

OUTPUT,

Million

Btu

17 22 27 32 37 42 47

OUTDOOR TEMPERATURE BINS, F W\ COMP HEAT rvxj ELCT HEAT

Figure 4.12 Heat Output vs. Outdoor Temperature - Unit 2

47
HEAT

OUTPUT.

Million

Btu

3.5 UNIT NO. .3

OUTDOOR TEMPERATURE BINS, F

fZ71 CO'MP HEAT FT\1 ELCT HEAT

Figure A. 13 Heat Output vs. Outdoor Temperature - Unit 3

48
PERCENT

OF

TOTAL

HEAT

OUTPUT

0.4

UNIT 1

0.35 -

OUTDOOR TEMPERATURE BINS. F _ \/ /

COMP. HEAT 1\ \j AUX. HEAT lOl. HEA!

Figure 4.14 Percent Heat Output vs. Outdoor Temperature - Unit 1

49
PERCENT

OF

TOTAL

HEAT

OUTPUT

UNIT 2

7 1 2 1 7 22 27 32 37 42 47

OUTDOOR T E M PE RATU RE B 1 N 0 , F

52 57

EZ3 c CMP. HEAT r\Xl AUX. H EAT Eva TOT. HEAT

"Figure 4.15 Percent Heat Output vs. Outdoor Temperature - Unit 2

50
PERCENT

OF

TOTAL

HEAT

OUTPUT

0.4

0.35 -A

0.3 -

U . 2t>

0.2 -

0.15 -

0.1 -

0.05 -

UNIT 3

0

•kg F~

E3

o

9o<9o r*‘ -^O

k\$ Au;$

- /\XL *X <>

1/

o /

/

A

/

foi 9o

o

1/ &

9

X

9v

9

K>W \ &

[71 IRi

97 37 4: =,7

COMP- H LAT

OUTDOOR TEMPERATURE BINS, F

P\\i AUX. HEAI TOT. HEAT

Figure 4.16 Percent Heat Output vs. Outdoor Temperature - Unit 3

51
3

UNIT NO. 1

Figure 4.17 Cyclic COP vs. Outdoor Temperature - Unit 1

52
3

UNIT NO* 2

CLO

o

o

o

2.S - 2*6

2.4

— n

I *o

1 .6

1 .4

1 .2

1 0*8

0.6

0*4

0.2

0

-57T7

1 / >#

K,>g / xx

/>£<

'V' ./ XX

V^c - ;< x /&y’y / 99, /&

/ xSi:

r-' >T:-; XX .a

/>£

/ > V% / >&' /5^

' &?

/" &>

/£<

, C>0 /jS

<0

/$&

?y. *vs

iZTI WITHOUT ELEC HEAT

22 27

OUTDOOR TEMPERATURE BINS. F

gvx^ WITH ELEC

Figure 4.18 Cyclic COP vs. Outdoor Temperature - Unit 2

HEAT

53
UNIT NO

OUTDOOR TEMPERATURE BINS. F

S7~7\ WITHOUT ELEC HEAT WITH ELEC HEAT

Figure 4.19 Cyclic COP vs. Outdoor Temperature - Unit 3
YCLES

PER

HOUR

UNIT NO. 1

f

)

[ 3 , 0.4 0.6

FRACTIONAL ON-TIME

Figure 4.20 Compressor Cycling Rate - Unit 1

55
CLE5

PER

HOUR

UNIT NO* 2

Figure 4.21 Compressor Cycling Rate - Unit 2

56
CYCLES

PER

HOUR

UNIT NO* 3

F RACTi GNAl_ ON — TIME

Figure 4.22 Compressor Cycling Rate - Unit 3

57
C

AP

AC

ITY, Q

t

u/

rnI

n

Y = 9o + 9*04 X

Figure 4.23 Capacity of Defrost Cycles - Unit 3

58
POWER

INPUT,

Btu/min

150 + 1.41 X

Figure 4.24 Power Input of Defrost Cycles - Unit 3

59
COP

Y = 0.31 + 0.037 X

Figure 4.25 COP of Defrost Cycles - Unit 3

60
APACITY,

Btu/min

Y — d. U5 + 7.11 X

Figure 4.26 Steady State Capacity - Unit 3

61
ENERGY

INPUT,

Btu/min

100 -

yo

iA

30 - 60 - 40 - 20 -

0 —

0 20 40

OUTDOOR TEMPERATURE, F

Figure 4.27 Steady State Power Input - Unit 3

62
STEADY'

STATE

COP

Y = 1,57 -+- 0,019 X

Figure 4.28 Steady State COP - Unit 3

63
HEATING

LOAD

FACTOR

(HLF)

Figure 4.29 Heating Load Factor vs. Fractional On-Time - Unit 3 (all data available)

64
HEATING

LOAD

FACTOR

(HLF)

DATA OMITTED BELOW' 42 F OUTDOOR TEMF.

1

0.9

0.3

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0 0 . 2 0.4 0 .

0 . o

FRACTIONAL ON-TIME

Figure 4.30 Heating Load Factor vs. Fractional On-Time - Unit 3

(data omitted below 42°F outdoor temperature)

65
PART

LOAD

FACTOR

(PLF)

Y = 0,663 + 0.332 X

Figure 4.31 Part Load Factor vs. Fractional On-Time - Unit 3

66
PART

LOAD

FACTOR

(PLF)

H ELATI NG LOAD FACTo R ( H L_F )

figure 4.32 Part Load Factor vs. Heating Load Factor - Unit 3

67
CYCLING

RATE,

CYCLES

PER

HOUR

EXCLUDING DEFROST CYCLES

Figure 4.33 Cycling Rate (excluding defrost cycles) - Unit 3

68
PACITY,

BTU/MIN

UNIT 3

OUTDOOR TEMPERATURE, F

(1-1) MELDED Eh ROST (2-2) hltLD,S.S.

Figure 4.34 Comparison of Laboratory and Field Test Results

69
NBS-114A irev. 2-80

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report NoJ 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions) REPORT NO.

NBSIR 87-3528 February 1987

4. TITLE AND SUBTITLE

FIELD PERFORMANCE OF THREE RESIDENTIAL HEAT PUMPS IN THE HEATING MODE

5. AUTHOR(S)

James Y. Kao, William J. Mulroy, and David A. Didion

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covere

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS ( Street. City , State, ZIP)

U. S. Department of Energy

1000 Independence Avenue, SW

Washington, DC 20585

10. SUPPLEMENTARY NOTES

j Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200»word or less factual summary of most significant information. If document includes a si gnificant

bi bl iography or literature survey, mention it here)

This report presents the results of a field performance study of three heat pumps

operating in the heating mode. The objective of this study was to evaluate the

thermal, energy, defrosting, cycling, and other related performance under in-situ

conditions and to confirm the validity of Department of Energy (DoE) test procedures

by comparing these field results with those obtained in the laboratories. The

seasonal COPs without auxiliary heat were 1.83, 2.31, and 1.92. The seasonal COPs

with auxiliary heat were 1.71, 1.95, and 1.60. General agreement was found in two

houses for cycling rates and building load estimation. Defrost penalty was found

to be light above 40 °F. One house was analyzed for cyclic performances. The

cyclic degradation factor (C^) was found to be worse than the optional factor

(0.25) of the DoE procedure.

12. KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key words by semicolon s) defrosting; field performance; field performance £>f heat pumps; heat pumps; heat

pump test methods; heating seasonal performance

13. AVAILABILITY

|X j Uni imited

j

i For Official Distribution. Do Not Release to NTIS

! | Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

i_Xj Order From National Technical Information Service (NTIS), Springfield, VA. 22161

USCOMM-OC 6043-P8

14. NO. OF

PRINTED PAGES

79

15. Price

$ 13.95