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NIST BUILDING SCIENCE SERIES 171

NET

Field Monitoring of a Variable-Speed

Integrated Heat Pump/Water Heating Appliance

A, Hunter Fanney

TA

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//171

1993
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NIST BUILDING SCIENCE SERIES 171

Field Monitoring of a Variable-Speed

Integrated Heat Pump/Water Heating Appliance

A. Hunter Fanney

Building and Fire Research Laboratory Sponsored by:

National Institute of Standards and Technology Allegheny Power System

Gaithersburg, MD 20899 R&D Project RP 89-60

Cabin Hill June 1993 Greensburg, PA 15601

U.S. Department of Commerce

Ronald H, Brown, Secretary

National Institute of Standards and Technology

Arati Prabhakar, Director
National Institute of Standards and Technology Building Science Series 171

Natl. Inst. Stand. Technol. BIdg. Sci. Ser. 171, 60 pages (June 1993)

CODEN: NBSSES

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1993

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
TABLE OF CONTENTS

Page

ABSTRACT 1 KEYWORDS 2

INTRODUCTION 3

RESIDENCE 4

HEAT PUMP DESCRIPTION 6

INSTRUMENTATION 10

SIGNAL PROCESSING 15

EXPERIMENTAL RESULTS 16

Electrical Energy Consumption 16

Hourly Electrical Demands 24

Indoor and Outdoor Temperatures 34

Advanced Integrated Heat Pump System Performance 39

SUMMARY , 49

ACKNOWLEDGMENTS 52

REFERENCES 53

iii
LIST OF FIGURES

Page

Figure 1 - Monitored Residence 5

Figure 2 - Instrumentation Schematic 7

Figure 3 - Typical Thermocouple Calibration Curve 12

Figure 4 - Air Flow Measurement Station 13

Figure 5 - Monthly Energy Consumption for Base Load, Heat Pump,

Supplemental Space Heater, and Water Heater 21

Figure 6 - Energy Contributions of Heat Pump and Electrical Resistance

Elements to Water Heater 22

Figure 7 - Distribution of Energy Consumption 23

Figure 8 - Monthly Peak Electrical Demands 26

Figure 9 - Monthly Electrical Demands Coincident with Allegheny Power

System's Peak Demand 27

Figure 10 - Monthly Electrical Demands Coincident with Potomac Edison

Company's Peak Demand 29

Figure 11 - Average Energy Consumption of Heat Pump, Supplemental Space

Heater, and Water Heater Versus Outdoor Temperature During

1990-1991 Heating Season (SI Units) 30

Figure 11a - Average Energy Consumption of Heat Pump, Supplemental Space

Heater, and Water Heater Versus Outdoor Temperature During

1990-1991 Heating Season (IP Units) 31

Figure 12 - Average Energy Consumption of Heat Pump and Water Heater Versus

Outdoor Temperature During 1991 Cooling Season (SI Units) 32

Figure 12a - Average Energy Consumption of Heat Pump and Water Heater Versus

Outdoor Temperature During 1991 Cooling Season (IP Units) 33

Figure 13 - Monthly Average Indoor Temperature 35

iv
LIST OF FIGURES (continued)

Page

Figure 14 - Variation in Living Room Temperature During January 1991 36

Figure 15 - Variation in Master Bedroom Temperamre During January 1991 37

Figure 16 - Variation in Family Room Temperature During January 1991 38

Figure 17 - Monthly Average Outdoor Temperature 40

Figure 18 - Monthly Heating Load Versus Heating Degree Days 41

Figure 19 - Monthly Energy Consumption of Heat Pump in Various Operational

Modes 42

Figure 20 - Monthly Water Heating Coefficient of Performance Versus Average

Monthly Outdoor Temperature 46

Figure 21 - Monthly Combined Performance Factor 48

V
LIST OF TABLES

Page

Table 1 - Space Heating Load, Energy Transferred from Heat Pump to Water Heater, and Energy Consumptions During Space Heating

Months 17

Table 2 - Monthly, Seasonal, and Annual Performance Summary, SI Units 19

Table 2A - Monthly, Seasonal, and Annual Performance Summary, IP Units 20

Table 3 - Comparison of Measured Energy Consumption Using Electronic

Digital Power Analyzer and Electric Utility Watthour Meter 25

vi
ABSTRACT

This report summarizes a study in which a variable-speed integrated heat pump/water healing

appliance was monitored for 2 years while meeting the space conditioning and water heating

needs of an occupied residence. Experimental results are presented which show that the total energy consumed by the residence was significantly reduced compared to previous years in which electric baseboard heat, a wood stove, and window air-condilioners were used.

During the two space heating seasons, the variable-speed integrated heat pump/water heating

appliance used 60% less energy than would have been consumed by an electric furnace with

the same air distribution system and a storage-type electric water heater.

The monthly space cooling only coefficients of performance ranged from 2.50 to 4.03,

whereas, the monthly space heating only coefficients of performance ranged from a low of

0.91 to a high of 3.33. A proposed index to quantify the overall system performance of

integrated water heating/space conditioning appliances, referred to as the combined

performance factor, ranged from 1.55 to 3.50. The majority of larger values occurred

during months in which space cooling dominated. The combined performance factor for the

entire 2-year study was 2.45.

A conventional watthour meter supplied by the local electrical utility and an electronic digital

power analyzer were used to measure the energy consumption of the variable speed heat

pump in order to discern if variable-speed equipment introduces errors in conventional utility

metering equipment. Measurements made using the two instruments were in excellent

agreement.

The monthly energy consumption and peak electrical demands of the residence, integrated

heat pump/water heating appliance, supplemental space heater, and water heater are discussed. The influence of outdoor temperamre on electrical power demand is presented.

1
KEYWORDS

building technology; coefficient of performance; combined performance factor; field study;

heat pump; HSPF; integrated water heating; peak demand; SEER; thermal performance;

variable speed
INTRODUCTION

Nearly one out of three new single-family houses built in the United States uses an electric

heat pump for space conditioning. Since the early 1950's, when heat pumps were introduced

into the residential market, manufacturers have continuously strived to improve reliability,

increase efficiency, improve thermal comfort, and meet increasingly stringent environmental

concerns while remaining competitive with oil and gas-fired residential space conditioning

equipment.

During the past decade, heat pumps have evolved from units utilizing a single-speed

reciprocating compressor to units which incorporate variable-speed components, rotary and

scroll compressors, microprocessor controls, demand limiting features, and integrated water

heating. These technological advances have resulted in heat pumps which are significantly

more efficient than traditionally designed units, although they have yet to gain a significant

share of the heat pump market. Additional technological advances, including thermal

storage, multiple condensers, and adaptive controls, are currently being introduced into the

market.

This report summarizes a research project in which a commercially available, technologically

advanced, integrated heat pump/water heating appliance (hereafter referred to as heat pump)

was extensively instrumented and monitored under field conditions. The heat pump selected

for this study incorporates a variable-speed compressor and indoor fan, microprocessor

controls, and a refrigerant-to-water heat exchanger. The unit attempts to improve thermal

comfort by controlling the ratio of indoor fan speed to compressor speed in a manner which

improves humidity control during the cooling season and avoids the occasional blowing of

cool air during the heating season. Rather than extracting heat from the conditioned space to defrost the outdoor coil, the heat pump uses energy stored within the water heater.

The research was undertaken to determine the thermal performance of an integrated heat

pump system and the electrical load characteristics of an occupied residence equipped with

such a unit. Secondary objectives were to investigate if the variable-speed components

within the heat pump system introduce errors in conventional residential watthour meters and

to provide data for future computer simulation validation studies.

This report describes the residence, heat pump system, and monitoring equipment. Results

are presented which include comparison of the total electrical energy consumption of the

residence prior to and after installation of the heat pump system, the portion of energy used

by each end use within the residence, a comparison of the heat pump's energy consumption

using a conventional watthour meter and an electronic digital power analyzer, and the hourly

electrical demands imposed on the utility. The thermal performance of the heat pump system

is reported on a monthly, seasonal, and annual basis using conventional performance

indicators in addition to using an index, proposed by NIST, which quantifies the overall

system performance of integrated appliances.

3
RESIDENCE

The residence in which the integrated heat pump was tested, Figure 1, is located

approximately 19 km (12 mi) south of Hagerstown, MD. Space heating and cooling is provided to 153.6 m"^ (1653 ft^) of living area within the residence. The integrated heat

pump system and accompanying water heater are located in the 53.5 m^ (576 ft^)

unconditioned below-grade basement. The first level of the conditioned space includes a family room, bathroom, and laundry room. A living room, dining room, and kitchen are located on the second level. Three bedrooms and two full baths are contained within the

third level.

The first level's exterior walls consist of nominal 50.8 mm by 101.6 mm (2 in by 4 in) studs on 0.406 m (16 in) centers, with R-11 fiberglass batts between the studs, positioned against an 0.203 m (8 in) concrete block wall. The exterior walls of the second and third levels

consist of nominal 50.8 nun by 101.6 mm (2 in by 4 in) studs spaced 0.406 m (16 in) apart.

The walls are insulated with nominal R-11 fiberglass batts between the studs and 25.4 mm

(1 in) of extruded polystyrene sheathing fastened to the exterior beneath vinyl siding. The

uninsulated exterior walls of the basement are constructed of 0.305 m (12 in) concrete

blocks.

The windows throughout the residence are vinyl clad double-glazed, double-hung wood units.

Exterior insulated steel doors are located in the kitchen and living rooms. The remaining

exterior doors, one in the walkout family room and one leading onto the deck from the

dining room, are double-glazed sliding units. Attic insulation consists of R-30 fiberglass

batts placed between the 0.610 m (24 in) on center roof trusses.

Prior to the installation of the variable-speed integrated heat pump, the residence was heated

by electric baseboard heaters in each room and a wood stove located in the family room.

Approximately five cords of wood were burned each heating season prior to the installation

of the heat pump. Space cooling was provided to approximately one-third of the residence

through the use of two 1.46 kW (5,000 Btu/hr) window air conditioners, one located in the

living room and the second one in the master bedroom. The domestic water heating needs of

the residence were met through the use of a nominal 0.197 m^ (52 gallon) electric storagetype water heater.

4
MONITORED RESIDENCE

FRONT ELEVATION

REAR ELEVATION

Figure 1

5

Scale 1/4" = r-O"
HEAT PUMP DESCRIPTION

The variable-speed integrated heat pump system was installed in the residence during the

month of March 1990. The system consists of three distinct components: (1) an indoor fan

coil; (2) an outdoor fan coil; and (3) a compressor section which accommodates the

compressor, a refrigerant-to-water heat exchanger, a water pump, a bi-directional electronic

expansion device, and the majority of the heat pump controls.

The heat pump is connected to a 0.197 m^ (52 gallon), dual 4500 watt element, electric

storage-type water heater. The water heater's thermostats were maintained at 51.7 °C

(125 °F) throughout the study. Water is removed from the water heater by a tee connection on the cold water supply pipe, circulated through the refrigerant-to-water heat exchanger, and

subsequently returned to the storage tank through the port normally used to drain the water

heater. Figure 2.

The heat pump system incorporates several unique technological innovations. The

compressor and indoor fan both have electronically commutated, permanent-magnet motor

drives. These variable-speed components are used to enhance both comfort and efficiency.

The control logic maximizes the efficiency of the heat pump by operating the blower and

compressor at the lowest possible speeds at which the conditioned space temperature can be

maintained within 0.6 °C (1° F) of the thermostat's setpoint. If the relative humidity is too

high, the control logic decreases the indoor fan speed, relative to the compressor speed. The

evaporator coil temperature decreases; thus, increasing the rate of dehumidification. In order

to improve comfort levels during the heating season, the unit cycles on and quickly ramps

the compressor to maximum speed while operating the indoor fan at minimum speed until the

indoor coil warms up. This procedure avoids the "cold blow" associated with conventional

heat pumps. During defrost cycles, energy is removed from the water heater as opposed to extracting energy from the conditioned space.

The heat pump can operate in five distinct operating modes: space cooling only, combined

space cooling and water heating, space heating only, combined space and water heating, and

water heating only. A microprocessor controls the operating mode of the system and the

heating elements within the storage-type water heater. A brief description of the logic

employed by the heat pump system for each mode follows.

Space Cooling Only - The heat pump system provides space cooling in proportion to the

space load by varying the compressor and indoor fan speeds. For systems equipped with a

humidistat, the humidity level within the residence is controlled by varying the indoor fan

speed relative to the compressor speed. When the humidity is above the setpoint, the

compressor and fan speeds are varied to satisfy the sensible cooling load with the lowest

practical indoor coil temperature.

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space Cooling Plus Water Heating - In this mode heat removed from the house is transferred

to the water heater and outside air. If the outdoor fan is off, the heat pump operates in a full condensing mode, in which the majority of the heat is delivered to the water heater.

Whenever the outdoor fan is operational, the heat pump operates in a desuperheater mode, in

which the majority of the heat is dissipated by the outdoor coil and a smaller portion to the

water heater. Outdoor fan operation is based upon the cooling and water heating loads. If a

substantial cooling load exists, the unit will operate in the desuperheater mode since the

space cooling capacity is not diminished. The heat pump will operate in a fully condensing

mode if the space cooling load is small and a large water heating load exists. Although the

space cooling capacity is decreased in this mode, the maximum contribution to the water

heating load is obtained. If both the space cooling and water heating loads are small, the

heat pump will operate in the desuperheating mode.

Space Heating Only - The control logic varies the compressor speed to meet the space

heating load while the indoor speed is varied to maintain comfortable supply air

temperatures. The maximum compressor speed is 5300 rpm; however, at temperatures

between -8.3 °C (17 °F) and -17.8 °C (0 °F) the compressor speed is limited to 3600 rpm.

If the space heating load exceeds the heat pump's capacity, supplemental resistive heat is added. At temperatures below -17.8 °C (0 °F) the compressor is turned off and the total

space heating load is met using auxiliary resistive heating.

Space Plus Water Heating - The condenser heat is shared by the space and water heating

loads. The compressor is typically ramped to and maintained at maximum speed until

operation in the space plus water heating mode is discontinued. The distribution of heat

between these two loads depends upon the indoor fan speed which is controlled to meet the

space heating load. At a high fan speed, the majority of heat is supplied to the conditioned

space. As the fan speed is lowered, heat delivered to the water heater increases. If the

space heating requirement exceeds that of the compressor, water heating by the heat pump

ceases, and the electric resistance heaters provide all needed water heating.

Water Heating Only - The integrated heat pump used in this study can heat water even if a space conditioning load does not exist. The system monitors the water temperature in the

bottom of the tank by means of a sensor located in the water heater drain port. If the

controller senses that the water temperature is low, it will energize the pump, which

circulates water from the water heater through the refrigerant-to-water heat exchanger for

3 minutes, so that a representative water temperature can be obtained. At the end of this

sampling period, the compressor and outdoor fan will start if the water temperature is low.

The unit will operate in the water heating mode when the outdoor temperature is between

8.3 °C (17 °F) and 35 °C (95 °F). The heating elements within the storage tank will be

enabled by control logic within the heat pump system, if the water heating capacity of the

heat pump is insufficient to meet the water heating load. The heat pump will heat water to 54.4 °C (130 °F) under most conditions, and then the electric elements are energized if the

water heater thermostats are set higher.

8
The Air-Conditioning and Refrigeration Institute (ARI), an independent rating organization,

lists the cooling capacity of this heat pump as 10.78 kW (36,800 Btu/h), and the seasonal

energy efficiency ratio (SEER) as 14.05. This SEER corresponds to a cooling season

coefficient of performance of 4.12. The heating capacity and heating seasonal performance

factor (HSPF) are listed as 10.37 kW (35,400 Btu/h) and 9.05 respectively. This HSPF

corresponds to a heating season COP of 2.65. These values are obtained from tests where

the heat pump operated in the space heating only and space cooling only modes. Existing

test methods do not capture the additional benefit of integrated water heating. NIST is currently developing a test method, under the sponsorship of the U.S. Department of Energy

and the Electric Power Research Institute [1,21, which will quantify the benefits of water

heating for all integrated space conditioning/ water heating appliances.

9
INSTRUMENTATION

The integrated variable-speed heat pump in the Hagerstown house was extensively

instrumented by NIST, as shown in Figure 2. This section describes the instrumentation and

the procedures used to calibrate the individual instruments. All instrumentation was

calibrated prior to the beginning of the monitoring period and upon completion of the 2-year

data collection period.

Watt/Watthour transducers were used to measure the energy consumption of the house, water

heater, and resistance strip heaters. These transducers provide an analog voltage

proportional to the instantaneous power and a digital signal that is proportional to the

electrical energy consumption. Current transformers were utilized to scale the measured

current supplied to the house and resistance strip heater to a level compatible with the

maximum current capability of the watt transducers, 20 amperes. Each watt/watthour

transducer was individually calibrated using a watthour standard. An electronic digital power

analyzer was used to measure the electrical power consumed by the heat pump. The

electronic digital power analyzer was used in lieu of a watt/watthour transducer due to concerns regarding the accuracy of the watt/watthour transducers when subjected to harmonics produced by the variable-speed components [3-4]. The Potomac Edison

Company, the electric utility to which the residence is connected and sponsor of this

research, installed a watthour meter upstream of the electronic digital power analyzer which

permitted an assessment of the error which would be encountered if conventional residential

metering equipment was used.

The indoor temperature of the residence was monitored in three locations—the family room,

the living room, and the master bedroom—using radiation-shielded thermocouples. The

outdoor temperature sensor consisted of a shielded thermocouple located on the north side of

the residence. All thermocouple and thermopiles used in this study were constructed of

premium type-T thermocouple wire. An eight junction thermopile was used to determine the

air temperature difference across the heat pump. The thermopile junctions were positioned

such that each junction represented an equal cross sectional area within the duct.

Thermocouples were installed in the supply and return ducts in the vicinity of the thermopiles

to provide redundant measurements. Sheathed thermocouples were used to measure the cold

water inlet temperamre, the hot water supply temperature, and temperatures within the

storage tank at the center of six equal vertical volumes.

The inlet and outlet water temperatures associated with the refrigerant-to-water heat

exchanger were measured using sheathed-platinum resistance temperature detectors immersed

in the water at the entrance and exit of the heat exchanger. A constant 100 microampere

current, supplied by the data acquisition system, passed through each of these sensors

resulting in voltage drop proportional to the temperature.

The thermocouples, thermopile, and platinum resistance temperature detectors were

calibrated at the field site by immersing each sensor in a constant temperature bath containing

10
a NIST calibrated thermometer. The temperature sensors were calibrated over the

temperature range to which they were subjected during the monitoring period. The indicated

temperamres were compared to the NIST calibrated thermometers, and correction algorithms

developed for the data reduction software. The calibrations were performed "end-to-end,"

that is the sensor, connecting wire, and data acquisition system were calibrated as a unit. A

typical thermocouple calibration curve is shown in Figure 3. A turbine flowmeter was used to measure the flow rate through the water side of the

refrigerant to water heat exchanger. The pulsed output of this turbine flowmeter is fed to an

electronic signal conditioner which converts the turbine flowmeter's output frequency to an

analog voltage signal proportional to flow rate and a digital pulse output corresponding to the

integrated volume of water through the flowmeter. An integrating-type flow meter measured

the quantity of water circulated through the water heater. This flowmeter provides a pulse

output with a resolution of 3.8 x 10"^ m-^ (0.01 gallons). Both flowmeters and associated

electronic packages were calibrated at NIST. An airflow measurement station was used to measure the velocity of the air in the 0.457 m (18 in) by 0.609 m (24 in) return duct. This

device, Figure 4, contains parallel cell honeycomb panels which straighten the air flow prior

to it arriving at the averaging pitot tube station. The pitot mbe station contains total and

static pressure manifolds which average 26 individual measurements of total and static

pressure. Equivalent cross sectional areas are monitored by each individual sensor. The

averaged total and static pressures are supplied to an electronic differential pressure

manometer which incorporates an integral square root extractor to convert the differential

pressure into an analog output voltage proportional to flow rate. This unit was factory

calibrated and checked periodically during the 2-year period by comparing it to a second

reference unit.

The relative humidity entering and leaving the indoor coil of the heat pump was measured

using thin-film capacitive humidity sensors. Electronic signal processing converted the

measured capacitance into an analog voltage. The relative humidity transmitters were

calibrated three times during the 2-year study: at the beginning, after 1 year, and at the

conclusion of the smdy. During calibration, the sensors were placed in a small

environmental chamber with temperature and humidity control. A calibrated thermocouple

and dew point hygrometer were placed in close proximity to the relative humidity

transmitters within the chamber. Using the measured dew point and chamber temperatures,

the relative humidity within the chamber was determined and compared to that indicated by

the relative humidity transducers.

The status of the indoor fan, water circulation pump, defrost valve, and reversing valve were

determined by measuring their respective control signals. Logic within the data reduction

software was able to discern the operational mode of the heat pump system based upon these

control signals.

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All of the instrumentation used in the study was connected to a microprocessor based data

acquisition system. The data acquisition system combines a 5 1/2 digit voltmeter, a clock, a precision current source, and an IEEE-488 interface to transmit the scanned data to a personal computer. The voltmeter has a 1 microvok sensitivity, is fully guarded, and uses an integrating analog to digital conversion teclinique. Data is captured at a rate of 50

readings per second. Installed within the data acquisition system are two multiplexing analog

relay cards and two digital counter cards. One mukiplexing card is dedicated to analog

voltage signals; for example, the relative humidity transmitter signals are supplied to this

card assembly. The second multiplexing card, which incorporates type-T thermocouple

compensation, is used to sample the signals from the thermocouples. The digital counter

cards are used to count the pulses which are generated by the flow meters and the

watt/watthour transducers.

14
SIGNAL PROCESSING

The acquired data were processed in real time using a personal computer interfaced to the

data acquisition system. The computer controls the data acquisition system, converts the sensor signals into engineering quantities, corrects the measurements using calibration data,

integrates or averages the data over appropriate time intervals, displays the current

measurements on a video monitor, and records the data. All sensors are scanned every

10 seconds.

The energy delivered from the heat pump to the residence is computed using the measured

air velocity, the cross sectional area of the return duct, the density of the air at the flow

measurement station, and the change in enthalpy. The change in enthalpy is calculated from

the temperature and humidity measurements at the heat pump's entrance and exit. The

energy supplied to the water heater is computed using the temperamre difference across the

water side of the refrigerant-to-water heat exchanger, the flow rate of the water, and the

density and specific heat of the water. These values are integrated over 1-hour time intervals

yielding the hourly thermal load of the residence and the amount of energy delivered to the

water heater during each hour. The energy delivered to the water heater takes into account

the energy removed from the water heater during the defrost cycle. The hot water load is determined by integrating the product of the temperature difference between the water

temperature entering and exiting the water heater, the hot water load flow rate, and the

density and specific heat of water whenever a hot water draw occurs.

The average temperatures for the outdoor ambient, family room, living room, and master

bedroom are recorded each hour. Temperature, relative humidity measurements, and air

flow rates associated with the heat pump operation are only averaged during operation of the

heat pump. Thus, any convective heating or cooling which takes place, due to a temperature

difference between the indoor coil and surrounding air when the indoor fan is not operating,

is ignored. It should be noted that these averaged values are not used to calculate the energy

delivered by the heat pump, which is computed every 10 seconds based on instantaneous

measurements whenever the heat pump is providing space conditioning. Measurements of

the electrical energy supplied to the house, heat pump, water heater, and supplemental air

heater were integrated to give the total energy consumption on a hourly basis.

At the end of each hour, values are recorded on a floppy disk. The values are recorded on a single disk for 10 consecutive days. At the end of the tenth day, the computer begins storing

data on the second disk and displays a message on the monitor instructing the homeowner to remove the disk and replace it with a blank formatted disk. This scheme provides a maximum of 20 days of data collection without operator intervention. The homeowner of

this residence, a Potomac Edison Company employee, monitored the system to ensure proper

operation and mailed the data disks to NIST for final data reduction. Upon arrival at NIST,

the individual 10-day files were combined into monthly data files. The monthly files were

imported into a spreadsheet program for final analysis. During this smdy over 205 million

measurements were taken and processed (32 measurements every 10 seconds). Over the

2-year monitoring period 99.8% of the available data was captured and processed due to the

quality of the instrumentation, the use of an uninterruptible power supply, and the integrity

of the data collection software.

15
EXPERIMENTAL RESULTS

Electrical Energy Consumption

Prior to the installation of the advanced integrated heat pump system, the residence was not

monitored. Thus, a direct comparison between the energy required for space conditioning,

water heating, and other uses before and after installation of the integrated heat pump system

is not possible. It is possible, however, to compare the bimonthly billing data for the entire

residence. For the 2-year period from October 1986 through September 1988, the total

electrical energy consumed by the residence was 116,143 MJ (32,262 kWh). In addition,

approximately 10 cords of oak wood were burned during the two heating seasons. Assuming

a fuel value of 28,784 MJ (27.3 million Btu) per cord [5] and a 40% wood stove efficiency

[6], an additional 115,116 MJ (31,977 kWh) of electricity would have been consumed if electric resistance heat had been used in lieu of the wood stove, resulting in a total estimated

energy consumption of 231,259 MJ (64,239 kWh) for the residence. Space cooling was

provided to approximately 30% of the home through the use of two 1.46 kW (5,000 Btu/hr)

window air conditioners during the cooling seasons.

The energy consumed by the residence from October 1989 through September 1991 was

110,405 MJ (30,668 kWh), representing a 4.9% reduction in electrical energy consumption

and an estimated 52% reduction in total energy consumption. The total electrical energy

consumed by the residence was reduced by 6.1% for the period of time in which space

heating was required and 1.0% for the months in which space cooling occurred. During this

2-year period, the integrated heat pump system was operational, the wood stove was not

used, and the entire residence was space conditioned during both the heating and cooling

seasons. It should be noted that differences in weather conditions, temperatures within the

conditioned spaces, and hot water consumption before and after installation of the integrated

heat pump system are not taken into account in this comparison.

A comparison can be made between the total energy consumption of the advanced integrated

heat pump and associated water heater during the monitoring period to the energy which

would have been consumed if an electric furnace and an identical water heater had been used

during the months in which space heating occurred. Months during which both space heating

and cooling occurred, September 1990 and May 1991, were not included in this comparison.

The measured space heating load, energy supplied to the water heater, and energy supplied

from the heat pump to the water heater were combined to represent the equivalent amount of

electrical energy required to space condition the residence with an electric resistance furnace

and provide hot water. Table 1. The use of an electric furnace with the same air distribution

system and an identical electric water heater would have resulted in 112,094 MJ

(31,137 kWh) of energy being consumed to meet the space and water heating loads over the

two seasons, assuming that the heating elements within the water heater have an efficiency of

98%. This compares to an actual energy consumption of 45,092 MJ (12,526 kWh) to perform these two functions, or a savings of 67,002 MJ (18,612 kWh), a 60% reduction.

16
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A comparison can also be made to the total energy which would have been consumed if an

identical water heater and electric baseboard heat had been used. The air distribution system

for this study was installed under direct supervision of Potomac Edison personnel. The

entire duct system is located within interior wall partitions and between floor joists.

Approximately 70% of the air distribution system is located in the conditioned space with the

remaining portion within the unheated basement. During installation every effort was made

to minimize air leakage by sealing each individual seam. The portion of the air distribution

system within the basement was insulated to an R-5 level. Thus, for this particular duct

system, a thermal efficiency value of 85% is assumed. With this assumption, the space

heating loads using electric baseboard heat would be 15% less than the values given in Table

1. Thus, the use of an identical water heater and electric baseboard heat during months in

which space heating was required would have resulted in 97,900 MJ (27,194 kWh) of energy

being consumed to meet the space and water heating requirements compared to the measured

energy consumption of 45,092 MJ (12,526 kWh), a 54% reduction.

The energy consumed by the residence, water heater, supplemental heaters, and heat pump is given in columns D, E, F, and G of Tables 2 and 2A on a monthly, seasonal, and annual

basis. Table 2 uses the SI system of units whereas Table 2A uses the conventional IP system

of units. The tables are discussed in greater detail in the section entitled "Advanced

Integrated Heat Pump System Performance." The base load, which includes all miscellaneous uses of electricity within the residence such as lights, stove, clothes washer,

dryer, refrigerator, and small appliances, may be determined by subtracting the electrical

energy consumption of the heat pump, water heater, and supplemental heater from the total

energy consumption of the residence. Figure 5 shows the monthly energy consumption for

each end use. The heat pump system is the primary end user for the months of November

through March. The primary end user of electricity during the remaining months is the base

load.

The energy supplied to the resistive heating elements within the water heater represents a small fraction of the total energy consumption, ranging from 0 MJ (0 kWh) in October 1990

to 306 MJ (85 kWh) during the month of May 1991. The May 1991 value is unrepresentative due to a 1-week test during this month in which the heat pump was

prevented from heating water. During this 1-week interval, an energy balance was

performed on the water heater to ensure that the hot water load was accurately being

measured. The energy supplied by the heat pump to the water heater and energy consumed

by resistive elements within the water heater are shown for each month in Figure 6. Over

the monitoring period, the water heater represented only 1.2% of the total energy consumed,

followed by the supplemental duct heaters (3.6%), heat pump (44.7%) and base load

(50.5%), Figure 7.

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An objective of this project was to compare the measured energy consumption of the heat

pump system using an electronic digital power analyzer to measurements made using a conventional residential watt hour meter. The utility industry is concerned whether the

harmonics produced by variable-speed equipment will introduce errors in conventional watt

hour meters. For the current and voltage ranges used in this experimental investigation, the

accuracy of the electronic digital power analyzer is specified as 0.8% of the actual power

over a band width of 20 to 100 H^. The Potomac Edison Company calibrated a conventional

watthour meter in accordance with ANSI Standard CI 2- 1975 and found the meter accurate to within 0.2%.

Table 3 gives the energy consumed by the integrated variable-speed heat pump as measured

by the electronic digital power analyzer, the conventional watt hour meter and the percent

difference. With the exception of 4 months, there is less than a 0.63% difference, which is within the error bands of the two instruments. The cause of the greater disagreements

observed for the months of June 1990, October 1990, May 1991, and May 1992 is not

known. Over the entire 2-year monitoring period, the energy consumption measured by both

instruments was essentially identical, 50,662 MJ (14,073 kWh) versus 50,669 (14,075 kWh).

This finding is consistent with studies performed by Baldwin et al [3] who found that the

average meter error due to distorted current waveforms caused by a single-phase variablespeed AC motor drive was less than 0.8%. Grady [4], however, has voiced concern over

possible metering errors which may result if a significant number of variable-speed motors

are connected on the same utility feeder.

Hourly Electrical Demands

The maximum hourly electrical energy demand for the total residence, heat pump, water

heater, and supplemental heaters is shown on a monthly basis in Figure 8. Excluding the

peak for the residence (which is the sum of the base load, water heater, heat pump, and

supplemental), the greatest peak demand was due to the supplemental space heaters,

5.30 kJ/s (5.30 kW) which occurred during the month of January 1991. The peak demand

imposed by the heat pump ranged from 1.89 kJ/s (1.89 kW), measured in August 1991, to 3.70 kJ/s (3.70 kw) measured during the month of February 1991. The highest electrical

demand recorded for the water heater was 2.97 kJ/s (2.97 kW) occurring during the month

of February 1992. The peak demand imposed by the total residence ranged from 5.80 kJ/s

(5.80 kW) in June 1990 to a high of 17.00 kJ/s (17.00 kW) recorded during the month of

November 1990.

The Allegheny Power System consists of three utilities, Monongahela Power Company, West

Perm Power Company, and The Potomac Edison Company which is the electrical utility to which the residence is connected. An objective of the project was to document the

relationship between the electrical loads of the residence and the peak loads encountered by

The Potomac Edison Company and overall the Allegheny Power System. The hourly

electrical demands present when peak load conditions were being experienced by the

Allegheny Power System (APS) are shown in Figure 9. A comparison of the monthly peak

24
TABLE 3 COMPARISON OF MEASURED ENERGY CONSUMFFION USING

ELECTRONIC DIGITAL POWER ANALYZER AND

ELECTRIC UTILITY WATTIIOUR METER

Year Month

Electronic Power

Digital Analyzer

Electric Utility Watt Hour Meter I CI CClll Difference (%) MJ kWh MJ kWh

1990 June ivj / 1 .U zy / . 3

1 ACT Q 105 /.j 293.7 + 1.3

1990 July 1 "lAl o I ZHZ. .U 1z3j.j 343.2 + 0.5

1990 August 'XA 1 9 1 .z

1 99 A Q izzD.y +0.1

1990 September oy 1 .U 947 S Zt / .J 8Q4 9 9/1 Q /I -0.4

1990 October 1 1 /Z.J jZJ . /

I 1 QQ Q I I yy .y 1 T 1 T J J J .J -2.4

1990 November ODo . 1 9zjy"107 6 / .0 AAA o 000.

u

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1990 December QQ9 6 JJJD.O 088 yoo .un +0.5

1991 January Afil') HU 1 / Z . 1

11 9Q7 Z!7 / . 8o 467^ HO 1 J .y0 1 908 ^ -0.0

1991 February y^J . / jjyy. 1 044 y44 9.Z +0.2

1991 March 909^ 7 819 7 o 1 Z. / 9097 zyz / .3 8o 1119 J .Z -0.1

1991 April 1 "^Q^i 1 1 J 7U . 1 ^87 J o / . 8o 1 "IQfl 7 186 1 + 0.4

1991 May 1 UL) . -? 1 06 9 719 / 1 Z . 8o 1 08 n -0.9

1991 June 1 ^Q9 1 1 jyL . 1 ^86 7 1

1 "^04 jy4.o6 187 JO / .44 -0.2

1991 July 1 son 8 AA 1 Q 1 7 1 J jy. / 449 7 44Z. / -0.2

1991 August 1470.

U

416 410.11 1i4yAQl 9 / .z 4 1 S 0 1 J .y 0.0

1991 September 7n7 A 1 06 7ni 1 1 OS 1 1 yj . J +0.6

1991 October 11 ZU9611 . 8

o

3*in S 1766 i zoo . 8o 'KS 1 0 -0.4

1991 November 2541.2 705.9 2542.7 706.3 -0.1

1991 December 3740.4 1039.0 3739.0 1038.6 +0.0

1992 January 4063.7 1128.8 4063.3 1128.7 0.0

1992 February 3548.5 985.7 3545.3 984.8 0.1

1992 March 3297.6 916.0 3297.2 915.9 0.0

1992 April 1553.4 431.5 1563.1 434.2 -0.6

1992 May 779.4 216.5 790.6 219.6 -1.4

Total 50662.4 14072.9 50668.9 14074.7 0.0

Percent Difference = Electronic Digital Analyzer - Watthour Meter Measurements

Electronic Digital Analyzer Measurement

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hourly demands, Figure 8, and the hourly electrical demands present when APS was

experiencing peak load conditions, Figure 9, shows that the only peak load at the monitored

residence which coincided with any APS peak was the supplemental heater during the month

of April 1992. The hourly electrical demands present when peak load conditions were being

experienced by The Potomac Edison Company are shown in Figure 10. Peak loads

coincident with the Potomac Edison peaks occurred during February 1992 for the total

residence and during the months of November 1991, February 1992, and March 1992 for the

water heater.

The average hourly energy consumed by the heat pump, supplemental heaters, and water

heater are plotted versus outdoor temperature for the 1990-1991 heating season, Figures 11

(SI) and Ua (IP), and the 1991 cooling season, Figures 12 (SI) and 12a (IP). The graphs were produced by averaging the hourly energy consumption measurements within each

2-degree outdoor temperature increment. The heating season includes all hours of data

between September 1, 1990 and May 27, 1991, the period during which the homeowner

operated the heat pump in the space heating mode. The homeowner operated the system in

the space cooling mode between May 28, 1991 and September 31, 1991. Each temperature

entry includes all hours during which the temperature was greater than or equal to the value

and less than the temperature entry to its right. For example, the temperature increment

labelled 0 °C (32 °F) on Figure 11 includes all hours of data during which the outdoor

temperamre was greater than or equal to 0 °C (32 °F) but less than 2 °C (35.6 °F).

During the heating season (see fig. 11), above temperatures of 4.0 °C (39.2 °F)

supplemental energy was not required to meet the space heating load. As the outdoor

temperamre decreased below 4.0 °C (39.2 °F), the use of supplemental heat increased,

reaching an average hourly value of 15.94 MJ (4.43 kWh) when the outdoor temperature was

equal to or above -12.0 °C (10.4 °F) and less than -10.0 °C and (14 °F). It is interesting to note, Figure 11a, that as the outdoor temperature decreased below -6.7 °C (20 °F), the

average hourly energy consumed by the heat pump decreased and became essentially

constant. This is attributed to the heat pump's control logic which limits the compressor

speed to approximately two-thirds its maximum value for outdoor temperatures below - 8.3 °C (17 °F). The accompanying reduction in space heating capacity resulted in the heat

pump operating continuously during each hour in an attempt to meet the space heating load,

with the supplemental heat providing the difference between the space heating load and the

heating capacity of the heat pump.

The difference between the actual temperamre at which the hourly energy consumed by the

heat pump decreased, -6.7 °C (20 °F), and the control logic value of -8.3 °C (17 °F), is attributed to a temperamre difference between the outdoor temperature sensor and the sensor

utilized by the heat pump's control logic. The outdoor sensor is located on the north side of

the residence at an elevation of 8 feet. The heat pump's sensor is located on the exterior of

the heat pump at an elevation of 6 inches. A short-term experiment was conducted in which

two calibrated thermocouples, one positioned at the outdoor temperature sensor location and

a second one adjacent to the heat pump's outdoor temperamre sensor, were used to measure

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the temperature at these two locations for ten days. During the experiment the outdoor

temperature ranged from -7.8 °C (18 °F) to 0.6 °C (33 °F). The average temperamre

measured adjacent to the heat pump's sensor was found to be 1.3 °C (2.4 °F) less than that

measured by the ambient sensor, which explains the discrepancy in outdoor temperature at which the compressor's speed reduction occurred.

The energy consumed by the resistance elements within the water heater tends to be

negligible for outdoor temperatures between 0 °C (32 °F) and 18 °C (64.4 °F) during the

heating season. At temperatures below this range, the energy consumed by the water heater

increased with decreasing outdoor temperature. As the space heating load increases, the

indoor fan speed increases, supplying more heat to the space heating load and less to the

water heating load. Additionally, whenever supplemental heat is required, the control logic

prevents water heating by the heat pump and only the resistance heaters within the water

heater are used to meet the water heating load. Finally, when the outdoor temperature is less

than -8.3 °C (17 °F) the control logic does not permit water heating by the heat pump.

As expected, the average hourly energy consumption of the heat pump increased with

outdoor temperature during the cooling season. Figures 12 and 12a. The average energy

consumed by the water heater is less than 0.36 MJ (0.1 kWh) for any 2-degree temperature

increment and in general decreased as the outdoor temperature increased. The greater usage

of energy for heating water at the lower ambient temperamres during the cooling season may

be attributed to the fact that the lower outdoor temperatures tend to occur during the early

morning hours which coincide with the greatest demand for hot water within this residence.

Indoor and Outdoor Temperatures

The thermostat, located within the living room, was set to 25.6 °C (78 °F) during the

cooling seasons and 22.2 °C (72 °F) and 21.1 °C (70 °F) during the first and second heating

seasons, respectively. The measured average indoor temperamre for each month is shown in

Figure 13. During the cooling seasons, the average monthly indoor temperature ranged from

23.4 °C (74.2 °F) to 25.2 °C (77.3 °F), with an overall average of 24.3 °C (75.7 °F).

Average indoor temperatures of 21.4 °C (70.6 °F) and 21.1 °C (70.0 °F) were maintained

during the 1990 and 1991 heating seasons, respectively.

The variation in living room temperature for a representative month, January 1991, is shown

in Figure 14. The radiation-shielded thermocouple which measures the living room

temperature is in close proximity to the thermostat. As expected, the master bedroom and

family room temperatures, Figures 15 and 16, show greater variations than those measured

within the living room. During the month, with a 22.2 °C (72 °F) thermostat set point, the

average temperature within the living room was 22.3 °C (72.1 °F) with hourly minimum and

maximum values of 21.3 °C (70.4 °F) and 22.9 °C (73.2 °F). The master bedroom's

temperature ranged from 19.4 °C (67.0 °F) to 24.4 °C (75.9 °F) with an average value of

22.4 °C (72.3 °F). The average family room temperature was 20.7 °C (69.3 °F) with

temperamres varying from 17.7 °C (63.9 °F) to 22.6 °C (72.7 °F).

34
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36

38
A similar temperature variation between the three rooms exists during the cooling season months. As an example, during the month of August 1991, the average living room

temperamre was 25.4 °C (77.7 °F), the average master bedroom temperature was 25.0 °C

(77.0 °F), and 23.7 °C (74.7 °F) was recorded for the family room. The consistently lower

family room temperamre, observed during both the heating and cooling seasons, is attributed

to the presence of an on-grade concrete slab floor.

The average monthly outdoor temperatures are shown in Figure 17, ranging from a value of

25.0 °C (77.0 °F) recorded for the month of July 1991 to a monthly average of 1.1 °C

(33.9 °F) recorded for January 1991. The highest hourly temperamre recorded during the

2-year study was 37.1 °C (98.8 °F) recorded at 5 p.m. on July 21, 1991. The lowest

temperature recorded was -12.2 °C (10.1 °F) on January 19, 1992 at 9 a.m. The number of

18.3 °C (65 °F) heating degree days was 4,156 during the 1990-91 heating season and 4,711

during the 1991-92 heating season. Figure 18 shows the relationship between the space

heating load and the number of heating degree days for each month.

Advanced Integrated Heat Pump System Performance

The advanced integrated heat pump system became operational in February 1990, 3 months

before the monitoring effort commenced. After 3 years of operation, there have been two

problems associated with the heat pump system. A noisy electrical contactor was replaced

during the monitoring period with no loss of data. The water pump used to circulate water

from the water heater through the refrigerant-to-water heat exchanger failed after the

monitoring was complete.

The performance of the heat pump is summarized in Tables 2 and 2A on a monthly,

seasonal, and annual basis. The thermal load of the residence is separated into heating and

cooling loads, column C. The space conditioning loads for the two heating seasons were

essentially equal, whereas the 1991 space cooling load was substantially greater than the

space cooling load measured in 1990, 14,707 MJ (4085.4 kWh) versus 11,322 MJ

(3145.0 kWh). During the months of September 1990 and May 1991 the heat pump operated

in both the space heating and cooling modes. The total energy consumed by the heat pump

system (neglecting the supplemental heater), column G, is divided into energy consumed in

the various operational modes in columns H through L. Figure 19 shows the energy

consumed by the heat pump, ignoring the supplemental heater, in its various modes for each

month from June 1991 to May 1992. The data collection software did not initially permit the

breakdown of total heat pump energy consumption into the energy consumed during various

modes of operation, and was altered at the end of July 1990 to obtain this additional

information. During the 1991 cooling season (May 1, through September 31), 2,235.6 MJ

(621.0 kWh) of energy was consumed in the combined space cooling and water heating mode

compared to an energy consumption of 1,881.7 MJ (522.7 kWh) while operating in the space

cooling only mode. When a substantial space heating load exists, for example, November

1991 through March 1992, the majority of energy is consumed during the times in which the

39
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42
heat pump is operated in the space heating only mode 8,414 MJ (2337.2 kWh), followed by

space and water heating 5,640 MJ (1566.7 kWh), and finally water heating only, 2,715.5 MJ

(754.3 kWh). The heat pump consumes the largest amount of energy while operating in the

water heating only mode during temperate months, such as September, October, March, and

April. Column N lists the space conditioning mode in which the heat pump operated during

each month.

The monthly cooling coefficients of performance, Column O, and monthly heating

coefficients of performance, Column P, are computed using data collected when the heat

pump was operating in the space conditioning only mode. Thus, the energy consumed by the

heat pump and space conditioning loads during time intervals in which the heat pump was

operating in the combined or water heating only modes are not included in these columns.

The total parasitic energy, the energy consumed when the unit is not space conditioning

and/or water heating, is included in the calculation of the monthly cooling and heating

coefficients of performance. Parasitic energy is computed by taking the total heat pump

energy, column G, and subtracting the energy consumed for each of the operational modes,

columns H through L. During months in which both space heating and cooling took place,

the parasitic energy is allocated in proportion to the length of time the heat pump operated in

each mode.

The monthly cooling coefficient of performance is defined as

Qlsco MCCOP = z!±}±L (1)

^SCO ^ ^PAR

where Qlsco monthly space cooling load when the heat pump provides space

cooling only, MJ (MBtu),

E^j-Q is the monthly energy consumed by the heat pump when the unit operates

in the space cooling only mode, MJ (kWh),

and ^?AR represents the monthly energy consumed by the heat pump when the unit

is not providing any space conditioning and/or water heating, MJ (kWh).

The monthly cooling coefficient of performance ranged from a low value of 2.50,

September 1991, to 4.03 recorded for the month of June 1990. The inclusion of parasitic or "standby" energy has a significant impact on both heating and cooling coefficients of

performance. This impact is greatest for months in which a low space conditioning and/or

water heating load exists. For example, during the month of September 1991 the coefficient

of performance was 2.5, but would have been 4.40 if no parasitic energy was consumed

during standby intervals.

43
The cooling seasonal coefficient of performance is defined as,

n Qlsco

CSCOP = ^1 (2)

n n ^^SCO ^ XI ^PAR

i=l i=l

where the monthly quantities Qlsco ' ^sco^ ^par summed over the number of

months, n, is which space cooling only took place. The cooling seasonal coefficient of

performance for the 1990 season was 3.72 (corresponding to a SEER of 12.68 Btu/Wh),

whereas for the second cooling season, the heat pump achieved a cooling seasonal coefficient

of 3.52 (corresponding to a SEER of 12.02 Btu/Wh). Without parasitic energy consumption,

the SEER values would have risen to 14.83 Btu/Wh and 14.49 Btu/Wh, respectively. The

annual cooling coefficients of performance, 3.73 for the first year of the study and 3.50 for

the second year, are calculated using eq (2) and summing the variables over each year.

In a similar manner, the monthly heating coefficient of performance is defined as MHCOP = - ?^ (3)

^SHO ^SUPP ^PAR

where Qlsho the monthly space heating load when the heat pump provides space

heating only, MJ (MBtu),

Egupp is the monthly energy consumed by the supplemental electric resistance

heaters, MJ (kWh),

and ^suo monthly energy consumed by the heat pump when the unit

operates in the space heating only mode, MJ (kWh).

The monthly heating coefficient of performance ranged from a low of 0.91, May 1991, to 3.33 for the month of April 1991. The lower values tended to occur primarily during

months in which the energy consumed by the heat pump in the "standby" mode is significant

in comparison to the energy consumed by the heat pump while operating in the space heating

only mode. The higher heating coefficients of performance occurred for months in which a

significant space heating load existed, which was met without the assistance of the

supplemental resistance heaters.

The heating seasonal coefficient of performance is computed in an identical manner to that

used to compute the monthly heating coefficient of performance, eq (3), except the space

heating load, energy consumed by the heat pump while operating in the space heating only

mode, supplemental energy consumption, and parasitic energy are the seasonal totals, rather

than monthly values. The heating seasonal coefficients of performance and annual heating

44
coefficients of performance were all identical with a value of 2.63 corresponding to a heating

seasonal performance factor of 8.98. Without parasitic energy consumption, the heating

seasonal coefficient of performance would have risen to a value of 2.82 for the 1990-91

heating season and 2.80 for the 1991-92 heating season.

Column Q, the water heater coefficient of performance, is a performance index based on data

collected during times in which the heat pump operates in the water heating only mode, i.e.,

COP = ^^^^^

(4)

^WHO

where Qhpwh the energy delivered by the heat pump to the water heater when the

unit operates in the water heating only mode, MJ (Btu),

and Ey^ho represents the energy consumed by the heat pump when the unit

operates in the water heating only mode, MJ(kWh).

The monthly water heating coefficients of performance are plotted versus average monthly

outdoor temperature in Figure 20. As expected, the higher the average outdoor temperature

the greater the water heating coefficient of performance, ranging from a value of 1.11,

January 1991, to an upper value of 2.05 for July 1991. The seasonal and annual values were

calculated by summing the variables in eq (4) over the appropriate time intervals. The

seasonal water heating coefficients of performance for the 1991 and 1992 cooling seasons are 1.92 and 1.96, compared to 1.42 and 1.40 for the heating seasons. The annual water heating

coefficients of performance were 1.47 for June 1990 through May 1991 and 1.50 for June

1991 through May 1992.

The combined performance factor, Column R, is an index proposed by Dougherty [1-2] to quantify the performance of combined appliances. This factor represents the ratio of the

energy delivered by the heat pump and water heater in the form of space heating, space

cooling and/or water heating loads to the energy consumed by the heat pump, supplemental

heaters, and water heater, i.e.

^pp, ^ QcL ^ Qhl Qhwl

^HP ^ ^SUPP ^WH

where Q(^^ is the total monthly space cooling load, MJ (MBtu)

QhlIS the total monthly space heating load, MJ (MBtu)

Qhwl ^^^^^ monthly domestic water heating load, MJ (MBtu)

45
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46
Efjp is the total monthly energy consumed by the heat pump excluding

supplemental energy consumption, MJ (MBtu)

E^upp is the total monthly energy consumed by the supplemental heaters,

MJ (MBtu)

and E^,f^ is the total monthly energy consumed by the water heater, MJ (MBtu).

Figure 21 shows the combined performance factor for each month which ranged from a low

of 1.55 to a high of 3.5. The combined performance factors are substantially greater during

the cooling months as opposed to months when space heating is required. Tables 2 and 2A.

This can be partially attributed to the fact that during the space cooling season, energy

removed from the house is transferred to the water heater, the supplemental resistive heaters

are not needed, and energy is not removed from the water heater to defrost the outdoor coil.

The cooling season, heating season, and annual combined performance factors. Tables 2 and

2A, are computed in an identical manner to that used to compute the monthly combined

performance factors except the values in eq (5) are summed over appropriate time intervals.

The combined performance factor for the entire 24 month monitoring period is 2.47. Thus,

for every unit of energy consumed by the heat pump and water heater, 2.47 units were

supplied in the form of domestic water heating, space heating, and/or space cooling. The

effect of parasitic energy consumption has a relatively small effect on the combined

performance factor. For example, if the heat pump had not consumed any parasitic energy

during the second year, the combined performance factor would have increased from 2.45 to 2.51, a 2.4% increase.

47
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48
SUMMARY

An integrated heat pump/water heating appliance was extensively monitored for 2 years. The

heat pump system incorporated variable-speed components, microprocessor-based control

logic, and a refrigerant-to-water heat exchanger. The heat pump used in this study operates

in five-distinct modes: space cooling only, space cooling and water heating, space heating

only, space and water heating, and water heating only.

The heat pump was instrumented with temperature, relative humidity, watt/watthour, air flow

rate, and water flow rate transducers. An electronic digital power analyzer was used to monitor the energy consumption of the heat pump in addition to a conventional residential

watthour meter, in order to address concerns regarding the accuracy of conventional utility

metering equipment when variable-speed equipment is present within a residence.

The total energy consumed by the residence after installation of the heat pump system was an

estimated 52% less than the amount consumed prior to the study, by electric baseboard

heaters, a wood stove, and window air-conditioners. The latter were used to cool

approximately one-third of the residence. A comparison between the electrical energy

consumed by the heat pump and water heater during the monitoring period to the energy

which would have been consumed if an electric furnace with the same air distribution

systems and an identical water heater had been used during the space heating months

suggests a 60% reduction in total electrical energy consumption.

The electric resistance heaters within the water heater accounted for 1.2% of the total energy

consumed by the residence, after the integrated heat pump/water heating appliance was

installed, followed by the supplemental resistance heaters (3.6%), heat pump (44.7%), and

base load (50.5%). Agreement between the measured energy consumption of the heat pump

system using two different instruments, a residential watthour meter and an electronic digital

power analyzer, over the entire 2-year monitoring period was excellent. Month-to-month

variations ranged from -1.4% to 2.4% with variations for the vast majority of months being

within the error bands of the two instruments, 0.6%.

The maximum hourly demand for the residence, heat pump, water heater, and supplemental

heaters was recorded for each month. The peak demand of the residence ranged from

5.80 kJ/s (5.80 kW) in June 1990 to a high of 17.00 kJ/s (17.00 kW) during the month of

November 1990. The highest peak demands recorded during the study were 3.70 kJ/s

(3.70 kW) for the heat pump, 5.30 kJ/s (5.30 kW) for the supplemental resistance heaters,

and 2.97 kJ/s (2.97 kW) for the water heater.

The average energy consumed by the heat pump, supplemental heaters, and water heater was

computed for 2 °C and 2 °F increments over the range of outdoor temperatures encountered

during the study. During the heating seasons, the use of supplemental heaters was not

required to meet the space heating load when outdoor temperatures exceeded 4.4 °C (40 °F).

As expected, the average hourly energy consumption of the supplemental heaters increased

49
with decreasing outdoor temperature, reaching a value of 15.94 MJ (4.43 kWh) as the

outdoor temperature approached -11.1 °C (12 °F). As the outdoor temperature decreased

below -6.7 °C (20 °F), the hourly energy consumed by the heat pump became constant due

to control logic which limits the compressor speed to two-thirds of its maximum value for

outdoor temperatures below -8.3 °C (17 °F), while supplemental energy consumption

increased to meet the space heating load. During the cooling season, the average hourly

energy consumption of the heat pump increased with increasing outdoor temperature reaching

a value of 6.59 MJ (1.83 kWh) for ambient temperatures exceeding 36.7 °C (98 °F). The

average hourly energy consumption values for the water heater during the cooling season were always less than 0.05 MJ (0.05 kWh), independent of the outdoor temperature.

The majority of energy used by the heat pump during the heating season is consumed while

providing space heating only, closely followed by energy consumed when operating in the

combined space and water heating mode. During the cooling seasons, the energy consumed

by the heat pump while operating in the space cooling mode is roughly equivalent to that

consumed by the heat pump while operating in the combined space cooling and water heating

mode. The quantity of energy consumed while operating in the water heating only mode

tends to be substantially less than that used during operating in the space conditioning only or combined modes. The exception is for temperate months such as September, October, April,

and May. The monthly parasitic energy was relatively constant having an average value of

100.8 MJ (28 kWh).

The monthly cooling coefficient of performance ranged from a low value of 2.50 to a value

of 4.03. The inclusion of parasitic or "standby" energy had a significant impact on the

monthly cooling efficiency ratio for months in which the space cooling load and/or water

heating load is small. For example, the lowest value of the monthly cooling coefficient of

performance was 2.5, but would have been 4.40 if parasitic energy was not consumed during

standby intervals. The seasonal cooling coefficients of performance were 3.72 (SEER of

12.70 Btu/W) and 3.52 (SEER of 12.02 Btu/W) for the 1990 and 91 cooling seasons,

respectively.

The monthly heating coefficients of performance ranged from 0.91 to 3.33. The higher

values were recorded during months in which a significant space heating load existed which

was met without the assistance of supplemental resistance heaters. The lower monthly values

occurred during periods in which parasitic energy was a significant portion of the total

energy consumed by the heat pump. The heating seasonal coefficients of performance were

identical for the two heating seasons, 2.63 equivalent to an HSPF of 8.99 Btu/Wh.

The monthly water heating coefficients of performance ranged from a value of 1 . 11 to an

upper value of 2.05. The values for the cooling seasons were 1.92 for 1990 and 1.96 for

1991, as compared to the 1.42 and 1.40 values recorded during the 1990-91 and 1991-92

heating seasons. The water heating coefficient of performance was found to be proportional

to the outdoor temperature.

50
A performance indicator proposed by Dougherty [1-2] to quantify the overall performance of

combined appliances was utilized in this study. This indicator, named a combined

performance factor, is the ratio of the space conditioning and water heating loads divided by

the energy consumed by the heat pump for space heating and cooling, supplemental heaters,

and water heater. A combined performance factor of 2.0 would indicate that for every unit

of energy consumed by the heat pump, supplemental heaters, and water heater two units of

energy were delivered by the heat pump and water heater to meet the space cooling, space

heating, and/or water heating loads. The monthly combined performance factor ranged from

a low of 1.5 to 3.5. The seasonal combined performance factors for the cooling seasons were substantially higher than those obtained during the heating seasons. For example, the

1990 cooling season combined performance factor was 3.18 compared to a value of 2.34 for

the 1990-91 heating season. The combined performance factor for the entire 24 month

monitoring period was 2.45. Thus, 2.45 units of energy were delivered for space

conditioning (heating and cooling) and water heating for every unit of electricity purchased.

51
ACKNOWLEDGMENTS

This research has been supported by the Allegheny Power System through The Potomac

Edison Company. The author would like to thank the following employees of the Allegheny

Power System: Timothy Croushore, Jerry Davis, Bill Guyker, and John Hose for project

guidance; Merle Guyton, Chuck Barger, and Dave Raymer for installing the advanced

integrated heat pump system and associated duct work; and Chuck and Mary Barger who

volunteered their home for the study and assisted NIST in all phases of the project.

Kevin Dunshee and John Ferguson of the Carrier Corporation have been extremely helpful in

answering questions related to the operation of the heat pump system used in this study.

Their eagerness to help is greatly appreciated.

The following NIST personnel were instrumental in conducting the project: Donn Ebberts

for calibrating and installing the instrumentation; Teresa Wright for writing the data

reduction software; Ken Kramp, Daniel Shapiro, and Chris Saunders who assisted in the

preparation of this report; Brian Dougherty, George Kelly and Steve Petersen for providing

insight and valuable suggestions throughout this project; Ray Mele for producing the graphics

within this report; and Flora Parsons for preparing the manuscript.

52
REFERENCES

[1] Department of Energy Proposed Rule on a Uniform Method for Measuring the

Energy Consumption of A Combined Heat Pump - Water Heating Appliances. To be

published in the Federal Register.

[2] Dougherty, Brian P. Laboratory Performance of A Combined Heat Pump - Water

Heating Appliance. Electric Power Research report in preparation.

[3] Baldwin, A. J. and Planer. Evaluation of Electrical Interference to the Induction

Watthour Meter. Electric Power Research Institute. Report No. EL-2315; 1982

April.

[4] Grady, W.M. Power System Harmonics and the Potential Impact of Residential ASD

Heat Pumps. Presentation to the EPRI Advanced Heat Pump Interest Group; 1991

April.

[5] Gray, L. The Complete Book of Heating with Wood . Charlotte, Vermont, Garden

Way Publishing; 1977.

[6] ASHRAE. 1992 ASHRAE Handbook-HVAC Systems and Equipment. American

Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.; 1992.

p 30.5.

53

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Field Monitoring of a Variable-Speed Integrated Heat Pump/Water Heating Appliance

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ABSTRACT (A 1 500-CHARACTER OR LESS FACTUAL SUMMARY OF MOST SIGNIFICANT INFORMATION. IF DOCUMENT INCLUDES A SIGNIFICANT BIBLIOGRAPHY OR LITERATURE SURVEY, CITE IT HERE. SPELL OUT ACRONYMS ON FIRST REFERENCE.) (CONTINUE ON SEPARATE PAGE, IF NECESSARY.)

This report summarizes a study in which a variable-speed integrated heat pump/water heating apphance was monitored for two years while meeting the space conditioning and water heating needs

of an occupied residence. Experimental results are presented which show that the total energy consumed by the residence was significantly reduced compared to previous years in which electric baseboard heat, a wood stove, and window air-conditioners were used. During the two space heating seasons, the variable-speed integrated heat pump/water heating appliance used 60% less energy than would have been consumed by an electric furnace with the same air distribution system and a storage-type electric water heater.

The monthly space cooling only coefficients of performance ranged from 2.50 to 4.03, whereas, the monthly space heating only coefficients of performance ranged from a low of 0.91 to a high of

3.33. A proposed index to quantify the overall system performance of integrated water heating/space conditioning appliances, referred to as the combined performance factor, ranged from 1.55 to 3.50. The majority of larger values occurred during months in which space cooling dominated. The combined performance factor for the entire two-year study was 2.45.

A conventional watthour meter supplied by the local electrical utility and an electronic digital power analyzer were used to measure the energy consumption of the variable speed heat pump in order to discern if variable-speed equipment introduces errors in conventional utility metering equipment. Measurements made using die two instruments were in excellent agreement.

The monthly energy consumption and peak electrical demands of the residence, integrated heat pump/water heating appliance, supplemental space heater, and water heater are discussed. The

influence of outdoor temperature on electrical power demand is presented.

KEY WORDS (MAXIMUM 9 KEY WORDS; 28 CHARACTERS AND SPACES EACH; ALPHABETICAL ORDER; CAPITALIZE ONLY PROPER NAMES)

building technology; coefficient of performance; combined performance factor; field study; heat pump; HSPF; integrated water heating; peak demand

SEER; thermal performance; variable speed

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Order the following NIST publications — FIPS and NISTIRs—from the National Technical Information

Service, Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PUB) — Publications in this series

collectively constitute the Federal Information Processing Standards Register. The Register serves

as the official source of information in the Federal Government regarding standards issued by

NIST pursuant to the Federal Property and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717 (38 FR 12315,

dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

NIST Interagency Reports (NISTIR)— A special series of interim or final reports on work

performed by NIST for outside sponsors (both government and non-government). In general,

mitial distribution is handled by the sponsor; public distribution is by the National Technical

Information Service, Springfield, VA 22161, in paper copy or microfiche form.
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