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PUBLICATIONS

IMBSIR 81-2372

AlllOb 4D7D3Q

Development of An Energy Test

Method for A Dedicated

Water-Heating Heat Pump

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Washington, DC 20234

November 1981

Issued January 1982

Prepared for U.S. Department of Energy

Washington, DC 20545

^ak Ridge National Laboratory

ak Ridge, Tennessee 37830

31-2372

1981

c. 2
Printed in the United States of America. Available from

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road, Springfield, Virginia 22161

NTIS price codes—Printed Copy: A04 Microfiche A01

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency

thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein

to any specific commercial product, process, or service by trade name, trademark,

manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not

necessarily state or reflect those of the United States Government or any agency

thereof.
NBSIR 81-2372

DEVELOPMENT OF AN ENERGY TEST

METHOD FOR A DEDICATED

WATER-HEATING HEAT PUMP

NATIONAL IVUitl

or STAKftUEM

UBNAJtT

FEB 1 0 198?

not ate..

a

C. Andrew Wan

Robert L. Palla, Jr. James E. Harris

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Washington, DC 20234

November 1981

Issued January 1982

Prepared for U.S. Department of Energy

Washington, DC 20545

and

Oak Ridge National Laboratory

Oak Ridge, Tennessee 37830

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
SWMAWAS'JS *9-0

'J «A»SiW

r .? r m
FOREWORD

This report is submitted to the U.S. Department of Energy /Oak Ridge National

Laboratory by the Building Equipment Division, National Bureau of Standards,

under the Interagency Agreement No. EW-78-I-05-5750 , Task C. The purpose of

this report is to present a test method for the water heating heat pump

coupled with a 50-gallon electric water heater and an appropriate formula for

calculating the energy consumption of the system based on test measurements.

The work was focused on a unit having a water flow control device. Subsequent

to the initiation of this work, other manufacturers developed units which do

not have a water flow control device. An approach is suggested to normalize

this feature but verification of its reasonableness has not been done.

In general, the International System of Units (SI) is used as the primary

system with the customary equivalent in parentheses. In other cases, only

the customary units are provided where customary usage is well established

or where consistency with the units of the published test procedure in the

Federal Register is provided. Table 6 for conversions of units is provided

on page 43.

Many of the usual rating features depend on the size and materials of the

water heater. Because this study involved only one water heater and hook-up

to the water heating heat pump, the general applicability of the results is

limited.

Thus, although the report provides insight for preparation of an acceptable

test procedure, it should be used only as a starting point.
'
Table of Contents

Page

I . INTRODUCTION 1

II . DEFINITIONS 2 1. Water-Heating Heat Pump 2 2. Temperature-Sensitive Water Flow Control Valve 2 3. First Pass 2 4. Latter Passes 2

III. TEST METHOD - PROPOSED MODIFICATIONS 2 1. Installation 2 2. Test Room 3

3. Thermocouple Installation - Interior 3

4. Thermocouple Installation - Test Room 3

5. Test Room Ambient Temperature 4

6. Test Room Relative Humidity 4

7. Setting the Tank Thermostat 4

8. Water Supply 4

9. Setting the Flow Control Valve (FCV) 4

10. Recovery Efficiency 5 11 Standby Loss 5

12. Recovery Efficiency of Latter Passes 6

13. Power Input Determination 6

IV. RATIONALE AND COMMENTS FOR TEST METHODS AND PROCEDURES USED 6

1. Installation 6

2. Test Room 7 3. Thermocouple Installation - Interior 7 4. Thermocouple Installation - Test Room 7 5. Test Room Ambient Temperature 7 6. Test Room Relative Humidity 8

7. Setting the Tank Thermostat 8

8. Water Supply 8

9. Setting the Flow Control Valve 8

10. Recovery Efficiency 9

11. Standby Loss 9

12. Recovery Efficiency of Latter Passes 10

13. Power Input Determination 10

V. LABORATORY TEST PROGRAM 10

1. Introduction 10

2. System Description 10

3. Test Facilities and Instrumentation 12

4. Tests and Results 13

5. Performance Indices ^ 18

VI. CONCLUSIONS 19

REFERENCES 44
List of Tables

Page

Table 1 Results of recovery efficiency tests 21

Table 2 Results of standby loss tests (based on E = 2.40) 21

Table 3 Water draw schedule 22

Table 4 Daily energy consumptions calculated based on measured

recovery efficiency and standby loss and assigned

temperature rises and water consumption 23

Table 5 Comparison of calculated and measured daily energy

consumption 23

Table 6 Units Conversion Table 43
List of Figures

Page

Figure 1 Water heater heat pump setup 24

Figure 2 Schematic of water supply system for draw tests 25

Fiugre 3 Schematic representation of data acquisition/reduction

system 2o

Figure 4 Temperature inside the water storage tank during

97

recovery tests *•'

Figure 5 Average water temperature, ambient air temperature,

and heat pump power during recovery test 28

Figure 6 Heat pump inlet and outlet water temperature during

recovery test 29

Figure 7 Recovery test efficiency and power input vs. ambient

temperature, T£-12.8°C, Tf=62.8°C. FCV setting =46.1°C 30

Figure 8 Temperature inside the water storage tank during standby

test 31

Figure 9 Average water temperature, ambient air temperature, and

heat pump power during standby test 32

Figure 10 Standby loss versus ambient air temperature 33

Figure 11 Temperature inside water storage tank during a draw test 34

Figure 12 Average water temperature and ambient air temperature

during draw test 35

Figure 13 Temperature inside the water storage tank during recovery

test with the FCV removed 36

Figure 14 Temperature inside the water storage during recovery test

with FCV setting = 48.3°C 37

Figure 15 Heat pump inlet and outlet water temperature during recovery

test with FCV setting = 48.3°C 38

Figure 16 Recovery efficiency at different FCV settings with a 24°C

ambient temperature 39

Figure 17 Average water storage tank temperature and ambient

temperature during cooldown test 40

Figure 18 Daily energy consumption 41

Figure 19 Coefficient of performance versus heat pump inlet

temperature, with a 27 °C ambient temperature 42
ABSTRACT

Modifications of the Department of Energy test procedure for water heaters

"Uniform Test Method for Measuring the Energy Consumption of Water Heaters"

were made to include a dedicated water heating heat pump, system equipped

with a 50-gallon electric water heater tank. Also presented are laboratory

tests and results which provided the basis for the test methods used. Tests

included determination of recovery efficiency, standby loss, and water heater

jacket loss — all under static or no-draw conditions — and a dynamic test in

which water is withdrawn according to a "typical-use" schedule. Energy re- quirements predicted by the proposed (static) procedure were in good agreement

with measured energy consumption for the dynamic test in limited testing.

Key words: energy conservation; energy consumption; flow control valve;

heat pump; stratification; test method; water heater
I . INTRODUCTION

Conventional water heaters (WH) for which accepted test methods exist use oil,

gas, or electricity as the energy source. With the effort to conserve energy

in recent years, novel appliances that require less energy usage to satisfy

hot water needs have been developed. One of these appliances is an integral

type heat pump water heater (HPWH) , for which a test method was recently

developed [1]* by the National Bureau of Standards (NBS) for the Department

of Energy (DOE) /Oak Ridge National Laboratory (ORNL) . This report now concerns

the separated type appliance; namely, a dedicated water heating heat pump (WHHP)

connected to an electric water heater (EWH) tank.

The WHHP is a separate heat pump (HP) system intended for retrofit to an existing electric, oil, or gas-fueled water heater and as a substitute for the

electric heating elements or burner. The WHHP refrigerant loop consists of an evaporator, a compressor, a condenser, a refrigerant expansion device, a dryer,

and the connecting tubes. A fan blowing ambient air over the evaporator en- hances heat transfer between the evaporator and the ambient air. A pump

circulates water from the storage tank through the condenser.

The WHHP is connected to the WH tank with pipes or hoses. The drain of the

WH is connected to the inlet of condenser via the circulation pump. The hot

water outlet of the WH is connected to the outlet of the condenser via a temperature-regulated flow control valve (FCV) . Therefore, the pump, condenser,

connecting pipes or hoses, and WH form the closed water loop. When operating,

the WHHP transfers heat through the condenser to the water which is circulated

through the WH. The FCV regulates the flow rate of water passing through the

condenser to maintain an approximately constant exit water temperature. For the

WHHP used in this investigation, the FCV throttles the flow rate to a minimum of

0.2 gpm** for a minimum water temperature to the WH of 115 °F**. The FCV opens,

increasing to a maximum flow rate of 1.5 gpm** for water to the condenser

greater than 115 °F.

The HPWH described in Reference 1 and the WHHP-EWH system investigated here

differ in several important ways. The HPWH previously investigated consisted

of a heat pump (HP) and a water heater combined within one assembly. The

condenser coil of the HP was physically located in the water storage tank

and transferred heat from ambient air via the HP refrigerant directly to the

surrounding tank water during HP operation. The WHHP-EWH system has an external condenser in a circulating water loop for transferring heat from

the refrigerant to water. Also, the WHHP may be fitted to any water storage

system while the HPWH is an integral system with the condenser and storage tank

supplied as a unit. The different design and operation necessitates using a different test method for a WHHP-EWH. The development of this test method was

the objective of the present study.

*Numbers in brackets indicate references.

**These values apply only for the particular WHHP model tested.
The results of the study are presented in the next four sections. In Section

II, a list of new definitions is given. Proposed test method modifications

are given in Section III, and the rationale for these modifications are given

in Section IV. The results of an experimental study of the WHHP connected to a 50-gallon EWH are given in Section V. The experimental study was conducted in

order to develop the modifications to the WH test methods to cover the specific

WHHP-EWH system tested. A generalized test procedure for other new innovations

or combination to other sizes of storage tanks would require an extension of

this work.

II. DEFINITIONS

1. Water-Heating Heat Pump

A WHHP is a free-standing heat pump system designed to heat water in an external

water heater storage tank.

2. Temperature-Sensitive Water Flow Control Valve

A temperature-sensitive water FCV is a valve designed to regulate the flow

rate of water circulating about the condenser. The FCV acts to control the

minimum temperature of water flowing to the WH from the WHHP.

3. First Pass

The first pass is the portion of a recovery test of a WHHP-EWH system from the

beginning of the recovery test, until the time when the FCV opens above its

minimum discharge temperature or the equivalent FCV is manually opened.

4. Latter Passes

Latter passes are the portion of a recovery test of a WHHP-EWH system from

the termination of the first pass until the end of the recovery test,

III. TEST METHOD - PROPOSED MODIFICATIONS

This section describes modifications to Reference 2, "Uniform Test Method for

Measuring the Energy Consumption of Water Heaters," necessary to expand coverage

of that method to include a test method for the WHHP system investigated in this

study. Except as noted, all mention of particular section numbers refer to

sections in Reference 2.

1. Installation (Section 2.1)

Install the WHHP and the 50-gallon EWH in a test room. The EWH should be installed according to Section 2.1. In accordance with manufacturer’s installation

instructions, the electric heating elements of the EWH should be deactivated.

2
The WHHP should be placed in the vicinity of the EWH. The water connections

between the WHHP and EWH, and the FCV installation should be made in accordance

with the manufacturer's instructions. If the FCV is not adjustable and cannot

be set according to the requirement, then an equivalent FCV may be used. The

equivalent FCV system is shown schematically in figure 1. The flow control

system should be constructed of material compatible with the water connection

between the WHHP arid EWH.

The control wires of the WHHP should be connected to the thermostat of the EWH

according to the manufacturer's instructions. The power lines of the WHHP

should also be connected according to the manufacturer's instructions.

2. Test Room

The test room should be sufficient in size and capacity to provide an un- impaired operation for the WHHP-EWH system, and to provide the ambient temperature

and relative humidity specified.

3. Thermocouple Installation - Interior (Section 2.5)

The portion of Section 2.5 concerning the installation of the interior thermocouples is applicable with the addition of the provision that at least the two

uppermost thermocouples should not be installed in line with the WH return line

inlet

.

In order to determine the FCV setting, additional thermocouples should be installed as follows:

a. WHHP Inlet

A thermocouple should be installed in the water line between the EWH and

the WHHP inlet in order to measure the WHHP inlet temperature. The

thermocouple should be positioned in such a way that it is as close to

the center line of the pipe or the hose as practicable. The thermocouple

should be installed as near to the EWH as practicable.

b. WHHP Outlet

A thermocouple should be installed in the water line between the EWH and

the WHHP outlet. The thermocouple should be positioned in such a way that

it is as close to the center line of the pipe or hose as practicable. In case heated water from the WHHP returns to the EWH via the EWH hot water

outlet, then the thermocouple should be installed as near to the EWH as practicable; otherwise it may be installed anywhere along the pipe.

4. Thermocouple Installation - Test Room (Section 2.5)

The portion of Section 2.5 concerning the installation of a test room thermocouple is applicable with the addition of the provision that the test room thermocouple should be shielded against the air current originating from the

3
WHHP. The test room thermocouple should also be kept away from the water

line connections between the WHHP and the EWH. Further, the test room

thermocouple should be kept away from any air currents from the heat pump

evaporator and the heating coils of the test room’s heating and cooling

units if such units are installed.

5. Test Room Ambient Temperature (Section 2.8)

The ambient air temperature of the room should be maintained at 75 °F + 3°F

at all times during the test, The test room ambient temperature should be

taken periodically at intervals no greater than 15 minutes throughout the

duration of the test.

6. Test Room Relative Humidity (new section)

Maintain the relative humidity of the test room between 40 and 60 percent.

Relative humidity to be measured periodically at intervals no greater than

15 minutes throughout the duration of the test.

7. Setting the Tank Thermostat (Section 2.6)

In setting the tank thermostat, the procedure given in Section 2.6 is

applicable when amended by the proposed changes described in Reference 1

(i.e. , 145°F + 5°F)

.

8. Water Supply (Section 2.3)

The procedures described in Section 2.3 are applicable when amended by the

proposed changes described in Reference 1 (i.e., 53°F to 57°F)

.

9. Setting the Flow Control Valve (new section)

The recovery test of the WHHP-EWH is divided into two sequential phases. The

first phase — called first pass — lasts from the beginning of the recovery

test until the time when the FCV or its equivalent begins to open above its

minimum discharge temperature. The second phase — called latter passes —

lasts from the end of the first pass until the end of the recovery test. To ensure that the FCV or its equivalent is set correctly, the following procedure

should be observed:

Install WHHP with a EWH according to Section III.l and initiate a recovery

test

.

a. WHHP Equipped With a FCV Having a Fixed Non-Adj us table Setting

Ascertain that the FCV setting is at least 60°F above the inlet temperature

of the supply water. If not, the WHHP should be installed with a flow

control system according to Section III.l at the outlet of the heat pump.

4
A recovery test should be started with bypass Valve 3 fully closed so that the heated water passes through the needle valve. The heat pump

inlet and outlet water temperature should be monitored and the needle

valve adjusted so that the temperature rise, ATpp , is 60°F during the

first pass. Valve 3 should be opened fully for the latter passes.

b. WHHP Equipped With an Adjustable FCV

Monitor the water temperature at the WHHP inlet (Tjjpj) continuously or

at least once a minute. Determine whether the FCV is fully open at the

time when Tppp is at least 60°F or more higher than the water supply

temperature. If the FCV does not open fully at that time, drain the heated

water from the water heater, adjust the FCV setting and restart the re- covery test. This procedure should be repeated until the FCV fully opens

at a time when Tppp reaches a value 60°F higher than the water supply

temperature.

The condition of the FCV should be determined by monitoring the WHHP

temperature rise, ATpp (i.e., the WHHP outlet water temperature, TppQ,

minus the WHHP inlet water temperature, Tppj) . The FCV is considered

open if the 5-minute moving average of ATpp decreases to a quarter of

its initial (1st pass) value within 10 minutes of the time when Tppj

first exceeds 60°F above the initial supply water temperature. The FCV

is considered as open properly if, after ATpp has reduced to less than a quarter of its initial value, ATpp remains less than a quarter of its

initial value for the remainder of the test.

10. Recovery Efficiency (Section 4.1)

Install the WHHP with a 50-gallon EWH according to the procedures given in

Section III.l and adjust the FCV according to Section III. 9. The resistance

heating elements should be deactivated and the recovery test performed according to the test method as amended by the proposed amendment given in Reference

1 except for the WHHP-EWH system using an equivalent flow control device for

flow rate regulation.

For the WHHP-EWH system using an equivalent flow control device, the needle

valve should be adjusted according to Section III. 9 and then perform the recovery

test as described above. The heat pump inlet and outlet water temperatures

should be monitored at one-minute intervals. When THPI reaches a temperature

60°F higher than the supply water temperature, the shut off valve should be

opened fully so that AT^p decreases to less than 25 percent of its initial

value. The temperature rise , ATjpp, should then remain at this level for the

remainder of the recovery test. If either T^pp or Tjjpg exhibit a fluctuation,

the 5-minute moving averages of the temperatures should be used instead of

the individual measured temperatures*.

11. Standby Loss (Section 3.4)

The system of the WHHP coupled with a 50-gallon EWH should be installed according to Section III.l. The resistance type heating elements should be deactivated

and a normal operation should be established within the mean tank temperature

5
limits specified in Reference 1, For the system using an equivalent flow

control system, the shut-off valve should be fully open (Valve 2, figure 1) , Perform a standby loss test according to Reference 1 and as revised by the

proposed amendments in Reference 4,

The standby loss of the system, S, should be calculated as follows:

Z x 3412 AT,

g - _J?—kxVxAT^Xt AT

3 xtxEr2

where E^

~ the recovery efficiency of the WHHP during the latter passes as measured according to the procedure given in the next section.

All other terms are as described in Reference 2.

12. Recovery Efficiency of Latter Passes (new section)

Initiate a recovery test and record the mean tank temperature and the cumulative

energy flow to the WHHP at the beginning and at the end of the latter passes

.

The recovery efficiency of latter passes, E^ » is calculated as:

_ kxVx(T

f -TFCV)

r2 Z 0 x 3412

r2

where Z

^ = total electrical energy flow to the WHHP during the latter

passes, determined in accordance with Section 3,2.3 (in

Reference 1) in kWh.

T

f = final mean tank temperature, measured in accordance with

Section 3.6 in °F,

Tp^ = mean tank temperature at the time the FCV opens, measured

in accordance with Section 3.6 in °F.

13. Power Input Determination (Section 3.2)

The power input should be determined in accordance with the proposed procedure

of Section 3.2 of Reference 1.

IV. RATIONALE AND COMMENTS FOR TEST METHODS AND PROCEDURES USED

1. Installation

The resistance heating elements were deactivated according to the manufacturer’s

instructions for the WHHP investigated here. Operation of the resistance heating

elements would reduce the effective efficiency of the WHHP-WH system.

6
The performance of the system is a function of the FCV setting as shown in

Section V; therefore the system should be tested under the same FCV control

or equivalent conditions. A fair way of dealing with this in a general test

procedure has not been established.

2. Test Room

The selection of a narrow ambient temperature with fluctuation allowed only

within this range will minimize errors in testing. These limits do not

necessarily require an environmental chamber for testing but will require a conditioned and controlled laboratory space.

3. Thermocouple Installation - Interior

The current test method requires that the thermocouples installed to measure

the mean xvater temperature be positioned as far as possible from any obstructions such as the heating element, anodic protective device, or a water tank

or flue wall.

The interior thermocouples should be installed so that they measure the mean

tank temperature accurately, and are not affected by the stream of heated water

returning from the WHHP.

One additional thermocouple is required for tests with the WHHP equipped with

a FCV which requires adjustment under Section HI. 9. The additional thermocouple

is installed in the inlet line to the WHHP for measuring Tppp.

If the WH hot water outlet pipe thermocouple can not be used to measure TppQ,

a thermocouple should be installed in the outlet line of the WHHP.

4. Thermocouple Installation - Test Room

The current test method requires that the test room thermocouple be shielded

against direct radiation from the water heater. The WHHP also generates

convective air currents around the water heater because of the evaporator fan;

therefore, the test room thermocouple should also be shielded against this

convective air current.

5. Test Room Ambient Temperature

Tests conducted on the electric HPWH indicate that both the standby loss and

the recovery efficiency are affected by the variation of the room ambient

temperature. Therefore, the room ambient temperature should not be allowed

to vary over too wide a range. HPWH data indicate that this effect can change

recovery efficiency (Ep) by one percentage point in the measured value per

Fahrenheit degree (dry bulb)

,

Test data presented in Section V indicate that an average ambient air temperature

within a range of 75°F + 3°F is required in order to maintain the average

daily energy consumption, Cy, with + 2 percent of its value at 75°F.

7
6. Test Room Relative Humidity

Tests conducted at NBS on the electric HPWH indicate that, in general, over

the specified room ambient air temperature range, variations of 40 to 60

percent relative humidity do not appreciably affect HPWH operation. However,

high humidity conditions do tend to improve the system efficiency.

7. Setting the Tank Thermostat

Water heater thermostats are normally .factory-set at 140°F for gas and at

150°F for electric WH. DOE uses the average value of the two common factory

settings of WH thermostats. Since NBS has determined that the national average

water supply temperature is 55°F, the difference between these two temperatures,

90°F, is the required water temperature rise in the current test method. The

55 °F supply water temperature is now proposed for the electric HPWH and the

WHHP. With a required water temperature rise of 90°F, the tank thermostat

setting is specified at 145°F.

The mean tank temperature after initial cutout, therefore, should be 145 °F + 5°F

to maintain the same temperature differential and tolerance as in the current

test method.

8. Water Supply

The National Bureau of Standards has determined that the national average water

supply temperature is 55°F. The current test method specifies a 70°F supply

water temperature for the reason that a 70°F supply water temperature is less

burdensome to obtain for use in the testing of TO. Furthermore, for the general

types of gas, oil, or electric storage type TO, the supply water temperature has

a negligible effect on the determination of the water heater’s recovery efficiency

For most testing facilities, climatic conditions or other factors are such that

for all or part of the year water supply temperatures exceed 55°F. Therefore,

if a 55 °F supply water temperature were specified in the current test method,

these facilities would have an added cost of equipment and testing time to cool

the available supply water prior to conducting a test.

Using the same 70°F supply water temperature with a 90°F temperature rise for test

ing of an electric HPWP or WHHP, however, imposes a penalty on the recovery

efficiency for this type of TO. This is due to the fact that the heat pump

works more efficiently at a lower condenser temperature for the same evaporator

temperature (room temperature). A 55°F supply water temperature, therefore, is

specified for the electric HPWP as well as the WHHP.

Furthermore, in order to establish the same tolerance for variation as in the

current test method, the water supply temperature to the electric HPWH and WHHP

inlet is required to be maintained between 53°F and 57 °F.

9. Setting the Flow Control Valve (FCV)

Tests described in Section V indicate that the recovery efficiency of the system

is a function of the FCV setting. With the WHHP used in these tests, the FCV

8
setting of 115°F offers the highest heated water tempeature during the first

pass without significantly adversely affecting the recovery efficiency.

a. WHHP Equipped with an FCV Having a Fixed Non-Adjustable Setting

The FCV should act to control WHHP outlet temperatures to a minimum

temperature rise of 60°F, thus preserving a high degree of stratification

in the storage tank. If, when the flow control valve opens ATjjp is less

than 60°F, the adjustment of the first pass flow rate may be achieved by

using either the equivalent flow control system (figure 1) or by monitoring the. heating rate. For a given working condition, the WHHP has a constant heating capacity. This means a smaller flow rate gives a higher

temperature rise and vice versa. The adjustment of the needle valve is

needed to give a temperature rise of 60°F above the 55°F + 2°F supply

water temperature.

b. WHHP Equipped With an Adjustable FCV

The opening of the FCV may be identified by changes in various measured

parameters such as the sudden increase of flow rate observable via an inline flow meter; the beginning of an increase in the average power input; the end of the slight cyclic fluctuation in the WHHP outlet water

temperature; and the end of the cyclic fluctuation in input power.

Several of these indicators might be used to identify the opening of a FCV, but some might be difficult to interpret. The increase of the water

WHHP inlet and outlet temperatures and the concurrent decrease of the

temperature rise between the same outlet and inlet, however, are un- mistakable. As explained in Section V, the opening of the FCV is not a sudden and abrupt action. Therefore, the FCV is considered open if,

after the WHHP inlet temperature has risen substantially, the temperature

rise between the WHHP outlet and inlet temperature decreases substantially.

20. Recovery Efficiency

As discussed previously, the recovery efficiency is a function of the FCV

setting. Experiments discussed in Section v indicate that a FCV setting of

115°F for the WHHP used in this evaluation gives the hottest water with one pass

without degrading the efficiency significantly. In these tests, the resistance

type heating elements were deactivated. Ideally, the WHHP-WH system would be

sized such that the electric elements are not needed. A fair way of dealing with

this in a general test procedure has not been established.

11. Standby Loss

During the standby operation of the system the WHHP operates at a temperature

range higher than the FCV setting; therefore, in case an equivalent flow control

system is used, it should be arranged to allow full flow. For the same reason,

the WHHP has a higher inlet water temperature and operates at a lower recovery

efficiency. To reflect this fact in the calculation of the standby loss, a

9
different recovery efficiency is used in the equation. This recovery efficiency - called the recovery efficiency of latter passes and denoted by the symbol Er 2 - is used in the standby loss calculation.

The general way to handle standby loss is not resolved for several reasons,

including the validity of modifying a unit, the size of tank and its characteristics, and details of the WHHP to WH hookup.

12. Recovery Efficiency of Latter Passes

This recovery efficiency may be obtained with no additional testing. It provides

a more realistic calculation of the actual operation of standby loss.

13. Power Input Determination

One major difference between the EWH with immersed resistance type heating

elements and the electric HPWH and WHH is in the power output variability per

unit of power input. The former operate at a constant power input when energized

the latter operates at variable power input when the heat pump is energized. The

amount of energy an electric HPWH and WHHP consumes depends strongly on its

operating conditions.

The average input power, as such, must be determined in the recovery test as a time-averaged energy input over the duration of the recovery test. Therefore,

in the recovery test, the amount of electrical energy consumed must be determined

along with the duration of the recovery test. The average power in kilowatts (kW)

is determined as the ratio of energy used (Zr

) in kWh to the time of the recovery

test (t r ) in hours.

V. LABORATORY TEST PROGRAM

1. Introduction

This section summarizes the test program done in support of the modifications

proposed in this report. It reports the results of laboratory studies of a WHHP having a water FCV when coupled with a 50-gallon EWH. The purpose of

this work was to identify those operating characteristics and features of the

WHHP which must be addressed in modifying the existing DOE water heater test

procedures to accommodate this class of devices. It should be noted that the

results obtained and reported herein were for an EWH with specific volume,

water inlet-outlet configuration and water storage tank insulation. Performance

of a WHHP system is dependent on water heater capacity and design and will be

different for other WHHP-WH combinations

.

2. System Description

The WHHP system is comprised of a WHHP unit, including a FCV, and a water storage

tank (typically an existing EWH). A detailed description of each of these com- ponents follows.

10
2.1 Water Heating Heat Pump

The WHHP used in this investigation is packaged in an enclosure, 0.46m in

height, 0.46m in width, 0.36m in depth (18 in x 18 in x 14 in). Air is blown

over the evaporator coil by the fan while water is circulated from the bottom

drain valve of the hot water storage tank, through the ref rigerant-to-water

condenser, and back to the hot water outlet of the storage tank by the water

pump

.

The WHHP is designed as an add-on (or retrofit) to any existing WH. Although

similar to the integral HPWH described in Reference 1, a basic difference

exists between the two. This difference is in the interface between the

refrigerant condenser and the stored hot water. The HPWH condenser is submerged in the WH storage tank. The water-side heat transfer is governed by

natural convection that occurs between the coil and the surrounding water.

In the case of the WHHP, heat transfer is via a refrigerant-to-water heat

exchanger located external to the storage tank. The water-side heat transfer

is governed by forced convection. Further, the condenser of the HPWH operates

against a water temperature averaged over the height of the condenser coil.

The condenser of the WHHP, on the other hand, operates against the water

temperature at the bottom of the storage tank. This difference makes the WHHP

more susceptible to stratification in the storage tank than the HPWH. In order

to maintain a high degree of stratification for a good portion of the recovery

phase, a thermostatic FCV is used in the hot water outlet of this WHHP unit,

2.2 Water Heater

The WH used in the current tests was a 50-gallon EWH; it is shown schematically

in figure 1. The WH was originally equipped with upper and lower 4500 W heating

elements and a thermostat for each. The heating elements were deactivated for

the purpose of the current experiments and the lower thermostat was used to

activate the heat pump.

The cold water inlet is located at the top of the WH. A dip-tube is installed

inside the storage tank such that cold water is introduced at the bottom portion

of the storage tank. The dip-tube extends from the water inlet at the top to

5.1 cm (2 in) above the bottom. The drain valve is located at the side of the

WH 2.5 cm (1 in) above the bottom of the WH. The hot water outlet is located at

the top of the TO.

The water connection between the WHHP and the TO is made with 1/2 in copper

tubing. The tubing is insulated with 1/2 in polychloroprene

.

To set the TO thermostat, the TO was filled with supply water and purged of any

residual air. The water connection was also purged of air and the WHHP primed.

The tank thermostat was set and the WHHP energized. At the thermostat cut-out,

the maximum mean water heater tank temperature was measured. The thermostat was

set to maintain the maximum mean tank temperature in the range of 62.8°C + 2.8°C

(145°F + 5°F) . If the maximum mean tank temperature was not within this range

the above procedure was repeated until the requirements were met.

11
2.3 Flow Control Valve (FCV)

Since the heating capacity of the heat pump at a given working condition is

constant, the temperature rise of the water passing through the condenser is

inversely proportional to the volume flow rate. To maintain a high heat pump

water outlet temperature so that cold water is not introduced into the top of

the water storage tank, a thermostatic FCV is utilized. The FCV is located at

the outlet of the heat pump as shown in figure 1. The function of the FCV is

to restrict the flow of water through the condenser when inlet water temperatures

are low, while allowing full water flow for high inlet water temperatures. The

FCV restricted the flow rate to approximately 0.01 L/s (0.15 gpm) at the minimum

outlet water temperature of 46,1°C (115°F). The FCV opened completely and

allowed the circulating pump to maintain a flow rate of 0.10 L/s (1.5 gpm) when

the inlet water temperature to the heat pump heat exchanger exceeded 46.1°C

(115°F).

With the FCV restricting the heat exchanger outlet temperature to 46.1°C (115°F)

the temperature rise is designed to be approxiamtely 33°C (60°F) for the first

pass through the heat pump with an inlet temperature of 12.8°C (55°F) and a flow

rate of 0.01 L/s (0.15 gpm). The low flow rate allowed the stratification in

the water heater to be maintained.

3. Test Facilities and Instrumentation

3 . 1 Environmental Chamber

To perform tests at closely controlled ambient temperature, the WHHP system was installed inside an environmental chamber. During the recovery experiments, the

WHHP is an approximately constant cooling load for the environmental chamber while

the water storage tank is an increasing heating load. During the standby tests,

the heat pump is a cyclic cooling load on the enviornmental chamber, while the

water heater is an approximately constant heating load. As a result, the

environmental chamber responded differently to a standby test and to a recovery

test

.

In order to maintain approximately the same average ambient air temperature for

the different tests, a preliminary test was conducted at a desired condition and

the average ambient temperature calculated and correlated with the temperature

set point of the environmental chamber. To measure the ambient temperature, a shielded thermocouple was installed 0.61m (2 ft) from the water heater and WHHP

at a level midway between the top and bottom of the water heater.

3.2 Instrumentation

Six thermocouples were placed inside the storage tank of the water heater along

a line parallel to the axis of the cylindrical storage tank, each measuring one sixth of the water volume (see figure 1) . The thermal energy content of the water

was computed from the average of the six thermocouples. Thermocouples were also

installed at the inlet and outlet of the water heater to measure water teirneratures

during draw tests.

12
The temperature of water entering the WHHP was measured with a thermocouple

at the inlet to the WHHP. Similarly, the thermocouple at the outlet of the

heat pump measured the temperature of water exiting from the WHHP. The

temperature difference of the two thermocouples gives the temperature rise

generated by the WHHP during periods of WHHP operation.

A watt meter was used to measure the power consumption of the WHHP. A watthour meter with digital output was used to measure the cumulative energy

consumption

.

3.3 Water Supply System

In order to maintain an inlet water temperature of 21.8°C (55°F) as specified

in the test procedure, the city water (usually warmer than 55°F during the course of the tests) was mixed with ice water via a mixing valve before entering

the water heater. During draw tests, three different flow rates were selected

by opening the appropriate solenoid valve/flow rate branches shown in figure 2.

Valve operation was controlled by a microprocessor, which opened and closed

valves at preprogrammed times

.

3.4 Data Acquisition

The data acquisition system included a datalogger and a digital recorder /printer

,

as shown schematically in figure 3. The sensors included 11 thermocouples, a watt meter and a watt-hour meter. The datalogger scanned all sensors at 5-minute

intervals during non-draw periods. During draw tests at predetermined times, the

microprocessor opened one or more of the three solenoid valves to allow supply

water to flow into the water heater and the heated water to flow out of the water

heater. Concurrently, the microprocessor sent an alarm signal to the datalogger

and also turned on the supply water pump. When an alarm signal was received by

the datalogger, the datalogger changed its mode of operation. The second mode of

operation allowed the datalogger to scan the sensors at 10-second intervals.

At the termination of a draw, the microprocessor turned off the alarm signal.

The termination of the alarm signal causes the datalogger to revert back to the

regular mode of operation, sdanning sensors at 5-minute intervals, and turning

the supply water pump off.

Data scanned by the datalogger were recorded on cassette tape and simultaneously

printed for purposes of on-site monitoring. For data processing, the cassette

tape data were transmitted to the NBS UNIVAC 1108 main frame computer.

4. Tests and Results

Five different types of experiments were performed: 1) recovery, 2) standby,

3) draw, 4) recovery at different FCV settings, and 5) water heater cooldown.

The water heater tests were conducted under conditions specified in the test

method of Reference 2 where appropriate.

4.1 Recovery Tests

In preparing for the recovery tests, the WHHP was turned off. The residual air was eliminated from the WH, and the tubes between the WH and the WHHP were filled

13
with water and purged of air. The WH was filled with supply water at an average temperature slightly lower than 12.8°C (55°F) . The data acquisition

system was started when the average water temperature inside the WH was approximately constant. The WHHP was also started. The heat pump operated

until the average water temperature in the WH reached a value of 62.8°C (145°F)

,

At that temperature, the thermostat acted to cut out the heat pump. After the

final set of data was recorded, the data acquisition system was turned off.

Test results for a typical recovery test are shown in figures 4 through 7. In

figure 4, the temperature recordings of the six thermocouples inside the WH are plotted with respect to the elapsed time of test. As seen in figure 4, after the

inception of the recovery test, the water at the bottom of the WH was pumped

through the WHHP for the first time (the first pass) , causing the water temperature

at the top of the tank as measured by thermocouple 1 (TCI) to rise. A temperature

rise of 34°C (61°F) above the water temperature at the bottom of the tank was measured. As the heated water accumulates at the top of the tank, the hot/cold

water interface descends towards the bottom of the tank in a piston-like manner.

The first pass is completed when the front reaches the bottom of the storage tank.

The distinct stratification layers during the first pass are quite evident.

For example, at an elapsed time of 30 minutes, TC3 through TC6 were still at the

supply water temperature, while TC2 was at 42 °C and TCI at 47 °C, This meant

there was very little mixing of heated water with cold water - due in part to

the low flow rate caused by FCV throttling. Furthermore, the whole tankful of

water was heated in the first pass, in a uniform manner. This is demonstrated by

the similarity of the heating curve of the six thermocouple temperature tracings

in the first pass.

After the temperature interface reaches the bottom, the warmed water is heated

further (through latter passes) by the WHHP, causing the FCV to open, resulting

in the maximum water flow rate. As a result of the high flow rate, the temperature

rise in the latter passes is reduced. The high flow rate causes some mixing as can be seen at the latter part of the recovery test in figure 4 (the temperature

tracings become almost parallel)

.

The average water temperature was plotted in figure 5 for comparison with the

power of the WHHP and the ambient temperature. The average water temperature

increases monotonically with respect to the elapsed time. The ambient temperature

shows some fluctuations within a narrow range.

The power curve may be divided into two portions, the first pass portion and the

latter passes portion. The first pass portion lasted from the beginning of the

test until 110 minutes. The latter passes portion lasted from the end of the

first pass until the end of the recovery test. The first pass portion of the

power curve is distinguished by a small fluctuation. The fluctuation was caused

by the action of the temperature-sensitive FCV. When the water exiting the WHHP

(and entering the FCV) is at a low temperature, the FCV closes to allow the minimum

flow rate. This small flow rate causes the incoming water to be heated to a higher temperature by the WHHP. The warmer water causes the FCV to increase its

opening causing a higher flow rate. The higher flow rate, in turn, produces a lower

outlet water temperature. The relative colder outlet water causes the FCV to close

to its smallest opening. This sequence of events repeates itself again and again

14
until the temperature of the WHHP outlet water rises above the FCV setting. The

cyclic action of the FCV causes a fluctuating load on the heat pump compressor

and water pump which is reflected in the fluctuation of the power curve 9 f

figure 5. After the first pass, the FCV opens fully and the power curve no longer fluctuates but continues to increase with WHHP inlet water temperature

which establishes the heat pump condenser temperature.

The inlet water and outlet water temperatures of the WHHP are plotted in

figure 6. The inlet temperature remains constant during the major portion of

the first pass. During the latter portion of the first pass, the warm front

approaches the bottom of the storage tank causing the inlet water to increase.

The outlet water temperature in the first pass fluctuates as discussed previously.

During the first pass, the temperature rise is 35°C (63°F) . The temperature

rise after the first pass is about 7°C (13°F)

.

The recovery tests are summarized in table 1. They are plotted in figure 7 as

a function of ambient air temperature. In the range of interest, the recovery

efficiency increases as the ambient temperature increases. The recovery efficiency

for the WHHP tested is interpolated to be 2.32 at an ambient temperature of 75 °F.

4.2 Standby Tests

The standby test is a static test performed to determine the energy required to

maintain the stored water at some temperature above ambient. For this test,

the WH was filled with supply water, residual air was eliminated, and the connection pipes between the WH and the WHHP were purged of air. The WHHP was primed

and then turned on. The system was continuously monitored until the average

water temperature in the storage tank almost reached the cutout point. At this

time, the data acquisition system was turned on and the standby test started.

During the standby test, all the sensors were scanned and recorded at 10-minute

intervals. The standby tests lasted 60 hours. If, at the end of 60 hours, the

WHHP was operating, the standby test was continued until the WHHP cut out.

Results for a typical standby test are shown in figures 8 through 10. In figure 8,

the temperatures of the six WH thermocouples and average of the six are shown as

a function of time. The curves show the typically cyclic nature of a WH standby

test curve. At a water temperature controlled by the thermostat upper limit, the

thermostat cuts out the WHHP causing the WH to go into a cooldown . phase. In the

cooldown phase of WH operation, the average water temperature decreases in an exponential fashion [1] . When the water temperature decreases to a level below the

thermostat lower limit, the thermostat triggers the WHHP to operate, causing the

water temperatures to increase rapidly.

In figure 9, the average WH temperature is plotted for comparison with the ambient

air temperature and the heat pump power. As shown, the average water temperature

starts at 64.5°C (148.1 °F) then follows five cycles of heat pump on and heat pump

off. The peak average water temperature for each of the cycles remains approximately

the same, 62°C (143. 6°F). The mean average water temperature for the entire duration

of the standby test is 59.9°C (139. 8°F). The ambient temperature averaged 27.5°C

(81.5°F), The power is plotted at the bottom of figure 9. There are spikes of

short duration coinciding with periods in which the average water temperature is

restored to the maximum stored water temperature.

15
The standby tests are summarized in table 2 and plotted in figure 10. In

the range of interest, the standby loss decreases almost linearly as the

average ambient temperature increases. The standby loss is interpolated to

be about 1.24 percent per hour at an ambient temperature of 24°C (75°F).

4.3 Draw Tests

The draw tests were performed to measure the energy consumption of the system

under simulated draw conditions. Each draw test lasted at least 24 hours. The

draw schedule for a 24-hour period is the same as the one used in Reference 1

and is reproduced in table 3. In table 3 the first column gives the beginning

and the end of an individual draw. The second column gives the volume of the

individual draw as a fraction of the total draw volume. The total draw volume

is designed to be 243 L (64.3 gallons).

The water supply temperature was measured by the thermocouple installed at the

inlet to the WH and was adjusted as close to 12.8°C (55°F) as possible. Preliminary draw tests were conducted to correlate the setting of the mixing valve

(figure 2) with the measured average water supply temperature.

Temperature during a typical draw test is shown in figures 11 and 12. In

figure 11, the temperature recordings of the six thermocouples inside the WH

are plotted with respect to the elapsed time of test. Since the water supply

entered the water heater at the bottom, the water temperature at the bottom

(TC6) showed the largest variation as a function of the draw. This is clearly

demonstrated in figure 11; for example, at an elapsed time around 700 minutes,

there were a series of draws (draws #12 through #17 in table 3) causing TC6 to

fluctuate between 40°C and 20°C. TC6 increased sharply after four draws (draw

#14 through #17) due to the operation of the heat pump. During the same time

period the temperature at TC5 changed very little.

It should be noted that TCI decreases a little more than TC2 due to draws. This was because the concurrent operation of the WHHP causes tempering of the hot water

at the top of the WH by the WHHP outlet water temperature controlled by the FCV.

In fact, the tempering showed up several times after relatively heavy draws

causing TCI to drop below TC2

,

The average WH temperature and the ambient temperature were plotted in figure 12.

Again the sharp decreases in average temperature were due to relatively heavy

draws, and the increases in temperature were always because of the operation of

the WHHP. The ambient temperature fluctuated within a narrow range.

4.4 Recovery Tests at Different FCV Settings

Recovery tests at FCV settings differ from the manufacturer's setting of

46.1°C (115°F) were conducted to determine the effects of the FCV on the WHHPEWH system performance. The results are shown in figures 13-16.

16
One recovery test was conducted without the restriction of the FCV, allowing

a full flow of 0.1 L/s (1.5 gpm) to be maintained by the circulation pump for

all passes including the first. To do this. Valves 1 and 2 in figure 1 were

closed and Valve 3 was fully open. The temperature versus time variations for

this run are shown in figure 13.

For the recovery test conducted with the FCV removed, flow between the water

heater and the heat pump was unrestricted, resulting in a constant flow rate

of 1.5 gpm. The six temperature versus time curves for this recovery test are shown in figure 13. Although the stratification in the water heater is minimized

relative to that in a recovery test with FCV operating, it can still be seen that

30 minutes elapsed before the temperature at the bottom of the tank increased.

The sloping parallelism of the temperature curves during the first 30 minutes

indicates a significant degree of mixing of the stored water induced by the

higher flow rate.

A major difference of the two systems is reflected in the temperature recordings.

This difference is the availability of heated water shortly after a recovery mode

is started. Specifically, the system with a FCV produced a temperature rise of

32°C at TCI in about 30 minutes (figure 4), which means at least 1/2 tank of

water has been heated to 46.1°C (115°F). In the same 30 minutes, the system

without the FCV (figure 15) produced a temperature rise of only about 9°C.

Additional recovery tests at different FCV settings were performed by manual

control. This was done by closing Valve 1 and Valve 3 while keeping Valve 2 open causing water to flow through the needle valve. The needle valve was adjusted so the outlet water temperature would be the same as for a regular

recovery test using FCV during the first pass. The WHHP outlet water temperature

was monitored continuously. Valve 3 was manually opened when the heat pump

outlet water temperature reached the desired level after the first pass. Tank

temperatures for a recovery test with the FCV setting at 48.3°C (119°F) are shown

in figure 14. Figure 15 shows the water temperature variation at the WHHP inlet

and outlet for a FCV setting of 48.3°C (119°F) , A slight overshoot, due to

manual control of the globe valve, is indicated on the completion of the first

pass. The oscillatory variation of the WHHP outlet temperature that is

characteristic of the action of a FCV is not evident in figure 14 because of

the manual flow control being used. The watt-hour and the power curves are similar to those of the regular recovery test, except for the lack of any

significant oscillatory motion in the first pass portion of the power curve.

The recovery efficiency, E

r , plotted in figure 16 as a function of the FCV

setting shows that E

r for this unit is approximately a constant for FCV settings,

perhaps decreasing slightly for higher settings.

4.5 Water Heater Cooldown Tests

The standby loss, the recovery efficiency and the daily energy consumption of

the WHHP-EWH system depends on the size and construction of the water heater as well as the WHHP-WH. In order to characterize the thermal performance of this

particular WH, a cooldown test was performed. This test yields the WH time

constant — a measure of the water heater insulation properties and other thermal

losses.

17
To conduct the test, the WH was filled with supply water, purged of any residual

air, and energized until the average water temperature reached a level slightly

higher than 62.8°C (145°F). At this time, the data logger was started to monitor

and record at 10-minute intervals the temperature readings of the six thermocouples

inside the water heater and the one thermocouple of the ambient temperature in the

environmental chamber. The cooldown test was run for 21 hours.

The results of the cool-down test are shown in figure 17, in which the average

water temperature and the ambient air temperature are plotted. The WH cooldown

loss can be determined by fitting the average water temperature curve to an exponential cooldown curve [1]

.

Here Q is the thermal energy content of the WH referred to the ambient temperature,

0o is the same thermal -energy at the beginning of the cooldown test, and t is

the time elapsed of the cooldown test. The cooldown loss, n s , is found to be

0.0199/h. The cooldown loss is equivalent to standby loss for electric water

heaters with immersed heating elements. For a WHHP system, the measured standby

loss will be less than the cooldown loss because the heat pump replaces the

lost energy with a coefficient of performance greater than one. A value of

2%/h for a cooldown loss is typical of EWH with fiberglass insulation.

5. Performance Indices

5.1 Energy Consumption Calculations

As discussed previously and shown in figure 10, the standby loss decreases

linearly as the ambient temperature increases. As such, the standby loss may

be interpolated or extrapolated for ambient temperature equal to 20.6°C (69°F)

,

23.9°C (75°F), and 27.2°C (81°F) . A similar procedure may be applied to determine

the recovery efficiency and average power at the three ambient temperatures. The

resultant standby loss, recovery efficiency, and average power are tabulated in

table 4.

Using the equation for calculating the average hourly hot water storage energy

consumption, cug , as given in Reference 2

Calculations were made for the three ambient temperatures. Results are tabulated

In table 4. The daily water heater energy consumption, Cw^ , was also calculated

using the equation given in Reference 2:

c.us

= S x k x V X at6

( 2 )

k x U X AT

5 (3)

E

r

18
The average daily energy consumption, Cy, is given as a function of the storage

energy consumption, water heating consumption, and power input as follows:

The results of these calculations are tabulated in table 4.

The average daily energy consumption is plotted in figure 18 as a function of

the ambient air temperature. It is seen that in the range of interest, the

average daily energy consumption decreases in a near-linear fashion as the

ambient temperature increases. If the average daily energy consumption is

allowed a variation of + 2 percent of the value at 23.9°C (75°F), then the

ambient temperature may be allowed to vary between 22.6°C (72.7°F) and

25.2°C (77.3°F). This result indicates that the average ambient temperature

under which the system is tested may not be changed over a wide range without

affecting energy consumption substantially. Too wide an ambient air temperature

range may give misleading results on the merit of the system.

5.2 Comparison Between Calculated and Measured Energy Consumption

The energy consumption for a 24-hour draw discussed in Section 4.3 is presented

in table 5. The measured daily energy consumption is 8.15 kWh for the test, which

consisted of a total draw of 64.3 gallons with an average WH inlet temperature of

12.2°C (54°F) and a corresponding outlet temperature of 60.0°C (140°F) . The

draw test was conducted in an ambient temperature of 24.2°C (75.6°F). Also reported

in table 5 is the calculated average daily energy consumption under these particular water storage and draw conditions. The favorable agreement between the

measured daily energy consumption and the calculated average daily energy consumption

(8.30 kWh/day) indicates the validity of the test methods and the equations used

for calculation for the chosen example. However, further work is needed to

investigate the agreement for other WHHP sytems, such as those not having flow

control valves.

C

y 3412 (4)

In eq 4, = J

c = 0 since no heat traps were installed in the experimental

setup

.

VI . CONCLUSIONS

• The standby loss of the WHHP-EWH system is approximately a linear function of

the ambient air temperature over the measured range between 21°C (69.8°F)

and 27 °C (80.6°F). The standby loss decreases as the ambient temperature

increases.

• Both the recovery efficiency and the input power of the WHHP-EWH system

are linear functions of the ambient air temperature over the measured

range approximately between 21°C (69.8°F) and 27°C (80.6°F). Both increase

as the ambient temperature increases.

19
a The water in the storage tank was heated in a highly stratified manner

during the first pass of a recovery operation when the FCV or an equivalent was used. Cold supply water stayed at the bottom of the

storage tank; heated water stayed at the top. There was very little

mixing because of the low flow rate of heated water maintained by the

FCV.

• The recovery efficiency of the WHHP-EWH system is a function of the FCV

setting. It maintains a constant value for some minimum FCV setting.

It decreases rapidly at FCV settings above this minimum.

e Tempering of the hot water at the top of the storage tank by water not

as hot occurs during recovery after a heavy draw. This is because supply

water entering the bottom of the storage tank after a heavy draw was pumped

to the WHHP, heated only to a minimum FCV operating temperature and returned

to the top of the WH, causing the temperature at the top of the storage tank

to be tempered.

® The daily energy consumption, calculated using the calculation procedure

of the current DOE test method, decreases as the ambient temperature increases.

a Allowing the daily energy consumption to vary only within + 2 percent of

its value at 75°F would permit the ambient temperature range to vary no greater than 4.6°F.

«* The calculated daily energy consumption of the system studied agrees well

with the measured energy consumption for a 24-hour draw test.

20
Table 1. Results of recovery efficiency tests

Ta(°F) 69 75 81

E r 2.19 2.34 2.43

P (Kw) 1.236 1.246 1.257

Table 2. Results of standby loss tests (based on

E r

= 2.40)*

Ta(°F) 69 75 81

S(*/h) 1.31 1.23 1.14

*T. = 55°F, T

f

= 1 45°F , FCV Setting at 1 1 5°F

21
Table 3. Water draw schedule

Draw

Time

Fractional

Number Draw

1 7: 1

7: 1

.00935

2 7: 5

7:10

.234

3 7:25

7:25

.00935

4

8: 0

8: 0

.00935

5 10: 0

10: 2

.125

6

10:22

10:23

.0623

7 10:30

10:30

.00935

8 12: 0

12: 0

.00935

9 12:45

12:45

.00935

10

16: 0

16: 0

.00935

11

17:20

17:20

.00935

12 18: 0

18: 0

.00935

13 18:20

18:22

.0467

14 18 : 28

18:30

.0467

15 18:36

18:38

.0467

16 18:44

18:46

.0467

17 13:52

18:54

.0467

18 22: 0

22: 0

.00935

19 22: 5

22:10

.234

20 22:25

22:25

.00935

21 23:30

23:30

.00935

22
Table 4. Daily energy consumptions calculated based on measured

recovery efficiency and standby loss and assigned

temperature rises and water consumption

Ta

(°F) E

r P(Kw)

dT

5

(°F)

U (Gallon)Cwh

(Btu/d)

S

(%/hr) *T

6

(°F)

c

us (Btu/h)

Cy

(KWh/d)

69 2.19 1.236 90 64.3 21800 1.31 90 440 8.82

75 2.34 1.246 90 64.3 20400 1 .23 90 413 8.30

81 2.43 1.257 90 64.3 19650 1.14 90 383 7.94

Table 5. Comparison of calculated and measured

daily energy consumption

Recovery Standby Calc. Draw

E rP (Kw)

Ta

(°F)

S (%/hr)

Tw

(°F)

Ta

(°F)

Cy

(KWh/d)

Cyd

(KWh/d)

U (Gallon)

T

in

(°F)

T

0

(°F)

Ta

(°F)

2.34 1.246 75.4 1.23 137.8 75.9 8.30 8.15 64.3 54.0 140.0 75.6

23
Cl. CO

•-< ZD Q I—

X;i=*l-3f •

24

1/2

INCH

COPPER

TUBE

INSULATED

WITH

1/2"

POLYCHLOROPRENE
SOLENOID VALVE

FLOW CONTROLLER

Figure 2. Schematic of water supply system for draw tests

25
SOLENOID VALVES

Figure 3. Schematic representation of data acquisition/reduction system

26
WATER

TEMPERATURE

Figure 4. Temperature inside the water storage tank during recovery tests

27

WATER

TEMPERATURE
Average

Water

fa ‘aaMoa

a_ ‘ aanxvaaawai O o o o

Ln o o

o o o O o • » • CN o 00 rH 1“H rH

rH i—

l

t 1 pH

1 1 <S> LO

ru

a:

LU3

O

CL

a

28

Figure

5.

Average

water

temperature,

ambient

air

temperature,

and

heat

pump

power

during

recovery

test
WATER

TEMPERATURE

Figure 6. Heat pump inlet and outlet water temperature during

recovery test

29

WATER

TEMPERATURE
Figure 7. Recovery test efficiency and power input vs. ambient

temperature, 1^ = 12. 8°C, Tf=62.8°C. FCV setting =46.1°C

30
Figure

8.

Temperature

inside

the

water

storage

tank

during

standby

test
Average

Water

a

q

* aanivHaawai

O O CM o

m ‘nmod

u~l O LO O'

Ixl =3O

CL

O

Cf>

ElO

OH

n:

(/) <cQ

t Q

hH ck

<r3

Ixl O

<E

OH

LU

I>

<E

O

<S> 00

<S> 
 co

o

o ‘aaniVHaawai

cu




cn©

f£> E

>

CD

32

Figure

9

Average

water

temperature,

ambient

air

temperature,

and

heat

pump

power

during

standby

tost
STANDBY

LOSS,

PERCENT/HOUR:

S

(%/h)

1.40

1.30

1.20

1.10

65

18

70 75 80

AMBIENT AIR TEMPERATURE, °F : T

a

(F)

{

I I

4

I 20 22 24 26 28

AMBIENT AIR TEMPERATURE, °C: T (C)

&

I 30

FIGURE 10. STANDBY LOSS VERSUS AMBIENT AIR TEMPERATURE

33
TEMPERATURE,

C

TEMPERATURE

, C

TEMPERATURE

70

- 150

— 140

M

PiPH

.1 _ 130 eS

; w

pl,

v. ft

i- 120

dotv m [

4 5 —i—[ —r—r—*—i—i—i—i

1—i—i—i—

r

0 250 500 750

1 —i—i—i—r—'—i—i—

i

1000 1250 I

W

Pi

ppH

2

w

p<2

w

H

P-i

W

Pi

w

p<

Figure 11. Temperature inside water storage tank

during a draw test 34
70

60

50

40

30

20

10

DOTAflMR DDL I D \ T

H

Figure 12. Average water temperature and ambient air temperature

during draw test

35

TEMPERATU
4180

aanivaaawai aaxvw

36

Figure

13.

Temperature

inside

the

water

storage

tank

during

recovery

test

with

the

FCV

removed
WATER

TEMPERATURE,

C

WATER

TEMPERATURE,

C

WATER

TEMPERATURE

w

pi

£3H

W

Piw

H

<35

Figure 14. Temperature inside the water storage during

recovery test with FCV setting = 48.3°C

37
80

60

40

20

0

-160

0 50 100 150

T I ME ( MINUTES )

200 250

Figure 15. Heat pump inlet and outlet water temperature during

recovery test with FCV setting = 48.3°C

38

WATER

TEMPERATURE
RECOVERY

EFFICIENCY,

20 60

FCV Setting, (°C)

30 40 50

Figure 16. Recovery efficiency at different FCV settings

with a 24°C (75.2°F) ambient temperature

39
TEMPERATURE

T I ME ( MINUTES ) D0T\RMB S0LIDXTN

Figure 17. Average water storage tank temperature and ambient

temperature during cooldown test

40

TEMPERATURE,

op
AMBIENT

TEMPERATURE

41

AMBIENT

TEMPERATURE,
140

o

CJ

42

Figure

19.

Coefficient

of

performance

versus

heat

pump

inlet

temperature,

with

a

27°C

ambient

temperature
TABLE 6.

UNITS CONVERSION TABLE: Sl/lNCH-POUND/SI

TO

CONVERT MULTIPLY BY TO OBTAIN

gPm 0.06309 L/s

(Gallons/minute) (Liters /second)

L / s 15.83 gpm

(Liters/second) (Gal Ions /minute)

g L

(Gallons) 3.785 (Liters)

L 0.2642 g

(Liters) (Gallons)

in 2.54 cm

(Inches) (Centimeters)

cm 0.3937 in

(Centimeters) (Inches)

ft 0.3048 m

(Feet) (Meters)

m 3.281 ft

(Meters) (f eet)

BTU kJ

'British Thermal Units) 1.055 (kiloj oules)

kJ 0.9479 BTU

(kilojoules) [British Thermal Units)

TEMPERATURE (T) , CONVERSION EQUATIONS:

FOR TEMPERATURE USE:

°F to °C

:

°C to °F

[ (T) °F -32°F ] (5/9) = (T)°C

[(T)°C ] (9/5) + 32°F = (T)°F

FOR TEMPERATURE DIFFERENTIALS OR TOLERANCES USE:

°F to °C

:

°C to °F

(T)°F (5/9) = (T)°C 1

(T)°C (9/5) » (T)°F~|

43
REFERENCES

[1] Wan, C.A., "Energy Test Method Development for Electric Heat Pump Water

Heaters," NBSIR 79-1951, Center for Consumer Product Technology, National

Bureau of Standards, Washington, D.C., January 1980

[2] Appendix E - Uniform Test Method for Measuring the Energy Consumption of

Water Heaters - The Code of Federal Regulations. Title 10, Chapter II,

Part 430, Subpart B, published in Federal Register, Vol. 42, No. 192,

Tuesday, October 4, 1977, p. 54117-54119.

[3] Wan, C.A., "Computer Simulation of Water Heater Standby Loss, Heat Transfer

in Energy Conservation," Goldstein, R.J., et al, editors, 1977 WAM, ASME.

[4] Sushinsky, G.F., and Kweller, E.R., "Proposed Amendments to Test Procedures

for Water Heaters to Include Heat Pump Water Heaters," Letter Report prepared

for Department of Energy, April 1981.

44
1NBS-114A (rev. 2-80

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NBSIR 81-2372 January 1982

[I 4. TITLE AND SUBTITLE

Development of Energy Test Methods for a Dedicated Water Heating Heat Pump ::

5. AUTHOR(S)

C. Andrew Wan, Robert L. Palla, Jr., James E. Harris

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

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

United States Department of Energy

and

Oak Ridge National Laboratory

Oak Ridge, Tennessee

10. SUPPLEMENTARY NOTES

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 significant

bibliography or literature survey, mention it here) Modifications of the DOE test procedure for water heaters "Uniform Test Method

for Measuring the Energy Consumption of Water Heaters" were made to include a dedicated water heating heat pump, system equipped with a 50 gallon electric

water heater tank. Also presented are laboratory tests and results which

provided the basis for the test methods used. Tests included determination of

recovery efficiency, standby loss, and water heater jacket loss -- all under

static or no-draw conditions -- and a dynamic test in which water is withdrawn

according to a "typical-use" schedule. Energy requirements predicted by the

i proposed (static) procedure were in good agreement with measured energy con- sumption for the dynamic test in limited testing.

12.

KEY WORDS (S/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

energy conservation; energy consumption; flow control valve; heat pump;

stratification; test method; water heater

[13. AVAILABILITY 14. NO. OF

PRINTED PAGES

[T5J Unlimited

| | For Official Distribution. Do Not Release to NTIS 52

f 1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402. 15. Price

[~y~| Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $9.00

USCOMM-DC 6043-P80
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