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Laboratory Testing of Residential Heat Pump Water Heaters
Pacific Gas and Electric Company
PY2009 Emerging Technologies Program
Application Assessment Report #0917
Laboratory Evaluation of Residential
Heat Pump Water Heaters
(San Ramon, CA)
Issued: March 2010
Project Manager: Xin (Sherry) Hu
Pacific Gas and Electric Company
Prepared By: PG&E Applied Technology Services
Performance Testing and Analysis Unit
ATS Report #: 491-09.17
Legal Notice
This report was prepared by Pacific Gas and Electric Company for exclusive use by its
employees and agents. Neither Pacific Gas and Electric Company nor any of its employees and
agents:
(1) makes any written or oral warranty, expressed or implied, including, but not limited to those
concerning merchantability or fitness for a particular purpose;
(2) assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of
any information, apparatus, product, process, method, or policy contained herein; or
(3) represents that its use would not infringe any privately owned rights, including, but not limited
to, patents, trademarks, or copyrights.
© Copyright 2010, Pacific Gas and Electric Company. All rights reserved.

Prepared by: Reviewed and Approved by:
Robert A. Davis Emanuel G. D’Albora
Senior Mechanical Engineer Supervising Mechanical Engineer
491-09.17.doc ii

CONTENTS
EXECUTIVE SUMMARY .......................................................................................................................... v
ACKNOWLEDGMENTS ........................................................................................................................... vi
INTRODUCTION ........................................................................................................................................ 7
Background............................................................................................................................................... 7
Prior Research........................................................................................................................................... 7
Objectives ................................................................................................................................................. 7
METHODOLOGY ....................................................................................................................................... 8
Thermodynamics and Terminology.......................................................................................................... 8
Testing Standards...................................................................................................................................... 9
Test Apparatus .......................................................................................................................................... 9
Measurements and Instrumentation ........................................................................................................ 10
Data Acquisition System......................................................................................................................... 10
Test Conditions ....................................................................................................................................... 11
Test Procedure ........................................................................................................................................ 11
RESULTS ................................................................................................................................................... 12
Test Units................................................................................................................................................ 12
First Hour Rating .................................................................................................................................... 15
Energy Factor.......................................................................................................................................... 16
Temperature Sensitivity .......................................................................................................................... 18
Cooling Effect......................................................................................................................................... 19
Economics............................................................................................................................................... 20
CONCLUSIONS......................................................................................................................................... 21
Recommendations for Follow-on Activities ........................................................................................... 21
REFERENCES ........................................................................................................................................... 22
APPENDIX...............................................................................................................................................A-1
LIST OF TABLES
Table 1: Summary of First Hour Rating / Energy Factor Test Results........................................................ v
Table 2: DOE Standard Energy Factor Test Conditions for HPWHs........................................................ 11
Table 3: Summary of Test Units................................................................................................................ 12
Table 4: Test Unit Rated Performance....................................................................................................... 13
Table 5: First Hour Rating Results ............................................................................................................ 15
Table 6: Energy Factor Test Results.......................................................................................................... 17
Table 7: Instrumentation List...................................................................................................................A-3
491-09.17.doc iii

LIST OF FIGURES
Figure 1: Basic Refrigeration Cycle............................................................................................................. 8
Figure 2: DOE Standard Test Stand............................................................................................................. 9
Figure 3: ATS Water Heater Laboratory (Six Test Stands)....................................................................... 10
Figure 4 Add-on AirTap A7 HPWH above tank ....................................................................................... 13
Figure 5 Rheem Integral HPWH................................................................................................................. 13
Figure 6: Rheem HP50 Modes of Operation ............................................................................................. 15
Figure 7: First Hour Rating Test – AirTap A7 Heat Pump Only.............................................................A-4
Figure 8: First Hour Rating Test – AirTap A7 with Upper Heating Element..........................................A-4
Figure 9: First Hour Rating Test – Rheem HP50 Energy Saver Mode....................................................A-5
Figure 10: First Hour Rating Test – Rheem HP50 Energy Saver Mode..................................................A-5
Figure 11: First Hour Rating Test – Rheem HP50 Normal Mode ...........................................................A-6
Figure 12: DOE Standard Energy Factor Draw Profile ...........................................................................A-6
Figure 13: Energy Factor Test Start – AirTap A7 Heat Pump Only........................................................A-7
Figure 14: Energy Factor Test Start – Rheem HP50 Normal Mode ........................................................A-7
Figure 15: Energy Factor Test Start – Rheem HP50 Energy Saver Mode...............................................A-8
Figure 16: HPWH Power Sensitivity to Tank Temperature ....................................................................A-8
Figure 17: AirTap Recovery Efficiency Sensitivity to Ambient Temperature ........................................A-9
Figure 18: Rheem Recovery Efficiency Sensitivity to Ambient Temperature ........................................A-9
Figure 19: AirTap Average Power Sensitivity to Ambient Temperature ..............................................A-10
Figure 20: Rheem Average Power Sensitivity to Ambient Temperature...............................................A-10
Figure 21: Net Cooling Effect from Heat Pump Water Heater..............................................................A-11
Figure 22: PG&E Residential Electric Rate E-1....................................................................................A-11
491-09.17.doc iv

EXECUTIVE SUMMARY
A limited evaluation of two new heat pump water heaters (HPWHs) was conducted in the water heater
laboratory at the PG&E San Ramon Technology Center. The objective of the testing was to investigate
the operating characteristics of HPWHs in comparison with other types, and their energy savings potential
and cost effectiveness. Most of the testing followed the test procedures described in the DOE standard
water heater testing procedure. The average test results are included below in Table 1.
Table 1: Summary of First Hour Rating / Energy Factor Test Results
Model
AirTap A7
Rheem
HP50
Operating
Mode
491-09.17.doc v
Manufacturer Ratings Test Results
First Hour
Rating
Energy
Factor
First Hour
Rating
Energy
Factor
Normal n/a n/a 57 1.97
HP Only 42.5 2.11 45 2.07
Normal 72 1.5 61 1.33 a
Energy Saver 62 2.0 60
1.61 a
1.98 b
Electric Heat Only n/a n/a n/a 0.82 a
a At an average water outlet temperature of 133°F
b At an average water outlet temperature of 129°F
n/a means data was unavailable or no test was done.
The results should not be considered directly comparable to the official ratings because not all of the
standard requirements could be met during these tests. In particular, the space condition could not be
controlled in the lab space, as a controlled environmental chamber was unavailable. The ambient
temperature averaged slightly high (69.0°F versus DOE Standard 67.5±1°F), but the relative humidity
was lower than required (44% versus DOE Standard 50±1%), thus reducing the available heat source
from the water vapor. However, the low humidity is more typical of the California climate, and the
results may be more indicative of local performance. In addition, the average wet bulb temperature of
56.0°F during the testing is only slightly lower than the DOE standard result of 56.3°F, and the wet bulb
temperature should be the more influential parameter on performance. (Air conditioning system
performance is usually modeled in terms of evaporator air inlet wet bulb temperature and condenser air
inlet dry bulb temperature.)
The HPWHs evaluated use about half of the energy as conventional electric water heaters, and draw less
demand. The trade-off is that the recovery rate is slower than either gas or electric resistance water
heaters, particularly apparent with the small capacity add-on unit. The heating capacity and power use are
both affected by the ambient condition and the temperature of the water, the latter having the largest
influence. The water setpoint temperature also affects when the water heater will need to switch to
electric resistance heat, as the heat pump unit operation is limited by a maximum operating temperature.
Thus, it is especially important with HPWHs to keep the thermostat setting as low as possible for best
energy efficiency and lowest power demand, in addition to the general recommendation for all water
heaters for reducing standby losses.

ACKNOWLEDGMENTS
The following list of people contributed to the testing project and the production of this report:
• Sherry Hu – Senior Program Manager, Emerging Technologies
• KC Spivey – Supervisor, Emerging Technologies
• Robert Davis – Senior Mechanical Engineer, Applied Technology Services
• Al Beliso – Technologist, Applied Technology Services
• Esteban Rodriguez – Senior Engineering Technician, Applied Technology Services
491-09.17.doc vi

INTRODUCTION
Background
While the majority of residential water heating in PG&E’s service territory uses natural gas combustion,
there are some areas where gas service is unavailable or there may be no provision for exhaust venting
from the building, and thus electricity is used for water heating. While they use a more expensive energy
source, electric resistance water heaters tend to be very efficient from a site energy perspective, with
Energy Factors ranging from 0.90 to 0.98. The high efficiency comes from the resistive heating elements
transferring 100% of the electrical energy into the water (with no combustion or stack losses like fired
units), and from a high level of insulation, including the bottom of the tank (which cannot be done with
most bottom-fired gas systems). Because the range of Energy Factor for electric water heaters is narrow
and because of their higher cost of operation, no conventional electric resistance heater has been
considered under the recently introduced EnergyStar program for water heaters.
The use of heat pumps to heat water has been looked at as a way to get more efficiency into electric water
heaters as far back as the 1950s. They experienced a resurgence of interest during the energy crisis of the
1970s, but while these models showed some promise, they suffered from reliability problems and high
cost, and few products survived to become installed on a large scale. Because of the reliability problems,
most of these early products and the interest in them faded away in time. With the recent national
emphasis on energy efficiency, and with significant improvements in refrigeration system components,
heat pump water heaters (HPWHs) have received renewed interest, with new consumer products being
introduced to the residential markets from several major manufacturers. The only electric water heaters to
receive EnergyStar designation are heat pump systems.
Because of this recent introduction and the low number of available consumer products, little is known
about the operation and performance of heat pump water heaters or their potential for energy savings
relative to other types of water heaters. In order to compare various types of water heaters, the PG&E
Emerging Technologies (ET) program contracted with PG&E Applied Technology Services (ATS) in
2008 to develop a water heater test laboratory at the San Ramon Technology Center. By simulating realworld
conditions, the test facility can evaluate the actual energy savings potential of hot water heaters
beyond what is available from the available ratings. The objective of the water heater testing program is
to enhance PG&E’s Mass Market program by providing supporting data for fact sheets and to provide
data for cost effectiveness calculations to help determine appropriate incentives.
The purpose of the study described in this report was to assess two types of HPWHs through laboratory
testing, and provide energy performance data to the Emerging Technologies program. The scope of work
included conducting laboratory testing to quantify the energy performance of these products, and evaluate
the general functionality of the systems as consumer products.
Prior Research
This is the second laboratory testing project regarding residential water heaters conducted within PG&E.
This project builds upon the 2008 PG&E Emerging Technologies gas water heater evaluation, described
in Reference 2. Some initial investigation was made into the testing standards for HPWHs, including
international standards as well as DOE and ASHRAE Standards.
Objectives
The objective of this project was to evaluate the operating characteristics of two new HPWH products,
and to determine the performance parameters commonly used for rating water heaters. The performance
parameters include:
• First Hour Rating
• Recovery Efficiency
491-09.17.doc 7

• Energy Factor
The emphasis was mostly on the operation, as the test lab lacked the environmental control needed to test
within the tolerances needed for producing a performance rating. Of secondary importance was to
determine how system performance is affected by the operating conditions of ambient temperature and
humidity and tank temperature setpoint.
METHODOLOGY
Thermodynamics and Terminology
A heat pump uses the familiar refrigeration cycle to move thermal energy “uphill” from a low temperature
source to a high temperature sink. For an air conditioner, the cool space where energy is absorbed would
be the interior of a building or car, and the warm space where the energy is discharged is the ambient air.
For a heat pump water heater, the warm space for energy discharge is the water in the tank, while the
cooled space for absorbing energy is the room air around the water heater or from some other source
(such as a water loop used in a ground-source heat pump).
All refrigeration cycles contain four basic components: an evaporator to absorb energy, a condenser to
reject energy, a compressor to raise the pressure and create flow, and an expansion device to control the
flow. The system works with a fluid, or refrigerant, that evaporates (transitions from a liquid to a vapor)
at a low pressure and temperature, and condenses (transitions from a vapor back to a liquid) at a
reasonably high pressure and temperature. The majority of the energy consumed is the input to the
compressor, with smaller contributions from devices that move the heat absorption or rejection medium
through the evaporator or condenser (such as air or water). The energy rejected at the condenser is the
sum of the energy absorbed by the evaporator and the energy consumed by the compressor. Since heat
pump efficiency is measured as the heat rejected divided by the total input energy (compressor and fans
or pumps), values in excess of 100% are possible, with numbers approaching 300-400% achievable in
some cases.
Expansion Valve
Figure 1: Basic Refrigeration Cycle
Heat Absorbed
(from ambient air)
As a thermodynamic heat engine in reverse, the heat transfer capacity, the amount of compression energy
required, and thus the system efficiency, are all a function of the evaporating and condensing temperature
difference. As either the condensing temperature rises or the evaporator temperature drops, energy
consumption increases, and capacity and efficiency both decrease. When applied to a heat pump water
heater, in order to keep the electric energy input low and efficiency high, the evaporator temperature
491-09.17.doc 8
Condenser
Evaporator
Heat Rejected
(to the water in
a HPWH tank)
Compressor
Electric
Energy

should be kept high by absorbing heat from a warm (and preferably humid) environment, and the
condenser temperature should be kept low by not setting the water temperature too high.
Testing Standards
There are a number of different parameters to describe the energy performance of domestic water heaters,
usually with provisions for the particulars of HPWHs. For most residential systems, the applicable test
standard is the USDOE Code of Federal Regulations 10CFR430, Subpart B, Appendix E (Reference 3).
According to the DOE standard, residential water heaters are rated according to three parameters, defined
as follows:
• “First Hour Rating means an estimate of the maximum volume of hot water that a storage-type
water heater can supply within an hour that begins with the water heater fully heated (i.e. with all
thermostats satisfied). It is a function of both the storage volume and the recovery rate.”
• “Recovery Efficiency means the ratio of energy delivered to the water to the energy content of the
fuel consumed by the water heater.” Standby losses are a minor component of this factor, and it
is roughly equivalent to the Thermal Efficiency rating for large water heaters.
• “Energy Factor means a measure of water heater overall efficiency.” It is a combination of
energy recovery efficiency following a series of water draws and 24-hours of standby loss.
For HPWHs that do not include an integral tank, the DOE standard requires that they are to be connected
to a tank-type electric water heater with a capacity of 47 gallons, two 4.5 kW heating elements that do not
operate simultaneously, and an Energy Factor above the current minimum energy conservation standard.
ASHRAE Standard 118.2 (Reference 1) currently lists most of the same information that is in the DOE
standard, although with different adjustment methods for the Energy Factor. ASHRAE Standards serve
as a path to try out different rating methods before they are adopted into the Federal standards.
Test Apparatus
The guidelines in the DOE and ASHRAE standards were followed as to the construction of the individual
water heater test stands (Figure 2). The lab is set up with six test stations that draw from the same source
of water, such that several heaters can be tested almost simultaneously under the same environmental and
load conditions. The lab was also constructed in a room with its own space conditioning system to
achieve the desired consistent environment and not affect other spaces in the building.
Figure 2: DOE Standard Test Stand
491-09.17.doc 9

Figure 3: ATS Water Heater Laboratory (Six Test Stands)
The conditions of the standard Energy Factor test also influenced the test apparatus. The standard Energy
Factor test requires a water supply temperature of 58°F, which means a method of tempering the supply
water to maintain that temperature was needed. Since the water draws are a short-term event process
rather than continuous, the test apparatus was designed with a storage tank that was normally maintained
with a supply of chilled water by an external chiller. Before entering the supply header to the test units,
the water passes through a 3-way valve to mix tap water with chilled water to achieve the desired supply
temperature.
The outlet from each test water heater is controlled by a solenoid valve, and fed into a common outlet
header. This header passes through a high-accuracy Coriolis mass flow meter for hot water discharge
flow rather than a weigh tank. The flow rate is controlled by an array of four flow control valves in
parallel, with each set to a different flow rate and activated by solenoid valves at their outlets. The DOE
standard flow rate for the Energy Factor, First Hour Rating, and Recovery Efficiency is 3 gallons per
minute (gpm), so one of the valves was set to this flow rate.
Measurements and Instrumentation
The measurements are mostly those required by the DOE test standard, and includes those necessary to
measure the energy removed in a hot water draw (flow and temperatures in and out of the tank), the
energy consumed by the water heater (electric energy input to the heat pump and/or electric resistance
elements), the change in stored energy in the tank (tank temperatures), and the ambient conditions (air
temperature, humidity, and pressure). Additional measurements were needed for the feedback control
system. The complete list of measurements and the instruments used for them is shown in Table 7 in the
Appendix.
Prior to testing, all of the RTD temperature probes were calibrated against a laboratory standard
temperature sensor in an ice bath (32°F), a gallium melting point cell (85.6°F), and in a flask of hot water
(~120°F). Pressure sensors were calibrated against a portable pneumatic calibrator.
Data Acquisition System
The instrumentation was connected to multiple rack-mounted Compact FieldPoint modules from National
Instruments, depending on the signal type. The signal conditioning modules included different units for
RTDs, thermocouples, voltage and pulse count (water and gas meters) inputs, plus both analog and digital
491-09.17.doc 10

output modules for the mixing valve and solenoid valves, respectively. Each rack includes an Ethernet
communications module that enables the system to be accessed from anywhere on the local network.
A local computer connected to the Ethernet network ran a program written in National Instrument’s
LabVIEW graphical programming language. This program was developed to read all the measurement
devices, display the readings and additional calculated values on screen, and save the data to disk for later
analysis, as well as control the water draws and inlet temperature. The system was programmed such that
only one water heater could be active and sending water through the common flow meter. The scan rate
for sampling from the FieldPoint modules and updating the screen was set at 2 Hz, although the internal
scan rate of the modules was 10 Hz.
The frequency at which data were averaged and recorded to disk depended on the status of the water
heater. During a water draw, readings for the active water heater were recorded at 5 seconds in
accordance with the DOE test method. When the water flow was stopped and the heater was still drawing
energy (elevated electric demand), the logging rate would be reduced 15 seconds. Finally, when the
heater was in standby (minimal electric demand), data were logged every 5 minutes. Separate log files
were maintained for each water heater under test (since the log rate varied for each), plus and additional
file for the environmental conditions and other slow parameters, which was updated at the standby log
rate. A Microsoft Excel macro was created to combine these separate log files into a single workbook for
analysis.
Test Conditions
Most of the test conditions for the Energy Factor test are defined in the DOE standard, and these are
summarized in Table 2. In addition, the standard draw quantity is 64.3 gallons in six equal draws of 10.7
gallons. Recovery Efficiency is supposed to be derived from the first draw of a standard Energy Factor
Test, but the results appear to be more consistent from the subsequent draws.
The ambient temperature constraint for heat pump water heaters is more stringent than for other types (±
2.5°F), and in addition it requires a very narrow range of relative humidity. This requires that heat pump
water heaters be tested in controlled environmental chambers. Unfortunately, while this kind of facility
does exist at the laboratory, it was undergoing refurbishing at the time of the testing. Thus, the
environment could not be controlled to the desired tolerance, so the results should not be considered
official ratings. It also limited the ability to measure the performance sensitivity to ambient conditions.
Table 2: DOE Standard Energy Factor Test Conditions for HPWHs
Ambient Dry Bulb Temperature 67.5 ± 1 °F
Ambient Relative Humidity 50 ± 1%
Heater Inlet Water Temperature 58 ± 2 °F
Average Storage Tank Temperature 135 ± 5 °F
Water Flow Rate 3 ± 0.25 gpm
Supply Water Pressure 40 PSIG to max spec
Line voltage ± 1% of spec
Test Procedure
The standard rating parameter tests were conducted in accordance with the methods described in the DOE
test standard. In summary:
• First Hour Rating: One or more pre-draws are taken from the tank, which means releasing water
until the heating system is activated. After the thermostat is satisfied and the heating system cuts
out, the average tank temperature is watched until a maximum is reached, and this number is
recorded. A draw at 3-gpm is then initiated and marked as time zero. The tank outlet
temperature is monitored and a maximum value recorded, and the draw continues until it drops by
25°F from the maximum, at which point the flow is stopped. The heating system is then allowed
491-09.17.doc 11

to bring the tank back to temperature, and after cut-out the cycle is repeated, if the time is less
than one hour from the start of the first draw. At the end of one hour, if a draw is occurring it is
allowed to finish according to the previous criteria. If a draw is not occurring, one is started and
allowed to continue until the outlet temperature reaches the shut-off temperature from the
previous draw. The first hour rating is the total volume of water released from the start of the
first draw.
• Energy Factor is the result of a 24-hour simulated use test beginning immediately after the water
heater is fully heated (burner cut-out after drawing enough to activate it). It divides a total draw
of 64.3 gallons of hot water into six draws each an hour apart, with the remainder of the 24-hours
with the unit in standby. The Energy Factor is the energy in the hot water delivered with a 77°F
temperature rise divided by the total energy consumed in the 24-hours. The calculation of the
factor includes adjustments for off-standard test conditions and for the change in stored energy in
the tank as the result of starting and ending the test at different average tank temperatures.
• Recovery Efficiency is based on the ratio of the energy contained in the first 10.7-gallon draw in
the Energy Factor test divided by the energy consumed to bring the tank back to the fully heated
state (burner cut-out). Standby losses are a minor component of this factor because of the
relatively short duration.
The data acquisition and control computer was programmed to conduct tests automatically according to a
script. At the start of a draw event, a bypass valve was opened at the end of the heater supply header, and
the mixing valve was controlled to precondition the header to the proper water temperature. Once the
temperature criteria was satisfied at the bypass valve, the test heaters were activated in sequence starting
from the unit closest to the bypass valve and working back along the supply header towards the tempering
valve to ensure a consistent supply temperature.
RESULTS
Test Units
There are very few commercial HPWH products on the market, but more are proposed. This first round
was limited to two models with distinct differences in their design. The first unit listed is not a packaged
HPWH, but is an add-on for existing electric water heaters. As such, it required the purchase of a
separate electric water heater. While the DOE standard requires a 47-gallon tank, one of this capacity
could not be located. The test tank was larger at 55-gallons, and had 3.8 kW elements rather than the
required 4.5 kW. In keeping with the manufacturer’s recommendation, the lower heating element was
disabled, and the upper heating element would only activate if there was enough cold water in the tank to
activate the upper thermostat.
Table 3 below contains a summary of the specifications for the test units (including the electric water
heater for the add-on unit), and Table 4 contains a listing of their rated performance characteristics.
Following the tables are detailed descriptions of each water heater.
Manufacturer Product Line Model Number
AirGenerate AirTap A7
Kenmore PowerMiser 6 153.3265562
Rheem HP50 JP4A-A050510
Table 3: Summary of Test Units
491-09.17.doc 12
Product
Description
Add-On
Immersion
Electric
Resistance
Combination
Pump Circulation
Tank
Capacity
(gallons)
Dimensions
(inches)
Refrigerant
- R-22
55
50
60¼ H ×
20½ Dia
75½ H ×
21 Dia
-
R-410a

Manufacturer Product Line
Table 4: Test Unit Rated Performance
Maximum
Input
Power
(W)
491-09.17.doc 13
First
Hour
Rating
(gallons)
Energy
Factor
Energy Guide
Label
(kWh / year)
AirGenerate AirTap A7 900 - 2.11 -
Kenmore PowerMiser 6 3,800 61 0.90 4,879
Rheem HP50 4,000
Figure 4
Add-on AirTap A7 HPWH
above tank
72 (Normal)
62 (Energy Saver)
1.50 (Normal)
2.00 (Energy Saver)
Figure 5
Rheem Integral HPWH
AirTap A7
The installed base of electric water heaters likely have several years remaining in their useful lives.
Recognizing that many consumers would still like to reduce the cost of heating water without the cost and
hassle of replacing the entire water heater, the AirTap system was designed to be retrofitted to existing
tanks. The main components of the heat pump (the compressor, evaporator and air circulating fan) are
enclosed in a box that sits on top of the tank on support feet and clamps to the inlet and outlet water pipes.
The system uses a special fitting on the hot water outlet tap, through which is passed bare copper
condenser tubing that is designed to coil up near the bottom of the tank. Also passed through this fitting
is a thermostat bulb meant to sit about ¾ of the way down into the tank to trigger the heat pump
operation. Air to the evaporator is drawn in through a filter on the back near the water pipes, and
discharges upwards out of the top. An adapter can be fitted to the air discharge to duct it to where cooled
air might be wanted. The unit plugs into a regular 115 VAC outlet, while the electric resistance heater in
the tank requires a dedicated 230 VAC connection.
2,195

The manufacturer requires that the bottom element of the existing electric water heater be disabled so as
not to override the heat pump coil. The upper element may be left active to provide quick heat to the
upper part of the tank during large use events, or it may also be disabled as well to ensure high efficiency
operation with just the heat pump. (Electric resistance water heaters typically have upper and lower
heating elements that operate alternately depending on which one’s thermostat is activated; for most draw
events only the lower element will operate.)
There were fewer tests conducted on this unit as the result of a number of errors unrelated to the HPWH
itself. Upon heater startup, the electric resistance element was showing a low power draw even though it
was supposed to be off. Either through a manufacturing defect or because the element may have been
activated without water, the upper heating element had failed and passing current to ground through the
water. While the system could (and would mainly) be tested without supplemental resistance heat, it was
desired to include it as more representative of the typical installation. In case it might have been
damaged, the tank temperature thermocouple array inserted through the anode rod penetration was also
removed for inspection. Unfortunately, the thermostat for the heat pump had become tangled in the
thermocouples, and broke off when they were removed. Thus, the evaluation unintentionally
demonstrated that the system thermostat can be replaced without affecting the other system components.
All of the test results for this unit are from after the thermostat replacement and installation of a new
heating element in the tank.
As an add-on unit rather than a system, the AirTap does not have official performance ratings listed, and
the overall system performance will depend on the efficiency and capacity of the attached water tank. A
test report from GAMA was provided with the unit listing an Energy Factor of 2.11 and a first hour rating
of 42.5, but it does not say how large of a storage tank was used.
Rheem HP50
This is a new product design of an integrated heat pump system with supplemental resistance heat. In this
system, all of the heat pump components including the condenser are located on top of the tank, and water
is circulated by a pump loop that draws water from the bottom of the tank, through the condenser, and
back into the top of the tank. With this circulation, the tank water temperature stays very consistent with
very little stratification. Air to the evaporator is drawn in through a round filter on top of the unit, and
discharged through a coil that forms about 2/3 of a cylinder on the back side of the unit. Because of the
location of the heat pump components, there are no penetrations in the top of the storage tank: the water
inlet and outlet connections are on the sides. The tank also does not have an end-user serviceable
sacrificial anode rod. Because there was no top penetration, the tank temperature thermocouple array had
to be inserted using the pressure relief valve tap, while keeping this safety valve available through a tee
fitting. Because the cool air discharging the evaporator is directed out and down from the top of the tank,
the tank environmental temperature may be depressed, possibly resulting in an increased potential for
standby loss unless the space is adequately ventilated.
This unit also has resistive elements for supplemental heating; however, the element capacity is about half
of that for other similar-sized electric water heater tanks at 2 kW each. The system is enabled with three
distinct modes of operation – Normal, Energy Saver, and resistance heat only - as illustrated in Figure 6.
The chart shows the overlapping trends of power consumption for the three modes following a draw in
the standard Energy Factor test (~10.7 gallons at 3 gpm). In “Normal” mode, the heat pump turns on first
and is allowed to heat the tank up to a certain temperature. As the water temperature rises, the heating
capacity of the heat pump decreases, so one resistance element is brought on some time later to assist the
heat pump. Eventually, once another temperature threshold is reached, the heat pump is turned off in
favor of the resistive element. The “Energy Saver” mode is not all that different, other than allowing the
heat pump to run longer by itself, and then switching over to resistance heat when needed while not
allowing the two components to operate simultaneously. Thus, the Energy Saver mode not only reduces
energy consumption, it also reduces the maximum power demand by about a third. The last stage of both
these modes with the resistance heat operating alone is only needed if the thermostat is set above the
491-09.17.doc 14

maximum for the heat pump, which appears to be around 130°F. The third mode of operation with both
of the resistive heating elements operating together would likely only be used when the recovery rate
needs to be fast, or when the environment around the heater is very cold and there is little heat resource.
Figure 6: Rheem HP50 Modes of Operation
2.5
Water Draw:
10.6 Gallons
491-09.17.doc 15
GPM / kW
4.0
3.5
3.0
2.0
1.5
1.0
0.5
Resistance Heat Only Mode:
2.08 kWh
in 34.7 minutes
Normal Mode:
1.23 kWh
in 41.4 minutes
Energy Saver Mode:
1.08 kWh
in 54.9 minutes
0.0
0 10 20 30 40 50 60
The tank temperature setpoint for the most of the tests was at “hot” to achieve the DOE Standard required
average tank temperature of between 130 and 140°F. Subsequent tests were conducted with the setpoint
between Normal and hot, which resulted in higher Energy Factor numbers because the electric resistance
elements were operated less often. The “Normal” temperature setting would likely result in a tank
temperature of 120°F and the resistive elements may not be needed at all to achieve this.
Testing of the Rheem unit began December 2 (through January 22), while that for the AirTap was delayed
until December 15 because of the described installation problems.
First Hour Rating
The first hour rating test was conducted twice on each heater to include two different modes of operation:
Normal and Energy Saver (or with the resistance element disabled for the AirTap). The results of the first
hour rating test are found in Table 5. Graphical representations of each of these tests are included in the
Appendix, and the figure numbers are noted in the table.
Table 5: First Hour Rating Results
First Hour Rating (gallons)
Operating Appendix Manufacturer
Model Mode Figure Ratings Measured
AirTap A7
HP Only
Normal
Figure 7
Figure 8
42.5
-
45
57
Energy Saver Figure 9 62
60
Rheem HP50 Energy Saver Figure 10 62
59
Normal Figure 11 72
61
Minutes

For both of the HPWHs, their recovery rates were insufficient to return the tanks to their cut-out
temperatures at the end of an hour. Thus, the second draws were all done to the shut-off temperature
from the first draw, and the systems were actively heating throughout the second draw.
For the AirTap unit in the heat pump only mode, the system was unable to recover enough heat in the
tank to produce an outlet temperature in excess of the termination temperature for the first draw. This
means that its first hour rating is only the amount taken in the first draw. As described in the test
procedure, the second draw at the one-hour mark was only 30-seconds to see what temperature was
available. For the first draw, the maximum outlet temperature recorded was 132.5°F resulting in a shutoff
temperature mark of 107.5°F. The maximum outlet temperature observed from the second draw was
only 100.5°F before it began to fall off again, so none of this second draw was included in the rating.
Adding supplemental heat from the upper resistance element did allow the tank temperature to recover
enough to provide additional hot water to the rating for the “Normal” mode. It is also notable in Figure 8
how quickly the two highest tank thermocouples reacted to the operation of the upper heating element.
The Rheem was thought to have been tested in two modes of operation, but the power usage trend for the
Energy Saver mode test suggests otherwise as both the heat pump and resistance elements were allowed
to operate together. In the two tests in Energy Saver mode (it was repeated to confirm the result from the
first), the unit did not switch on the resistive elements as soon as it did in the Normal mode test, so the
test unit may have switched to Normal mode as an override following an especially large draw of hot
water. However, since the manufacturer reports separate ratings for each mode, this seems unlikely that
this is by design, unless the resistance element was locked out in achieving their rating. All three of the
test results are close to the manufacturer’s listing for their Energy Saver mode.
Energy Factor
The simplest interpretation of the Energy Factor is the daily hot water energy output divided by the total
energy consumed (with the electrical consumption converted to a Btu equivalent by multiplying the kWh
by 3,412). The rating is based on a specific volume of hot water removed at a set temperature rise. The
DOE and ASHRAE testing standards include alternative procedures to correct the measured test results to
the standard volume and temperature conditions, and to compensate for changes in the stored energy (as
the result of the average storage tank temperature being different at the beginning and end of the 24-hour
period). Both the measured values adjusted by the two standard methods are included in Table 6 below,
along with a simple calculation method. The “Simple” Energy Factor values use just the sum of the hot
water energy removed and the increase in stored thermal energy divided by the electric energy input.
In many cases, the Energy Factor test for a particular mode of operation was repeated to confirm an
earlier result or when some parameter was changed. The columns marked EF#1 through #4 are the
number of tests run in each mode beginning with the earliest test run. The one major change was with the
Rheem system where the thermostat was adjusted down, and the results are reflected in the EF tests #3
and #4 for the Energy Saver mode tests. The final test in this group (CR Profile) was one done following
a draw pattern developed by Consumer Reports ® for a water heater test program (Reference 5), and used
to represent a more real-world profile. This test should actually produce higher numbers than the
standard Energy Factor test because the total volume was higher (77 gallons versus 64.3), so the tank
standby losses have a lower impact. Only one test was done at this profile, with the systems set to their
Normal operating mode with electrical resistance heat backup. How often the resistance heat is activated
has a large effect on the daily Energy Factor.
491-09.17.doc 16

Model
AirTap
A7
Operating
Mode
Table 6: Energy Factor Test Results
Rated Energy Factor / Recovery Efficiency Test Results
Energy
Factor
Calculation
Method
491-09.17.doc 17
EF #1 EF #2 EF #3 EF#4
CR
Profile
Average
Simple 1.99 1.86 1.99
Normal - ASHRAE 1.98 1.98
Energy 2.11
Saver
DOE 1.97 1.97
Recovery
Efficiency
250% 250%
Simple 2.05 2.14 2.10 2.10
ASHRAE 2.10 2.22 2.20 2.17
DOE 2.07 2.14 2.21 2.14
Recovery
Efficiency
237% 253% 253% 248%
Simple 1.34 1.35 1.33 1.69 1 1.34
Normal 1.5 ASHRAE 1.34 1.37 1.31 1.34
Rheem Energy 2.0
HP50 Saver
Resistance
Only
DOE 1.33 1.37 1.30 1.33
Recovery
Efficiency
160% 157% 160% 159%
Simple 1.60 1.59 1.87 1 2.03 1,2
ASHRAE 1.63 1.62 1.89 1 2.03 1,2
DOE 1.61 1.60 1.87 1 2.08 1,2
Recovery
Efficiency
190% 189% 228% 1 242% 1,2
1.60
1.95 1
1.62
1.96 1
1.61
1.98 1
190%
235% 1
Simple 0.79 0.84 1 0.81
ASHRAE 0.79 0.85 1 0.82
DOE 0.79 0.85 1 0.82
Recovery
91% 92%
Efficiency
1 91%
Notes: 1 Thermostat setpoint reduced to between Normal and Hot (~129°F) from Hot (~133°F).
2
Heat pump water return J-tube rotated 90° to horizontal and away from the upper heating element.
For the majority of cases, the DOE and ASHRAE corrections do not change the results by much from the
simple measure, indicating good conformity with the standard conditions. The results were expected to
be lower than the rated values because of not having good control over the environmental conditions.

For the AirTap A7, the test results agree very well with the test result provided with the unit. However,
the results are suspect because the recovery rate of the system was insufficient to return the tank to its
initial temperature in the time following each draw, so the average tank temperature was less than what
the system should have had. With a lower average tank temperature, the efficiency of the system is
higher than it would be if the temperature stayed close to the tank temperature setpoint. The CR Profile
test allowed more time for recovery between draws, and included two draw events that caused the upper
tank heating element to activate, and thus produced a lower EF.
The lower than rated Energy Factor numbers seen for the Rheem in the first tests is directly a result of the
system switching over to electric resistance heat once the tank temperature reached about 130°F. As seen
in the later test results, the unit certainly can meet and exceed their published rating so long as the system
only uses the heat pump. Most consumers will likely leave the temperature setpoint at “Normal” where
the electric resistance elements will likely not be activated in the Energy Saver mode. Consumers should
also be actively advised to operate the system in the Energy Saver mode over the Normal mode to achieve
consistently high performance. Another concerning result from these tests are the low numbers for the
operation with electric resistance heat only, with numbers significantly lower than what would be
expected from a typical electric water heater. Some of this can be attributed to a standby power draw of
at around 5½-Watts that is present even when the system is not actively heating, which may primarily be
due to the indicator lights. (The AirTap indicated no measurable standby power.) Another factor is the
external pipe for circulating water through the heat pump, which even though insulated still creates
additional surface area for heat loss.
Several sample charts of the start of an Energy Factor test are included in the Appendix. Figure 12 shows
the general DOE standard draw profile in terms of when the flow draws occur and the quantity of each.
While this chart shows the full 24-hours of the test window, the subsequent figures in this group only
show the first 8-hours or the first third of the test. Figure 13 shows the test for the AirTap unit in heat
pump only mode, and it can be seen that the heat pump was on continuously throughout the test and
continued to run for more than two hours following the last draw until the thermostat was satisfied. It
also indicates a decreasing trend in the maximum water outlet temperature for each draw. In contrast, the
charts for the Rheem HP50 unit in Energy Saver (Figure 15) or Normal mode (Figure 14) show that in
both modes the system was able to heat the water back up to the setpoint following the standard draw, and
the outlet water temperature was consistent.
Temperature Sensitivity
Determining the sensitivity of the system performance (in particular power consumption) as a function of
the water temperature and the ambient air temperature is subjective to the ability to control and measure
these parameters and the ability of the test unit to react consistently to them. The results obtained from
this test program are not completely clear and are open for interpretation, and could use a more rigorous
examination than was included in this program.
The sensitivity of power consumption to the average tank temperature was apparent in the test results
shown in the charts for Energy Factor and especially First Hour Rating (because of the larger draw
quantity and the resultant large range in tank temperature). As these tests were all done while keeping the
room temperature relatively constant, the ambient conditions have little impact. Data were consolidated
from the various standard tests and extracted from the periods when only the heat pump was operating (no
electric resistance heat) and no draw was occurring. Curves were fitted to the consolidated data set, and
these are shown in Figure 16 without the underlying data. Bounding parallel curves indicating one
standard error of the estimate (SEE) are drawn with dashed lines to signify the tightness of the data set to
the curve. The curves for the Rheem are cut off below 105°F because no data were collected below this
temperature. The important point to gather from these curves is the rise in power consumption as a
function of the tank temperature, which is set by the system thermostat. Lowering the thermostat thus has
the effect of capping the maximum amount of power that the heat pump will draw when heating water.
491-09.17.doc 18

Comparing the power demand at a tank temperature of 105°F versus a tank temperature of 135°F, the
AirTap unit power is lower by 20% and the Rheem is lower by 23%.
Determining the sensitivity to ambient conditions was particularly difficult since the testing was not done
in a tightly controlled environmental chamber as it should have been. In an attempt to observe
performance over a range of ambient conditions, a special test was set up consisting of a draw pattern
repeated every four hours, and set to run over a weekend with the space conditioning system turned off so
that the room temperature was allowed to float as influenced by the outside temperature. The draw
pattern consisted of initiating a draw at 3-gpm until the power cut-in, stopping the draw and waiting until
the power cut out, then taking a draw of 10 gallons also at 3-gpm. This pattern was used so that the
average tank temperature at the start of the second draw and after cut-out following the second draw
would be about the same, thus reducing any correction for the change in tank temperature. The data from
this test run are a collection of reheats following a consistent draw quantity at a consistent temperature
rise, thus causing the ambient condition to be the main variable. There is still some variability in the
average tank temperature depending on when the thermostat sensed the temperature to shut down.
Unfortunately, the range of ambient conditions experienced through this period was not very large, so the
ambient temperature effects are inconclusive. The results are shown in Figure 17 through Figure 20,
which include trends of Recovery Efficiency (defined here as the hot water energy removed divided by
the electrical energy input for each event) and unit average power (which is still affected by the tank
water temperature). The data set for the Rheem has been enhanced by including some of the data from
Energy Factor tests conducted under the same draw conditions but under a controlled ambient
temperature. This was not added for the AirTap unit because it could not complete a system reheat
following an Energy Factor draw, so the results are not comparable. The results are shown as functions of
both ambient dry and wet bulb temperatures, and since their ranges do not overlap, are included on the
same chart. The data has also been grouped into bins of average tank temperature during the reheat event
(±0.1°F) to identify if the residual variation in tank temperature had any significant effect.
Both test units show an increasing trend in the Recovery Efficiency as a function of the ambient
temperature, both dry and wet bulb. Part of this may be due to a reduction in tank standby loss as the
result of a smaller temperature difference, but the rest should be the result of the larger heat resource in
the air. The average power draw of the systems during the reheat, however, showed different
characteristics between the units. While the average power from start to finish remained fairly constant
for the Rheem, the results for the AirTap showed an upward trend with rising temperature; something
contrary to what was expected. A possible explanation is that as air temperature increases, it becomes
less dense, so there is less mass flow passing through the evaporator from which to collect heat. The
phenomenon is more likely to be coincidental and apparent only because of the limited data set.
Cooling Effect
Much attention (both good and bad) has been placed on the cooling effect that a heat pump water heater
will have on the space around it. If the water heater is within a conditioned space, then the cooling effect
can offset some of the cooling required in the summer, but it will increase the need for heating in the
winter. The best location for any type of heat pump is one with a warm air resource, like near a furnace
or the exhaust from a refrigerator or freezer. Installation in an attic where the cooling effect will help to
reduce summer cooling loads may also be an option, so long as the installation is in full compliance with
the manufacturer’s requirements.
The magnitude of the cooling effect is a direct function of the amount of hot water used, and the portion
of that quantity that is actually heated by the heat pump and not electric resistance heaters. In fact, if no
hot water is drawn from the heater over a period, then there will actually be a net heating effect to the
space around the water heater due to the tank standby losses and the energy input to maintain temperature.
This is demonstrated in Figure 21, which is based on a tank heat loss rate of 4.5 Btu/hr-°F (slightly more
than what was measured for each of the two tanks), a heat pump COP of 2.4 (a rough average between
491-09.17.doc 19

them), and the standard temperature conditions for the DOE Energy Factor test. In this example, the
break-even point for the net effect of cooling and standby loss is a daily use of about 8 gallons at a 77°F
rise. At the Energy Factor standard quantity of 64.3 gallons, this example water heater would have a net
cooling effect of 1.76 ton-hours per day, or about the same as running a 1-ton window air conditioner for
1¾ hours. This relationship does not include the heating effect from direct contact of the produced hot
water with the air in the space, such as from a shower or faucet, since this would normally not be in the
same area as the water heater.
Economics
The test results are conclusive that the heat pump water heaters will have an economic advantage over
conventional electric resistance water heaters, by providing the same amount of hot water for as little as
half the electric energy input. The size of the difference will depend on how the system is operated and if
the use of the backup electric resistance elements is minimized. Heat pump water heaters also offer a
significant demand reduction of as much as 3½ kW. However, the cost effectiveness in comparison with
gas water heaters is less clear; and for most PG&E customers, gas water heating is still the most
economical option.
The analysis of cost effectiveness is complicated by PG&E’s tiered residential electric rate, where the
more energy is used, the higher the cost. The tiers are separated by a factor of a baseline quantity, which
varies according to which of ten regions the customer is in, the season (summer or winter), and whether
the customer has only electric service. Figure 22 shows an example of the current E-1 rate structure and
how it varies with the baseline quantity. The customer’s average electric rate may be found as the slope
of a line drawn from the origin until it intersects the appropriate trend.
Comparing the cost of operation for different water heater systems may be done based on the knowledge
that the Energy Factor rating represents a total hot water use of 150 therms or 15 million Btu per year
(64.3 gal/day × 77°F rise × 8.3 lb/gal × 1 Btu/lb-°F × 365 days/year). Using the conversion factor of
3,412 Btu/kWh, this can also be figured as 4,396 kWh per year. The cost to operate either a gas or
electric water heater under the standard conditions is then:
Operating Cost: $/Year = [ 150 therns/year / Energy Factor × $/therm ]gas
= [4,396 kWh/year / Energy Factor × $/kWh ]electric
Assuming a customer is under the baseline amount and being billed at the current minimum of
$0.11877/kWh (as of 3/1/2010), a heat pump water heater with an Energy Factor of 2.0 would have an
equivalent operating cost as a gas water heater with the Title-24 minimum Energy Factor of 0.59 if the
average gas cost is $1.03 per therm. The more electricity the customer uses, the less economically
attractive it becomes, particularly if switching from gas to electricity pushes the user into a higher rate
tier.
The DEER database lists an average annual energy consumption for a 50-gallon standard electric water
heater in a single family residence of 3,579 kWh, based on an average Energy Factor of 0.86. If for
example, the Rheem unit operated always in heat pump mode and achieved an average Energy Factor
close to the measured average 1.98, it would consume about 1,555 kWh/year; representing a reduction of
2,024 kWh/year or 57%.
491-09.17.doc 20

CONCLUSIONS
In this test program, two examples of commercially available heat pump water heaters were evaluated for
their operating characteristics and economic advantages in comparison with other water heaters. The
scope of testing was limited due to a narrow test window, and most of the results are based on tests
performed close to the conditions required in the DOE standard test procedure.
The following conclusions may be drawn from this testing:
1. Heat pump water heaters (HPWHs) offer distinct advantages over conventional electric resistance
water heaters in terms of both energy use and demand. In both test units, DOE Standard Energy
Factors above 2.0 were produced, although achieving this level of performance requires operating
the systems in such a way that backup electric resistance heat is unused. Operating the systems
with high temperature setpoints or with large draw quantities may activate the resistance elements
and result in lower Energy Factors.
2. The main disadvantage to HPWHs is a slower recovery rate than either gas or electric resistance
water heaters. This is particularly apparent in the add-on AirTap unit, which took nearly five
hours to recover from a first hour rating test without supplemental resistance heat.
3. The performance of HPWHs is particularly sensitive to the tank water temperature, and somewhat
to ambient temperature and humidity. Lower tank temperatures and higher ambient temperatures
and humidity result in higher heating capacity, lower power demand, and higher efficiency.
4. The tests were conducted under environmental conditions that were slightly different from the
rating test standard specifications, so the results cannot be directly compared with the official
system ratings. While the ambient temperature was close to the standard value (and within the
range allowed for other water heaters), it was outside the ±1°F tolerance for HPWHs.
Additionally, the humidity level was too low, averaging close to 40% instead of the required
50%. While low, this is more typical of the California climate where humidity levels are
normally low. Therefore, the tests produced results indicative of operation in a dry climate.
Recommendations for Follow-on Activities
Similar to the behavior of air conditioning products, the performance of heat pump water heaters will vary
with the ambient conditions, which are in turn a function of water heater location (garage, basement, attic,
closet). It is not known whether the standard rating condition provides an adequate representation of the
system performance throughout an entire year of operations. A good simulation model of system
performance is needed, along with sufficient field test data to verify the results. As with other air
conditioning products, the performance measures may be calculated as a function of the evaporator
entering air wet bulb temperature and the average stored water temperature.
491-09.17.doc 21

REFERENCES
1. ANSI/ASHRAE Standard 118.2-2006: “Method of Testing for Rating Residential Water Heaters”,
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1791 Tullie Circle,
NE, Atlanta, GA 30329, 2006.
2. Davis, R. and Katrina Leni-Konig, Pacific Gas and Electric Company PY2005 Emerging
Technologies Application Assessment Report #0510, “Laboratory Testing of Residential Gas Water
Heaters”, PG&E/TES Report 491-08.5, December 2008.
(http://www.etcc-ca.com/component/content/article/29-Residential/2842-laboratory-testing-ofresidential-water-heaters)
3. United States Department of Energy, Code of Federal Regulations, Title 10 (Energy), Appendix E to
Subpart B of Part 430 (10CFR430, SubPt. B, App. E): “Uniform Test Method for Measuring the
Energy Consumption of Water Heaters”, 1996, amended 2001.
http://edocket.access.gpo.gov/cfr_2008/janqtr/pdf/10cfrAppEB430.pdf
4. Zimmerman, K. H., “Heat Pump Water Heater Laboratory Test and Design Model Validation”, Oak
Ridge National Laboratory, Oak Ridge, TN, March 1986.
5. “Tankless Water Heaters”, Consumer Reports ® , October 2008, 28-29.
491-09.17.doc 22

Appendix
APPENDIX
491-09.17.doc A-1

Appendix
(This page intentionally left blank for duplex printing.)
491-09.17.doc A-2

Appendix
Table 7: Instrumentation List
Performance Parameter Units Sensor Type
Temperature
Ambient Dry Bulb °F 1/4" RTD Probe (3)
Heater Inlet Water °F 1/4" RTD Probe (1 per unit)
Heater Outlet Water °F 1/4" RTD Probe (1 per unit)
Cold water supply °F 1/4" RTD Probe
Tempering tank outlet °F 1/4" RTD Probe
Tempering valve outlet °F 1/4" RTD Probe
End of supply header °F 1/4" RTD Probe
Coriolis meter °F 1/4" RTD Probe
Storage Tank °F Type T thermocouple (6 per tank)
Discharge Air Temperature °F Type K thermocouple (1 per unit)
Relative Humidity
Ambient % RH General Eastern MRH-1-V-OA
Pressure
Barometric in Hg Qualimetrics 7105-A electronic barometer
Supply water PSIG Rosemount 3051C gage transmitter
Flow
Common outlet water flow rate pph MicroMotion R050S Coriolis mass flow meter
Individual tank inlet water flow rate gpm Omega FTB4707 Single-jet paddle wheel flow meter (6)
Power
Power W
Yokogawa 2533 3-element Power Meter (240V Power)
Yokogawa 2475 Power Line transducer (120V Power)
Line voltage
Other
V Scientific Columbus VT110A2 voltage transducer
Flow control valves gpm Kates MFA1-1 (3)
Tempering water tank Bradford-White M-2-50TSDS electric water heater
Tempering water tank chiller Advantage M1-1.5AR
491-09.17.doc A-3

Appendix
°F
°F
140
130
120
110
100
90
80
70
60
132.5°F
Figure 7: First Hour Rating Test – AirTap A7 Heat Pump Only
50
0.0
0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300
140
130
120
110
100
90
80
70
60
25°F
45.5 Gallons
First Hour Rating:
45.5 Gallons
Minutes
491-09.17.doc A-4
Six Tank Thermocouples (°F)
Average Tank Temperature (°F)
Water Inlet Temperature (°F)
Water Outlet Temperature (°F)
Water Flow Rate (GPM)
Heat Pump Power (kW)
December 22, 2009
Figure 8: First Hour Rating Test – AirTap A7 with Upper Heating Element
133.0°F
25°F
45.0 Gallons 11.8 Gallons
First Hour Rating:
56.8 Gallons
50
0.0
0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300
Minutes
Six Tank Thermocouples (°F)
Average Tank Temperature (°F)
Water Inlet Temperature (°F)
Water Outlet Temperature (°F)
Water Flow Rate (GPM)
Heat Pump Power (kW)
Resistance Power (kW)
December 22, 2009
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
GPM / kW
GPM / kW

Appendix
°F
°F
140
130
120
110
100
90
80
70
60
Figure 9: First Hour Rating Test – Rheem HP50 Energy Saver Mode
133.9°F
50
0.0
0 15 30 45 60 75 90 105 120 135 150
140
130
120
110
100
90
80
70
60
25°F
34.3 Gallons 25.5 Gallons
33.9 gallons
First Hour Rating:
59.8 Gallons
Minutes
491-09.17.doc A-5
Six Tank Thermocouples (°F)
Average Tank Temperature (°F)
Water Inlet Temperature (°F)
Water Outlet Temperature (°F)
Water Flow Rate (GPM)
Power (kW)
Figure 10: First Hour Rating Test – Rheem HP50 Energy Saver Mode
134.2°F
25°F
First Hour Rating:
59.2 gallons
25.3 gallons
December 22, 2009
50
0.0
0 15 30 45 60 75 90 105 120 135 150
Minutes
Six Tank Thermocouples (°F)
Average Tank Temperature (°F)
Water Inlet Temperature (°F)
Water Outlet Temperature (°F)
Water Flow Rate (GPM)
Power (kW)
January 6, 2010
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
GPM / kW
GPM / kW

Appendix
°F
GPM
140
130
120
110
100
90
80
70
60
134.2°F
Figure 11: First Hour Rating Test – Rheem HP50 Normal Mode
50
0.0
0 15 30 45 60 75 90 105 120 135 150
5
4
3
2
1
35.5 Gallons
25°F
25.1 Gallons
First Hour Rating:
60.6 Gallons
Minutes
491-09.17.doc A-6
Six Tank Thermocouples (°F)
Average Tank Temperature (°F)
Water Inlet Temperature (°F)
Water Outlet Temperature (°F)
Water Flow Rate (GPM)
Power (kW)
Figure 12: DOE Standard Energy Factor Draw Profile
DOE Draw Profile
64.3 Gallons
in 6 Draws
GPM
Gallons
December 23, 2009
0
0
12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM
8
4
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
20
16
12
GPM / kW
Gallons / Draw

Appendix
°F
°F
140
130
120
110
100
90
80
70
60
127.1°F
Figure 13: Energy Factor Test Start – AirTap A7 Heat Pump Only
128.4°F
127.5°F
125.9°F
124.4°F
50
0.0
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00
140
133.9°F
130
120
110
100
90
80
70
60
491-09.17.doc A-7
123.1°F
Hours from Start of First Draw
Six Tank Thermocouples (°F)
Average Tank Temperature (°F)
Water Inlet Temperature (°F)
Water Outlet Temperature (°F)
Water Flow Rate (GPM)
Power (kW)
Figure 14: Energy Factor Test Start – Rheem HP50 Normal Mode
133.9°F
134.0°F
133.8°F
134.1°F
133.9°F
December 16, 2009
50
0.0
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00
Hours from Start of First Draw
Six Tank Thermocouples (°F)
Average Tank Temperature (°F)
Water Inlet Temperature (°F)
Water Outlet Temperature (°F)
Water Flow Rate (GPM)
Power (kW)
December 15, 2009
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
GPM / kW
GPM / kW

Appendix
°F
Heat Pump Power (Watts)
140
130
120
110
100
132.7°F
90
80
70
60
Figure 15: Energy Factor Test Start – Rheem HP50 Energy Saver Mode
134.0°F
133.9°F
134.0°F
134.2°F
50
0.0
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00
1,300
1,200
1,100
1,000
900
800
700
600
491-09.17.doc A-8
134.2°F
Hours Since Start of First Draw
Figure 16: HPWH Power Sensitivity to Tank Temperature
Standard Error
of the Estimate
Rheem
AirTap
Six Tank Thermocouples (°F)
Average Tank Temperature (°F)
Water Inlet Temperature (°F)
Water Outlet Temperature (°F)
Water Flow Rate (GPM)
Power (kW)
December 3, 2009
500
100 105 110 115 120 125 130 135
Average Tank Temperature (°F)
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
GPM / kW

Appendix
Recovery Efficiency
Recovery Efficiency
230%
225%
220%
215%
210%
205%
200%
195%
Figure 17: AirTap Recovery Efficiency Sensitivity to Ambient Temperature
491-09.17.doc A-9
Average Tank Temperature
190%
48 50 52 54 56 58 60 62 64 66 68 70 72
230%
225%
220%
215%
210%
205%
200%
195%
190%
185%
Wet Bulb Temperature Trend
Ambient Temperature (°F)
123.2°F 123.4°F 123.8°F 124.2°F
Dry Bulb Temperature Trend
Figure 18: Rheem Recovery Efficiency Sensitivity to Ambient Temperature
Wet Bulb Temperature Trend
Average Tank Temperature
126.0°F 126.2°F 126.4°F 126.6°F
180%
48 50 52 54 56 58 60 62 64 66 68 70 72
Ambient Temperature (°F)
Dry Bulb Temperature Trend

Appendix
Average Heat Pump Power (Watts)
Average Heat Pump Power (Watts)
680
675
670
665
660
655
Figure 19: AirTap Average Power Sensitivity to Ambient Temperature
491-09.17.doc A-10
Average Tank Temperature
650
48 50 52 54 56 58 60 62 64 66 68 70 72
1,075
1,070
1,065
1,060
1,055
1,050
Wet Bulb Temperature Trend
Ambient Temperature (°F)
123.2°F 123.4°F 123.8°F 124.2°F
Dry Bulb Temperature Trend
Figure 20: Rheem Average Power Sensitivity to Ambient Temperature
Wet Bulb Temperature Trend
Average Tank Temperature
1,045
48 50 52 54 56 58 60 62 64 66 68 70 72
Ambient Temperature (°F)
126.0°F 126.2°F 126.4°F 126.6°F
Dry Bulb Temperature Trend

Appendix
Net Cooling Effect (Ton-hours per Day)
Monthly Cost
2.0
1.5
1.0
0.5
0.0
1.76 ton-hrs
Figure 21: Net Cooling Effect from Heat Pump Water Heater
491-09.17.doc A-11
64.3 Gallons
-0.5
0 10 20 30 40 50 60 70
Tier 1
0-100%
$0.11877/kWh
E-1 Basic
Average Rate
Gallons of Hot Water Used per Day (at a 77°F Rise)
Figure 22: PG&E Residential Electric Rate E-1
Tier 2
101-130%
$0.13502/kWh
Tier 3
131-200%
$0.28562/kWh
Rate as of 3/1/2010
Tier 4
201-300%
$0.42482/kWh
100% 130% 200%
kWh / Month
300%
Tier 5
Above 300%
$0.49778/kWh
Fraction of Baseline Quantity