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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
Page 1 and 2: Laboratory Testing of Residential H
Page 3 and 4: CONTENTS EXECUTIVE SUMMARY ........
Page 5 and 6: EXECUTIVE SUMMARY A limited evaluat
Page 7 and 8: INTRODUCTION Background While the m
Page 9: should be kept high by absorbing he
Page 13 and 14: Manufacturer Product Line Table 4:
Page 15 and 16: maximum for the heat pump, which ap
Page 17 and 18: Model AirTap A7 Operating Mode Tabl
Page 19 and 20: Comparing the power demand at a tan
Page 21 and 22: CONCLUSIONS In this test program, t
Page 23 and 24: Appendix APPENDIX 491-09.17.doc A-1
Page 25 and 26: Appendix Table 7: Instrumentation L
Page 27 and 28: Appendix °F °F 140 130 120 110 10
Page 29 and 30: Appendix °F °F 140 130 120 110 10
Page 31 and 32: Appendix Recovery Efficiency Recove
Page 33: Appendix Net Cooling Effect (Ton-ho

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