Cold climate field test analysis of an air-source heat pump with two-stage compression and economizing
A Department of Defense project was established to conduct a field demonstration led by Purdue University with several industry partners. The technology investigated was an air-source, two-stage heat pump with closed-loop economizing. The field demonstration site was a military barracks on a National Guard base, Camp Atterbury, in southern Indiana. Two heat pumps were built at the Ray W. Herrick Laboratories and installed into two almost identical, barracks buildings. Data on the heat pump operation and building conditions were to be collected over an entire heating season. Due to complications with the system, the amount of runtime data collected from both systems amounted to about 400 hours combined. The heat pump operation was compared against the operation of an existing natural gas furnace by evaluating; the primary energy consumption, operating costs, CO2 emissions, building thermal comfort, and heat pump, installation and maintenance. The heat pump was able to achieve a 19% reduction in primary energy consumption and CO¬2 emissions while the operating costs were break even when using residential utility costs of Indiana. With the utility rates of Camp Atterbury, the heat pump had a 44% higher operating cost than the furnace. A building simulation coupled with an EES model of the heat pump was created in TRNSYS. The simulation enabled the forecast of a seasonal heating performance of the heat pump while operating at the conditions of the field demonstration. The initial results of the simulation predict a seasonal heating COP of 3.75 which corresponds to a seasonal heating performance of 12.8 BTU/W-hr. Due to a lack of data capturing an entire heating season, the building simulation was updated with the collected experimental data. The internal EES model was adjusted to match the recorded heating capacity and COP of both heat pumps to provide a performance prediction in line with observations in the field. The updated building simulation predicted a seasonal heating COP of 2.25, and the seasonal heating performance to be 7.7 BTU/W-hr with the experimental data. Several recommendations are provided to improve the performance of the heat pump in the attempt of reaching the initial predicted performance.
Groll, Purdue University.
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