Experiments and Exergy Analysis for a CO2 Ground-Source Heat Pump in Cooling Mode
Harrison M. Skye, Wei Wu
A prototype CO2 ground-source air conditioner (GSAC) comprised of a vapor-compression cycle with a liquid-line/suction-line heat exchanger (LLSL-HX) was tested in an environmental chamber per ISO standard 13256 1 for rating liquid-to-air heat pumps. The system operated in a subcritical cycle for entering liquid temperature (ELT) ≤ 25 °C and a transcritical cycle for ELT > 25 °C. At 'Standard' conditions the COP was 4.14, the total capacity was 6690 W, the sensible capacity was 5400 W, and the SHR was 0.81. For the 'Part-load' conditions the COP was 4.92, the total capacity was 7240 W, the sensible capacity was 5640 W, and the SHR was 0.78. The GSAC was also tested at the 'Minimum', and 'Maximum' ISO 13256-1 conditions, and five 'extended ELT' tests with ELT ranging (10 to 36.8) °C, where COP ranged (7.3 to 2.4). Compressor efficiency correlations were shown for these and 118 'additional' tests. An exergy analysis was performed for all tests; at the 'Standard' rating condition the major defects were compressor: 0.32, ground heat exchanger: 0.19, condenser: 0.11, evaporator: 0.11, EEV: 0.07, pump: 0.07, and fan: 0.04. The defects were sensitive to ELT, though the compressor was always the largest. Estimated performance of the cycle without the LLSL-HX showed for ELT (10 to 39) °C the HX reduced the EEV throttling defect by (0 to 0.08) and compressor defect by (0 to 0.015) but increased the condenser/gas-cooler defect by (0 to 0.06). The estimated net effect of the LLSL-HX was a COP penalty of about (1 to 2) % for ELTs ranging (10 to 25) °C, and a benefit of (0 to 5) % for ELTs ranging (30 to 39) °C.
International Journal of Refrigeration-Revue Internationale Du Froid
and Wu, W.
Experiments and Exergy Analysis for a CO2 Ground-Source Heat Pump in Cooling Mode, International Journal of Refrigeration-Revue Internationale Du Froid, [online], https://doi.org/10.1016/j.ijrefrig.2021.08.018, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=932437
(Accessed December 2, 2023)