Thermo-economic Investigation of Carbon Dioxide Direct-Expansion Ground Source Heat Pump using Expander and Internal Heat Exchanger

In the present paper, a comparison was made among four carbon dioxide (CO2) horizontal direct-expansion ground source heat pumps by using the thermo-economic analysis. For four study cycles, the unit cost of heat (LCOH, $/kWhth) was determined for two cases with constant a) Space Heating (SH) and b) Domestic Hot Water (DHW) loads with the peak of 8kW. Upon the obtained results, the (EVC+HE) and (EC+IHE) were found to have the lowest unit cost of heat and the highest COP, respectively. Also, it was shown that for the SH/DHW loads, 19% /11% increase in the COP results in 11% /7.5% increase in the LCOH for the electricity cost of 0.025$/kWh. Also, for the mentioned percentages increase in the COP and considering the electricity cost of 0.25$/kWh, LCOH is increased by about 6% for the SH and DHW cases, respectively. It was also concluded that the configuration with the highest COP is not that with the lowest unit cost of heat.