A comparative exergo-economic analysis of four configurations of carbon dioxide direct-expansion geothermal heat pump

• Published in: Applied thermal engineering 2019-12, Vol.163, p.114347, Article 114347
• Main Authors: Ghazizade-Ahsaee, Hossein, Ameri, Mehran, Baniasad Askari, Ighball
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Configurations; Direct expansion geothermal heat pump; Economic analysis; Electricity pricing; Exergo-economic analysis; Exergy; Expander; Gas expanders; Geothermal power; Heat exchangers; Heat pumps; Heat transfer; Internal heat exchanger; Pumps; Space heating; Studies; Transcritical carbon dioxide cycle
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2019.114347

•Exergy-economic analysis of four CO2 DX-GHP is developed.•The effect of expander and IHE in CO2 DX-GHP is investigated.•Two cases with constant a) SH and b) DHW loads are studied.•Shown that the (EVC + IHE) and (EC + IHE) have the lowest cq and the highest ηex.•Shown that the configuration with the highest ηex is not that with the lowest cq. The present paper deals with a comparative exergo-economic analysis among four different horizontal Direct-Expansion Geothermal Heat Pumps (DX-GHP) with Carbon Dioxide (CO2) refrigerant in transcritical cycle. The studied configurations include the cycle with (a) expansion valve (EVC), (b) with expander (EC), (c) with expansion valve and Internal Heat Exchanger (EVC + IHE), and (d) with expander and IHE (EC + IHE). The unit cost of heat ($/kWhex) for each configuration was determined under two scenarios of a) constant Space Heating (SH) and b) constant Domestic Hot Water (DHW) loads with the peak of 8 kW. The results showed that the lowest unit cost of heat (cq) and the highest total exergy efficiency (ηex) are associated with the (EVC + IHE) and (EC + IHE) configurations, respectively. Also, it was shown that for the SH (or DHW) load, 20% (or 14%) increase in the ηex results in 21.5% (or 20%) increase in the cq considering the electricity cost of 0.025 $/kWh. For the electricity cost of 0.25 $/kWh, however, 11% (or 20%) increase in ηex results in increasing the cq by about 7% (or 13%). It was also concluded that the configuration with the highest ηex is not that with the lowest cq.