Thermal energy from transcritical CO2 heat pumps for small marine applications

Heat pumps are a more efficient method to heat water compared to conventional electrical heating systems. However, the harmful environmental effects of traditional CFC and HCFC refrigerants require more sustainable alternatives to be adopted. In marine applications, leaked HCFCs can cause substantial harm to sensitive coastal ecology and are powerful greenhouse gases. Standard CO₂ (R744 when used as a refrigerant) is a promising replacement for HCFCs due to its low global warming and ozone depletion potential. This paper investigates adapting the traditional ground loop of a geothermal heat pump to a marine loop for use with seawater or coastal applications. New analytical results on the use of thermal energy from marine water for domestic water heating with a transcritical CO₂ heat pump are presented in this paper. Substantial research has recently been performed on transcritical CO₂ heat pump cycles, including cycle enhancements and optimization techniques. However, the research has been primarily focused on traditional heat pump configurations, with ambient air usually being the heat source. Geothermal temperatures vary on average between 8°C to 12°C throughout the year. A large body of water in this temperature range can provide a consistent source of thermal energy and thus effectively replace the ground source used in typical geothermal heat pumps.