Organic Rankine Cycle-assisted ground source heat pump combisystem for space heating in cold regions

Abstract

This paper presents an Organic Rankine Cycle (ORC)-assisted ground source heat pump combisystem for the cascaded utilization of low-grade energy and shallow geothermal energy in cold regions. The ORC unit was added to conventional ground source heat pumps to solve the cold accumulation problem, which can lead to performance degradation of heat pumps. The existing types and novel types of the combisystem were then modeled with the Transient System Simulation Program (TRNSYS). During the heating season, the ORC unit and heat pump unit were combined for space heating, and during the non-heating season, the ORC unit was connected to ground heat exchangers for seasonal storage. System performance was simulated over periods of one year and twenty years. The twenty-year simulation results showed that the proposed combisystem could maintain a higher annual average coefficient of performance (COP) of approximately 3.8 because of the steady soil temperature, whereas the annual average COP of the conventional ground source heat pump system decreased from 3.7 to 3.2. Additionally, the total power consumption per unit heating area of the heating system decreased from 2.2 × 103 kW·h/m2 to 3.3 × 102 kW·h/m2 when the ORC unit was added to the conventional ground source heat pump. This translates to electricity cost savings of ¥ 908/m2 over twenty years. Moreover, in the combisystem, the ORC unit provides 55.6% of the total heating capacity; compensates for 78.5% of the heat pump unit’s power consumption. And 94.1% of the thermal energy storage from the non-heating season can be used during the heating season by the heat pump unit.