A highly efficient solution for thermal compensation of ground-coupled heat pump systems and waste heat recovery of kitchen exhaust air

This paper proposed a highly efficient solution for both thermal compensation of ground-coupled heat pump systems and kitchen exhaust air waste heat recovery (KHR-GCHP) in cold climatic regions. A new analysis and calculation method was developed for non-finned coil heat exchangers of KHR-GCHP systems. Moreover, two indexes were defined to evaluate KHR-GCHP and other relevant systems: the thermal compensation capacity per unit energy consumption (TEC) and the system specific net energy saving (S-SNES). Through comparing and analyzing TRNSYS simulation results and experimental data, it is concluded that the KHR-GCHP system has higher energy efficiency with TEC up to 36.78 kWh/kWh, significantly higher than that of normal boiler-GCHP systems (0.90 kWh/kWh) or frequently-used hybrid solar-GCHP systems (15.73 kWh/kWh). Furthermore, the S-SNES of the KHR system reached 2.37 W·h/m3, which was at least 1.86 times as high as common kitchen exhaust air waste heat recovery systems (ranging from 0.85-1.27 W · h/m3). Additionally, to facilitate KHR-GCHP's wide application, a simplified criterion was developed: for both circumstances where air-water temperature difference (Td) was higher than 9.43 °C (current project; suitable for the hybrid solar-GCHP system) or higher than 3.99 °C (other projects), the KHR-GCHP system demonstrated advantages over other systems.