Paper No 140 – Investigation of the performance of a ground-coupled CO2 heat pump for space and water heating – 14th IEA Heat Pump Conference, Chicago, USA
A parametric investigation on a ground-coupled CO2 heat pump for space and water heating was performed using a model developed with Modelica. The CO2 heat pump, with a tripartite gas cooler configuration, was modeled using the Thermal Systems library and then calibrated with experimental data, while the Borehole Heat Exchangers (BHEs) were modeled using the MoBTES library and sized following the ASHRAE methodology. Different design and operating parameters were varied to see their effects on the system’s coefficient of performance (COP). Simulations showed that there is an optimal high-side pressure that maximizes the COP. The evaporator’s water-side mass flow, the BHE’s length, the grout’s thermal conductivity, and the compressor speed all have an inverse relationship with the COP, while the low-side pressure of the heat pump and the valve’s throttle area are directly related to it. However, changing these parameters to increase the COP has limits because doing so decreases the amount of heat that the system can deliver. This study serves as a starting point for the design and optimization of a bigger system that utilizes other low-temperature resources with the CO2 heat pump.