Comparison of the Thermodynamic Performance of Direct Expansion Ground Source Heat Pump Using Hydrofluoroolefins (HFOs) Based on Theoretical Analysis

HFO-1234yf and HFO-1234ze[E] have low GWP and zero ODP. If they are used in the direct expansion ground source heat pump (DXGSHP) system substituting for HFC-134a, the system will be beneficial to mitigating climate change. This study aims to find out the thermodynamic characteristics of the DXGSHP system using HFO-1234yf or HFO-1234ze[E] by theoretical calculation. The results indicate that HFO-1234yf system in an actual cycle has the highest COP. HFO-1234yf and HFO-1234ze[E] have such smaller capacity per unit of swept volume that they need larger compression capacity if providing the same heating or cooling loads. For a given unit when HFC-134a is replaced with HFO-1234yf or HFO-1234ze[E], the capacity will decrease. More refrigerant charge is required in the HFO-1234yf or HFO-1234ze[E] system. The results also present that more refrigerant charge is required in the cooling mode than in the heating mode.