Abstract
HFO-1234yf and HFO-1234ze[E] have low global warming potential and zero ozone depletion potential. If they are used in the direct expansion ground source heat pump 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 direct expansion ground source heat pump 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.
Highlights
Direct expansion ground source heat pump (DXGSHP) has only copper loops circulating refrigerants which exchanges heat directly with the soil through the walls of the copper tubing
HFC-134a has the highest capacity per unit mass flow rate
The results show that refrigerant charge of HFO-1234yf system is 21% more than that of HFC-134a system, whereas cooling capacity and heating capacity of HFO-1234yf system are 2% and 8% less than those of HFC-134a system respectively
Summary
Direct expansion ground source heat pump (DXGSHP) has only copper loops circulating refrigerants which exchanges heat directly with the soil through the walls of the copper tubing. It is an energy-efficient and environmentally clean space conditioning system. It has the risk of ground contamination if refrigerant leak into the ground, as the loops containing refrigerant are directly buried in the ground. Refrigerants with high GWP are facing to be phased out. In 2007, DuPont and Honeywell co-developed hydrofluoroolefins (HFOs) to replace HFCs in air conditioning units. HFO-1234yf and HFO-1234ze[E] are the two most suitable to the air conditioning system [3]
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