Evaluating Applicability of a Scroll Expander for CO2 Refrigeration System at Warm Climate

Performance of a trans-critical CO2 refrigeration cycle equipped with a scroll work recovery expander is investigated using a semi-empirical model of the scroll, for high ambient temperature application. Maximum isentropic efficiency of 61% is obtained, for a pressure ratio of about 3.7 for the scroll expander. Simulation results obtained are further validated against the reported experimental results. It is also observed that, about 20% of the total energy consumed can be recovered with the help of scroll expander during trans-critical operation. Based on year-round ambient temperature data, at New Delhi (India), an economic analysis is carried out for installation of work recovery scroll system. Total payback period (PBP) for scroll expanders of various capacities are also determined. It is noted that the PBP of scroll expander is about 1 to 2 years or less, which is encouraging. Total Equivalent Warming Impact (TEWI) of the system is compared with that of a conventional trans-critical CO2 refrigeration system and system running on low global warming potential (GWP) hydrofluoroolefin (R1234yf) refrigerant. Trans-critical CO2 system along with work recovery scroll expander appears justified as the same has about 15% lower TEWI compared to conventional trans-critical CO2 system but is 50% more than R1234yf system.