Energy Analysis and Working Fluid Selection of Combined ORC-VCC Refrigeration System Operated by Low-Grade Thermal Energy Sources

Abstract

Combined Organic Rankine Cycle (ORC) and Vapor Compression Cycle (VCC) is one of the most common systems used for refrigeration and R22 is one of the most common refrigerants used in the system. However, global warming is one of the today’s biggest concern which is driving the world towards adoption of environmentally friendly products and processes. In this regard, many of the widely used refrigerants such as R22 are on the verge of being phased out due to their global warming potential (GWP) and ozone depletion potential (ODP). Hence, there is dire need to find refrigerants with not only low GWP and ODP but also promising performance. In this paper, thermodynamic analysis of a combined ORC-VCC system powered by low-grade energy source is presented. The system is modelled in Engineering Equation Solver (EES) and its performance is assessed using two parameters: Cooling Capacity (CC) and Coefficient of Performance (COP), calculated under complete refrigeration mode, i.e., all the turbine power output is consumed by compressor. Three working fluids with low GWP and ODP from different working fluid categories are selected: R290 (hydrocarbons), R152a (hydrofluorocarbons) and R1234yf (hydrofluoroolefins), and a comparative thermodynamic performance analysis of selected working fluids against R22 is conducted. From the results, it is concluded that both R152a and R290 are potential candidates. From performance point of view, R152a, with low but some GWP, is a high performing working fluid, having COP lower than that of R22 by approx. 2.8%. Whereas, from environmental perspective, R290 has no GWP, provides the highest CC under same operating conditions, and has COP lower than that of R22 by around 8.5%.