Design and modelling of a small-scale reversible heat pump – organic Rankine cycle system for industrial waste heat recovery

The organic Rankine cycle (ORC) and heat pumps (HP) are technologies well known for industrial waste heat recovery. Considering the similarities in the configurations for both ORC and HP, a system that can be reversed between HP and ORC modes is possible with few modifications. The reversible system according to the requirement of the industry can exploit waste heat in a lower temperature band operating as a heat pump to provide useful process heat or as an organic Rankine cycle system generating power and thus increasing the efficiency of waste heat exploitation. This study discusses the design aspects of a small-scale reversible HP-ORC system, including the system layout, component selection, selection of a low global warming potential (GWP), zero Ozone depletion potential (ODP) refrigerant, the operating conditions for both modes, and sizing of equipment. R1233zd(E) was selected as the preferred refrigerant to replace R245fa in the reversible system and an automotive open drive scroll compressor was found to be suitable which can also be employed as an expander for ORC with minimum modifications. The study also presents the modelling of the reversible system in ORC and HP modes including performance analysis of scroll machine in expander and compressor roles attaining isentropic efficiency values up to 62.4% and 75.4% respectively. The modelling results show a cycle efficiency of 5.9% (Tev = 102°C, Mr = 0.064 kg/s) in ORC mode and a COP of 3.88 in HP mode (for a temperature lift of 50K with Tsource: 75 - 85°C).