Performance evaluation of modified compound organic Rankine-vapour compression cycle with two cooling levels, heating, and power generation

Abstract

This work analyses a novel combined organic Rankine-compound ejector vapour compression cycle for power, cooling and heating production using a low-grade ground heat source as the primary heat source. Ultra-low global warming potential working fluids (R1234ze(E), R1243zf, and R1234yf) and parameters quantifying energy and exergy efficiency are considered. The system can be adapted to three operating modes, depending on the ground source temperature, ranging from 55 to 90 ◦C: power-cooling, power-heat pump heating, and powerground source heating. The results indicate that this system notably increases the overall performance of all investigated refrigerants. Compared to conventional organic Rankine and vapour compression cycles (ORC and VCC), the R1234ze(E) power-cooling mode shows the highest coefficient of performance (COP) increase, 18 %. Besides, including a recapture heat exchanger for condenser waste heat recovery can increase power generation by 58 %. At ground source temperatures up to 65 ℃, power generation and thermal efficiency increased in the power-heating mode due to the absence of the compressor power consumption. The exergy efficiency follows the ground source temperatures for all modes. In power-ground source heating mode, the exergy efficiency notably increased due to the absence of the heat pump exergy destruction.