Off-design performance of an organic Rankine-vapor compression cooling cycle using R1234ze(E)

In this study, a 264 kW(th) organic Rankine-vapor compression cycle (ORVC) was experimentally tested over a range of conditions to quantify the individual impact of off-design external conditions. The ORVC was designed to recover waste heat at 91 degrees C, reject heat to a liquid condenser stream at 30 degrees C, and produce chilled water at 7 degrees C. The condenser heat rejection temperature was varied from 16.6 degrees C to 32.6 degrees C, the chilled water delivery temperature was varied between 2.1 degrees C and 13.1 degrees C, and the heat input temperature was varied from 91 degrees C to 120 degrees C. As the condenser heat rejection temperature decreased, the coefficient of performance (COP) of the ORVC improved from 0.558 at 30 degrees C to 0.682 at 16.6 degrees C, despite a reduction in compressor isentmpic efficiency. Although the chilled water temperature variation had almost no impact on the organic Rankine cycle performance, the compressor efficiency decreased when the delivery temperature was below 7 degrees C. At the highest chilled water temperature, 13.1 degrees C, the COP of the ORVC was 0.643. Compressor stall was noted when the condenser heat rejection temperature was greater than 32.6 degrees C and the chilled water delivery temperature was below 2.1 degrees C. Increasing the driving heat source inlet temperature improved the COP of the ORVC and the thermal efficiency of the organic Rankine power cycle, while decreasing the efficiency of the compressor and the COP of vapor compression cycle. In addition, the integrated part load value of the system was determined through experimentation to be 0.682, which provides a realistic estimate of real-world performance.