Improved water to water heat pump design for low-temperature waste heat recovery based on subcooling control

Traditional heat pumps designs have been optimized for heating applications based on small secondary temperature lifts (around 5K); however, in applications with other characteristic temperature lifts, different design criteria could be required. For instance, transcritical cycles have demonstrated to have a high efficiency for domestic hot water production with high water temperature lifts. This work presents the experimental results of a new water-to-water heat pump composed by the basic heat pump components (condenser, compressor, evaporator, expansion valve and liquid reliever) able to adapt its performance depending on the required water temperature lift. Domestic hot water production from grey water waste heat recovery has been chosen as experimental application to test this heat pump. Results show COP values up to 5.5 at the design condition (20-15 degrees C at the inlet-outlet of the evaporator and 10-60 degrees C at the inlet-outlet of the condenser) and an optimal degree of subcooling of 47 K. (C) 2019 Elsevier Ltd and IIR. All rights reserved.