Ammonia-based hybrid chemisorption-compression heat pump for high-temperature heating

Abstract

Conventional compression heat pumps employing natural refrigerant of ammonia can barely meet the requirement of high-temperature heating above 90 °C, while ammonia-based chemisorption heat transformers characterised by high-temperature heating require driving heat source temperature above 80 °C. To address these issues, a novel ammonia-based hybrid chemisorption-compression high-temperature heat pump employing SrCl2-NH3 as the working pair is designed and established in this paper. Particularly, a conventional normal temperature compressor instead of an expensive high-pressure ammonia compressor can be adopted to upgrade the abundant 50–80 °C waste heat to 90–120 °C high-temperature heat. Simultaneously, due to that chemisorption reaction heat is larger than condensing heat of refrigerant, this heat pump has significant potential for improving coefficient of performance (COP). For the first time, regulation strategies of key parameters such as sorption pressure, desorption pressure, and sorption reaction exothermic time are proposed, and these provide the theoretical support for the stable and efficient operation of the heat pump. Moreover, its performance is evaluated by varying operating conditions. The results indicate that at heat output temperature of 100 °C, the optimal sorption pressure and reaction exothermic time are 1.70 MPa and 22 min, respectively. At waste heat temperature of 70 °C and heat output temperature of 110 °C, the COP of the heat pump is 4.58, i.e., its efficiency is 14.5% more than that of R245fa compression one.