Experimental results of an absorption-compression heat pump using the working fluid ammonia/water for heat recovery in industrial processes

Abstract

The full potential of hybrid absorption-compression heat pumps, which can cover heating demands at temperatures of around 100 °C and provide additional cooling in industrial processes, has yet to be exploited. Although research has also been conducted on alternative systems, the natural working pair NH3 and H2O still has numerous advantages, being a very economic and thermodynamically well-suited refrigerant for this application. Striving for the development of a heat pump system that can cover a large range of heating demands at a temperature of about 80 °C and create useful cooling power in industrial processes, a test rig was designed and built at the Institute for Thermodynamics at the Leibniz University in Hanover. According to the targeted heating power of 50 kW, the components of the system are chosen based on a simulation model that solves mass, energy and component-specific balance equations for each of the parts simultaneously. This simulation is later used to compare and evaluate experimental data. Constant parameters are water-inlet temperatures at the heat source of 59 °C and at the heat sink of 50 °C. Depending on the mass flow of ammonia-poor solution and the condensation pressure, the heating capacity and the COP of the test rig are investigated. The range of the poor solution mass flow is from 0.21 kg/s to 0.31 kg/s, while the absorption pressure is varied between 13.5 bar and 16.5 bar. The COP of heating reaches a maximum of 2.5, providing more than 40 kW of heating power at a maximum internal temperature lift of 43 K.