High-temperature heat pumps based on natural working fluids to produce district heating from industrial waste heat.

Abstract

The amount of industrial waste heat produced in Europe annually corresponds to the total annual heating demand in buildings. Common barriers for utilizing this heat are the lack of required infrastructure, i.e. a district heating (DH) network, and too low temperature of the waste heat. To address the last-mentioned barrier, high-temperature heat pumps may be applied to upgrade the heat. This study evaluates the possibility of utilizing a heat pump to supply DH using industrial wastewater at 40 °C as a heat source. Different heat pump technologies based on natural refrigerants were compared at steady state operating conditions: single- and two-stage ammonia, and ammonia-water absorption-compression (hybrid) heat pumps. The highest COP as well as the lowest operating pressure were obtained with a two-stage hybrid heat pump. Moreover, the COP for hybrid heat pumps was hardly affected by an increase in the desired DH supply temperature.