*2.7. Heat Pump*

The operating principle of HP is based on the supply of high temperature heat to a heat sink thanks to the heat supplied by a low temperature source combined with mechanical work performed by a compressor. The sum of the heat supplied by the source plus the mechanical work of the compressor is the useful thermal heat obtained.

Currently commercial high temperature heat pumps can reach sink temperatures of at least 90 °C up to 165 °C with heating capacities ranging between 20 kW and 20 MW. The heat source temperatures range between 20–65 °C from brine, water or waste heat [42].

Because of the limited maximum temperature of 165 °C a closed cycle for a heat pump system is technically not possible for the sterilisation process of pet food which is analysed in the following case study. In food processing plants, there is an opportunity to take advantage of a large amount of water with still a high energy potential from waste heat that is available after cooling the processes. This water is stored in a reservoir at about 70–80 °C. To take advantage of this potential, a steam recovery system with a multi-stage of 8 blowers for the open cycle simulation has been designed. Commercial industrial heat pumps can achieve coefficients of performance (COP) ranging between 2 and 6.
