On the development of high temperature ammonia–water hybrid absorption–compression heat pumps

• High temperature development of an ammonia water hybrid heat pump is investigated.
• Three maximum pressure cases were studied 28 bar, 50 bar, and 140 bar.
• Two maximum compressor discharge temperature cases were studied 170 °C and 250 °C.
• For 170 °C a heat supply temperature of 111 °C, 129 °C and 147 °C is attainable.
• For 250 °C a heat supply temperature of 182 °C, 193 °C and 223 °C is attainable.

Ammonia–water hybrid absorption–compression heat pumps (HACHP) are a promising technology for development of efficient high temperature industrial heat pumps. Using 28 bar components HACHPs up to 100 °C are commercially available. Components developed for 50 bar and 140 bar show that these pressure limits may be possible to exceed if needed for actual applications. Feasible heat supply temperatures using these component limits are investigated. A feasible solution is defined as one that satisfies constraints on the COP, low and high pressure, compressor discharge temperature, vapour water content and volumetric heat capacity. The ammonia mass fraction and the liquid circulation ratio both influence these constraining parameters. The paper investigates feasible combinations of these parameters through the use of a numerical model. 28 bar components allow temperatures up to 111 °C, 50 bar up to 129 °C, and 140 bar up to 147 °C. If the compressor discharge temperature limit is increased to 250 °C and the vapour water content constraint is removed, this becomes: 182 °C, 193 °C and 223 °C.