Ammonia and Carbon Dioxide Heat Pumps for Heat Recovery in Industry

This paper presents a generic, numerical study of high temperature heat pumps for waste heat recovery in industry using ammonia and carbon dioxide as refrigerants. A study of compressors available on the market today, gives a possible application range of the heat pumps in terms of temperatures. Calculations of cycle performances are performed using a reference cycle for both ammonia and carbon dioxide as refrigerant.

For each cycle a thorough sensitivity analysis reveals that the forward and return temperatures of the heat sink (condenser or gas cooler) of the heat pump are most important for the coefficient of performance, COP. By comparing the cycles it is found that for each set of operating conditions the two refrigerants perform equally well at one given inlet temperature of the heat sink.

Above this temperature ammonia cycles have the best COP and below CO2 cycles perform best. A general conclusion is that ammonia heat pumps are best at heat sink inlet temperatures above 28°C and CO2 is best below 24°C, independent of other parameters.