16 September 2011
Since synthetic refrigerants may cause environmental damages, by depleting the ozone layer or by contribution in global warming, many researchers, in recent years, have focused on the use of natural refrigerants such as ammonia to replace the synthetic ones.
Although ammonia has been used in large refrigeration systems, its application in small units, say a small heat pump, is quite rare.
The work presented in this paper is design and test of a small water-to-water ammonia heat pump, providing about 7 kW heat, sufficient for space heating and tap water heating of a
single-family house. To reduce the charge and to overcome the problem of accumulation of oil at the bottom of evaporator, a minichannel heat exchanger is used as evaporator. Oil
miscible in ammonia is also used to facilitate the oil return to compressor. A permanent magnet motor together with an inverter is used to run the compressor. Supplying the 7 kW
heat, the heat pump runs efficiently with heating capacity to compression work ratio of 5.1 at evaporation and condensation temperatures of -5 °C and 40 °C.