Amonijačne unutrašnje reverzibilne toplotne pumpe/čileri vazduh–voda

This paper will give an account of the background for and the stages in the development of an internally reversible ammonia air-to-water heat pump / chiller. (IRAW HP).The background for the development of the first version was a project where the specification demanded an ammonia chiller system that also could be used as a heat pump. There is neither river nor seawater available, boreholes where excluded partly due to fiscal considerations (investment cost app. €300 000), partly because the necessary ground area was not available. Therefore the heat dump / heat source had to be air. The solution suggested by the contractors included two chillers that would operate as a two stage system, but with a glycol circuit in between, and a dry cooler system as heat source. The overall system efficiency at design outdoor temperature of -8⁰C and a heat delivery temperature of 50⁰C was very low, as temperatures went up and down in the system configuration.The idea of moving the reversible action into the chiller unit was inspired by the defrost system of critically charged systems, developed by Star Refrigeration, but somewhat modified in the final design.Since this first system, the design has evolved, and further two systems have been supplied to the Bergen area in Norway and a fourth is under way, in yet a modified design.