Heat pumps: trends and possibilities

Abstract

The recent developments in heat pump technology have been prompted by a change from using refrigerating machines to real heat pump design. The compressor must be built for higher pressures and higher pressure ratios. The drives of heat pump compressors are not only electrical motors but are also diesel or gas-energized motors. This gives a large change in primary energy consumption. For all types of drives there is a tendency towards varying speed for capacity control. Electrical motors can do it by a change of frequency whereas combustion engines can change the speed un to 3 : 1 without any hard change of relative energy consumption. Higher speed ratios are sometimes very critical for the suction- and dischange-valves of the piston compressors. Therefore it is necessary to look for on-and-off control with a short-time heat storage. In several parts of the world investigations are going on into the influence of suction gas cooling on the energy consumption of heat pumps. A wide range of refrigerants and refrigerant mixtures must be considered as suitable for heat pumps. Quite a large field of development is in the area of thermal heat pumps. The absorption refrigerating machine is very well known but for heating purposes, new system designs and especially new working couples are necessary. Even with knowledge of the criteria for the refrigerants and solvents, it will be hard work developing optimal substrates. Beside advances in adsorption machinery there will also be developments in the fields of adsorption and resorption heat pumps. Looking towards total energy systems Rankine-cycle heat pumps are of great interest. The applications of heat pumps lie not only in low temperature heating with air, water or earth as the heat source, but also in a wide range of heat recovery systems for industry. In future the temperature range of industrial heat pumps will be going up to 573 K (300°C) or more. The development of heat pumps and their applications is in its infancy. There will be a lot of work to be done. Let us do it.