Economic possibilities and limitations of heat pumps with electric drive

Abstract

The principles of the heat pump are analysed with special reference to the heating of homes and buildings, use being made of the concepts ‘Exergy’ and ‘Anergy’. Economic criteria are introduced to take account of capital and installation costs and the rates of amortization and interest to be applied to both heat pumps and conventional fuel systems. Also, the relative costs of fossil fuels and electricity are used, together with a mean coefficient of performance of the heat pump. A comparison is made not only between the two systems but also for composite systems in which the output of the heat pump is supplemented or replaced by direct heating (electrical resistance or fossil fuel) during winter peaks. The effect of the electricity tariff on the attractiveness of a heat pump system is examined, together with the potential advantage of heat storage systems. It is concluded that the most attractive application of heat pumps arises with district heating schemes due to the lower capital charges associated with large installations. In certain cases, however, the combination of a small heat pump designed to meet say 70% of winter demand, supplemented by burning stored fuel at times of peak demand, could be economic for individual installations, especially if the capital cost of the supplemental system could be reduced. The scope for improving the coefficient of performance of heat pumps is outlined.