Optimisation of a heat pump space heating system

Because the heat pump has a very high capital cost compared with other forms of space heating, and also because the peak space heating demand in the U.K. only occurs for a few hours in the year, it has become recognised practice to install low capital cost supplementary electric heating to meet peak demands. A technique is described which optimizes the mix of heat pump and supplementary capacity to minimize the total cost of operation. A simulation model is employed which uses a weather tape containing hourly outside air temperatures to generate a space heating demand profile for a building of known thermal characteristics. The technique specifically allows the examination of intermittent heating, and in this paper is applied to a small factory operating on a variety of shift patterns. This application is of particular interest because it considers the effect of maximum demand charges on the economics of heat pump space heating systems. It is concluded that the optimum heat pump capacity depends strongly upon the length of shift, and that optimum oversizing of the heat pump system for intermittent heating appears to be lower than for conventional heating systems as a result of maximum demand pricing.