Economic and thermodynamic aspects of vapour compression heat pump systems

Abstract Equations are presented which relate the payback period of a heat pump system to the fixed capital cost, the annual usage factor, the unit cost of input energy and the actual coefficient of performance. The latter is related to the theoretical Rankine coefficient of performance by a factor which depends upon the design of the particular heat pump system. It is shown that for a given condensing temperature of the working fluid and compression ratio, the gross temperature life and the theoretical Rankine coefficient of performance are fixed for a particular working fluid. The sensitivity of the relationhip between payback period and actual coefficient of performance to fixed capital cost and input energy cost is illustrated graphically.