A ‘Self-Regulating’ Heat Pump for Renewable Energy Applications

Summary

Several European countries have embarked on major programmes for the development of wind power. These have been primarily directed at supplying electrical power to the grid. However, since wind power cannot be relied upon to meet base loads, the economics have been based on the resulting fuel savings at base-load stations. These calculations, not surprisingly, show wind energy in a very unfavourable light. Nevertheless, many processes may be operated with a time-variable energy input: greenhouse heating, drying and desalination are examples. Such thermal processes are particularly suited to windpower, since the wind can supply not only shaft work, but also low-grade thermal energy, particularly in the form of the latent heat of its moisture content. Thus a heat pump system that is capable of upgrading ambient thermal energy over a wide range of shaft power input could be driven by a wind turbine generator (or wind-driven compressor) to supply heat for moderate temperature thermal processes.

The use of a working fluid of variable composition in a compression heat pump makes possible the abstraction of heat at useful temperatures over a range of compressor work inputs. Such a system has been designed and constructed to use a zeotropic mixture of R113/R114, whose composition is automatically adjusted in response to variations in the available shaft power. Prelimin ary operating experience and experimnetal results from this prototype are described. For the system to be used in conjunction with windpower devices, the fluid composition must respond rapidly. A method of achieving this is described, with the aim of matching the self-regulating heat pump to wind energy applications.