A shot in the cold: a new open regenerative cycle for heat-pumps and refrigerators
Although Stirling heat-pumps and refrigerators offer the possibility of environmentally-friendly operation by using air as the refrigerant, the Coefficient of Performance (COP) of low-cost Stirling systems is only about the same as that of conventional vapour-compression technology. For this reason, Stirling machines have been perceived as lacking the significant advantages required to supplant vapourcompression systems in heat-pump and refrigerator applications. This paper discusses a new open regenerative cycle for heat-pumps and refrigerators that offers similar performance to practical Stirling systems. Additionally, it eliminates the need for a heat absorbing heat-exchanger (the most costly component of conventional vapour-compression heat-pumps), and has inherent frost-free operation (frosting significantly degrades the performance of conventional vapour-compression heat-pumps at low temperatures). An experimental prototype has been designed by modifying the MAG1 Regenerator Test Rig. Sage simulations of the experimental prototype suggest that an indicated Heating COP of at least 3.4 may be possible at the standard heat-pump rating temperatures of 20ºC (hot space) and 5ºC (cold space). Although the new open regenerative cycle has low Heating and Refrigeration Effect per unit volume, it appears to offer a number of potential advantages over both Stirling and conventional vapourcompression machines in the context of small systems.