Implementation of a scroll booster compressor into a single-stage air-water heat pump for peak winter day

This paper shows an implementation of a scroll booster compressor mounted at the suction line of a single-stage air-water heat pump. The compressor selected to be used as booster is a beltdriven scroll compressor initially dedicated to automotive refrigeration. For the tests reported here, it is driven by an electrical motor and has been modified to obtain a lower built-in volume ratio. The computations for those modifications have been made with our own software called GeoScroll. Tests of the heat pump at A-11/W65 show a large improvement of the heat output, which is doubled (raising from 7.39 kW, in the normal single-stage configuration, up to 15.7 kW) while the COP decreases by less than 10% (from 2.08 to 1.89). This performance degradation is not due to bad performances of the booster compressor, that are at the level expected, but to a decrease of the evaporation pressure (1 bar, which is equivalent to 11 K), as the evaporator has not been designed for such heating powers. Even with working conditions outside its design range, the heat pump behavior with the booster has been proved to be very stable (the experiments were performed over few weeks). Furthermore, no oil accumulation has been noticed in the booster compressor, which is favorable to an integration of the device into existing heat pumps, currently in service. Indeed, it can be easily included into existing single-stage heat pumps with few adaptations. The concept is attractive in comparison to backup with heating devices, used in case of low temperatures, with a far better exergy efficiency and with contribution to the reduction of the electric demand peak.