Article,
Techno-economic evaluation of a solar assisted combined heat pump – Organic Rankine Cycle system
Energy Conversion and Management, 94 (0): 430 - 437 (2015)
DOI: 10.1016/j.enconman.2015.02.011
Abstract
The economic feasibility of the addition of an ØRC\ to a combined solar system coupled to a ground-source heat pump is discussed. The ØRC\ prevents the stagnation of the solar loop and reverses the heat pump cycle. The working fluid is evaporated in the condenser of the heat pump, expanded in the scroll compressor, which becomes a scroll expander, and condensed in the brine heat exchanger. The only additional investments for the ØRC\ system comprise a pump, valves and upgraded controls and are estimated to be 400 € for a single-family-house unit. Flat-plate collectors are the preferred collector type as the higher collector efficiency of evacuated tube collectors does not outweigh the higher costs. The thermal recharging of the ground during ØRC\ has a negligible impact on the \COP\ of the heat pump. However, the recharging leads to less deep boreholes compared to a conventional system. Because of the low investments for the ORC, even small reductions in borehole depth make a significant contribution to the economic feasibility of the system. The addition of the ØRC\ overall generates a small profit of 155 € at Ankara and 74 € at Denver for a rocky soil and a thermally enhanced grout. On the contrary, the conventional solar combisystem coupled to a ground source heat pump was found to be economically unreasonable at all locations. The working fluid isobutane is interesting for future applications because of the lower global warming potential and the smaller saturation pressures compared to R134a. The latter allow for the installation of a mass-produced rotary vane pump reducing the additional investments for the ØRC\ to 200 €. This way the ØRC\ becomes reasonable at all locations with profits of 505 € at Ankara, 375 € at Denver and 189 € at Bochum.
