Solar Community Energy and Storage Systems for Cold Climates

For a hypothetical solar community located in Toronto, Ontario, the viability of two separate combined heating and cooling systems were investigated. Four TRNSYS integrated models were developed for different cases. First, an existing heating only solar community was modeled and compared with published performance data as the base case with suggested improvements. The base case community was then used to develop a hypothetical solar community, located in Toronto, requiring both heating and cooling. In this second model an absorption chiller was added – Solar Thermal Chiller (STC) system. The chiller received its source heat from the solar thermal system with the supplemental heat from a natural gas boiler. The STC system was designed with two borehole thermal energy storage units (BTES). One was high-temperature BTES for the solar thermal energy storage, and another was medium-temperature BTES for the chillers’ heat rejection. The twenty year simulation results showed that by the fifth year in the heating season, the community operated with 100% solar fraction (SF). In the cooling season, the chiller received 18% of its required energy from the same number of solar collectors as the heating-only community system. The third model was based on the central heat pump system with borehole thermal storage for the heating and cooling, using a PV system as the heat pump power source - Heat Pump Photovoltaics (HPPV) system. The simulation results showed that the system operated favorably from the first year and did not have any significant performance degradation in 20 years. On average, the heat pumps performed with the seasonal COP of 3.3 in the heating mode and 5.9 in the cooling mode. The fourth system, Solar Thermal-Heat Pump Photovoltaics (ST-HPPV), a solar thermal system with borehole thermal energy storage as a supplemental heat source to the HPPV, was investigated. The simulation results showed that this system would be beneficial for a community with the annual heating and cooling difference of more than 75%. By adding a solar thermal system to the HPPV system, the heat pumps’ performance improved by 26% in the heating mode, and exhibited a negligible drop in the cooling mode.