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A centralized solar hybrid heating and cooling system satisfying the thermal, cooling and sanitary water demands of a typical Italian small district composed of six residential buildings situated in Naples (southern Italy) is modelled, simulated and analyzed through the software TRNSYS over a period of 5 years. The plant is based on the operation of solar thermal collectors coupled with seasonal borehole storage; the solar field is also composed of photovoltaic solar panels connected with electric energy storage. An adsorption chiller powered by solar energy is adopted for cooling purposes, while a condensing boiler is used as an auxiliary unit. The performance of the proposed system has been assessed from energy, environmental and economic points of view and contrasted with the operation of a typical Italian heating and cooling plant, highlighting the following main results: (i) saving of primary energy consumption up to 40.2%; (ii) decrease of equivalent CO2 emissions up to 38.4%; (iii) reduction of operating costs up to 40.1%; (iv) simple pay-back period of about 20 years.

In this study, a TraNsient SYStems (TRNSYS) simulation model for solar thermal systems is developed to assess the potential of solar energy utilization in cold climate zones, such as Ulaanbaatar (Mongolia), which is one of the five cities with the worst air quality in the world. Since air pollution contaminates solar collectors and decreases their efficiency, this model accounts for dust deposition behavior so that the best cleaning time for the collectors can be estimated. The simulation results show that the best cleaning time falls between the middle of January and the beginning of February. In addition, a collector cleaned once during the heating period is estimated to produce 12% more energy compared with a collector that has not been cleaned.

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