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Under the thermal storage strategies in present studies, the power generation unit (PGU) in combined cooling, heating, and power (CCHP) system is turned on/off only based on the state of storage tank; or the operation state of PGU is determined by thermal demand or/and electric demand, which has no relationship with the state of storage tank. For these traditional strategies, either energy demands or state of storage tank is considered for the operation of system. This paper proposes a novel thermal storage strategy (TSS2) for CCHP systems, which determines the operational state of the PGU based upon electric demand, thermal demand and the state of thermal storage device. In this paper, the operation principle of TSS2 is described and compared with the traditional strategies. A hospital in Shanghai was used to evaluate and compared the performance of the system operating under different storage strategies. The results show that TSS2 improves the performance of CCHP system more significantly compared with the traditional strategies. TSS2 can make both PGU and capacity of thermal storage tank be fully used by CCHP system to produce more electric and thermal energy to meet demands of building. Compared with system without thermal storage, the minimum and maximum increase rates of annual total cost saving for traditional strategies are 0% and 14.84%, respectively. However, for TSS2, they can reach 3.79% and 20.22%. Similar conclusions could be achieved for CO2 emission reduction and primary energy saving. The effect of TSS2 on the CCHP system performance is different under different operation strategies.

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In this paper, a feed-in tariff policy which can contribute to both energy and economic performance of a CCHP system is proposed. By applying this feed-in tariff policy, the impact on design optimization (power generation unit capacity and operation strategy) and system performance (economic, energy, and matching performance) of a hospital CCHP system used in different climate zones are evaluated and analyzed. In policy one (Pol 1), no electricity is allowed to be sold. In policy two (Pol 2), the electricity selling price is constant. In policy three (Pol 3), the selling price of electricity is proportional to the PER (Primary Energy consumption Ratio) of the system when the PER is not lower than a critical value. Otherwise, the selling price is zero. The results show that Pol 3 can ensure both energy and economic performances of CCHP system. The effect of feed-in tariff policy to improve the performance of CCHP system reduces gradually from the cold zone to the hot zone. Multi-criteria decision making results show that Pol 3 with reasonable parameters is the best choice in all climate zones except for the hottest zone in this study. When improving PER is attractive, following thermal load operation strategy is the best choice under Pol 3. In the hottest zone of this study, little excess

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