Abstract Tri-generation system is efficient in supplying thermal energy and electricity. But it is very difficult to satisfy multiple load demands simultaneously in real applications. Therefore, the benefit of tri-generation system is not so easy to realize. If the electric load is separated from the thermal load, difficulty of control would be avoided. In this work, combined cooling and heating (CCH) mode of tri-generation system is proposed. The generated electricity is only used to power the HVAC device, which converts all the electricity into thermal energy. Namely, there is only thermal output in this kind of mode. As for the rest electric load of user, it can be ensured by the public grid. Considering 20% of total energy consumption and 50% of building energy consumption may come from the HVAC system in developed countries. The CCH mode of tri-generation system would be potential in energy saving. The influences of system capacity, HVAC performance, public grid efficiency, and energy prices on system performances are analyzed. Results show that the CCH mode of tri-generation system can be much better than an independent HVAC system. For a system with generator capacity over 100kW, the payback period could be less than 4 years.