The long-term system simulation and economic analysis of solar-assisted cooling/heating system (SACH-2) was carried out in order to find an economical design. The solar heat driven ejector cooling system (ECS) is used to provide part of the cooling load to reduce the energy consumption of the air conditioner installed as the base-load cooler. A standard SACH-2 system for cooling load 3.5 kW (1 RT) and daily cooling time 10 h is used for case study. The cooling performance is assumed only in summer seasons from May to October. In winter season from November to April, only heat is supplied. Two installation locations (Taipei and Tainan) were examined. It was found from the cooling performance simulation that in order to save 50% energy of the air conditioner, the required solar collector area is 40 m(2) in Taipei and 31 m(2) in Tainan, for COP(j)= 0.2. If the solar collector area is designed as 20 m(2), the solar ejector cooling system will supply about 17-26% cooling load in Taipei in summer season and about 21-27% cooling load in Tainan. Simulation for long-term performance including cooling in summer (May October) and hot water supply in winter (November April) was carried out to determine the monthly-average energy savings. The corresponding daily hot water supply (with 40 degrees C temperature rise of water) for 20 m(2) solar collector area is 616-858 L/day in Tainan and 304-533 L/day in Taipei. The economic analysis shows that the payback time of SACH-2 decreases with increasing cooling capacity. The payback time is 4.8 years in Tainan and 6.2 years in Taipei when the cooling capacity >10 RT. If the ECS is treated as an additional device used as a protective equipment to avoid overheating of solar collectors and to convert the excess solar heat in summer into cooling to reduce the energy consumption of air conditioner, the payback time is less than 3 years for cooling capacity larger than 3 RT. (C) 2011 Elsevier Ltd. All rights reserved.