A Central Solar Heating Plant with Seasonal Storage (CSHPSS), which is under construction in Korea, is simulated using TRNSYS to predict thermal performances and economic aspects. The system is located in Cheju Island, a far southern part of Korea, and consists of two arrays of collectors, a medium-sized storage tank, and two thermal loads. The loads are an office building and a greenhouse for agricultural research. Simulation results clearly reveal that Cheju Island is climatically best suited for solar heating in Korea showing 50 to 80% more solar fractions than other inland areas. The main reason for the better thermal performance for Cheju is its warmer winter climate. The system under construction has a 184 m(2) collector area (A) and 600 m(3) of storage volume (V). TRNSYS prediction for the system is that about 39% of the total heating load of 885 000 MJ/year can be provided from the sun. The estimated Return Of Investment (ROI) range from 25 to 30 years. The validity of the design is checked through a ＇what-if＇ test around the design point of A =184 m(2) and V= 600 m(3). The solar fraction for different system sizes and the ＇virtual solar self-sufficiency＇ conditions are also calculated even though the actual system is not economically viable with the designed small size. Our calculation reveals that low-cost CSHPSS systems could be constructed anywhere in Korea, provided only that the system size is sufficiently large.