A simulation program has been developed for Changi International Airport Services (CIAS) solar heating system and predicted results are compared with observed performance. The solar system consists of energy collection and storage device, heat exchangers, air cooling units, and auxiliary heaters. Established engineering principles have been used for the simulation of the components, and the meteorological data have been used as the driving function. Experimental results are compared with predicted values, both on hourly and daily basis. Simulated results are found to agree reasonably well with the measured data within the accuracy of measurements. This helps to establish the validity of the model for system simulation and thus it can be used for the evaluation of long term performance of a solar system applied to industrial process heating.