Considering the fact that Warri is located in the sub-tropical region of Nigeria which is characterized by excessively high temperature and high humidity, it is necessary to develop an air-conditioning system which can reduce the hot and ambient temperature within a confined space for human comfort. This research presents the design of an air-conditioning system for comfort of occupants in a 400-Seater auditorium. The three independent variables considered for this design are; the number of occupants, air exchange rate and the outdoor temperature. The auditorium was properly measured and the heat generated by the bulbs, appliances and occupants were adequately considered to get the required cooling load. Regression analysis was used to predict and determine the cooling load. Optimization analysis was also done to determine the optimal condition for maximum cooling load. The plant capacity that will provide thermal comfort for the 400 occupants was calculated to be 25 ton of refrigeration (TR).