Diffuse ceiling ventilation system is an air distribution system, in which the outdoor air is supplied to the occupied room through the perforated panels installed in the ceiling. This method has been proven to have a higher cooling capacity compared to the conventional air distribution systems. This study is a part of an ongoing project consists of two phases. In the first phase, the project aimed to experimentally investigate the dependence of the cooling capacity on the location of heat sources in the room and the distribution of diffusive supply areas in the ceiling. The experimental study was carried out in order to calibrate the model of the test room with the perforated panels cover the entire ceiling. The second phase of the project numerically studied the cooling capacity of the system in several scenarios with different ratios of perforated to non-perforated panels in the ceiling, with even distribution of the heat sources. The obtained results showed that decreasing the area of the perforated panels can improve the cooling capacity of the diffuse ceiling system.