Complaints on thermal comfort and confusions on cooling load calculation are still two main issues for the design of stratified air distribution (STRAD) system. This paper investigated these two issues for STRAD systems applied in a large space lecture theatre. The simulation results revealed that best satisfied thermal environment was obtained when supplied air from floor level, terrace and desk-edge mounted grilles simultaneously. A new method for the calculation of the occupied zone cooling load, which is based on CFD (computational fluid dynamics) simulation was proposed and tried. The effective cooling load factor concept was further clarified, which can be conveniently used to calculate the occupied zone cooling load and then determine the supply airflow rate. The concepts of occupied zone cooling load reduction and the associated but different cooling coil load reduction were differentiated, and it was illustrated that cooling coil load reduction up to 16.5% of the space cooling load can be achieved with split location of return and exhaust grilles. These simulation works provide a good basis for full-scale experimental validation of the key energy saving features of a well-designed stratified air distribution system. (C) 2012 Elsevier B.V. All rights reserved.