Applying the numerical simulation program TRNSYS, the energy costs of a VAV system and a cooling ceiling system have been compared. Also, the first costs and the space requirements for the plants have been collated. The cooling ceiling system was combined by the mechanical ventilation for the supply of outside air rate. Several parameters were varied to determine their influence on costs. A cooling ceiling system incurs lower energy costs and space requirements than VAV systems. Concerning the first costs there is a break even point at a specific cooling load of 45-55 W m(-2). At higher cooling loads the first costs of a cooling ceiling system ate more favourable.