States that building operation strategies can greatly affect occupant comfort and energy use, especially in thermally-massive buildings. Building simulation tools can provide the HVAC system designer with detailed information about the dynamic behaviour of a building, enabling him to optimise the capacity and operating schedules of the HVAC system to take advantage of the thermal mass of the building. Presents a technique for using an hour-by-hour building simulation program for sizing calculations. States the simulation tool is especially applied to determining optimum setback strategies. Maintains that this design approach produces systems with smaller capacities that provide superior comfort with lower first costs and lower operating costs.

KEYWORDS: Calculating, buildings, heavy, thermal inertia, designing, heating, ventilation, air conditioning, computer programs, sizing, night setback.