Varying cooling load requirements in HVAC system become a major concern to many consumers because of the additional cost of electricity. The cooling load variation of HVAC system usually occurs when the domestic house door is frequently kept open for prolonged durations, which is particularly important in hot seasons. The present study, addresses a comparison of energy consumption due to the thermal disturbance during domestic house door keep opened for various duration when the Variable Frequency Driver (VFD) and ON/OFF controllers are installed in HVAC system. The experiments are carried out in two identical houses d uring six warm days in a hot season where the outdoor temperatures have similar patterns throughout the days. The energy response of HVAC system is analysed incorporating the thermal and the electricity consumption data because of the change of the indoor temperature during opening of the house main door. The cost analysis is carried out and it is extended to
include several repeats of door opening durations. It is the first time demonstrated that the energy consumption for
HVAC system increases dramaticall y when the house main door is kept opened for several times in a day. The energy
consumption and additional cost increase significantly for the case when the period of the main door opening is
extended. In this case, VFD A/C controller unit achieves more e nergy savings than that of ON/OFF A/C controller
unit.