This paper is aimed at estimating the effect of various factors on the heating energy consumption and introducing night ventilation strategies to reduce cooling load in Korean apartment using TAS Modeller, TAS Ambiens and QuickSTREAM. The factor considered this paper type of remodelling, insulation level, window type and reset an internal temperature. The natural ventilation strategies considered here night ventilation, night flush cooling and solar chimney. Base on some assumption, an actual apartment unit is simplified into a model that is used for heating load in winter and looking into internal condition in summer night. The simplified model is validated by showing a good agreement with the actual one in heating load result. Refurbished balcony has a benefit in reducing heating load by 15%. Remodelled apartment is sharply increased in thermal load which must be avoided in view of energy conservation as well as structural problem. The most efficient and the easiest way of reducing heating load in current apartment are to set the internal temperature at 20 C. In second part of the simulation, we confirmed that it is possible to use natural ventilation for physiological cooling, night flush cooling to cooled structure and cooperating with solar chimney during the summer night time to reduce PAC's operating hours. The best case exceeds the bench mark temperature which is based on all windows being open all day. The CFD and Psychrometric chart results support to use of natural ventilation strategies in Korean apartments and shows that when Korean apartments adapt the night ventilation strategies, the occupants does not feel turning on the PAC system during cooling period time
