Since the 1960s, the construction of high-rise apartment buildings has been prolific across Asia. These buildings, nowadays, are required to reduce excessive energy consumption in order to mitigate carbon emissions. Various measures of refurbishment strategies have focused on measuring energy saving. A building energy model, one of the more dominant measurement methods, needs to be advanced for more reliable and achievable results. However, the current approaches for existing apartments in the context of South Korea is unsatisfactory due to influential factors, being disregarded in the process. This study aims to develop a building energy model of existing apartment buildings for energy-efficient refurbishment in South Korea by integrating the influencing factors that cause variation in actual energy consumption. The developed building energy model implemented to evaluate refurbishment strategies of reducing energy consumption with respect to future climate change. The overall results can be summarised as follows: firstly, the prioritisation of the physical characteristics affecting energy consumption provides one determinant building feature, construction years, and two subsidiary features, heating methods and unit sizes, to classify existing buildings. Secondly, the 90% probability of occupants' behaviours, inferred from actual consumption, is set with 17-20°C set temperatures and 3-8 hours of operation for heating. Electricity consumption is derived from 3-6 hours of operation with several influential appliances. Thirdly, variation among the middle floors requires the building energy model specified with individual units. Moreover, a numerical model of individual heating controls showed 18-22°C set-point temperatures in apartment units with different locations with 7-8 hours of heating. Lastly, the refurbishment strategies based on the thermal regulations in 2011 efficiently reduce energy consumption. However, further improvement of increasing insulation is not efficient. Climate projection for a heating dominant climate would have a limited impact on the total energy consumption, with only 600 kWh/year in 2050.