The Korean government has introduced the building energy saving measures, including higher insulation levels for building envelope. In addition, the government announced its plan for the implementation of energy consumption certification system in which energy consumption information should be attached to at the time of any real estate transactions. However, there are still many existing buildings that tend to consume more energy for heating and cooling than new buildings as they were built under the former building code requiring relatively higher U-values of walls and windows. Accordingly, in order to improve energy efficiency in existing buildings, green remodelling of building envelope and building services is required. For existing buildings, building services improvements have been achieved through energy service company(ESCO), but much attention has not been paid to building envelope improvements for various reasons, such as uncertainty of energy saving effect, design issues and costs. The aim of this study is to evaluate the impact of building envelope improvements in an existing office building on its heating and cooling energy loads. For this purpose, this study carried out building energy simulations for a case building using the EnergyPlus simulation program. Through the simulation results of the case building, this study selected the remodeling elements applicable to the building envelope, and analyzed the energy saving effect of the green remodeling.
During the energy modelling process for the building, heat loss of the case building was found to be big in the order of the infiltration, windows, and opaque envelops. Accordingly, this study made a comparative analysis of building energy performnce according to remodeling elements, such as airtightness, and insulation performance of the windows and opaque envelops As a result, when improving at a level of a ''passive house'', the annual energy demand was reduced by about 26.9% with the improvement of airtightness, and according to the improvement in insulation performance of the windows and opaque envelops, was reduced by 9.4% and 4.8% respectively. In case all elements are applied, the energy demand was reduced by the maximum 34.4%. On the other hand, in case all elements are improved at a level of a passive house, energy demand reduction rate was found to be 31.9%.
In actual management of a building at a level of a passive house, the control method to cope with cooling loads such as movable shading or night ventilation should be applied, even though this study didn''t reflect this area as it mainly focused on insulation level of building envelope. In other words, in order to increase the energy saving effect through the building envelope remodeling, it''s necessary to consider the reduction of internal heat gain during summer and the release of the internal heat through natural ventilation.