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An adequate window system is one of the most important retrofit strategies for effective energy conservation of a building, because the U-value and solar heat gain coefficient of windows have enormous impact on the heating and cooling loads of buildings. Therefore, this paper presents methods for improving the energy efficiency of existing residences that have various window sizes and envelope insulations, through a window retrofit using optimal U-value and solar heat gain coefficient values. Furthermore, the window retrofit strategy has been standardized using analysis of the correlation between the properties of the retrofitted window and energy saving rates. The results show that the annual heating and cooling energy demand decreases by 7.9–16.7% when changing the U-value of the windows in a poorly insulated house, and that the relationship between the lower U-value and energy saving is strong for poorly insulated houses regardless of window size. However, for houses with better insulation and larger window sizes, the total energy usage decreases by 18.4–29.7% when the solar heat gain coefficient is lower, and the energy saving effect of the U-value decreases while that of the solar heat gain coefficient increases.Practical application: This study was focused on improving the energy efficiency of existing residences by applying retrofitting technology. By exploration of the contribution of the specific qualities of windows and the thermal envelope (insulation) system of buildings via simulation, it was determined that it is necessary to adjust the U-value and SHGC of retrofitted windows, in relation to the thermal performance and window-wall ratio of an existing residence, to achieve high energy efficiency. [ABSTRACT FROM AUTHOR]

In relation to recent attention focused on the use of energy by lighting, there is a large potential for commercial buildings to save energy in this respect. The use of energy-saving bulbs or dimming controls triggered by daylight, not only enables lighting energy saving, but delivers cooling energy through a reduction in indoor heat production. In this study, we examine the energy use in commercial buildings by evaluating lighting energy saving methods and the effect of using dimmer controls with a heat control method, which can both maximize the cooling load reduction during summer and save energy. Results show that the total energy from the reference commercial building was reduced by 20.9% by replacing LFL T12 bulbs with LEDs, together with an additional saving of 19.9% in cooling energy by using the lighting heat & dimming control method. [ABSTRACT FROM AUTHOR]