Abstract
Energy loss through windows can be high relatively compared to other opaque surfaces because insulation performance of fenestration parts is lower in the building envelope. Electrically heated window systems are used to improve the indoor environment, prevent condensation, and increase building energy efficiency. The purpose of this study is to analyze the thermal behaviors of a heated window under a field experiment condition. Experiments were conducted during the winter season (i.e., January and February) with the energy-efficient house that residents occupy. To collect measured data from the experimental house, temperature and heat flux meter sensors were used for the analysis of heat flow patterns. Such measured data were used to calculate heat gain ratios and compare temperature and dew point distribution profiles of heated windows with input power values under the changed condition in the operating temperature of the heated glazing. Results from this study indicated that the input average heat gain ratio was analyzed to be 75.2% in the south-facing and 83.8% in the north-facing at nighttime. Additionally, compared to January, reducing the operating temperature of the heated glazing by 3 °C decreased the input energy in February by 44% and 41% for the south-facing and north-facing windows, respectively. Through such field measurement study, various interesting results that could not be found in controlled laboratory chamber conditions were captured, indicating that the necessity of establishing various control strategies should be considered for the development and commercialization of heated windows.
Highlights
Windows are one of the most important architectural elements in a building and an important factor in building energy performance
Large windows or balcony windows without railings are often installed in living rooms for visual comfort
Condensation mainly occurs when hot and humid air in the indoor space comes into contact with an inner window surface that is below the dew point [6]; this reduces the scenic views and visibility, which are the most important functions of a window [7]
Summary
Windows are one of the most important architectural elements in a building and an important factor in building energy performance. Large windows or balcony windows without railings are often installed in living rooms for visual comfort. Large windows are commonly designed on the south-facing walls of passive houses in the Northern Hemisphere to obtain as much solar heat as possible [3,4]. Condensation on the glazing surface is relatively frequent because energy loss through windows is more than 30% which is the most vulnerable part of the building envelope to poor heat insulation [5]. Condensation mainly occurs when hot and humid air in the indoor space comes into contact with an inner window surface that is below the dew point [6]; this reduces the scenic views and visibility, which are the most important functions of a window [7]
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