Energy Efficient Window Systems. Effects on Energy Use and Daylight in Buildings.

• Main Author: Bülow-Hübe, Helena
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Lund University, Lund Institute of Technology, Division of Energy and Building Design, P.O. Box 118, SE-221 00 LUND, Sweden 2001
• Subjects: Building Technologies; simulation; thermal transmittance; solar energy transmittance; shading device; solar protection; cooling; heating; energy demand; building; low-emittance coating; window; glazing; comfort; user aspects; operative temperature; Architecture; Building construction; Byggnadsteknik; daylight; perception; interior design; Arkitektur; inredningsarkitektur; Energy research; Energiforskning; Northern Sweden
• Online Access: https://lup.lub.lu.se/record/42204

This thesis deals with energy-efficient windows in Swedish buildings. Parametric studies were performed in the dynamic energy simulation tool Derob-LTH in order to study the effects of window choices on energy use and indoor climate for both residential and office buildings. A steady-state program was used to evaluate two years of measurements of energy use and indoor temperatures of an energy-efficient row-house. Two behavioural studies regarding (1) daylight transmittance, view and room perception using super-insulated windows and (2) the satisfaction with the daylight environment and the use of shading devices in response to daylight/sunlight were conducted in full-scale laboratory environments exposed to the natural climate. Results show that as the energy-efficiency of buildings increase, window U-values must decrease in order not to increase the annual heating demand, since the heating season is shortened, and useful solar gains become smaller. For single-family houses with a window-to-floor area ratio of 15 % and insulated according the current Swedish building code, the U-values should thus on average be lower than 1.0 W/m²K. For houses insulated according to 1960s standard, the U-value may on average be 1.6 W/m²K. For colder climates (northern Sweden), the U-values should be somewhat lower, while slightly higher U-values can be tolerated in milder climates of south Sweden. Thermal comfort during winter is improved for energy-efficient windows. However, overheating problems exist for both super-insulated houses and highly glazed office buildings showing a need for very low U-values in combination with low g-values. Daylight experiments indicate that the use of two low-emittance coatings tints the transmitted daylight enough to be appreciated, and colours may be perceived as more drab and rooms more enclosed. A compromise between energy-efficiency and daylighting may be needed, and it is suggested that only one coating be used except when very high energy-efficiency is required.