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

Helena Bülow-Hübe

Research output: ThesisDoctoral Thesis (compilation)


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.
Original languageEnglish
Awarding Institution
  • Division of Energy and Building Design
  • [unknown], [unknown], Supervisor, External person
Award date2001 Dec 10
Publication statusPublished - 2001

Bibliographical note

Defence details

Date: 2001-12-10
Time: 09:15
Place: Carolinasalen, Kungshuset, Lundagård

External reviewer(s)

Name: Hastings, S Robert
Title: Professor
Affiliation: Architecture, Energy & Environment GmbH, Switzerland


Subject classification (UKÄ)

  • 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


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