Roadmap for improving roof and façade windows in nearly zero-energy houses in Europe

Abstract

Windows are central for the development of liveable nearly zero-energy homes and require careful consideration. Various studies have indicated that the effect of windows on energy consumption may change significantly with improved building insulation levels. Current guidelines on windows may therefore not apply in very well-insulated buildings, and more up-to-date information is needed about window solutions that are appropriate for the new conditions. This study maps the effect of multiple combinations of window size and basic glazing and frame properties on energy, daylighting and thermal comfort in nearly zero-energy houses located in the European cities Rome and Copenhagen. The aim was to identify options that can support the easy and robust design of future homes with typical use of roof and façade windows. Hourly daylight levels were calculated in DAYSIM, while space heating demand and operative temperatures were calculated in EnergyPlus. The results support previous findings on the limited ability of nearly zero-energy buildings to utilise solar gains. It was found that U-values are becoming increasingly important for the energy performance of windows. The paper sketches the increased flexibility and related possibilities that may appear with improved roof window frame constructions and glazing U-values far lower than currently standard levels.

Detailed and simplified window model and opening effects on optimal window size and heating need

“…They said that windows have to be carefully dimensioned to reach the daylight target without overheating South-oriented rooms. Similar suggestions were given by Skarning et al [8] for the climate of Denmark and they added that slighly higher U-values could be used in the climate of Rome. Skarning et al [8] also pointed out that focus should be set on minimizing thermal transmittance of glazing and frames instead of maximizing solar gains in South-oriented rooms, which increases the risk of overheating.…”

“…Similar suggestions were given by Skarning et al [8] for the climate of Denmark and they added that slighly higher U-values could be used in the climate of Rome. Skarning et al [8] also pointed out that focus should be set on minimizing thermal transmittance of glazing and frames instead of maximizing solar gains in South-oriented rooms, which increases the risk of overheating. Opening windows is an effective method to reduce overheating according to Mavrogianni et al [9] and Rijal et al [10].…”

The effect of dynamic solar shading on energy, daylighting and thermal comfort in a nearly zero-energy loft room in Rome and Copenhagen

“…Similarly, a systematic parameter study by Petersen [7] on window size, user patterns and cooling strategies in future homes based on the same daylight target doubts that it is even possible to achieve adequate daylighting in very low-energy buildings unless solar shading is applied to reduce overheating and thermal comfort is evaluated in accordance with the ATC model. Other studies on very well-insulated houses and nearly zero-energy homes, however, have questioned the importance of dynamic solar shading in buildings with a very low space-heating demand, due to the reduced need for solar gains in these buildings [2,[15][16][17][18]. They suggest that solar control coated glazing with lower solar energy transmittances (gvalues) and high selectivity for daylighting could be used to prevent overheating in such buildings, without critically affecting the space-heating demand.…”

Determination of Equivalent Thermal Conductivity of Window Spacers in Consideration of Condensation Prevention and Energy Saving Performance

“…As the condensation can deteriorate not only the building durability but also occupants' health, many studies have suggested methods to avoid the condensation; for example, insulative window spacers [4], improved window frame using a material with low-thermal conductivity [6], double window system with ventilation slits [7], dynamic insulation windows using airflows [8], and so on. As for the energy aspect, the energy regulations of low-energy residential buildings now demand a high-insulation performance regarding the building envelopes, which can be achieved by improving the thermal insulation and/or air-tightness of the windows [9][10][11][12][13][14][15][16].…”