Overall evaluation of windows - possible improvements within 5 years
Based on the combined effect on indoor climate and space heating demand in domestic buildings the potential - both technical and economical - for development of energetic improved windows within a time horizon of 5 years has been investigated.
Development of windows has been focused on reducing the U-value of frame and glazing. Only in few cases the net energy flow through the window during the heating season has been evaluated and in that case often only for south oriented windows. Initial calculations on a single family house shows a 30% reduction in heating demand related to the total window area if a double glazed low energy glazing with low iron glass is used compared to use of triple glazed super insulating glazing due to the larger solar energy transmittance of the low iron glazing. The main goal of this project is to stimulate the development of windows with an improved overall energy performance in preparation for the coming Danish Building Code 2005. The overall evaluation includes the interaction of U-value, g-value, window-wall joint and conditions for application, e.g. influence on indoor thermal enviroment and risk of condensation - inside as well as outside. Participation of glass-, glazing- and window professionals ensures that the results of the project are realistic and could form the basis for product developments concerning energy efficient windows
Furthermore the problem of outside condensation on super insulating glazing has been addressed. Several measures for energetic improvement of windows i.e. increased solar transmittance (low iron glass, anti reflective glass, slimmer frame solutions) and lower U-values (triple glazing, insulating glazing rim seals/spacers, frames with built-in insulation) are already available on the market. Detailed analysis of the increased risk of over heating caused by use of improved windows shows a significant energy saving potential but it is essential to include automatic controlled solar shading devices and/or venting and night cooling by outside air. An economical evaluation of the different technical options shows that only the warm edge solution for sealed glazing units and the anti reflective glass solution are profitable. Application of triple glazing will only be energetic favourable if combined with use of low iron glass, but this makes the solution too expensive at the present. It has not been possible to economic information for improved frame solutions e.g. the German 'Passiv Haus' windows. A computer program has been developed for investigation of different measures to reduce the risk of outside condensation. The most promising solution is a low emissive hard coating on the outer glass surface, which eliminates the problem but result in a decreased solar transmittance. Overhangs leads to significant decrease of the condensation problem but influences the architectural expression of the building
Key figures
Category
Participants
Partner | Subsidy | Auto financing |
---|---|---|
Pilkington Floatglas A/S | ||
Scan-Gobain Glass A/S | ||
Teknologisk Institut |
Contact
Brovej Bygning 118
DK-2800 Kgs. Lyngby, Denmark
Schultz, Jørgen M. (forskningslektor), 45251902, js@ibe.dtu.dk
Øvr. Partnere: Pilkington Floatglas A/S; Scan-Gobain Glass A/S; Vinduesproducenternes SamarbejdsOrganisation (VSO); Teknologisk Institut. Byggeri