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

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

A breakthrough for coated glazing in Sweden. Will double-pane windows take over the market?

Ever since the end of the 1970s triple-pane windows have been ”standard” in new construction of dwellings and non-residential premises in Sweden. The background was the first oil crisis in 1973, which led to a dramatic sharpening of the thermal requirements regarding the thermal envelope of Swedish buildings. These were introduced in the new building code SBN 75 which was brought into practice in 1976. The code required that windows should have a maximum permissible Uvalue of 2,0 W/m2K. With the technology available at that time, this required in practice that triple-pane windows were introduced, since the so-called low-e coated glazing still wasn’t good enough. The share of low-e coated windows has thus far been low in Sweden, and this could probably be attributed to the early introduction of the triple-pane window. However, during the last two to three years there has been en remarkable increase in the share of low-e coated windows

ESTIMATION OF THE PERFORMANCE OF SUNSHADES USING OUTDOOR MEASUREMENTS AND

Solar shading devices can significantly reduce cooling loads, improve thermal comfort and reduce potential glare problems in commercial buildings. However, measured data or tools to facilitate a comparison among various shading devices have previously not been available to designers. The Solar Shading Project at Lund University was initiated in 1997 to increase the knowledge on shading devices. This paper describes results from an extensive measurement program and recent developments of the software tool ParaSol v 2.0. The total solar energy transmittance (g-value) of various shading devices has been estimated by means of measurements in a real climate using a double hot-box arrangement. Monitored results are shown for external products (awnings, Italian awnings, venetian blinds, horizontal slatted baffle, fabric screens, solar control films), interpane (between panes) and internal products (pleated curtains, roller blinds, venetian blinds, solar control films). The software tool ParaSol has been further developed to include all these types of products. In general, external shading devices are the best in reducing cooling loads, internal products are the worst, while interpane products fall between these two. Further, internal products must have a high reflectance in order to yield a low g-value. The monitored average g-value within each group (g-sunshade) was 0.3 for external products, 0.5 for interpane products and 0.6 for internal products. On average, external products are twice as good as internal products in reducing peak cooling loads. With the software tool ParaSol, it is possible to estimate the effective g-value of shading devices for various orientations in combination with an arbitrary glazing system. Further, effects on heating and cooling (both peak loads and annual energy demands) and operative temperatures of an office room can also be simulated