Cooling Demand and Daylight in Commercial Buildings The Influence of Window Design

Doctoral thesis, 2008

The modern design of office buildings shows a tendency to increase the window share per facade to be more impressive with grand visibility and well daylit rooms. An increased window share results in general in increased use of energy and costs for cooling, but these disadvantages can be reduced considering a more careful design. The aim of the thesis is to investigate the influence of window design and room layout on cooling demand and daylight availability in office buildings in Northern Europe. The study is based on a literature survey, measurements in a couple of buildings and design calculations for two different room types, together with measurements on two room models in a daylight laboratory. The field monitoring show considerable cooling demands as a result of the room and window design. Calculations show the influence of window design parameters on the cooling demand. The daylight measurements show the influence of window design parameters on the availability for daylight, as well as the risk for glare due to direct solar radiation. The two studies have then been combined to show the possibilities for daylight in relation to cooling demand for different window orientations. The result is that, in most cases, it is possible to find a combination of window share and window solar factor that is feasible from a cooling, as well as a daylight point of view. The design calculations show that designs with large window shares (> 60%) and a high window solar factor (0.7) can result in extreme cooling loads. The daylight measurements show on the other hand that a moderate window share and a moderate solar factor are advantageous when it comes to the possibilities to use daylight and reduce the energy used for lighting. Here, the product of window share and solar factor is introduced as a guideline to find feasible designs.