Thermal performance, glare control, and occupant appraisal of an office window in a direct gain passive solar strategy

Abstract

In addition to maximizing the solar heating performance, the problem of sizing the window in a passive solar direct gain strategy is compounded by the potentially high glare and the probable visual noise caused by too much sunlight penetration. Instead of the daylighting prediction methods, the use of the human eye is proposed in this study to assess glare and the visual impact of sunlight as the size of the window varies. The qualitative aspect of lighting is found even more important in spaces where occupant performance is crucial such as office. This study concentrates on an office module part of a skin-load-dominated building applying a direct gain strategy. In addition to the window size, the amount of sunlight penetration is introduced as an important design parameter. In this study, the window size and the amount of sunlight penetration are the continuous independent variables while the observer position relative to glare and occupant appraisal is a discrete one. This study examines the relationships between the independent variables and the three primary parameters addressed (thermal performance, glare potential and occupant appraisal), and also the trade-offs involved between them. There is a positive relationship between the window size and the solar heating performance when sufficient thermal mass, glazing layers and night insulation are used. Glare is impacted by the change of window size when the direction of view is normal to the window. For the same seating position feeling of relaxation is affected primarily by sunlight penetration, but not window size. From a sideways position, moderate sunlight penetration provided the highest feeling of relaxation. When all the above factors are considered, window sizes between 30 and 60 percent of the wall area should be generally avoided. The experiments were conducted in a field setting and in a simulated environment of slides of a scale model. Distinct differences were found between the field and simulated environments. Excerpts from this work have been presented at the Symposium on Architecture and Building Construction Issues in Baton Rouge, Louisiana, in 1989, and in the ASES/90 Solar Energy Conference in Austin, Texas in 1990.