Occupant control of passive systems: the use of Venetian blinds

The way occupants interact with passive control features is poorly understood. Venetian blinds are a key element in the passive control of a building’s environment. They help to control glare, daylighting, and overheating, all of which affect both the comfort of occupants and a building’s energy consumption. However a building’s environmental design is very dependent on assumptions regarding occupants use of blinds. This paper examines the current assumptions in occupants use of blinds and the impact these assumptions have on a building’s environment. It then compares the assumed use with the actual use from monitored data of blind use in both summer and winter conditions in three buildings. In particular, the impact of façade orientation, sunshine, and electric lighting on blind use is investigated. Preliminary results confirm that on average, 40% of a building’s façade is obscured by blinds resulting in a reduction in daylight. This reduction in daylight is equivalent to an unobstructed glazed area of 68% of the building’s façade assuming that 20% of light penetrates a blind when it is fully drawn. Occupants use of blinds is predominantly not affected by solar availability as often modelled, although there is a weak relationship between orientation and window occlusion.