Pattern 8: Blinds and Shades

Blinds and shades provide a range of methods to control direct sunlight and re-direct diffuse daylight. Assuming a reasonable relationship between section depth and window head height (does not exceed 2:1), sufficient daylight can be provided by windows on just one side of a space. However, blind type and use play a paramount role in how the daylighting will actually perform on an annual basis. This case study examines the use of multiple blind types and positions given various weather conditions to illustrate an often overlooked, but absolutely critical aspect of good daylighting design. While fixed external shading can provide significant benefits, it is rare that glare control can be entirely solved without some form of blinds or shades.

There are several types of blinds available, however in office spaces it is most common to find standard louver blinds or fabric roller blinds. These are most commonly manually operated, and it is a fact that operating blinds is not a high priority for most office occupants. Research suggests that blinds often go weeks and even months without being moved. Too often, this results in blinds positioned partly to mostly closed for large portions of the year, regardless of sky condition. Often, blinds will be closed due to a short period of glare and rarely if ever reopened. This can make an otherwise well daylit space virtually non-daylit. To solve this problem, advanced facades sometimes incorporate motorized roller shades or louver blinds. This allows blinds to be repositioned open after a preset time step or at least each morning. More advanced systems use irradiance sensors to control blind position given sky condition and sun position. Finally, some advanced blind systems incorporate ‘daylight enhancing’ features with special optical characteristics to increase daylight penetration through blinds while still blocking direct sun penetration.

The case study example used here is the Genzyme Building at 500 Kendall Street in Cambridge, MA, designed by Behnisch Architekten. This pattern sequence highlights simulations primarily under sunny sky conditions during September at noon but to illustrate the impact of not repositioning blinds on overcast days, a few cases are run under both sunny and overcast days. Workplane illumination data are represented in lux. Typical office lighting criteria range from 300-400 lux and 300 lux was selected as one of the daylighting design criteria examined herein. The percentage of floor area above this value is presented for each permutation. It is important to note that the Genzyme building uses automated motorized daylight enhancing blinds based upon irradiance data and allows for user overrides of the system. However, to illustrate important points about blinds use, several other types of blinds and blind control assumptions are included.