Innovative daylighting systems often work by redirecting light from the sky and sun onto the ceiling from where it is diffused to light the space. This can cause problems for ceiling mounted photoelectric control sensors. The performances of three types of ceiling sensor were studied in the Building Research Establishment’s mock-up rooms. The window systems included venetian blinds, prismatic film and a light shelf as well as ordinary clear glass. A completely unshielded sensor gave surprisingly stable performance compared with horizontal working plane illuminance. The main exception to this was when direct sunlight reached the sensor itself. Unfortunately the ratio of sensor illuminance to horizontal illuminance was significantly greater under sunny skies than under overcast skies. This could lead to uneven control performance under different sky conditions. An alternative sensor shielded by a darkened tube was also tested. This proved to be very susceptible to the location of patches of sunlight in the space. In a real room it could also be affected by the positions and reflectances of furniture and even occupants. A possible compromise is the use of a partially shielded sensor. This can receive light from all directions except the window. Care is needed in aligning the shield correctly during installation.
An Integrated Application of Control Performance Assessment and Root Cause Analysis in Refinery Control Loops