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On the Calibration and Commissioning of Lighting Controls
Francis Rubinstein, Douglas Avery, Judith Jennings, Steven Blanc
Lawrence Berkeley National Laboratory, California, U.S.A.
Abstract
Lighting controls provide building operators with the means to more efficiently manage the way lighting energy is used in buildings. These systems use various control strategies to
1) reduce wasted hours of lighting in unoccupied spaces
2) automatically adjust electric light levels in synchrony with available daylight or age-related changes in luminaire output or
3) selectively shed lighting loads to moderate peak demand (DOE 1993). Lighting control systems have been installed in a number of buildings worldwide but few of these installations have been adequately monitored to validate the system performance and energy savings potential of lighting controls. In the few monitored studies available, lighting controls have been shown to capture significant energy savings when the controls have been properly designed, specified, installed, commissioned and maintained. In some cases, these savings have been shown to persist for years.
Yet these early projects have also tended to uncover various deficiencies in current lighting controls equipment and practice that will likely prevent today?s controls from sustainably reducing lighting energy use in routine practice. Some of these flaws can be traced to the need to commission and calibrate the lighting controls after installation to assure satisfactory system operation. (Other issues relating to design, specification and installation are not treated in this paper). This paper discusses the importance of commissioning and calibrating today?s lighting controls systems and presents some practical advice for effectively calibrating these systems.
A lighting control system typically consists of the following basic elements:
1) A sensor that is capable of measuring or detecting a physical parameter of interest (e.g. available daylight) and translating this into an electrical signal (a current or voltage, e.g.).
2) A controller that can accept the electrical signal from the sensor and convert this signal using a built-in algorithm into an electrical signal to a dimmer
3) A dimmer 1) that can accept the electrical signal from the controller and drive the electric light levels up or down accordingly.
Sometimes, the controller and dimmer functions are combined in the same hardware. For example, the most common topology for daylight-linked control in a private office in the US is to connect the low-voltage control loop for the electronic dimming ballasts to a two-wire photosensor. Here, the controller and dimmer are built into the dimming ballast circuitry itself and the only calibration adjustment is on the photosensor.
To obtain satisfactory results, these components must be intelligently specified so that the different components work well together as a system in the particular building application. Specification is difficult, in the US. at least, because the components that comprise the final system are not usually produced by the same manufacturer and inter-operability of components from different manufacturers has always been problematic in the building controls industry.
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