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Photo Sensors for Daylight Harvesting |
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rev. 2008-11-25
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Photo Sensors for Daylight Harvesting |
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rev. 2008-11-25
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Existing Conditions
Lighting circuits can be readily adapted to independent control of perimeter fixtures.
There are numerous large windows in the xxx and in the xxx which let in substantial ambient daylight. Lights near the windows remain on during normal occupancy hours, but do not contribute to space lighting when daylight is plentiful.
Retrofit Conditions
We recommend installing photo sensors (and appropriate power packs) in the xxx, xxx, xxx and xxx. The photo sensors should control the fluorescent, compact fluorescent and metal halide fixtures located within about 15 feet of the windows, as listed in the lighting inventory.
Daylight sensing and control, or 'day lighting', uses a light sensor to measure illumination in a space. At a pre-set level, when daylight on its own is enough, some or all of the lights in the space will turn off. <For this analysis, we have calculated results on the basis of fixtures within 12’ of the outside wall being put under daylight control.>
Corridors and open cubicles near windows, particularly those with task lighting, are good candidates for day lighting controls. Private offices with windows can also be equipped with individual daylight sensors. Initial commissioning and calibration of light sensors and controls is critical for effective day lighting, because poorly calibrated daylight sensors can result in little or no savings, and may annoy occupants.
<In the past few years, lighting control vendors have expanded their product lines to incorporate motion and daylight sensing in a single device, which is more cost-effective and reliable than separate control devices. We have done the analysis in this report taking motion sensing as the primary technology, and then considering the incremental cost and benefit of incorporating daylight sensing in suitable perimeter areas.> <This measure includes reconfiguring lighting circuitry so that perimeter fixtures can be controlled independently.>
Further Benefits
Application Details
Install interior photo controls to exploit day lighting.
A technique with great untapped potential. Don't overlook any lighting that would benefit, such as emergency lighting. May be tricky to design and install. Expect to combine photo control with other types of control.
Issues and Concerns
References
Analysis
Photo sensors should be used near exterior windows. There are two basic types of photo sensor control:
| 1. | On/off control of existing fixtures. This type of control yields limited savings. |
| 2. | Dimming of existing fixtures. This type of control is preferred, as it yields significantly higher savings and is accepted more readily by the occupants. It has a higher installation cost as each fixture requires a dimmable ballast. |
Savings
Rough Savings Estimates: Photo sensor on/off control consumption savings will be around 30%, with no demand savings. Photo sensor dimming savings will be in the 50% to 70% range during normal office hours. Dimming outside of this timeframe will yield 10% to 15%. Demand savings will be approximately 10% to 20%.
Costing
Rough Costing Estimates: Assume $900 total plus $80/fixture for dimmable ballasts.
Talk to the local Watt-Stopper distributor for unit pricing on their various technologies. Get help determining the appropriate parts (sensors, transformers, controllers,…) technologies and get an understanding of how they are retrofitted into existing circuitry.