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Wireless Sensor and Actuator Networks for Lighting Energy ...

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At the rate of 9.62 cents per kWh as used in the analysis in Chapter 9.5.1, the<br />

annual electricity cost <strong>for</strong> the intelligent control is $213. Compared to the original nondimmable<br />

control with $515 annual cost, use of the research system in a 15-occupant<br />

office generates $302 savings. The payback period <strong>for</strong> implementing the intelligent<br />

lighting system in this particular office is six years.<br />

The energy savings could be much greater, since worst-case <strong>and</strong> conservative<br />

assumptions were used in the calculation. Recall that all the requests <strong>for</strong> the maximum<br />

possible illuminance were defined to occur during the night. Moreover, it was assumed<br />

that the office was fully occupied during regular hours; more energy could be saved as<br />

the lighting <strong>for</strong> absent occupants would be discounted by the system. It should also be<br />

noted that these calculations <strong>and</strong> estimates do not take into consideration the savings<br />

due to the implementation of other lighting energy management strategies that could be<br />

integrated into the system, such as load shedding.<br />

261

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