HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Energy and Power Management, Distributed Control Trendsest monthly demand, considerable savings are possible in rate reductions.In periods other than the highest demand period, some energy isstill saved.Before the era of high energy costs, load shedding was used mainlyto avoid demand cost penalties. Now, it is used to limit energy consumption,by cycling loads on and off for brief periods, as well as toreduce demand.Other methods used to limit energy use include computer optimizationof start times, setpoints, and other operating parameters based onweather, temperatures, or occupancy.Meter ConnectionEnergy management devices base their control actions on the demandlevel in each demand period. They get two signals from the electricalutility meter (Figure 2-4). These signals are usually momentarycontact closures of about 500-ms duration which indicate the beginningof each demand period or the consumption of one kWh of electricalenergy.Figure 2-3. Reduced demand from cycling a major load off for a brieftime period.©2001 by The Fairmont Press, Inc. All rights reserved.