Proper Sequencing of Loads at a Large MA High School Reduces Summer Peak Demand Charges
AEI was engaged by the prime contractor to study the sequence of operations and discover opportunities for peak demand mitigation at two separate campuses of a large high school system in Massachusetts, with a combined total of 783,000ft2 and 3,300 students. Peak demands during the summer cooling season—normally expected to be an unoccupied time of the year—showed the largest variability in electric demand. The unpredictability of the demands made it difficult to consider any demand response initiatives until the nature of the swings could be determined.
Solutions & Opportunities
Using the utility main meter interval data we applied our AEI SoftStart™ analytics to profile the school’s energy use. We first disaggregated the main meter data into three separate seasonal 24-hour average profiles for heating, cooling and shoulder seasons to compare average loads and the variability within sample periods. The Summer cooling profile for one meter quickly stood out with significantly more volatility than any other account or season. The load for this single meter starts the day at 50kW and then rises as expected to an average of about 200kW.
We reviewed the available JCI Metasys BAS data and used our analytics and visualizations to quantify efficiency opportunities, including a better O&M approach to seven VFDs that were operating at 100%. Through proper control of the VFDs, the result was the discovery of over $150,000 in annual energy savings.
We determined that three 55kW chillers were being operated on identical schedules rather than sequenced to avoid coincident demand. In any given 15 minute period during the day, the demand could swing as much as 165kW as the three chillers would turn on and off together.
By sequencing the chillers and deferring the start for the third stage at a few critical points during the day, we showed the peak demand for an average hot day could be reduced by 46kW without affecting cooling capacity or comfort. The resulting savings on demand charges alone amounts to over $1,200 per month during the summer cooling season, and reduces the school’s risk by as much as $4,800 per month when utility demand charges increase as expected over the next two years.