Carlisle Gleason Library Prepares for Demand Charge Increases
The Town of Carlisle’s Gleason Library is a recently renovated 11,000ft2 facility and is a relatively small piece of the Town’s energy footprint. But like many facilities on “demand charge” utility rate schedules, 60% of its monthly bill is based on the highest demand used by the customer in the billing period.
At Gleason Library, each kW of peak demand in the period costs about $200/year and with typical peaks around 40kW, a 10% reduction is worth about $800 per year but could be worth up to $3,200/yr if utility demand charges will increase as rumored.
Discoveries and Next Steps
Using GC Grant Program funding in FY2014, the Library installed a SiteSage sub-metering system for the electric circuits in the building. With a small amount of 2015 GC funding, AEI automated the data analytics from the library data to better understand how the energy is used. Based on preliminary findings, we see that demand is 60% to 100% higher in the heating and cooling season than during shoulder months. Electric demand is dominated by lighting first and then cooling.
Even when outside air is as low as 65°F, the cooling equipment consumes half the total load of the building. It makes sense in those cases to limit the next top 5 loads in the building, which are a combination of lighting circuits and pumps. The value of having sub-metered data is that we can establish a few basic responses for the building in cases on hot days with low to medium occupancy states. For example, if OAT is 80°F at 8am in the morning, there’s a good chance that the billing period peak will occur that afternoon. In those cases, consistently limiting occupancy to fewer controlled spaces could lead to lower average and peak demands. Or certain DR responses could be hard-wired and automatic based on rules that we can define based on the data trends.
An aggressive DR stance might only amount to $1,000/yr in savings, but the Library supports our contention that the best way to reduce peak and average demand is to have the analytics that show the next largest negotiable loads that might be curtailed to avoid peaks.
View the interactive AEI report to Town of Carlisle and learn more about AEI at www.aeintelligence.com/town-of-carlisle.