The Town of Carlisle, like many towns in MA, has several facilities on utility rate schedules where 70% or more of the bill is composed of “demand charges” that are based on the highest demand used by the customer in the billing period. In the case of the Carlisle Public School, each kW of peak demand in the period costs $19.19 and with typical peaks exceeding 250kW, a 10% reduction is worth over $480/month. If rumored increases in demand charges come true in 2016 and beyond, the risk of doing nothing could cost an extra $5,000 to $15,000 per year at the school alone. Carlisle, like many towns, is driven to efficiency by an Energy Task Force composed of top-flight “professional volunteers”, and there is general agreement that a data-driven approach to understanding the current usage profiles is key to determining the next best conservation measures they might employ.
Solutions & Opportunities
With funding from the MA Green Communities Grant Program, AEI continues to develop a baseline of utility usage for the Town of Carlisle.
In 2015, the Carlisle Public School complex had an average electric demand of 52.3kW, yet regularly had peak demands five times that. In the worst-case month of September, the school hit its peak on the first day of school when all of the buildings were at full tilt, with outside air at 91°F. The peak demand for that month was 349.8kW, nearly 7 times the average month. That first day of school cost the Town $2,000 in demand charges compared to an “average” month when the peak demand is around 250kW.
AEI is proposing to Carlisle that we engage targeted low-cost sub-metering at key panels in the facility to learn the best opportunities for peak demand mitigation when weather and occupancy indicate that a peak for the billing period is imminent. In light of rumored increases in demand charges, a sub-metered approach to understanding the load profiles is also a low-cost insurance policy for the future. Reducing peaks also has the nice side-effect of reducing overall demand. In the case of CPS, a 10% kWh reduction is worth about $1,200/yr.