At Stowe Middle & High School in Vermont, the new Facility Director Dave Bullis wanted to improve the operation and efficiency of the school when he took over. Dave knew from experiences managing other facilities that getting an Energy Audit or doing a Retro-Commissioning project would help identify opportunities to reduce energy consumption. Still, the upfront cost of doing those projects can sometimes reduce the total savings and the return on investment. That’s when Dave reached out to Control Technologies and Nick Rock, a Building Performance Engineer, to help reduce energy and improve the operation of the HVAC equipment and Building Automation System (BAS).
Dave and Nick worked together on the existing BAS and HVAC systems at the school and started looking for opportunities. They were able to use Nick’s experience with Mechanical and Control Systems and Dave’s knowledge of the school to identify energy reduction measures that were low cost to implement. One such measure was the optimizing of the hot water system. The school had added three wood pellet boilers several years ago to the existing hot water system that had two older steam oil boilers. The pellet boilers would stage on and off based on their internal controls; then, the building automation system would turn on the steam boilers as a backup when the hot water temperature dropped below a low setpoint. Because of the two separate control systems at work, there were many times when both the pellet boilers and steam boilers were running together and producing higher hot water temps then what was needed. There was also short cycling happening
on the equipment, and the pellet boilers would not burn efficiently, creating excess ash and more maintenance to keep clean. By tuning the BAS controls and taking control of the pellet boilers individually, they were able to improve the operation and staging of the boilers. The pellet boilers would burn cleaner and produce less ash, the less efficient steam boilers would run less, and the hot water system would not overproduce for what the building needed for heat. Later, when the steam boilers were removed and replaced with a new hot water oil boiler, the hot water system was tuned again to account for the changing between the steam boilers and the new hot water boiler.
Some of the other measures put into place were improving the chilled water and ice storage system, optimizing the electric demand response and tuning the VAV and AHU temperature adjustment sequences. All these measures had a common theme, energy reduction measures that were low cost to implement. No significant changes in the mechanical system or large capital projects, instead they used the existing BAS to tune and optimize the existing mechanical equipment to the best it could be. Usually, in Energy Audits or Retro-Commissioning, these measures are researched, and calculations are made to help determine if specific measures will produce good energy savings. This upfront work can be costly and time-consuming, instead, Nick and Dave took the approach of implementing changes they discussed and let the savings be calculated afterward.
Efficiency Vermont, the energy efficiency utility in the state, was brought in to help calculate the savings after all the measures were implemented. The results were outstanding! Efficiency Vermont stated that typical electrical savings for control optimization projects like this are around 5-10%. For this school, that would mean a range of 26,000-52,000kWh for the year, but the actual savings were 150,900kWh, a reduction of more than 25%. That electric reduction ends up being $16,500 a year in savings for the school!
The savings didn’t stop with the electricity either; there were significant savings in their heating fuels as well. There was a 26% reduction in their wood pellet usage, which results in $12,000 in savings a year. The oil usage wasn’t calculated because of the switch from steam boilers to a new hot water boiler, but Efficiency Vermont did state that there was a reduction in oil usage as well.
Efficiency Vermont was also able to give the school additional rebates on top of their energy savings. For doing the control optimization project, a $5,000 rebate was giving. For saving 150,900kWh, an additional $15,100 rebate was awarded, bringing the total in rebates to $20,100.
“This is one of the most successful controls optimizations efforts we’ve seen to date…an outstanding success!”Sandra LaFlamme, Senior Energy Consultant at Efficiency Vermont
“CTI worked closely with me to evaluate the entire system and find the most affordable way to maximize efficiency and savings. The improvements paid for themselves many times over.”David Bullis, Stowe School District Director of Facilities