In NC State’s latest move to reduce campus energy costs, timing is everything.
Later this month the Facilities Division will begin using a new thermal energy storage tank to more strategically create the chilled water that supplies mechanical systems at more than 20 buildings on Centennial Campus.
Instead of cooling water on demand, the Centennial Campus Utility Plant will generate chilled water at night when electricity rates are lowest. The water will be pumped to the new 3.3-million-gallon tank for storage and deployed to cool buildings during the day when electricity is most expensive.
“The tank is storing energy like a battery would but – in our case – it’s storing chilled water to dispense to campus buildings when electricity costs are highest,” said assistant plant engineer Claire Stevens. “We will still consume the same amount of electricity but it will pull down our peak energy use and avoid cost.”
Electricity rates on Centennial Campus are based on time of use, meaning that electricity is more expensive at high-demand times such as during the day and early evening. Use of the new storage tank is expected to reduce the university’s energy costs by an estimated $250,000 annually.
Saving While Growing
The vision for thermal energy storage on Centennial Campus began a decade before the university began planning the project in 2016. With the construction of several energy-intensive buildings on the horizon, the utility plant needed more capacity.
“Without thermal energy storage, we would have to expand the utility plant. That cost would be much higher,” said plant engineer Bill Ferrell. “Now, we’re saving money in our electricity rates while also deferring the need to expand the plant.”
After an initial fill up, the tank will use no additional water because the chilled water system is a closed loop that recirculates. The water is filtered regularly, and any future maintenance inside the tank will be completed with divers or robots.
Thermal energy storage is the latest efficiency boost at the Centennial utility plant. Last January, the university began creating 6.5 megawatts of electricity on-site through cogeneration technology. With cogeneration, the waste heat from electrical production is used to create steam, which heats many campus buildings.
In the first year of using cogeneration at the Centennial utility plant, NC State purchased less electricity because 43% of the electricity consumed on Centennial Campus was generated on-site. The university also has cogeneration technology at its Cates Utility Plant, which supplies North and Central Campuses.
The Utilities and Engineering department, which operates five central utility plants on the university’s Raleigh campuses, is preparing for the strategic savings opportunity that these two systems bring. Time management and forecasting are critical to maximize savings.
“This is a significant project, but our building occupants will never experience the difference. We’re seamless and will provide them service 24/7,” said Paul Reynolds, who manages plant operations.
As part of its commitment to sustainability and stewardship, NC State is aiming to achieve a 40% energy use reduction per gross square foot as compared to its 2002 baseline. As of last fiscal year, the university had reached a 34% reduction.
“Projects like Centennial Campus thermal energy storage and combined heat and power are strategic investments,” said Alan Daeke, director of utilities and engineering. “These infrastructure improvements are important steps toward achieving our energy reduction goal.”