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One of the fastest growing campuses in the state of Florida, FGCU currently has 21 buildings with 900 full-time employees and over 10,000 students. Cooling from the main chiller plant is shared by campus academic classrooms, computer rooms, laboratories, child-care facilities, astronomical observation buildings, administration offices, sports facilities, research facilities, and public television and radio buildings. Cooling requirements can reach 2,700 tons per hour with peak electrical demand as high as 3.375 megawatts (MW).
To save energy and reduce costs, installation of a thermal energy storage (TES) system to make ice and store it at night has proved to be a more cost-effective option to support campus cooling needs during the day when outside temperatures reach 95°F and the relative humidity reaches 70 percent and higher.
In 2002, the university completed an engineering study and individual facility hydraulic and ventilation review to determine what potential energy savings options might be available. Some of the ideas eventually implemented were:
1. Construction of chilled water valve control on facilities using existing tertiary pumps.
2. Implementation of reset of demand control ventilation.
3. Introduction of TES.
As in many warm weather states, Florida electric companies have offered incentives to encourage the use of TES for cooling. FGCU’s local utility provided storage incentives to help defray the cost of the ice storage tanks necessary to operate the system, an investment of approximately $800,000.
In the TES system, ice is produced nightly during off-peak hours when utility rates are lower and stored in large tanks using a plate and frame heat exchanger, water cooled chiller plant, and variable speed pumps.
The tank contains a plastic coil filled with DOWTHERM SR-1 Heat Transfer Fluid chilled to a temperature of 23° to 31°, which circulates inside the coil and freezes the water to make ice. During the day, the same fluid is used to melt the ice in the ice tanks when the system is in cooling mode.
Over 44,000 gallons of SR-1 fluid circulate through the heat exchangers, chillers, piping, pumps, and tanks at two FGCU sites. The fluid is mixed with water at 25 percent concentration to meet service temperature requirements.
According to FGCU staff, the SR-1 fluid runs cycle-after-cycle, day-after–day without degradation and performs reliably during each melt and cooling cycle. Yearly fluid tests verify fluid conditions remain excellent.
Prior to investing in TES, energy costs at the university were approximately $6-$7 per square foot. Today, plant and building pump energy costs are $2.10 per square foot, among the lowest in the state. In four years, the university documented total savings of $1.4 million. Florida Gulf Coast University currently has 92 thermal energy storage tanks and 14,760 tons of ice storage with a planned expansion to 146 tanks and 23,360 tons of ice storage.
For more information, visit www.dow.com.
Publication date: 05/10/2010