IceBank® Energy Storage: Cooling for a Greener, Smarter Future
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U.S. Green Building Council Energy Star ARI Education Engineer



Fossil Ridge H.S.l - Fort Collins, CO LEED Silver

Fossil Ridge H.S.
Fort Collins, CO

Energy storage can help reduce the energy and operating cost of a a school or university so it can reinvest those dollars toward improving the education of it’s students.

What is energy storage and how does it work? energy storage is a proven technology that takes advantage of low-cost, off-peak electric rates to produce cooling energy for use when electric rates are higher. A facility’s chiller is used to charge CALMAC’s ICEBANK® thermal energy storage tanks with ice during less-expensive, off-peak hours at night. The ice is stored in the ICEBANK tanks and then used the next day during the discharge cycle to cool the school during on-peak hours. Click here (PDF, 371 Kb) for system schematics and a technical review of the energy storage process.

Efficiency of air-cooled screw compressorOperating chillers during nighttime hours improves energy efficiency by 2 to 8 percent over non-storage systems operating during the day. Dry-bulb temperatures are about 20°F lower and wet-bulb temperatures 5°F lower at nighttime hours, compared to daytime hours. Nighttime operation improves the efficiency of all chillers, but especially air-cooled chillers because the condensing temperature is controlled by ambient dry-bulb temperature.

There are at least three energy storage strategies to consider: full storage, partial storage, or a combination. Full storage shifts a building’s entire cooling load to off-peak hours. The building’s chiller only runs at night in order to charge the ICEBANK tanks. During the discharge cycle, the stored ice is used to cool 100 percent of the building’s load the next day. Full-storage systems offer the best savings and simple operation.

With partial-storage, ICEBANK tanks work in tandem with the chiller. The chiller charges the ICEBANK tanks at night and continues to run the following day during the discharge cycle. During the discharge cycle, the chiller cools up to 70 percent of the facility’s load and the stored ice cools the remaining load.

Annual hours of full-load operationA partial load energy storage system configuration enables chillers to operate at or near full load continuously, thus eliminating the inefficient cycling and capacity modulation that accompanies part-load operation and normally causes a chiller to operate at peak efficiency only 25 percent of the time.

Lastly, tighter construction in newer school buildings and humidity management are increasingly important. Energy storage provides engineers with a tool for reducing humidity levels in order to improve the comfort of students. For example, “Cooling the primary air to 45°F (versus 55°F in a conventional system) will lower conditioned-space relative-humidity levels from 60 percent to 35 percent, which generally improves the perceived comfort of occupants.” (Federal Technology Alert) With better comfort comes increased productivity. Teachers teach better and students learn better in high-performance school facilities.

Click here (PDF, 371 Kb) for system schematics and a technical review of the OPC process.

Additional design engineer benefits

  • Provides a design with a chiller that is 40 to 50 percent smaller, to minimize inefficient operation of oversized equipment with minimal risk.
  • Thermal energy storage design is similar to a chilled-water system and is not complicated.
  • Provides customers with a demand-responsive cooling system.
  • Provides customers a cooling system with fuel-source flexibility, on-peak or off-peak energy.
  • Offers architects a path to ASHRAE 90.1 compliance or improved LEED™ ratings.
  • Added design costs, if any, can be easily paid for with life-cycle savings.
  • The size of air handlers, motors, ducts, and pumps can be reduced by 20 to 40 percent, which saves design time.
  • CALMAC can provide a wealth of information to help engineers efficiently design a energy storage system.
  • Click here for a complete list of other benefits.

Misconception: Installing thermal energy storage is just not worth the trouble. CALMAC’s technology and the tools available to help design, install, and operate Thermal energy storage systems have changed dramatically over the years. Energy storage can be reliably and affordably applied and is easy to operate. Saving significant energy costs is always worth the effort, particularly in today’s challenging economic environment. Partial-storage energy storage systems can reduce a school system’s energy costs by 20 to 60 percent. Energy storage also has environmental benefits beyond the meter, and other benefits that can help school districts negotiate better rates with their energy provider.

Mike Boehm, maintenance and operations supervisor for the aforementioned Montgomery school system, said, "We were able to shift 120 kilowatts off peak. During the fall and spring, I can usually operate the air conditioning on ice alone and never bring on the chiller during the day. With a demand rate of $9.15 kW, we can achieve a two-year payback over a conventional chilled-water system with demand savings only."

Click here for a partial listing of energy storage projects.

Please click here to contact any of CALMAC’s regional managers for additional information or questions.

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