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



Moorhead Federal Building Tanks

Moorhead Federal Building Tanks

If you are designing an HVAC system for new construction or retrofit office/commercial applications, you should consider the numerous advantages that a CALMAC energy storage system can provide.

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 building’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 building during on-peak hours. Click here (PDF, 371 Kb) for system configuration information and a technical review of the energy storage process.

Efficiency of air-cooled screw compressorAir-cooled chillers perform most efficiently when the outdoor temperatures are relatively low, as naturally occurs during cooler nighttime hours. Operation at night with 20 degree lower condensing temperatures can improve energy efficiency typically by 2 to 8 percent over non-storage systems operating during the day.

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 can be ideal when an existing chiller is already in place and a building owner wants to reduce energy costs.

Annual hours of full-load operationWith 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, cooling up to 70 percent of the building’s load, and the stored ice cools the remaining 30 percent. A energy storage system configuration enables chillers to operate at or near full load continuously, 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.

Click here (PDF, 371 KB) for system configuration information and technical review of the energy storage process.

Additional design engineer benefits

  • 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.
  • Provides a design with a chiller that is 40 to 50 percent smaller, to minimize inefficient operation of oversized equipment with minimal risk.
  • 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 an energy storage system.
  • Click here for a complete list of other benefits.

Misconception: I understand partial energy storage, but I don’t like the risk I’m taking with downsizing the chiller. Look at an example comparison of conventional cooling with two 50-ton chillers for a 100-ton building and partial storage. The energy storage system for this example might be two 30-ton chillers and one CALMAC 1320 IceBank energy storage tank. If only one chiller operates on the conventional system, 50 tons of the 100-ton peak-cooling load can be met. If only one chiller is available on the partial ice storage system, over 50 tons of the 100-ton peak cooling-load tons can easily be achieved. Thirty tons come from one chiller and 40 to 50 tons come from the ice stored in the IceBank tank. The systems have similar capabilities, should one machine be inoperable. The risk of a component being down is the same for each system.
Moorhead Federal Building in Pittsburgh, Pennsylvania

Moorhead Federal Building
Pittsburgh, Pennsylvania

For example, two 990-ton chillers were originally installed at the Moorhead Federal Building located in Pittsburgh, Pennsylvania. The consulting and project engineer decided to replace the 990-ton chillers with two 600-ton, high-efficiency centrifugal chillers, along with a CALMAC energy storage system that included 39 IceBank energy storage tanks rated, at 190 ton-hours each, for a total of 7,410 ton-hours (or 26,000 kW-hours).

On mild days during the cooling season, the chillers are not run at all during peak times, and 100 percent of the cooling is provided from the stored ice.

Click here for complete product and specifications information.

Click here for a partial listing of IceBank energy storage projects..

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

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