United Laboratories Building

When planning the expansion or retrofit of an existing building, engineers should consider the advantages that a CALMAC Off-Peak Cooling (OPC) system can provide.

What is Off-Peak Cooling (OPC) and how does it work? OPC 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 schematics and a technical review of the OPC process.

Operating 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 OPC 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. OPC is an ideal strategy for meeting the cooling load of a new building expansion without adding chiller capacity.

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 building’s load and the stored ice cools the remaining load.

A partial-load OPC 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.

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

Additional design engineer benefits

• OPC works in conjunction with a customer’s existing chiller to meet a building’s increased cooling load while reducing energy costs.
• Provides a design with a chiller that is 40 to 50 percent smaller to minimize inefficient operation of oversized equipment, with minimal risk.
• TES 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 an OPC system.
• Click here for a complete list of other benefits.

Misconception: I installed an OPC system years ago and it never worked properly and was nothing but headaches. The OPC market started 20 years ago with over 30 manufacturers, all employing different technologies. Since that time, the technology has evolved, changed, and matured, and today, CALMAC is the recognized off-peak cooling leader. The products that CALMAC designs and manufactures have a proven track record for performance and they are easy to apply. Today’s systems use standard commercial chillers and factory-assembled ice tanks. CALMAC also can provide information to help the designer, contractor, and operator install the OPC system.

Click here for complete product and specification information.

Click here for a partial listing of CALMAC’s project list.

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