Underwriters Laboratories Inc. Headquarters, Northbrook, IL

When planning the expansion or replacement of a cooling system in an existing building, owners should consider Off-Peak Cooling (OPC). OPC is a demand-responsive system that can eliminate electrical-system upgrades, electric demand-charge increases, reduce maintenance, and reduce energy costs. With OPC, owners can also avoid the significant expense of installing additional chiller capacity.

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. CALMAC’s ICEBANK® thermal-energy storage tanks work in conjunction with a building’s chiller to make ice during less-expensive off-peak hours at night. The ice is stored in the tanks and then used the next day to cool the building during more-expensive on-peak hours.

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

With partial storage, ICEBANK tanks work in tandem with the chiller. The existing chiller will produce ice at night and continue to run the following day, cooling a percentage of the building’s load up to 70 percent, depending upon rates and building usage. The stored ice in the ICEBANK tanks cools the remaining percentage of the building’s load. A partial-storage strategy enables building owners to meet the increased cooling load of their expanded building without adding chiller capacity, or to replace the existing cooling system with smaller chillers, cooling towers, and pumps.

Underwriters Laboratories Inc. (UL) chose off-peak cooling for the energy efficiency and operating flexibility it provided. Since the installation of Off-Peak Cooling in 2001, they have saved $350,000 on their utility bill annually. "Overall, the new system reduced operating cost from $0.14 to $0.066 per tn-hr.", a 52 per cent savings according to Volker Kotscha, UL's Director of Facilities Operation. This air-conditioning system is entirely redundant. "We can cool the entire facility with ice for a minimum of six hours to take advantage of any energy curtailment incentive windows offered by the local utility", said Volker, Kotscha

Click here (PDF, 440 Kb) for more information regarding the OPC process.

Additional retrofit benefits

• OPC lowers operating costs up to 40 percent depending upon electric rates.
• OPC is demand responsive, providing further savings opportunities.
• OPC gives owners the ability to expand the size of a building without increasing chiller capacity. OPC works in conjunction with an existing chiller to meet a building’s increased cooling load while reducing energy costs.
• The payback period is typically two to five years. Some owners have received payback in less than one year.
• Lower operating costs increase a building’s property value.
• The size and cost of air handlers, motors, ducts, and pumps can be reduced by 20 to 40 percent, further increasing cost savings.
• Click here for a complete list of building-owner benefits.

Misconception: I do not have enough space for the tanks. Very little space is required for ICEBANK^™ tanks. It is easy to relate the space needed for partial ice storage to space needed for a residential water heater. A typical 1700 square-foot home has a 4 square-foot water heater. The water heater uses (4 square feet/1700 square feet) or 0.23 percent of available floor space. An ICEBANK tank can provide approximately 20 tons of cooling over 8 hours. With the 500 square foot per ton rule, a 70 square-foot ICEBANK tank provides enough cooling for about 10,000 square feet of building space, and uses about 0.70 percent of floor space (full-storage system). Most OPC systems are partial storage, where storage accounts for about 30 percent of the total cooling required reducing the floor space needed to about ¼ of 1 percent of the conditioned space. A 100,000 square-foot building would require only 2,500 square feet for the ICEBANK tanks. ICEBANK tanks can be place indoors or outdoors. Outdoors, the tanks can be placed on the roof or on grade, or they can be partially or totally buried.

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.