Johnston County Schools Raleigh, North Carolina

Schools and universities are ideal applications for Off-Peak Cooling (OPC) because the cooling loads of these buildings are variable and OPC can minimize electrical demand charges, resulting in significant cost savings.

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 facility’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 school 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 systems offer the best savings and simple operation.

Tanks at Johnston County Schools Raleigh, North Carolina

With partial storage, ICEBANK tanks work in tandem with the chiller. The chiller produces ice at night and continues to run the following day, cooling up to 70 percent of the facility’s peak load. The stored ice in the ICEBANK tanks cools the remaining load. As a result, a school district can install a chiller that is 40 to 50 percent smaller, while reducing energy costs. Good partial-storage designs in schools can pay back very quickly. Full- or partial- storage decisions are based upon building usage and local energy rates. With CALMAC’s modular system, partial-storage systems can be converted to full storage systems when rates change and make full-storage economically viable.

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

Additional benefits for school administrators to consider

• Cooling costs can be reduced up to 40% or more.
• The payback period for partial storage is typically under two years. Some schools have demonstrated paybacks in less than one year.
• Over the life of the facility, the cost savings can add up to millions of dollars.
• OPC also improves classroom comfort for students and staff by lowering humidity levels.
• Click here for a complete list of the economic benefits.

Misconception: OPC is too expensive for a school district to install. Installation of partial ice storage is very affordable because the chiller needed is 40 to 50 percent smaller. For example:

In the above example, the cost of the partial-storage system is essentially the same as a conventional HVAC system. However, energy-cost savings of 20 to 60 percent, as well as a 20 to 40 percent reduction in the size and cost of air handlers, motors, ducts, and pumps, were not factored into the above calculation. These additional elements provide school districts with significant cost savings.

For example, Bill Gilbert, energy director for Johnson County School located southeast of Raleigh, has analyzed the economic benefits of ice storage in specific school applications and has found the results to be impressive. “We have found simple project paybacks of as little as two years, always less than four. Over the anticipated life of the school of 40 years or more, we believe the total savings could be as great as $1.2 million in a typical middle school.” (Johnson County School Case Study, “Air-Cooled Chillers, Ice Storage Provide Lifetime Savings for School System,” Trane)

Click here for additional information regarding how CALMAC Off-Peak Cooling systems can benefit schools and universities.

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.