St. Francis Medical Center - Liliha Honolulu, HI

Hospitals and medical centers can reduce demand charges with Off-Peak Cooling (OPC). In addition, a portion of the stored cooling is always saved on a daily basis to be used for emergencies or load control. If power is lost, or a load-control emergency is in place, smaller standby generators can run the pumps and fans to cool the facility using the saved stored cooling that the OPC system provides. The OPC system reduces the size and cost of the standby generator, while allowing for flexible operation.

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 hospital’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 hospital during on-peak hours. Click here (PDF, 371 Kb) for system schematics and a technical review of the OPC process.

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 very expensive in a hospital.

With partial storage, ICEBANK tanks work in tandem with the chiller(s). The standby chiller charges the ICEBANK tanks at night and provides backup for a daytime base-load chiller. Efficient base-load chillers handle the nighttime load and continue to run the following day during the discharge cycle. During the discharge cycle, the chiller cools a portion of the hospital’s load and the stored ice cools the remaining load. Utility rates, and facility operation and layout, will determine how much ice to install.

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

• 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 customers 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.
• In new facilities, 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 compete for my clients work and I can't afford to provide an OPC design in my bid package. There are some equipment and control specification differences with an OPC design, but the majority is similar to conventional chilled-water design. A designer’s first few OPC projects may cost more than conventional cooling in order to develop procedures and OPC specifications. There may be state and federal energy grants or rebates available to help offset these costs. Experienced OPC designers say that after a few projects, their designs cost the same as conventional cooling. Some designers consider any added costs as an investment in marketing to develop a niche that provides them with a significant competitive marketplace advantage. Some designers compete for a client with a conventional scope, then provide a cost add for a TES design. The additional costs can be repaid with shared energy savings.

Grossmont Hospital La Mesa, California

Grossmont Hospital (PDF, 89 Kb) located in La Mesa, California is also enjoying the benefits of Off-Peak Cooling. A feasibility study determined that the hospital had an additional design day-cooling requirement of 740 tons. This demand was met with a 320-ton chiller and 22 CALMAC ICEBANK tanks. Bill Keaton, the hospital’s chief engineer said, "The new ice-storage system enabled Grossmont to shift 232 kW off peak and avoid a non-ratcheted $14.42 per kW time-of-use demand charge." Keaton estimates the energy cost savings to be $17,000 per year and the payback period to be about three years.

Click here for complete product and specifications 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.