Thermal storage for cooling allows chillers to run during off-peak periods (e.g., at night) to fill an insulated tank with ice or chilled water for use the next day. Chiller compressors account for the lion's share of energy and demand for most cooling systems. Peak demand charges related to cooling (rising across the country and quite high in several urban areas) may be greatly reduced in the process. Vendors of such systems (e.g., Calmac) have offered their products since the 1980s for central chilled water systems, typically several hundred tons (or larger) in capacity. For much smaller systems (starting under 10 tons), Ice Energy™ Corp. (www.ice-energy.com) now offers the Ice Bear™.

Designed to serve the small commercial and residential markets (where split A/C systems are common), the Ice Bear connects directly to a compressor's refrigerant lines, allowing it to freeze water sealed inside the Ice Bear unit, which holds about 50 ton-hrs (sufficient to carry a 7.5-ton load through a normal workday without running the system's compressor). Using a small built-in refrigerant pump, the Ice Bear circulates refrigerant through its sealed ice block, returning liquid refrigerant for use in the A/C system. No changes in A/C settings or operation are necessary, so occupants are unaware of the difference.

Where This Makes Sense

Wherever peak demand charges are high (e.g., over $10/kW month during the cooling season) and time-of-use or real-time rates apply (wherein daytime $/kWh rates are much higher than at other times), shifting chiller demand to off-peak periods will save money. Where retail electricity has been deregulated, flattening one's hourly load profile may also elicit a lower rate for power. On the other hand, where rates are flat (e.g., in some rural states or under a fixed price power contract) such shifting will not produce significant savings.

Depending on night climate, energy efficiency may also be improved since running the A/C unit's compressor when outside air is cooler (and no solar load exists) may allow it to produce cooling using fewer kWh. Standby losses are quite low: Ice Energy claims less than 1%/day, even on the hottest days. Power draw by an Ice Bear is minimal: a combined 300W for the refrigerant and water pumps.

At the wholesale power price level, any reduction of the system-wide summer peak will likely cut the hourly market clearing price (MCP), thus minimizing the overall cost to supply power. In some states, efforts to cut peak demand are rewarded through programs supported by utilities, state agencies, and/or grid operators. New energy codes may also encourage thermal storage. Municipal utilities in southern California are already embracing the Ice Bear, recently purchasing 10 units to test the technology.

So What's Inside the Box?

An Ice Bear storage module is essentially an insulated plastic container (roughly 6 ft by 6 ft by 5 ft) filled with tubing, water, two small pumps, and a refrigerant management system. Total weight is 5,560 lb, most of which is the 570 gal of tap water that fill the unit once it is in place (empty weight is 800 lb). Pad mounting is no problem, but roof mounting may require minor structural bracing.

Integrating With Existing A/C Systems

Ice Bears may be used individually or ganged in parallel to provide more ton-hrs and/or cooling capacity as needed. In all cases, existing refrigerant is sucked out, connections are made to existing condenser and evaporator lines, and the system refilled with refrigerant. Where concern exists over warranty for an existing system, Ice Energy offers to extend the warranty for condensers less than five years old.

No Endorsement Implied

While the neatest HVAC device seen by this writer in some time, the Ice Bear is quite new and is presently (October, 2005) installed in only a handful of locations. Interested readers should check out Ice Energy's website (www.ice-energy.com) and make their own determination regarding this technology. It has, however, received an Innovation Award from ASHRAE and is well-positioned to address the ever-rising demand for power in many areas. ES