With energy-consuming equipment, such as water heaters and refrigerators, we have good data on energy consumption and can set clear standards accordingly. In some product categories—clothes washers, for example—Energy Star standards were adopted because those standards provide a high enough threshold to represent just the very top segment of the product market (less than 10%). In other product categories—e.g., refrigerators and dishwashers—we set a higher threshold than ENERGY STAR: for example, exceeding those standards by 10% or 20%. With lighting and lighting control equipment, certain generic products qualify, such as compact fluorescent lamps and occupancy/daylighting controls, while in other categories only a subset of products qualify. In some cases, products that meet the energy efficiency requirements are excluded, because of evidence of poor performance or durability. Microturbines are included here because of the potential for cogeneration (combined heat and power) that they offer.
The IceStor is an external-melt, ice-on-coil, thermal energy storage system for commercial use. The system uses a tank containing thousand of 1/4" polymer heat exchanger tubes with a glycol solution flowing through them. Ice forms on the tubes during off-peak hours, and during on-peak the chilled solution flows out to cool the building. There are no moving parts and no metal parts in contact with the water, minimizing the risk of corrosion. Fafco offers eight separate models capable of delivering between 125 and 600 ton-hours of cooling.
Off-peak cooling, or thermal energy storage (TES), is an alternative to conventional chiller operation in commercial buildings. Off-peak electricity is used to provide some or all of a building’s cooling requirements by chilling thermal-storage media during times of low electrical demand. Building operating costs are typically lowered through the use of off-peak pricing by the utility company. In new construction, much smaller chillers can often be specified for use in conjunction with the ice storage; the smaller chillers will provide constant full-load operation at their highest efficiency compared to larger units which will run sporadically and at lower efficiencies. Additionally, using primary air that is 10° to 12°F cooler than the usual 55°F requires much less airflow—air handlers, motors, ducts and pumps can often be downsized by 20-40%. These systems can increase total energy use at the site, even while reducing costs and peak demand. Though point-of-use energy savings may not occur, nighttime power generation and distribution by electric utilities may be significantly more efficient than in the daytime, resulting in a potentially significant overall energy savings.
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