Permanent Load Shifting

Permanent load shifting (PLS) refers to the shifting of energy usage  from one time period to another during the course of a day on a regularly recurring basis. Building cooling (space cooling) is one of the major factors leading to high electricity costs for office buildings, retail stores, and other facilities. Space cooling also represents one of the largest loads on the grid, making afternoons the typical on-peak period, as the greatest cooling load is present during this time. On very warm days, the afternoon peak can reach a critical level. More and more, customers are paying electricity prices that vary with the time of day and it is not unusual to see the highest prices during the on-peak hours. PLS is a strategy to deal with electricity costs that are based on this type of pricing.


  • Technology Overview: Chilled Water TES Systems
    October 16, 2013
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    Chilled Water systems are one of the most popular options for thermal energy storage (TES). Chilled water systems are appealing for many applications because they are less complex and have lower operating costs than alternative technologies, but require more physical space as they offer lower storage density than other options.

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  • Technology Overview: Ice Storage TES Systems
    October 16, 2013
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    Ice storage thermal energy storage (TES) systems rely on ice instead of chilled water as a storage medium. Ice storage systems are less often used than chilled water systems due to being more complex and less efficient, but offer the densest storage capacity. Ice storage tanks are about 75% smaller than chilled water tanks.

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  • Technology Overview: Rooftop Unit TES Systems
    October 16, 2013
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    Thermal energy storage (TES) systems can be used with commercial and residential packaged rooftop units (RTUs), to shift energy use to off-peak periods.  RTU-TES systems can be designed for new construction or retrofit applications.

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  • Technology Overview: Eutectic Salts TES Systems
    October 14, 2013
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    Eutectic salts Thermal Energy Storage (TES) systems use a phase change medium instead of ice. Eutectic salts have a higher freezing point temperature than water. The phase change material is encapsulated in plastic containers that are stacked in the storage tank as water is circulated around them.

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