Technology Overview: Eutectic Salts TES Systems

October 14, 2013
 
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Eutectic salts Thermal Energy Storage (TES) systems are similar to encapsulated ice storage systems, but storage tanks contain eutectic salts as a medium instead of ice. Eutectic salts are a type of phase change material, with 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. Eutectic salts have a freezing point of up of 47-48°F which means less energy is needed to create the phase change of the salts compared to ice.

Phase change materials store more cooling capacity than chilled water systems but less capacity than ice storage systems, putting its efficiency between chilled water storage systems and ice storage systems (eutectic salts store about 60 Btu/lb, compared to 1 Btu/lb for chilled water storage and 144 Btu/lb for ice storage).

Basic Function of Eutectic Salts Storage Systems

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Eutectic salts storage is one type of Thermal Energy Storage (TES) technology. TES is the most popular way to implement the demand-side energy management strategy known as 'Permanent Load Shifting' (PLS).

During off-peak hours, the system’s chiller creates 40°F water that is pumped into the eutectic salts storage tanks to freeze the phase-change materials inside (“charging” mode). A phase-change material system chiller has the same kW/ton rating as a conventional chiller. When there is cooling load in the daytime, the storage medium is allow to melt, and the water is pumped from the tank at about 47-48°F through the cooling system’s chilled water circuit (“discharging” mode). The chilled water is circulated to the air handling system’s chilled water coils to cool the space.

Benefits and Disadvantages of Eutectic Salts Systems

Benefits

  1. Requires 30-50% less space than chilled water systems
  2. Can use conventional chillers and water temperatures (Charge @ 40°F)
  3. More economical operation due to higher charging temperatures
  4. Higher cooling capacity, per cubic foot, than chilled water systems

Disadvantages

  1. More expensive and complex solution than chilled water systems
  2. Warmest discharge temperatures (near 50°F)

Requires supplemental chiller operation to further reduce chilled water supply temperature unless dehumidification requirements are low.

 

 
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