What is phase-change energy storage?

Thermal energy storage (TES), also commonly called heat and cold storage, allows the storage of heat or cold to be used later. To be able to retrieve the heat or cold after some time, the method of storage needs to be reversible. Thermal energy storage can be implemented by storage of Sensible Heat or Latent Heat.

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WHAT IS Sensible Heat STORAGE? and WHAT IS Latent Heat STORAGE?

The most common way of thermal energy storage is as sensible heat. As shown in the figure, heat transferred to the storage medium leads to a temperature increase of the storage medium. Hot water storage for domestic heating & domestic hot water is a very common example.

The Phase Change Materials by melting and solidification can store large amounts of heat or cold. Melting is characterized by a small volume change, usually less than 10%. If a container can fit the material while it is in it’s liquid state, the pressure is not changed significantly and consequently melting and solidification of the storage material proceed at a constant temperature. Upon melting, while heat is transferred to the storage material, the material still keeps its temperature constant at the melting temperature, also called the Phase Change Temperature. If the melting is completed, further transfer of heat results again in sensible heat storage. The heat supplied upon melting is called latent heat, and the process latent heat storage.

Sensible Heat vs Latent Heat

LHvsSH

Temperature Control during phase-change energy storage

TempControl

APPLICATION OF LATENT HEAT STORAGE with phase change material?

The latent heat storage with phase change materials is commonly used for the solid-liquid phase changes. The application is divided as a simplification into temperature control and storage and supply of heat and cold with small temperature change.

Phase Change Material (PCM)

Inorganic PCM are engineered hydrated salt solution made from natural salts with water. The chemical composition of salts is varied in the mixture to achieve required phase-change temperature. Special nucleating agents are added to the mixture to minimize phase-change salt separation and to minimize super cooling, that are otherwise characteristic of hydrated salt PCM. Salt Hydrates are characteristic of being non-toxic, non-flammable and economical.

Bio-based PCM are organic materials that are naturally existing fatty acids such as vegetable oil. Based on their chemical composition, their phase-change temperature can vary. These products are non-toxic, non-corrosive and have infinite life cycles. They however can be expensive and flammable at high temperatures.

Organic PCM are naturally existing petroleum bi-products that have their unique phase-change temperature. These products are manufactured by major petrochemical companies so their availability could be limited. They can be toxic, flammable and expensive. They have infinite life cycles and the price varies with changes in petroleum prices globall

Advantages of phase-change energy storage

  • Store thermal energy at the temperature of process application
  • Store thermal energy as latent heat which allows higher thermal energy storage capacity per unit weight or material without any change in temperature
  • Store thermal energy from thermal energy source or electrical energy source when available and use when needed
  • This technology would lead to sizing HVAC equipment for average load rather than peak load

Economical & Environmental benefits

  • Store natural thermal energy for facility heating and cooling needs. Reduced energy demand reduces facilities carbon footprint
  • Store thermal energy during off demand hours and use during peak demand to save on energy cost and help stabilize grid load
  • Shift of heating and cooling load also reduces peak time stress of heating and cooling equipment that can lead to reduced operating & maintenance cost.
  • This technology would lead to sizing HVAC equipment for average load rather than peak load

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