Energy and environment are the two major issues facing human beings nowadays. Industrial developments and population boom in the past few centuries have resulted in an enormous increase in energy demand. Building is one of the leading sectors of the energy consumption. And the energy consumption of heating, ventilation and air conditioning systems is still increasing with the increasing demand for thermal comfort. Under this circumstance, thermal energy storage systems with high potential to save energy in buildings have gained more and more attention.
Thermal energy storage can be generally classified as sensible heat storage and latent heat storage according to the heat storage media. In sensible heat storage, the heat is stored or released accompanied with temperature change of the storage media, whereas in the latent heat storage the heat is stored or released as heat of fusion/solidification during phase change processes of the storage media. By contrast, latent heat storage with phase change materials (PCMs) provides a high heat storage density and has the capability of storing a large amount of heat during the phase change process with a small variation of PCM volume and temperature. Using latent heat storage in the buildings can meet the demand for thermal comfort and energy conservation purpose.
PCMs in building walls, other building components than walls and in separate heat or cold stores. The first two are passive systems, where the heat or cold stored is automatically released when indoor or outdoor temperatures rise or fall beyond the melting point. The third one is active system, where the stored heat or cold is in containment thermally separated from the building by insulation. The advantages of organic PCM are : 1. availability in a large temperature range; 2. freeze without much super cooling; 3. ability to melt congruently; 4. self-nucleating properties; 5. compatibility with conventional material of construction; 6. no segregation; 7. chemically table; 8. high heat of fusion; 9. safe and non-reactive; 10. recyclable.
Impregnation of PCMs into construction materials: 1. Incorporation methods: 1.1 Traditional methods：1.1.1 Direct incorporation; 1.1.2 Immersion; 1.1.3 Macroencapsulation; 1.2 Microencapsulation; 1.3 Shape-stabilised PCMs; 2. Containers;
How to enhance heat transfer processes in a latent heat thermal storage (LTHS) unit is a question. There are two methods are considered to be the most attractive: application of finned surfaces embedded into the heat storage medium (HSM) and an introduction of matrix structures with a high heat conductivity into HSM (orimpregnation of HSM into porous matrix structure).
There is an example about the practice of PCM. In Fig. 11, a sheet steel tray serves as a container for the PCM/gypsum composite while providing the panels with the required mechanical stability. A mix comprising microencapsulated PCM and gypsum is poured into the tray. Active control of the thermal mass is achieved by incorporation of a capillary water tube system in the gypsum compound. If required, thermal conduction in the composite may be improved by the inclusion of aluminum fins. While the panel is primarily designed for ceiling installation, fitting to walls is equally straightforward. The system allows use of renewable energy sources for the heating and cooling of office and industrial buildings.
1. A PCM is a substance with a high latent heat which is capable of storing and releasing large amounts of energy at a certain temperature. 2. Latent heat of fusion of water is about 334kJ/kg whereas sensible heat at 25° Celsius (77°F) is about 4.18kJ/kg. These dates can be used to compare with my test's dates. 3. Temperature can cause phase change of the material. 4. All materials store heat and can be used as PCMs, but it is necessary to consider the economics of the material.
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