Cooling of buildings using new salthydrates
In the project PC-Cools_V two new phase change materials (PCM) on a
salthydrate basis with a narrow melting range around 21°C and around
15°C are developed. The latter was intended for the implementation in
central cold storages whereas the PCM melting at 21°C was designed for a
decentral, room integrated storage application, especially cooling
|Project status||Project completed|
|Storage type||Latent heat storage salt hydrate|
|Research objective||Storage material|
|Projekt duration||December 2012 until January 2017|
In a system study, the heat transfer mechanisms in a cooling circuit for room cooling with cooling ceilings are examined. Further, a water vapor tight encapsulation for a porous core material infiltrated with a salthydrate-based PCM will be developed. Such a granular material in size of some millimeters can be used for different kinds of storages. In this project, also the leadership of the working group “Compact Thermal Energy Storage – Material Development and System Integration” is organized.
Progressing PCM technology in the building environment
The aim of this project is to close the gap of available salthydrate-based PCM in the temperature range suitable for building climate control. This is an important and necessary step for a broader dissemination of latent heat storage technology in the building sector.
To bring the material development into the context of a complete system, theoretical investigations are carried out, which address the cold distribution in a building, additionally considering innovative mechanisms of heat transfer.
For cooling ceiling applications, there is no PCM available which fits the requirements of an optimal melting range and little subcooling. Therefore, a salthydrate-based PCM with a narrow melting range around 21°C will be developed. Additionally, a PCM with a melting range around 15°C will be investigated for the use in central cold storages. A material which can store a large amount of heat (or cold respectively) in this temperature range can be loaded more efficiently by refrigerating machines or even from regenerative cold sources than for example ice storages.
Further, especially adjusted and optimized porous core materials of calcium silicate are developed, which can be infiltrated with the PCM and are mechanically and chemically stable. The core materials are compounded in granular form with diameters of some millimeters and encapsulated with a water vapor barrier coating. With such a “meso-encapsulation” the usage as bulk material or even – with small particle size – the implementation in building materials is possible. Additionally, macroencapsulations (metal containers) for the new PCMs are developed.
The theoretical investigations concerning the cold distribution in buildings are finished. Cold distribution in a typical office building using water and phase change slurries as heat transfer fluid as well as heat pipes was calculated and analyzed. Several parameters were examined and evaluated. The results of this system study led to a modification in the target phase change temperature of the two new PCMs: 20°C for cooling ceiling applications and 13-14°C for central storage applications.
Development of salthydrates, calcium silicate cores and mesoencapsulation
In the context oft the PCM development, promising candidates for both melting temperatures were found. These will be further investigated and optimized.
A process for the fabrication of salthydrate-filled calcium silicate granules could be established. The mesoencapsulation of the granules is in progress on a laboratory scale. Possible encapsulation materials have been identified.