Civil Engineering Reference
In-Depth Information
• High specific heat to provide additional significant sensible heat storage.
• High thermal conductivity of both solid and liquid phases to assist the
charging and discharging energy of the storage system.
• Small volume change on phase transformation and small vapour pressure at
operating temperature to reduce the containment problem.
• Congruent
melting
of
the
phase-change
material
for
a
constant
storage
capacity of the material with each freezing/melting cycle.
• Reproducible phase change: to use the storage material many times (also
called cycling stability).
2. Kinetic properties—nucleation and crystal growth
• High nucleation rate to avoid super cooling of the liquid phase and to assure
that melting and solidification proceed at the same temperature.
• High rate of crystal growth, so that the system can meet demand of heat
recovery from the storage system.
3. Chemical properties
• Complete reversible freeze/melt cycle.
• No degradation after a large number of freeze/melt cycle.
• No corrosiveness to the construction materials.
• Non-toxic, non-flammable and non-explosive material for safety: for envi-
ronmental and safety reasons.
4. Economics
• Abundant.
• Available.
• Cost effective: to be competitive with other options for heat and cold storage.
For their use, PCM must be encapsulated, either encapsulating the material or
encapsulating the building composite, as otherwise the liquid phase would be able
to flow away from the location where it is applied.
Encapsulation is carried out either by microencapsulation, where small,
spherical or rod-shaped particles are enclosed in a thin, high molecular weight
polymer film; or by macroencapsulation, where the PCM is in some form of
package such as tubes, pouches, spheres, panels or other receptacle (Cabeza et al.
2011
). On the other hand, in shape-stabilised PCM the storage material is included
in an unsaturated polyester matrix or integrated with the building materials without
encapsulation (Farid et al.
2004
; Zhu et al.
2009
).
2.2 Microencapsulated PCM
Nowadays, microencapsulation technology is the prominent for use of PCM in
building materials. With the advent of PCM implemented in gypsum board,
plaster, concrete and/or other wall covering materials, thermal storage can be part
of the building structure even for light weight buildings (Tyagi et al.
2011
;
