Civil Engineering Reference
In-Depth Information
In the melting process 4-5, the warm surrounding fluid adds sensible heat to the
PCM. This in turn increases the temperature of the PCM. In the process 5-6, with
the addition of continuous heat energy, the commencement of melting (phase
change) of PCM takes place at constant temperature.
Further heat addition in the process 6-7 leads to the complete melting of the
solid phase to liquid phase, and the PCM would acquire the equilibrium temper-
ature condition with that of the surrounding heat transfer medium.
Interestingly, during the processes 2-3 and 5-6, the latent heat phase trans-
formation of the heat storage material is substantial such that higher amount of
thermal energy is being stored and released at constant phase change temperature.
This is the most essential characteristic of PCMs, which explores their TES
capacity highly suitable for building cooling and heating applications.
The PCMs are generally classified into inorganic, organic and eutectic mix-
tures. The latent functional phase change energy storage materials are meritorious
in terms of their rate of charging and discharging characteristics, high latent heat or
enthalpy of fusion, energy storage density per unit volume and so on (Dincer and
Rosen
2011
).
Though the inorganic and organic PCMs exhibit supercooling phenomenon,
dissociation of material during phase change, incongruent freezing and melting
characteristics, when subjected to the cyclic cooling and heating processes, they
are still preferred much for catering the energy redistribution requirements in
modern dwellings.
The integration of LTES system with building cooling and heating system
indubitably serve to bridge the gap between the energy supply and its usage without
losing the energy savings potential in buildings (Parameshwaran et al.
2012
).
From this perspective, the LTES systems using a variety of PCMs exhibiting
suitable thermal properties being integrated with the building HVAC systems have
been extensively discussed in Parameshwaran et al. (
2012
) and Cabeza et al. (
2011
).
The selection of an active or a passive TES system mainly depends upon the
cooling/heating demand of the occupied zones in building envelope and the phase
change characteristics of the heat storage material, including the enthalpy of latent
heat, phase transition temperature, thermal conductivity, heat storage and release
capacity, thermal stability and thermal reliability. The incorporation and appli-
cations of some of the PCM-based passive and active systems in the building
envelopes are shown in Fig.
17
(Xin et al.
2009
).
In majority of the present latent thermal storage systems being integrated in
buildings, the organic PCMs are widely utilized because of their excellent latent
heat of fusion, low supercooling, thermal stability, less corrosion, ease availability
and moderate cost. Paraffins and their derivatives are widely considered as PCM in
the LTES systems for accomplishing effective energy redistribution in buildings.
The limitations of the PCMs as mentioned in the earlier section and in the research
works performed by Parameshwaran et al. (
2012
) and Cabeza et al. (
2011
) can be
considered as challenging factors for their implementation in the LTES systems.
The constraints of using the PCMs in buildings are being investigated by
several research groups worldwide, which have resulted in good solutions that are
