13 Review on PCM Application for Cooling Load Reduction …
257
13.3.2 Material Characterization
The characterization plays a significant role in material selection for TES systems.
It is necessary for design, modelling and implementation of these systems. The
available knowledge on PCMs is limited and in some cases even found to be inaccurate/incomplete (Saxena et al. 2017). PCMs (salts in particular) show incongruent
melting (with melting occurring non-uniformly) and also showing sub-cooling. Thus,
there is a need to characterize these PCMs to determine the temperature dependence
of different thermophysical properties Energy efficient building constructions, incorporating PCM storage require accurate assessment of PCM properties with respect
to temperature as single data point may not define the system with accuracy. The
specific heat, latent heat, phase change temperature, sub-cooling has been accurately
determined using differential scanning calorimeter. Thermal conductivity is measured using thermal conductivity meter.
Differential Scanning Calorimetry: Differential Scanning Calorimetry is a
method in which heat transfer to sample and reference pan is measured along with
rise in temperature. The difference in heat flow and rise in temperature profile gives
the latent heat, phase change temperature, specific heat of the sample. It also determines the sub-cooling as well. Differential scanning calorimeter (DSC) is used to
accurately evaluate these thermal properties and their temperature dependence.
Thermal Conductivity Meter: It determines the dispatchability of the TES systems, which is one of the most important characteristic property for any energy
storage system. The thermal conductivity measurement in different phases is generally done by two methods, that is steady-state and transient. The heat flow meter
and guarded hot plate techniques are steady-state methods both based on Fourier’s
law, which suits the solid phase measurements, but requires a lot of time attain stable
temperature gradient within the specimen. The transient techniques on the other hand
measures thermal conductivity within minutes, therefore researchers now often use
this method for PCMs. Transient plane source, transient hot wire and laser flash are
the example of transient methods (Khodadadi et al. 2013).
13.4 Methods of PCM Incorporation
The integration of TES in buildings can be of two types i.e. active and passive. In
Active systems, energy required is often derived from renewable resources whereas,
passive systems concentrate on energy saving using seasonal shadings, blinds,
increasing thermal mass or thermal insulation, focusing on reducing the energy
demand. The thermal mass may be increased by PCM incorporation in building
components. Thus, it is necessary to understand different methods that may be used
for the purpose and their respective merits and demerits as discussed in Navarro et al.
257
13.3.2 Material Characterization
The characterization plays a significant role in material selection for TES systems.
It is necessary for design, modelling and implementation of these systems. The
available knowledge on PCMs is limited and in some cases even found to be inaccurate/incomplete (Saxena et al. 2017). PCMs (salts in particular) show incongruent
melting (with melting occurring non-uniformly) and also showing sub-cooling. Thus,
there is a need to characterize these PCMs to determine the temperature dependence
of different thermophysical properties Energy efficient building constructions, incorporating PCM storage require accurate assessment of PCM properties with respect
to temperature as single data point may not define the system with accuracy. The
specific heat, latent heat, phase change temperature, sub-cooling has been accurately
determined using differential scanning calorimeter. Thermal conductivity is measured using thermal conductivity meter.
Differential Scanning Calorimetry: Differential Scanning Calorimetry is a
method in which heat transfer to sample and reference pan is measured along with
rise in temperature. The difference in heat flow and rise in temperature profile gives
the latent heat, phase change temperature, specific heat of the sample. It also determines the sub-cooling as well. Differential scanning calorimeter (DSC) is used to
accurately evaluate these thermal properties and their temperature dependence.
Thermal Conductivity Meter: It determines the dispatchability of the TES systems, which is one of the most important characteristic property for any energy
storage system. The thermal conductivity measurement in different phases is generally done by two methods, that is steady-state and transient. The heat flow meter
and guarded hot plate techniques are steady-state methods both based on Fourier’s
law, which suits the solid phase measurements, but requires a lot of time attain stable
temperature gradient within the specimen. The transient techniques on the other hand
measures thermal conductivity within minutes, therefore researchers now often use
this method for PCMs. Transient plane source, transient hot wire and laser flash are
the example of transient methods (Khodadadi et al. 2013).
13.4 Methods of PCM Incorporation
The integration of TES in buildings can be of two types i.e. active and passive. In
Active systems, energy required is often derived from renewable resources whereas,
passive systems concentrate on energy saving using seasonal shadings, blinds,
increasing thermal mass or thermal insulation, focusing on reducing the energy
demand. The thermal mass may be increased by PCM incorporation in building
components. Thus, it is necessary to understand different methods that may be used
for the purpose and their respective merits and demerits as discussed in Navarro et al.