Abstract
Thermal energy storage (TES) is an often
unrecognized but important component of the developing market for energy
storage systems. Most often used to provide cooling capacity for commercial
buildings, TES systems are also increasingly seen as an effective means of
shifting electricity use from daytime peak periods into less expensive periods
of the day or at night, saving money and increasing overall system efficiency.
Globally, TES is expected to grow substantially through 2020, with worldwide
revenues of $3.6 billion and added capacity of 3,824 MW in that year. (Pike
Research analysis). Newer forms of TES using different temperature phase change
materials (PCM) and advancement in designs to increase the efficiency of
storage is becoming the trend. This article attempts to discuss the application
of PCMs in building material and its benefits.
What is a PCM
Phase
Change Materials falling under the broad category of smart materials are
essentially chemicals which in normal state could be in solid, liquid or semi -
solid or waxy state. These chemicals are engineered to change their form or
phase at specific temperatures. Now the question is what is special about phase
change materials and its role in thermal energy storage. These chemicals as
they change their phase they absorb and store the energy. Once the entire phase
transformation has happened, this chemical is now capable of providing back the
very same temperature back until all of its energy is released.
We could
draw an analogy with water to better understand PCMs. Water is a natural form
of PCM and most temperature control packaging use water by utilizing its high
thermal energy storage capacity during its change of phase from liquid to solid
or vice versa. The properties that make water an ideal material for storage
& transport of materials for applications requiring temperature maintenance
in the range of -2°C to 4°C are as follows,
·
Consistent, repeatable,
reliable phase change material temperature of 0° C.
·
High latent heat of fusion.
·
Non-Toxic.
·
Easily packaged into pouches
or bottles.
·
Inexpensive and easily
Available.
A good
phase Change Material should mimic these properties but change phase at
different temperatures. It has the ability to store and release large amounts
of heat/energy while maintaining a constant temperature as shown in figure 1.
Application
of PCM
To simply understand the possibilities with
PCM we must understand the three main functions it provides. One can say it is
three products in one; A battery, A passive heating or cooling unit and a
temperature regulator.
To take advantage of the above function false ceiling
tile using advanced savE®
PCMs can be used. The functions and looks of a PCM based tile is close to any
other false ceiling tile. In addition these would save energy cost of the
building by reducing the HVAC load and providing other benefits which are
elaborated further. The below figure 2 illustrates a model of the false ceiling
tile.
*
Benefits
of incorporating PCM in the false ceiling tile
Thermal Inertial
Thermal inertia is a property of buildings
that resists the fluctuation of building environment with fluctuations in the
outside ambience the building is exposed to. Thermal inertia is directly
correlated to the building material’s specific heat capacity (in the
temperature range of function) and the amount of material (mass) incorporated
in the building design. The figure 3 illustrates the fluctuation in temperature
outside of the building and corresponding fluctuation inside the building which
is narrower due to PCM.
HVAC
load
Modern day buildings aim to be sleeker
and lighter; however continue to use conventional building materials. As a
result, these buildings have lesser thermal inertia, and consequently, major
loads of maintaining thermal comfort within the building fall on the HVAC
systems. Approximately 20-25% of the HVAC load can be brought down simply by
reducing the temperature fluctuations.
PCMs can be tailored to be most
effective depending on the different region and varying air-conditioning
requirements. PCMs selected such that they melt or freeze at a specific temperature,
absorbing or releasing energy at that temperature in the form of latent
enthalpy of the material. By this virtue, phase change materials have more
energy storage capacity at a given temperature than the heat storage capacity
of any other material on that temperature.
Due to this property, PCMs can increase
the overall specific heat density of building materials, in turn increasing
their thermal inertia if the application can be extended even to the external
envelope of the building.. This can be used to save immense amount of energy as
peak temperatures in the climate can be resisted by the building. In fact, in a
recent study, it was shown that 5 mm PCM can be used to replace the thermal
mass of 50 cm of concrete. Thus lightweight buildings can be constructed
without compromising their thermal inertia.
Durability
and Sturdiness - Form Stable PCM
Encapsulating and
containing PCM from leakages during the phase change can be quite a challenge,
when incorporating in building materials. Granulated solid particles of PCM may
be mixed in concrete or paint before using in construction; however, these can
ooze out during melting and this can affect the structural integrity of the
building as well as performance of the PCM. To tackle this problem, form stable
PCMs are available specially designed for the application in construction and
building materials. The advantage is that physically these remain sturdy and
retain their shape even during phase change making it compatible to be
incorporated into buildings with ease.
Smart
materials such as PCMs in the field of chemicals have a huge potential to add
value and contribute to energy efficiency in buildings pushing the bar a level
up aiming for smarter cities!
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