SavE® Phase Change Materials – Smart Materials for smart cities
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.
· 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 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.
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!