What are Phase Change Materials?

PCM stands for Phase Change Material. These are materials whose phase change, from solid to liquid, and liquid to solid, are used to store and release heat. In PCM's, energy is stored for use at a later time. The principle of phase transfer materials as heat-accumulating materials is as follows:

  • Heat absorption melts the material (at a certain temperature)
  • During melting, the material absorbs large amounts of heat from the environment (the space becomes cooler)
  • When the temperature drops, the material solidifies and releases heat (the space becomes warmer; good ventilation control may result in excessive heat loss)
  • -By storing the Phase Change Materials in insulated buffers, the "latent heat or cold" can be used at a later time.

Example: when ice melts and there's still heat adding, the temperature does not increase as long as there is still ice. The heat is "stored" and can be released at a later time during freezing (solidification). This is also called "latent heat" or in engineerings jargon enthalpy.

The value of PCM's is that at warm outdoor temperatures the indoor space doesn't get warmer as well, because the PCM is absorbing the heat, and when the temperature cools down the Phase Change Materials releases the heat again. This results in a "more evenly temperature" in the building. When the Phase Change Materials are stored in a well-insulated buffer, "latent heat" can be retained and used at a later moment. This can also be called a heat accumulating battery. Through inlets and outlets at the buffer, warm air or water can be cooled and cold air or water heated. The buffer with Phase Change Materials works here as a heat-cold storage.

Phase Change Materials are not new. This technique has been known for over 4000 years. The Romans already knew how the principle worked. This principle is and was based on heat that is kept in buildings, due to the large building mass. These walls remain warm for months after the summer, so heating was almost unnecessary. Conversely, these buildings with thick walls accumulate the summer heat so that it stays cool inside. Old Roman buildings, medieval churches and castles have this property thanks to its thick walls. Even the turf huts of Dutch peat workers offered some comfort in the winter in the nineteenth century thanks to this principle. Thick walls and floors, i.e. mass seems to have advantages. But most buildings nowadays don't have that anymore. They consist largely of glass, steel and aluminum. This comes with a short construction time and squeezed m2 prices. Another aspect is that many architects look more at the esthetic character of a building and much less at the "mass" needed to achieve a good energetic efficiency. Steel, glass and aluminum have a little mass, unlike ancient cathedrals and castles. For many architects, energy consumption in the past was hardly a problem.

Of course: there was a lot of equipment that could heat, cool and ventilate buildings. But with rising energy prices, the operational costs of buildings increased enormously. Fortunately, this is different now. Architects and builders are also aware of the need to build differently. The remedy might be; make outer walls, walls, floors and ceilings "thicker" just like the past builders did. However, a building would become unprofitable. But with Phase Change Materials it is possible!

There are several types of Phase Change Materials. Phase Change Materials is a collective name for a number of materials such as paraffins, salt hydrates and fatty acids. All of these PCM materials have their specific advantages and disadvantages. For example, for cooling of deep-frozen applications, so-called eutectic liquids are used. That is a mixture of two substances that realize a freezing point below 0°C, the so-called eutectic point.

Water-based

These PCM's contain mostly water. Cold storage systems or ice storage systems are mainly used in the air conditioning or process industry. Think about traditional building cooling or beer breweries. The freezing point is reduced by adding glycol or ethanol, allowing storage temperatures up to -30 ° C. Everybody knows the so called freezing elements are in the cool box.

Salt hydrates

Salt hydrates contain inorganic salt and water. The melting point temperature range is between 8 °C and 90 °C. Benefits of salt hydrates are favorable material costs, high latent melting heat, good thermal conductivity and non-combustible. A disadvantage may be that poor crystal formation makes salty hydrates more sensitive to supercooling. In other words, the solidification of the material is lower than the actual freezing point. However, for some applications this may also be an advantage. Also, ordinary water is subject to the supercooling effect. This is usually solved by including additives to the material.

Paraffins

Paraffin or wax is a derivative of petroleum. The melting point temperature range is comparable to that of salt hydrates. The latent meiting heat is reasonable and they do not have any problems with supercooling. The disadvantage is that the prices are linked to oil prices and are therefore not stable. And not unimportant, like all fossil fuels, the extraction of petroleum has a big impact on the environment. A major disadvantage is the flammability of the material, which makes it impossible to apply in the building environment without special measurements.

Plant-based

These are organic PCM's because they come from plant oil or animal fat. The range of melting temperatures is wide and lie between -30 °C and 150 °C. The latent heat is good and most vegetable fats derived from fatty acids have better efficiency than salt hydrates and paraffins. A big disadvantage, however, is the high price per kg that makes large-scale applications in the building environment for the near future too expensive.

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