Phase Changing Materials used as Building Material

by Rojan P.V

Introduction

Modern architecture is Attractive, flexible and light weight this leads to less thermal storage capacity and more solar heat gains. Phase Changing Materials (PCM) used as Interior finishing alternatives stores much larger amount of thermal energy per unit mass than conventional building materials. Requires less amount of energy for production. This presentation involves microencapsulated PCM use, its applications, etc.

Principle

When heat is applied to any substance, heat transfers in two ways : Sensible heat & Latent heat. PCMs works on the principle of latent heat. Latent heat enables PCMs to control room temperature

Working

PCMs used in construction change from solid to liquid at 23ºC – 26ºC. They melt, absorb heat from room and room temperature is kept constant until the change of state is complete. PCM then returned to solid state by night time ventilation / mechanical means. The phase change cycle repeats

Types of Phase Changing Materials

There are many types of PCM but not all are suitable for use in buildings. The two main types of PCM used in construction are inorganic salt hydrates and organic paraffin or fatty acids. Both materials have a set of advantages and disadvantages that must be taken into consideration.

Inorganic salt hydrates

Salt hydrates are a low-cost, readily available PCM. They have a high latent heat storage capacity and high thermal conductivity. They are also non-flammable.

Organics: paraffin’s and fatty acids

Paraffin’s and fatty acids do not expand as they melt, and freeze without much super cooling, They are chemically stable, compatible with conventional construction materials and recyclable. Paraffin’s are hydrophobic, which means they are water-repellant. Paraffin’s are hydrophobic, which means they are water-repellant. As a result, their phase-change points are reliable. Pure paraffin’s are also highly durable, and do not degrade in contact with oxygen.

PCM Incorporation :

Impregnated into building materials by 2 ways :

Either directly or as pellets (Paraffin wax – most promising material used)
Micro-encapsulation

Micro-encapsulation most preferred always. Night cooling considered as the main difficulty. Mechanical ventilation is provided.

Micro-encapsulation

A process by which individual particles of solid/ liquid material are coated with a continuous film of polymeric material to produce capsules called microcapsules. Microcapsules – small sphere with uniform wall round it. Micrometer to millimeter range. Appearance of beads, powder. Polymer sphere shaped

Structure of a micro-capsule

Material inside is called core. Wall is called shell or coating.

Morphology :

Depends on core material and the deposition process of the shell. Basically 3 types :

Mono-nuclear
Poly nuclear
Matrix encapsulation

Also mono-nuclear with multiple shells, or clusters of micro capsules.

GlassX

An insulated glazing unit that can be used as full glass walls and windows. It has an outer pane of glass that reflects high-angle sun and allows low-angle sunlight to pass. Sunlight transmitted through this outer pane of glass passes through inner polycarbonate channels that are embedded with salt-hydrate PCMs. These PCMs store the heat from the sunlight, release the heat to the interior of the building as the temperature cools.

Selection criteria

A melting temperature range in construction is 23°C or 26°C.
A high latent heat of fusion per unit volume minimizes the area of PCM tiles that are needed.
High thermal conductivity.
Minimal changes in volume
Congruent melting
A completely reversible freezing/melting cycle.
Durability over a large number of cycles.
Non-corrosives to construction materials.
Non-flammability.

Floating ball of Rotterdam, Netherlands

Three semi transparent domes of 18.5,20,24m diameter
Building has been built in one of the city harbor of Rotterdam
Climate is managed in different way in different room
Exhibition hall temperature is kept about 15 ˚C
Conference hall temp is maintained about 21˚C
Temperature is varied with the help of PCM

Conclusion

Improves thermal comfort levels and obviate or reduce the need for air-conditioning. Reduction in peak temperatures is possible. Used in Residential buildings too. Significant advantages for both commercial and residential buildings. Night ventilation- an integral part. Likely to become a valuable tool for improving thermal comfort in domestic buildings.