Solutions

Passive cooling

Houses anywhere in the world can be covered with a special paint that reflects the infra red radiation of the sun that gives the heat.

The extraordinary results lead to bringing these achievements to the forefront.

In disadvantaged areas, air conditioning is too expensive. A house paint that reduces the temperature by 5-7 degrees Celsius may represent the difference between comfort and discomfort.

There is hope for comfort and for the underprivileged.

The infrared reflective pigments have the following properties. They do not absorb in near infrared region. They either reflect it or transmit it.

Weather Protect Paint

Weather Protect Paints use various levels of polymer coatings which are made with cenosphere which enable weather protection and allow the inpainted house to remain cool during summers and warm during winters.

Abstract

Solar energy is essential for human race. It spreads itself thin on the entire surface of the globe. The large buildings, which are now essential for the world’s growing population, need to be made comfortable for its residents. In certain parts of the year these radiations are not required for the comfort of the residents. If the buildings are allowed to receive these radiations, the expenditure of cooling is excessive. Coatings that reflect the infrared radiation in the near IR region responsible for heat from the solar radiation are formulated with special pigments. In the present paper, patents devoted to preparation of these pigments have been reviewed. Some research work carried out at University Institute of Chemical Technology has also been included. It has been found that there are no theories to predict the infrared reflectivity of a pigment and the best way to find one is to scan the available pigments for their IR reflectivity.

Infrared Region (700-2500 nm): Forty-five percent of the total solar energy is in the nonvisible infrared region. Heat is a direct consequence of infrared radiation incident on an object. Infrared radiations range from 700
2500 nm wavelength. The heat-producing region of the infrared radiations ranges from 700
1100 nm. These radiations on absorption result in heating up of the surface. Infrared reflective inorganic pigments are complex inorganic color pigments, which reflect the wavelengths in infrared region in addition to reflecting some visible light selectively. The reflectivity and absorptivity of the pigment 68 Recent Patents on Chemical Engineering, 2008, Vol. 1, No. 1 Malshe et al. are independent of each other. Thus an IR reflective pigment may have any color. These pigments are synthesized by subjecting mixtures of metal hydroxides, nitrates, acetates or even oxides, to very high temperatures in a process called calcination. Metal oxides or salts are blended together and strongly heated, generally at temperatures of over 1000°C. At the calcining temperature the solids themselves become reactive. Metal and oxygen ions in the solids rearrange to form new, more stable crystal structures such as spinel or rutile structures [4]. IR reflective pigments are increasingly used for roof and building coatings because of their excellent weatherability. They have an ability to maximize reflectivity in the near infrared region. These IR-reflective pigments find increased use as the formulators make an attempt to produce dark coatings and minimize heat buildup in the underlying structure. Nickel manganese ferrite blacks (Pigment Black 30) and iron chromite brown-blacks (CI Pigment Green 17, CI Pigment Browns 29 and 35) are some of the infrared reflective pigments that are used to provide dark colors with reduced heat buildup. Other commercially available infrared reflective pigments are Pigment Blue 28 Pigment Blue 36, Pigment Green 26, Pigment Green 50, Pigment Brown 33, Pigment Brown 24, Pigment Black 12 and Pigment Yellow 53 [5]. In urban areas, the design of roofs has a major influence on the heat absorption of sunlight. The hot buildings also known as “Concrete Jungle” radiate heat and warm the air in the surrounding. If there are several such buildings in the vicinity, the combined effect leads to a phenomenon known as ‘Urban Heat Island Effect’. The amount of heat radiated in the surroundings varies depending on the roof construction, type, elevation and also the color of the coating used. Significant amount of heat is also absorbed into the building by means of conduction. With such increasing heat energy in the building, there is a need for variable energy in the form of air-conditioning to keep the interiors of the building cool and tolerable for people to work and live in them. To reduce the increasing demand for energy consumption for air conditioning, there is a need for cooler roofs. Reflecting most of the sun’s heating energy minimizes the amount of energy absorbed by the building. These pigments are highly stable and chemically inert. They can withstand the chemically aggressive environments and still retain their color. They do not fade in the presence of ozone, acid rain, SOx, NOx or other air pollutants common in industrial areas. They even remain colorfast in the presence of strong acids, bases, oxidizing or reducing agents. They are non-migratory, and do not dissolve or bleed when in contact with solvents. Because of these properties, these pigments last as long as 30 years in outdoors. Formulating paints with them is a major challenge since the binders degrade much faster. The most expensive component of the formulation is the IR reflective pigment. In addition to excellent chemical stability, these pigments are also stable to high temperatures. Due to high heat stability, they can be used for high-heat coatings, such as muffler and stove coatings, fireplace paint, and high-heat powder coatings. Porcelain enamel and decorative ceramic coatings also use these pigments.

REFLECTION MECHANISM OF INFRARED RADIATIONS

The infrared reflective pigments have the following properties. They do not absorb in near infrared region. They either reflect it or transmit it. Their refractive index is different from that of the binder in the infrared region. This causes diffused reflection in IR region. If the refractive index of the pigments in the IR region is similar to that of the binder’s refractive index in the IR region, the pigment would be transparent to near infrared light (NIR). In such a case, any reflection in the near infrared region would be due to the undercoat. Absorption of light occurs when light energy promotes electrons from one bonding state to another. If light of a different wavelength is used to cause this energy transition, it will not be absorbed e.g. iron chrome blacks absorb light through the visible region. This means there are electronic transitions responsible for absorbing light with wavelengths of energy from 400
700 nm.

Light of lower energy (>700 nm) is not absorbed. In this case, a beam of light with a wavelength of 1500 nm is too low in energy to cause any electronic transitions in the material. Thus it will not be absorbed. Instead the 1500 nm light beam is refracted, reflected and scattered (depending on the refractive index) leading to diffuse reflection of NIR light. There is no method to predict the IR reflectivity of an inorganic or organic compound. This property appears to be an inherent characteristic property just like density, thermal conductivity, color, refractive index etc.

BENEFITS OF INFRARED REFLECTIVE COATINGS General benefits:

Longer life-cycle due to less polymer degradation and thermal expansion due to lower temperature.

Aesthetically pleasing colors.

Cooler to touch for better handling

Improved system durability and less thermal degradation. In addition to the above mentioned benefits, the IR reflective coatings also have certain Roofing benefits:

Less heat to transfer into buildings.

Reduced ‘Urban heat island effect’.

Low energy demand for air conditioning, particularly in equatorial regions.

Reduction in air pollution due to low energy usage, power plant emissions, and reduction in urban air temperatures.

Installation crews can work longer during the day before the roof gets too hot to work on.

Very high durability coatings. Some coatings have been in use for as long as 25 years.