Radiant barriers are also known as reflective barriers. They inhibit transfer of heat by thermal radiation. Heat can also be transferred through convection and conduction. But the radiant barriers do not protect against such methods of heat transfer.
As a result of their temperature, every material emits energy by thermal radiation. The extent of energy radiation is dependent on the surface temperature and emissivity. Emissivity is directly proportional to the amount of heat radiated at a particular wavelength. Reflectivity is a measure of how much energy is reflected by the material at a particular length.
Emissivity of this should be low (like 0.1 or less) at those wavelengths at which they are supposed to function. Usually for buildings, the range of wavelength in the mid and the long-infrared spectrum lies between 3-15 micrometers. The value of reflectivity is not fixed. This is because both emissivity and reflectivity don’t add up to one for different wavelengths. Thus, low thermal emissivity can be used to create surfaces that are visibly dark in color. For proper performance, It should face towards open surfaces like air or vacuum so that there is no radiation.
Application of radiant barrier
NASA came up with a material that was light, reflective and made up of a plastic substrate that had a vapor deposited coating of aluminum. This is popularly known by the name space blanket. It is used for protection of equipments, astronauts and spacecraft from radiation and also for the retention of heat as temperature fluctuations are a common thing in space. This is more effective in space than on earth because heat transfer in space only takes by radiation. The heat transfer on earth can take place by conduction and convection even if it is deployed.
It can also be deployed for reducing indoor heat loss.
There are basically two methods by which it can be installed-
1. Radiant Barrier Decking
2. Radiant Barrier Attic Foil.
On sunny days, the roof absorbs the solar energy. The roof sheathing gets heated up and radiates the heat downward to the attic floor. When placed on the attic floor reflects the heat received towards the roof. This makes the top surface cooler. It also effectively removes the heat from entering into the rooms. Thus, it is quite an effective device.
The conventional attic insulation and radiant barrier differ from each other. Their functions are similar but their methods of achieving the same differ. It decreases the amount of heat radiated in areas near to it. The conventional attic insulation technique reduces thermal radiation by means of convection. Air is trapped within insulation in this technique. The rating of such a technique is done by R-value. There are no R-values for radiant barriers since they depend upon many factors.
Radiant barriers come in different ranges. The cost primarily depends upon the one who is installing it. Other factors include the extra features which some people like to incorporate in it. The price is different for a new house and an existing one.
Needless to say, this is highly effective and desirous. They are of vital importance and preferred these days.