What is a radiant barrier and how do they work?


What is a radiant barrier?

A radiant barrier is a material or combination of materials designed to block the transfer of radiant heat energy, a common method of heat transfer in a home or building.

How do buildings heat up?

A residential attic is an easy example. If you have ever been in an attic especially during the summer months,you will notice the temperature is much hotter than the outside air temperature. The radiant heat, from the sun is absorbed and passes through the roofing materials unobstructed into the attic. There is nowhere for the heat to go and even the best attic ventilation can only remove so much so the attic heats up. This increased heat buildup continues to radiate down into the ceiling on the rooms below the attic.

How do radiant barriers work?

An effective way to illustrate how a radiant barrier works is by understanding how a thermos works.





Understanding how heat moves: The three methods of heat transfer.

To better understand how radiant barriers work and where they can be used to increase your comfort and lower your energy costs, it is important to understand the three methods of heat transfer. What’s the Difference Between Conduction, Convection, and Radiation? by Carlos Gonzalez clearly explains the different methods.




Conduction: Heat transfer by conduction happens when two solids touch each other or physical contact. “Conduction transfers heat via direct molecular collision. An area of greater kinetic energy will transfer thermal energy to an area with lower kinetic energy. Higher-speed particles will collide with slower speed particles. The slower-speed particles will increase in kinetic energy as a result. Conduction is the most common form of heat transfer and occurs via physical contact. Examples would be to place your hand against a window or place metal into an open flame.



Convection: Heat transfer by convection is heat that moves through a fluid. “When a fluid, such as air or a liquid, is heated and then travels away from the source, it carries the thermal energy along. This type of heat transfer is called convection. The fluid above a hot surface expands, becomes less dense, and rises. At the molecular level, the molecules expand upon introduction of thermal energy. As temperature of the given fluid mass increases, the volume of the fluid must increase by same factor. This effect on the fluid causes displacement. As the immediate hot air rises, it pushes denser, colder air down. This series of events represents how convection currents are formed.





Radiation: Heat transfer by radiation is invisible to the eye and not affected by air flow. The overhead heat from the sun is a great example of radiant heat. Heat transferred by infrared waves is called radiation. “Thermal radiation generates from the emission of electromagnetic waves. These waves carry the energy away from the emitting object. Radiation occurs through a vacuum or any transparent medium (either solid or fluid). Thermal radiation is the direct result of random movements of atoms and molecules in matter. Movement of the charged protons and electrons results in the emission of electromagnetic radiation. All materials radiate thermal energy based on their temperature. The hotter an object, the more it will radiate. The sun is a clear example of heat radiation that transfers heat across the solar system. At normal room temperatures, objects radiate as infrared waves.



Why You Need an Air Space When Using Radiant Barriers

Radiant Barriers work by reflecting radiant heat that strikes its reflective surface across an OPEN-air space. The air space prevents conductive heat transfer. You must have ¾” or more on (1) one or both sides of the insulation to be properly installed. It does not matter which side of the insulation has the air space. Not maintaining an airspace can negate the benefit of a radiant barrier. Bubble foil insulation will still perform but it's radiant barrier properties can also be negated. Always plan for at least one air space when working with reflective insulation. This is normally accomplished by using furring or spacers between layers of material during the construction process.



Example Industries where Reflective Insulation is Used

Reflective insulation and radiant barrier technology are used in many of our everyday items or services we use.





Radiant Barriers and Reflective Insulation for Construction Applications:

In construction applications, there are two types of reflective insulation used





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