Radiant barriers: How They work

How Do Radiant Barriers Work?

A radiant barrier actually reverses or blocks the radiant heat energy (heat from the sun) instead of trying to absorb it like conventional insulation. A radiant barrier also reduces convective heat transfer by eliminating air flow, thus not allowing the convective loop to occur. The aluminum found in radiant barriers has two properties that enable it to reflect heat:

• Reflectivity: When you look at alluminum you cannot help, but notice how "shiny" the metal looks. The reason for this is because of the material's ability to reflect - or reflectivity. The shining metal is reflecting the light source and redirecting it and the same could be said about radiant heat.
• Emissivity: All materials have emissivity's ranging from 0% to 100%. The lower the emittance percentage of a material, the lower the amount of radiant heat radiated from its surface. The naturally low emissivity property of aluminum facing an air space results in very low emittance of heat from itself; it does not radiate much of its own heat from itself. This naturally low emissivity property makes aluminum ideal for use in radiant barriers

Radiant Barriers and "Air Space"

No matter how you plan to install a radiant barrier, it must have at least one air space on one side - meaning one side of the barrier can't be touching anything. It does not matter which side of the radiant barrier the air space is located. The purpose of the air space is to prevent conductive heat transfer.

 

Air space can be difficult to understand, so we will use a baked potato analogy. For example, if you warm a baked potato (wrapped in foil) and put your hand near it, but not touching, you will not feel any heat emitting. Conversly, if you actually touch the foil that holds the baked potato, you will indeed feel the heat. This is because foil transfers heat only if it touches something, we call this conduction. A radiant barrier works the same way, in essence. If the barrier has an air space, there will be no conduction.

Can I Count on a Radiant Barrier?

Radiant barriers were first tested in both small scale and full scale laboratories by The Florida Solar Energy Center at Cape Canaveral. The findings concluded that radiant barriers do indeed reduce heat transfer. These findings were also backed up by the Tennessee Valley Authority and the University of Mississippi.  There were aditional thermal winter tests conducted by Northeastern Illinois University and the photos showed significant resistance to heat transfer over conventional insulation. Lastly, all radiant barrier products meet the Standard Specifications for Sheet Radiant Barriers for Building Construction Applications: ASTM C1313 and the State of California Title 24 Insulation Standards.

Supplementary Radiant Barrier Research

"A radiant barrier system can stop 97% of the thermal radiation across an attic space. If it is not stopped, that radiant energy would be absorbed by the ceiling insulation and eventually be transferred to the living space below." - Quarterly Newsletter of the Florida Solar Energy Center.

"The heat storage capacity of reflective insulation is low. As a result, it does not store heat during summer days, only to pass it on down into the rooms of the house from the attic at night when coolness is most apt to be desired from the point of view of sleeping comfort." - Progressive Architecture, Nov. 1949, Page 76.