How Does Radiant Barrier Work?
In our previous article about Radiant Barriers, we discussed heat transfer. In this article, we’ll discuss how a radiant barrier stops heat.
B: How Radiant Barriers Stop the Heat
A radiant barrier is a material with a very low emissivity and high reflectivity giving it the ability to virtually stop the transfer of radiant heat or thermal conductivity. This allows the radiant barrier to reduce heat gain in the summer and heat loss in the winter, thus reducing the net heating and cooling needs of the structure.
There are two key values that determine the effectiveness of a radiant barrier, and those are its reflectivity (higher is better) and emissivity (lower is better) values.
The reflectivity value of a radiant barrier is pretty easy to understand, the higher the reflectivity value, the more light energy (heat) the radiant barrier is able to reflect.
Reflectivity values are expressed as a percentage number (%), which basically describes how much light energy the surface will reflect. The emissivity value is basically the ratio of heat energy radiated by a material to the heat energy radiated by a true black body at the same temperature. This may sound a bit confusing, so let’s talk in layman’s terms. Basically, if we were to take a pure black object (theoretical) which reflects no light energy and absorbs all light energy that touches it, it would have an emissivity value of one ( = 1). Any real object, weather it is black or not would have an emissivity value of less than 1. So, what this definition is really saying is that the darker an object is, the more light energy it will absorbed and re-radiated. And subsequently, the lighter and more reflective a material is, the less light energy it will absorbed and re-radiated. Radiant barriers, even though they have little or no “insulation” properties can effectively block most of the heat coming in or leaving a structure. This is because radiant heat is the most efficient type of heat transfer, and stopping radiant heat transfer is the most effective way to decreasing your heating and cooling needs. In the summer, less radiant heat entering your attic makes your AC system run more efficiently, and in the winter, less heat energy being lost through the roof makes your heater more efficient.
In our next post, we’ll talk about what type of savings you can expect from a Radiant Barrier. Eastin Air proudly serves Dallas and surrounding areas. We specialize in Highland Park and University Park.