Calculations for Savings From Radiant Barriers

Radiant

• The most common material used in the production and installation of a radiant barrier is aluminum, although other highly reflective materials are also used, according to Oak Ridge National Laboratory. This reflective material is placed on the exterior side or on both sides of another material, such as Kraft paper, plastic film or cardboard, before installation. Radiant heat is absorbed by most materials, but in the case of radiant barriers is reflected in a straight line away from a roof. Where a radiant barrier is not installed, an attic space can become heated, leading to increased cooling costs in summer months.

Calculations

• The calculations relating to radiant barriers include the amount of emissivity, according to the U.S. Department of Energy. Emissivity is the calculation of the ratio between the amount of radiant energy emitted from a radiant barrier compared to that of a black body that is heated to the same temperature and located in the same environment. This ratio is calculated as a number between 0 and 1. The closer to the number 1, the greater the amount of emissivity and thus the more radiant heat that is reflected from the surface. Another calculation concerning the radiant barrier is reflectivity, which regards the amount of radiant heat reflected by a surface. Again this number is represented as a number between 0 and 1, with the higher the number the greater the reflectivity. The angle at which the radiant heat strikes the surface is used as a guide to energy savings: the closer to a right angle the better the radiant barrier.

Products

• Products manufactured for use as radiant barriers require an emissivity rate of around 0.1 or less and a high reflectivity rate of at least 0.9. The U.S. Department of Energy reports the majority of products available in 2011 offer similar thermal energy ratios, with emissivity rates of 0.03 to 0.05 and reflectivity rates of between 95 and 97 percent. The aim of radiant barriers is to create a large difference between the exterior and interior temperatures of a building.

Tests

• To measure the effectiveness of radiant barriers in southern climates of the U.S., radiant barriers were installed and peak loads and energy costs monitored, Oak Ridge National Laboratory reports. In buildings in Florida that have air-conditioning equipment located in the attic, installing radiant barriers produced cooling savings of around 9 percent. The peak load of monitored buildings were reduced about 16 percent.