Radiation heat gain is frequently neglected in building construction. Many ignore the subtle yet profound impact it can have on an entire building envelope system.
What Is Radiation Heat Gain?
A building in direct sunlight will absorb electromagnetic particles, converting them into heat. This heat mass will then try to dissipate (2nd law of thermo dynamics) to reach equilibrium with the surrounding environment again. Some is lost to convective breezes and some is re-radiated from the roof or sidewall away from the structure. The rest is absorbed into the assembly (the amount varies, depending on substrate and color) until it penetrates the interior of the building.
What Are Interior Radiation Control Coatings?
It's this radiant heat that causes discomfort for occupants and A/C systems to labor. Many methods are used to help control interior temperatures: higher SEER HVAC, increased R-value, and creative ventilation. But there is a technology available that addresses the heat at the source: interior radiation control coatings (IRCCs). Employing IRCCs will make the space more comfortable and increase the operational efficiencies of the insulation, ventilation, and HVAC & ductwork packages that now operate in cooler temperatures.
IRCCs are aluminized paints, reflective to infrared, that reduce radiant heat gain by lowering a surface’s emissivity (ability to radiate heat). The lower the “e,” the less able that substrate is to emit or radiate heat inward, and the more efficient it is at keeping the structure cooler. IRCCs give the designer or constructor a novel approach to make a building more energy efficient at low cost.
IRCCs have similar reflective properties to radiant barrier foils, but are installed in a fraction of the time with standard paint sprayers. They add virtually no weight or dimension to the envelope system, are moisture permeable and electrically non-conductive. IRCCs will not tear or delaminate, and are mold resistant. Many are also Class "A" fire rated. They have no known degrading effect on external roofing materials.
Where Can IRCCs Be Beneficial?
Metal buildings are ideal for IRCC use. Their large expanses of nonporous wall and roof deck assemblies produce superb coverage rates.
IRCCs are effective in buildings that utilize high temperature radiant heaters, working to retain heat within the structure. In addition to their effective thermal properties, IRCCs are also reflective to light and will increase interior lighting levels, potentially reducing the number of fixtures and providing another source for energy savings.
Most structures in a wide range of climate zones can be improved with IRCC technology to control radiant heat gain. In addition to energy savings, IRCCs also produce another subtle thermal effect. By lowering the interior surface temperatures, they help to balance the mean radiant temperature – where net radiant heat transfer between the skin and that of its surroundings is roughly equal. Because human skin is so sensitive to radiant heat, this balance can have a big impact on occupant comfort and increase productivity within the same space.
ASTM created a standard of efficiency for IRCCs, those with emissivities at or below 0.25. RIMA-I conducted a survey of IRCCs meeting this standard. You can find those results and additional resources below:
RIMA-I Coatings Study
ASTM Standard for IRCCs
A Review of IRCC Research
Effect of Radiant Barrier on External Roofing Materials
Using IRCCs to Insulate Metal Building
Robert Aresty is president of SOLEC-Solar Energy Corporation, celebrating its 40th year in business in 2014. He is an ASHRAE Lifetime Member, was a former director of SEIA and is a member of ASTM, ISES, the prestigious Explorer’s Club and is a Solar Fellow of the American Solar Energy Society. He is holder of several patents including the largest to a US citizen in the solar field at the time of issue. He has been involved in the design and construction of several solar-heated, super efficient buildings, including SOLEC’s 10,000 sq. ft. manufacturing facility. He invented the IRCC technology back in 1978 for use in solar applications, but its uses have since expanded across a multitude of industries around the globe.