by eyetee | October 2, 2013 8:30 am
By Lynn Walters
Unwanted building envelope heat transfer can be a unique problem in commercial construction and retrofit. With the nationwide push for energy conservation and more efficient buildings, architects, engineers, and designers are being asked to come up with viable solutions. There is a large array of products to choose from that can solve many of these obstacles—one in particular is the interior radiation control coating (IRCC).
IRCCs are liquid-applied products for interior surfaces; they work like the low-emissivity (low-e) coatings on windows by lowering the heat transfer associated with radiant energy. Emissivity is a measure of a surface’s ability to manage infrared radiation. Unlike the R-value of traditional conductive insulation (i.e. where the larger the number, the longer it takes the heat to transfer from one side to the other), surface emissivity is gauged on a scale of 0 to 1. The objective for unwanted heat transfer is a surface emissive value closer to ‘0,’ which designates no emission and no absorption of radiant energy. A ‘1,’ on the other hand, designates full emission or full absorption of radiant energy.
Of all the different proprietary ingredients found in IRCCs, highly polished aluminum flake is the infrared-controlling mechanism. The aluminum is carried and held in place by an infrared-neutral binder that can be water-based or waterborne formulations. When applied to a paintable surface, IRCCs have a finish appearance of silver paint. As a coating, they must meet federal and state laws concerning volatile organic compound (VOC) content. The maximum VOC level for this type of coating is listed as less than 500 g/L. (Most manufacturers are now well below those levels—some are less than 50 g/L.)
By designation, IRCCs are classified as having an emissive value of 0.25 or less. They must meet the criteria of ASTM C1321-04, Standard Practice for Installation and Use of Interior Radiation Control Coating Systems in Building Construction. Most of today’s manufacturers have pushed that value down to around 0.20. This low emissive value gives an 80 percent radiant energy reduction of the potential radiant heat transfer.
Since surface emissive values deal with emission and absorption, the reduction in radiant heat transfer works no matter which way the heat is flowing. The hot summer roof in Fresno, California, has a tremendous amount of potential heat to transfer down to the air-conditioned structure. The application of an IRCC to the roof deck’s underside will substantially diminish that potential. The snow-covered roof in Stoughton, Wisconsin, has the ability to absorb a tremendous amount of the structures’ heat in winter. Here again, IRCC application diminishes the potential for absorption and, hence, loss of the structure’s heat.
New construction is a given when looking to lower the amount of heat transfer into and out of the structure. Most energy codes are pushing their way toward net-zero buildings by 2030, but the biggest potential for nationwide energy reduction comes from retrofitting older buildings.
Most energy codes, like California’s Title 24, Part 6 (also known as the California Energy Code), came about after the energy embargo of the 1970s. Of course, there are many structures built in North America before that time; they are, for the most part, not very energy-efficient.
Armed with an understanding of the dynamics of radiant heat transfer, specifiers and architects can take advantage of the versatility of liquid-applied radiant-energy-reduction coatings. Large metal and wood structures in a non-shaded open setting not only receive high heat gain from the roof, but also from the east-, south-, and especially west-facing walls. If these buildings do not rely on air-conditioning to cool the contents in summer, the heat sink is the contents itself and the concrete slab on which it sits.
Heat will transfer from all heated surfaces to these cooler areas throughout the day, trying to reach equilibrium. Coating the underside of the roof deck and the heat transfer walls will reduce this effect, keeping the building cooler for longer.
For structures relying on air-conditioning to cool the content and personnel, reduction of downward and sideways radiant heat transfer can be significant. IRCC placement on the roof deck’s underside is even more significant when the HVAC ducts are located in an unconditioned attic space. The reduction of duct surface temperature has a direct effect on the unit’s cooling efficiency. The HVAC cooling load is reduced with a cooler duct.
Another aspect to take into account is installation cost, which can unfortunately be the determining factor in whether an energy efficiency project is approved. The labor-hours needed and IRCCs’ low cost per square foot should factor positively toward the approval decision. New construction project costs vary from $0.35 to $0.55 per square foot of applied surface; retrofit, depending on the amount of preparation, will cost $0.50 to $1.10. Longevity should also be a factor in the approval process. Most IRCCs are formulated to last for 20 years or more without appreciable degradation.
The versatility of an IRCC is simply its ability to be applied to a wide variety of surfaces (e.g. plywood, oriented strandboard [OSB], metal, and drywall), and its flexibility to be applied at any time during a new construction or retrofit project. An IRCC coating on the large expanse of a building’s roof deck will have a positive effect to the energy conservation and human comfort of the structure.
For more information on IRCCs, visit the Reflective Insulation Manufacturers Association (RIMA) website at www.rimainternational.org.
Lynn Walters has worked in the commercial and residential building materials industry for almost four decades. He has been responsible for merchandising, sales management, and product development for Fortune 500 companies Louisiana Pacific, BASF, and now STS Coatings Inc. Walters is an active participant in RIMA International, ASTM, the American Institute of Architects (AIA), and the Air Barrier Association of America (ABAA). He can be contacted at email@example.com.
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