ABC's of Infrared Heating
Unlike forced hot air, convectors, or baseboards, infrared heating ideally conveys nearly all of its energy to a target by line-of-sight radiation, just like light. There is no delay in such heat transfer, and no medium is needed (e.g., all heat from the sun comes through a vacuum).For a short tutorial on the physics involved, go to www.solarproducts.com and find "IR 101" under its "Resources." But here's the bottom line: Infrared energy is essentially light at a greater wavelength, so thinking in terms of "task heating" (like task lighting brightens some areas over others) can help designers take advantage of IR's characteristics.
By properly locating IR heaters and directing their output, one may shape heating zones without walls such that their centers are comfortably warm while surrounding areas are heated to only 40 degrees to 45 degrees F by other systems. The end result is a reduction in total energy consumption of 50% to 80%, depending on local climate and other factors.
Directing The Heat To Where It's Needed
Like a bare light bulb, IR heat radiates in all directions, unless focused by reflectors and/or lenses. One of the important technical changes in the last decade was the commercialization of a 1984 patent (held by Radiant Optics Inc. of Woodinville, WA,www.radiantoptics.com) that successfully focuses IR energy like a lens focuses light. Called the IRLens(tm), the device is really an eggcrate-style louver that narrowly directs IR energy that would normally spread out rapidly with distance.While I was at first skeptical, side-by-side tests in my basement convinced me that the IRLens actually does focus heat much better than other infrared heating devices. For the same wattage, a sample Radiant Optics unit raised the temperature of a surface roughly three times faster than other units.
While some units have curved reflectors also designed to focus IR energy, many suffer from the same problem as early reflectors used to focus light from compact fluorescent lamps (CFL). The ideal shape for focusing a point source of radiation (whether heat or light) is a parabola - all beams emanating from its focal point will become parallel as they leave the reflector.
As early designers of CFL fixtures found, however, one would need a very large parabolic reflector to collect the light from a bundle of fluorescent tubes that are not a point source of light. Reflectors not much larger than the energy source ended up simply scattering the light after it had bounced around inside the reflector, losing intensity with each bounce.
An odd-shaped IR source (e.g., a grille of wiring, or glowing quartz tubing) yields the same situation. The IRLens, however, focuses the IR energy as it leaves the fixture, not while inside it. IR heating systems come in all shapes and sizes, however, some (such as flat panels) require no focusing.
Controls Complete The Picture
IR heating technology yields savings when one reduces heating from a central system (e.g., ducted forced air) down to minimum temperatures (e.g., for freeze protection or to avoid surface condensation) while maintaining comfort where people are working.A well-designed IR heating system will have heaters located to avoid "toasting" one side of an employee while the other side freezes, and sophisticated controls to minimize IR heating within both time and temperature limits.
One of the major vendors of such controls is Solid State Heating Corp. Inc. (www.sshcinc.com). SSHC has offered line voltage timer setback controls, occupancy sensors, customized thermostats, and other devices for controlling operation of radiant heating systems. For more information on its products (and some good background documentation on verified savings using IR technology), go to www.solidstateheating.org.
