Infrared Heating Merits A Second Look

October 7, 2004
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Patio heating for restaurants and hotels is a growth area for infrared heating. Southern Season Restaurant, Raleigh, N.C., uses twelve 46,000-Btu parasol heaters for its patio seating area. (Photo courtesy of Schwank Heaters.)
Rising energy costs and conservation concerns have helped spur renewed attention in infrared radiant heating technology. Infrared heating can be an efficient option for space heating in many applications. While factories, warehouses, agricultural buildings, and other industrial applications have used infrared for decades, there are new uses and markets contractors can tap into.

For example, some restaurants are using perimeter infrared heating or parasol floor models to extend their outdoor seating seasons. Combine outdoor dining with the emerging trend of restaurants and hotels creating outdoor areas to accommodate smoking customers affected by new city anti-smoking codes, and the future grows brighter.

Construction site usage is also a trend. Cold walls tend to attract condensation, which is problematic in drywall and paint applications. Heating the wall through radiant heat can cut drying time by up to 60 percent.

Contractors with aggressive sales departments can create new niches from these emerging markets. Additional uses include driving ranges, car repair/oil change outlets, parking garages, airplane hangars, ice rinks, and athletic buildings.

The two major types of infrared heating today are luminous (high-intensity) and tube heaters. The up-front costs for tube heaters are generally lower than those for luminous heaters, but radiant efficiencies ranging from 25 percent to an estimated 45 percent make them more expensive in the long run when compared to luminous heaters, which can be up to 81 percent efficient, depending on the model.

With tube heater technology, a gas flame is fired inside a tube, which heats up to 1,300 degrees F and can range from 10 feet to 80 feet in length. The longer the tube, the less radiant heat generation at the vent end of the tube. Consequently, tube heating doesn't provide a uniform temperature along each individual tube heater length.

Luminous consists of ceramic tiles that are heated to approximately 1,650 degrees F. This method can be more efficient and provides more even heat distribution.

CSA International, a Toronto-based testing agency that certifies gas-fired appliances, ensures that all luminous heaters meet minimum radiant efficiency standards. However, there's no standard yet for rating the radiant efficiency of tube heaters. Contractors must be wary of product specification claims that are not backed by independent laboratories and studies.

Applications

As is the case with most HVAC equipment, there are applications where infrared heating is not suitable. Buildings with explosion-proof requirements, which can include industrial settings such as paint booths, or areas containing combustibles are not suitable. Manufactured as a sealed combustion system when fitted with outside combustion air, tube infrared heaters are typically not acceptable in explosion-proof environments because the tube is a hot surface that may ignite fumes.

Infrared radiant heaters are suitable for most applications involving space or spot heating. Even occupied spaces requiring a specified amount of air changes per hour, such as gymnasiums, are suitable because design/build engineers can combine the energy efficiency of infrared with the air changing ability of air handlers.

Sizing infrared heating is a matter of calculating an accurate heat loss as per methodologies supplied by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE).

The industry standard is to reduce the calculated heat loss by 15 percent to establish the required input for a regular infrared system. High-efficiency infrared systems can provide a greater in-put reduction due to increased levels of infrared energy delivered to the workspace.

Probably the greatest disadvantage of infrared heating is the fact that more units need to be used compared to forced-air unit heaters. While the capital equipment costs are similar to unit heaters in an application, installation costs could be five to 10 percent higher. Of course, this difference can be offset by the energy savings in the first year.

Infrared sizing depends on the type of infrared heater specified, heater size, and the mounting height of the heater in relation to the floor.

Geographical location is an important consideration. A colder region might warrant a heater with a higher efficiency rating, thus delivering a faster payback for a more expensive system. Conversely, a lower efficiency and less expensive heater might better suit a building in a southern region where there are fewer cooler months of the year.

Providing infrared heat coverage is similar to designing lighting for a building wherein shadowing, light throw, and reflectors are important considerations.

Only here it is heat throw, not light throw, that is important. Luminous infrared heaters are analogous to the new low-power industrial high-intensity lights in that they can be used for both spot and whole-building applications. With a properly engineered design and installation, very uniform heat output and comfort can be provided over an entire area.

Infrared tube heaters represent more of a floodlight effect in coverage area and are more conducive to low heat loss and low ceiling applications. It's not unusual for a project to combine both types of infrared heat.

System Placement

The ultimate goal in any infrared heating design is a uniform flux density at floor level. Once the optimum input and placement angle are achieved, the heat distribution is very even compared to the peaks and valleys sometimes found with convection-style heating. Infrared heaters can be installed angle-mounted or positioned parallel to the floor. Perimeter systems are generally mounted at angles ranging from 30 to 45 degrees and aimed toward the center of the space. The more efficient heaters perform better in a horizontal position because more heat stays trapped around the radiating source in the appliance and less heat escapes through convection.

While placement and sizing can be challenging on complex projects, most of the major infrared manufacturers have in-house engineering departments that can assist in sizing and placement.

Unlike forced-air heaters, luminous infrared heaters usually are installed with indirect flue venting to the outside via interlocked exhaust fans. The volume of air removed is very low and usually less than a standard flue vent on a forced-air system.

Tube infrared usually requires direct venting according to local codes. Generally, there's enough air leakage into a structure to provide sufficient combustion air for either type of system.

Infrared heaters are typically hung using much lighter hanging materials than required for forced-air unit heaters. Placement and angle is critical for proper efficiency and heat distribution.

Like forced-air space heating, infrared-heating operation is controlled by thermostats placed to operate zones of heaters. A typical 5,000-square-foot factory area, for example, might take into account the heat of the machinery, infiltration from other zones, proximity to achieve a specified temperature with one thermostat. Of course, the best temperature and comfort control is one that senses both ambient and radiant temperatures.

With radiant heating systems, the average between radiant temperatures (Tr) and ambient temperatures (Ta) is known as the comfort temperature (Tc) and can be calculated using the following formula:

Tc = Tr + Ta/2

This results in a lower ambient temperature than forced-air systems within the workspace. In a structure with a calculated 1 million Btuh heat loss, a 1.25 million Btuh input of forced air space heater would be needed to maintain a 70 degree F temperature at floor level.

Figures supported by ASHRAE indicate the input required for a standard infrared heating system is typically 15 percent to 20 percent less than the calculated heat loss. The gas input needed in this example would be only 850,000 Btu for a 70 degree comfort point. The result is less energy consumption and greater indoor comfort. As the radiant output efficiency increases, the total gas input equipment size reduces beyond the typical 15-percent input reduction.

Whether it's a retrofit or a design/build project, contractors should take a close look at the infrared heating alternative to space and spot heating. Infrared heating offers contractors a unique opportunity for extended profit margins while still saving the client operational costs and conserving natural resources.

George Horich is a 36-year-veteran of the HVAC industry and is currently president and general manager of both Schwank Inc., Waynesboro, Ga., and its sister company, Schwank Ltd., Mississauga, Ontario. Schwank is an ISO 9001:2000-registered company that manufactures high-intensity luminous and low-intensity tube infrared radiant tube heaters.

Publication date: 10/11/2004

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