The Basics of Gas-Fired Infrared HeatingUnderstanding this technology, as well as advances such as two-stage controls, can give technicians and contractors a leg up on competitors when discussing heating options with customers.
By
Michelle KostusykWhen it comes to serving the heating needs for buildings, forced air—such as a large unit suspended from the ceiling blowing hot air—is often the first consideration for many owners. While that option might work well for some, independent reports reveal that gas-fired infrared heating can save 20%–50% in fuel consumption versus forced air heating.
Gas-fired infrared heating systems emulate the true efficiency of the sun by generating radiant heat energy. They consist of three main components: a burner control box; black-coated radiant emitter tubes; and a highly polished reflector assembly. Heaters are typically suspended from the ceiling by chains and controlled with a thermostat. They can be installed either vented or unvented, may use outside air for combustion if necessary and, depending on the heating requirements, can be installed in a variety of configurations.
The highs and lows
The two types of infrared heating are high intensity and low intensity. Available since the 1950s, high-intensity heaters require high mounting heights due to an open flame that covers a ceramic surface. High-intensity heaters have a reflector to help direct the heat where it needs to go, are used to spot heat areas with few workers and typically are unvented.
Conversely, low-intensity heaters have an enclosed flame. When heat is required, the burner control box ignites a gas/air mixture and hot gases are pushed through steel radiant tubing by an internal fan. As these gases pass through the assembly, the tubing is heated and emits infrared energy, which is then directed toward the floor by highly polished reflectors. This energy is absorbed by objects in its path, such as the floor, equipment and people. Objects in the infrared energy path in turn re-radiate this heat to create a comfort zone at the floor level. This allows the source of heat to begin at the floor level and not the ceiling. With infrared heat, the floor acts as a heat reservoir; when doors are opened, the floor slab looses very little of its heat, and when the doors close this mass acts as a huge heat sink to warm the surrounding air. This creates an efficient and effective heating method in most commercial and industrial applications.
Weighing both sides
Radiant heaters offer several operational and design benefits. For example:
Infrared heaters do not blow dust and debris while heating, creating a cleaner and quieter work environment;
Their zoned capability allows a group of units to function together or independently;
Units can be mounted at heights of up to 60 ft, depending on which heater is chosen for a given application;
They allow spot heating to certain areas where workers are few;
Units can provide directional heating, with the reflectors rotated to direct heat where it is most needed;
Outside air can be used for combustion;
Low-intensity heaters can be vented together to reduce the number of roof or wall penetrations; and
Design is flexible, allowing for heater placement in configurations that will supply heat where it is needed most.
There are, however, a few important things to take into consideration when installing an infrared radiant-heat system. Care needs to be taken when laying out the system to maintain clearances to combustibles. Infrared radiant heaters require higher clearances than forced air units. Therefore, a mounting height of 10 ft or higher is recommended depending on the application and the model.
Very little maintenance is required, especially when bringing in outside air for combustion. This setup is recommended when dust or contamination is present inside the building. Periodic dusting of the reflectors is beneficial both for safety and the overall efficiency of the heater.
Safety considerations
A critical safety factor to consider before installing an infrared heating system is clearances to combustibles. Clearance to combustibles is defined as the minimum distance that must be maintained between the radiant tube heater surface and the combustible item. Considerations also must be made for moving objects around the infrared heater and materials that have lower temperature ratings, such as plastics. Additional examples of combustibles include; lights, overhead doors, gas and electrical lines, parked vehicles, cranes, and any other obstructions or hazards. Shielding of these items may be necessary. Unless otherwise indicated, infrared heaters are not certified for residential use or where flammable gasses or vapors are present, such as spray booths.
It is important to provide warnings to alert individuals to potential hazards and safety actions. Signs must be posted to specify maximum stacking heights in order to maintain clearances to combustibles, especially in storage areas.
In addition, observing recommended mounting heights will optimize comfort conditions in the space. If infrared heaters are mounted too high or too low, the end result may be a lack of heat or discomfort. However, certain applications such as freeze protection, outdoor patio heating or spot heating may require the heaters to be mounted at other than the traditional recommended mounting heights.
New technology
An advanced feature of low-intensity infrared tube heaters is the use of two-stage controls. A two-stage infrared heater is characterized by its ability to operate in preset “high” and “low” fire modes. Since infrared heating systems are typically designed around “worst-case scenarios” (which only occur 10%–20% of the time), a single-stage system becomes oversized on milder days, creating more on/off cycles (heat/no heat). With two-stage technology, input (fuel usage) is reduced by 35% (100% input in high-fire and 65% input in low fire). Field reports, as well as independent studies by RDM Engineering in Canada, have proven a minimum fuel savings of 12% and a reduction of on/off cycles up to 30 % with the majority of heater operation in low fire. A two-stage heater allows application design flexibility based upon the possible worst-case changes in the environment.
In addition to fuel savings, reduced on/off cycles and design flexibility, additional benefits of two-stage heaters include faster heat recovery, higher downstream tube temperatures, longer flame and longer equipment life. More importantly, a two-stage heater will provide a softer and more comfortable heat source for occupants compared to a single-stage heater that is either operating at full output (sometimes too much heat) or cycles off (not enough heat).
Vacuum style of infrared heating
Multiple-burner, low-intensity, vacuum infrared heating systems have been a mainstream product offering for many years; the technology itself is more than 40 years old. As the infrared heating industry has evolved through the development of unitary heaters featuring equal or superior energy efficiency, multiple-burner low-intensity vacuum infrared heating systems have often been seen as old technology. The primary difference between a vacuum-style heater and a positive-pressure tube heater is that the burner box is under a negative pressure instead of a positive pressure. A pump, located at the end of the system, pulls the gases down the tube. This type of infrared heating system offers some application benefits not found with other types of infrared equipment.
Vacuum-style infrared heaters may have up to six burners common vented by a single vacuum pump. Fewer roof or sidewall penetrations are the resulting application benefit. The vacuum-style unit may be installed as either a condensing or non-condensing system. A condensing system allows for longer system lengths and higher system thermal efficiency. A non-condensing system more efficiently utilizes the highly emissive black coating on the radiant tubes at a more reasonable equipment cost over the condensing system.
The price of staying warm
While radiant heating does require a cost investment, it can be a good choice depending on the application. Gas-line connections must be considered and hanging the unit is at least a two-person job. The initial cost of a standard, 40-ft-long unitary tube heater is approximately $1,100. Therefore, upfront costs are higher than traditional heating methods. However, this investment will pay for itself over a short period of time due to the energy saving benefits of radiant heaters. And the installation of a system that incorporates two-stage technology can offer an additional 12% fuel savings over a standard single-stage radiant heater.
Although the installation may be fairly easy, system design and layout can be more difficult. It is critical that the equipment is installed properly to assure a safe and effective heating system. Most manufacturers sell product via local representatives. This allows a professional to review the desired needs and select the proper equipment for a specific application.
Gas-fired infrared heaters offer the option of placing heat where and when it is needed. This ability, coupled with excellent operating costs, gives a clear advantage to infrared heaters. And if you want to get the most for your money go with heaters equipped with two-stage technology. You can rest assured that providing a comfortable environment within your application will be well received by both you and other building occupants.
Michelle Kostusyk is part of the Product Support team at Detroit Radiant Products Co. For more information, e-mail
From the September 2008 issue of RSES Journal.
