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The Basics of Gas-Fired Infrared Heating


When we think about building heat, our first thought may be of forced air -- you know, the big unit suspended from the ceiling blowing hot air with the force of a jet engine. While that might work for some, independent reports reveal that gas-fired infrared heating can save 20-50% in fuel consumption over forced air heating.

Low-intensity 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. The heaters are typically suspended from the ceiling by chains and controlled by a thermostat. They can be installed either vented or unvented, may use outside air for combustion if necessary, and may be installed in different configurations depending on heating requirements.

Two Types of Infrared Heating

The two types of infrared heating are high and low intensity. High-intensity heaters have been around since the 1950s and require high mounting heights due to an open flame that covers a ceramic surface. High-intensity heaters also have a reflector to help direct the heat where it needs to go. These are used to spot heat areas with few workers and are typically unvented.

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, machinery, and people. Objects in the path of the infrared energy in turn re-radiate this heat to create a comfort zone at the floor level.

This method of heating -- as opposed to filling a room with warm air -- allows the source of heat to begin at the floor level and not the ceiling. With a forced air system, heat escapes as doors are opened; when the doors close, the system has to reheat the air as if from a cold startup. However, with infrared heat the floor acts as a reservoir. When doors are opened, the slab loses very little of its heat and when the doors close, this mass acts as a huge heat sink to warm the surrounding air. This is the most efficient and effective heating method under the diverse conditions present in most commercial and industrial applications.

The Positives of Infrared Heating

Radiant heaters offer several operational and design benefits not available with conventional heating units. For example:

  • Up to 50% fuel savings over forced air units.
  • Does not blow dust and debris around like heaters that rely on blowers for heat distribution. This makes for a much cleaner and quieter environment.
  • Zoned capability allows a group of units to function together or independently.
  • Capable of mounting heights up to 60 ft depending on which heater is chosen for the application.
  • Delivers spot heat to certain areas where workers are few.
  • Directional – it can be installed along a sidewall and the reflectors can be rotated to direct heat where it is most needed.
  • Can use outside air for combustion.
  • Low-intensity heaters can be vented together to reduce the number of roof or wall penetrations.
  • Flexible design. Heater placement can be in the middle of the shop or perhaps even in a “U” or “L” shaped configuration around a workstation where the heat is needed most.

The Negatives of Infrared Heating

A few important things need to be considered when using radiant heat. While such systems are easy to live with, 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, recommended when dust or contamination is present inside the building. Periodic dusting of the reflectors is beneficial not only for safety, but for overall heater efficiency. This is easily done by vacuuming the unit’s surfaces occasionally or blowing it off with an air-compressor hose.

Safety Considerations

A critical safety factor to consider before installing an infrared heating system is clearances to combustibles, defined as the minimum distance that must be maintained between the radiant tube heater surface and the combustible item. Considerations must also be made for moving objects around the infrared heater and materials that have lower temperature ratings, such as plastics. Shielding of these items may be necessary. Additional examples of combustibles include lights, overhead doors, gas and electrical lines, parked vehicles, cranes, and any other obstructions or hazards.

It is important to provide warnings alerting 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.

Unless otherwise indicated, infrared heaters are not certified for residential use or locations where flammable gases or vapors are present, such as spray booths.

In addition, observing recommended mounting heights will optimize comfort conditions in the space. If infrared heaters are mounted too high or too low, they may result in 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 pre-set “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 studies performed by RDM Engineering of Ontario, 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 worse 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 when compared to a single-stage heater, which 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 part of the mainstream product offering in infrared heating systems for many years -- in fact, the technology is over 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 main difference between a vacuum style heater and a positive pressure tube heater is that now the burner box is under a negative 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, resulting in fewer roof or sidewall penetrations. And the vacuum style may be installed as 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

If you count pennies, you might want to stay with the forced air method. But if you can live with a small investment, radiant heating may be a wise choice. Gas line connections must be considered, and hanging the unit is at least a two-person job. The initial cost of a standard, unitary tube heater 40 ft long will run approximately $1,100. Therefore, upfront costs are higher than with 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. Interested in even more fuel savings? Install a system that incorporates two-stage technology, which can offer an additional 12% fuel savings over a standard single-stage radiant heater.

Distribution and Applications

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 manufacturers’ representatives. This allows a professional to review the desired needs and select the proper equipment for a specific application. A local representative may also provide guidance in suggesting a contractor familiar with installing infrared heating systems.

Here are some typical applications where infrared heating works well.

  • Harsh Environments
  • Fire Stations
  • Aircraft Hangars
  • Wood Shops or Pole Barns
  • Car Washes
  • Auto Shops
  • Restaurants
  • Agricultural Buildings
  • Driving Ranges
  • Warehouses
  • Home Garages
  • Manufacturing Buildings

 Summary

 In the end, it comes down to whether you wish to provide a good heat source in your 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.

 

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