Types of Direct-Fired Gas Heaters
 
Constant Volume System
Constant Volume System

The constant volume 100% direct-fired make-up air system heaters provide a constant rate of supply air to the space. The gas flame in the unit heats the fresh make-up air directly, eliminating energy losses associated with other types of heating. For most applications, introducing slightly more make-up air into the space than what is exhausted produces the best results. A slightly positive building pressure assures the best performance. Some applications, such as the commercial kitchens, require more air exhausted than introduced to control over pressurization of the kitchen.




Two-Speed System
Two-Speed System

The two-speed, direct-fired make-up air system functions the same as constant volume, however provides two different air-delivery rates by using either an 1800/900 RPM motor or 1800/1200 RPM motor. Two-speed units offer flexibility to buildings with two, fixed-exhaust loads or where an increase of airflow is desired.

Units for buildings with two fixed-exhaust loads should have CFM ratios that match the available two-speed motor RPM ratios. The low speed is interlocked with the first exhaust fan, while high speed operates when both exhaust fans are running, allowing one unit to handle two different exhaust loads.

The example above illustrates the use of a two speed unit for transit or automotive type facility. Low speed is used for general ventilation and heating. However, if the co-detector senses high limits of carbon monoxide, the two speed unit goes to high speed and the second exhaust fan turns on to ventilate the space. There are many uses for the two-speed system, however another use is for paint booths designed for painting and curing of paint. High speed use in paint mode and low speed is used in curing mode to dry the painted surface.




Variable Air Volume System
Variable Air Volume System

The variable air volume (VAV) system allows variable amounts of make-up air through one heater. This system allows a heater to turn down to as low as 25% of its designed CFM by use of a variable frequency drive (VFD) or airfoil blade designed discharge reduction damper. One unit can handle varying exhaust loads by changing the CFM out put of the unit. This system is ideal for spaces that have multiple exhaust loads and recirculated air is not an option.

The use of the VFD in the system offers the highest level of operating efficiency of any of the direct fired systems, using only the required electrical energy to provide the CFM needed. The VFD can be setup to operate in many different ways to change the CFM required to the space. A potentiometer can be used to manually position output CFM, multiple set points can be set in the VFD to vary output CFM, or a building pressure control device can be used to vary output CFM by sensing pressure in the space.

The use of the discharge reduction damper in this system offers a low cost up front investment with the same operation benefits of the VFD. By closing the reduction damper, the output CFM is reduced. This design has the ability to be setup as a two position CFM rate unit or a varying CFM unit based off pressure in the space.

Both VAV systems have been designed with additional safety features and controls to insure safe burner operation.




80/20 System
80/20 System

80/20 systems can be a variable make-up air unit, a total-building heat unit, or a combination of both. By re-circulating air, this system provides the most efficient building heat system.

One unit can handle multiple and varying exhaust loads as a variable, make-up air unit using the 80/20 System. This system offers constant discharge airflow but varies the amount of outside air introduced to the building. With the use of the 403M or the 404M space-temperature control system, the unit can be a complete building-heating system for either fixed or variable exhaust loads.

The 80/20 System supplies at least 20% outside air to the building and mixes with re-circulated room air at a maximum of 80%, without the return air re-circulated through the burner. A building-pressure switch controls the modulating-burner bypass and return-air dampers introducing more outside air as the building’s exhaust load changes. The varying exhaust-air loads automatically and continually adjust the amount of make-up air introduced into the system.

All of our direct fired systems are provided with terminals to integrate operation with the building exhaust system.


80/20 System Features

The 80/20 System is simple to operate and maintain, with both heating and make-up air combined into one unit. With its ability to control static pressure, it automatically manages outside air percentages and either space or discharge temperature, eliminating the need to interlock exhaust fans with separate make-up air units. The 80/20 System automatically adjusts to the building's pressure changes to bring in outside air, up to 100%. No flue through the roof means no leaks or flue maintenance. Finally, due to its high combustion efficiency, 80/20 System is economical to operate.

 
 
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