SECTION 9: AIR SUPPLY SYSTEM
An air supply free of dust and corrosive contaminants is essential for proper operation and best life expect- ancy with any heating system. With
•Room air, a filter is standard for each burner.
•Outside air system to duct air from an uncontami- nated source. The outside air system can be designed as a pressurized or
The first alternative above is usable when the dust load is not excessive and there is no usage of corro- sive contaminants such as solvents or vapors inside the building.
The outside air system must be used in all applica- tions where corrosive contaminants may be present in the air even in trace amounts (few parts per million).
It is important for designers and owners of heating systems to note that the presence of contaminants in the combustion air supply will greatly accelerate the rate of corrosion on tube surfaces and will shorten the useful life of the heating system. This is true regard- less of whether the heating system is
With the unique vacuum powered burners, the fuel/air mix remains constant, even if combustion air filters are dirty. It can be expected that the use of an outside air system will reduce but not eliminate the potential for corrosion due to contamination.
In a way similar to the
9.1 Pressurized
For pressurized outside air supplies, the outside air blower motor has a pressure switch that must be used. Wire this switch
DON® ULTRAVAC™ or relay transformer, a separate load relay package is required. Wire the control for the relay in parallel with the pump. The outside air blower must have a separate 20 A, 120 V power supply.
9.2 Non-Pressurized
For a
9.3Outside Air System Design Requirements 9.3.1 Non Pressurized
•6" diameter duct must not exceed 90' (27 m)
•4" diameter duct must not exceed 90' (27 m)
•Elbows are equivalent to 10' (3 m) of duct length.
•See the
9.3.2 Pressurized Systems
•6" diameter duct must not exceed 120' (36 m) total per system.
•4" diameter duct must not exceed 120' (36 m) per radiant branch.
•See the
FIGURE 27: Air Supply System Capacity by Duct Length and Diameter
NOTE: For capacity requirements larger than shown, use 8" duct.
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Units | 120 |
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100 |
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| 7" |
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80 |
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Flow |
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60 |
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| 6" |
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| 40 |
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| 5" | Duct | ||
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| 4" | |||
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| 0 | 50 | 100 | 150 | 200 | 250 |
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Straight Duct Length (feet)
28