| SBD DIRECT GAS - FIRED SERIES The Need for Make-up Air
Air exhausted from industrial or commercial buildings must be
replaced. If provisions are not made for make -up air, there likely will be air starvation
creating negative pressure within the building . This negative pressure, in turn, causes:
outside air infiltration and cold drafts; down or back drafts in heating equipment
flues,ventilators and stacks;reduced exhaust fan air volumes resulting in inadequate
removal of contaminants; uncomfortable, and in many instances, unhealthy working
conditions; and other problems.
The Source of Make-Up Air
With most applications requiring exhaust air provisions, replacement
air must enter buildings either by infiltration through openings such as doors or windows,
or supplied by a make -up air system. Infiltrated air is unheated, draft ridden and
unfiltered resulting in an uncomfortable, uneven, and often unclean environment. A
controlled source of make -up air eliminates the many problems of infiltration.
The SBD Direct Gas - Fired Systems
The SBD series of direct gas - fired make -up air system was
designed to furnish fresh, clean and heated air from a controlled source by the most fuel
efficient and cost effect means. The SBD system employ a method of supplying heated air
into a building by passing fresh air directly over a gas flame in the air stream. The
burner utilizes the kinetic energy of the air flow to complete combustion with the
products of combustion well within code prescribed safely limits. The direct gas- fired
burner, depicted in Figure 1. consists of drilled port cast iron pipe and two perforated
stainless steel combustion baffles. The arrangement and shape of the air hole in the
bafflies provide the injection of proper combustion air at all rates of firing over a wide
turndown range of up to 25:1. Since all the heat of the fuel goes into the air
stream being heated, the direct gas- fired unit has 100% combustion efficiency and 92%
overall thermal efficiency (with 8% of the total heat lost in the latent heat of water
formed in combustion)
HOW CAN YOU RECOGNIZE
THE NEED FOR MAKE -UP AIR?
Symptoms:
Back drafts and frequent pilot
outages on natural draft heating equipment
Doors difficult to open
Exhaust fans not exhausting air
Cause:
Negative inside pressure from too little
air replacing the air being exhausted
Symptoms:
Heaters not heating
buildings
Cold drafts
Dust and dirt being drawn
into building
Cause:
Untreated outside air
infiltrated into building because of negative inside pressure
Symptoms:
Employees develop nausea and
headaches
Cause:
Build-up of inside contaminants due to
inadequate ventilation
Figure1
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