Ventilation Air: In addition to air needed for
combustion, sufficient air must be supplied for
ventilation, including air required for comfort and
proper working conditions for personnel in the
boiler room. In colder climates, provision should
also be made to heat the boiler room, if
necessary, for personnel comfort.
CAUTION
Protection from combustion air contamination:
Where corrosive or flammable process fumes are
present in the vicinity of the boiler room or the air
stream for the combustion air supply, it is
essential that suitable means be provided for their
safe
disposal. The boiler room and the combustion air
supply must not be exposed to the fumes. Such
fumes include, but are not limited to, carbon
monoxide, hydrogen sulfide, ammonia, chlorine,
and halogenated hydrocarbons.
NOTE: Halogenated hydrocarbons are
particularly injurious and corrosive after exposure
to high temperatures.
1.8 CHIMNEY, FLUE PIPE & DRAFT CONTROL - FORCED DRAFT BOILERS
CODE COMPLIANCE
The installation must conform to the requirements
of NFPA 54, the National Gas Code (ANSI
Z223.1-1984), Part 7, "Venting of Equipment", or
to the applicable requirements of all local building
codes. For factory-built and listed chimney
systems (such as type B vent), consult the
system manufacturer's instructions for correct
installation procedures. Gas vents may be of any
of the construction types listed in this manual. No
portion of a venting system may extend into or
pass through any circulating air duct or plenum.
MINIMUM SAFE PERFORMANCE
Venting systems must be designed to develop
positive flow adequate to remove flue gases to
the outside atmosphere. Guidelines are provided
in this manual and in the National Fuel Gas Code,
NFPA 54, for sizing and design of flue gas
venting systems. For additional reference to good
practice in vent design, refer to the "Chimney,
Gas Vent, and Fireplace Design" chapter of the
ASHRAE Equipment Handbook.
OUTSIDE VENTS AND CHIMNEYS
Outside uninsulated single wall pipe is not
recommended for use in cold climates for venting
gas-fired appliances since temperature
differentials may cause corrosion in such pipe, as
well as poor draft on start ups. When local
experience indicates that condensate may be a
problem, provisions should be made to drain off
the condensate in the gas vent or chimney.
ESTIMATING FLUE GAS FLOW RATE (ACFM)
Flue gas volumetric flow rate in SCFM (standard
cubic feet per minute) and ACFM (actual cubic
feet per minute) can be estimated by using the
information in 1.8.1A. Divide the Total Input of
appliances connected to the chimney or vent by
1000. Then multiply this result times the factor
listed in the SCFM and ACFM table. The ACFM
data is required for determining stack exit velocity
and induced draft fan requirements.
ESTIMATING STACK EXIT VELOCITY
First, determine the ACFM for the stack as
described above. Multiply the total ACFM times
the Velocity Factor from the Velocity Table in
Table 1.8.1B for the stack diameter used. The
result is the Stack Exit Velocity in feet per second.
ESTIMATING STACK EMISSIONS
Table 1.8.1C lists approximate emissions of NOx
(oxides of nitrogen) and CO (carbon monoxide).
The table lists both the concentration, in parts per
million (ppm), and the flow rate, in pounds per
hour (PPH), of each compound: Divide the total
input of appliances connected to the chimney or
vent by 1,000,000. Then multiply this result times
the value listed in the table for PPH emissions.
MANUAL REFERENCES
See Figure 1.8.1 for a graphics listing of
applicable sections of this manual for each
section of the vent system.
Содержание Forced Draft Steam Boilers
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