Weight of air to be handled by fan, lb/hr
Excess air required at burner
Leakage in air heater
Total net requirement
proper safety margin
Total test block requirement
Ps = Pfr
Pfr + Psm = Pbp
Static pressure at fan discharge, inches of water
Add proper safety margin
Total test block pressure
Ta + 25
degrees F (13.9 degrees C) = Ttb
Temperature of air, degrees F
Total test block temperature
Induced Draft Fan
a) Weight of gas to be handled by fan, lb/hr = Total net
requirement = Theoretical air for combustion + Excess air required at burner +
Fuel burned (assume no ash) + Infiltration + Leakage in air heater.
Add proper safety margin = Total test block requirement.
b) Draft to be provided by fan, inches of water =
Total net draft
Add proper safety margin = Total test block pressure
c) Temperature of air, degrees F
Net temp. + 25 degrees F (13.9 degrees C) = Total test block
Selection of fan controls is a balance of
Fan Control Methods.
engineering and economic factors.
The manufacturer's fan curves must be
supplied for each fan.
a) Dampers. Dampers are used on fan discharge to raise system
resistance and raise operating points higher on the fan curves. Input power