Boiler Combustion Air Source

[MJCronin]

To all,

Our client has asked a question is about the pros/cons of using outdoor air for combustion in a district heating boiler. The two boilers are:

- Watertube, "D type" 155,000 lbs/hr MCR at 175 psig
- Dual fueled (gas & oil) with FGR
- Burner mounted FD fan, 150 hp
- Boilers installed in a boiler room - Cleveland, Ohio

Should vent ducts be extended outside of the boiler room to draw in combustion air or should the "boiler room" air be used for this purpose ?

I am aware that properly sized building louvers are required in a room where boilers draw combustion air, but are there legitimate reasons to draw in outdoor air ?

Are there any books/websites that someone can direct me to ?

Thank You in Advance....

MJC

 

[TBP]

I'd worry about running the fan intakes directly outside, unless they were heated. You might be able to have a draft through an off-line boiler, and freeze something during cold weather. If combustion air is being drawn into the boiler room, there's not much chance of this happening.

On the upside, running the intake outside will take most of the fan noise with it. It'll be a lot quieter in the plant. But does that leave you with noise problems elsewhere? I've run into that before - having to hit ridiculously low noise levels at the property line. Between the traffic noise off the street, and the property backing onto the main line railroad tracks at a level crossing (close - maybe 50 feet away), the test instruments regularly got "pinned" anyway, even before the plant was running.

 

[pmover]

MJ Cronin,

yes there are books and codes! the uniform building code and/or international mechanical code (imc) will provide you with guidance. the imc is updated every 3 years and a new edition is issued this year. suggest contacting the local boiler inspector or insurance representative for guidance as well.

regardless of location, boiler will need combustion air from the outside. if fdb is indoors and in an enclosed space, the building will need sufficient openings in building to allow outside air into boiler room for combustion.

understand that fdb is at burner and 150 hp.
couple of thoughts: 1) investigate alternatives w/ burner mfg and think about placing fdb outdoors and install ducting from fdb to burner, 2) place boiler in a position where boiler front is outdoors - may need to consider overhang/canopy.
good luck!
-pmover

 

[davefitz]

For small boilers, the use of inside air has the following advantages:

a) the radiation loss implied with a small boiler is partly offset by having the building air ( heated by the radiation loss) used as combustion air

b) the buidlig will run at a slight vaccuum always, so as to leak ambient fesh air int the building and reduce the liklihood of building up combustion products or combustible gases in the building.

To offset this , in cold climates the building negative pressure can cause excessive cold air inleakage so as to imply heat tracing all buidling piping.