Post Purge

Post Purge

PostBy: billw On: Tue Jul 08, 2008 8:18 pm

How important is it to have a post purge (dump zone) on a coal boiler? My current controller is a B & G that's 15 years old and doesn't have a post purge function.

I've looked at TACO's -exp system and B & G's new system. If I'm reading their manuals correctly the dump zone is the zone that last called for heat. After the T-stat is satisfied the B & G system runs that zone(s) for 90 seconds. The taco is adjustable up to 7 minutes. If I put a dump zone in the system I would want it to always be my basement/garage, not the 1st or 2nd floor. Is that doable with either of these controllers? If not are there any controllers that have this capability?
billw
 
Stove/Furnace Make: EFM 520
Stove/Furnace Model: GOODBYE OIL COMPANY

Re: Post Purge

PostBy: LsFarm On: Tue Jul 08, 2008 9:22 pm

You don't need it.. unless you are running your water temp up near boiling.. the overshoot on the water temp is minimal.. maybe 10*.. I keep my water at 160-170*, up to 180* if it is really cold out.. at 160*, a 10-20* overshoot [never seen more than 10*] is nothing to worry about..
Save your money for coal..

Greg L.

.
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Post Purge

PostBy: billw On: Tue Jul 08, 2008 9:35 pm

Thanks Greg.
billw
 
Stove/Furnace Make: EFM 520
Stove/Furnace Model: GOODBYE OIL COMPANY


Re: Post Purge

PostBy: Sting On: Tue Jul 08, 2008 9:55 pm

A heat dump is as simple as a signal from a strap on Honeywell control to operate your zone pumps IF you begin to over temp. I wire mine to prevent catastrophe - not as a normal event as Taco advises.

Sure - Greg is right - I am not saying he is not - you don't need it


UNTIL THAT ONE TIME WHEN YOU DID!
Sting
 
Other Heating: OBSO Lennox Pulse "Air Scorcher" burning NG

Re: Post Purge

PostBy: JOE.G On: Mon Jul 28, 2008 8:49 pm

What happens if you you don't have it? will it just blow the pressure vavle off?
JOE.G
 

Re: Post Purge

PostBy: LsFarm On: Tue Jul 29, 2008 11:06 am

Yes, the PRV would open, relieving pressure in the boiler,, the supply line from your water supply would sense the drop in pressure and add cold water to the system.. the water temp in the boiler would drop.

I run my boiler at 165* in the summer, with 25* differential temp spread.. so it starts the combustion fan/auger/stoker when the water cools to 140*, turns off at 165*.. if my timer cycles for it's 1minute burn just after the aquastat just shut off, I might see 180* water temp. but nowhere near the 205* I have my high-limiting aquastat in the timer circuit set at... so I don't have any over temp spiking problems..

It would not be difficult to add a strap on make-on-rise aquastat to the system and use it to trigger the system to circulate the water.. I'd use the whole house or a basement circuit.. I originally planned on using my shop as the dump zone, untill I found out it was a problem for wood systems, not stoker coal boiler systems.. so I don't have any dump zone.. But some installs may need one or owners feel better having one.. personal prefferences.

Greg L
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland