Should A Constantly Running Modulating Pellet Boiler Be A Goal?

[velvetfoot]

Is getting a modulating pellet boiler to run almost constantly good for it? At a minimum 30% power level and with the buffer tank, I can see there being long stretches during the winter where it might never shut down. I think the BioWin cleans itself as it runs, so it wouldn't have to shut down for that.

I understand that creosote shouldn't be a problem, but does it run more efficiently at 30% (the specs in the install manual seem to indicate that)? How about wear and tear: Is it made for this constant duty?

I can see fewer startup emissions and having the boiler at the ready to supply a zone is also great.

(Edit: Marc tells me that it shuts itself down every 6 hours for a few minutes to cool down.)

 

[Chris Hoskin]

Yes, long run times and infrequent start/stops are very desirable from an efficiency stand point and a equipment wear and tear standpoint. The boiler should handle the long run times no problem. Yes, it is likely that the efficiency is higher at lower output because the heat exchanger (boiler tube surface area) is large compared to the heat output at high fire. Even with a widely modulating boiler, however, there will be times when your load is very low (this time of year, for example) and the boiler will need to shut off. A buffer tank is especially useful for that.

 

[Deering]

Regarding wear and tear, seems to me if you need a certain amount of BTUs from the boiler in a day, assuming the efficiency is the same at different modulation rates, it will have to auger the same amount of pellets, blow the same amount of combustion air, and auger out the same amount of ash. Only the rate differs, but the number of motor shaft rotations should be about the same.

Maybe the more frequent thermal cycling is the biggest wear component.

 

[Chris Hoskin]

Regarding wear and tear, seems to me if you need a certain amount of BTUs from the boiler in a day, assuming the efficiency is the same at different modulation rates, it will have to auger the same amount of pellets, blow the same amount of combustion air, and auger out the same amount of ash. Only the rate differs, but the number of motor shaft rotations should be about the same.

Maybe the more frequent thermal cycling is the biggest wear component.

Actually I was thinking mostly about the ignitor, but I think it is fair to say that any piece of equipment has an easier time of it when running at steady state than when frequently cycling on and off.

 

[Deering]

Good point! Hadn't considered the igniter.

 

[heaterman]

That's how I run mine but your system has to be set up for it by using constant but metered flow to your heat emitters.

Right now we are at 24* with about a 10 mph west wind. I have the temp setpoint at 149* in the boiler and it is firing at 34% output. Boiler size is the 210 so it's producing roughly 24,000 btu's/hour. As outdoor temp drops I'll raise the water temp in 5* increments when i notice the house dropping below it's normal 73*.

 

[velvetfoot]

I think there's a 0-10 v. thermostat connection on the board in my unit? Nothing fancier. Is that something that an outdoor or indoor reset could tap into? Not that I would, with my emitters, tank, etc.