Need corn furnace / boiler advice
Buddy’s dad in Wisconsin has a corn / compressed wood pellet furnace / boiler for in-floor heating for his house, okay? I don’t have the model info yet.
Boiler is out in a little separate building. Full hopper of pellets lasts a month or more.
PROBLEM:
When the water returning to the HeatX reaches a certain temp, the furnace cuts off (auger stops bringing in pellets), just like you would expect. When the fuel in the chamber is consumed, the fire goes out.
But, there’s no automatic re-light when heat is called for again – he has to go out with a MAPP gas torch and restart the corn in the combustion chamber. Cold activity in the winter.
His work-around is to set the thermostat up so high in the house that the cut-off water-return temp is never reached, so he doesn’t have to go out in the snow and re-light.
Not real efficient.
It appears that’s just the way the system is designed.
Any ideas on how to re-plumb/re-wire to make the burner “idle”? Slow the auger down to a minimum feed speed to maintain combustion? One of those “instant-on” propane torches for a lighter?
I’ve been talkin’ you guys up – help a brother out.
Forrest
Replies
Maybe you should consider retrofitting the automatic lighter element from another brand of stove/furnace. Most of the manufacturers publish their owners' manuals, complete with schematics. Here's one:
http://www.harmanstoves.com/doc/p68m.pdf
This model seems to use a sort of electrical resistance element as the starter. Of course, I know you won't have a problem adapting the electronics to control the lighter cycle.
As for the feed rate, from what I've been reading, most manufacturers use duty cycle rather than speed for the feed auger. They pulse them on and off periodically to control the feed/burn rate.
Bob
My first thoughts are that the unit is grossly oversized.
And possibly and smaller/slower auger is needed. Maybe a reset control with the auger speed controlled by the OAT.
But I don't have any idea of how those system work.
What does the thermostat control?
I gather this cutoff is a over temp limit and not the normal control.
How often does this happen?
And if the house temp has not dropped drastically when the boiler is relite how long is it until it goes out again?
And is this a low mass or high mass radiant system?
William the Geezer, the sequel to Billy the Kid - Shoe
Okay - got more info.
There's a primary closed loop that goes from the boiler to a secondary heat exchanger. Various house loops are also pumped through this secondary heat exchanger, with thermostatically-controlled zone valves. There is a temp sensor in the flue that turns the auger simply "on" or "off" to maintain the combustion process. The fan blowing air into the combustion chamber stays on constantly.
What's causing the problem is the overtemp sensor in the primary, or boiler loop. When not enough zones are calling for heat, the primary loop continues to heat up until a safety cut-off around 160°. When that temp is hit, the auger and the fan shut off until manual restart.
System works fine when its -20°, but on a sunny 30° day (new house designed for solar gain), less heat is called for. By the time the house begins to cool down in the evening and heat is called for, the furnace is out, and has to be restarted and allowed time to reheat the system.
Forrest
That is a fairly crude control system.And I think that there are ways to improve it, some what.But probably the auto relight system is what is really needed.There are going to be lots of times coming up in the spring and fall when the house might not need heat for 1,2,3 days and then lots of it. And that is a difficult juggling act to keep the unit burning for days and not over temping..
William the Geezer, the sequel to Billy the Kid - Shoe
The fan blowing air into the combustion chamber stays on constantly.
That's your problem. The fan in a wood, pellet, or corn burner should not stay on all the time. It should shut off when the thermostat stops calling for heat. The load will then sit there and smolder ( which is basically why these are banned in so many locations )
With the fan not running, the hot fuel mass will stay that way until the fan comes on again and starts the process over again.
"With the fan not running, the hot fuel mass will stay that way until the fan comes on again and starts the process over again."But even that is limited.Does it still need an automatic lighter. We are gettting a couple of days around 65. Then to the 50's and 20's..
William the Geezer, the sequel to Billy the Kid - Shoe
Generally, there is a big mass of fuel stored in the burner. The fan is the primary temperature control for the heated water. As soon as the thermostat in the boiler stops calling for heat, the fan should shut off.
The big mass of hot coals will sit there and smolder for a long time. I have never seen it burn up completely before the thermostat starts calling for heat again.
We have installed dozens of these units and I have never seen one operate the way he described it. Something is wired wrong or the fan relay is stuck.
Most of them have pretty precise control of water temperature because of the large volume of water contained in the boiler itself.
Here's more info, from the guy's dad -
I have a Thor 200 corn furnace. However, when I looked on the internet for the company that made the Thor, I found it listed under a new company located in <!----><!---->Minnesota<!----> instead of <!----><!---->Iowa<!----><!---->. The <!----><!---->Iowa<!----><!----> company must have been bought out. The web site is aes-mn.com. I found a picture of my unit on this site although with a hopper instead of a corn bin like mine.
Is this any help?
Forrest
Did someone set this up for him? or did he buy the place with the boiler already installed?
Someone locally must have experience with them.
As I said before, the fan must stop running when the boiler thermostat stops calling for heat, otherwise the whole fuel charge will be burned up and the water temperature in the boiler will be out of control.
That's what he needs to fix. If he doesn't have the skills to do that, then he's going to have to get some professional help.
These units have an aquastat in the boiler that controls the operation of the fan and in his case the auger. They will cycle constantly to maintain the boiler water at the set temperature. Even if the house is not calling for heat, the boiler should be firing periodically to maintain the set temperature in the boiler water as it cools.
As I said before, I have never seen a situation where the entire charge of fuel will go out before the boiler fires up to heat the water again to the set temperature. ( Unless the fan stays on and burns the whole charge of fuel without the auger operating) ....which is not how it is supposed to operate.
This should be an easy fix.
Edited 2/10/2009 11:40 pm ET by BoJangles