Over heat zone circuit

[goosegunner]

To really protect my system I am thinking I should take advantage of my overheat circuit on my controller.

I have the Econoburn 200 and I have the no power dump zone set up with the automag for that situation.

But what about over heat if say my boiler pump fails and fan keeps runnning?


The boiler has an aquastat set at 205 that will kill the fan. The controller will also energize another circuit for an additional pump. I have considered adding T's in my main boiler supply near boiler and tank so if I had an overtemp from a pump failure it would start pump and dump the excess in to the tank.

If this is a good idea what size pipe would you use for this? My supply pipe is 1 1/2" copper. Would 1" handle an overheat?

My other thought was to put a RIB relay before the Auto mag. I could have it normally closed. If the overheat circuit energizes it would open the automag circuit so it would lose power and open. Boiler could then shed heat through no power dump zone.

So what do you think would work?

What method would you recommend.

gg

 

[ewdudley]

To really protect my system I am thinking I should take advantage of my overheat circuit on my controller.

I have the Econoburn 200 and I have the no power dump zone set up with the automag for that situation.

But what about over heat if say my boiler pump fails and fan keeps runnning?


The boiler has an aquastat set at 205 that will kill the fan. The controller will also energize another circuit for an additional pump. I have considered adding T's in my main boiler supply near boiler and tank so if I had an overtemp from a pump failure it would start pump and dump the excess in to the tank.

This would make a good fail-safe for the main boiler-to-storage circ, and you could also add logic to have it kick in at a lower temperature in addition to the main boiler-to-storage circ as a storage-is-hot-need-more-boiler-flow-to-prevent-idling circ.

If this is a good idea what size pipe would you use for this? My supply pipe is 1 1/2" copper. Would 1" handle an overheat?

If I'm following you you're saying add another pump in parallel with the main storage-to-boiler circ that would bypass the return temperature protection and the storage-to-boiler circ. 3/4" would pump over 13 gpm with a 007 IFC and still be under 10 feet per second, not a problem.

My other thought was to put a RIB relay before the Auto mag. I could have it normally closed. If the overheat circuit energizes it would open the automag circuit so it would lose power and open. Boiler could then shed heat through no power dump zone.

So what do you think would work?

Gravity dump zones are typically sized for ten percent of nominal boiler output, which probably wouldn't be adequate in a runaway fan situation.

What method would you recommend.

The secondary storage-to-boiler circ should do the trick, but to pass FMEA you need a mechanical high limit aquastat in series with the draft fan motor. Most any Honeywell bulb unit with an open-on-high-limit aquastat off ebay or craigslist would work, just locate the bulb well where it can see the boiler overtemp and go straight in to the aquastat push-to-release terminals with with your draft fan power wire on its way to the draft fan.

This works even if you have the fail-safe circ but forget to open the ball valve on the boiler-to-storage line after you work on the boiler. At least that's what a friend told me.

 

[Singed Eyebrows]

GG, I'd personally keep it simple & use a Honeywell STS20 or Danfoss equivalent. Put the bulb in the boiler water at the top & inlet at the top of the boiler. Hopefully your feed water enters at the lower fittings. These are reliable & are not dependant on electricity, Randy

 

[goosegunner]

My boiler already has an aqua stat in the supply pipe within 3 feet of the boiler. It is wired to interrupt the fan if temp hits 205.

The controller also has connections to energize a pump if a set over temp is hit, right now it is set at 200. I can lower if needed.

So do I need the extra pump for a safety or is stopping the fan adequate?

gg

 

[ewdudley]

My boiler already has an aqua stat in the supply pipe within 3 feet of the boiler. It is wired to interrupt the fan if temp hits 205.

The controller also has connections to energize a pump if a set over temp is hit, right now it is set at 200. I can lower if needed.

So do I need the extra pump for a safety or is stopping the fan adequate?

gg

Stopping the fan won't leave you any worse off than a power failure, so if your power-fail dump subsystem is A-OK then you're good to go safety-wise.

--ewd

 

[jebatty]

This is another question that involves assessing the risk: the likelihood of the risk event occurring and the magnitude of the harm resulting. One thing that comes up very little on this forum is circulator pump failure. They seem to be highly dependable and, I would assume, likely to give some warning, such as squeaks, rattles and other noise, before complete failure. So it would seem likelihood is low and probably preventable.

To assess the magnitude of harm, you might cut the power during high burn and see what happens. How quickly does the fire calm down, do you have an air leak that keeps it going, is your natural draft such that it continues to fuel the fire with air? If the fire calms down quickly, good result. Next, how well does your gravity fed dump zone work when the Automag opens up? Does it prevent the boiler from blowing its stack with steam out of the pressure relief valve? And if pressure does rise too high, what happens? Lots of blow or a little before the fire calms down? What's the danger of some blow off? Is it enough to damage the boiler? Other things?

The magnitude of harm may be very low. The fire in my Tarm calms down very quickly when the fan goes off. Besides the Automag dump zone, which heats pretty well, I get a little ghost flow, which is good for me as the heat goes where I want it anyway. Unless the Tarm was near maximum temperature with a good supply of wood yet to burn, I doubt any harm would come from a power failure. Any I no longer load the Tarm so that it has much wood to burn as it approaches maximum temperature.

All in all, the fear may be unjustified, but rather than speculate and fear, run some tests and assess the risk. Peace of mind and not having to do anything may be the result.

 

[maple1]

I had a circulator pump give up once - it just stopped turning. Not much or any warning - I just noticed one day that the water was running the wrong way through my system - my mixing circ was still going and creating a reverse (reduced) flow with the other one not running. So they do quit, and might not give any warning.

Is there any way you could wire it so the fan interrupt circuit also sends an interrupt to a normally open overheat zone valve at the same time? That would seem to cover all the bases?

 

[PassionForFire&Water]

As a manufacturer of indoor wood boilers we looked at a lot of options and different approaches.
One thing is for sure it cost relatively lot of money to come up with a "fail safe" system.
My personal opinion is that a small electrical generator is your best bet.
This is especially the case for cord wood boilers or any manual fed system, because they run a limited number of hours an a full load of wood.
Also a generator can be used for other things, besides powering your boiler system.

 

[maple1]

I think the closest one could come to 'fail safe' is not relying on electricity at all. When the power goes out, either the door on your draft closes from loss of electricity to hold it open or your fan stops from power loss, AND normally open zone valves open (the more the better) to allow natural water flow to happen through thermosiphoning. If you tie those valves into your regular heating zones, there should be more flow and the heat will end up where you want it anyway - the living space (although it might get a bit warm upstairs for a while). That is assuming a basement unit under heating zones though - if a shed unit, you'd need to plumb in as much radiation as possible as high as possible into a zone that might only get used for dumping. I would likely also plug my main circ pump into a UPS (with added batteries) if the dump zone is not high enough above your unit. I would not rely primarily on a generator - they need someone home to dig out, fuel up, plug in & get going - and even then are noted for not starting or running right if they've been sitting for a while or the fuel system picks up dirt.

 

[PassionForFire&Water]

I think the closest one could come to 'fail safe' is not relying on electricity at all. When the power goes out, either the door on your draft closes from loss of electricity to hold it open or your fan stops from power loss, AND normally open zone valves open (the more the better) to allow natural water flow to happen through thermosiphoning. If you tie those valves into your regular heating zones, there should be more flow and the heat will end up where you want it anyway - the living space (although it might get a bit warm upstairs for a while). That is assuming a basement unit under heating zones though - if a shed unit, you'd need to plumb in as much radiation as possible as high as possible into a zone that might only get used for dumping. I would likely also plug my main circ pump into a UPS (with added batteries) if the dump zone is not high enough above your unit. I would not rely primarily on a generator - they need someone home to dig out, fuel up, plug in & get going - and even then are noted for not starting or running right if they've been sitting for a while or the fuel system picks up dirt.

Hi Maple1,
I don't want to be a smart ass, UPS and batteries are nice, but you need to charge them and more important they cost a lost of money and maintenance.
Also, last weekend we had a power loss from Saturday 9:30AM till Monday 4:00AM.
I had 2 fully charged batteries keeping a small sump pump going for 16 hours, after that game was over, I still needed to go and rent a generator at the HomeDepot.
I didn't even had my wood boiler working on the batteries.
After last weekend I'm pretty much decided, it will be a generator with Thanksgiving that I will shop for.
$500 to $600 will buy me 6000Watts.
But I also need to admit that generators are known for not starting when you need them

 

[maple1]

Actually, I'm a firm believer in redundancy. So in this case, I would first plan the system to automatically without any user intervention cut the fire & open the zones with a power outage (my furnace does this now), then secondly have my main circulator on a UPS (they don't cost that much if using a small one and add on a car battery - circs don't draw that much power - just plug in and it will do the rest - you could put a plug on your circ and have a plug & play setup - it would charge any time the power is on and the circ is running - also no user intervention when the power goes out), then thirdly have a generator to haul out if it came to that (I also have a generator if needed). IMO, I think the biggest possible issue when the power goes out and there's a fire on is there being nobody home when that happens to deal with it - no doubt a generator is a very good thing to have, but unless you have a high dollar auto-start setup, it is useless if there is nobody home.

 

[ewdudley]

I think the closest one could come to 'fail safe' is not relying on electricity at all.

Yeah, a low-forward-resistance check-valve in parallel, or the Termovar/Laddomat loading units, set up with elevated adjacent storage is a nice simple high capacity solution if the situation makes it possible.

 

[Floydian]

I think the closest one could come to 'fail safe' is not relying on electricity at all.

Yeah, a low-forward-resistance check-valve in parallel, or the Termovar/Laddomat loading units, set up with elevated adjacent storage is a nice simple high capacity solution if the situation makes it possible.

Probably worth taking the extra steps to make it possible-period. I know it is for me as Varmebaronen requires such a setup.

Noah