Circ Failure/Overheat/Automag question

[dogwood]

Say your primary circulator fails while your wood boiler is burning. How could you get a normally closed Automag valve on the overheat loop to automatically open (as it would in the case of a power failure) so excess heat would go into the dump zone. I've got a Tarm Solo Innova and I didn't find anything in the manual that addressed this contingency. Any ideas? Does anyone already have their system set up to take care of this potential problem?

Mike

 

[ewdudley]

. Any ideas? Does anyone already have their system set up to take care of this potential problem?

I've got an old Honeywell low-limit/high-limit "triple" aquastat on the boiler outlet.

There's a low-limit make-on-rise contact used to energize a pump on a parallel circuit. This circuit will come on in normal operation if the tanks get hot and the return temperature gets high enough, but is serves as a fail-safe for the main circ as well.

Then there's a break-on-rise contact that shuts down the draft fan on high-limit. I don't have an automag, just therm-siphon to storage in case both pumps fail.

This has worked well in testing; by disconnecting the main circulator under full fire, by closing off the boiler supply side ball valve, or by killing power altogether.

Since it probably wouldn't be convenient for you to add an extra circulator in parallel, I would suggest just a DPDT Ranco [edit: doesn't look like there is such a thing as a DPDT Ranco] or similar aquastat with the bulb on the boiler outlet pipe. It might work well simply to configure the Ranco in 'heat' mode, adjust setpoint to 200 degF or whatever, route the draft fan 120VAC power through one relay contact pair and the automag 24VAC power through the other.

Alternatively, it may well be -- same as most boilers -- that your boiler controls already kill the draft fan on high-limit, in which case you could control an RIB relay with the draft fan voltage and route the automag control current through that, so then if the boiler controller shuts the draft fan off the automag would lose power as well.

Also some solid fuel boiler controls have a high temperature SPDT relay alarm circuit that you could route the automag control current through.

--ewd

 

[dogwood]

Thanks Eliot. My boiler controls do have the high limit fan turnoff which kicks in at 212 degrees. I was thinking I might be able to tie into that circuit somehow with one of those RIB relays which could cut power to and open the Automag. However, since the high limit fan turnoff is set at the boiling point, I am a bit scared of what disaster might occur if the water was already boiling when the Automag opened the dump zone. I was thinking of something like 200 degrees, as you mentioned, as a good point to open the Automag. I like your idea about an aquastat on the outlet pipe to open the circuit.

I read a couple of old posts on the subject this morning:

Jim (Jebatty) suggested the following in an older 2008 post: "I added a surface aquastat to the boiler supply plumbing, connected the low voltage supply to the Automag to the aquastat, and set the aquastat at 210F. Now if at anytime the boiler overheats to 210F with power on, such as with pump failure, power is cut to the Automag and dump loop is activated. This does not affect the power failure activation of the Automag. "

In an October 2011 reply to Goosegunner on this subject you mentioned if using the draft fan circuit, "to pass FMEA you need a mechanical high limit aquastat in series with the draft fan motor". If I used Jim's idea, and went with a well-type aquastat not tied into the fan circuit, would that satisfy the FMEA. That way I wouldn't have to mess with the fan circuit at all. By the way what does FMEA stand for?

I am a little confused too, on what aquastat to get. I am assuming Jim used a SPST. I would think I think i want DPST aquastat, so if desired I could upgade to adding a parallel circ at a later date, as you recommended to Goosegunner. However you mentioned a DPDT Ranco to me so I'm confused on which type would work, or if DPST aquastats are even available for this use. There are so many aquastats on the PexSupply site, http://www.pexsupply.com/Honeywell-Aquastats-294000 . Would you or anyone be kind enough to recommend a specific model on that site or elswhere? Hope I'm making sense here. I'm trying not to screw this up. That recent post with pictures of stihlwoody's garage burning scared me and I want to make everything safe as possible. Thanks so much.

 

[ewdudley]

My boiler controls do have the high limit fan turnoff which kicks in at 212 degrees. I was thinking I might be able to tie into that circuit somehow with one of those RIB relays which could cut power to and open the Automag. However, since the high limit fan turnoff is set at the boiling point, I am a bit scared of what disaster might occur if the water was already boiling when the Automag opened the dump zone. I was thinking of something like 200 degrees, as you mentioned, as a good point to open the Automag. I like your idea about an aquastat on the outlet pipe to open the circuit.

If you feel you can trust your boiler controls then you should be OK to use loss of draft fan power to turn off the automag by de-energizing a 120VAC RIB coil to open a normally open contact when the draft fan shuts down. 212 is more or less the boiling point of water outside the boiler, but inside boiling point would be more like 230 degF if you have at least 20 psisg in the system.
( http://www.engineeringtoolbox.com/boiling-point-water-d_926.html ) So opening the automag at 212 would flow nice hot liquid water to the dump zone, so much the better for getting rid of heat. (If somehow the system were vented to atmosphere, as with the PT valve opening up, then there would be some angry and violent steam and water shooting out of the system, but then the whole point of the PT valve is to 'blow off some steam' before the unit blows up.)

If you would rather trust a separate aquastat, or want a lower setpoint, then do just like Jim did and use the normally open contacts of an off the shelf aquastat like a single pole double throw Ranco ETC-111000-000.

If you would like some redundancy you could use the boiler control draft fan power to run a DPDT aquastat, and then run the draft fan power again in series through one of normally open contacts and run the aquastat power through the other normally open contacts. I don't know who makes a DPDT aquastat (I goofed above when I suggested that Ranco made one; there's DPDT RIBs available but not DPDT aqusatats), you might have to use a SPDT aquastat and an auxiliary RIB relay if you wanted to get this carried away with it.

FMEA is failure mode effects analysis. Generally when there's an element of safety involved it's best not to trust microprocessor controls in dead-man-on-the-throttle situations. So like in a refrigeration unit, the computer is supposed to shut the compressor off if the head pressure gets too high, but this assumes the pressure sensor isn't lying and that the computer hasn't gone off in the weeds. In situations like this a redundant mechanical safety may be required depending on the level of risk.

 

[Clarkbug]

Just wanted to say thanks for making this post, as it made my brain work.

I currently have an aquastat mounted in one of the top ports of my boiler that is a make-on-rise Honeywell. Its set so that if I hit 205, it closes and turns on the biggest zone in my house to use it as a heat dump.

But Im also realizing that my automag valve has a set of contacts on it that would go to a thermostat to allow it to open. I am now going to connect the automag to this same aquastat, so that if I hit an overheat situation Ill have the house and the overheat loop as a dump zone. Might be belt and suspenders, or completely worthless, but its something.

 

[dogwood]

Thanks a lot Eliot. I think I will go with the separate aquastat as I am not sure the pressurized system would maintain the 20 psisg you say would be needed to keep things from boiling over. I'll looked up the Ranco ETC-111000-000, but it has a microprocessor contol like you point out one shouldn't in a "dead-man-at -the throttle" application. Is there a more fail-safe type of aquastat that might do the same job, or are they all pretty much the same?

Mike

 

[ewdudley]

Thanks a lot Eliot. I think I will go with the separate aquastat as I am not sure the pressurized system would maintain the 20 psisg you say would be needed to keep things from boiling over. I'll looked up the Ranco ETC-111000-000, but it has a microprocessor contol like you point out one shouldn't in a "dead-man-at -the throttle" application. Is there a more fail-safe type of aquastat that might do the same job, or are they all pretty much the same?

Sorry, I misread the table. It's listed as psi, which I took to be psig, but the table is psia. 5 psig gets you 228 degF, 10 psig is 240 degF, and 20 psig is 260 degF. So I wouldn't be concerned with the 212 setpoint of the boiler control.

In a perfect world it would be nice to have a break on rise mechanical bulb aquastat in the boiler outlet. I happened to have an old found-on-site mechanical aquastat from the dusty corners of our ancient basement, so it was convenient to put the aquastat well in the boiler outlet and that's what I went with.

But I can't say authoritatively that an electronic Honeywell or Ranco aquastat wouldn't be reliable enough for this application. The electronic ones are very handy and it seems like they ought to do the trick, it's your call.

In any event, the critical fail-safe is the draft fan shutdown. If you're springing for an extra aquastat I'd think you'd want to put it in series with the stock draft fan circuit and then use an auxiliary RIB relay to de-energize the automag. This way both the boiler control and the redundant aquastat would have to fail in an energized state before the draft fan would fail to shut down, which should be enough to satisfy most any design review.

Cheers --ewd

 

[dogwood]

Thanks for your advice and time looking into this, Eliot. I looked at the Solo Innova manual, found it has an extra well on it. I'm going to put a SPST break on rise, manual reset aquastat in it, set it at 210 degrees, run the 24 volt line to the Automag through it, and hope for the best. That seems foolproof enough if the electonic parr of the aquastat doesn't let me down. Wish I had a purely mechanical aquastat like you were able to dig up. Later on maybe I'll add a parallel circ fed from a relay on that same circuit. Thanks again.

Mike

 

[dogwood]

That's a good idea Clarkbug. If I put a back-up parallel circ in I thought I'd dump the excess heat into storage and/or whatever was calling for heat like the DHW or W/A hx, but sending it into the home directly might be a better way to go because the extra heat in the house would alert you something is wrong.

Next up is figuring out how to put a Laing circ into the overheat loop run off a trickle charged marine battey or maybe a UPS to ensure the overheat loop can really dissipate the heat it needs to, whether it be from a primary circ failure or a power outage. I don't trust gravity enough to do the job unaided.

Mike

 

[Floydian]

Hey Mike, hope all is well for you.

You must be getting close to firing up that Innova, as your figuring out your overheat system.

Looking forward to photos of your install,

Best of luck,

Noah

 

[Clarkbug]

That's a good idea Clarkbug. If I put a back-up parallel circ in I thought I'd dump the excess heat into storage and/or whatever was calling fot heat like the DHW or W/A hx, but sending it into the home directly might be a better way to go because the extra heat in the house would alert you something is wrong.

Next up is figuring out how to put a Laing circ into the overheat loop run off a trickle charged marine battey or maybe a UPS to ensure the overheat loop can really dissipate the heat it needs to, whether it be from a primary circ failure or a power outage. I don't trust gravity enough to do the job unaided.

Mike

This is actually from the Tarm diagrams. They suggest the aquastat tied into the house as overheat protection.

My loop in the basement was really only designed for a power outage, but I might as well use the automag since its right there, and I dont see the harm in dumping a lot of heat at once.....

Gravity is really only supposed to help you dissipate the heat after the primary fan goes out (power loss), so its assuming you are just dealing with the latent heat in the boiler. You are right that you would want a pump if you truly overfired the boiler or had the primary circ pump die on you.

Good luck getting things finished up!

 

[dogwood]

It's been a long haul Noah. The week after I bought the Solo Innova two years ago, I had to transfer jobs to Northern Virginia. Due to the recession the governor closed down all the correctional facilities in Western VA, including where I worked. I've only been able to get home on weekends, so the install has slowed to a snails pace. Just got the w/a hx in recently, the boiler room is framed in, the Solo Innova is assembled, and storage is in place. Plumbing and electrical are next, soon as it it warms up a bit. I have most of the parts, just need to find the time to get them in. On the positive side, at least our oak firewood has had the time to age properly and the boilers paid off. I'm hoping my wife can run the system while I'm away weekdays. Otherwise it'll be there when I retire five years hence.

Are you are up and running now? Like to see pictures of what you have going too. Good to hear from you.

Mike

 

[dogwood]

Clarkbug,

Has your overheat zone had a power failure workout yet? If so, how did it go? I was wondering how long it takes to dissipate the excess heat.

Mike

 

[Clarkbug]

Clarkbug,

Has your overheat zone had a power failure workout yet? If so, how did it go? I was wondering how long it takes to dissipate the excess heat.

Mike

Nope, not as of yet. *knocks on wood* I actually need to purge the line out tomorrow since I know that I have a bunch of air trapped in it. The way its piped into my system allows it to collect air right behind the automag, and Im worried that if the pocket is big enough, no thermo siphon for me. Not sure if I can get something in there to allow for venting or not, but hopefully this will be the last little bit of air in the system, since I have been up and running for three and a half weeks or so.

 

[dogwood]

Good luck with getting that last piece of air out Clarkbug. I am curious how would you have piped the automag differently to avoid the air pocket problem? What about the piping arrangement causes air to collect there?

Mike

 

[woodsmaster]

For those of you that havn't tried your overheat protection what are you waiting for ? a power outatage ? just turn the
power off and try it allready. You don't want to test it durring an actual outage.

 

[Clarkbug]

Thanks Mike.

The Varmebaronen has three ports directly on the top of the boiler, as well as two on each side. I piped my overheat loop directly off of the top of the boiler, so any air that is getting pushed back from my house seems to collect in the small riser pipe there. I have a spirovent on the outlet of the boiler, which I think helps with the small bubbles. For the large air pockets, they seem to end up in the overheat loop. This has mostly been from my playing and not doing an adequate job of purging out my zones first.

In hindsight, I wouldnt change anything about the piping arrangement, but I would add in an automatic air vent on the elbow leaving the boiler. Hopefully once the air is gone I wont have to deal with it again.

 

[Clarkbug]

And an update on this idea...

Not going to connect the thermostat connection points on the Automag to my overheat Aquastat. I currently have that aquastat connected to my Taco zone controller, and the wires are landed to the same terminals as my thermostat for my house. As I was getting ready to tie-in the Automag, I felt that little tingle of voltage, and it clicked in my brain.

The zone control is feeding voltage out to my house thermostat, and the Automag feeds out voltage on its thermostat terminals. I figure its not a good idea to feed voltage back into my zone controller, so no interconnection for me.