AutoMag valve

Constantin

I'm just a homeowner myself, but let me throw out a couple of ideas.

It seems to me that you are basically trying to build a gravity water system to dissipate whatever excess energy your boiler will build up in case of a power failure. That may work quite well, depending on how the valve is set up.

One concern though is the pressure drop that the valve develops. Gravity hot water systems rely on very low pressure drop and even a large valve with big passages might be a insurmountable hurdle.

Another option could be to have an air shutter that guillotines the air supply shut whenever a solenoid doesn't hold it open (simple electromagnet). That could produce some nasty combustion products though.

Yet another simple solution is to put your whole heating system pump array on a big inverter/UPS that can power it for long enough to let the wood burn itself out.

Have you contacted the manufacturer to see what the effects of firing the boiler w/o a load are? Perhaps the design is meant to use the PRV on the few occaisons that this happens.

Eric Johnson_3

AutoMag valve

First, please pardon my ignorance of the terminology of what I'm going to describe, and also my ignorance in general.

I have an indoor wood-fired boiler set up in an insulated room in an outbuilding. Hot water is pumped to a heat exchanger in the basement of my house with a Grundfos 15-99 circulator (big one). Given that the boiler is above ground level and about 100 feet away from the heat exchanger in the basement, I'm pretty well screwed in the event of a power outage or pump failure, especially if the boiler is full of wood.

To help remedy that, I piped a loop in above the wood-fired boiler leading into a couple of old cast-iron radiators in the barn attic--only a couple of feet directly above the boiler. If there's a problem that I know about, I can go up into the attic and open two ball valves, allowing the boiler to (hopefully) dissipate enough heat through convection to keep it from overheating and/or opening the PR valve.

Concerned that a power outage or pump failure might happen when I'm asleep or not around, I picked up an AutoMag "normally open" valve that I was hoping to wire up to the pump circuit so that it would open the loop up automatically in the absense of power.

Unfortunately, I read the instructions when the valve arrived (Ebay), and it says it has a "system head" limit that is exceeded by my pump. I take it that "head" has nothing to do with pressure and everything to do with flow rate. Since the AutoMag would go on what's basically a dead-end appendage to my system, would the head limit still apply? Maybe this is an obviously stupid question, but do you think the AutoMag will fail if I try to install it as described? And what is "failure" anyway? Will the vavle just jam open?

Thanks.

Eric Johnson_3

thanks

Actually, it seems to work pretty well the way it's set up now when I open the isolation valves. The radiators get pretty hot and I could always add more radiant capacity if I found out it wasn't getting rid of enough heat quickly enough. So far, I haven't had to use it under actual battlefield conditions.

What would happen if the pump quit pumping and the gravity loop valves weren't open would be that the pressure in the system would build to 30 psi, the PRV would open, domestic water would feed into the system and that routine would continue back and forth until the fire burned down. Unfortunately, all my glycol would wind up on the boiler room floor.

I like the idea of the battery backup. Probably should have just done that first. How long do you think a $100 computer battery backup unit would run a circ pump like the one I've got?

Constantin

well,

Here is the issue: It's not just the 135W of the 15-99 you have to take care of, you also have to move the heat inside the house. There are plenty of UPS's around that can handle 135W, but I'd be careful to get one that not only is compatible with large electric motors but that can last a while under those conditions. Such a UPS is likely to cost a lot more than $100.

Eric Johnson_3

true enough

True enough. That's a 15-42 to pump water through the heat exchanger and one or more circs on the zones to distribute the heat up into the house. That sounds more like a generator.

Which brings us back to the $35 AutoMag valve/cast iron radiator alternative and my original question.

Constantin

Just be careful...

but if its just $35, why not install it as you think you ought to, followed by a test? Bringing in a HVAC-tech familiar with this kind of a setup might help unearth some previous "experiences" before they cost you a lot of money (or life and limb). Any feedback from the manufacturer re: your proposed idea, BTW?

If the valve is not in the path of the water flow and the pressure drop through the boiler is very low, I doubt that the valve will see a lot of suction or pressure. If the system as installed is safe under all conditions, i.e. dumps when overheating, I see relatively little potential for mayhem.

Another thing to consider though is what happens when the valve comes back on. If the boiler is toasty hot, hopefully there isn't a lot of PEX tubing on the way to house waiting to get fried. In other words, be sure that the system cannot damage the balance-of-plant once the power comes back on.

Since this is a glycoled system, is it closed or open to atmosphere? If open, are ALL components that touch the glycoled water made of materials that can handle being washed with hot, oxygenated water? This includes the Mag-Valve!

Eric Johnson_3

Now you're talking

Now we're getting somewhere.

It's a closed loop, 1" copper, pressurized system. No Pex or anything exotic. The Mag valve looks like brass to me. Sweat fittings.

And you're right, the gravity loop just tees off the supply and return lines. No flow when the ball valves are closed.

I'm not sure what you mean about pressure drop through the boiler. It generally runs between 15 and 20 psi. I've got pressure gauges at both the boiler and the flat plate heat exchanger and they read the same. Water temps are variable between 140 and 180.

You're also right about it not costing too much to try it out and see if it works, except I thought I'd try to find out if it's obviously a bad idea before I partially drain the system and solder it in.

I assume since the instructions say not to exceed X amount of head, the mfg. would say it's a bad idea as a matter of policy. Trying to explain this application to them would probably be an exercise in futility, in any event.

Thanks for your time and suggestions. I'm open to any and all.

Constantin

Actually,

I meant did you get any response from the boiler manufacturer?

As for the pressure drop, my point is that the pump in the house is pumping away at the 1" pipe and the boiler in the loop. If the boiler has very little internal flow resistance, then the water getting pushed by the pump will always preferentially go through the boiler instead of pushing against the valve. It follows the path of least resistance.

On the other hand, if there is a lot of flow resistance through your boiler, then it'll develop considerable pressure drop, which is the "head" that your valve will experience while the pump is operating (I'm assuming that the radiators are piped off the supply and the return of the boiler). Most wood boilers seem to have very little flow resistance due to wide flow passages...

John Martin

Automag Valve and power loss

I think the automag valve is the way to go.

head is the pressure, roughly 2 feet of head equals 1 psi of pressure. The head rating in the automag valve deals with overcoming that back pressure, since it is installed so that the solenoid valve fights that pressure. If it's not installed in the loop with the pump, that pressure is negligible.

The automag valve drops open on a power out. It is ideally suited for just this sort of operation.

I speak as an "expert" from the last oil crisis, engineering for a now gone outfit called Woodheaters Supply Company back during the "Arab Oil Crisis" years. I used a lot of automag valves, and even in a zoned powered system with the boiler in the basement, they usually allowed enough circulation during power out to keep the boiler in check.

I also just had my wood boiler overheat in a power out, and blow the PEX to the house, dumping all coolant and damn near burning down, causing enough noxious gasses and acids to be produced from the propylene glycol that I had to perform a pretty formal waste cleanup to not hurt somebody. I wish I had gotten around to installing a dead drop zone like you propose before now. It'll be done within a week or so.

hope it helps
John Martin