Troy Smith

Oh, a temperature mixing valve, yes those are already installed in multiple places in the system.

Good points Rufus,

Our system is not open, it's pressurized. What I thought that open meant was that the fluid going through the boiler is actually the water that will eventually come out of the faucet, as opposed to a contained separate fluid like the solar heating loop.

Great point about the possibility of poisoning from a leak in the solar loop, I hadn't thought of that! I'll have to check with the owner about what exactly is in there. We don't usually consume the hot water due to it being nor difficult to keep clean of bacteria and such (the whole system is fed from rainwater catchment). We do shower in it though.

I'll do some googling on "thermostatic tempering valve", I don't know what that is.

John, at Dancing Rabbit Ecovillage, near Rutledge, MO.

Irene, no sensors currently, but we need some, and a controller. That's a separate issue though, and i don't want to chase that tangent in this thread. I'd be happy to elsewhere though!

Travis, up-sizing everything would be a bugger of a job, i doubt the owner would go for it. Also, i wonder if that would work if there were still a couple of spots that couldn't be upsized, like the fittings at the boiler and the water tank? And again, what if it doesn't work? It would be a lot of effort and expense.

I really lean toward an electric pump because I think it's the thing that is most likely to really work. However, i'm not sure what are best practices to make it as safe and functional as possible in the event of failures or power outages.

Moving the tank could be a pretty big job, it would require changing a fair amount of plumbing... i'll look at it and consider that. I'd be afraid that we'd make the effort and still not have satisfactory results. It would be nice to keep it simple and passive though.

There is a mixing valve on the hot tank output that controls output temp to the hot water system (and a separate one controlling output temp to the floor tubes) so that the water in the tank could be very hot but still only 120 coming into the fixtures.

Floor tube pump is operated by a wall switch.

The boiler circulates the actual water in the tank, there is not a coil or heat exchanger, i believe that's called an open-system, right? The solar tubes circulate through a coil in the tank, indirect heat. They use an antifreeze mixture to prevent damage in the outdoors parts of the system.

Thanks again for the feedback

High everybody, thanks for the feedback so far. I'll try to address all the questions.



The stove is fairly new, it's an Esse Ironheart. The boiler is indeed a tank style (as opposed to coil) on one whole side of the firebox.

The tubing run is copper, 3/4 or 1" i think. It has several bends including basically a 180 and has a very flat total rise/run ratio. The tank is a Superstor Contender 50 gal. It's not very high off the ground and that may be part of the issue as well (that the tank is not much higher than the stove). The tank is only a few feet away from the stove.

There are multiple TP valves and expansion tanks in the system, so it should be reasonably safe. It's still quite disconcerting though when it boils over and we certainly try to avoid it.

We are grid tied and have solar power as well, however, it's still not assured that we'll always have power. Whatever we implement must be safe without electricity.

We also have evacuated solar tubes outside that heat a coil inside the Superstor hot water tank (when they're not pumping cold fluid, but that's for another post).

There is no thermostat or controls.

If we need to dump heat we can run the radiant floor system or just run hot water at the taps, most of the time though, we don't have enough heat.

I'd love to be able to get the tank temperature up in the 160-180 degree range, so that we'd have a greater quantity of usable hot water and also the tank would stay hot longer, also we could use the radiant heat more. Some of the other buildings here have very large water tanks that they heat up to 160-180 with big wood fired boilers.

I think the system has always worked this way, the owner and past tenants have mentioned it happening to them.

I wonder if we have a poor/weak thermosiphon due to low-ish tank height, kinky plumbing, and/or other issues. Is thermosiphon force proportional to the temperature differential? It seems like the water warms up reasonably well from room temperature up to 100 or so, but then it's much slower to get it warmer beyond 100. Perhaps as the water in the tank warms up, the thermosiphon force is reduced because the temperature differential becomes lower. This effect could be something of a downward spiral to the point where the water is barely flowing from the boiler, and since it's spending a lot of time there, it gets overheated and that's how we wind up with boiling water in the hot part of the system even though the storage tank temp is quite low (120 maybe).

Possibly relevant is that in the summertime the water is heated by the solar tubes only, and I'm not sure i recall it ever getting much above 110-120 then either. That system is actively pumped.

Would installing a 120VAC pump on a control that ran when the boiler is hotter than the tank work well and be safe? It would need to not substantially impede the water flow when off, so that the system would be safe during power outages.

I have a woodburning cookstove with a boiler insert on one side that is plumbed to thermosiphon into a hot water tank. It works but not as well as i'd like. It does pretty well at getting the water tank up to 100-110 degrees, it will eventually get it up to 115-120, but really struggles to get the tank higher than that. The water coming from the boiler to the tank is often around 140 but can be higher (i've had it up to 220!).

One major indicator of our problem is that the TPV release valve will start sputtering because the water is overheating in the boiler, but the water in the tank will still only be 110 degrees or so!

This leads me to believe that the thermosiphon is not performing well and that if i could get the water to circulate more quickly from the tank to the boiler and back, that I'd end up with cooler water (not overheating) in the boiler and hotter water in the tank. What do you all think?

I wonder if installing a pump would do the trick, and if so, what kind of pump, how to install it and how to control (automate?) it and keep everything safe and reliable?

PS - This is not my house, i'm renting it. The house is somewhat experimental and the owner is open to making changes / improvements.

Thanks!
Troy
Dancing Rabbit Ecovillage