Hot Water Heat Exchanger "Help"

[Martin Gray]

First the background; I've had a outdoor wood boiler for a few years now to heat my

house, shop and hot water. I have used this syphon flow heat exchanger for two years

now with no problem. Then I replaced the 60 gallon water heater with a 40 gallon tank.

Now when the hot water tap get turns on, it draws water strictly from the bottom of the

tank instead of the top hot outlet. The pipes did get replaced with pex so the lengths and

sizes are slightly different. What I can't figure out is why is the hot water supply pipe is

drawing water from the bottom of the tank, instead of the top, when it worked perfect

before?

Maybe someone can figure it out from this picture.

Martin.

[Ralph Day]

Martin,
Perhaps in manufacture the coloured plastic discs denoting hot and cold got put on the wrong pipes coming out of the tank?

How much thermosiphon action can you get if the tap from the heat exchanger is closed?:amazed:

Ralph

[Martin Gray]

Ralph, The hot water tank works fine on it's own, but when the valve from the heat exchanger is opened. All the water comes from that pipe, not from the top outlet on the tank.

The problem with that is, recently the wood boiler is only on a couple times a week when it's a little cold or damp outside.

So the exchanger isn't always hot but the water flow is always coming threw the exchanger from the bottom of the tank.

It must be in the configuration of the top hoses. Just trying to figure out why!

Martin.

[Ralph Day]

Hi Martin
I think you're right about the top pipe config. I have an Enerworks SDHW system and the ''loop" is below the hot water out to house. If you call for hot water as you are now connected the easiest route for water to travel is not down into the tank and out again...it's from just above the hot water out line, which is from the bottom of the tank.

A re-plumbing of the loop to below the hot water out line might help. Is there another line from the wood boiler that's not in the picture?

Let us know how it works out.

Ralph

[Martin Gray]

Hey Ralph,

I tried what you suggested, but the colder water from the bottom of the tank still wins the race.

I even used 3/4" pex for everything right up to the top, where it reduces to 1/2" for the main hot pipe.

Yes, there is another line from the boiler, entering the heat exchanger at the bottom.

I don't understand whats going on here, because I had this system working before on the 60 gallon tank.:wacko:

Martin.

[Ralph Day]

Martin,
Do you mean if there's no boiler heated water coming to the exchanger to heat your domestic hot water you get cold water coming up from the bottom of the tank through the exchanger? That would make sense. Or do you mean when you have the boiler in operation you still get cold water coming up through the exchanger and it is essentially unheated? That would make sense too.

My system has a check valve in the thermosiphon line. When you call for hot water the little plastic ball is pushed up and blocks the flow of raw cold water into the ts line. Unless the tank full of water is really hot, then the plastic ball doesn't always do that, and you get a shower of lukewarm or cold water (it's bypassed the checkvalve and run up to the hot out fitting and into your shower. I think the check valve is proprietary to Enerworks, someone's PHD work on the density of the plastic ball, it's size and a whole lot of other design stuff.

If your system worked on the 60 gallon tank (same top feed cold?), then maybe it's something to do with how far the heat exchanger is from the top of the tank. Are things in much the same position on both tanks? My 60 gallon tank has a bottom feed cold. The thermosiphon action is not fast on the solar system.

Maybe if you found a regular flap type check valve and put it in line below the exchanger it would let water flow in siphon, but when hot water was called for it would slam shut (up) and prevent bottom of tank water from passing through the exchanger until there was no longer any demand (then drop open again). This would only be a dollar or two investment , plus your time. Might be worth a shot. The principle is the same as my Enerworks checkvalve, but cheaper.

Ralph

[Martin Gray]

Ralph,
Yes, when the boiler isn't on there is cold water coming up through the exchanger unheated.
One difference between the old 60 gal. tank and the new 40 gal. tank, is the old one had a bottom feed inlet and the new one has a top feed inlet.
Maybe thats why it not working properly.

Martin.

[Ralph Day]

Hi Martin
If your 60 gal tank had a bottom cold water inlet how is your thermosyphon working now...is it connected to the drain outlet on the tank bottom?

Could you plumb the 40 gal tank like the 60, in that you'd cap the top cold inlet and use the drain opening in the bottom to inject cold water into the tank? Just be sure to allow for a drain tap down there for clearing sludge (probably less if the cold went in there). There'd be a ''t'' at the bottom for cold supply into the tank and cold supply into the exchanger.

Again, it's low cost, just your time and seeing if it works. If it worked that way before it'll probably work again. I think I remember seeing this setup somewhere before...using the tank drain as the cold water inlet allowing for a thermosiphon setup.

Good luck

Ralph

[Martin Gray]

Ralph,
Yes, it's connected to the drain outlet now.
Hey thats a good idea, capping off the top cold inlet & using the bottom drain for the cold inlet. Just like the old 60 gal. tank.
I'll try it. Thanks Ralph.
Martin.

[Ralph Day]

Good luck Martin,

If the direct capping of the top cold and using the drain outlet for cold inlet works, great. I'd try that before monkeying around with a check valve in the line, especially if it used to work that way.

A problem might be when the boiler is not running and you need cold water in the bottom of the tank. A shutoff valve at either end of the thermosiphon for when the boiler is not in operation is a must (in one of your pictures already?). I've seen water controlled solenoids on the web before...perhaps they could be latched to a relay dependant on the boiler operation? That way, when the boiler is in operation the thermosiphon is active, when no boiler it's bypassed. Or if you're like me, everything has manual control...less to go wrong and it makes me feel important!

Ralph

[Martin Gray]

I've worked out this bug in the thermo syphon exchanger.

I connected the hot pipe from the heat exchanger to the top of the tank where the

pressure relief valve is. So now the freshly heated water from the bottom of the tank

drops into the top of the tank. And doesn't get sucked directly out the hot water out hose,

along with the fresh cold water at the bottom of the tank.

It's kind of hard to explain but, IT WORKS!

Here's a pic to explain better.

[Ralph Day]

An elegant solution Martin. The black marker really helps one figure out what you're doing. I'll archive it in case I can't get a water heater with the cold inlet at the bottom next time. This should help anyone with similar situation.

Ralph