heat exchangers and OWB

[Go Figure]

Good afternoon gents, i just installed a 50 plate heat exchanger on my Royal 6200 boiler, my supply temp coming in from my wood boiler is 180 and my discharge temp is 120, but my supply water going into my house boiler is only 125. Shouldn't my heat transfer be a little greater than that? My heat exchanger is 5x12 and installed in the vertical position. My pump for my wood boiler is on the return side. Am i missing something?

 

[maple1]

Possible air lock on boiler loop?

 

[E Yoder]

I agree, pulling water on the return is a good recipe for an airlock.

Would need more info like pipe sizing and distance from the wood boiler to FPHX to troubleshoot further. Flow rates might be low...

 

[E Yoder]

Make sure FPHX is counter flow.

 

[maple1]

I agree, pulling water on the return is a good recipe for an airlock.

That's not quite what I said - I was more thinking about just not getting all the air out on re-start. Both my circs pull on return - loading unit & zone circ - with no issues.

Is this a new setup, or more changes made - or is it just an exchange of HXs where one was working good in the same spot before?

 

[E Yoder]

That's not quite what I said - I was more thinking about just not getting all the air out on re-start. Both my circs pull on return - loading unit & zone circ - with no issues.

Is this a new setup, or more changes made - or is it just an exchange of HXs where one was working good in the same spot before?

Sorry, I misspoke.

My thought was if his OWB is an open system (which I think it is) the return pumping would tend to be more of a problem with negative pressure in the lines causing air to come out of suspension. Cavitation issues.
Maybe I missed something though.

 

[Go Figure]

Hears the deal guy's. Great reply's thank you. I installed my Royal 6200 like 5-6 years ago, it is a pressurized system. When the guy that sold me this unit showed me the heat exchanger for it i thought no way that thing will heat my house, so i piped it directly into my boiler. It's been working great except this year i started having air issues, i have an air scoop on my supply line coming in from my owb so i would think that would take any air out of my system. So i decided to go with a 50 plate heat exchanger (5x12) and was hoping that would take care of the issue but like i said the exchange is way off, not sure y. I have 1 inch lines coming in from the owb, and it's 25 feet from the house. Supply water comes into the bottom of the heat exchanger goes out the top, return from the house boiler is opposite.

 

[maple1]

Still sounds like an airlock.

 

[E Yoder]

Sounds like low flow rates. Air lock like maple1 said sounds probable to me too. A couple times I've seen a rotor on a circulator break off and just barely move water. Will drive you nuts. Could you turn a valve somewhere to see if you can tell if you've got good flow?
I was wrong on the open system. Oops. Where does the wood boiler expand? Ideally the circ would pump away from that point. Dan Holahan's "pumping away " principle.

 

[maple1]

Don't think I would have introduced an exchanger into a closed system that had been working OK for 5 years - not seeing how that would have helped with air issues that arose this year?

Just throwing ideas out - your 'air issues' could have been caused by a circ getting tired - flow rates dropped & the water was no longer moving fast enough to move the air out to a vent. If that same circ is still in place, it's still causing you problems. Or, whatever caused the 'air issues' - is still causing you air issues. Kind of a coincidence if both issues aren't related.

We don't know much about your system though, and what exactly those 'air issues' were....

 

[E Yoder]

I assumed that the flat plate was added because the
OWB was run at atmospheric pressure. If both boilers are pressurized units what purpose would the heat exchanger serve?