water to water HX fouled?

[mgp141]

I've got a Polar G3 OWB and Baxi propane backup feeding an air handler and in floor heat. When propane is on the Baxi provides about 150degF at the in floor hot manifold. With the G3 running I'm only getting about 90 degF at the in floor hot manifold, it hardly keeps the house at 22 degreesC.

From the OWB water is 190degF. It comes into the water to water HX at 172degF and out at 144degF. The HX send to floor loop is 92degF and HX return from floor loop is 77degF.

Does this indicate the HX isn't providing enough heat transfer between boiler and indoor loops?

I've got grundfos ups15-58fc pumps on both loops.

 

[warno]

When did this problem start happening?

If your OWB is at 190°F how are you dropping to 172°F before hitting the plate HX? What is in between the boiler and HX to lose 18°?

Do you know roughly how many gpm you are flowing through the loops?

It sounds like you have a flow issue but I could be alot of things. How difficult would it be to pull the HX and look into the ports?

 

[TCaldwell]

What are you using to measure temps? Is that 150deg out to the floor? Not knowing underground pex size or distance, seems like the 15-58 could be undersized. Did this just start happening?

 

[mgp141]

This is our first winter in the new (to us) house. The drop is from the lines from the OWB to the house. I suspect poorly insulated and not deep since we are on bedrock and a part of the route is first to melt snow.

I don't know how many GPMs are flowing through the loops. Shouldn't GPMs be fixed based on the pumps? HX is soldered in with all copper so would require quite a bit desoldering.

 

[mgp141]

There are temperature gauges on the OWB water jacket and on the hot and cold manifolds in the house. I was actually using a digital meat thermometer to obtain the other temps which I compared to the temps on the hot and cold manifolds and was within a couple of degrees.

 

[maple1]

150 is most likely too hot for a floor supply.

Pictures of everything will help, for starters. And likely more system details.

What speed are the circs set at?

 

[mgp141]

Here are some pictures and a detailed but messy diagram of the system.

Both pumps are on speed 2 (out of 1,2 or 3)

 

[warno]

Holy couplers and elbows batman!

That's kind of confusing. So the circ tucked behind all that plumbing is the OWB circ? How far from the home is the OWB?

 

[maple1]

Good lord. Dont think I'll be much use figuring that out. Yikes.

 

[Eureka]

 

[maple1]

You said it feeds an air handler, and infloor.

But if the OWB heated water doesn't go to the air handler before it gets mixed for the infloor, which I think your diagram is showing it doesn't, IMO there is a design flaw. Your mention of oil heated 150 water going right to the floor (I think that's what you said) also raises a design flaw flag.

Are you sure your diagram is right? Can't get my head around how that would work, with 3 different types of system emitters which should all need different supply temps, looking like they're being fed by the same water. Of maybe there are other details not drawn on it that would make sense.

Aside from that, if the HX isn't transferring heat to the inside system, that would be the first issue, yes. But I'm not sure it isn't, with the way you worded that temp info & all the stuff that looks like is between the HX & the infloor manifold & other parts of the system.

What are accurate temps, of OWB water going into & coming out of the HX, and system water going into & coming out of the other side of the HX?

 

[Woodman1]

Who ever plumbed that should be taken out behind the woodshed! How the heck do you ever get all the air out let alone change a component!? Start with an accurate reading from wood boiler to first heat exchanger. I hope you are not really loosing 18 degrees to he ground.

 

[maple1]

a part of the route is first to melt snow.

OK, missed that - the HX not transferring isn't the first issue. This is - underground lines transferring heat to the ground. HX transferring or not would be second behind that. If you want to use this OWB in years to come, new underground lines should be in order for this summer. Hope they aren't long - the right ones are in the $10-20/foot range. And make sure they are sized right. Which brings another important point - are the current ones and the circulator sized right? How much underground do you have & what size is it? With a big OWB burning a crap load of wood, you might be able to overcome the heat loss to the ground with brute force and a lot of wasted wood, but you would need to be moving a lot of water to the house. Which I doubt is the case with a 15-58 on speed 2. Without knowing anything about the loop.

 

[warno]

I looked up the polar G3 OWB it seems to be a decent burner.

Here it is if anyone wants to see

If you are burning good dry wood I don't believe the OWB does have any trouble keeping you warm.

With that said I would definitely like to know the length of the underground run and what kind of underground lines they are. If you are losing your first 18° to the dirt you are fighting an up hill battle from the start.

I believe all that plumbing could be simplified pretty easy. But it did take some time on your end. And I wouldn't recommend doing it until spring. But your OWB should feed your FPHX on one side then simply tie it in line with the other boiler loop.

I would think you could get away with 1 circ and a couple zone valves inside the home. One zone being your air handle and the other running through a mixing valve to your floor heat. Unless the in floor is really long, then maybe a second circ. I believe most concrete should only see 125° max. That is simply based on reading though as I do not have any first hand experience with that.

 

[mgp141]

I've attached a more simple drawing with the recorded temperatures at each location. Length of underground is maybe 60 feet if not less of 1 or 1 1/4". Again I'm not sure how well insulated.

We havent been going through much wood heating about 2000 sqft (about 1.5 Ford since mid November but hitting this real cold snap seem to have trouble keeping up.

I think I'll re work the plumbing in spring as itll br the cheaper option than replacing underground but might consider both options. I just though heat transfer across the PHE seems low and that was a main issue.

I increased pumps to speed 3 but no real improvement.

 

[maple1]

That is a low transfer but not sure why. Flows play a part also.

Do you know how old the HX is or how long it has been since it was cleaned? I'm not seeing from the pics an easy way to clean it. Or even isolate it to pull it out for cleaning. Another reason for a re-plumbing. You might have to get through the winter as-is. If you up the OWB circ to speed 3 and lower the other one to speed 1 that should change some numbers. If the numbers don't change, it might point more to an HX problem.

 

[mgp141]

I can only assume it's original (2002-2004) and never been cleaned based on your observations above.

I could put the system back on propane but I'd be relying on the two 3way valves for isolation and who knows how well they are sealing or if they are passing.

If I were to replace the HX would it make sense to go with larger area plates or more plates?

 

[maple1]

I can only assume it's original (2002-2004) and never been cleaned based on your observations above.

I could put the system back on propane but I'd be relying on the two 3way valves for isolation and who knows how well they are sealing or if they are passing.

If I were to replace the HX would it make sense to go with larger area plates or more plates?

That looks like a pretty big one in the picture so not sure a bigger one would do more. Bigger is better with these things but looks like you might be there already. Any numbers on it?

Given the piping arrangement, you might be just as well to carry on through the winter as you are - at least the OWB is giving the house some heat?

And ya that is a long time for a plate HX to be in service without being cleaned. When/if you do get around to tearing into things, lots of isolation valves and boiler drains should be added so you can easily flush it by hooking hoses up & turning some valves. Then no need to take anything apart.

Others could hopefully give input on the recipe of stuff to give it a good cleaning with.

 

[peakbagger]

About 30 years ago I used to have to mess with large plate and frame heat exchangers and I learned to hate them. They look good on paper and have great efficiency but they are designed for very specific velocities, too high and they have a big pressure drop, too low and they plug. These units could be taken apart to be cleaned but they were a PITA as there were multiple plates with differing designs and each one had to go in the right place. There were also all sorts of gaskets. I learned to appreciate shell and tube units as one set of flange bolts and they could be waterblasted. My absolute favorite heat exchanger was spiral heat exchanger but they weren't cheap and I don't think anyone makes small cheap one.

If the heat exchanger is plugged its probably some sort of lime scale. You can try Acetic Acid but the stuff to use is diluted sulfamic acid preferably heated with a circulator pump to circulate it through the heat exchanger. Make sure you have the right equipment to pump it and the right safety equipment. You definitely need ventilation.

 

[warno]

I'm curious about what looks to be a mixing valve on the house side of the FPHX. Just after the HX in between the supply and return. Is that what it is? If so I wonder if it's mixing your supply water down to 92°. I mean that's probably ok for your floor heat but that WAHX in your duct work is going to want better than that.

 

[mgp141]

I've isolated the mixing valve but I think it is part of the issue.

 

[warno]

Do you have an IR temp gun? Even a cheapo harbor freight one will do. Take some flat black paint and paint a 1" stripe on the pipes indicated in this picture. Then hit those lines with the temp gun.

If you can get an accurate temp read there then you can see if your mixing valve is leaking past into the supply line.


I really find it strange you are only getting 92 out of the hx when you're feeding it with 170ish unless that thing is plugged about full.

Also because it will be quick and easy switch your "in home" circ to speed 1 and your "OWB" circ to speed 3. See if slowing down your in home flow will give a higher delta T.

 

[mgp141]

The ball valves next to the markers you've drawn are both closed to remove the mixing valve from the equation (hot and cold leg of mixing valve).

I've swapped the pump speeds to owb on 3 a and in home circ to 1. I will report back once temp stabilize.

It's been -29degC for the last couple of days so maybe not best time to troubleshoot

 

[warno]

@mgp141 I see the valves are shut. I'm just wondering if the seals are leaking past and letting cooler water into the supply line.

 

[E Yoder]

I've found "The Works" toilet bowl cleaner does wonders on mineral buildup in a flat plate. Cheap and available at Walmart.