Heat not transferring to secondary loop

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Old 11-08-15, 09:15 AM
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Heat not transferring to secondary loop

Morning all,

Well after what I thought was going to be a good improvement, it appears something is still wrong. To fix a return temperature problem in a gravity conversion i re-piped it for primary/secondary. Problem is everything appears to be pumping and warming up as expected, but the heat isn't transferring into the secondary loop. Everything gets hot right up to the supply tee but the DHW loop only warms to about 90 degrees. Ditto for the heating. Return temp below the ESBE hovers around 130-140. The boiler shuts off at 180 but continues to tick up in temp eventually tripping the reset at 200. I.e. all that heat isn't going where it's supposed to.

Thought 1: It's a circulator sizing issue.
Thought 2: The horizontal primary meeting the horizontal secondary isn't proper thermodynamics and i have a bit of a heat trap. The basement has a low ceiling complicated with tight clearance below the old gravity mains, but my thought was to lower the top of the primary loop 6" and elbow up vertically into tees.
Thought 3: The near piping on either side of the tees should've been upsized to 1-1/2" to better accommodate the pressure drop and/or reverse flow.

Any help or other opinions are greatly appreciated. Thanks all.

Winter is coming.



 
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Old 11-08-15, 11:06 AM
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Step back and take some pictures of the whole piping layout...I don't see any pump on your secondary piping loop, there is one , isn't there?
 
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Old 11-08-15, 11:32 AM
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No problem, here you go. These were taken prior to adding the globe valve at the ESBE.

 
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Old 11-08-15, 08:00 PM
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Beer, would it be possible to draw a diagram of what you've got?

Doesn't have to be fancy, just something to untwist all the pipes in the head.
 
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Old 11-08-15, 09:01 PM
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You bet. In a nutshell I'm this first pic only with DHW thrown in. All pipe is 1-1/4". Bottom pic is an overlay of where it currently sits. I didn't diagram the expansion tank, scoop, etc. but of course they're all present.



 
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Old 11-11-15, 08:28 PM
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Well I believe I've uncovered at least part of the issue. I was trying to merge onto the interstate at 60mph during rush hour...

The heat loss is 87k, the existing rads EDR is just below that @170 degrees, and the boiler has a DOE of 108k. Using the GPM+BTUH/(dTx500) gives me a target flow around 8-9gpm and the recommended upsizing from Dan Holohan and others gives a target around 12gpm since it's a gravity conversion and we need to keep things moving a little faster.

After re-running the head loss numbers as expected their all very low, but this time I did an exact inventory and spreadsheet to find out for certain. Primary is 1.70 total head-feet, Secondary loop is 5.77 (higher than the 3.5 rule of thumb on my system anyway) and the DHW loop portion, since it's set to priority and tees off the the secondary loop, was 2.49.

I had an extra 007 circ (no flow check) that came with the boiler and figured, hey, the primary doesn't really need flow check. So that's what i used "knowing" that it was in the 12gpm range with low head. And of course it's not. The 007-IFC is. At 1.70 of head I am likely moving approx 21gpm around the primary loop, and probably with laminar flow issues because that's exceeding the velocity for a 1-1/4" pipe!

So I also have a spare 007-IFC laying around. I'm going to swap that for the primary circ., leave the 007-IFC for the DHW circ, and keep the 015 on medium for the Secondary loop, although it looks like a 010 at medium would be a better fit. Wish me luck.

 
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Old 11-12-15, 07:53 PM
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I would have kept it simple and just done p/s and restricted the flow though the partially closing down the supply valve to a 30 -40f delta-T. Works well on those low return temp boilers from Burnham. I know where there are about 8 or 9 on gravity hot water jobs for years and no corrosion on the iron.
Heat loss of 87K means the system requires between 8 & 9 GPM and the boiler needs 5-10 GPM.
I was really confused by all your talk of P/S due to you referring to the boiler piping as primary when it is in reality secondary piping. Keep in mind the primary pipe is always the run of the tee's and the primary also has the blend area where the primary flow and secondary flow mix together.
The only rule for the secondary is the piping that comes off the side or branch of the tees is always secondary.
We could make this very interesting and discuss the primary and secondary pipes can move dependent on what pumps are runnig and what is in demand. Or even worse jobs with multiple primary secondary systems running at the same time.
 
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Old 11-13-15, 06:24 AM
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If you have NO flow getting out of the boiler loop, look at the piping around the esbe valve. If they are not piped properly they will block flow.
I have also found that they can air lock easily.

I would not be to concerned about flow rates ATM, sounds like you getting NO flow around the boiler. Check that this circ is getting power, ensure it's not airlocked, even visually check that it does spin when power is applied. I have seen broken shafts on wet rotor circs, so a visual check will verify this.

Proper primary / secondary piping would have allowed you to have a low boiler delta T and would have been simpler than what you've ended up with
 
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Old 11-15-15, 12:55 PM
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Thank you rbeck and TOHeating for weighing in.

I was really confused by all your talk of P/S due to you referring to the boiler piping as primary when it is in reality secondary piping.
You're absolutely right. Sorry for the confusion. In my head I had been associating the heat loop off the boiler as "prime" when it really depends on who is teeing into who.

I have also found that they can air lock easily.
I think you may be on to something here. I don't have a proper purge valve upstream of the ESBE, only downstream. I'll fix that and bleed it at the thermostat as well. For that matter I think first I'll double check that it's even opening at the proper temperature in a pan of hot water. I've read about others that have had faulty elements that didn't release above 140 degrees. I'll double check the circ too.

After that all checks out I'll re-purge the lines and try throttling each circuit to slow the flow a bit if necessary.

Proper primary / secondary piping would have allowed you to have a low boiler delta T and would have been simpler than what you've ended up with
Can you elaborate on what you mean?

Thanks again!
 
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Old 11-17-15, 05:05 PM
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with P/S piping you hydraulically separate each loop.
Therefore it is possible to set up your flow rates in each loop to control the mix point at the closely spaced TEE. This can be set to temper the water out to the load, or it control return water temp to the boiler.

If you had a CI boiler (100,000 btu) with a primary loop flow rate of 20 GPM, this would give a delta T of 10 F. if you tee in a load of 100,000 BTU with a flow rate of 10 GPM (20 degree delta T) then the boiler return would be hotter then the load return.
Make sense ?
You can trim you flow rates to give you the system caracteristics you need, with in resonable limits>
 
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Old 11-19-15, 08:02 AM
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It does, thank you. I think I'll be swapping out the ball valves for globe valves currently on the hot side of the supply loop and the one in front of the air separator on the primary loop to get better fine tuning of the flows. I tried throttling with the existing ball valves but by the time I started to get heat flow into the circuit loop the 007 was cavitating. Hopefully stepping it down with the spare 007IFC i have should get me close to a 12gpm starting point instead of 21.
 
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Old 11-20-15, 05:20 PM
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the valve change is not going to make that much of a difference for the cost and labor. Resistance is resistance.
 
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Old 11-20-15, 05:28 PM
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10-4 rbeck. I was thinking about that today. I wish i would've used globe valves in those locations but i think first i'll try slowing the flow with the ball valves. Only wish i'd taken the time/expense to use shut-off flanges on that boiler circulator now. Live and learn!
 
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Old 11-22-15, 04:09 PM
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Thanks all for helping out. The imbalance of the pump flows was the underlying problem. I swapped out the boiler pump, purged everything, and it's cruising along exactly that way it's supposed to! When heating the house it hovers around a 163-165 degree boiler temp with 140 degree return temp and all valves wide open. Brought the DHW tank up to temp in short order as well. No banging pipes, no condensing...It's beautiful!
 
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