Boiler Temp & Gravity Conversion

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  #41  
Old 01-07-15, 09:19 PM
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Thank you NJ Trooper & Lawrosa for taking the time to weigh in! The wise seek wise council, and you guys definitely know your #*%&. PM me a cell number to paypal some beer money if that's all within the site rules

A picture's worth a thousand words so after some head scratching and consideration of how to best "get it right" for the long term I've come up with the following. The re-piping really isn't more than a half day's effort not including the downtime for draining, refilling, etc. etc. The primary/secondary setup just makes sense when you're expecting a little 4 gal capacity boiler to heat 70gals of water over the 130 degree mark? It's becoming more apparent why so may like mod-con's for gravity conversions. But i do like the simplicity of the old cast iron boiler technology; no $1k circuit boards to burn out and all that. I await your unfiltered opinions

http://s802.photobucket.com/user/bpa...T.jpg.html?o=0

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  #42  
Old 01-07-15, 10:56 PM
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Here is the process... IMO you may be wasting your time doing the repipe. What are you going to gain?

Set the boiler supply valve to fully open position,
and the boiler bypass valve to half throttle. Operate
the boiler and adjust the bypass valve to achieve
180F to 200F supply water temperature by closing
the bypass valve to decrease supply temperature or
opening the bypass valve to increase water
temperature. If the bypass valve is fully opened and
the boiler water temperature is still below 180F,
slowly begin closing the boiler supply valve to
achieve 180F to 200F supply water temperature.
Caution:
Never fully close the boiler supply valve.



Be mindful of the delta T across the boiler when adjusting the bypass flow. You don't want more than a 40F DT across the boiler, and that's about the 'hairy edge'...
For large volumes I think 30-40 is the norm......


AND some good news! As you suggested throttling the return by about half with the other 2 bypass valves wide open is allowing the boiler to reach the shutoff temp after about 7-10 minutes. I'd swear i tried that before but must've had my head stuck elsewhere and thought it wasn't doing the trick. It's highs in the single digits today and it takes about 4-5 minutes for the system water (about 120-130) to cool the boiler below the low set point of 140 before it fires back up.
So whats the issue? IMO open the return more to get a longer burn time. This will heat the system more. Try 15 min burn time to 180 F.

What you have there is a poor mans out door reset. As the temp drops outside and the boiler kicks on more often the system will eventually get to near boiler temps..

This is why set back on t stat should be avoided.. Set it and forget it...

Where is the t stat located again?

I would have to figure some but I may consider changing the taco system pump to a 3 speed unit is all..


But please give us some temp #'s during operation.

Supply temps of course should be 180 before boiler near kicks off on limit.. ( with circ still running)
Whats the return temp at that point?
Whats the supply after bypass?
Whats the return temp to boiler from bypass and system?
 
  #43  
Old 01-08-15, 07:07 AM
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If you can mitigate the condensation with adjusting the bypass, and not exceed a 40 DT across the boiler, and the home heats properly, then I agree with Mike.

I dunno about changing the pump to a 3 speed though, not sure the point of that...

the boiler bypass valve to half throttle
Ball valves 5uck for throttling, and 'half travel' on the handle is NOT ANYWHERE NEAR half throttle.

I would guess that 85% of the throttling on a ball valve occurs in the last 15% of handle travel. They are NOT linear. They should have been good quality GLOBE valves.

I would adjust differently because I think you are going to end up with the bypass all the way open anyway.

I would start with the bypass all the way open and throttle the boiler flow until I reached the desired delta T across the boiler.
 
  #44  
Old 01-08-15, 07:08 AM
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If you DO decide to repipe anyway, my quick look at the marked up photo tells me that the closely spaced tees are not configured properly. I need to look at the full size version to be sure... later...
 
  #45  
Old 01-08-15, 02:20 PM
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But please give us some temp #'s during operation.
Going to do some testing tonight and I'll report back with my findings. I think I'm close.

If you DO decide to repipe anyway, my quick look at the marked up photo tells me that the closely spaced tees are not configured properly.
Piping needs to be horizontal for a distance on either side of the T's? Something closer to:

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  #46  
Old 01-08-15, 03:21 PM
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Piping needs to be horizontal for a distance on either side of the T's?
Doesn't have to be horizontal, but you should have minimum distances before and after the tees of straight pipe...

 
  #47  
Old 01-12-15, 04:28 PM
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What you have there is a poor mans out door reset. As the temp drops outside and the boiler kicks on more often the system will eventually get to near boiler temps..
Thanks Lawrosa. That's always been my understanding and it does seem to be functioning as such. More on that below...

This is why set back on t stat should be avoided.. Set it and forget it...
That seems to be a heavy consensus and that's what I've always done. It's set to a static 70d with a Honeywell WiFi Smart Thermostat located in the middle of an interior wall in a very large open downstairs living/dining room. Same place as the old thermostat. ONE thing I did discover while checking temps was that the thermostat has a configuration setting specifically for Boiler & Steam Heat. I overlooked that previously. Boiler heat, which is kind of buried in some options, wasn't checked before and i think that may have been part of what was contributing to the short cycling. They don't clarify in the manual but i assume the Boiler vs. forced air settings have a wider temperature curve, although it still never shows on the display that the temp gets higher or lower throughout the day by even a degree. But it sure seems to be more time between cycles on a 20 degree day.

But please give us some temp #'s during operation.
Supply temps of course should be 180 before boiler near kicks off on limit.. ( with circ still running)
It is kicking off at 180
Whats the return temp at that point?
After some experimenting with the bypass valve settings i've found that the systems is holding about a 30 degree Delta T with all valves wide open
Whats the supply after bypass?
by throttling the supply valve even as little as half the boiler temp will climb to 180, but the mixed return temp won't get higher than 110 degrees, about 10 degrees higher than the return above the bypass
Whats the return temp to boiler from bypass and system?
ON AVERAGE it's between 90 and 110 degrees depending on the outside temp. Currently on a 25 degree day the downstairs rads read a 88-90 degree temp with seems to jive with the 90-95 degree temp on the boiler return downstairs. The boiler is now running about 10-14 minutes rising from a resting temp of 120 to 130/140 with a return around a 30 degree delta. A few nights ago when the temps were single digits it was running in the 150-160 rangle before the thermostat clicked off.

I'm going to continue to monitor the readings. My unofficial conclusion right now is that while the heat lost calc is 80k and the radiator output per Burnham's charts is 78k at 170, those are both design case scenarios. The reality is that, and NJ Trooper suspected this already, the old radiators are oversized for what is now an insulated house. It's great they're keeping the house a steady 70 (and the fuel bill is down from last year) with a barely detectable 90 degree temp, but it's keeping the return temp so low I probably need to revisit a primary/secondary setup after this season to get the condensation issue in check. The old gravity boiler was 165k BTU and made the radiators almost painful to touch with 5 degree swings throughout the house. But again, that's just one guy's theory
 
  #48  
Old 01-12-15, 05:29 PM
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the systems is holding about a 30 degree Delta T with all valves wide open
Confused...

boiler temp will climb to 180, but the mixed return temp won't get higher than 110 degrees
So you're saying that there's a SEVENTY DEGREE Delta T across the boiler then? I don't think that's good for the boiler.

How is it that you can have a 30F DT across the system, and a 70F DT across the boiler?

Or are you saying that the boiler will only hit 180F if you throttle that valve?

And not throttling that valve you are running at a 110F return with a 140F supply?
 
  #49  
Old 01-12-15, 05:40 PM
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Or are you saying that the boiler will only hit 180F if you throttle that valve?
Correct. If I throttle the supply between 1/3 and 2/3, it does climb to 180. Obviously the more closed it is the faster it rises, but the return below the bypass doesn't reciprocate that same degree of rise, or at least not nearly as quickly. The amount that it outpaces the return makes me nervous.

And not throttling that valve you are running at a 110F return with a 140F supply?
That's what she's doing right now. It's about 20 degrees outside. Running wide open is around 150(boiler)/110(return) and it cools to about 120/90 before the next call for heat.

It's looking like my real condensing issues are happening during the day when the outside temps are warmer and the radiators are running cooler.
 
  #50  
Old 01-12-15, 06:13 PM
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the return below the bypass doesn't reciprocate that same degree of rise
No, and with a boiler bypass it won't... well, it will, eventually... but not as fast as it would need to.

That's what I don't care for about boiler bypass. Yes, it protects the boiler to a degree by raising the AVERAGE temperature in the boiler... but it does this by increasing the DT across the boiler. DT across a boiler of more than 40F is not a good idea... how do you spell STRESS?

You still have cold water returning to the boiler with boiler bypass.

With system bypass, the average temp in the boiler is also increased, but by RAISING the temp of the return by mixing some supply back in.

SYSTEM bypass has it's drawbacks too. It means reducing the flow in the system piping and this leads to poor heat distribution because the water is moving slowly through the radiators and the first on the line pull all the heat out before the ones on the end of the line can get any.

THEREFORE... a COMBINATION of system and boiler bypass IMHO is best for gravity conversion applications... hence my drawing of P/S with the ESBE thermic valve.

The P/S piping allows BOILER BYPASS until the ESBE begins to open. But you've also got SYSTEM bypass at the SAME TIME!

Meanwhile, before the ESBE opens, (which it does slowly, and modulates partly open) the boiler is allowed to come up to temp because ALL of the supply is going to the return.

So boiler gets hot and ESBE starts to open... and some of that hot is injected into the system. Because the system has a dedicated pump, there is full flow in the system and the heat that gets pushed in goes further around before cooling off... and the boiler gets hotter... and more hot is injected into the system...

To put it another way, when the boiler fires and the system is cold, you have BOTH full BOILER and SYSTEM bypass.

As the boiler heats and the ESBE opens, the proportion of both system and boiler bypass decreases... and the boiler is protected from cold return...
 
  #51  
Old 01-20-15, 09:51 PM
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Thank you both for all of your time weighing in on the problem i was having. I think at the end of the day there's a little re-piping for a good primary/secondary setup to best solve the issues with this particular gravity conversion long term, but at least we're good and comfortable for the time being. Cheers!
 
  #52  
Old 01-20-15, 10:07 PM
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Let us know if and when you do any repiping... also the final outcome if it improves your situation...
 
  #53  
Old 11-03-15, 02:25 PM
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Re-piping update

NJT and Lawrosa asked for revised pics so for what it's worth I thought I'd upload some now that the conversion to primary secondary is "almost" done.

1. Yes I forgot the $%&#* globe valve between the ESBE and the supply line, so I'll be taking a few pieces apart to get that corrected.
2. Please disregard the temporary wiring. I'm still working out the relay/ODR wiring for the primary circulator and haven't buttoned everything back up.

Any comments or critiques are welcome!

Thanks all.







 
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  #54  
Old 11-03-15, 03:48 PM
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Is that esbe oriented correctly? The square mark on pump side? Triangle facing close tees?
 
  #55  
Old 11-03-15, 08:49 PM
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Yes sir. Square is on the pump return, triangle is to the tees.

What I don't like about it currently is the slight uphill angle from the supply line. I don't want air to get trapped so when I take it apart to add the balancing valve I'm going to see if i can't get that lower to avoid that possibility, or just adding another purge valve above the return temp gauge. That probably means having to change the 45's to 90's to buy more distance between supply & return. I hate to add more friction but i figure for a short run like that boiler loop it beats moving both gas and electrical hookups to drag the boiler away from the wall another 6" or so...
 
  #56  
Old 11-03-15, 08:56 PM
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Just saying cause the label up the square and triangle are opposite . But maybe they are putting labels on both sides?
 
  #57  
Old 11-04-15, 07:23 AM
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Yeah it came with additional labels for each side so i stuck them on there just for grins.
 
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