Adding a full-sized bypass loop


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Old 12-13-06, 04:49 PM
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Adding a full-sized bypass loop

I'm thinking about adding a full-sized bypass loop this spring, and want to be sure I am planning to do it right. I assume I should have two gate valves, one on the bypass loop, and another on either the supply or return for the boiler before the loop. As I understand it, the loop is adjusted by balancing the settings for the throttle valves on the loop and boiler. Open one slightly, close the other an equal amount? How can you tell when the loop setup is optimum? Can the loop cause the boiler to short cycle? (Too much throttling on the boiler port limiting the flow through the boiler?)

Also, I'd think the sensor for the outdoor reset would be located where it senses the temperature of the boiler supply water after it is mixed with the cooler return water that is being shunted around the boiler?

Pete
 
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Old 12-13-06, 06:36 PM
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By pass loop

Save yourself some agrivation & install a thermostatic by-pass valve. It will adjust the amount of by-pass automaticly.
I would agree with the location of the temperature sensor but not being sure, I suggest talking with the control manufacturer.
 
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Old 12-13-06, 06:44 PM
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Question Thermic Valve

Grady

If I install a 140 degree thermic valve, what do I set the boiler minimum for on the Tekmar???? Right now it is set for 140 degree boiler min. I fear it would defeat the benefits of having the outdoor reset if I have to bump the boiler min higher. I could go with a 115 degree valve, but it might not do much good???

Pete
 
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Old 12-13-06, 07:00 PM
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Priorities

You have to determine which is more important to you; saving money on operating costs by operating at lower temps OR protecting the boiler from condensation. Personally, I would choose protecting the boiler but that's me. At 115, you are going to get condensation. I gar-un-tee.
 
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Old 12-13-06, 07:09 PM
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Talking cold start

The boiler is designed for cold start, and supposedly is able to withstand cool return temps for periods of time according to the manufacturer. I trying to go one step further for extra piece of mind... Personally, I think a triple aquastat and keeping the boiler HOT 24/7 is the way to go. Nothing is clear cut or easy!
 
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Old 12-13-06, 07:38 PM
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Hot 24/7

I agree completely. A hot boiler is a happy boiler. But you are absolutely right in saying nothing is that clear cut & easy. All we have to do is figure out how to keep the boiler at 160 for free. I know how!!!! Just move to Washington D.C. & use the methane from all the bull spread from Capitol Hill.

I looked into handling the Biasi (marketed under another name) a few years ago & decided against it solely because of a lack of a local distributor. The interesting thing is, the boiler came with a thermostatic mixing valve as standard equipment.
 
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Old 12-14-06, 11:18 AM
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Pete, you should have bought a Viessmann!

I believe you want the 260 supply sensor basically where it enters the space heating zones, i.e., the last point downstream, after any mixing, shunting, bypassing or whatever. It's trying to figure the supply temp needed in the zones based on the outdoor temp. If you mixed or bypassed after the sensor the supply temp might change and you might not get the right water temp to the emitters.

I'm on board with Grady re: temps. "period of time" is not "a lot of the time" which is what you'd get with a 115F bypass and the tekmar doing its job. Acid rain in the boiler....

You have a good partial outdoor reset system as it is. I wouldn't mess with it by adding a bypass.

If you're bound and determined to mess with it, then repipe the whole thing in primary/secondary using an injection pump and you can do full outdoor reset with a hot boiler loop. Dan Holohan's book (P/S Made Easy) and the tech essays at tekmar would be good starting points.

But a larger question is, have you done the heat loss and supply temp calcs that tell you how much of the heating season you can do at
 
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Old 12-14-06, 12:58 PM
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bypass or thermic valve

Originally Posted by xiphias
I believe you want the 260 supply sensor basically where it enters the space heating zones, i.e., the last point downstream, after any mixing, shunting, bypassing or whatever. It's trying to figure the supply temp needed in the zones based on the outdoor temp. If you mixed or bypassed after the sensor the supply temp might change and you might not get the right water temp to the emitters.

I'm on board with Grady re: temps. "period of time" is not "a lot of the time" which is what you'd get with a 115F bypass and the tekmar doing its job. Acid rain in the boiler....


.
Xiphias... Well, it is 60 degrees here today, and this has been a year that an outdoor reset will really pay off. I haven't done the calculations, but like you, I would be tempted to monitor the readings and keep bumping the settings back until the system started reaching constant circulation.

Regarding the sensor, it would be hard to use the thermic valve with a Tekmar since the sensor would have to be located AFTER the heating circulator, and AFTER the Tee that shunts the hotwater back towards the return line. That pretty much screws up the Tekmar being able to monitor DHW system, which has it's own circulator...

Using a bypass loop seems to make the most sense with the Tekmar. I can keep the lower boiler limit @140 on the Tekmar--or maybe even lower, while running the boiler hot, and not screw up the sensing for the DHW portion of the system. Unless my thinking is wrong, the bypass loop (once set up right) is pretty close to emulating what a P/S piping arrangement would provide?

The Biasi is designed for cold start, and they seem to run well; and the manufacturer told me that I don't need a bypass or thermic valve... I'm just trying to improve it's operation. Not quite like I'm trying to cold start a SlantFin pin boiler.


Pete
 

Last edited by radioconnection; 12-14-06 at 01:01 PM. Reason: added comment
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Old 12-14-06, 02:26 PM
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Need Grady for this one.

I'm reading this: http://www.danfossheating.com/products/pdf/TV_%20thermic%20valve.pdf and wondering whether with outdoor reset and BOIL MIN you really need to do this at all. I could be totally wrong (and it's likely I'm not thinking this through all the way), but I don't think you really gain anything. The tekmar wants to control the boiler using supply temperature to govern the firing calls. Not sure what will happen when you're down near the BOIL MIN which is also near the bypass min.

I need a seminar in bypass theory and practice. Anyone?
 
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Old 12-14-06, 02:38 PM
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Wink Boiler temps

Xiphias

My understanding, as muddled as it is, is that the return temps on the boiler shouldn't be allowed to run below 120 degrees for extended periods; and should be above a certain temp before the burner shuts down. The manufacturers are very vague on specifics.

I'm reading a lot of comments on forums where homeowners have had boilers with bypass loops installed by their contractors that were never set up from day one.

The P/S piping system seems to be the best thing since sliced bread on all fronts: boiler temp and differential, Tekmar sensing, and for achieving continuous circulation.

Pete
 
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Old 12-14-06, 02:52 PM
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I'm gonna read this http://www.burnham.com/pdfs/htghelper.pdf tonight. Start on about p 30.

I'm at least partly wrong. I think.

And this http://www.bellgossett.com/Press/BG-insand.asp
 
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Old 12-14-06, 03:26 PM
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bypass loop

The bypass loop simply shunts some of the cooler return water around the boiler, so the boiler can maintain a hotter temperature. I've seen the B&G suggested piping, but since I am using IFC valves on the circulators their piping arrangements would create problems with unwanted flow paths on my setup!

Checkout page 23 here:
http://www.burnham.com/pdfs/CurrentPDFfiles/MPO_I&O.pdf

Burhham suggests a full size loop with throttle valves on the loop and on a boiler port to control how much water flows through the boiler and how much is bypassed around the boiler. The suggested bypass loop is directly piped between the return and supply ports, and not after the circulator.

Pensotti suggests a simple 1/2" bypass with throttle valve across their Blueline boilers, but without a throttle valve on either the supply or return port I don't see how they control how much return water is actually forced through the bypass loop. I have some issues with the cheap iron nipples I used on my boiler (leaks), and I am going to replace them with some Made in the USA material in the Spring. Figured that would be a good time to add the full sized bypass if needed.
 
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Old 12-14-06, 05:05 PM
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Originally Posted by xiphias
Need Grady for this one.

I'm reading this: http://www.danfossheating.com/products/pdf/TV_%20thermic%20valve.pdf and wondering whether with outdoor reset and BOIL MIN you really need to do this at all. I could be totally wrong (and it's likely I'm not thinking this through all the way), but I don't think you really gain anything. The tekmar wants to control the boiler using supply temperature to govern the firing calls. Not sure what will happen when you're down near the BOIL MIN which is also near the bypass min.

I need a seminar in bypass theory and practice. Anyone?
Yeah, exactly what I was thinking.. With the Tekmar calling for 140 degree boiler temp, the supply water would apparently never circulate through the emitters. It would be shunted back to the boiler return continually. I'd have to set the boiler min. well above the 140 degree thermic valve rating from what I understand??? I need the same theory class too!
 
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Old 12-15-06, 04:12 PM
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Theory

Actually, I liked the L4006 idea. K.I.S.S.
 
 

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