Expansion tank, air scoop location....

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Old 11-29-08, 12:01 PM
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Expansion tank, air scoop location....

I know this must be a highly controversial subject because I keep running into contradicting information.

I am setting up a 10 zone, multiple temperature, primary secondary system with multiple boilers(probably Buderus g234xs) and have come to a halt installing the air scoop/ expansion tank.

I planned on locating the pump on the return side and the air scoop/ expansion tank before the pump. Also if the air scoop is on the return, how do I prevent air from getting to the radiators. should I also add an air scoop on the supply?
Also, are the air scoops better than the spirovents?

Where is the correct location of the air scoop and/or expansion tank? Some diagrams(including manufacturers) say supply side some say return. Who can shed some light on this.
 
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Old 11-29-08, 01:22 PM
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The location of the expansion tank should be on the suction side of the circulator pump. So, decide where your pump will go (supply or return), and then put the tank on the suction side of the pump.

Many years ago, this issue might have been controversial, but I don't believe it is today.
Doug
 
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Old 11-29-08, 02:15 PM
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You will need two purge devices. One on the primary loop and another on the secondary loop. Note that the scoop will have a purge device that vents to the atmosphere. I base this on the assumption that you will be using a bladder tank.

A 2-pipe system should have the circulator pushing the water through fast enough to move any air along with it. Where it may then be purged.

The expansion tank and air scoop may be placed in separate locations.

Al.
 
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Old 11-29-08, 02:39 PM
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I think the Spirovent is better than the cast iron scoop type ... that's a 'micro bubble' separator ... I think the B&G EAS is also that type ... there's others as well ...

If I were building it, On the boiler loop, I would put the pump on the supply side ... with the air separator and tank ahead of it... then, on the system loop, the pump on the supply side, with just the air separator ahead (upstream) of it, no tank, plug the hole, or stick a boiler drain in it...

You could _probably_ get away with just one air separator on the boiler loop ... but the air will get out faster with one on each loop... or maybe put an el-cheapo in one spot, and the fancy-schmancy in the other ... yeah, a cast iron scoop on the boiler side, and the Spirovent (or similar) on the system side ...
 
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Old 11-29-08, 09:03 PM
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Why oh why in such a high-end heating system would you choose such low-end efficiency and technology in a boiler? Much less two of them?

10 zones screams for a large modcon, or a pair of staged smaller ones. You will frequently have small loads and potentially lots of cycling, even in a p/s system. If you design the system for condensing-range temperatures, the full benefit of condensing boilers will accrue, and you can take the savings to the bank.

If you're fond of Buderus, get a pair of GB142's. Otherwise, look at the Knight. I believe it comes with built-in staging controls.

Strongly suggest rethinking the boilers before worrying about where you put the air elimination system. That's trivia. Ultimately, this system will need to have the pumps located per the manufacturer. Air elimination location is commonly of choice, but convention is on the supply. The tapping on the bottom of most air eliminators is convenient for the expansion tank, but the tank should be placed per manufacturers instructions. Failing specific instruction, it should, as others have said, be on the inlet side of the circ.
 
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Old 11-29-08, 10:37 PM
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The reasons I decided not to use a mod/con boiler are

1. I understand that the savings are heard when the boiler is operating under 145 f and I only have 1 floor heat now and ultimately 2 floors heated.
2. I can buy 1 g234xs now for $2100 and buy a second one after i get done with the house or if I feel I need it. My feeling is that I might not even need the second boiler.





Originally Posted by xiphias View Post
Why oh why in such a high-end heating system would you choose such low-end efficiency and technology in a boiler? Much less two of them?

10 zones screams for a large modcon, or a pair of staged smaller ones. You will frequently have small loads and potentially lots of cycling, even in a p/s system. If you design the system for condensing-range temperatures, the full benefit of condensing boilers will accrue, and you can take the savings to the bank.

If you're fond of Buderus, get a pair of GB142's. Otherwise, look at the Knight. I believe it comes with built-in staging controls.

Strongly suggest rethinking the boilers before worrying about where you put the air elimination system. That's trivia. Ultimately, this system will need to have the pumps located per the manufacturer. Air elimination location is commonly of choice, but convention is on the supply. The tapping on the bottom of most air eliminators is convenient for the expansion tank, but the tank should be placed per manufacturers instructions. Failing specific instruction, it should, as others have said, be on the inlet side of the circ.
 
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