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Expansion Tank In Closed Loop Cooling System


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#1 rsk

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Posted 23 July 2008 - 11:40 AM

As elaborated in excel please enlighten when & where to connect the expansion tank to system.
whether pressure profiles will be different & this in turn reflect in pressure rating of system equipments.

Attached Files



#2 djack77494

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Posted 23 July 2008 - 12:19 PM

Let me answer the easier question first-
QUOTE (rsk @ Jul 23 2008, 07:40 AM) <{POST_SNAPBACK}>
please enlighten when ... to connect the expansion tank to system.

I'd recommend you do this during construction.

QUOTE (rsk @ Jul 23 2008, 07:40 AM) <{POST_SNAPBACK}>
please enlighten ... where to connect the expansion tank to system.

I believe that the best location for the expansion tank is connected to the pump's suction. This is the location of minimum pressure and is just as effective as anyplace else in the system for performing its primary function. In your case, it's also the coolest location in your system and so it should result in the cheapest (and safest) possible tank.

#3 Art Montemayor

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Posted 23 July 2008 - 02:13 PM

RSK:

My comments are on the attached re-work of your workbook. I agree with Doug's comments and thoughts.
Attached File  Expansion_Tank_in_PumpAround_Loop.xls   118.5KB   469 downloads


#4 JoeWong

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Posted 23 July 2008 - 07:22 PM

I have experience in hot water closed loop system. The expansion tank is located at pump suction to maintain a good pressure to avoid flashing and pump cavitation problem.

Expansion tank also evacuate any gas in the loop (which came from Heat exchanger minor leakage). The tank should be located at pump suction as it is the return line and point where it has lowest operating pressure within the loop

#5 rsk

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Posted 24 July 2008 - 11:59 PM

thanks Mr Art
u very nicely pointed out the difference between the two cases
1. If expansion tank is connected in suction side of pump, Level will in expansiosn tank will remain same in pump operating condition as was in static condition.
2. If expansion tank is connected in discharge side, level in expansion tank will change from corresponding to that of static head to that corresponding to the dynamic head at the connecting point.
for eg if i take the pump central line at 0m & expansion tank at 25m so static head is 25m. The pump devloped head is 22m & corresponding to the circuit hydraulic resistance of 22m. when pump is operated expansion tank will overflow till dynamic head at pump discahrge comesdown to 25m and with drop throgh circuit resistance head at suction will come to 25-22=3m. That here elevation of expansion tank will play a graet role in ensuring NPSH to the pump.
Please clarify

#6 fallah

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Posted 03 June 2009 - 12:55 AM

QUOTE (JoeWong @ Jul 23 2008, 08:22 PM) <{POST_SNAPBACK}>
The tank should be located at pump suction as it is the return line and point where it has lowest operating pressure within the loop


This can not be right in the cases the loop is routed vertically and the users are located in elevations higher than that of the pump.

#7 djack77494

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Posted 03 June 2009 - 03:49 PM

QUOTE (fallah @ Jun 2 2009, 09:55 PM) <{POST_SNAPBACK}>
QUOTE (JoeWong @ Jul 23 2008, 08:22 PM) <{POST_SNAPBACK}>
The tank should be located at pump suction as it is the return line and point where it has lowest operating pressure within the loop


This can not be right in the cases the loop is routed vertically and the users are located in elevations higher than that of the pump.

You can both be right (and should be for a good design). The expansion tank should be elevated to the point where it is the highest point in the system. It is still attached to the pump's suction line, however.

#8 Art Montemayor

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Posted 05 June 2009 - 02:16 AM


Fallah:

You don´t say it, but I think you are interpreting Joe Wong´s comment literally - the expansion tank cannot be located at the pump suction flange. And you would be correct.

Joe, I believe, meant to say that the expansion tank should be connected to (not "located at") the pump suction.

Doug is stating the second most important point (besides the tank being connected to the suction side): The expansion tank should be elevated to the point where it is the highest point in the system. This feature ensures that the tank can successfully work as an expansion chamber and one where the non-condensables can collect, act as an expansion fluid, and also be expelled as they accumulate. The design of the system all depends on the characteristics, piping, and scope of work. I hope this has helped in understanding the features and understandings of an expansion tank application.


#9 fallah

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Posted 05 June 2009 - 02:38 AM


Dear Art,

Generally,you are right for best location of expansion tank that would be highest point (or lowest gauge pressure),but in many applications there is no possibility to locate the tank in high elevation besides the problems regarding availability,maintenance,service,......

In those cases it would be better to locate the tank at grade before pump suction with higher reliability for deaerating and also providing sufficient positive pressure (for balancing the pressure and prevening air ingress) in the loop by blanketing the tank's top space using N2.

#10 Art Montemayor

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Posted 05 June 2009 - 04:24 AM


Fallah:

There has never been an application in my experience where the expansion tank could not be located at the highest level due to "no possibility to locate the tank in high elevation besides the problems regarding availability, maintenance, service". The basic and simple design of an expansion tank is one where you do not need access, or availability for maintenance and servicing. There simply is no maintenance or servicing on almost all expansion tanks.

There are literally millions of residential homes and commercial buildings in the USA that use forced circulation of hot water for winter heating and these installations all employ what I have described. This system is used a lot simply because it works so well and requires no maintenance.

Please use an Excel sketch (as I supplied) to clearly explain and describe what you mean. Your explanation that "higher reliability for deaerating and also providing sufficient positive pressure (for balancing the pressure and prevening air ingress) in the loop by blanketing the tank's top space using N2" does not apply to a grade-location for an expansion tank -- as least not to one without a membrane.


#11 fallah

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Posted 05 June 2009 - 04:50 AM

QUOTE (Art Montemayor @ Jun 5 2009, 04:24 AM) <{POST_SNAPBACK}>

Fallah:

There has never been an application in my experience where the expansion tank could not be located at the highest level due to "no possibility to locate the tank in high elevation besides the problems regarding availability, maintenance, service". The basic and simple design of an expansion tank is one where you do not need access, or availability for maintenance and servicing. There simply is no maintenance or servicing on almost all expansion tanks.

There are literally millions of residential homes and commercial buildings in the USA that use forced circulation of hot water for winter heating and these installations all employ what I have described. This system is used a lot simply because it works so well and requires no maintenance.

Please use an Excel sketch (as I supplied) to clearly explain and describe what you mean. Your explanation that "higher reliability for deaerating and also providing sufficient positive pressure (for balancing the pressure and prevening air ingress) in the loop by blanketing the tank's top space using N2" does not apply to a grade-location for an expansion tank -- as least not to one without a membrane.


Dear Art,

You are requested to refer to "Industrial Proffisional" Forum and read the Topic of "Criteria For Setting Pressures On Cooling Water Network" initiated by me.

The sketch you mentioned could be found there.

It should be mentioned that closed loop cooling/heating water network could be existed in an industrial plant rather than residential homes and commercial buildings,and such plants are involved with limitations may not found in homes and buildings.

#12 fallah

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Posted 05 June 2009 - 05:18 AM

Attached file may help out regarding the location of expansion tank in the cooling water loop/network.

Attached Files






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