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Thread: Expansion Tank

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    Expansion Tank



    Dear Friends ,

    What are the main reasons for installing an expansion tank in the chilled water system and where it should be installed (at what height , how many feet above the AHU) ?


    Thanks for your cooperation.



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    Re: Expansion Tank

    Hi Summit

    if you mean a storage tank, my understanding is you need a storage tank when you have a variable load and the minimum requirement of that load can drop below the minimum capacity of the water chiller

    without a storage tank/vessel you would have too many stop/starts and in some cases you may require cooling but the chiller can not start as is timed out

    R's chillerman
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    Re: Expansion Tank

    Hi summit

    after re-reading your post, expansion tank is there for the reason of allowing the expansion/contraction of the water to take place without causing too much varient in the water system overall pressure

    I am not aware of a issue with positioning although I think all that i have seen sit at a higher level than the pumps

    Maybe another member will give a better answer to that one

    R's chillerman
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    Re: Expansion Tank

    Thanks Chillerman for your prompt reply,

    I also know expansion tank are installed to accommodate the expansion and contraction of the water.But its height is the main issue , generally it is placed above the last AHU.

    I hope my seniors will share their knowledge and will give the better clarification.

    Have a good time.

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    Re: Expansion Tank

    Expansion tanks should be installed at the highest point of chilled water system on the return water side, height above determined by pressure at that point in system, 2.3 feet head = 1 psig. The usual method is to have a pressure compensation vessel, rather than having a open vessel tank miles up in the air.

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    Re: Expansion Tank

    Sumit, depending on what the system looks like and the piping height, fill pressure etc, expansion tank placement can be important for proper flow. Typically the tank should be on the suction side of the pump as should the water make up system. The point of intersection of the tank with the piping is the "point of no pressure change" and if your tank is on the suction side of the pump, the pump adds head pressure to the static pressure (1 bar + pump (,1bar for example)) will give a higher pressure output ahead of the pump. If the pump is on the other side of the tee, the output pressure stays constant at the static pressure (1 bar for example) but the pressure at the pump suction will be 1 bar - ,1 bar = .9 bar and if the pump is big enough, could start to cause cavitation issues.

    Always best to design a system with the above considerations. More to it but that is the basics. Cheers

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    Re: Expansion Tank

    Hi Summit

    have done some digging today as normaly dont have to touch the water system

    and over here it is as 'Magoo' said, expansion tanks are not normaly in use due to plant/pump room is often much lower than chiller (on roof) and there fore, pressurisation vessels are used instead

    Regards Chillerman
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    Re: Expansion Tank

    Question to be asked:-

    Is the chilled water system to be an open vented system or is it to be a sealed system?

    Different type of expansion system required.
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    Re: Expansion Tank

    Quote Originally Posted by Brian_UK View Post
    Question to be asked:-

    Is the chilled water system to be an open vented system or is it to be a sealed system?

    Different type of expansion system required.
    Hi Brian

    would I have worked on chillers connected to vented systems & not noticed the difference, I presumed all were sealed systems, until I see the responses here

    R's chillerman
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    Re: Expansion Tank

    Gee wiz Brian, ya got me there. So seldom do we use vented systems in North America (except for some cooling towers) that i forgot you still have them in the UK, so I would never have thought of them with a chiller.

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    Re: Expansion Tank

    Very rare agreed, but consider the location of the questioner.
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    Re: Expansion Tank

    First of all , thanks to all for sharing their views.But i would like to ask few things more :

    1. Brian , can you please throw a light on the open vented systems as I have never seen it and how they work.

    2. How pressure compensation vessels works and how they differ from normal expansion tanks which we use in the sealed chilled water system.

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    Re: Expansion Tank

    No posts on weekend

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    Re: Expansion Tank

    Sumit, the sealed system expansion tank takes the place of the cistern system. All the advantages of the cistern system can be achieved with a "bladder expansion tank" and the expansion tank can theoretically be placed anywhere in the loop without special piping to a high level, where a cistern would be placed.

    Expansion in the heating system pushes the liquid up and cooling lets it drop. A loss of water for any reason (evaporation, leaks, etc) results in the more water being introduced. Unfortunately, this also can introduce oxygen and in some systems can corrode piping.

    The expansion tank rubber bladder performs the same function by allowing the air on one side of the bladder to be compressed by the liquid on the other side. Completely sealed, no corrosion, no evaporation and better for component placement. As i said before, pump at a low point, expansion tank and water feed on the suction side and you should pump INTO the load (AHU, heat exchanger, radiators, whatever).

    Cheers

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    Re: Expansion Tank

    Hi MikeHolm.
    very well explained, can only add that the closed loop system should be treated with additives and regular sample testing for PH balance control.

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    Re: Expansion Tank

    Hi Nike, MikeHolm and Magoo,

    I will be thankful to you , if you provide me any material related to " bladder expansion tank " as I have never seen it and even not able to get it on internet. In addition , the good explanation by Mikeholm goes over my head, not get it 100 %.But still I appreciate his efforts.

    Cheers

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    Re: Expansion Tank

    Sumit, what is your level of experience with these systems?
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    Re: Expansion Tank

    Hi Brian ,

    I have been working on chilled water systems last one year , I have never seen centrally heating systems.May be because of that I have never seen " bladder expansion tank " or may be these are not used in India.Anyways , thanks Nike ; the links you have posted will clear all my issues regarding the same.

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    Re: Expansion Tank

    can somebody show me the piping diagram for expansion tank....
    thanks...

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