Proper Expansion Tank Placement

[servman]

I have a question I am hoping those of you with vast more knowledge then myself can help with. I was having a discussion with my boss about the proper location of an expansion tank in a glycol condenser water loop. We had a customer that had a glycol leak on a riser of their condensers water loop. The leak was on the 2nd floor of a 4 story building, drycoolers and pumps are on the roof. Due to the location of the leak, we had to drain the system down below the leak because there was no way to isolate the leak.
The top of the expansion tanks (two 100 gallon non-bladder tanks) are 3 feet below the highest point in the system. I was always taught/told that expansion tanks in this type of system (drycooler/pumps on the roof) needed to be at the highest point in the system and on the suction side of the pump. Especially if a non-bladder expansion tank. I asked the customer if they wanted me to raise the tanks up while we had the system down and drained. The mechanical prints even showed the tanks when installed were supposed to be above the highest point in the system. The customer asked me to throw them a price together real quick, so I did.

My boss turned around and told them not to worry about it said it does not matter where the tank is located. It could be in the basement, there just needs to be one on the system.

I did not think this was right, I said that the prints showed the tanks at the highest point in the system and should be there but could not come up with the reason why. My bosses reason that the expansion tanks did not need to be raised was because he has seen expansion tanks on hot water boiler loops in the basement so they do the job no matter where they are, just that there is one.

Looking for reasons why expansion tanks are placed in the system where they are.

[klove]

It's easier if they're at the highest point most of the time, but if you have the proper fittings and valving for air charging at the tank, and your tank is sized correctly, it really doesn't matter. The trick is to check the tank a couple of times a year and keep it charged.

[RcOKC]

As long as they are on the return side and/or suction side of the pump or loop then there placement doesn't really matter. The expansion and contraction of the fluid takes place throughout the entire loop not at the highest point. Expansoin tanks are not air bleeds so there is not any real benefit for them being at the highest point of the loop. Like Klove said they do need to be checked occassionally for proper air charge according to water side system pressures.

[servman]

I was trying more to see if someone could come up with a good reason or knew why engineers spec expansion tanks to be at the highest point in the system. I have seen this on more then one set of mechanical prints and manf installation guides.

[blabath]

If this is a cooling system the proper term for the tank is most likely "compression tank". Compression tanks can be any where in the system, as has been stated in other answers to your post.
Expansion tanks are used in hot water hydronic sytsems and are put there by engineers because engineers tend to "rubber stamp" systems just like every engineer before them has ever done. They rarely, if ever, have an original idea or think about anything except how much extra crap to spec into a job so they can make more money. They are paid on a percentage basis in case you didn't know.
So, to answer your question, engineers put expansion tanks at the top of a system because they have ever since the 1920's or thereabout.
You gotta love engineers.... I do!

[klove]

Bladderless tanks are put at the top of a system for two reasons (both of which can be overcome by proper placement or sizing if going to a lower point): First, if you can get it on the return riser at the top, it will have a tendency to "self-charge" as air moves through the system. Second, if you have a system in a tall (define tall?) building and you place the pumps and tank at the low point, you have to contend with static head on the water side compressing the air at the top of the tank to an unacceptable level before you even get started. For example, if they're at the high point and you add 15 pounds of pressure to the static, you compress the tank to 15 psig. If they're at the low point of a 46' tall building with 15 psig added to remain positive at the top, now the pressure at the tank is 35 psig. In a bladderless tank, there's no way to compensate for this, unless you fit it in such a way that you can manually pressurize it after normal charging is completed.

[vstech]

Bladderless tanks are put at the top of a system for two reasons (both of which can be overcome by proper placement or sizing if going to a lower point): First, if you can get it on the return riser at the top, it will have a tendency to "self-charge" as air moves through the system. Second, if you have a system in a tall (define tall?) building and you place the pumps and tank at the low point, you have to contend with static head on the water side compressing the air at the top of the tank to an unacceptable level before you even get started. For example, if they're at the high point and you add 15 pounds of pressure to the static, you compress the tank to 15 psig. If they're at the low point of a 46' tall building with 15 psig added to remain positive at the top, now the pressure at the tank is 35 psig. In a bladderless tank, there's no way to compensate for this, unless you fit it in such a way that you can manually pressurize it after normal charging is completed.

perfect answer klove. exactly right... a glycol system still has air in the lines, so you will get "some" "self-charge" I bet the reason it was not exactly placed in the highest point is due to the accessibility of the tank for pressure maintenance. if there's a same floor access point for the tank that makes it simple to get to, I'd put it there.

[hvac248]

ALWAYS "pump away" see B&G tech docs.

[jack marcotte]

Don't waste money on putting in a plain steel tank. Review the values and benefits of a Bladder tank on pump efficiency and pipe corrosion protection. You want to eliminate air not control it. Install on the suction side of the pump. Add an air eliminator along with the bladder expansion tank.