Multiple Expansion Tank Locations

DanHolohan

exactly what happens.

Dave_12

Multiple Expansion Tank Locations

I am looking for some technical feedback on how to treat a commercial system with several expansion tanks located in several parts of a building.

How does having several "point of no pressure change" locations effect the design of a system.

This is a general question, I do not have a specific project.

Thanks,

Dave

Empire_2

Hi Dave

Since your pump delivers a positive pressure thruout the system, the pump, Ideal location is on the supply side of the boiler. Expansion tank location should always be on the suction side of the pump. This will guarentee a 12 psi PONPC at the pump and anything after the pump would be seen as an increase in pressure. Dan has a great book on pumping away that would make it all clear. I am not sure why you would want multiple tanks, but you can have them if you need them. If you are using a Primary/Secondary set up let us know, but still only 1 (ponpc) is needed. Just remember to pump away..

Mike T.

Dave_12

Thanks, Mike

I am refering to an existing system in a commercial building where several expansion tanks now exist at several remote locations. Boiler is piped primary-secondary, with a boiler loop pump and expansion tank at the suction side of the pump. Then there are several system pumps pumping to remote sections of the building, with several expansion tanks throughout the building. I have read & re-read Pumping Away and cannot find reference to this situation. I am trying to understand the impact on pressure at various parts of the building and the effect these remote expansion tanks have on pressure. If I were designing the system, I would put one or more expansion tanks in one location, that location being at the suction side of the boiler loop pump. If anyone knows how to examine this existing condition technically, I would appreciate the input.

Thanks,

Dave

[Deleted User]

Extremely confused pumps...

Too many PONPC's... The main pump is probably splitting its pressure differential in half.. or maybe not.

Contact Rhomar water. They have a kit that you can use to determine how many gallons of water are in the system. That is usually the biggest bugaboo in determining proper expansion tank sizing on commercial jobs.

Once you have that down pat, then you can fine tune the system and become the hydronic hero...If the smaller outlying ET's are not necessary, get rid of them. Just make sure that any secondary pumps are pumping away from teh main, because that is their point of reference as it pertains to the PONPC.

Sometimes, plumbers get into a visual habit thing, and they don't understand whats going on. They just keep doing the same thing they've done in the past, because "it works". I seriously doubt any engineer in his right mind would do that from scratch.

ME

Empire_2

Trt this

In "Pumping Away" ON pages 28 and on it will explain how the differential pressure of the pump works, where it should be placed and how it can be benificial to the entire system. Then look at pg 133 for a typical Primary/Secondary set up for your particular building. Note that the remote zones have pumps, but not exp. tanks. With the primary loop havaing a benificial increase in pressure, the secondary pumps can generally be smaller needing only enough flow at lo head to move its desired load thru that zone. Check it oput and let me know what you think. In your particular set up, every time you are tapping in with a Expansion tank for your remote zone, you just knocked all the benificial positive pressure of your primary pump back down to 12 psi or where ever the tank (PONPC)pressure is at.

Mike T.

Ron Schroeder

It would be hard to predict pressure changes in that system. It will depend on the size, location and individual charge pressure of the various tanks. If the system really needs the volume of all of the tanks, move them all to the suction side of the primary circ. Multiple expansion tanks can and often are piped in parallel to a single point.

Ron

Empire_2

I agree Ron

I was thinking that the primary pump may be to small and thus someone tried to add larger pumps for the remote zones and then added expansion tanks. I guess the safest way to reconfigure is to reexamine the entire building. Like I said It is only a guess.

Mike T.

Ron Schroeder

With your eyes closed and knowing absolutly nothing about a system except that the pump is the wrong size, if you always guess it is too big, you will be right more often than you will be wrong. ;-)

Yes, you do have to look at the whole system.

Ron


P.S. How do you know a boiler is too big?....because it's there. ;-)

Empire_2

Ouch...........:-)

Just trying to help a little Ron. You know how things end up when everyone has their hands on it.....I guess without being there I can only emagine on what is wrong. Crystal ball is broken so I must use senerios.....

Jerry Boulanger_2

In a system that

has only one tank the tank connection becomes the 'point of no pressure change' because the pump can neither add water to the tank nor remove water from the tank, respectively because there is no place to take it from and no place to put it. This changes when there is more than one tank. Operation of the pump can now take water from a tank on the inlet side of the pump and put it into a tank on the discharge of the pump. There will be no predictable 'point of no pressure change'.

This is not recommended. If there is more than one tank they should all be connected at the same place, close to the inlet of the pump.

Weezbo

*~/:)

Alfred Hitchcock, i presume....?

No, ...Maxwell Smart.

Too many pressure tanks spoil the structural integrity of a building just last week there was a post of an overgrown expansion tank on top of a building,seriously undermining its moudus of elasticity

Dave_12

Thanks for the input

Thanks for all the input on this question, especially you Jerry. You provided what I consider the correct analysis.

While the answer is now "obvious", the question of how to analyze system pressure when you have multiple expansion tanks at different locations had me stumped for awhile.

I had my blinders on and thought that (excluding thermal expansion) you could neither add to or remove water from an expansion tank, therefore the pressure at the expansion tank would not and could not change. While this is still true for a well designed system with one point of expansion tank tie-in, it is not true in my example of having expansion tanks in various locations. They collectivly share the water--one tank can give up what another tank takes in in response to the action of pumps and system pressure losses. I knew that you could not "fool mother nature", but I could not understand what was happening.

Thanks again for the help.

Dave

JimGPE_21

Why?

Why did the engineer cross the road? Because he checked his files and that's what he did last time....

bob_50

Two tanks

additional info

bob_50

Two tanks

additional info