Chilled water system expansion

[skylane]

Does anyone out there have a rule of thumb for calculating the size of a standard expansion tank (non-bladder) for a chilled water system? For hot water systems the rule of thumb I use is 2.0 gallons of capacity per boiler horse power for small systems and 1.5 for large systems. I know some say you don't need expansion for chilled water systems but they're still installed.

Thanks

 

[walkes]

I don't use rules of thumb for most things, I like to run the numbers through appropriate equations or software.
Most expansion tank catalogs will have the calculation procedure in the back.
Another option is to visit websites:
Bell and Gossett has their ESP Software that has Hydronic Specialties including sizing compression/ expansion tanks.

Wessels has downloadable software at:

http://www.westank.com/index.php?page=tank

Good luck

 

[imok2]

For a chilled water system with a closed non bladder tank if you multiply the total system volume by 2.21% you should be about right, that's good for about 100*F. Now if you go to

http://www.automatedbuildings.com/

and click on software library, go down to HVAC Engineering calculators online and click on 'Tank Volume" it will calculate the tank size for you

 

[KenRad]

skylane,

Although the expansion of water is of a lesser magnitude in a chilled water system vs. a hot water system, you still need to accommodate fluid expansion. If your chillers shutdown, your loop can go from chilled water temperature to ambient (or higher), with a corresponding increase in system pressure. In any closed loop without a path for expansion, pressure rises very quickly with temperature. Your system may have a relief valve, but it should not be your means of pressure control.

Is there a reason that you are not considering a bladder or diaphragm style tank?

---KenRad

 

[cme]

Take into account the glycol (if applicable) expansion rates also.