Sizing expansion tank for a system that uses chilled water.

drooplug

I working on sizing the expansion tank for my system. It will be using chilled water in the summer. The formula requires "the density of the fluid at its initial (cold) temperature". With a heat only system, that would basically be room temperature. Since I will be chilling my water in the summer, should I use my lowest temperature for this formula?

hot_rod

Hot off the press

https://www.hpacmag.com/features/expansion-tank-dos-and-donts/

EBEBRATT-Ed

@drooplug

The temperatures you should use is your expected chilled water operating temperature for the low temperature and the high temperature would be the warmest expected temp inside the building (within reason)

Have a relief valve on the system and if antifreeze is used pipe the relief valve outlet to a tank or barrel.

mikeg2015

hot_rod said:

Hot off the press

https://www.hpacmag.com/features/expansion-tank-dos-and-donts/

My favorite #5 “Do consider oversizing”. Virtually every commercial system I’ve worked on had functionally undersized expansion tank and system pressure varied wildly. I verified the calculations, but I suspect the actual piping volume was higher than I estimated. Wonder if they forgot to include boiler volume in the calc.

hot_rod

I like the Amtrol commercial sizer program as it lets you input volume, temperatures, and acceptable pressure swing.

Of course you are correct that knowing the actual volume is a key number.