I am concerned by the amount of expansion tank volume being recommended above to include Ahona recommending two SX110s for 1000 gallons and particularly the ASME table recommending 150 gallons for 1000 gallons of storage. Similar to Jim, for 1000+ gallons of storage, I'm installing an Amtrol Extrol SX-160 and an SX-30 . That would add up to 100 gallons of expansion tank size (86 + 14 gallons) with an total acceptance volume of 57.3 gallons (46 + 11.3 gallons). I based this sizing in part on two earlier posts by Joe Brown from Brownian Heating and Jim (jebatty) using acceptance volume as my yardstick.
Here are quotes form those posts:
Joe said, "If I'm using the chart correctly, you have an expansion factor of 0.0351 (assumed for a worst-case 40-200 degree reheat).So, if you have 1000 gallons, that means you need a tank that can accept 35.1 gallons. Of course, you want to size this for the whole system, not just the tank, so add the fluid volume of each boiler, and a few percent more for piping. It never huts to over-size an expansion tank, except when you have to write a check for it... (let's call it 40 gallons, for the sake of discussion)"
Jim said, "After running a quick search, did not find answer in this forum as to how much water expands with temperature, which is important in sizing a non-pressurized tank and in sizing an expansion vessel in a presurized system. After *oogling this, these are helpful:
http://www.newton.dep.anl.gov/askasci/chem03/chem03335.htm
http://www.ucdsb.on.ca/tiss/stretton/chem2/data19.htm.
A statement is made that, “from freezing to boiling, [expansion] is 4.3%.” Looking at the data table, this seems to indicate that expansion in moving water from 50F (10C) to 200F (95C) is 3.8%. So, 1000 gal of storage needs at least 38 gallons of expansion over this temp range. Plus a margin of error—maybe plan for 5% as a rule of thumb?"
I've more expansion room than these two calculations say is needed, but considerably less than Heaterman's ASME table would indicate is warranted. I can't find any fault with Jim or Joe's calculations or reasoning. Jim's system as mentioned above sounds like it is working just fine. So Heaterman or Jim or any other knowledgeable person, are the ASME calculations overkill? Am I missing something here?
Mike
