Expansion Volume needed? 1200 gallons

[NE WOOD BURNER]

My buddy is installing a 1000 gallon tank and his total volume for system is 1200 gallons. What would you recommend for expansion volume?

 

[Bob Rohr]

use this free online calculator at Wessel. If you use the Expansion window it will show you both the bladder type, and blank, plain steel tank.

Notice how large a plain steel tank must be for that much capacity.

http://westank.com/calculator/

 

[maple1]

My buddy is installing a 1000 gallon tank and his total volume for system is 1200 gallons. What would you recommend for expansion volume?

He could also try an open expansion tank located up high above the rest of the system - that would allow him to get by with something like a used 30 gallon hot water heat with 10 gallons or so to spare.

I have a 110 gallon propane tank for closed expansion for my 660 gallons of storage.

 

[NE WOOD BURNER]

He is using a figure of 4.3% for expansion comes to 51.6 gallons.

This is his math:
Extrol #30: = .4 gal tank with 2.5 gal acceptance

Extrol #60: = 7.6 gal tank with 2.5 gal acceptance

Extrol sx-160: = 86 gal tank with 46 gal acceptance

Just wanted to double check. The 4.3% number seemed low to me from my recollection of previous conversations.

 

[henfruit]

Two extrol 110s will do it. I have one 160 and it works also but it is border line.

 

[Bob Rohr]

Two extrol 110s will do it. I have one 160 and it works also but it is border line.

Here is the calc from the Amtrol Extrol online calculator

 

[NE WOOD BURNER]

Thanks for the replies. I think he will be tight with the one 160. two 110s would be the best, but he has one 160 already. Ill leave it to him. Henfruit: you have one 160 and have you experienced any issues?

 

[maple1]

Been checking into this stuff some.

The 90v is 44 gallons with 34 acceptance.

The 110v is 62 gallons with 34 acceptance.

I thought acceptance was key - so no advantage going with the 110 over the 90?

(Only difference is the 110 is a foot higher, on the face of it).

Just a bit confused that's all...

 

[ewdudley]

Been checking into this stuff some.

The 90v is 44 gallons with 34 acceptance.

The 110v is 62 gallons with 34 acceptance.

I thought acceptance was key - so no advantage going with the 110 over the 90?

(Only difference is the 110 is a foot higher, on the face of it).

Just a bit confused that's all...

Acceptance is the maximum volume the unit can take in without stretching the membrane too much. Typically the tank needs to be sized to be 8 to 10 percent of the volume of the system. But acceptance only needs to be the volume of system expansion from minimum temperature to maximum temperature, typically 4 percent or less of system volume.

Usually acceptance volume for a given tank is significantly larger than needed because the limiting factor is the tank size. The 90v and 110v both have enough acceptance for about a 900 gallon system, but the total tank size is only big enough for about a 440 gallon and 620 gallon system respectively.

 

[maple1]

Think I figured it out in the shower after I posted (seem to do a lot of thinking there). The other side of the volume would be air capacity, so the bigger it is the less the psi will rise when taking on the same amount of acceptance.

I seem to be spending a lot of thinking time on my expansion situation and how to improve it without intruding into places where I really don't want to or can't put it.

 

[ewdudley]

I seem to be spending a lot of thinking time on my expansion situation and how to improve it without intruding into places where I really don't want to or can't put it.

Expansion tanks can go pretty much anywhere, but often it is important to connect to the system at a particular point, in which case you have to run a line all the way from the tank(s) to that point. The distance could be a couple hundred feet if you're using 3/8" or 1/2" PEX (for instance) to tie it in.

 

[rkusek]

Two extrol 110s will do it. I have one 160 and it works also but it is border line.

sx110v seem to cost almost $500 only about 20 bucks less than a sx160v. I'm looking at a sx160v and a sx40v which would cost about $640 instead of a thousand bucks for 2 sx110v's. Am I missing something or wouldn't the cheaper option yield a combined 106 gal with 54 gal acceptance?

 

[maple1]

I've been over every scenario about where I could move my current tank, or how I could replace it with smaller ones, or all kinds of different options. I think if I do anything it will be a mix of a couple of conventional non bladders in the joists, one each on my boiler and storage (already have one above the boiler), and an sv-90 sized bladder tank on the floor beside storage. An ideal spot for one big non bladder would be beside a chimney chase in the master bedroom 2 floors up, but no way that idea will fly with my other half. I think for now I will add the second joist tank to top of storage for this winter, and maybe see if I can get an air pig full of nitrogen to recharge my floor tank with. It seems to have lost some air over the summer. The two joist tanks should add up to 30 gallons.

 

[Bob Rohr]

Expansion tanks can go pretty much anywhere, but often it is important to connect to the system at a particular point, in which case you have to run a line all the way from the tank(s) to that point. The distance could be a couple hundred feet if you're using 3/8" or 1/2" PEX (for instance) to tie it in.

But also, if you mount the tank below the connection point to the system, several feet for example, you do add some static pressure to the tank and slightly reduce the expansion capability. Unless the tank is sized dead nuts on, this should not be an issue.

Same thing happens if you over-pressurize the tank, for example fill pressure 12 psi, air charge 15 psi, as some suggest. adding that 3 psi above the fill pressures reduces a common #30 Extrol tank acceptance by almost 1 gallon.

Had to try that in the shop to see how much it changed. Keep in mind a #30 tank only has a 4.3 gallon acceptance, so over-pressurizing a tank could cause pressure to rise, possibly dumping the pressure relief.

Really the best method is pre-charge to match fill.

Solar guys sometimes over-charge to handle low temperatures in the collector, but the tanks on solar are quite a bit larger to handle temperatures from Ambient to 300° or even higher with evac tube solar collectors, so acceptance volume is accounted for. Typically in hydronics we size the tank for a temperature operating range 65F- 190F.

 

[jebatty]

My system with 1000 gal storage has about 1100 gal total. One SX-160V was not enough to maintain pressure when the system cooled down to about 59F over the summer to fall start-up and 195F maximum system temp (about 22 psi max and 10 psi min, single floor no basement structure). I added a SX-40V and that maintains pressure.

 

[DaveBP]

But also, if you mount the tank below the connection point to the system, several feet for example, you do add some static pressure to the tank and slightly reduce the expansion capability. Unless the tank is sized dead nuts on, this should not be an issue.

But isn't the inverse also true: If the expansion tank is mounted above the boiler/circulator it can ADD usable expansion volume?
Like ,say, up on the second floor in a basement boiler system>

 

[ewdudley]

But isn't the inverse also true: If the expansion tank is mounted above the boiler/circulator it can ADD usable expansion volume?
Like ,say, up on the second floor in a basement boiler system>

Yes, that's right. If the system requires 12 psig static pressure at the boiler in order to have 4 psig at the top of the system, and if the expansion tank is at the same elevation as the boiler, and max desired pressure is 28 psig (at the boiler), then the tank goes from 12 psig to 28 psig.

But if the expansion tank is at the top of the system then the expansion tank would be preset to 4 psi and would go from 4 psig to 20 psig while the boiler was going from 12 psig to 28 psig.

For the same size tank It takes more water to go from 4 to 20 psig than it does to go from 12 to 28 psig.

 

[Bob Rohr]

But isn't the inverse also true: If the expansion tank is mounted above the boiler/circulator it can ADD usable expansion volume?
Like ,say, up on the second floor in a basement boiler system>

Sure, but you do want the pump located as close as possible to the tank connection. Locating the tank upstairs, you would want to pipe it down to the circ location

 

[DaveBP]

Sure, but you do want the pump located as close as possible to the tank connection. Locating the tank upstairs, you would want to pipe it down to the circ location

Yes. In my case, the expansion tank connects to the system just upstream of the boiler circulator.
And I see almost exactly the pressure numbers that Eliot's example suggested.