Well and Hot Water Expansion Tank

[Bannerman]

Your well system pressure settings are 40/60 psi. The thermal expansion tank will not be required unless the system pressure exceeds 60 psi. Setting the thermal X tank pre-charge to 60 psi will then result in 0 water in the X tank under normal 40/60 psi conditions, and the maximum available space for water expansion when 60 psi is exceeded.

Reducing the X tank pre-charge will cause water to enter the tank under normal usage conditions, which will reduce available space for expanded water when the system pressure exceeds 60 psi. Setting the pre-charge to only 40 psi will then result in water entering at only 40 psi, so the tank will be substantually filled to capacity @ 60 psi, leaving minimal space remaining to absorb expansion above 60 psi.

While there are frequent discussions about the pressure home piping will tolerate, the weak spot in the system will usually be rubber hoses to connect the clothes washer and similar movable appliances. Due to degradation from drying-out, flexing and pressure variations, it is recommended to replace those hoses every 5-years, but how many homeowners actually do that?

With a 60 psi pre-charge, the thermal expansion tank calculator Reach4 linked in another thread, indicates the minimum thermal X tank required for a 60 gallon WH when raising the water temp from 80℉ to 140℉ @ 60 psi is 1.5 gallons to accept 0.74 gallons expansion.

Since I used a higher 140℉ setting than most people set, and a lower 80℉ incoming temp than the recommended 90℉ to account for higher than average hot water use, your 4.8 gallon tank should be more than sufficient.

http://tools.watts.com/ETP/

Edit: Since your Clack based iron filter incorporates a check-valve, is it actually an AIO or Ozone system? Iron removal filters do not normally utilize a check-valve otherwise.

 

[Rotaris]

Thank-you Bannerman! I do have cold incoming water 46F in winter, and Hot water set at about 130F/140F. 40 gallon HW tank.
The Iron filter is air injection, Thus the reason for the check valve. Thanks for the link to the watts tool!
I really appreciate everyone's feed back. Great learning here!
Just puzzles me so much as to why pressure in the line exceeds the 60 psi in expansion tank, after hot water is being used. to me it could go up a couple psi, maybe 5psi or so, not 10. I am going to have to do more testing when time permits.

When using the watts tool I am coming up with Total Volume 6.6, my tank is 4.8 gallon. Maybe I just need slightly larger tank. If i read this right?

Tank is drained with large tub, and wifes long showers hmmmmmmmmm. Maybe I am a little shy on expansion tank sizing?

 

[Sponsor]

 

[Reach4]

Just puzzles me so much as to why pressure in the line exceeds the 60 psi in expansion tank, after hot water is being used. to me it could go up a couple psi, maybe 5psi or so, not 10.

How motivated are you to understand it?

Simplified version: figure out how much extra water volume gets created when your WH heats the water. There are equations for that.

Then figure out how much pressure increase you get when you push that water into a pressure tank, and thus compress the precharge air by that volume. There is something called Boyle's law that says that for a fixed amount of air molecules, the pressure of the air is proportional to the volume the air. But in doing the math, you have to convert pressures to absolute pressure (add about 14.7 psi), rather than gauge pressure, and convert back to gauge pressure after the calculations (subtract about 14.7 psi).

 

[LLigetfa]

Just puzzles me so much as to why pressure in the line exceeds the 60 psi in expansion tank, after hot water is being used.

Very basic physics... as the expanded water starts to flow into the tank, it compresses the volume of air into a smaller space. As air is compressed, the pressure increases.

 

[Bannerman]

Based on the info you provided, the sizing tool specifies a 1.64 gallon tank @ 40 psi pre-charge to accept 0.6 gallons expansion. With 60 psi pre-charge, then a 1.2 gallon tank to accept that same 0.6 gallons expansion.

A larger X tank than needed will contain additional air which will not be compressed as much from that 0.6 gallons so the resulting pressure increase should be lower. From the tool, we are not told the amount of pressure increase expected for a 1.2 gallon tank to accept 0.6 gallons expansion.

Your expansion will actually be less than above because I input 45 degrees incoming water temperature but a higher temperature is usually used since the amount of 45 degree incoming water will be usually only a portion of the entire tank capacity.

If your tank is holding the correct pre-charge long term, a 10-psi increase above 60 psi should not be a concern.

 

[Rotaris]

Thanks guys, yes I understand the math do do all this, for me though, there are a quite a few un-knowns. Distance of 1"pipe (approx) 200 feet under 9 feet of soil (what is temp). temp of water in tank after x amount of use. I just thought from very small research that the 4.8 gallon expansion tank would be more than enough to cover the expansion. I understand the workings of the expansion tank.
I Just do not understand why it does not fully defeat the excess pressure.
I think we have given this horse its fair share. I digress!

 

[Rotaris]

Based on the info you provided, the sizing tool specifies a 1.64 gallon tank @ 40 psi pre-charge to accept 0.6 gallons expansion. With 60 psi pre-charge, then a 1.2 gallon tank to accept that same 0.6 gallons expansion.

A larger X tank than needed will contain additional air which will not be compressed as much from that 0.6 gallons so the resulting pressure increase should be lower. From the tool, we are not told the amount of pressure increase expected for a 1.2 gallon tank to accept 0.6 gallons expansion.

Your expansion will actually be less than above because I input 45 degrees incoming water temperature but a higher temperature is usually used since the amount of 45 degree incoming water will be usually only a portion of the entire tank capacity.

If your tank is holding the correct pre-charge long term, a 10-psi increase above 60 psi should not be a concern.

I fully concur with you Bannerman!!

 

[Reach4]

Thanks guys, yes I understand the math do do all this, for me though, there are a quite a few un-knowns.

I think we have given this horse its fair share. I digress!

So your GAS level is too low to use a spreadsheet to work on it. You had asked that question a bunch of times, and got consistent answers for the most part.

 

[Rotaris]

So your GAS level is too low to use a spreadsheet to work on it. You had asked that question a bunch of times, and got consistent answers for the most part.

Consistent and fantastic answers!
I thank everyone once again for the time and patience. Hope I did not come across as ungrateful?
As of now, being busy with work I need to move this project to a later date.
With all the information I have, I need to hold up my end of the deal.
I will report back.

 

[LLigetfa]

I don't recall mention of Boyle's Law but that explains the pressure rise.

 

[Rotaris]

Did an experiment today, drained hot water tank, incoming water about 48F. Had Expansion tank pre-charged to 59psi. Let system hit high cut-off of 60psi.
Did not touch anything for 4 hours. Pressure climbed to 68psi.
Wanted to leave it longer, but accidently hit the flush on toilet..doh!
Think I am good with that.
Still want to leave it longer and see if pressure wants to come down after x time.
Wife is off this weekend, so doubt its going to happen next couple of days.
"WHEN CAN I USE THE WATER" I can here it now. lol