newb & over pressurization of back-up boiler

[stayalert]

yesterday I had the pleasure of performing the first burn in my new Tarm Solo Innova 50 w/ 800 gallons of pressurized storage.

After several hours I started to bring the whole system up to temp. and was a little lax in bleeding some h20 every now and then....Thus my old boiler (propane) was overcome (in a pressure sense) and dropped a few gallons on h20 on the floor....No big deal just thought I share so other news can learn from my mistake.....Bottom line is when you heat ALOT of water it gets bigger......I'm on day 2 and starting to feel like things are stabilizing absit.....

Best,

Rob "not so stayalert?" M
Norwich, VT

 

[maple1]

What is your expansion tank set up? How much pressure did you get to? And not sure about what you meant by the bleeding water comment - there are spots in the system you'd want to bleed air (e.g. high spots in distribution loops), and spots where you'd likely not want to bleed anything (e.g. expansion tank).

 

[thecontrolguy]

Thus my old boiler (propane) was overcome (in a pressure sense) and dropped a few gallons on h20 on the floor....No big deal just thought I share so other news can learn from my mistake.....Bottom line is when you heat ALOT of water it gets bigger......
Best, Rob "not so stayalert?"

Rob; It has been increasingly my experience that engineered hydronic systems are being installed with the intenetion of covering the narrow operating band of, say 160 -185 F, for expansion needs. This keeps the system pressure near the intended operating pressures of say, 18 psi, most of the time. OUTSIDE of this, the pressure varies widely and can put some parts of various systems into sub-atmospheric pressure ranges and cause severe cavitation issues with pumps. I think the general consensus is that most systems are designed this way as the suggested engineering practices are are for fossil-fueled boiler systems and reducing the installed cost of individual components. This then, should work as those systems typically operate inside of the engineered parameters. However, at startup, and any time the operating temperature falls, or is set back, the system pressure will vary widely if your expansion tank(s) volume does not accomodate the variance. Do any system integrators on this list design wood or solar heated systems differently as far as operating limits and expansion volumes are concerned?

How much total volume do you have and how much expansion room is there?

 

[stayalert]

At the Tarm I was about 20 psi, the expansion tank provides 12 psi......must have been ~30 psi at the propane boiler to start having that let some h20 out......Things seem to have stabilized now though....

 

[stayalert]

sorry control guy...posts crossed....I need to learn some more about the volume of my system and volume of the exp. tank before I can post anything useful.....Meanwhile I had a nice short power outage which provided a nice test of the "no electricity overheat loop".....

 

[stee6043]

I think the general rule of thumb is that you should have 5-10% of your total system volume in acceptance volume. I've got 120+ gallons of expansion tank volume on my 1,100 gallon system and my pressure ranges from 15/16psi (60 degrees everywhere in the system) to 26/27psi (190 degrees everywhere in the system).

If you're letting water "out" when the system is hot I think you're going to have some challenges when the system cools. Whether this is a weekend or a summer. If all you have is a small expansion tank or two you're going to have some challenges managing pressure. Post up some photos!

 

[maple1]

There was another thread here a while ago about big pressure in only one part of the system. I still don't see how that happens - would seem to me the pressure should be the same throughout the system?

 

[stayalert]

here's the set-up.....2 x400 storage, 1 Tarm solo Innova 50, 62 gallon exp. tank.......Magnetic flames optional!

 

[stayalert]

The wood boiler/storage are ~ 8' higher (elevation) than the propane boiler......Is that a factor?

 

[thecontrolguy]

I think the general rule of thumb is that you should have 5-10% of your total system volume in acceptance volume. I've got 120+ gallons of expansion tank volume on my 1,100 gallon system and my pressure ranges from 15/16psi (60 degrees everywhere in the system) to 26/27psi (190 degrees everywhere in the system).

Yup, that's what I was talking about "the rule of thumb" ! This general thought is for fossil fueled systems where the operation temperature, and thus pressure, is quite consistent. I feel that system integrators, and home brewers need to consider that these rules need to be reconsidered for a system where the temperature can fluctuate more than the 'usual' and thus require different engineering practices. So, what I am suggesting is that more expansion room is required for a system that has a widely fluctuating delta-T such as the 'average' wood fired system.

Also, and this is the important note, as Stee .. pointed out, the acceptance volume is NOT the size of the expansion tank, but the total volume that it can accept. Thus a 42 gallon expansion tank may only 'accept' 25 gallons of liquid. Just sayin ...

 

[jebatty]

Just as the size of the expansion tank is not the acceptance volume, acceptance volume is not the final factor. This Extrol brochure is the best guide I have seen to sizing an expansion tank. Look particularly at page 8 where it shows how to calculate total expansion tank volume and acceptance volume to determine what size expansion tank is needed.

 

[Clarkbug]

I would also say that you most likely need to add more expansion capacity in your system. I have only 660 gallons of storage, but I had to have three of the expansion tanks that you have (my max system pressure is around 23 PSI, so I have a much narrower range to play with). Use the reference that jebatty provided, and you can get exactly what you will need.

Also, the fact that the wood boiler/storage is higher than your propane boiler means that your propane boiler will see a few more psi than the wood boiler. 2.31 feet of distance equals one PSI.