expansion tanks

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webie

Minister of Fire
Feb 21, 2009
651
Wisconsin
Ok guys useing pressurized storage of say 500 to 2000 gals . What are you useing for expansion tanks ?
 
I'm using a 250gal propane tank, sdrobertson is using a 335gal anhydruse tank. We each have 2000+ storage. We are on our second year and haven't had to add any air or had any problem. Using it like the old well presure water tanks. Because the water isn't moving much in the tank it doesn't lose it's charge like in a well situation. Water stays clear and isn't any seeable corrosion in the system.
Others are using bladder tanks. Make sure you use tanks rated for hot water.
leaddog
 
joecool85 said:
Yet another reason to use an unpressurized storage tank...

Expansion tanks add some degree of complexity and usually cost-- but on the other hand, you eliminate the costs and potential issues of tank liners, you omit the cost and efficiency losses of a heat exchanger (and, often, one or more additional pumps associated with the HX) and you gain the ability to run your storage up to a much higher top temperature than is generally feasible with unpressurized storage.

I'm doing unpressurized storage-- as there was no way I could fit one or more pressure-capable tanks down and into an early 19th century cellar-- but if I had the option to do pressurized, I probably would have.

It's not a matter of "better vs worse" it's a matter of which suits your own needs as to available space, funds, and which set of trade-offs you happen to prefer.
 
Thanks to leddog and SD I did the " home made" expansion tank route and it works great. With 1000 G storage I used a 100 G propane tank. Use the existing propane gauge to meter water level. Remove the fill valve and bush down and add a schrader valve to add or subtract air. I added a 1/2" pipe extending out of the bottom of the tank to connect to system. ( You could also drop a dip tube down where the fill valve was and have a tee with schrader valve on the side ). Since I added storage this fall I have not touched the tanks since.
Rob
 

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I used a 40 gal water heater tank for my system with 500 gal storage. The water level fluctuates from ~1/4 full to ~2/3 full over the storage temperature range. I also have a small extrol tank on the boiler, I put this on in case I have to run without storage for some reason. I'd think you would want a larger tank for anything over 500 gal. I use the water heater tank as it was free, it cam out of my house when I put in the boiler.
 
I use a 500 liter Amtrol ASME 175 psi expansion tank on my 13 psi system w- 720 gallon storage tank. I paid $500 delivered for this new $7000.00 tank. Overkill? I'd say so. It was a good deal though. I would try a air charged tank thats seems to work well too, Randy
 
There is an on-line calculator that will tell you how much expansion tank capacity you need for given system sizes:
http://www.watts.com/pro/divisions/watersafety_flowcontrol/support/support_ETsizing.asp

I have heard several people say that unpressurized storage is "less efficient" due to the heat exchanger including in this thread. This is an unfortunate choice of words because it sounds to me that something is being lost. That is definitely not the case. When using a heat exchanger with a 10 degree delta T for example, you need to run the boiler up to 190 to get the tank to 180. The 180 tank will deliver water at 170 when drawing from it. In the case of pressurized storage, you don't get this temperature offset, so more of the BTU's are accessible at a higher temperature. However there are commercially available unpressurized storage tanks with very high insulation values. With pressurized storage it seems like people are on their own to find a way to keep the BTU's in storage. I would argue that the unpressurized solution can be very thermally efficient at storing BTU's for a long period of time. This has nothing to do with the fact that the system is pressurized or not, but rather the shape of the tank that makes it easy to insulate effectively. I hope there was a point in there somewhere...
 
With a non-bladder tank, keep an eye on the system pressure. If the tank gets waterlogged, or loses some of the air bubble, you will trip the pressure relief valve. Depending on where the boiler is located this could be a mess.

Also without an auto fill valve you could dry fire the boiler. Some add a LWC low water cutoff switch to cut the power, but a wood boiler can hold heat for some time after a power off. The LWC could protect all the pumps IF the relief tripped and the system lost water.

Compression (non bladder) tanks have been used successfully for years.
B&G builds an "airtrol" fitting to help maintain the air space.

hr
 
I'm using a small (100gal, I think) used propane tank with a home made dip tube.
 
HR or anyone,

While researching the Bell and Gossett Airtrol I found a link where some pros are apparently badmouthing these devices saying "they don't work". Any reason for concern?
http://forum.doityourself.com/archive/index.php/t-342085.html

I'm still trying to decide if I should go the same route as leaddog, RobC, or SD and make my own or shell out the big buck for a pair of bladder tanks to handle my 1000 gal and differences in elevation.

Is they a reason why nobody has tried using a different gas for the air bubble in a bladderless tank? I know the Jensen Tire chain stores here offer nitrogen inflation and I just read a site saying you can get bottles filled inexpensively at welding supply stores as long as you use a regulator to get it down to 50 psi (for tires). Nitrogen dissolves into water so I'm guessing this is why but is their nothing else out there that would work. Maybe not.
 
Pros and cons:

Open tanks, my least favorite choice

some fluid escapes by evaporation, replenishing add more O2 and corrosion potential
the height of the tank dictates the pressure in the system. You always want at least 5 psi at the uppermost piping. So the tank needs to be about 10 feet above the piping point.
Weight, freeze if in an un-heated space, and leak potential

Pressurized non bladder

air is in contact with the water. as the water cools, off season, etc it will resorb the air. Thermosiphoning carries the cooled water and air back in to the system. More corrosion potential.

Diaphragm tanks were developed in the '50's to address all of these problems. They require little if any maintenance, and last for 20 years or more if sized and installed properly.

ALWAYS pump away from the expansion tank, and never two tanks tied in at different locations in the piping, are other guidelines to follow.

I really think you get what you pay for with bladder tanks. The others WORK, but require constant monitoring and maintenance. That may work for you, but what about future owners and operators.

Personally this is not where I would cut corners, it is a vital piece of the system, protect you $$ boiler investment.

hr
 
ALWAYS pump away from the expansion tank, and never two tanks tied in at different locations in the piping, are other guidelines to follow.

Why can't you put tanks at different locations? In my situation I am going to add to the oil boiler system, witch has an expansion tank, I would like to put one at the wood boiler and another at the storage tank. I wanted to separate the storage and wood boiler so I can avoid running with the storage in the dead of winter if I don't need it. Is this not a good idea to have the three expansion tanks in the system? What kind of trouble does this create?
 
I'd like to nominate this thread for "Best resurection of old post - Year 2010". She almost went 7 full months between posts...
 
cheapsx said:
ALWAYS pump away from the expansion tank, and never two tanks tied in at different locations in the piping, are other guidelines to follow.

Why can't you put tanks at different locations? In my situation I am going to add to the oil boiler system, witch has an expansion tank, I would like to put one at the wood boiler and another at the storage tank. I wanted to separate the storage and wood boiler so I can avoid running with the storage in the dead of winter if I don't need it. Is this not a good idea to have the three expansion tanks in the system? What kind of trouble does this create?

The expansion tank connection and the location of the circ pump has a large effect on the pressure distribution in the distribution system. the expansion tank connection creates the PONPC point of no pressure change. When you connect tanks in multiple locations you risk pump cavitation, possibly pulling air IN through air elimination devices. Two or more tanks are fine, just connect them at the same location.

Now if you are going to valve a boiler out of service the tank of course needs to be seen by the other boiler.

Remember also the tank size changes a lot when you have multiple temperatures at play. For example a boiler running 180 F and the distribution system to a radiant slab at 110F. You should calculate the two different fluid capacity and temperature delta t.

here is an example from John Sigenthalers Modern Hydronics (watch for edition 3 with great additions this fall from Delmar)

A radiant heating system with 200 gallons in the radiant loops, manifolds, etc
A boiler loop with 15 gallons
180F, 13.5lb fill pressure, 60F fill water temperature, 30 lb relief = 21.6 gallons of expansion tank volume

With 200 gallons at 110F in the same system = 7.3 gallons of expansion tank volume

So if you boiler is operating a low, or lower temperature distribution you can calculate the expansion tank differently. with wood boilers seeing the large buffer at 180F this may not help. But if it is feeding a large shop radiant system it could make a big difference.
 
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