Post in 'The Boiler Room - Wood Boilers and Furnaces' started by stihlgoin, Mar 13, 2008.
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Nicely spotted. I stand corrected.
Well, after visiting Gary this morning, my wife and I are pretty much set on his 1450 gal. unit. To heat two homes and provide domestic hot water, it would average 1 firing/day, though maybe twice/day in the coldest months. I have a "neighbor" with this model, so I'll call him to check it out. The other option would be to get a 1050 gal. and have a 1,000 gal. propane tank for water storage, but it would take up most of my planned shed space. -I'd rather not build bigger due to property tax issues, so I'll most likely go with the 1450 as stated before. It's a very intuitive unit, and has SOME built in room for tweaking WITHOUT modification. His office unit ran very impressively, and he demonstrated how the different air variables affected the properties of the burn. You could see and hear the fire change almost instantly when any of the air flows were changed. Then, of course, Gary let the controls take over and you could hear the proper "roar" that came with the ideal balance of primary and secondary airflow. You could also see the stack temp (flue) fall back into the desired range at this point. It was good stuff, and a nice visit to boot. I'd like to add that I'm positive a Garn would suit our needs as well, but I REALLY like to keep my business as local as possible. So, no Garn bashing from me. They do their job well from what I've read, just with a different method to accomodate for operator error/variation.
Does Gary offer the expansion tank? If not, that could be pricey too.
It's included with every boiler Gary sells but in my install the total storage will exceed 3000 gal so I'm getting a 500 gal used propane tank for expansion.
Maybe I'm confused, but I thought that the whole function of a true expansion tank was to separate the atmospheric air from the expanding water with a bladder, not just a reservoir to dump excess water into and then siphon back in when it cools down. I my opinion that is a semi-closed system kind of like a coolant system on an automobile. You have to be able to separate the water from atmospheric air or the water will absorb o2 even if the reservoir tank is closed it is still filled with air that is sharing the same volume as the water. Is this right?
Over time all of the oxygen from the expansion tank will be consumed as it reacts with iron in the system. Once that is done, no further oxidation will occur unless the system has additional water added.
If thats the case, then why do expansion tank mfgs. put bladders in them? Like when a water well expansion tank ruptures the bladder the compressed air dissolves into the water and there becomes no room for expansion and the pressure switch starts to short cycle.
Are you saying that after the 20 some % of o2 is consumed the 78-80% of remaining gases will fill the compression void?
Your do have some valid points. Modern expansion tanks for bladders to prevent them from eventually becoming waterlogged. We use to bleed the old compression tank on our well about once ever two years. (Pre-bladder days) Plus the other gasses may well dissolve in the water over time although this happens more slowly at higher temperatures as gasses are less soluble at higher temperatures unlike most solids.
So I would agree that one would need to drain the expansion tank every so often and that would intorduce more oxigen into the system. Probably not much at all compared to a truely open system.
Any and all sealed/pressurized systems require an expansion or compression type tank. Water does not compress so therefore you must provide a place for it to expand or contract based on system temperature.
As previously pointed out a system containing a couple thousand gallons of water will require a fairly large tank. My design software says that given normal parameters of fill pressure, height to the top of the system, water temp and piping you need a tank volume of over 200 gallons.
I've noticed that some manufacturers of open OWB's are providing an internal "bladder" that compresses to help limit discharge when things heat up.
What I'm trying to clarify is that a true expansion tank with a bladder is needed in a sealed pressurized system to keep o2 out of the water. Even if water or air is pumped into a single chamber sealed tank only half full of either, the air will eventually dissolve into the water under pressure and the tank will in time become full of water leaving no room for further expansion. My point is that there needs to be a barrier between the air and water or it won't work.
Since we're talking sealed system, the remaining gasses have no where to go but stick around in the expansion tank. With a home water system (open system)new water is constantly passing by that can dissolve the remaining air. With a sealed boiler there is no where for the gasses to go. At higher temperatures gassse will actually come out of solution and be added to the expansion tank.
But most sealed systems have a low pressure reg. that is hooked to the potable water and have air traps to remove air that comes out of suspension when heated. My feel is that the air in the non bladder tank will always become entrained in the water and removed with the air trap until all the air is gone-thus no room for expansion.
Even if the system didn't have a constant fill valve the air trap should be installed. The operator would be constantly adding water in response to the drop in pressure from the air being removed with the air trap.
We obviously need someone with realife experience with such an animal to respond. My bet is that the losses would be very small and annual expansion tank draining would be plenty without too much oxygen added to worry about when you consider the amount of iron in the whole system.
It was Gary's idea to use a propane tank as my expansion. He does it often and has rarely had a problem.
He claims it will work fine as long as the expansion tank is at end of line (single pipe) with no water flow passing.
A well tank for potable water has constant flow and therefore requires the bladder. This situation was not so complicated
when speaking with Gary. I trust him and will follow his advice
the expansion tank on the Switzer ,Ed and I looked at in Mansfield Ct. did have a bladder in Gary's own manufactured expansion tank. as for the propane tank I have no idea.
The Mansfield boiler install is a typical one for Gary from what I understand. But he did suggest I go with the used propane tank. I will call Gary and a few local "old school" plumbers tomorrow to clarify this and report the results. I don't want to make a mistake on 3k storage at 200* + temps.
Expansion tank clarification...............hopefully.
In a sealed and pressurized system one has to account for the expansion and contraction of the heated fluid be it straight water or a glycol mix. This is the sole purpose of an expansion tank. Not to capture and retain air that may be in the system piping. That air you definitely want to get out via the air scoop or air elimination device. In a captive air type tank (bladder or diaphragm) a cushion of air is maintained on one side of the membrane and system water is on the other side. These tanks can typically be of smaller volume than an "open" tank for a given total system volume.
Now...remember that the air or gas in an open style tank or compression tank if you will, consists of components other than oxygen, which is the stuff that causes corrosion. Once the oxygen is dissolved into the system and eliminated through your "air" elimination device you are left with a mostly benign mixture consisting of nitrogen and a few other inert gases.
In a captive air type tank or true expansion type tank, there is no direct interface between the system water and the air cushion. The system water can expand against the bladder or diaphragm and keep the system pressure where it should be. These tanks must be precharged to about 2PSI less than what the system will require for operation.
The bottom line in both cases, expansion or compression style tanks, is that their function is to maintain system pressure, not capture and/or eliminate air.
check this out for expansion tank sizing http://www.watts.com/pro/divisions/watersafety_flowcontrol/support/support_ETsizing.asp
Guess I need to make more calls Monday...
Thanks Heaterman for the facts. I'm curious, would you use a expansion or compression in a large pressurized system?
It would depend on the various factors of the installation. An expansion tank can be mounted anywhere. On the floor, hung from the ceiling, strapped to a wall sitting on a shelf plus they will service a larger volume of water for a given physical tank size. One would want to connect it to the system at the same location as the feed water pressure reducing valve.
A compression tank has to be mounted above the water level of the boiler for obvious reasons. Sometimes this works out really well and in many cases where we have installed a new boiler(s) in an existing system we re-use the compression tank if it's in serviceable shape.
Then there are matters concerning ASME rating for commercial systems with large tanks (they are considered to be a pressure vessel also along with the boiler)......... So many factors, so little time.........
In most circumstances we will use an expansion style bladder or diaphragm tank.
Not needing an expansion tank or bladder of any kind is one of the nice features of a Garn.
Well, construction has started on my "Switzer Shed". It'll be 18'x24' and will house a 1450 gal. Switzer boiler and anywhere from 3-6 full cords of wood. Things got rolling quicker than I was ready for, (contractor availability) so it's been a whirlwind. We're running Thermopex piping between the boiler and our house (75') and my inlaw's (220'). I'll post pics as they become available. Right now, I'm waiting for the slab to be poured tomorrow, and my builders have constructed the walls already. I'm busy dropping trees w/ new leaves so they'll dry for the next couple of months before I cut them and split them. Fun stuff!
My Switzer 3 pass 1050 w/ the two 1000 gal propane tanks was fired today for the first time. We raised the temp of all 3050 gal from 60* to 140* in just over 3 hours. Started the burn with two year seasoned splits and had no smoke out the chimney in less than 5 min. then added some two week old fresh cut and unsplit rounds to see what she could do... a little smoke and lowered stack temps but a suprisingly clean burn. Those green rounds hung around till the end even after we loaded more dry stuff an hour later so I will always try to avoid green wood. It's not worth the lost BTU's. The burn averaged @ 675,000 btu but when loaded with the dry stuff she chugged out over 850,000! IMHO the Garn is the next best thing, after a Switzer....
Next week I will try to get her up to 7 digits....
When are you guys going to post pics? For all I know you guys could be a bunch of retired used car salesmen
Better than a Garn....Thats impossible!
With all do respect , I have watched a Garn burn and also now have my Switzer running. Its not even close.
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