Now I have found a milk tank for sale locally that could be used for storage .....can anyone tell me if these are pressurized or not? Any other input on using them for heat storage would be welcome again. Thank you, RH
Milk tanks for storage ...pressurized?
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headrc said:
Milk tanks are very good storage tanks.
Generally, they are used as unpressurized storage, or minimally-pressurized storage.
In other words, you isolate the tank from your heating system with a heat exchanger (either immersed coil or flat plate), and then either leave the tank atmospheric, or use an expansion tank to capture the expansion, without pre-pressurizing it to the full 12-15 pounds that the rest of your heating system is set at.
Joe
So I assume hooking up a milk tank for storage requires being able to use a cutting torch, welder etc. ...and to be able to do this on stainless steel .....so you can install the heat exchanger? Thx ..RH
I don't think it has to be that complicated. I believe nofossil has a stainless steel milk tank with a big lid. No welding or cutting that I'm aware of, though I suppose he can speak for himself.
The tank I am looking at also has a cooling unit and a compressor with it ....don't know what I will do with that stuff ....hmmm...radiant cooling??? RH
I have a milk tank I'm going to use.... I'll have two hot water heaters up above it for expansion vessels..... I'm not using HX's, I'm going to be using it like pressurized storage, only at like, 4 psi (static pressure from the water in the expansion vessels pushing down...... gravity pressure if you will)
Don't bother with welding or a coil hx. Use a flat plate: highly efficient, small, and less expensive. I suggest getting with 1" inlets and outlets. If you Google these, you will find tables showing btu capacity based on dimensions and # of plates.
I'm using a tank that was made by cutting a large milk tank in half and standing it on end. Someone else did that work - all I had to do was weld a bunch of stainless nipples through the sides.
I used coils in the tank rather than flat plate because copper was cheap at the time and it saves me a couple of circulator pumps. Flat plate HX are nice, but they require an additional circulator for each. It gets a even more complicated if you want to reverse the flow for charging vs. discharging to maximize stratification.
With an open top tank, evaporation control is really important. I'll pull my lid this summer and see how it's held up for the past two years.
I used coils in the tank rather than flat plate because copper was cheap at the time and it saves me a couple of circulator pumps. Flat plate HX are nice, but they require an additional circulator for each. It gets a even more complicated if you want to reverse the flow for charging vs. discharging to maximize stratification.
With an open top tank, evaporation control is really important. I'll pull my lid this summer and see how it's held up for the past two years.
Nofo - does it need to be more complicated that this? Boiler aquastat turns on/off circs to charge tank depending on boiler temp. Zone circ has its own thermostat and draws from a T at the top of the tank. If boiler circs are on, then zone circ is taking hottest water directly off supply line, and if boiler circs are off, then zone circ takes from top of tank. Zone circ returns to bottom of tank. May also need zone valve on zone to prevent thermo-siphoning.
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Does this stuff ever get simpler?? Right now I am wondering if the milk tank is a better idea than the propane tank. Right at this moment I have the option for either of these ...although I may lose one of them if I do not make a decision soon. I really am starting to get cold feet because all of this stuff seems complicated ....so the obvious question is ....which storage solution is less complicated for installation and then for on-going management of the system? Thx, RH
I had open storage for all but the last month when I got the 1000 gal LP tank. There is no question in my mind that if you are able to get a good tank, pressure tank is my choice. I don't have to monitor water level, no water vapor/humidity issue, easy to maintain pH balance, no introduction of O2. Pretty much forget that I have storage.
Hi. I am new to the forum, but have been lurking around for a while now. Just one thought on the milk tanks. Is there any reason why they can't be used as pressurized storage? Most systems only run around 10-12 PSI, correct? Wouldn't the milk tank handle this?
jebatty said:
Looks like zones would be on the unpressurized side of the world. Is that OK? It also means that you'd be feeding your zones through the HX all the time, rather than directly. If the zones are baseboards that need the higher temp, you might be losing a bit of capacity that way.
That having been said, it should work. I think the integral check valve in the circ would prevent thermosiphoning.
forestrymike said:
Some milk tanks might, but many don't seem to be designed for it. 12 psi on a 48" diameter end bell is 21,000 pounds of force. I wouldn't try it unless the manufacturer says that the tank is good for it.
My current thinking is that pressurized storage is better if you have the choice, but I've had zero problems with my unpressurized, as far as I know.
nofossil said:
I'm not sure we're looking at this the same way, or maybe my view is in error. My tank is pressurized LP. I'm showing tank supply to zone T'ing with hx supply to tank. Water will take the path of least resistance, and my thought is that the draw will be all or mostly from the top of the tank and return to the bottom of the tank bypassing the hx. If instead part of the draw is from the hx, which also means pulling cooler water off the bottom of the tank, that easily could be solved by a NC zone value on the hx supply line to tank, which opens only when the hx circ supply is on.
jebatty said:
Sorry - I didn't read it carefully enough. I though it was a proposed solution for the non-pressurized milk tank.
If the tank is pressurized, then why the HX between the boiler and the tank? You could remove that, and then I think you'd have the simplest possible solution. Even with the HX, it's simple enough.
You're absolutely correct. Right now the hx is there because I started with an open system, and it was easier to plumb in the pressurized tank in place of the open tank rather than change the plumbing to pull out the hx.
Also, with the open system, and some concern from freeze-up during an extended absence in winter, I was willing to allow a freeze problem in storage but not the Tarm, so I have anti-freeze in the Tarm, and the hx isolates the systems. This all may change in the future, as I will need freeze protection on the pressurized tank investment (the open system cost me only $125 plus some plumbing -- it was my first experiment with storage, and I didn't want to invest a lot until I was convinced of its value).
Also, with the open system, and some concern from freeze-up during an extended absence in winter, I was willing to allow a freeze problem in storage but not the Tarm, so I have anti-freeze in the Tarm, and the hx isolates the systems. This all may change in the future, as I will need freeze protection on the pressurized tank investment (the open system cost me only $125 plus some plumbing -- it was my first experiment with storage, and I didn't want to invest a lot until I was convinced of its value).
You guys scare the S**t out of me. A milk tank is NOT a pressure vessel, was not ever intended to be a pressure vessel and will likely fail in a rather spectacular manner if used that way.
Think about it.. PLEASE!!
You have a closed system protected by a 30PSI relief valve so that's the minimum you have to consider, not the 10-15# avg working pressure. That pressure is PER SQUARE INCH
How many square inches of area are there on the end of a 4 foot diameter tank? I won't do the math here because if you don't know how to do it, you don't have any business doing what you're talking about. Suffice to say that you are talking TONS not pounds of force exerted on the end of the tank.
If there is one thing I have learned in years of piping and hydronic heating, it's that there are no shortcuts. It has to be done right or not done at all. Not trying to sound like a know it all or be condescending in any way. Hydronic systems have to be designed for the worst case scenario.
Remember, it's always what you don't know that will kill you. Be safe people, saving a few bucks is not worth losing life, limb or property. Do it once, do it right.
The soapbox is now open.
Think about it.. PLEASE!!
You have a closed system protected by a 30PSI relief valve so that's the minimum you have to consider, not the 10-15# avg working pressure. That pressure is PER SQUARE INCH
How many square inches of area are there on the end of a 4 foot diameter tank? I won't do the math here because if you don't know how to do it, you don't have any business doing what you're talking about. Suffice to say that you are talking TONS not pounds of force exerted on the end of the tank. If there is one thing I have learned in years of piping and hydronic heating, it's that there are no shortcuts. It has to be done right or not done at all. Not trying to sound like a know it all or be condescending in any way. Hydronic systems have to be designed for the worst case scenario.
Remember, it's always what you don't know that will kill you. Be safe people, saving a few bucks is not worth losing life, limb or property. Do it once, do it right.
The soapbox is now open.
I agree..... I was going to pressurize my tank too.... But I then decided not to after finding out that there would be 1 ton of force on the manhole lid alone!
I'm going to just have an open-top expansion vessel above the tank.. I'll have the advantages of pressurized (less O2 absorbtion, less evaporation) without the pending pressure explosion....
I'm going to just have an open-top expansion vessel above the tank.. I'll have the advantages of pressurized (less O2 absorbtion, less evaporation) without the pending pressure explosion....
Not to beat a dead horse, but don't try to pressurize anything that's not an approved, rated, pressure vessel, and then stay within the stated operating pressures.
Do a YouTube search on "MythBusters" and "water heater explosion" and you'll see that we're not fooling around with all this safety talk.
Do a YouTube search on "MythBusters" and "water heater explosion" and you'll see that we're not fooling around with all this safety talk.
So just to make sure ....there is not a problem using a propane tank for a pressurized system ....right? Or are there different levels of propane tank that are out there and I now have to be concerned with which type I have been able to get?? Thx, RH
Aside from the safety issue, pressurizing the milk tank would also mean that you would need to find a way to seal the cover against the pressure.
Since the milk tank is stainless, corrosion is not a big deal. Just isolate it from the pressure side with a heat exchanger, and you're good to go.
Joe
Since the milk tank is stainless, corrosion is not a big deal. Just isolate it from the pressure side with a heat exchanger, and you're good to go.
Joe
Eric Johnson said:
Ditto
A propane tank is an ASME listed pressure vessel. The thing to watch though is the re-test date on the tank. If you have one that's past its expiration date an inspector will turn it down and you insurance company will deny any and all claims even remotely connected with your heating system.
There are a lot of advantages to a pressurized heat exchanger sitting in an open tank.
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