Heat Storage

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Robby
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Post by Robby » Sun. Mar. 29, 2009 1:00 pm

Good Morning,

I am installing a 1200 gal. hot water, pressurized, storage tank. About 10,000 lbs. of water. The old 1lb water,1 degree =1 BTU. My question: How about the tank? My tank weighs upwards of 2000 lbs. Insulated with foam to about R45. Do you add the 2000 lbs of steel to the TOTAL # of pounds, that would then mean 12,000 lbs. of storage.

Robby

 
CapeCoaler
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Post by CapeCoaler » Sun. Mar. 29, 2009 1:15 pm

Yes.
Any mass on the inside of the insulation counts.
Steel is denser so it holds more heat but is not as conductive as water so it takes longer to dissipate the heat.
But it is thin so should not be problematic.

 
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steamup
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Post by steamup » Wed. Apr. 01, 2009 9:12 am

FYI
Specific heat of water is 1 btu/lb/deg. f.

Specific heat of steel is .12 btu/lb deg. f.

Although the steel will had to the mass storage, it will hold only 12% the heat that water will.

Don't forget to add expansion tanks to your pressurized storage system. 1200 gallons of water will require big expansion tanks on the system.

I am doing 500 gallons of pressurized storage and was shocked at the cost of the tank I will need. :shock: And I get my equipment wholesale though my business contacts.


 
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Robby
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Post by Robby » Wed. Apr. 01, 2009 10:35 am

Yeah, I know. I am keeping the original expansion tank, Watts ET90 (13 gal) and have purchased a ETSX160, which is 81 gal. According to Watts chart I have enough. Yes, expensive, but I did not see any choice. If system is done right it should out-last me.
I did not realize that steel was that poor a heat sink. I keep learning.
Besides, if the economy keeps going in the toilet, I might be the only one with heat!

Robby

 
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steamup
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Post by steamup » Wed. Apr. 01, 2009 10:50 am

Be very wary of the charts the manufacturer's publish. They are for "standard" systems and do not allow for high volume systems.

Fill pressure, relief valve pressure setting, intial fill temperature and maximum system temperature affect expansion tank sizing.

Based on 1200 gallons, 8 psi fill, 30 psi relief, 60 deg. intial water, you should be good to take your system to about 200 deg. F. before you run out of expansion tank and pop the relief valve.

Note that standard fill pressures are 12 psi which are higher than what is needed for most residential systems. Adjusting it down saves on expansion tank size a little bit in large volume systems.

 
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Post by coaledsweat » Wed. Apr. 01, 2009 11:10 am

steamup wrote:I am doing 500 gallons of pressurized storage and was shocked at the cost of the tank I will need. :shock: And I get my equipment wholesale though my business contacts.
500 gallons is about 1/2 of what I would recommend for the average home.

I looked long and hard at heat storage years ago. I personally think the systems create more cost, complexity and risk. With wood, it can be required in some cases. However with coal, I like it simple, cheap and reliable. I would suggest an appliance upgrade would be cheaper/easier/safer if yours has trouble meeting it's heating demand.


 
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Post by LsFarm » Wed. Apr. 01, 2009 11:25 am

What kind of costs are you expectiing with a storage tank system??

I agree with coaledsweat, that upgrading to a stoker boiler, a used and refurbed unit, would in most cases be less expensive. With wood, to be efficient, a storage system is just about a necessity, but coal doesn't loose efficiency with lower burn rates and BTU demands like wood does..

If your costs for a tank and all the added plumbing, valves, expansion tanks, controls exceedes $3000, you will never see a payback..

I'd convert to a refurbed EFM, AxemanAnderson, or Keystoker..

Greg L

 
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Post by steamup » Wed. Apr. 01, 2009 12:21 pm

coaledsweat wrote:
steamup wrote:I am doing 500 gallons of pressurized storage and was shocked at the cost of the tank I will need. :shock: And I get my equipment wholesale though my business contacts.
500 gallons is about 1/2 of what I would recommend for the average home.

I looked long and hard at heat storage years ago. I personally think the systems create more cost, complexity and risk. With wood, it can be required in some cases. However with coal, I like it simple, cheap and reliable. I would suggest an appliance upgrade would be cheaper/easier/safer if yours has trouble meeting it's heating demand.
My "storage" will be more of a "Buffer" tank to allow me to shut down when there is no heat load and only DHW load or to allow the system coast for just a couple of hours while the workshop is being brought up to temp. This is a hybrid system. I'll post something about it after I get my boiler installed.

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