Solar Space Heating Storage Tank Size [RE-wrenches]

[Tom Simko]

Travis,
 As to the heat exchangers, its pretty hard to beat a roll of type K copper
for cost effectiveness and ease of installation. I threw a 60' roll of 3/4"
K into my 500 gallon storage tank about 20 years ago, and its still working
fine, (glycol loop now serving 6 4x8 Heliodynes). I also augment the thermal
array with a wood fired boiler (my own design) if needed.  A finned
exchanger would be the way to go if room was a factor,but you'll have plenty
of course in the size tank you're considering.
 The ICE blocks should make a dandy storage tank, just make sure you dowel
the floor slab with rebar to lock the walls into place, and more foam sheet,
especially on the bottom sure wouldn't hurt, more is better in this case.
I'd suggest a 1,000 gal tank max, 750 minimum.
  
Tom Simko
Skyline Solar
Idaho 


on 3/6/04 9:41 AM, Travis Creswell, Ozark Solar at ozsolar at ipa.net wrote:

> Hello All,
> 
> I am designing a storage tank (atmospheric) for the radiant in floor heating
> system for my new shop.  The office portion the shop will be constructed of
> Insulated Concrete Forms (IFC's) with a concrete roof.  This will allow it
> to be also be used as storm shelter.  Three tornados missed us by less than
> 5 miles last spring.
> 
> These same forms will make a great tank as they are plenty strong and well
> insulated.  One wall of the storage tank can be shared with the office
> reducing the number of forms needed for the tank and the concrete pump trunk
> will already be on site for the office walls.  I've had an engineer look it
> over and he has given it his blessing to build a tank up to 8' tall!
> 
> Of course I will have to line the tank, which is easy enough with EPDM.  A
> reasonably tight insulated lid will need to be constructed as well.
> 
> I'll have 400 ft2 of liquid flat plates and a very efficient wood
> gasification boiler rated at 140,000 Btu's output.  Does 600 Btu's/ft2/per
> day sound right for the solar thermal array?  I'm thinking that is safe as
> here in Southwest Missouri our average winter daytime temps are reasonably
> mild.
> 
> My main questions are the size and shape of the tank.  I can build the tank
> in any size or shape (tall and skinny vs. short and wide for example).  In
> looking over some of my dated solar books, 2 gallons per sq ft seems to be
> the maximum ratio of thermal collector to storage.  I assume that "rule of
> thumb" was long before the widespread use of radiant in-floor heating.
> Since radiant in-floor requires lower temps than baseboards or forced air is
> it acceptable (or required) to use a larger storage tank?
> 
> I've built a very detailed spreadsheet that allows me to see how long it
> will take to "recharge" various sizes of tanks with the solar thermal array
> and the wood boiler.  The most efficient operation of the boiler is to be
> fill it with wood then run wide open until the wood is gone.  If the tank is
> not large enough then the boiler will shut down and smolder thus lowering
> the efficiency of the burn cycle.  The spreadsheet shows me that one firing
> of the boiler will easily charge up to a 1500 gallon tank.  But this size of
> tank amounts to nearly 4 ft2 of thermal per gallon of storage.  One idea is
> to build a tall skinny tank.  I could place the solar heat exchanger higher
> in the tank so it has less water to heat.  This is assuming that
> stratification will keep all that heated water up near the top.  Can anyone
> confirm if this is a reasonable expectation?  The space heating tanks that
> I've seen are very short but that might have been for structural reasons.
> 
> Does anyone have a source for the finned copper coils that were commonly
> used in these systems?  I'd rather use them than make my own coils.
> 
> Any thought and suggestions are appreciated.  I'd be glad to share the
> spreadsheet and the system diagram should anyone want it.
> 
> Thanks in advance!
> 
> Travis Creswell
> Ozark Energy Services, Inc.
> 
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