Solar Space Heating Storage Tank Size [RE-wrenches]

Tue Mar 9 07:27:13 PST 2004

Rules of Thumb:
*    When you exceed 3 gallons per sq. ft. of collector area you get no
benefit from additional storage.  Typically 1.75 to 2.5 gallons per sq. ft.
is the best ratio of gallons per sq. ft. if you are also space heating
during the day.
*    Make sure all penetrations are above the water level.
*    Get 30 or 50 gallon metal drums and roll form 3/4" copper type L pipe
around the drums to form a coil. Use 3 to 4 lineal feet of 3/4" copper per
sq. ft. of collector area.  Use bare copper ground wire to wire the spread
coil to a copper ground road. Pull your heat from the bottom coils to the
top.  You can buy finned coils from SEPCO, VAUGHN, or WOLVERINE COPPER - but
it is more cost effective to make your own.

Gator Tom

----- Original Message ----- 
From: "Tom Simko" <tom at skylinesolar.com>
To: <RE-wrenches at topica.com>
Sent: Saturday, March 06, 2004 11:20 PM
Subject: Re: Solar Space Heating Storage Tank Size [RE-wrenches]

> 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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