[Greenbuilding] Site Built Thermal Storage Tanks

don lush dlush at ca.inter.net
Tue Jul 21 16:21:13 CDT 2009 

Eli- I am in the final design phases and am planning on the following.

Under the long axis of the house (south facing) I am excavating down an
extra 7 ft and creating a space 12 ft x 40 ft. The sub grade walls will be
built with ICF walls insulated with foam board on the outside and under the
slab (to achieve an R-35) and lined with roofing membrane. The top ICF block
all around will have a brick ledge on the inside forming a 4 in lip. There
will be 2 internal ICF block walls separating the tank into 3 sections each
independently lined with membrane. The tank roof will consist of layered 4x8
sheets of foam (To achieve R-35) and covered with a roofing membrane resting
on the brick ledge and supported in the center by the ICF walls. I am then
planning on laying 2x6 pressure treated joists on 16 in centers on the
membrane and laying fibreglass batts between the joists. A plywood subfloor
will then top it. Access will be through the last set of joists on 2 ft
centers where the batts, membrane and rigid foam can be removed for access
and where the plumbing access will run. 
The plan with the 3 sections is to use one for rain water storage for
preheating hot water for washing purposes. The other 2 can either be
gradually filled with rain water over a few years or filled with well water
and used as a heat storage medium for use with solar hot water heaters. The
hot/warm water would then be run through a hot water tank to top up the
temperature as necessary for the hydronic in floor heat distribution or
through a heat exchanger to pre heat air for an air distribution system.

At this point it is still a concept and the plumbing details have yet to be
worked out.

If anyone sees any "fatal flaws" in the concept please let me know. 

Thanks Don

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Eli Talking
Sent: July-21-09 12:52 PM
To: greenbuilding at listserv.repp.org
Subject: Re: [Greenbuilding] Site Built Thermal Storage Tanks

My last inquiry did not generate much interest.  However, site built thermal
water tanks are a big issue.  Active solar requires a thermal water tank. 
If used for space heating the tank needs to be very large.  Purchasing
prefabricated tanks requires many units with greater surface area (material
and heat loss).  I hope there are some list participants that can share
their experiences, both positive and negative regarding site built thermal
(water) storage tanks.  As my message below describes, I am interested in
using the typical foundation as a tank.  The potential is great.  However,
maybe the vulnerabilities are also.

Eli

----- Original Message -----
From: "Eli Talking" <elitalking at hughes.net>
To: "Clarke Olsen" <colsen at fairpoint.net>; "Nick Pine" <nick at early.com>
Cc: <greenbuilding at listserv.repp.org>
Sent: Monday, July 13, 2009 4:21 PM
Subject: Site Built Thermal Storage Tanks


>I am interested in developing large thermal mass by using the building 
>foundation as the tank for water that is the full footprint of a building. 
>This is to achieve an impressive amount of energy storage by achieving a 
>large volume at a low cost since the structure is already paid for.
>
> When discussing this approach, I commonly get skeptics that question if I
> can reliably build a water and vapor tight installation.  Since I have no
> experience, I must take those concerns seriously. My initial proposal is 
> to
> seal all surfaces with R50 closed cell insulation.  2" is said to be a 
> vapor
> barrier.  Therefore, if I could achieve an air tight access panel, this 
> seems
> likely to prevent vapor from entering the building to cause problems.  One

> closed cell manufacturer is leery of standing water.  Therefore,
> another water impermeable layer may be needed on interior side of
> vertical and lower horizontal surfaces.  I am looking at a non pressurized
> situation.  Therefore, the upper side would not have standing water
> pressure.  I like foam and sprayed or brushed on products because 
> installation is continuous, avoiding the vulnerability of leaky seams.
>
> If I can truly make the tank tight, will it become pressurized from
> expansion of water volume by heating from 70F to 160F? Is this a problem?
>
> What is a good interior surface for reliable waterproofing? Could swimming

> pool technologies be applied?
>
> Bob Ramlow in his book, "Solar Water Heating" says on page 39, "There
> have been many attempts over the years to build storage tanks in place and
> line them with plastic or rubber.  These do not work and will fail.  The 
> liner
> in these tanks is not designed for withstand temperatures commonly
> encountered in the system. They will often become brittle and eventually 
> leak and crack."
>
> Nick Pine has strongly advocated for plywood box with rigid insulation and

> EPDM liner as a cost affective thermal tank.  Nick, has your experience 
> confirmed that this is a durable installation?
>
> I am looking at using a drainback system, that I now know is a standard
> application for active solar systems where the collectors only circulate 
> water when the sun is out.  It drains back to a tank where the heat 
> exchanger coils are always covered even when the collectors are filled to 
> the maximum.  A solar engineer from AET (manufacturer of flat plate 
> collectors) has told me that the water circulated to the drain back tank 
> from the main tank should be drawn for 1/3 the top of the tank.
>
> Can this loop of moving water and heat be done from a non pressurized 
> tank, or does there need to be another heat exchanger in large tank?  I 
> would think no heat exchanger would be more efficient. This would still be

> a closed loop, since the same water would be recirculated continuously, 
> even if tank is not pressurized to plumbing pressures.
>
> I am interested and open to hearing the advice of people that have
> experience and insights to site built thermal storage tanks.
>
> Eli
>
> ----- Original Message ----- 
> From: "Clarke Olsen" <colsen at fairpoint.net>
> To: "Nick Pine" <nick at early.com>
> Cc: <greenbuilding at listserv.repp.org>
> Sent: Saturday, July 11, 2009 12:38 PM
> Subject: Re: [Greenbuilding] Solar Tank temperature drop
>
>
>> Question: does anyone have an opinion about storage tank ratios? That 
>> is,
>> in building a 2 tank system, would you make
>> both tanks equal, make the second (cooler) tank bigger, or even put  the
>> greater proportion of water into the hotter tank?
>> My plan at present is to park a 1000 gal low-boy (40" high) septic  tank
>> in the exaggerated crawl space, pack it in foam,
>> spray the inside with Rubber -Wall, and place a foam divider in  the....
>> middle(?).
>> Clarke Olsen
>> 373 route 203
>> Spencertown, NY 12165
>> USA
>> 518-392-4640
>> colsen at fairpoint.net
>>
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