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Seasonal solar storage

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Posted by Bill Li on July 9, 2008, 10:29 am
 
I am currently planning to build a new house in the Vancouver, Canada area
(mild, marine climate).  I would like to be able to bring the grid energy
requirements down to near-zero.  For reference, Vancouver gets about 1.5
kWh/m^2 in the winter, and up to about 6 kWh/m^2 in the middle of summer,
averaging around 3 or so for the year.

The current plan has about 300-500 sq ft of active flat plate at latitude-10
deg facing due south up at roof height.  If needed, I have room for another
few hundred sq ft at a somewhat less optimal position at another part of the
roof, though I'd prefer not to as this part of the roof is earmarked for a
future PV system (whenever nanosolar becomes more widely available).  The
active solar thermal system will be used to heat DHW as well as space heat
via radiant floors.

The house itself is fairly large (~3500-4000 sq ft) due to use requirements.
The shell is intended to be superinsulated using SIPs, and I'm currently
picking over the design to try to minimize the heat loss rate.  Where
possible and economical, I am planning on making use of south-facing windows
for solar gain, but due to the house's location, a depressing amount of the
vertical south-facing walls are shaded by the neighbour too much of the
time.  I have also considered using an air thermosiphon on the part of the
south wall which seems to receive sun, but haven't really decided on this
yet.

My question is whether or not it is feasible to employ annualized geothermal
solar (AGS) as a means to reach or approach zero energy.  I am imagining to
run water lines from the active system under the house within the boundaries
of the insulated foundation wall system as a way to bleed off excess heat
whenever the primary solar water store (500-1000 gallons) gets to max
temperature.  Doing things this way is somewhat attractive from the point of
view of avoiding the extra bracing required if I had to bury a huge water
tank under the house.

Does this make sense?  Are there any easy ways to estimate the sort of
storage capacity I should have in order to realistically be able to get to a
point where I can get through the entire heating season, or should I just
run through historical temperature numbers?

The alternative to AGS I had in mind was to bury a huge insulated tank in
the middle of the courtyard.  Denser, but most likely more costly.  I am not
considering the notion of using earth air tubes as I am somewhat afraid of
mold, and I already have to have an active collection system anyways in
order to do DHW and controlled space heating.

I am looking for advice or consultation, preferably from someone who has
previously done this.

Bill
billdoors@shaw.ca



Posted by Bill Kreamer on July 9, 2008, 8:26 pm
 

Hi Bill,
Air yes, thermosyphon no. It always improves the bottom line to run a
fan on an air system.  I defer to others on your other questions.
-Bill K.

Posted by AstickfortheMULE on July 9, 2008, 10:16 pm
 Bill

You should give me a call as I have a couple of options for you.

check out www.energie-solaire.com

I am in seattle, have a SIPS house on ICF (roof too) and distributing
an unglazed system (from Switzerland) and have an idea for very large
heat storage.

The panels are a roofing system and they are stainless steel with a
selective coating.  You do not need to have them at more than 20
degree pitch if you are using seasonal heat storage.

They can work brilliantly with geothermal as well.

We also sell a heating and cooling panel that can heat with 80 deg F
water and cool with 50 deg F water

for large seasonal heat storage, use mud storage with pex lines and
EPDM liner with 12" of foam on bottom, top and sides.  Here is my
phone.

Eric Friedland

206#229#5093


Posted by nicksanspam on July 11, 2008, 10:53 am
 


Posted by gary on July 11, 2008, 9:35 pm
 Hi Bill,
You can get a rough idea whether you have any hope of it working out
by using one of these two tools to estimate your winter heat loss:
http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm
or,
HEED, listed on this page:
http://www.builditsolar.com/References/energysimsrs.htm

The first is a very simple home heat loss calculator that uses degree
days to estimate the full winter heat requirement, and the 2nd is an
hour-by-hour simulation that uses a TMY weather file that you download
for your area.  Both are free and easy to use.
Either of these gives you an estimate of the total heat requirement
for the winter.

You have to estimate solar heat gain from the collectors during the
winter -- as a very rough guide, just use the estimates you already
apparently have for winter sun, and assume around 50% collection
efficiency.
This gives you an estimate of the solar heat input for the winter.

The difference between the two is roughly what you would have to store
in the storage.

The heat storage capacity is:
(lbs of storage)(specific heat of storage material)(Storage
temperature range)

You then need to allow for losses from storage.  From what I have read
on real projects, this can be quite a bit -- good insulation for the
storage that holds up the the ground conditions is very important.


Just as a very very rough guess:

For a 60X60 ft house with R20 walls, R40 ceiling, low e double glazed
windows, and 0.5 ACH... and using 5000 deg-days for the climate,

I get about 81 million BTU minus internal gains of 21 million = 60
million BTU  winter heat requirement.

To store this in water with a temperature range of 140F down to 90F
would require:

(60M)/(140F - 90F)(1 BTU/lb-F) = 1,200,000 lbs or about 145,000
gallons -- it would be less than this by the net gain for heat
collected in the winter by the collectors.   Thats a cube of water 27
ft on a side without the insulation thickness.

Just my 2 cents, but I think you might come out better by investing
the annual storage money into excellent insulation, windows, sealing,
and a good solar collection system.

A CA house you might like:
http://www.riverdalenetzero.ca/Home.html


Gary














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