I agree, Pat, that solar has a steep learning curve. I was just reading
the latest Scientific American. A fellow from the Rocky Mountain
Institute has an article about how his house is all alternative energy
and how much he's saving, selling back to the industry, etc etc etc.
Yeah. Right.
The people I know here had tried 55 gal drums placed under the bench -
similar to what Bob Gordon suggests. With no great influence on their
heating costs. I expect to duplicate your experience, that the drums
will start putting their heat back into the GH in the afternoon and lose
their storage by dawn. I put the drums in on Sunday and the GH stayed at
60F instead of 58F...and we ain't even cold yet. (remember I'm in
California and we get a hard frost once every 10 years or so.)
As I write this I realize the cost of the water to fill the 3 55-gal
drums undoubtedly erased any savings I'll have on heating. *G* Here's
hoping you are right about reducing the number of cycles the heater
comes on.
K Barrett
Pat Brennan wrote:
"Not all that glitters is gold. Half the story has never been told."
Trying to heat my first greenhouse (12' X 20') via solar was as big a hobby
for me as growing orchids. Although I learned a lot, not much was scaleable
to the 32' X 96' ones I run today. Before you start any solar projects you
need to run the numbers to see if it will be worth the effort. Key to these
calculations is the fact that one pound of water holds 1 BTU for each degree
F rise. (One of my current greenhouse can use over 2,000,000 BTUs in a not
so bad winter night.) After doing the calculations, if you are still
worried about painting the jugs black you should redo your calculations.
Although some jugs will see the light, most light coming into the greenhouse
will hit the plants and warm the air and the warmed air will heat the water.
Have good air flow around the water storage area.
While doing the calculation do not fall into the trap of calculating the
potential heat storage based on the greenhouse's daily high temperature. If
you are simply adding jugs of waters, their temperature will peak shortly
after the greenhouse temperature peaks and then release their heat during
the late afternoon trying to maintain the no furnace required temperature.
The greenhouse with water storage as compared to a greenhouse without the
water storage, will be cooler in the morning as part of the solar heat is
used to warm the water and warmer in the afternoon as the collected heat is
released. During the night, the water will just be part of the thermal mass
that warms and cools as the furnace cycles on and off. The heat cost saving
will be negligible.
That being said, I still think it is a good idea to add the water storage.
First it adds to the greenhouse's thermal mass which makes the greenhouse
temperatures a little more stable and buys you some time if the heating
system goes down. Second it reduces the number of heating cycles required
during the night, although each cycle will be longer. I think reducing the
number of cycles does provide some fuel savings for a couple of reasons
including furnace startup efficiency and less water evaporation/condensation
cycles and air warms and cools on each furnace cycle.
Talking about evaporation. Try to keep your water storage system dry to
prevent it from becoming a evaporative cooling system.
The system I ended with involved making my benches enclosed, insulated, and
filled with 2 liter bottles filled with water. The benches had a vent on
one end and a blower on the other. The blower would turn on when the
greenhouse air was warn enough and warmer than the bottle temp and would
also turn on when the bottles were warm enough and the heating set point was
reached. With this system, the vents rarely opened (not also such a good
thing) and I saved a few hours of heating every night (it provided maybe 20%
of the total heating required).
'And now you see the light.'
Pat
"K Barrett" wrote in message
...
? wrote:
On Wed, 05 Oct 2005 09:20:09 -0400 in Rob
wrote:
I think keeping large amounts of water in the greenhouse is an excellent
idea. In containers painted black if you can, but for simplicity I've
just been filling gallon milk jugs and putting them under the benches.
With a toddler, I have lots of milk jugs. Or (around here at least)
I've seen them in the recycling center in thousand quantites, waiting to
be melted, they don't mind if you recycle a few hundred yourself. In
small units of a gallon, the water is easy to carry, and you can move
the milk jugs (or throw them away) if you end up needing the space that
they are in. If algae or other stuff grows in the jugs, more the
merrier. They will absorb heat better...
I've heard, granted mostly from the person that came up with the
following
idea, that water and other normal thermal masses aren't very effective
in a green house environment.
With that said, has anyone here tried sunny john's subterranean heating
and cooling system for a greenhouse with orchids?
http://www.sunnyjohn.com/indexpages/...reenhouses.htm
I may be setting one up for someone that needs to propagate grapes,
and will collect environmental data to see if it's compatible with
anything I grow.
But if someone else has done it, it'll save me a lot of trouble :-).
I haven't looked at the link about subterrenean heating yet, but figured
I'd add my 2 cents about water. Ray is the only person I know who has
used water to good effect in his GH. People here (Bay Area California)
don't really swear by it. That said nevertheless however I'm going to try
it anyway, because the science behind it seems strong and let's face it we
gotta do something.
K Barrett