"Rob" wrote in message
...

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...

An excellent idea, but likely most effective if the containers are painted
flat black, not glossy. Remember, if something looks bright, it is because
most of the light hitting it is reflected. If the object looks dark, it is
because most of the light hitting it is absorbed.

For our way up north people (like me), I also suggest covering vents with
styrofoam board. Only if the vents aren't going to open, of course (I
have two sets, and cover one set). Get some weather-stripping for your
greenhouse door, if it opens to the outside. If your walls are rigid
plastic or glass, get some bales of straw and stack them two high around
the perimeter of your greenhouse after the first week of hard frost.
Higher on the north wall (three or four bales high). Any earlier and the
mice and other rodents haven't found their winter homes yet. If your
greenhouse is soft poly, like mine, then the straw is probably a RBI
(really bad idea), due to rodent issues. You can recycle the straw as
garden mulch in the spring, and straw is cheap.


I am up about as far north as you are, I think. There is a grower here who
told me on the weekend that during the winter, day time temperatures inside
his greenhouse can reach clost to 30 degrees Celcius (for our american
friends, that is about 80 degrees F), while the outside temperature was
about -20 degrees Celcius. He was amazed that he could see a 50 degree
Celcius difference between the temperature inside the greenhouse and that
outside. But I know he takes great care in the construction and operation
of his greenhouse since he produces top quality plants, and has his humidity
up high enough that he can usually revive plants his friends thought they'd
killed. He reports that once the sun goes down, his heaters begin to run
non-stop. I have not checked to see if he uses any of the passive heating
options available.

The calculation of how much passive heating is needed (defined in terms of
water volume) is simple, once one has data on the rate of heat loss through
the greenhouse roof and walls and the specific heat capacity of air and
water (IIRC, for water it is 1 Cal/g - I have no idea what it is for air).

Rabbits... No, I'm serious. Or chickens. Both give off a lot of heat.
Of course they would have to be in cages, under the benches. I might try
rabbit heat someday when my daughter is old enough to appreciate the
rabbits. I used to raise rabbits as a kid.

Apart from heating the greenhouse, the best part of this idea is that both
are both nutritious and delicious when roasted, and then served with baked
potatoes, corn, asparagus, &c.

Cheers,

Ted


--
R.E. (Ted) Byers, Ph.D., Ed.D.
R & D Decision Support Solutions
http://www.randddecisionsupportsolutions.com/
Healthy Living Through Informed Decision Making