Keeping plants cool:
Sean Samia has some sort of refrigeration unit he's using to grow
highland Nepenthes. Tom Johnson can probably elaborate.
The following is from the Chula Orchid Newsletter, August 1993, written
by Harry, owner of Chula Orchids. I forgot what his last name is, but
he seems to be a heck of a nice guy from his attitude shown in the things
he writes in his newsletter.
The questioner asks about a "wet wall" and cheap swamp coolers:
"A wet wall is one wall of your greenhouse that has been fitted with a large
pad of some kind that easily passes air through. The opposite end of the
greenhouse has been fitted with large evacuating fans that will pull the
equivalent of all the air in the greenhouse throught the pads in one minute.
At the same time, usually rain gutters are fitted above the pad and below
the pad. A pump of any kind is used to fill the top gutter when the humidity
drops. The pump is controlled by a humidistat. Holes all along the top
gutter distribute the water along the pad and it drips down through the
pad to the bottom gutter. All the air passing through the pad picks up
water and besides raising the humidity, it also lowers the temperature.
Same principle as a swamp cooler only on a much larger basis.
A swamp cooler can use pads of 2.5 square feet, a wet wall could be hundreds
of feet long with 6 foot diameter fans on the opposite side. When the
humidity is raised enough or the temperature lowered enough, the pump goes
off and the water is collected back in the tank.
A successful variation on this conventional "wet wall" has been used by
a grower here in California. Energy shortage and water shortage got him
looking for another way. Here's what he did.
First the sump pump and the rain gutters were shut off. No water was sent
through the pump, hence a huge energy saving of pump(s) running most of
the day. No cistern to hold water was used so the persons checking on
water use were pleased. He first strung 3/8" poly tubing all along the top
of the wet wall on the outside. To this he fastened small plastic spray
heads like you would use for shrubs, the finest mist he could find with the
widest coverage. A solenoid valve used for lawn sprinklers was installed
in the 3/8" poly line.
The solenoid is run by a thermostat which seems to react sooner than a
humidistat. A high temperature opens the solenoid valve to turn on the
sprayers. The pads, usually excelsior, are misted and the air passing
through picks up the water. This not only cut costs on energy, it saved
water and power and reacts faster. An additional savings was realized
we think because the fans did not have to work so hard, that is, the wet
wall not being so saturated the air had an easier time passing through.
This place has about 2.5 acres of greenhouses so it was not a tiny
project but he is completely happy with the outcome. [Now THATS a
SERIOUS grower!]
[Regarding swamp coolers:]
If you have a big fan, use it. If not get one that is marked to move the
equivalent of the total volume in cubic feet of your greenhouse at least
once a minute and best up to two times that volume a minute. This fan
will be most efficient if mounted so it pulls air in from outside the
greenhouse but will work with reduced effectiveness if just encapsulated
in the greenhouse. Find a fine mist head, perhaps 2 to 8 gallons a minute.
It can be adapted to the end of a hose or mounted to a piece of PVC pipe
with a little creativity and a mess of PVC fittings, and probably a few
nylon "bushings" (reducers).
The cheapest way I can think of would be to leave the fan on all the time,
and turn the mist head on when the temperature gets too high. Putting
the mist head behind the fan will increase the humidity but the fan will
deteriorate much quicker.
>From this start you can customize more and more. Add an evacuation fan
180 degrees opposite the fan. If you have the typical hobby greenhouse
it will leak enough new air in through the cracks to make this fairly
efficient. Again, to help out, the fan should push out the volume once
a minute.
...Be sure to add a deactivated charcoal filter in the water line, cost
about $40 for a good one. That will cut out most of your mineral buildup
at heads etc, and they are very inexpensive to change regularly. It also
keeps the chunks out of the water so the heads don't plug up from debris in
the water line. It also keeps the white buildup off the plants."
-- Don Burden New Albany, Indiana, USA donb@iglou.com