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Let's think about how a shade cloth works - light reflection
and absorption: Most green and black cloths absorb far more than they
reflect, which results in the generation of a considerable amount
of heat. As part of the use of a shade cloth is to reduce the heat
stress on your plants, it doesn't seem to make a lot of sense to put the heat
source inside of the greenhouse with them. By suspending it several inches
above the greenhouse roof, the airflow takes the heat away and keeps the
greenhouse cooler.
Maybe heat generation inside the greenhouse is less of an
issue in coastal New England than farther south, and coupled with the wind
scenario mentioned, maybe it's a "lesser of two evils" situation.
Now then, I suppose Aluminet reflects more than absorbs, which
would reduce the heat buildup, so if I was going to be "forced" to use internal
shading, I'd go with that.
Or... Do what I do for shade: Grow vandas up
above everything and let them shade the plants below!
Ray Barkalow - First Rays Orchids - www.firstrays.comPlants, Supplies,
Artwork, Books and Lots of Free Info!
----- Original Message -----
Sent: Monday, April 18, 2005 8:32
PM
Subject: [OGD] Shading: internal or
external?
What are folks' thoughts on using shade cloth inside a
greenhouse, vs.
outside? I have just moved the orchids from a very
small, double-glazed
glass greenhouse into a much larger, triple-wall
polycarbonate greenhouse.
Both greenhouses were/are even span, had/have a
ridge vent and used/use
evaporative cooling, hot water heating. The
new greenhouse has a shutter
and a Kool-Cel evaporative pad setup in one
gable end, which can be used as
a source of fresh air in addition to, or
instead of, the ridge vent.
For the smaller
greenhouse, I suspended Aluminet reflective shade cloth
above the
greenhouse. Because of its small size, this was not only easy to
do
but necessary; there was no extra headroom to devote to it! The
new
greenhouse is quite high, and it would be simpler to suspend the
Aluminet
inside the greenhouse, a couple of feet below the peak, and a
couple of
feet above the plants; this would also protect it from high
winds, which
can be expected in coastal New England.
I now
live in coastal Rhode Island. I will depend upon the shade cloth
to
reduce both the light level and the temperature.
Most of
the new greenhouses I've visited recently seem to favor internal
shade
cloth. What are your experiences? How is this decision shaped
by
the transmission properties of polycarbonate?
--Lisa Thoerle,
pleurothallidiot from Little Compton,
RI
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