Re: Constructing a greenhouse

> From owner-ferns@hort.net Tue Sep 28 06:05:51 2004
> 
> Hi to all the fernies,
> 
> I want to construct a new greenhouse.  But I need some help on this subject
> as we build one but it did not work that well.  It was just a steel
> construction covered with UV plastic and again with white 100% shade cloth.
> It worked wonders in winter but came summer I almost lost all my ferns.  It
> got to hot inside.  I left open the doors but it did not help much.  We took
> it down.  Now we have a new corner that is part of the house it has three
> brick walls so all I need to do is put in a fourth wall and a roof and voila
> I would have a brand new greenhouse.  It would be 3mx3m and 2m high but I
> need to know if I should put in an extractor fan to suck out the hot air.  I
> have no idea if this is the right name for the fan I am talking about.
> 
> You see our summer temperatures are quite high it reaches about 38 degrees
> Celsius so with a greenhouse having only one door it is difficult to get any
> aircirculation as there are almost no wind and if there are any wind it is
> scorching hot.
> 
> If someone knows anything please help me out or even just a website where I
> might have a look.
> 
> Thanks a million
> Doret

You need openable/closeable vents near the ground, and openable vents right
up at the top of the ridgeline. The ridgeline vents should be LARGE. Make them
all the way down the ridge on both sides, and easily openable (hand-crank or
garage-door opener/motorized). They should reach ~25% from the ridge to the
eaves. If motorized, they can be set up on a thermostat to open when the 
temperature passes a certain point, and close again when it cools off. To
help even more, put misters down just inside of the ground-level vents.
The evaporation will cool the air, and natural passive convection will draw
the too-warm air out the ridgeline vents. No fans needed...

                 ---/\--- <-- Ridge vents
                   /  \
                  /    \
                 /______\
                /|      |\
                 |      |
                 |  ___ |
                 |  | | |
                 |  | | |<-- Ground-level vents

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