[permaculture] Re: Greenhouse design for southern climates

CAVM at aol.com CAVM at aol.com
Tue Dec 30 12:34:44 EST 2003


Arlene,

For your brief heating needs a conventional greenhouses of all glass or 
plastic can be heated by a variety of means including natural gas and propane but 
also by used motor oil furnaces and even biomass combustion.  Used motor oil 
has about 200,000 BTU per gallon.  Propane has about 85,000 BTU per gallon for a 
greater cost than used motor oil.  Of course, even solar heating is an option.

As you say, in your area though the major concern is keeping the greenhouse 
from overheating in the summer.  While the Sunny John system of subsoil air 
flows to keep temperatures down has many applications it is not suitable in all 
cases.  In some situations the cooling of the water bath in a hydroponics 
greenhouse may be sufficient with adequate ventilation.  Lettuce for example 
responds well to cooling water to fight pythium root rot.

The major opportunity for your situation though is to screen out the infrared 
rays of the sun yet letting in the white light.  This can be done with a 
hologram on the glass of the greenhouse.  Holograms are very adaptable and very 
inexpensive.  The light of the sun needed for the plants will enter but the heat 
producing IR will not.

In fact, you could build your greenhouse from a non-typical design and use an 
insulated structure which has only relatively little open area for the sun to 
enter.  Solar collectors can gather the needed level of light and project it 
into the windows.  A hologram will filter out the IR and distribute the light 
to the plants.  In this way you could even convert an existing solid wall 
building into a greenhouse which would be very economical to heat and cool.

This design has proven as good and even better than traditional greenhouses 
in tests done at the Univ. of Pennsylvania.

Many things can be done.

Neal Van Milligen
Kentucky Enrichment Inc.
www.kentuckyenrichment.com
cavm at aol.com

> Hi all,
>
> I just joined the list and am hoping to get some ideas on solar
> greenhouse design in the Southwestern United States. I live in Tucson,
> Arizona. We have very hot, dry summers, with temperatures hitting
> 100-110 degrees F for much of the summer and mild winters with
> occasional night temperatures below freezing.  We have lots of sun
> year-round but can't grow tropical plants outdoors due to the low winter
> temperatures and the hot, dry winds of the summer. The biggest challenge
> seems to be moderating the heat in the summer. Conventional greenhouse
> design tends to overheat the plants. We plan to use evaporative cooling
> but wonder about other strategies to control temperature extremes. Does
> anyone have experience with greenhouses in this type of climate?
>
> Thanks,
> Arlene
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