[permaculture] Re: permaculture Digest, Vol 11, Issue 31

Scott Pittman pci at permaculture-inst.org
Wed Dec 31 16:40:46 EST 2003

At 12:03 PM 12/31/03 -0500, you wrote:

>    1. Re:Greenhouse design (Claude William Genest)
>Greenhouses overheating are an issue even up here in Northern Vermont.
>What I've been thinking is: Since the sun is high in summer, low in winter 
>and heat rises, then why is a glazed ceiling necessary at all ?!
>Why not a solid insulated roof with say a couple of solar wells/tubes ?
>This would lower construction and maintenance costs, increase heat in 
>winter and block out sun in summer....

This is exactly what we do in New Mexico where it is a balmy 13 degrees 
Fahrenheit right now.  I have about one-third of my roof in triple layer
calcium carbonate (plastic glazing), which I have to cover with 50% shade 
cloth in summer to prevent overheating.  I need the extra light because I 
am growing tropical fruit plants and they need the extra sun from 
overhead.  It works fabulously in winter, with affordable heat loss at 
night.  I have loads of mass surrounding the greenhouse in the form of 
adobe walls and slab floor.  Overheating can also be controlled by venting 
at the roof peak.  I have two large vents with ceiling fans below that pull 
hot air up and out the vents, which I close in winter, and reverse the fans 
so they blow warm air down to the floor.


Scott Pittman
Permaculture Institute
PO Box 3702
Pojoaque, NM 87501

505 455 0514 phone
505 455 2003 fax
<pci at permaculture-inst.org> email
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