Date: Wed, 25 Oct 2000 07:04:18 -0500 From: "Susan Farrington" <sfarrington@ridgway.mobot.org> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg3096$foo@default> Subject: Re: Greenhouses
Ron wrote:
> Clearly, the intial costs of a greenhouse using
> polythene film is cheaper, and you can have a larger greenhouse.
> However, I would like to take into account the overall costs including
> the maintainence and operating costs. For instance, polycarbonate has
> a 10-year warranty. The polythene film has to be replaced more
> frequently, and you have to run a blower 24 hours/365 days a year to
> keep the space in between the double layers inflated. I'd be
> interested to see what your electric bill is (if you don't want to
> post it to the list, you can send it to me via email). The blower
> probably won't last 10 years running continously, so you may have to
> purchase replacement blowers over this period. Also, I haven't seen
> any numbers on the insulation capability of a double polythene film vs
> polycarbonate. If the insulation of the double polythene film is not
> as good, then your heating and cooling equipment are working harder,
> which further increases your electric bill.
>
I don't know how much the inflating blower's electricity has cost me,
since it's part of my overall electric bill, but my electric bill has never
been particularly high (and is the highest in the summer, when we are
running a/c, and my blower was turned off for the summer - I only use
my greenhouse fall through spring.) At a guess, I don't think it's
costing me more than $5 a month, and is most likely less. The blower
itself cost about $40, and it has lasted five years so far. I've seen them
last at least ten years running continuously at a garden center I've
worked at. As to the poly film itself... they now have film that lasts
four years, and it is pretty inexpensive. The only drag is you are stuck
with big sheets of plastic after four years that you don't want to clog
the land fills with... I've used my old plastic to make a tarp for under
my tent, to cover woodpiles, etc... Also, if you like to live
dangerously, you can usually extend the life of your greenhouse an
extra year or so beyond what the manufacturer recommends... at the
garden center I worked at, we had three year poly on for four years,
and that fourth year was VERY icy. It scared us to have old poly on
that year, but it held!
Finally, I suspect the insulating value of double film with an inflated air
space comes awfully close to any other material's insulating value, but
I'm not sure... I'll try to look it up in some references I have at home.
Susan
Susan Farrington
Missouri Botanical Garden
P.O. Box 299
St. Louis MO 63166-0299
susan.farrington@mobot.org
(314)577-9402
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