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  • From: "David Inglis" <mhcsa AT bcn.net>
  • To: <market-farming AT lists.ibiblio.org>
  • Subject: RE: [Market-farming] Re: Greenhouse- milk jugs
  • Date: Fri, 7 Feb 2003 22:30:35 -0500

Title: Message
I was told that in most parts of the U.S. there is 'theoretically' enough btu's coming in over the year to keep a Greenhouse at 65F year round. Most of us are farming in a less than theoretical world though.
People will tell you that it is difficult, and expensive' to provide enough thermal mass within the structure to eliminate the need for heat in a warm house but that need not be the only goal that would be worthwhile.
Under bench storage of thermal mass makes great use of unused space but if you are doing in ground growing of crops it wont work. 
 Hung milk jugs or soda bottles can contribute significantly to protecting crops in a cool house especially when combined with other measures such as row covers, sidewall or in ground insulation; the effect of combining each of these heat savers is more than accumulative, it is synergistic. As you say, milk jugs hung up will not provide enough warmth to eliminate the need for night heat but they will act as a thermal flywheel reducing the extremes of heat during the day and cold at night as well as slow the speed the temperature changes at.
On a daily basis the bottles are a more effective flywheel because they have a high surface area to volume ratio and therefore heat up faster and give up that heat faster. I think of it like charging and discharging a battery. What is the point of having a barrel full of water that is still warm after a long cold night? It is like having a nearly full irrigation pond at the break of a drought. 'The ideal is a just emptied pond when the first rains fall' [ P.A.Yeoman's ]
Barrels are more effective at carrying one season into the next.
Steve Moore in PA has done more than most in this area and I know he got a grant for temp. sensing equipment but I don't think the data is in yet.
I have a question for anyone with experience growing in unheated tunnels [Alison?]:
Which do you think is more damaging to 'winter' crops in unheated tunnels, temperature extremes or rapid temp. changes?
 
David Inglis
Mahaiwe Harvest C.S.A.

Marie,
    I'm not sure what you will be growing in it, and what temps are needed.
    For passive solar, I use 50 gallon plastic barrels on their sides, filled with water under my benches for about 120' total.  The 'free barrel source' ended before I got enough to complete the whole thing.  It does not provide enough release heat for that greenhouse, which is 75' x 20', and has solid, insulated 4' walls, and inflated bubble.   I keep potted tender herbs, fig trees, scented geraniums, etc. in it.  What the barrels do offer-  is to help with the night temps thus save me fuel $$, and since this heat is radiating up, I have found it great for propagating late summer cuttings.  Also, the barrel's did save plants when the heat went out one winter.  Lost a bit of foliage, but not the roots.  
   I'd Google it.  Good Luck-
Patricia
theherbgarden.biz



Today, it is 16 degrees and sunny here in north central Missouri.  Our
new hoop house is all toasty warm.  I wonder if I filled milk jugs with
water and stacked them up somewhere in the hoop house, would they warm
enough during the day to keep the house warm at night?  Does anyone have
any data on something like this? 

Marie in Missouri





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