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Author Topic: Low tunnels for winter greens production  (Read 2943 times)

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Offline CatManDo

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Low tunnels for winter greens production (water-filled poly-tubes)
« Reply #4 on: December 13, 2010, 05:51:56 AM »
Real good points about integrating phase change materials with water-filled poly tubes.

Historically the thermal tubes were developed in the 1980s in Greece and other
European / Mediterranean countries where protected culture production systems
are widespread.  They were used in the U.S. but you don't hear much about them
anymore -- so perhaps they didn't pan out or they didn't catch on.

On the other hand I've seen commercial phase change tubes in modern day solar
greenhouses, mostly at botanical gardens and educational display gardens.  Not
sure what commercial brands cost.  Based on your notes it sounds like one can make
them up.

It's an open book for on-farm and backyard experimentation, integrating systems
with solar greenhouses, high tunnels, and low tunnels.

Paul and Alison Wiediger on this Sanet list will present workshops on their
high tunnel production experience at the AR-OK Horticulture Industries Show
on January 16-17, in Ft. Smith, AR.

Unlike the land-grant college here in Texas which still seems to be "waiting" to
experience the light on sustainable and organic agriculture, the ag colleges in
Oklahoma and Arkansas started supporting sustainable ag in the mid-1990s
onwards.  A farmer is featured on the program every year and allowed
several hours of workshop time to share their story in detail. This year
it will be the Wiedigers.

Now the conference buys local foods for it's luncheons. For the remaining
traditional growers who were still scratching their heads on what this
"sustainable ag" business was all about, I think it disappeared when
they put two and two together with 95% of the meal coming from local
foods and the regional economy.  Plus the chefs at the hotels go nuts
over fresh and local food for real people, instead of 2-gallon cans
of green beans and processed foods.

Looking back at the sustainable ag experience over the last 20 years, I'd
say market farmers and sustainable farmers have been on the forefront of
both innovation and influence for the whole U.S. food system:   Farmers
Markets, CSAs, raw milk, grassfed beef, pastured poultry and hogs,
organic and non-GMO crops, local foods, farm to school, farm to table,
high tunnels, etc,

Steve Diver

Offline CatManDo

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Study About low tunnels for winter greens production
« Reply #3 on: December 10, 2010, 05:22:18 AM »
Steve, all,

On 12/9/2010 8:05 PM, Steve Diver wrote:
> Another method that could be integrated with low tunnels are thermal tubes. These are clear polyethylene tubes about 12 inches in diameter that are filled with water. They lay flat on the ground between rows, next to plants. They absorb solar energy by day and release heat at night.
>
> Kenn-Bar in Massachusetts used to carry this kind of poly tubing.  You could probably find some poly to modify into water-filled tubes.
>
> Then again, they might turn into an ice sickle on a really cold night!!

Poly tubing is actually widely available, but you need to look in non-ag places. ULine and Grainger Industrial Supply have it, for example, but they sell it for shipping purposes, where someone hangs up a roll of it and makes poly bags, of variable length, one at a time with a heat sealer for shipping different items. I have a fairly extensive spreadsheet list of places and prices for such bags, in various diameters and thicknesses, constructed this September. If anyone wants a copy, please write and I'll send it to you. (I gathered the info as part of an on-going exploration of using poly bags for small-scale biogas digesters.)

For a use such as you describe, the ends can be tied or clipped. They can also be heat sealed (which is most common when making bags), and they can be sealed by clamping the ends in various ways, such as by wrapping the end over a piece of plastic pipe, and then sliding another, slightly larger slit pipe over that.

Such tubes, as you no doubt know Steve, can be made into more efficient storage units for heat if a phase change material (PCM) is used (or they can incorporate smaller tubes filled with PCM, inserted in the larger tube). I don't think this is the time or place for a full explanation of phase change heat storage, except to say that a phase change is where a material transitions between solid and liquid (or as in your icicle example, from liquid to solid), or from liquid to vapor. At those points of change, very considerable amounts of energy can be stored or released. Some phase change materials with the proper characteristics (such as a sodium acetate slurry or even beeswax) are not toxic. Try this link http://freespace.virgin.net/m.eckert/index.htm]<[url]http://freespace.virgin.net/m.eckert/index.htm>[/url] for more info.

If a tube filled with water froze in a low or high tunnel, that might actually be a good thing, in fact, since it would tend to moderate the temperature in that unit because they would be releasing substantial amounts of heat in the process of freezing-- changing phase-- keeping the low/high tunnel itself near freezing rather than dipping much below, as it might well if the tube of water were /not/ there. (Many plants are not damaged at the point of freezing, but can be damaged at lower temperatures.) Of course, one pays for the privilege, in the sense that the heat deficit would have to be made up, and it might well take longer with a block of ice in the structure.


David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com



Offline CatManDo

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Low tunnels for winter greens production
« Reply #2 on: December 10, 2010, 02:56:01 AM »
Gil -

There is a Western SARE report on high tunnel production in Utah that
includes temperature data for low tunnels inside high tunnels, etc.
Here is the link to the summary.  The full SARE report might include specifics.

High Tunnel Lettuce in Utah
http://extension.usu.edu/files/publications/publication/Horticulture_HighTunnels_2010-04pr.pdf

One of the low tunnel warming practices being used by gardeners and small-scale
growers is the use of Christmas tree lights which are strung inside the low
tunnel -- the C7 style lights.    I've seen blogs report a of 5 to 20 F increase, but
obviously it depends on where you live. Your setup would be a great way to
measure this for New England.

As long as you have an extension chord strung out to the garden, propagation
heating mats and strips would provide warmth inside the low tunnel.

Another method that could be integrated with low tunnels are thermal tubes.
These are clear polyethylene tubes about 12 inches in diameter that are
filled with water. They lay flat on the ground between rows, next to plants.
They absorb solar energy by day and release heat at night.

Kenn-Bar in Massachusetts used to carry this kind of poly tubing.  You
could probably find some poly to modify into water-filled tubes.

Then again, they might turn into an ice sickle on a really cold night!!

Steve Diver
Texas



high tunnels,  low tunnels, winter greens production, Steve Diver, Eliot Coleman, winter harvest manual

Offline CatManDo

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Low tunnels for winter greens production
« Reply #1 on: December 09, 2010, 07:09:52 AM »
I am interested in learning about any reports of studies of low tunnels for winter greens production *that involved collecting data on temperature differentials, including such details as where to place sensors for the most useful temperature readings.* I have seen many reports describing techniques for growing winter greens or marketing them or the economics thereof, so I don't need citations to that type.

The context for my request is the following: This winter my wife and I are experimenting with winter greens production in a 20' long low tunnel in Ithaca, NY. Unfortunately we decided to "go for it" a bit late in the fall, so not at all surprisingly the plants of our 10 different crops are small & not likely to produce much until spring.  I have acquired some inexpensive wireless thermometer equipment and am collecting some temperature data to discern how our low tunnel design is performing in moderating outside conditions and maintaining inside growing conditions (temperature data I am collecting: outdoors, under the plastic cover but above the row cover, under the row cover, and 2" below the soil surface under the row cover).  My main goal for collecting the information is to assess whether adding a small amount of heat under the row cover at critical times could maintain the temperature above freezing and (as Eliot Coleman suggests) greatly increase productivity while not costing a lot in money or resources.

If anyone is interested, I would be happy to discuss any details of our experiment off list.

Thanks,

Gil
gwg2@CORNELL.EDU

WHY NOT LISTEN TO SOME GREAT COUNTRY MUSIC WHILE READING THE Forum? (OPENS IN A NEW WINDOW):
« Last Edit: December 10, 2010, 05:22:58 AM by CatManDo »