By
Andrew Mefferd, Johnny's Selected Seeds
DAY 1 — Whitewater Gardens’ Geoexchange Greenhouse,
Altura, Minnesota
Earlier this year, I flew out to La Crosse, Wisconsin to attend the Midwest Organic & Sustainable Education Services (MOSES) annual
conference. On the way in to the conference, I stopped by to visit with Sandy
Dietz at
Whitewater
Gardens Farm in Altura, Minnesota.
I was interested to see the farm because they are
incorporating a number of cutting-edge greenhouse
techniques in order to grow vegetables in short-season Minnesota as efficiently
as possible.
While they have several other
greenhouses plus areas for field production (all under
a blanket of snow at the time), what I was really there
to see this visit was their brand new 46'x126' geothermally
heated greenhouse.
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| Altura, MN in Winona County |
This greenhouse represents the wave of the
future when it comes to energy efficiency. The entire perimeter of the greenhouse is protected by a frost wall extending 4' down into the ground. This wall minimizes the amount of cold that
penetrates through to the greenhouse, a worthwhile measure for reasons that were obvious on the freezing day that I
visited. Insulation laid 4' down under the floor further
reduces the amount of cold that seeps through the ground into the
greenhouse.
One of the most unusual features of this greenhouse is that geothermal
energy is the primary source of fuel for its heating
system.
Ground-loop geothermal heating is a technology that takes heat from the earth and builds it up to usable levels with a
heat pump (also known as a
ground source heat pump, or GSHP). The water is heated and then circulated through tubes in the floor, which
literally heats the greenhouse from the ground up.
(Equally notable is that
geoexchange technology allows for excess heat to be transferred back into the ground — or, for cold air to be pumped to a cold-storage
area, for example — as well as for heating.)
When more heat is necessary than the geothermal can provide,
a forced-air propane backup system kicks in to make up the difference. What
I will be interested to learn after a few seasons of operation
is what proportion of the required heating
the geothermal can provide versus how much the propane backup
system will have to supply.
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| Whitewater Geothermal Greenhouse |
To date, there are very
few geothermal greenhouse systems in the United States. But based on the fact
that energy is the second-largest cost for
many greenhouse growers after labor, I would be surprised if we don’t see more
growers following the Whitewater Gardens lead.
Another innovation Dietz is pursuing is to install Solawrap
greenhouse covering this spring. Most heated greenhouses using flexible plastic
coverings have two layers of plastic inflated by a small fan. The air
between the layers of plastic provides a layer of insulation, greatly
increasing the heat-trapping properties beyond a single layer of plastic.
Instead of using a fan to inflate the layers
of plastic, Solawrap uses two layers of plastic with bubbles in between to form
the insulative layer. It looks like a giant sheet of bubble wrap. The advantage
is that it maintains the air layer, without having to constantly run a fan to
keep it inflated. The product is from Europe and not widely used in the US at
this point.
I look forward to checking back in with Sandy in the future
to see how all these innovations are working out on her farm. I really enjoyed
the visit and am always impressed with the things I can learn about from our
customers.
Learn more...
Check back for our next blog entry —
Day 2 of Andrew's Trip to Michigan & Minnesota
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