Thursday, April 23, 2015

Visit to Whitewater Gardens’ Geoexchange Greenhouse in Altura, Minnesota

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.

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.

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.

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Check back for our next blog entry —
Day 2 of Andrew's Trip to Michigan & Minnesota

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