Congratulations to Eric Barnhorst of Eva Mae Farm in Brighton, Ontario. He is the winner for this year’s Innovation Prize in partnership with the Ecological Farmers of Ontario.

His innovation is a solar powered heat exchanger and reservoir to buffer temperatures and to create a heated bench in an unheated seedling greenhouse. His innovation pumps  water through a home-made heat exchanger when the air temperature in the greenhouse and the water temperature in the reservoir are significantly different. This approach both pumps heat into the tank when the greenhouse gets warm in the day (when the air is hot and tank is relatively cool) and pumps heat into the air when the temperature drops at night (when the air is cold and tank is relatively warm). The water is stored in a homemade insulated tank / seedling bench. The tank is insulated on all sides with rigid foam except for the top, which is a plywood lid. Seedlings requiring mild bottom heat are placed on top of the tank. When especially severe weather threatens, a piece of agribon or other row cover can be spread over the top of the tank, providing extra protection for frost sensitive seedlings. Tomato and pepper seedlings can be on the bench by early March (temperatures as low as -10º C) with no problems.

The system is controlled by an inexpensive single board computer, using a program Eric wrote which reads temperatures from two waterproof temperature probes, and controls the circulation pump (a 12 volt fountain pump) and heat exchanger fan (a large computer case fan) with relays.

The heat exchanger is constructed from copper pipe wrapped in aluminum soffit material to increase surface area. The heat exchanger is strapped to the ridge purlin of the greenhouse and is sloped slightly towards one side so that it automatically drains when not running (to avoid freezing). The water tank is a plywood box with 2x3 bracing on the outside and 1” rigid foam on the inside, covered with scrap polyethylene plastic (leftovers from covering the greenhouse). Everything is powered from a 100 watt solar system (panel, charge controller and deep cycle battery) that is also used to run an inflation fan for the double layers of plastic on the greenhouse.

Overall the cost to construct the heat storage system was about $340. The solar system cost about $475 but was also needed to run the inflator fan. All in all, it was considerably cheaper than a furnace and requires no fuel of any kind.

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