4-Season Experimental Greenhouse
In the fall of 2011, a small group of Skills for Employment students at Yukon College and their instructor worked on a collaborative project with the Yukon Research Centre to build an insulated, year-round, northern greenhouse.
Arctic Entry
The research greenhouse design incorporates an arctic entry to provide a dry space for coats, boots, and equipment. During winter use, it prevents cold blasts into the main part of the greenhouse.
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Insulation
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Rigid insulation was used because it is less likely to be damaged by water infiltration and provides a higher R-value per inch than batts. Each sheet has been cut to fit and then foamed around the edges to minimize leakage.
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Heat Storage
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The space under the beds is an ideal place to put something massive which can store daytime heat and release it at night. Not only does this reduce heating costs, but also prevents overheating on sunny days. A small fan draws hot air from the highest point in the greenhouse and blows it down below the beds where the heat can be stored and later released. Since this greenhouse will be used year-round, bottles and cans of water are used. If freezing is likely, rocks would be a better choice. Although the heat storage capacity of water is greater per kilogram, rocks are more dense. In the end, the resulting storage capacity is almost the same for a given volume. Barrels full of water along the back wall also store and release heat to moderate temperature swings.
Maximize reflection
The walls and ceiling are stained white to reflect as much as possible of the incoming light.
Polycarbonate glazing
Polycarbonate glazing transmits light well and provides some insulation values as well. A triple wall glazing was chosen for this greenhouse since it will be used throughout the winter.
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Shutter
An insulated shutter on a track can be closed on very cold days and at night to reduce heat loss through the glazing. These shutters use vacuum insulated panels sandwiched between thin plywood. Other options would be press-fit styrofoam sheets inside the greenhouse, or even row cover fabric over the beds to keep the heat near the plants.
Lighting
Plants need a minimum of 10 hours of daylight for growth. For winter growth, additional lighting is required. Supplementing daylight with LED lights is a reasonably cost effective way to increase day length.
The project compared two types of LED lights. One set uses only 9 W. The other, more conventional LED grow lights, use 155W. Compare that to high intensity discharge lights which are typically 1000 W.
(Greenhouse supplemental light)
The project compared two types of LED lights. One set uses only 9 W. The other, more conventional LED grow lights, use 155W. Compare that to high intensity discharge lights which are typically 1000 W.
(Greenhouse supplemental light)
Vegetable choices
Cold weather greens were chosen for winter growing since they require the least in terms of supplemental heating or light. By keeping the beds warm, the air temperature can hover near freezing without problems. Excellent books on the subject of cold weather growing have been written by Eliot Coleman of Four Season Farm.
Seniors' Residence greenhouse
The greenhouse at the senior's residence near Yukon College was built with polycarbonate glazing on all four walls as well as the ceiling.
In the summer, the vents must be open during the day with a fan blowing almost constantly to get rid of excess heat. A propane furnace is then used to heat the greenhouse at night.
One raised bed was built with empty space below. This space would be better utilized with mass storage. Large containers of water, or rocks below the bed, could store some of the excess heat generated during the day and alleviate some of the night time heating costs.
In the summer, the vents must be open during the day with a fan blowing almost constantly to get rid of excess heat. A propane furnace is then used to heat the greenhouse at night.
One raised bed was built with empty space below. This space would be better utilized with mass storage. Large containers of water, or rocks below the bed, could store some of the excess heat generated during the day and alleviate some of the night time heating costs.
retro-fit
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Rick, a retired heating specialist, worked with the students on the research greenhouse. In the fall of 2012, a project to retrofit the greenhouse was undertaken. Insulation was added to the north wall and the north half of the roof.
These changes along with heat storage such as rocks or water are expected to significantly reduce heating and cooling costs.
These changes along with heat storage such as rocks or water are expected to significantly reduce heating and cooling costs.
Lendrum Ross Farm
A crank on the side allows rolls of ensofoil closed-cell foam insulation, held at the peak, to be rolled down over the roof to reduce heat loss at night or for shading.
The vertical walls are glass while the roof is woven poly. The north wall is plywood with styrofoam insulation. Heat storage is provided by two barrels of water, one on either side of the wood barrel stove as well as another tank of water which sits on the barrels and straddles the stove. The heating water is pumped out of that upper tank through copper tubing, around the chimney and then into pex pipes under the soil. The pump is on a timer, so it pumps intermittently through the night. For ventilation there is a door at either end, one in the north wall and a roof port (about two feet square) that can be opened or closed.
Raised beds hoops hold up floating row covers during the growing season. Through a combination of using the already heated and well lit space of their living room to start plants and rotating cold weather crops with heat lovers like basil and tomatoes, these farmers provide market-goers with their first harvest of spinach, spring onions, radishes and leafy greens in mid-May.
The vertical walls are glass while the roof is woven poly. The north wall is plywood with styrofoam insulation. Heat storage is provided by two barrels of water, one on either side of the wood barrel stove as well as another tank of water which sits on the barrels and straddles the stove. The heating water is pumped out of that upper tank through copper tubing, around the chimney and then into pex pipes under the soil. The pump is on a timer, so it pumps intermittently through the night. For ventilation there is a door at either end, one in the north wall and a roof port (about two feet square) that can be opened or closed.
Raised beds hoops hold up floating row covers during the growing season. Through a combination of using the already heated and well lit space of their living room to start plants and rotating cold weather crops with heat lovers like basil and tomatoes, these farmers provide market-goers with their first harvest of spinach, spring onions, radishes and leafy greens in mid-May.
Ensofoil didn't hold up as well as expected in the wind and so has been replaced with an insulated tarp.
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the galvanized tank straddles the wood stove and two barrels full of water
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