Solar greenhouse:
All greenhouses are solar heated to some extent. The naturally solar greenhouse traps the suns rays during the day, usually allowing enough heat to keep the plants happy and healthy.
It's at night that the temperature in the greenhouse drops dramatically. The greenhouse doesn't retain the heat that it held earlier in the day when the sun was hitting it directly.
Seventy Five to Eighty percent of the costs of heating a greenhouse is spent at night with artificial heat sources, such as heaters.
It is the solar energy that is built up during the direct light hours of the day that is needed to be retained.
Passive Solar Greenhouse Heating:
Solar greenhouse heating can be achieved in two ways - passive and active.
The easiest and most inexpensive way to solar heat your greenhouse is through passive solar heating.
This is achieved by incorporating more physical or thermal mass into the design and layout of your greenhouse garden.
Items that create Thermal Solar Mass:
Large Rocks
Water Filled Steel Drums (black or another dark non-reflective color is best)
Cement Filled Cinder blocks
Piles of rocks
Lean to greenhouses work great as the wall that they are attached to act as a great solar heat storing Thermal mass.
It is large areas of this Thermal Mass that capture and store the solar energy throughout the day and slowly radiate the heat out at night, when it is most needed.
Of course solar greenhouse heating has the best results when using these techniques in areas that receive lots of the days direct sun exposure.
No matter how well the solar heating setup is it is always good to have a conventional heating system ready as a backup. If there is no sun, then there is no heat. Conventional backup heating is always a good idea.
Retaining Captured Solar Greenhouse Heat:
It is important to retain the heat that is captured by the things that you are using as thermal mass. The best way to do this is to make sure that the greenhouse is air tight. Check out greenhouse micro climates for more information.
Things that can be done to retain the captured solar heat:
insulate walls that do not allow light in during the day
weather strip all doors and vents to reduce any air leaks
mono foam, caulk, or tape any gaps that may be allowing any loss of heat
install double or triple glazing
concrete wall or slab floor
line the inside walls with inflated layers of poly film - creates an insulating barrier of warmed air between the inside and outside temperatures.
Reflective Materials:
Just like you may have heard of greenhouse gardeners white washing their greenhouses during hot summer days to reflect the suns rays away from the greenhouse, using a reflective material on the inside can also be used to raise the amount of trapped heat.
If the north side of the greenhouse as a rule does not let the sunlight in during the day. It is the south side of a greenhouse that allows all of the light into the greenhouse, so by painting or covering the north in-side wall of the greenhouse with a reflective material or paint will trap more of the lights solar heat energy. By not allowing the sun's rays to travel through the reflective material will bounce them back into the greenhouse to be stored in the thermal solar storage masses.
Insulation and proper drainage of the greenhouse floor:
It is important that the floor of the greenhouse has proper drainage so that water is not allowed to accumulate and allowed to form into ice. It is also good to use a material that will retain the most heat.
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