Solar Heating and Cooling in the Growing Dome Greenhouse

Plant growth in any enclosed space is dependent on the plants receiving suitable range of ambient temperature and there obviously are many plants that are heat-loving plants and other plants that are cool hardy plants and cold tolerant plants. Each of these has different requirements.

Winter Growing:

The principle of winter growing is that we are trying to capture the heat of the sun in the day and store it inside the greenhouse and slow down the heat loss at night, thus maintaining an ambient overnight temperature, which would support year-round growing. The Growing Dome accomplishes this in the following manner:

During the day when the interior to the greenhouse is hot, we have an under soil heating system. This heating system consists of a solar powered fan, which is driven by a photovoltaic panel and the panel creates electricity to drive the fan, which blows hot air through ducts buried in the floor underneath the growing beds. Thus, all day long we are blowing hot air through the soil, creating soil heating. The growing beds, which are usually raised beds, are also insulated to prevent heat loss to the outside of the structure. This soil heating system is entirely free, as it uses no energy other than that of the sun.

The next way of storing solar energy inside the greenhouse is the use of a large water tank. This water tank has a primary purpose of storing solar energy simply by absorbing the sun's rays. The low winter sun shines on the dark painted metal tank, which absorbs heat all day long and at night releases this heat back into the greenhouse structure.

Heat loss during the cold winter nights is prevented or slowed down by the following methods: Firstly, energy efficient polycarbonate glazing consisting of either twin wall or triple wall polycarbonate structured sheets is used for the glazing of the dome structure. Secondly, the north wall of the structure is insulated with foil-faced bubble packed insulation panels covering the northern two fifths of the dome. These also slow down the heat loss at night.

The dome also has perimeter insulation which prevents frost penetrating under the wall of the dome, thus with a solar design we create a greenhouse structure that will continue to allow cool weather plants to grow throughout the winter. In very cold climates the solar energy can be augmented with the use of a small greenhouse heater, which is thermostatically controlled. The Growing Dome greenhouse is very energy efficient. Therefore, as the greenhouse heater is thermostatically regulated, only a small amount of heat is needed to keep the dome at the required ambient temperature. We calculate that the Growing Dome needs only ¼ of the amount of heat required by a conventional greenhouse structure.

Cooling the Solar Greenhouse:

In the summer all greenhouses will get hot, and most commercial and hobby greenhouses have either a ceiling fan or a ducted fan or an exhaust fan to cool the structure. The Growing Dome, however, uses four main methods of cooling which mainly use solar energy.

The first method is the Growing Dome has automatic vents - two at the top, two at the bottom. These are solar powered and consist of a solar vent actuator which opens the vents at a pre-determined temperature. The vent actuators are controlled by a tube of wax, which expands when the greenhouse gets hot. As it expands it pushes out a piston that operates a vent actuator and opens the vent. There is a chimney effect whereby the hot air escapes through the top vents and cool air comes in through the lower vents to replace it.

Secondly, the domes have an exhaust fan, which generally is solar powered. A solar panel drives the exhaust fan, which brings in extra cool air and is a thermostatically controlled cooling fan. Also, some people have installed ceiling fans to help exhaust the hot air through the ceiling of the Growing Dome. These are usually mains powered ceiling fans.

Thirdly, the water tank, itself, in the summer sits in the shade of the north wall insulation and keeps the dome cool. This solar cooling is very, very effective as there is a large amount of water. The mid-size dome has a thousand gallon water tank. This can become a water garden if you wish and you can grow aquatic plants, water plants, raise fish, and it creates a beautiful above ground pond.

The fourth method of solar cooling inside the greenhouse is the use of the under soil fan system whereby we blow hot air through the cool soil all day long that the sun shines, thus helping to cool the domes greenhouse structure. However, what we have found that in the summer, luxuriant plant growth shades the soil thus helping to keep the dome cool in the summer, and the plants themselves act as evaporative coolers.

These methods of climate control have proved to be an essential part of the greenhouse design and help to create optimal plant growth for organic vegetables and flowers.

 

 

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