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How a greenhouse works
Rays from the sun enter the walls and roof of the greenhouse
The heated air is less dense so it rises and is simultaneously replaced by cooler air.
The heat from the ground is transmitted to the layer of air next to it, which expands and becomes lighter than the air above it.
The temperature of the ground rises as it absorbs the radiation.
This cycle continues throughout the day. The stored warmth goes a long way towards keeping the plants protected from cold temperatures through the night until the sun rises again, although in some areas one may need to make arrangements to provide additional heat and light to the plants.
Creating the right greenhouse for you
1. Locate the greenhouse – when planning the location of a greenhouse, you’ll want to orient it either east to west or north to south, to maximize sunlight exposure. Make sure the area will not have sun blocked by buildings or trees. Since the greenhouse works by trapping solar radiation and converting it into heat, you’ll want to choose an area that is well exposed to light.
2. Decide on the greenhouse style – there are several choices of greenhouse structural frames such as the lean-to, even-span, span roof, glass-to-ground, Quonset, gothic arch, cold frame, and a-frame. The lean-to is non-freestanding and is attached to another building, alleviating water and electricity as a concern. Consider the building cost and availability of heat and water when choosing a freestanding greenhouse. The span-roof type is one of the more common freestanding varieties.
3. Choose the foundation – the greenhouse should be built on a strong foundation such as concrete, especially if you greenhouse will ultimately use glass instead of plastic. A wood foundation can be a viable alternative for smaller greenhouses. Species like cedar, redwood and cypress are resistant to moisture.
4. Best frame material – a good greenhouse frame should be of great strength as well as provide additional insulation. Frame material options include wood, aluminum, galvanized steel, resin and PVC plastic. Aluminum and resin are less expensive than wood and offer strength, however, they do not offer as much insulation. PVC frame insulates well, but lacks the strength of wood or metal.
5. Covering or glazing – Heat retention, light penetration, durability, repairability and budget are all factors to consider when choosing between glass, fibreglass, film plastic and double-wall plastic. Glass reduces heat loss and helps keep humidity levels consisten, but it is costly and can break, and requires you use a solid foundation. Plastic is less expensive but must be replaced every few years. Each covering has its own drawbacks and advantages.
6. Watering system – For a lesser number of plants, watering by hand may be the practical option for you. But for larger greenhouses you’ll want to examine your options for timers or mechanical evaporation sensors for automatic irrigation systems. There is an investment to consider when weighing your options but the extra cost and occasional need to fix the system is beneficial for busy people.
7. Lighting system – For winter and rainy seasons, it may make sense to install a lighting system so that the plants have plenty to eat all the time. As a side-note, the addition of extra carbon dioxide will work with the additional light to help the plants to grow better, as it is used with light in photosynthesis.
8. Heating system – The working of a greenhouse largely depends on the day and night temperature inside the building. As it is an insulated structure, the heating system is crucual for the healthy growth of greenhouse plants during winter. According to your convenience and budget, you can use a heater powered by electricity, gas, oil, wood or sun’s energy. Similarly, there should be cooling arrangements for the hot summer months.
9. Type of ventilation – You can use natural ventilation or mechanical ventilation to keep your greenhouse functioning efficiently. Roof and side vents, as well as louvre vents will vent air naturally, or you can opt for an exhaust fan or a motorized inlet louvres.
10. Air circulation – air circulation helps maintain a consistent temperature for the plants. Knowing the arrangement for air-mixing fans in your greenhouse is essential before you begin construction. During the winter, when heaters are needed to keep the greenhouse air temperature uniform, air-mixing fans are of great importance, and air circulation can aid in pollination as well. The greenhouse complexes in Almeria, Spain are among the largest of its kind in the world, covering almost 50,000 acres of land!