Heat transfer by conduction is most easily reduced by replacing a material that conducts heat rapidly with a poor thermal conductor (insulator) or by placing an insulator in the heat flow path. The rate of conduction between two objects depends on the area, path length, temperature difference and physical properties of the substance(s) (such as density). Heat is conducted either through a substance or between objects by direct physical contact. The heat demand for a greenhouse is normally calculated by combining all three losses as a coefficient in a heat loss equation. Usually many types of heat exchange occur simultaneously. Heat loss from a greenhouse usually occurs by all three modes of heat transfer: conduction, convection and radiation. Greenhouse heater requirements depend upon the amount of heat loss from the structure. Savings in labor could justify a more expensive heating system with automatic controls. Convenience, investment and operating costs are all further considerations. The cost and availability of these sources will vary somewhat from one area to another.
Suitable energy sources include natural gas, LP gas, fuel oil, wood and electricity. Any heating system that provides uniform temperature control without releasing material harmful to the plants is acceptable. A good heating system is one of the most important steps to successful plant production. Georgia greenhouses must be heated for year-round crop production. Tropical plants usually grow best in high humidity with night temperatures of 70 degrees F. These plants include rose, tomato, poinsettia, lily, hyacinth, cattleya orchid, gloxinia, geranium, gardenia, daffodil, chrysanthemum, coleus, Christmas cactus, calla, caladium, begonia, African violet, amaryllis and tulip. Some plants grow best in warm greenhouses with night temperatures of 65 degrees F. These plants include azalea, daisy, carnation, aster, beet, calendula, camellia, carrot, cineraria, cyclamen, cymbidium orchid, lettuce, pansy, parsley, primrose, radish, snapdragon, sweet pea and many bedding plants. Some plants grow best in cool greenhouses with night temperatures of 50 degrees F after they are transplanted from the seeding tray. Relative humidity may also require some control, depending on the plants cultured. Most plants require day temperatures of 70 to 80 degrees F, with night temperatures somewhat lower. The house temperature requirements depend upon which plants are to be grown. Warning devices might be desirable for use in case of power failure or in case of extreme temperatures. For this reason, use reliable heating, cooling and ventilation. Water, fuel and electricity make environmental controls possible that are essential for favorable results.
Consider the location of existing trees and buildings when choosing your greenhouse site. Greenhouses need exposure to maximum light, particularly in the morning hours. Greenhouses should provide a controlled environment for plant production with sufficient sunlight, temperature and humidity. Other Heating System Design Considerations.This is because evaporative cooling relies on the difference between outdoor and indoor conditions. Indeed, when conditions outside are humid, pad and fan system loses effectivity and provides a much lower cooling capacity. However, wet pad and fan system may not provide the desired results in tropical regions, where absolute humidity is often high during the night. Some greenhouses do require cooling at night, mostly in tropical regions. Then, the fans blow the cool air into the greenhouse, leading to an overall drop in temperature. Firstly, the air is blown through the pad, which constantly evaporates water, creating a cooling effect. Besides, this system uses exhaust fans to absorb air from outdoors into the greenhouse. During hot summer days, it is an effective way, for small greenhouses, to cool, putting plants in the best climate conditions. Pad and fan system cools down greenhouse temperature, using evaporative cooling (absorption of a large amount of heat, by the water, in order to evaporate).
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