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Cooling: The combination of manual and automatic ventilation is the most cost-effective way to cool down your greenhouse. Ventilation options include roll-up sides, ceiling vents, and vents along the long end of the greenhouse. Forced air ventilation fans pull air through the length of greenhouse using thermostat-controlled vents at the opposite end. Evaporative coolers are a relatively inexpensive way to provide cooling to the structure in hot, dry climates. Evaporative coolers work by pulling in outside air through a wet wall, cooling the air as it comes in. The wet wall is a frame that contains corrugated cardboard or synthetic
material that is saturated by water dripping over its surface (Figure 27). Excess water is collected in a reservoir and pumped back over the cardboard. Evaporative cooling walls are not efficient in climates with high temperature and high humidity.
Moving production into an insulated building is suitable for producers who want to be close to urban markets, have a lack of arable land, or live in a climate not suitable for outdoor or greenhouse production. No matter where a plant is grown, it still requires optimal conditions to reach its maximum yield potential. In addition to the controls discussed above, producers must also provide light suitable for optimal plant growth. For plants, light stimulates seed germination, food production, flowering, chlorophyll manufacturing, and branch and leaf thickening.
Photosynthesis is stimulated by the type and frequency of light received. Light is emitted as waves of photons, or bundles of energy. The amount of energy in each photon determines the length of the wave from crest to crest. Lower energy wavelengths emit a blue light (400 nm) and higher energy wavelengths emit a red light (700 nm). Plants utilize wavelengths between 400-700 nm. Blue and red light is required in different ratios at different periods in the plant's life. Blue light is primarily responsible for vegetative growth. Red light triggers cell elongation, vegetative growth, and flowering.