Why It's Important:
1. To control temperature and humidity
2. To avoid plant stress
3. To prevent over-irrigation
4. To ensure flower set
The selection of cooling systems depends on the amount of heat gained from the outside, as well as any heat generating equipment located within the indoor farm. Heat gain is a function of facility size and orientation, local climate, envelope materials, and sources of internal heat gain (eg. lights, people, equipment). Electricity will be required to operate mechanical ventilation and cooling systems. Renewable energy, generated from photovoltaics and wind turbines, can help offset the cost of energy. Water will also be required when using evaporative cooling systems. To reduce the use of potable water use rainwater harvesting and water recycling from the irrigation system. The HVAC system can also be engineered to remove water vapor from the exhaust air and reuse it for evaporative cooling.
For greenhouses, the cooling requirements are driven by solar radiation through the glazing, as well as the outdoor temperature. For vertical farms and indoor gardens, cooling is dictated by heats given off by the lamps, as well as moisture transpired by the plants (see Humidity Control). The paragraphs to follow describe the typical systems used for both greenhouses and closed plant production facilities.
Although shade curtains block out solar heat gain from the greenhouse, they are typically used as the last line of defense for cooling because they also reduce the amount of sunlight reaching the plants. Shading can be accomplished with a cloth-like material that is either draped over the greenhouse cover or installed inside the greenhouse and suspended over the plant canopy. Shading materials can be purchased to block anywhere between 10-60% of solar radiation, and be selective for plant-specific wavelengths of light. External shades have the benefit of preventing solar heat gain from entering the greenhouse, but must be removed seasonally.