Why is cooling important? Well, first to control temperature and humidity, secondly to avoid plant stress, then also to prevent over-irrigation and 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.
Read more at Dr. Greenhouse to see a description of the typical systems used for both greenhouses and closed plant production facilities.