Maintaining a uniform temperature in a greenhouse remains critical to the success of the plants grown there. Cooling requirements in greenhouses constantly change, making it necessary to make frequent adjustments to control the temperature and humidity. No matter what method of cooling you decide to use in your greenhouse, you'll need a ventilation system to help remove the heated air and exchange it with drier air used for evaporative cooling.
Some gardeners find shading helps cool their greenhouse when the structure gets too much light from the sun. While you do not want to take away the light needed for photosynthesis, using retractable shade materials inside the greenhouse helps control high temperatures. Open weave shade systems used inside that pull from east to west create a band of light that moves with the sun, important as the seasons change. You may still need roof vents or some type of air circulation system to move hot air trapped above the curtains. Some gardeners also use coatings or fixed screens to provide external shade, although these require more labor when making adjustments to handle sunlight shifts through the seasons.
The plants in a greenhouse provide some of the least expensive cooling available. Plants try to regulate their tissue temperatures by water evaporation, making them ideal air conditioners. To help your plants cool themselves, provide lots of water to the plants to help improve their transpiration rates, particularly on warm days. When providing extra irrigation, you need to keep the salinity of the rooting solutions low to prevent the salt from interfering with water intake. To help the plants better transpire, provide ventilation to move out the humid, moist air and bring in drier, cooler air.
One type of evaporative cooling system involves using a pad and fan system to bring in outside air. The pad and fan system uses a wet, porous pad that helps water evaporate while the fan moves the air around. The system requires ventilation to take out the humidified air and replace it with drier air. Mist and sprinkler systems offer another way to provide evaporative cooling. The system works best when used to directly cool or humidify air inside the greenhouse, but it still requires ventilation or some type of controlled air exchange.
One of the easiest and least labor-intensive methods for controlling the temperature in a greenhouse relies on an automated control system. The system uses sensors to analyze and regulate the temperature and turn on fans when needed. You can also set up the system to manage irrigation levels, operate retractable shades, and control ventilation rates.