Basic requirements for greenhouse growing are light, moisture and the proper temperature for the crops being cultivated. In order to prevent excessive heat buildup, some form of ventilation is almost always necessary during the height of the summer. Even in winter, a greenhouse can become excessively warm and humid, leading to less than optimal growing conditions for sensitive plants. Natural air circulation can be as simple as having roll-up or drop-down sides as a feature of the greenhouse design. An electric circulating fan or some sort of exhaust fan -- even screen doors -- can help provide interior air flow. However, for larger greenhouses, more sophisticated temperature and airflow controls will be necessary.
An evaporative cooler is one option. Sometimes known as a "wet wall," it is particularly effective in hot, dry climates because it not only cools the air but adds moisture to a greenhouse environment. In high-humidity locations, reverse-cycle heat pumps can be used to control temperatures to some extent both during the heat of summer and in the winter. Heat pumps are available to capture geo-thermal constant temperature, and are used in many locations. Fans, blowers, wall panels that can be opened and closed as needed, and supplementary heat and cooling must be specific to regional needs and designed to suit the size and type of greenhouse. There is no single solution that will apply to all greenhouses in all locations. Utility costs are vitally important to successful greenhouse operation, particularly for commercial enterprises, but utility costs can also become exorbitant for an individual home greenhouse. There are safety considerations as well, that must be factored into the planning and design.
