The most traditional design on the market and by far the lowest cost method to cool your greenhouse. Negative Pressure cooling uses exhaust fans at one end of the greenhouse to pull or exchange the air in the greenhouse out of the building with fresh outside ambient air temperature at least once per minute. The temperature can be lowered through evaporation of a simple pad system or cool cell. As the air is chilled through evaporation, it is pulled to the opposite end of the greenhouse and forced out of the building through the exhaust fans. This cycle happens over and over again up to 1.3 times per minute. While this is the most inexpensive capital expense as well as most economical operational expense, this is the least effective method for hot humid climates to produce cannabis. In fact, without switching completely to an extraction only operation during hot humid months in certain parts of the country, this method of growing may be unusable.

There are a lot of crops that do well in greenhouses with natural ventilation. The lower initial cost sidewall rollup curtains versus the high electrical cost of operating exhaust fans makes natural ventilation an attractive option. Greenhouse sidewall vents provide a low cost, low maintenance solution.