Ventilation

Figure 23: Greenhouse with exhaust fans. Source: Scott Sanford

Figure 23: Greenhouse with exhaust fans. Source: Scott Sanford

Mechanical Ventilation

Exhaust Fans
Most greenhouses have exhaust fans to increase the air exchange in the greenhouse to reduce temperature levels (Figure 23). The efficiency of exhaust fans is measured as cubic feet per minute per watt (i.e. air flow per unit of energy) and can vary widely. A 48-inch fan for the same application can range from 12 to 27 cfm/watt. Fortunately, the Bioenvironmental and Structural Systems (BESS) Lab of the University of Illinois tests these fans, publishes the data and makes it available on-line at no charge. In general, the larger the fan diameter is, the higher its efficiency. When purchasing exhaust fans, refer to BESS Lab for test data for the fans you are considering [6] and use Table 3 as a guide for the minimum recommended efficiency.

Table 3. Energy efficiency for exhaust fans. Source: Scott Sanford

Table 3. Energy efficiency for exhaust fans. Source: Scott Sanford

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