Chapter 5

Greenhouse Energy Conservation Strategies

Greenhouse Fans

Ventilation Fans

Ventilation, or exhaust, fans aid in regulating the temperature and sometimes humidity in greenhouses. Ventilation fans are a substantial user of electricity in a greenhouse, so installing energy-efficient fans will reduce production costs. The efficiency of a ventilation fan is measured as cubic feet per minute per watt (cfm/W), or airflow per unit of energy.

Maintenance

Ventilation fan maintenance is often neglected. The two most common maintenance issues are louvers that don’t open or close properly and loose belts. Louvers that don’t open can reduce airflow by up to 40 percent, while loose belts that slip can reduce airflow by 30 percent.

Horizontal Air Flow (HAF) Fans

Regardless of the type of heating system used, install a sufficient number of horizontal air flow (HAF) fans to adequately circulate the air inside the greenhouse (See Figure 5.1). Good air circulation will improve temperature and humidity uniformity in the greenhouse, which reduces the incidence of cold pockets in the greenhouse and improves plant quality and uniformity. Monitor the humidity level in the house, generally keeping it below 80 percent to minimize disease incidence, and vent when necessary.

Air Speed

Air circulation by the HAF fans should be maintained at 2 to 3 cubic feet per minute over the floor surface of the greenhouse. For example, a 28-foot x 96-foot greenhouse requires an airflow of 5,376 cubic feet per minute (28 x 96 x 2 cubic feet per min per square foot = 5,376 cubic feet per minute).

Fan Location

The HAF fans should be located 2 to 3 feet above the plants and aligned parallel to the sidewalls of the greenhouse so that the air is circulated around the house in a rotational pattern.

Winter Operation

The HAF fans should be run continuously during the winter to improve temperature and humidity uniformity in the greenhouse.

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