Last month our topic was humidity. This time we’ll discuss ventilation, a traditional, if inefficient, method to reduce humidity.

Growers in closed facilities face complicated challenges, one of the more complicated challenges being humidity.

Humidity inside a growing facility is generally caused by transpiration from plants. If humidity gets too high, drops of water form on the plants, causing humidity-related diseases such as Downy mildew, Botrytis, Alternaria, Powdery Mildew, Erwinia, Phytophora, or Clavibacter. Reducing the humidity inside growing facilities can prevent diseases and reduce the need for pesticides.

A traditional solution to treat humidity is ventilation. Ventilation is a relatively low-tech solution to humidity issues.

There are two main types of ventilation:

1. “Natural” ventilation is the opening and closing of a growing facility’s doors and windows to replace the humid air inside with external (hopefully) dry air.
2. “Forced” ventilation uses fans to replace the humid air inside with external (hopefully) dry air.

Plants transpire all day. They transpire around 88% of the water they absorb during the day. When the weather outside is dry, ventilation can be a very effective method to reducing humidity. Moreover, during daytime (when it’s warmer) ventilation can also lower the heat inside.

There are three main problems growers face during nights or on cloudy, rainy, or cold days:

1. Loss of energy. Opening a growing facility leads to loss of warm air, especially in colder conditions. A loss of heat energy often leads growers to use more energy in order to reheat the facility. In fact, according to experts, ventilation can be calculated as an average energy loss of around 75kw.
2. Moreover, when the air outside is just as humid, or more humid than the air inside the growing facility (on rainy days, cloudy days) ventilation becomes ineffective.
3. No uniformity. Taking in external air creates microclimates of temperature and humidity inside the growing facility. This difference in climate conditions affects the growing process and the development of the plant, ultimately leading to an inconsistent yield.

Editor’s Note: Colder, humid air can be brought in as well. Because the air is colder, it contains less water, but can have the same RH. If the cold, humid air is heated up, it lowers in RH. This is relatively inefficient method of dehumidification, but is a ventilation method of dehumidification.

These days, many growers are acknowledging the importance of dehumidifiers. DryGair products, for example reduce the need for ventilation during the night or on cloudy/rainy days. The goal is humidity reduction without ventilation. This can save upwards of 50% of the energy invested in the operation of the facility.

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