As we move into greenhouse season, many people are going to be purchasing or building their very own greenhouses to protect their plants over the winter. They will spend a signifigant amount of time sizing up all of their options, comparing features and prices, looking at the pros and cons of different coverings. Usually they are going to purchase a heater, especially if they are planning on growing (as opposed to just overwintering) this winter. But there is an oft overlooked system that can be overlooked by many a greenhouse owner, especially in larger homebuilt structures.

Air circulation can be very important in greenhouses of the right size. In smaller greenhouses, under 100 sq. ft. air circulation is usually handled efficiently enought by roof and/or side vents. But in larger greenhouses air can become water laden and stagnant if it is not circulated enough. This can lead to disease, pollination, and climate control problems.

Condensation problems can arise in any greenhouse with inefficient circulation. Condensation can form on the outside or inside of a greenhouse, and the type of covering won't necessarily affect the propensity of condensation to form (although some are better suited to deal with it once formed). A greenhouse works by stopping the natural convection currents that would normally cool any given volume of air. Essentially, in an unenclosed space molecules are free to move from a space with higher energy (warmer) to one with lower energy (cooler) and seek a balance between the two. In an enclosed space, molecules are not free to undergo this type of movement.

So during the day your greenhouse can build up heat, and once the temperature drops sufficiently enought outside you may see condensation form on the inside of your greenhouse if the air is adequately humid. The reverse will happen, that is, condensation can form on the outside of your greenhouse in the morning once the temperature rises outside.

While condensation on the outside of your building is something that can be coped with, condensation on the inside of the building can be harmful. Greenhouses are going to be humid environments, but too humid and it can propogate harmful mold or other fungus that can harm plants. The best way to combat this situation is have correctly sized heating and ventilation systems and to use them.

The ventilation system should include circulation fans. These fans will push an pull the air in your building and disallow any stagnation. This will help to evenly disperse temperatures and humididty levels throughout the building and fight the formation of condensation.

Additionally, circulation fans can aide in the pollination requirements of certain plants. Since they move air around in an environment that would otherwise be stagnant, fans help pollinate plants that need this type of assistance.

Lastly, circulation fans will help increase the efficiency of your climate control systems thereby saving you money. By not allowing warm or cool air to collect in on half or in one portion of your building, circulation fans can save you money by more evenly distributing your conditioned air throughout your building.

So as we move inside this fall and winter, take some time to consider the air circulation needs that your greenhouse might need. It may just save you time, money, and pain in the long run.