One way that growing in a greenhouse differs from that of traditional indoor growing is Greenhouse air circulation. Typically an indoor grower will have wall mounted oscillating fans blowing back and forth with no real ‘direction’ of the air. In a greenhouse we use Horizontal Air Flow, HAF, fans that will mount above the canopy and create a directional flow. One side of the greenhouse will have the fans point in one direction while the other side of the house will have the fans blowing in the other direction. This creates a vortex of air movement. By allowing the air to create a momentum there are several things that are accomplished that are not necessarily addressed with an oscillating fan approach.
- Air stratification, Thermal destratification is practically eliminated.
- Corners of greenhouse are ‘scrubbed’ eliminating temperature differentiations.
- By keeping a natural wind approach condensation is reduced which also helps to alleviate humidity in the greenhouse and most importantly within the the plant canopy.
- Carbon dioxide utilization is improved by properly circulating it throughout the greenhouse and through the different levels of the canopy.
- If plants begin to transpire the ‘wind’ will blow on the leaves creating an ‘evaporative cooling’ effect on each leaf surface. I like to say that a happy plant is a dancing plant.
The momentum of air is replacing sheer velocity as the major focus in greenhouse HAF use. The goal of a momentum based system is to create a stable mass of air as it travels through the greenhouse. Often, HAF fans spinning at too high of a RPM may cause turbulence and uneven drying through out the crop. High air speed can also be responsible for stratification of the air in the greenhouse. Fast moving air can prevent passive venting through buoyancy (the effect of hot and/or humid air rising) in a gutter or ridge vented greenhouse. Today’s HAF fans use more aerodynamic fans than in the past. By shrouding the fan in a housing more of the air is directed forward and not out the sides or down onto the crop. This helps to build stability of the air in a forward direction and reduces obstruction created from opposing air patterns. Additionally, the use of shrouds creates an intake as well as an exhaust. This intake can help keep the forward momentum going by pulling air in the desired direction. As a result of the increased distances and lower speed requirement of the momentum based system, they need fewer fans and use less electricity. It’s quite amazing to see the efficiency of HAF fans in action. 4-20″ HAF fans can properly circulate air in a 30’x60′ structure. When compared to wall mounted oscillating fans this is an exponential decrease in the amount of fans needed.
At FFG our AutoFlowerer kit comes with equipment hanging bars that are installed within the blackout area. These bars allow for the usage of HAF fans when the tarps are closed. More air flow equals less built up heat and humidity which translates as less molds, mildews and funguses. The usage of FFG’s Breathable Wall coupled with dual exhaust fans and intake shutters allow for FULL air flow within the growing area when controlling the photoperiod of the plants. We engineer our exhaust systems to allow for one full air flow per minute allowing ample air exchange when ridge and side vents are closed.
-Jonny Light Dep, JLD