Air Flow                                  Fan Calculation                       Controlling Your Environment

There are many reasons to start an indoor garden- to grow veggies year-round, to get a jump on the outdoor season, or maybe you don't have the space outdoors, a proper climate, or you have poor soil. Regardless of your reasoning, indoor gardening is a rewarding endeavor and can result in significantly higher yields in less time relative to outdoor gardening. There are many differences between indoor and outdoor gardening, most notably the element of control, and therefore responsibility, of the indoor gardener. Indoors we must provide water, light, carbon dioxide, nutrients, and the correct temperature and humidity for growth. Don't look at this as a liability, but an opportunity. The essence of indoor gardening is creating environments. The idea is that you cannot change the way a plant
grows; you can only enhance and idealize the building blocks available for the plant to use. The extra element of control allows the grower to take plant stress- in the form of cloudy days, nutrient deficiencies, pest infestation and disease, etc.- out of the scenario, resulting in higher yields.

The essence and advantage of indoor gardening is the ability to control your growing environment; the ability to attempt replication of indigenous

Indigenous : Existing or growing naturally in a region or country.
climates so as to maximize plant growth. Indoors, the grower is not forced to abide by the whims of nature- they ARE nature. The ability to manipulate and control the respective environment allows the gardener to create ideal conditions that result in higher yields and an overall healthier plant. Environmental control and calibration is one of the most commonly overlooked aspects of a growroom. Many growers assume that the best way to achieve successful growth is to use a multitude of products. The truth is, if you don't have your environment properly controlled the plant will never have the ability to use the products your giving them.

Air flow
One of the most overlooked environmental factors affecting plant development inside a growroom is airflow. Getting sufficient air movement across a leaf surface, and in and out of your growroom is vital to good production and yields, disease prevention, and can mean the difference between high rates of photosynthesis occurring or none at all. There are different levels of air flow- air moved around within a growroom, or circulation; and air moved in and out of the growroom, or intake and exhaust.

Circulation
Moving your air around in your growroom allows several benefits. A small amount of air movement - just enough to gently move or 'flutter' the leaf - has the effect of removing the stale, humid air from the boundary layer that lies just above and just below the leaf surface. This boundary layer of air supplies the leaf with CO2 and also retains much of the moisture transpired by the plant. If there isn't any air movement, diffusion of water vapor out of the leaf and CO2 into the leaf begins to slow as the boundary layer air mixes too slowly into the rest of the environment. Another benefit is disease control. Stagnant air invites certain diseases and molds to infest your growroom. These nuisances are always there, but by ensuring proper airflow they will not be able to come out to play. Circulating air also has a beneficial effect on the
turgor pressure of your plants. By simulating the wind that your plants would experience outdoors, the plant is less susceptible to wind damage and is hardier than if not experiencing any sort of stress from air movement.

Intake and Exhaust
It is important to have the ability to remove air from your growroom via an exhaust or intake system. Intake fans pull air into the growing area, exhaust fans push it out. Exhaust fans that are positioned to extract warm moist air from the crop are the most useful; however an intake fan that draws in sufficient fresh air with an adequate vent system to allow stale air to vent out works well. If one option must be chosen, use an exhaust fan to control your airflow. By removing the air from your room, negative pressure

Negative pressure : Pressure less than that of the ambient atmosphere; in a growroom this is experienced when air is removed (or exhausted) from your room. The result is the influx of fresh air from outside the room due to the vacuum created by removing the air.
is obtained creating a vacuum and ensuring that air can only come into your room, resulting in absolute control of your air and the assurance of fresh air and CO2 being brought in. Carbon Filters and Ozone Generators can be used most effectively inline on an exhaust system to control odor and pathogen distribution. You can imagine the effect of having an intake being the controller of your air. Positive pressure would force air out of your room, making it harder to control where you air will end up. Why not vent your indoor garden air into other areas of your house to reduce heating costs during cold seasons? Control of your air is especially important when odors and pathogens from growing materials and plants are unwanted outside the growing area. An exhaust system is normally used as a means of controlling humidity via a hygrometer or "brain". Some growers can get by using an exhaust as a means of temperature control, but in situations where there are high levels of HID light in a small area, high temperatures can be an issue.

Air-cooling reflectors
If an exhaust is not sufficient for maintaining proper temperatures inside your growroom you might want to air-cool your reflector. This is done by using duct work (like on the back of your dryer) to create an in-line scenario moving air through your reflector using tempered glass to encase the heat. This way, the hot air around your lamp will be physically removed from your room and the air will never have a chance to
incorporate itself into the room, resulting in dramatically less heat. There is a reason that an exhaust system and air-cooling your reflector are separated. It allows greater control over your environment, effectively separating your ability to control heat and humidity.

back to top

Fan Calculation
Getting the size of the intake and exhaust fans right for your growing environment is important for plant growth and development and disease prevention. Depending on the logistics of your setup, it is best to setup an intake vent relatively low down at one end or corner of the growing area, with an exhaust fan set higher up at the opposite end of the room. The idea behind this is that cool, drier air sucked in from outside will flow up, through and over the crop (assisted by mixer fans in the room), and warmer, moist air which rises will be extracted by the fan at the other end.

Step 1
The first step in working out the size of fan(s) required is to calculate the amount of air in the growing area. This is done by multiplying the length of the room x width of the room x the height of the room. This will give a value in cubic feet:

For example, a 12 x 12 foot room with a height of 8 foot:
12 x 12 x 8 = 1152 cubic feet of air inside the growing area.
Ventilation fans are rated in the number of cubic feet of air they can move per minute = cfm

Step 2
The faster your fan can exchange the air in your growroom the more control you have over your environment. In other words, it is more efficient to have a fan that will exchange your air in 5 minutes versus an hour. This allows you more flexibility in regards to CO2 implementation and overall environmental control compared to a smaller fan.

If excess heat in a certain growing environment is a common problem, or there is a large volume of plants growing in a very restricted space you need more airflow than for a larger growing area that doesn't suffer from too much heat build up with smaller plants.

Growers commonly underestimate just how much 'air exchange' is required to remove excess heat and humidity, bring in fresh CO2 and generally create fresh air movement over all of the plant surfaces. Having said that, some people have their exhaust fans running 24/7, which is a tremendous waste of electricity. As a comparison to greenhouse crops growing in full sunlight one air change per minute is often aimed for with large, mature crops growing under warm, humid conditions. However, in an indoor growroom situation, one complete air change obtained in 4-5 minutes is acceptable.

Step 3
Divide the air volume of the growing area by the number of minutes required to get one full air change:
If the room is 1152 cubic feet, divide by 5 minutes (one air change every 5 minutes)

Fan capacity required is 230 cfm (for just one exhaust fan).

Add on at least 2 medium-sized mixer fan (either wall or stand mounted), making sure these are equally spaced in the growing area. Smaller fans will be beneficial to increase airflow up and under plants in any 'stale air pockets' that may be prone to fungal or bacterial disease attack.

Conclusion
Air movement with the correct sized fan, well placed mixer fans to displace stale boundary layer air around leaf surfaces, and fan controllers to get maximum climate control are vital to the success of any indoor crop. Air movement is often overlooked, but an essential part of maintaining optimal growth conditions by modifying temperature, humidity, and CO2 levels at the leaf surface where the important plant processes of photosynthesis and transpiration are occurring. Getting fan size and air movement calculations right means plants have the best conditions for growth, development, and supreme yields.

back to top

Controlling Your Environment
Automating your growroom allows the essence of indoor gardening- control. Instead of trial and error and constantly molding your environmental control through jiving timers, etc. you can provide yourself with a "brain" that will control it all for you. Generally, light timers can be separated from environmental controllers because there is no need for constant variance of photoperiods. However, there are complete controllers that will automate everything from CO2 to lights to pumps to humidity control and everything in between.

"Brains" work via thermostats and humidistats similar to central air in a home. You set the environmental parameters. When they are exceeded, your environmental controls come on to recalibrate your environment.

Some environmental controlers integrate CO2 into their capabilities by ensuring CO2 delivery is cut off when your environmental controls are on. This prevents uneeded wastes of CO2. They also ensure that CO2 delivery does not occur at night when stomata are closed and the plant is being nurished by stored energy.

Premium CO2 control is accomplished with PPM monitors. You set the desired CO2 PPm range and the "brain" will maintain it for you.

"Brains" such as these are not vital for plant growth, but will go a long way in streamlining and maximizing the potential of your growroom. It will also make maintenance less of a burden so you can enjoy more time with your plants, which we are sure they will appreciate. The retrofit will more than likely pay for itself over time by utilizing your environmental controls only when you have to saving electricity costs and from the increase in plant yields. If you have any questions regarding implementation of environmentals controls and/or CO2 delivery, contact PG.

back to top