Controller boxes are even more efficient than thermostats for automating environmental control. Controller boxes may be simple for turning systems on and off at a set point, or they may be advanced computerized systems utilizing computer learning technology that provides environmental control customized to a particular greenhouse.

Some systems provide the added convenience of digital alarms and manual controls that reduce the need for manual on-site monitoring and intervention. If the power to the greenhouse goes out, nothing will work unless it is connected to a backup generator. Systems that offer alerts for power loss and high temperatures can let a designated greenhouse worker know if system failures occur. When power returns, the controller should return to normal operation based on the settings stored in its memory.

Efficiency is important since greenhouse fans generally need to be run constantly for at least 8-9 months of the year. Most fan manufacturers will provide an energy efficiency rating calculated by multiplying the cubic feet per minute fan output by amps multiplied by volts (ft2 output x amps x volts). An energy efficiency rating of 14-16 is average, but more efficient fans can exceed ratings of 18. The fan motor will influence the energy efficiency rating of a fan, with split capacitor motors performing more efficiently than shaded pole motors.

One 20 amp circuit can accommodate up to 15 fans at 1/10-1/15 horsepower (~100 watts electricity draw per fan). Horizontal airflow systems should be run constantly during fall, winter, and spring. On/off switches can be used to control the circuit, and power relays can be placed on the circuit to turn fans off when exhaust fans are activated or vents opened. When wired to a controller box or automated environmental control system, horizontal airflow fans should run during heating, setpoint, and low stage ventilation programs.

Hortitech's Senior Grow Expert Jerad Lauzier points out that controller box options are based on functional requirements. The box needs to have a sufficient power supply, the outlet power must match the controller's voltage, and the equipment must match the controller's voltage. Here's what Jerad wants you to know when it comes to controller box options:

"Basically, controller boxes are a series of instruments. They consist of a sensor which tells the "brain" what is going on, a "brain" which is programmed to control outputs based on the programmed setpoints, and then a "contactor box" which controls all of the power, the brain sends a relay signal to the contactor box which then gives power to the outputs.

The basic variables to control are temperature, humidity, CO2, light supplementation, and light deprivation. Basic controllers only work for temp and humidity and more advanced ones can handle all of the variables. Also, the advanced ones can be programmed to cut off components if certain thresholds are broken.

For example, if the temperature goes over 100 in an indoor room because of an AC failure then the brain will kill the grow lights. Also, the more complex controllers hook up wifi, remotely monitor and control equipment from a computer or cell phone, and can track data and metrics so you can look back and see what happened in the middle of the night or long term to track the performance of the room or greenhouse from and environmental standpoint."