Switching fans on & off
“Automated” fan switch: Thermostats and humidistats are
useful for activating both the inlet and the exhaust fan (Fig 5.7).
Position the thermostat’s sensor at the hottest point in the foliage,
the humidistat’s sensor at the most humid point. Determine these points
using a thermometer and hygrometer. For “day time” (lights-on) they should
be set to activate the fans when either the temperature exceeds ~27oC
(80oF), or the humidity exceeds 70% RH.
“night time”, the temperature should be allowed to drop below 20oC
(68oF), but no further than 15oC (59oF).
To achieve this, you will need a controller that allows separate settings
for both day and night. Alternatively, install a separate, dedicated set
of fans for both day and night. An ‘axial’ fan in the ceiling (controlled
with or without a timer) may be sufficient to produce the correct night
“Manual” fan switch: Control gear such as thermostats, are
often not essential in extremely hot or humid climates because it is
usually necessary to have fans running constantly anyway. However, the
above mentioned temperature and humidity targets still apply. A modest
degree of control can be gained using a timer - a
surprisingly effective aid especially if the weather is consistent or
Ventilation for extreme climates
Consider the following options if the grow room temperature is too high:
1. Shift the ‘lights on’ period to night.
2. Air-condition the incoming air.
3. Reduce the amount of lighting and/or
lights or shades that are air cooled (Fig 4.5).
5. Where the “hot days” are infrequent and
the ventilation system is otherwise satisfactory, turn some (or all)
lights off during those hot days.
6. Relocate the grow room to a cooler area.
For example, a shaded part of the building or that part most exposed to
the prevailing wind.
7. Use insulation in the surrounding rooms so
they do not amplify the temperature of the grow room.
the temperature is too low, consider pre-heating the incoming air. If air
is coming directly from outside, bring it from a warmer room. If incoming
air is not heated you may be restricted as to how frequently fans are
operated, especially at night when lights are off.
fan speed controller is a useful addition where the fan's flow rate is too
high during the colder or less humid months (Fig 5.8).