|
 Switching fans on & off
Automated method: Thermostats and humidistats are useful for
activating the inlet and exhaust fans (Fig
8.1). Position the
thermostat’s sensor at the hottest point in the foliage, and the humidistat’s sensor at the most humid point (determine 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. At “night time”, the temperature
should be allowed to drop to ~20oC (68oF). To
achieve this, you will need a controller that allows separate settings for
both day and night. Or, you will need 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 time conditions.
'Manual' method: In extremely hot or humid climates it is
usually necessary to have fans running constantly, so the absence of
control gear (thermostats, etc) is of little concern. The
temperature and humidity targets mentioned above still apply. A
modest degree of control can be gained using a timer, a surprisingly
effective aid especially if the weather is consistent or predictable.
A
fan speed controller is a further useful addition where the fan's flow
rate is too high during the colder, or less humid months.
|
We strongly suggest speaking to your local growshop when designing
your ventilation system. A system which is perfect for one particular
climate may be useless in another! |
Temperature is still too high?
Consider the following options:
1.
Shift the ‘lights on’ period to night.
2.
‘Air condition’ the incoming air.
3.
Reduce the amount of lighting.
4.
Employ air cooled lights/ shades (Fig 10.4).
Temperature is too low?
Low temperatures will cause humidity (RH) to increase. For example, the RH
of a body of air will increase from 55% to 100% if its temperature drops
from 25oC (77oC) to 15oC (59oC).
Therefore, consider pre-heating incoming air. If air is coming
directly from outside, bring it from another room where it has been able
to warm up first. If incoming air is not heated you may be restricted as
to how frequently fans are operated, especially at night when lights are
off. |
