caron 7310-22, Operation Manual

Page: 128 / 131

7310 Series Operations Manual REV E 11-19-19 Page 128 of 131
APPENDIX A – Dehumidification Performance (HUMD312, 313, 314)
Plant growth chambers with optional humidity control (HUMD312, HUMD313 and
HUMD314) have the ability to control the humidity level inside the chamber by adding or
removing moisture in the air. There are other factors that influence the humidity level
inside the chamber which the user should be aware of.
Relative Humidity
Relative humidity refers to the air’s moisture carrying capacity at a specific temperature.
The maximum relative humidity level is 100%. The higher the temperature, the more
water the air can hold. For example, air at 15°C can carry 74 grains of moisture per
pound of dry air. Air at 25°C can hold 140 grains of moisture per pound of dry air.
When the air temperature drops, it is unable to carry as much water. And when the
temperature is below the dew point, excess water will condense out of the air.
When the plant growth chamber set point is higher than the humidity level, the air’s
humidity is increased by injecting water into the air via a system of atomizers.
Conversely, when the chamber set point is lower than the chamber’s humidity level, then
moisture is taken out of the air by means of a mechanical refrigeration evaporator.
However, because relative humidity is dependent on temperature, a change in
temperature by itself (without changing the moisture content) also changes the (relative)
humidity level. This phenomenon can be seen when transitioning from day to night (and
visa versa). For example, if the day temperature is 22C with a 65% relative humidity
and the night temperature is 18C, then natural resultant humidity level at night will be
83%. Active dehumidification is needed to lower the humidity from 83% to the desired
65% during the night.
Indirect affect of heat from lights on humidity
Lights themselves give off convection and radiant heat. The first impact this has is to
raise the air temperature. As the immediate air temperature increases, the relative
humidity resultantly decreases. Caron chambers provide stable and gentle forced air
movement to maintain a uniform environment. The circulating air is also cooled to offset
the affects of heat radiating from the lamps. During this cooling process, the mechanical
refrigeration evaporator naturally condenses moisture from the air. This humidity loss is
made up for by the chamber automatically injecting compensating water.
The affect of lights on humidity can most easily be seen during a day to night transition.
This sequence of events will follow: the lights turn off, the heat generated by the lights
goes away, the cooling system no longer removes moisture from the air, and the result