Learning channel post.
I have some numbers to post and explain for folks modifying tents with heat and humidity modifications to both the lung room and the tent.
What I have found works for my 48x48
Vivosun el cheapo grow tent that comes with pinholes to fix before you can use it. Right where they sew the zipper.
Anyways in my tent I have found the long way what environmental changes effect positively in growing cannabis. The relationship of heat and humidity can be expressed as a vpd number. What I have found out is that cannabis is a very flexible plant that can adjust to many vpd settings but it does not like nor can it adjust to large swinge in your vdp.
If you look at a standard ACI app for controlling one of the screens you can look at is a bar graph that splits the VPD into .10 increments. It is always best to see one finger in this graph as it means your vpd over the time period your choose does not waver more than .10 meaning you have very precise control of your environment and the plant will not have any transperation issues associated with poor humidity control.
I say humidity because it is normally this environmental setting that is the easiest to control. Moving enough air with heat adding to control the VPD would be more difficult than an app controlled humidification or dehumidification for VPD control.
Lung room environmental control rules.
There are a certain bunch of rules that you must be aware of when you start changing your lung room heat and humidity settings. The first is that having a heater in the room that needs to lift the normal and expected basic temp of the lung room more than 5 degrees is going to drop your humidity bigly. I can not say home much your particular humidity will dive but I have found out the better sealed off the lung room is the more the humidity will dive down. In some cases this is beneficial but in early veg and seedling you will need a stable and high humidity in both the tent and the lung room . Ideally you will try to get within a 10 point window of what you want to see in your tent. If you want 70 in your tent and you have a
cloudforge type box for humidification it can deliver a .04 wave with an external humidity from the lung room that is between 60 and 65% RH
At lower humidity levels in the tent like say 50% you will find your humidity does not track well and the wave will widen to .10 up and down. This is still fine and will not present an environmental concerns.
Very low humidity levels in the lung room make it more difficult to control the humidity add. The incoming air has such a dry content that when the humidifier shuts off the dry air steals all the humidity and the settings for the humidifier are close to maximum. The tent goes from rein forest to alpine desert humidity about every 10 seconds and the plants will not be happy. Your VPD trace can expand to .20 or even higher. You set it for 1.0 and it flips back and forth from .9 to 1.1
Sometimes you can buffer the humidity drop during the
cloudforge " off " setting my modifying the " off. " Setting to deliver humidity at a 1 or 2 setting. This buffers the huge gulp of incoming air and reduces the high humidity crash to a low humidity spike.
Another rule for tents and even larger open room grows is the ability of the tent to spike humidity to the point of condensing on the tent walls just after lights out. Most tent growers have faced this and it is an excellent way to get Powdery Mildew if spores are available.
This is caused by the heat leaving the tent. Lower temps hold less water vapor so the same amount of vapor in a reduced temp will raise the humidity.
A simple raise of the duct fan 1 setting for a 1/2 hour should prevent this from happening and in most cases due to the reduced need for humidity at lights out leaving the fan on or scripting off for the whole night cycle should work without a problem.
Dehumidification in lung rooms.
This can be a pain as you will find yourself purchasing and using a substantial investment to modify humidity for less than 10% of your grow. But failing to address this part of tent growing will not very smart if you loose a substantial harvest to mold. It happens.
Dehumidifiers produce large amounts of heat and in some cases this is excess heat that will have to be dealt with. I have a 12x10 lung room and I can not run a 50 pint unit in the room. As this mostly happens in flower mid to late and I run at 75 a hot running dehumidifier is not going to work. I have a 30 pint with a condensate pump that auto dumps into the basement dump in the lung room . I also have a large 50 pint unit in the wet room of the basement that can keep the room at 40% humidity and a shuttle fan between the lung room and the rest of the basement right at floor level. It allows me to draw extra dry air into the lung room when demand hits a high spot. This fan is app controlled by the ACI app and works very well and I can always ensure a 45% RH even on rainy days in flower with high transperation plants and lights generating big heat but the lung room at 65 degrees and 40% humidity.
