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if you want the temperature in the tent to never exceed 80 degrees F, you will set that as your exhaust temperature.
Then you can take the temperature of your air outside of the tent, we'll assume 70 degrees F for the inlet temp.
And knowing the humidity the of the exhaust and the outside air will aid in the accuracy of this. But for this I will assume a 5% increase in humidity between the inlet air and the outlet air...just to demonstrate the effect it has.I will use 45% RH inlet and 50% RH outlet for this.
Using a Psychrometic Chart for Air at 1 atmosphere of pressure, you can look up the enthalpy of your inlet and exit conditions.
Inlet enthalpy: 38 KJ/KG of dry air Outlet enthalpy: 54 KJ/KG of dry air
Using this, you can assume a 1000W input of heat energy to the system from the light, which is equal to 1 KJ/s.
You can then plug these into the equation for heat loss through the air flow, where m = mass flow rate of dry air, and Q equals the heat flow out of the system:
Q = m (54 - 38)
substituting 1 KJ/s for Q, we find that m = .0625 kg dry air/second
from the psychrometric chart at the temp and RH of the exhaust, we find that the specific volume of the exhaust is .864 meters cubed/KG dry air.
and by multiplying m by the specific volume, we then find the volumetric flow rate of the exhaust needs to be .054 meters cubed / second.
This then converts to 114.4 cubic feet per minute, or about 115 CFM minimum.
Obviously, no one should run at the absolute minimum, and differences in inlet and outlet temps and humidity will effect the required flow rate, and this flow rate does not take into account the actual rate of water loss from the plant...so in order to keep the humidity down you may need to run higher flow rates.
If you need anymore help with this method or have questions feel free to ask.
Hope this helps, agmotes165
-------------------- “The Universe is under no obligation to make sense to you” -NDT
Ive also heard that replacing the entire volume of your grow room every minute usually works fine...and would probably be a lot easier to calculate haha
peace agmotes165
-------------------- “The Universe is under no obligation to make sense to you” -NDT