So we are going to build a garage/shop and I am going to add a dedicated grow room with a concrete floor with a drain. I plan on putting in a room about 10’x10’. It will have a mini split for environmental control. I am going to put these pvc wall panels and ceiling that should be easy to clean. Should I have an exhaust system of some sort? Or is there anything else I should add or do?
Fresh air in and transpired air out so yes both intake and exhaust unless you gas with CO2.
Ideally, a complete air exchange in 5 minutes or less.
Air comes in from outside, is conditioned by the AC and or dehumidifier and blown over the plants with air mover fans, then exits thru the exhaust.
Arrange air movers across from each other and in a crossfire pattern to prevent bud rot later and for good air mixing.
There's a lot of calculators online to figure out what you need.
Here's one that you enter the size of the space and it will calculate what you need in CFM power to make it happen then you shop for fans that meet those standards.
CFM calculator to precisely determine the room cubic feet per minute (CFM) required to replace the air in your grow room, based on the fact that your grow room's air need to be renewed at least once every 5 minutes.
www.hydrotekhydroponics.com
This one adds in more variables to calculate and is probably the most advanced
Use this calculator to determine the minimum air exchange required in cubic feed per minute (CFM). This calculation might be different at each stage of growth.
onlinecannabiseducation.com
Variables such as the heat from lights and ambient conditions from the intake as well as the cooling and humidity created by the plants themselves all factor into the control.
Another factor is that for every 90 degree turn in duct, you lose 50% of the CFM so if there's turns in your duct run you need a bigger than usual fan.
I usually focus on the most destructive variable and control it first.
For most of the grow my exhaust speed and run time on is controlled by a thermostat since heat is my biggest problem.
When plants are in flower I change the control to RH and around midway thru flower to prevent bud rot I take it off all control and run exhaust max speed 24/7 until harvest.
