G.A.S. Intelligent Humidity / VPD ControllerControl the Humidity & VPD in Your Grow Room for Optimum Plant Growth The GAS Intelligent Humidity Controller takes care of the humidity levels in your grow room for faster growth rates and happier plants. Air temperature and humidity are the two factors that affect something called Vapour Pressure Deficit (VPD), which is literally the "drying" ability of the air. For plants to grow at their max, the humidity needs to be within the right range for the