G.A.S Intelligent Humidity / VPD ControllerIntelligent Humidity Controller The Intelligent Humidity Controller monitors your environment and controls the humidity levels to VPD, vapour pressure deficit or relative humidity. Humidity is a complicated business. Dry air allows water to evaporate, which leads to plants transpiring or water evaporating from the leaves. In turn they draw up too many nutrients and burn the leaves. Whereas, if your humidity is too high condensation can form on the