One Air, Two Appetites

Every technology has a humidity envelope with failure at both edges — ASHRAE puts a data centre between 5.5 and 15°C dew point and 40–60% RH, static below, corrosion above. That claim is right and general. Two corrections follow: vapor pressure deficit is the wrong variable for dry hardware, because it measures evaporation from a wet surface; and the moss and the machine want opposite air. What keeps the living layer alive pushes the hardware toward its upper failure edge, which is the real design problem in stacking them.