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Fan curve

Fan curves describe the fan capacity and vary depending on the type of fan.

Operation point
The operation point, also known as the working point, for a fan depends on speed (rpm), air flow and total pressure increase. If a fan is run at constant speed and pressure in the system increases, the operating point will be moved along the graph to the left together with the speed curve, meaning that the air flow is reduced. Conversely, if the pressure decreases, then the operating point and speed curve are shifted along to the right. Steep fan curves mean that pressure changes in the system have relatively little effect on air flow. A speed-controlled fan is typically regulated by functions for pressure or flow control. This means that the operating point is not bound to the speed curve, but can be shifted by decreasing/increasing the speed to maintain either constant pressure or flow.