Centrifugal fan is essentially a variable flow constant pressure device. When the speed is fixed, the theoretical curve of pressure-flow of centrifugal fan should be a straight line. the actual characteristic curve is curved due to internal loss. The pressure produced in the centrifugal fan is greatly affected by the change of inlet air temperature or density. for a given intake volume, the pressure generated at the highest intake temperature (lowest air density) is the lowest. For a given pressure-flow characteristic curve, there is a power-flow characteristic curve. when the blower operates at constant speed, for a given flow rate, the required power increases with the decrease of the inlet air temperature.