A centrifugal fan is essentially a variable-flow, constant-pressure device. At a constant rotational speed, the theoretical pressure-flow curve of a centrifugal fan is a straight line; however, due to internal losses, the actual characteristic curve is curved. The pressure generated by a centrifugal fan is significantly affected by changes in inlet air temperature or density.
For a given inlet airflow rate, the lowest pressure is generated at the highest inlet temperature (corresponding to the lowest air density). A specific power-versus-flow characteristic curve corresponds to each pressure-versus-flow characteristic curve. When the blower operates at a constant speed, the power required for a given flow rate increases as the inlet temperature decreases.
