Investigation of the energy consumption in regulating the flow rate of fan systems

The ensuring of the required parameters of the air, used in air-conditioning systems, is directly related to the change of the flow rate of each fan that is installed in these systems. This change can be achieved by using different methods of flow rate regulation. However, it is well-known that the selected method determines the energy efficiency of the given fan system. This work represents a comparative theoretical analysis, concerning the energy efficiency of three different methods of regulating a fan's flow rate: by throttling, by using inlet guide vanes and by changing the voltage frequency - the motor's speed of rotation has been changed with the help of a variable frequency drive (VFD). For the aims of this research, the change of the coefficient of efficiency for some of the key system elements – fan, motor and VFD, at different work regimes, have also been indicated. To fulfil the objectives of this research a given number of fans, having different specific speeds of rotations: n_q = 3.31; 7.11 and 8.82 min⁻¹, have been selected. As a criteria of effectiveness, concerning the different methods of flow rate regulation, the specific fan power P_SFP - the invested energy in transporting a unit volume of fluid (gas), has been used: $P_{SFP}=\frac{p}{{\eta }_{tot}}\left[\frac{kW}{m^3/s}\right]$, where p is the total pressure of the fan; η_tot is the overall efficiency of the fan. As a result of this theoretical investigation some graphics representing the change of the specific energy consumption, when the three different methods of flow rate regulation are used and indicating the fan's initial work regime and its specific speed of rotation, have been given. (paper)