A method for operating a fan system using a centrifugal fan wheel rotating within a fan housing for drawing suction air and discharging discharge air, the method comprising: rotating a centrifugal fan wheel within a fan housing, wherein the fan housing defines a suction inlet opening for receiving suction air and defines a discharge air chamber for the discharge air; conveying the discharge air as supply air from the discharge air chamber to a comfort zone; adjustably restricting the supply air flowing to the comfort zone by way of a variable air volume, VAV, valve that is one of a plurality of VAV valves used in the fan system method; circulating the supply air through the comfort zone to create return air; conveying from the comfort zone at least some of the return air to the suction inlet opening of the fan housing; while conveying at least some of the return air to the suction inlet opening, conveying the suction air through a curved inlet cone (38; 38') that leads to the suction inlet opening, wherein the suction air includes at least some of the return air, the curved inlet cone includes a minor diameter and a major diameter, the minor diameter is in proximity with the centrifugal fan wheel and is downstream of the major diameter, wherein the inlet cone decreases in diameter continuously from the major diameter to the minor diameter, the inlet cone terminates at an inlet edge at the minor diameter; sensing, at an inner surface of the curved inlet cone at the minor diameter, a static gage pressure of the suction air; determining a total volume flow rate of the suction air flowing through the curved inlet cone based on the static gage pressure of the suction air at the inner surface at the minor diameter; and adjusting a rotational speed of the centrifugal fan wheel based on the static gage pressure of the suction air at the inner surface at the minor diameter. rotating a centrifugal fan wheel within a fan housing, wherein the fan housing defines a suction inlet opening for receiving suction air and defines a discharge air chamber for the discharge air; conveying the discharge air as supply air from the discharge air chamber to a comfort zone; adjustably restricting the supply air flowing to the comfort zone by way of a variable air volume, VAV, valve that is one of a plurality of VAV valves used in the fan system method; circulating the supply air through the comfort zone to create return air; conveying from the comfort zone at least some of the return air to the suction inlet opening of the fan housing; while conveying at least some of the return air to the suction inlet opening, conveying the suction air through a curved inlet cone (38; 38') that leads to the suction inlet opening, wherein the suction air includes at least some of the return air, the curved inlet cone includes a minor diameter and a major diameter, the minor diameter is in proximity with the centrifugal fan wheel and is downstream of the major diameter, wherein the inlet cone decreases in diameter continuously from the major diameter to the minor diameter, the inlet cone terminates at an inlet edge at the minor diameter; sensing, at an inner surface of the curved inlet cone at the minor diameter, a static gage pressure of the suction air; determining a total volume flow rate of the suction air flowing through the curved inlet cone based on the static gage pressure of the suction air at the inner surface at the minor diameter; and adjusting a rotational speed of the centrifugal fan wheel based on the static gage pressure of the suction air at the inner surface at the minor diameter.