Method and arrangement for estimating flow rate of pump

1. A method of determining a flow rate (Q) produced by a pump controlled with a frequency converter, which produces estimates for rotational speed and torque of the pump, wherein a QH curve and QP curve of the pump are known, the method performed by a processor configured to:

determine a shape of the QH curve of the pump;

divide the QH curve into two or more regions depending on the shape of the OH curve;

determine an operating region of the QH curve on which the pump is operating; and

determine the flow rate (Q) of the pump using the determined operating region of the QH curve, wherein determining the operating region comprises:

measuring a head produced by the pump;

estimating the flow rate using a QP curve-based method;

determining the operating region from the estimated flow rate wherein determining the flow rate uses the determined operating region of the QH curve and the measured head produced by the pump; and

controlling the pump based on the determined operating region.

2. The method according to claim 1 , wherein the processor is configured to determine the shape of the QH curve by determining a derivate of the curve; and

use the determined derivate to divide the QH curve into differing regions.

3. The method according to claim 2 , wherein the processor is configured to determine the shape of the QH curve in the frequency converter from the characteristic curve transformed to a rotational speed of the pump.

4. The method according to claim 1 , wherein the processor is configured to determine the shape of the QH curve in the frequency converter from the OH curve transformed to a rotational speed of the pump.

5. An arrangement for determining a flow rate (Q) produced by a pump when the pump is controlled with a frequency converter, which produces estimates for rotational speed and torque of the pump, and a QH curve and a QP curve of the pump are known, wherein the arrangement comprises:

means for determining a shape of the QH curve of the pump;

means for dividing the QH curve into two or more regions depending on a shape of the QH curve;

means for determining on which region of the QH curve the pump is operating; and

means for determining the flow rate (Q) of the pump using the determined operating region of the QH curve, wherein means for determining the operating region comprises:

means for measuring a head produced by the pump;

means for estimating the flow rate using a QP curve-based method; and

means for determining the operating region from the estimated flow rate;

wherein the means for determining the flow rate determines the flow rate using the determined operating region of the QH curve and the measured head produced by the pump; and

controlling the pump based on the determined operating region.

6. A method of determining a flow rate (Q) produced by a blower controlled with a frequency converter, which produces estimates for rotational speed and torque of the blower, wherein a pressure to flow rate curve and QP curve of the blower are known, the method performed by a processor configured to:

determine a shape of the pressure to flow rate curve of the blower;

divide the pressure to flow rate curve into two or more regions depending on the shape of the pressure to flow rate curve;

determine an operating region of the pressure to flow rate curve on which the blower is operating; and

determine the flow rate (Q) of the blower using the determined operating region of the pressure to flow rate curve, wherein determining the operating region comprises:

measuring a total pressure produced by the blower;

estimating the flow rate using a QP curve-based method;

determining the operating region from the estimated flow rate wherein determining the flow rate uses the determined operating region of the pressure to flow rate curve and the measured total pressure produced by the blower; and

controlling the blower based on the determined operating region.