Mixing

A specific volume of water at a pre-settable temperature is to be set or dosed by mixing up to three water quantities of known or measured temperature. Three water circuits (hot water, municipal water and chilled water) are available.

The temperatures of the three water circuits are measured directly at the tapping points by means of resistance thermometers. On the basis of the measured temperatures and the preset total water quantity, an open-loop control system calculates the volumes to be taken from the individual water circuits. The individual water volumes required are primarily calculated on the basis of economic aspects. The share of municipal water should be as high as possible, since provision of municipal water costs the least. The calculated partial quantities are dosed via three dosing control systems which receive their set-point value from a control system. The quantities flowing during the dosing operation are detected by means of flow sensors which are connected to the actual value or dosing inputs of the dosing control systems. Dosing is performed by means of two, parallel-connected solenoid valves with differing nominal diameters. At the start of dosing, both valves are open. To avoid overdosing, the larger valve is closed just before the target quantity is reached. A resistance thermometer in the water tank or mixing tank serves to indicate the mixing temperature.