The inverters specifc for circulating pumps are variable speed drives (VSD) of the asynchronous motor, having an algorithm specifififi cally studied for closed ring hydraulic systems for both cold and high temperature water, combined with special high-precision pressure transducers suitable for water temperatures up to 90°C. They are available for installation directly onboard motor or for wall and can communicate each other through serial cable RS485, having functions to assistance or alternation between 2 or more circulating pumps.
WORKING PRINCIPLE OF THE CIRCULATING PUMP INVERTERS :
Having such a models to work in order to maintain a water recirculation into closed water circuits, on the most of the cases heating systems, they have been designed to be able to do a feedback control of the differential pressure between suction (P1) and delivery (P2) of the circulating pump (or more circulating pumps, if they are in a group); in practice it’s pursued and maintained constant a differential pressure dP=P2-P1.
In order to do it, special pressure transducers have been specifically designed for maximum absolute values of 3 bar (K3T pressure transducer) and 5 bar (K5T pressure transducer) with very high precision up to high temperature (90°C) so as to reduce to few centibar the absolute error on the full–scale of each transducer, keeping into consideration that it should be measured differential pressure values of 0.10 .. 1.00 bar.
The pressure transducers are to be purchased separately, with flow rate 3 or 5 bar according to the application, fitting n°2 pressure transducer for one inverter. By group of two inverters, in order to have redundancy, it’s suggested (even if it’s not compulsory) to fit n°2 pressure transducers on each inverter, included n°2 transducers on the slave inverter into the two-pumps group since these ones will operate in case, for any reasons, there should be any problems on the pressure reading of the master unit.
The master needs compulsorily to have at least 2 transducers to read the pressures P1 and P2. The circulating pump inverters also have the auto-setting function, with the initialization check, in order to take all the electrical and hydraulic features of the pump, having just to set the absorbed current and the rotating direction of the pump, nothing else more.
All the other functions are similar to those ones that concern the standard motor-pumps for open water circuits, therefore it’s possible to check section 1 (pump-inverters).
For these devices, the Energy saving got from the running to low speed and without starting and stopping with high absorbtion, results even more important since the pumps must usually operate 24 hours for 365 days per year.