Campus Air-Conditioning Circulating Pump Drive in Yixing: Selection and Commissioning

The air-conditioning circulating pump is the core power component of a chilled-water system. Its job is to give the cold or hot water a continuous, stable motive force so that it circulates in a closed loop between the evaporator or condenser, the heat exchangers and the terminal units — fan-coil units and air-handling units. In cooling mode the pump pushes chilled water through the terminal units, where it absorbs room heat, and back to the chiller's evaporator, where the refrigerant takes that heat away and the water becomes cold again. In heating mode, with a boiler or heat pump as the source, the same pump pushes hot water out to the terminals and returns the cooled water to be reheated.

Because the pump serves the whole loop, its drive has to do more than spin a motor. It has to accept a start command and a speed reference from the building management system, report back whether it is running and whether it is faulted, and protect itself and the motor when anything goes wrong.

At this campus installation the pump is a 45 kW machine rated 91 A at 1480 rpm, and the only single-unit drive in the Yolico range that matches it is a YD580T4-37G/45P-T — a 37 kW normal-duty / 45 kW pump-duty frame. This is worth noting because it demonstrates why pump-duty ratings exist: a pump is a variable-torque load whose demand falls with the cube of speed, so a frame rated 45 kW for pump duty is the correct match for a 45 kW pump motor, whereas forcing the same motor onto a constant-torque rating would mean buying a larger frame for no benefit.

The control interface was set up for a building service. Terminal DI1 is the run command, so the BMS closes a contact to start the pump. AO1 provides the analogue frequency output. One relay, TA1/TC1, feeds back the running signal and a second, TA2/TC2, feeds back the alarm signal, so the BMS can distinguish 'running normally' from 'running with a fault' rather than treating both as simply energised. RST terminals take the supply and UVW feed the motor. Because the drive and the motor are mounted apart, both were earthed properly, which is the minimum discipline for any installation where the cable between them is longer than a few metres.

Commissioning was completed with the drive running at 50 Hz, where the measured output current was 68 A with all three phases balanced. Against a 91 A nameplate that is a healthy part-load figure and, more usefully, a baseline: any future drift upwards at the same frequency and the same loop conditions will point to a mechanical problem — a fouled impeller, a partially closed valve, or a failing bearing — rather than an electrical one. That is the practical value of recording the commissioning figures for a building pump, where the load changes with the season and there is no simple constant to compare against later.