Case Study

Optidrive keeps its cool

Optidrive keeps its cool


The demand for hot water pumped through a ring network to a city's residents varies and a method for ensuring pumps are optimised throughout the day was needed.


Invertek Drives' Optidrive Eco with Optiflow technology detects changes in flow and demand for water. It can then control the speed of pumps depending on the demand, even shutting off pumps when not needed, thus providing energy efficiencies.


Two thirds of the city of Almere, with a total of 160,000 inhabitants, is running on Nuon central heating systems using compact variable frequency drives from Invertek Drives, supplied through Rotero Holland BV.

Approximately 430 pump control stations are located in the city to handle water at 110 degrees centigrade. This is pumped through a ring network at 12 BAR pressure, with the pressure then being reduced in the pump control station via 1.5 and 4 kW Grundfoss pumps. A heat exchange system is then used to supply the hot water to every household in the areas being served. All pumps are controlled with a PLC system, which uses sensors to measure changes in pressure as a customer consumes hot water. This pressure change is then communicated to an Invertek Optidrive VFD as an analogue 0-10VDC signal, allowing the drive to control the speed of the pump and thereby maintain constant pressure.

In this application, tolerance of high temperatures and the high carrier frequency were considered to be of paramount importance. Over recent years temperatures with the pumping stations have reached up to 50 degrees Celsius.In these conditions, every drive was failing at various times.

Rotero Holland BV were able to provide the solution in the form of an Invertek Optidrive with a built in RFI filter, with power outputs up to 4kW and designed to operate in temperatures exceeding 50c.

The Invertek drive offers two critical performance advantages in this application. When the water demand is low the drive slows the pump down to work in the region of 20 to 40 Hz, providing significant energy savings and reliable operation despite the high operating temperatures. The other major advantage offered by Optidrive is the ability to provide a high carrier frequency at these high operating temperatures. This ensures very low audible noise from the pumps and even at 32kHz the Optidrive has continued to work perfectly in all conditions.

Mr Frank van Ingen, Senior Maintenance Engineer at Nuon, said: " I was astonished with the simplicity of the drive. I was really surprised that such a small version could operate so reliably at the desired temperature levels, even at high carrier frequencies."