A breath of fresh air is a breeze

A building management system incorporating frequency inverters from Lenze is successfully reducing energy consumption and running costs in the administration centre of building finance company BHW.

The HVAC system serving the basic needs of the building was replaced with a DDC-assisted building management system supplied by Inga, incorporating heating, cooling and ventilation systems. The system monitors, regulates and optimises the five macroclimate units providing a basic supply to the building’s five storeys.

Lenze frequency inverters, in an electrical power range of 35 to 90 kW, replaced the existing dampers on the individual fresh-air and extract fans. This gives a volume flow for the first four storeys of 100,000m3/h, and an outgoing air capacity of 40,000m3/h. Incoming air is supplied by to the individual storeys at a constant temperature. The amount of fresh air required is adjusted to individual requirements with the speed-controlled fans using a constant pressure control of 200 Pa differential pressure.

Although HVAC systems of this sort have to be designed to satisfy the least favourable conditions, for most of the time they operate under partial load. Simply by switching from dampers to frequency inverters has reduced energy consumption at BHW by 50%. This means that the installation of the frequency inverters will pay for itself within just one year. In this application, the inverters are controlled by a DDC outstation with a 0 to 10V analogue signal and instantaneous feedback of operating status and faults.

As well as the cost effective speed control of pumps and fans, frequency inverters can perform other tasks that make them even more valuable in building technology. The integral PID controller allows pressure, humidity and temperature to be controlled directly by the frequency converter. Where a V-belt drive is used it can be monitored electronically by the frequency inverter. If the V-belt breaks, causing the current to fall below a pre-set threshold, the inverter detects the fault and sends a signal to the BMS. This avoids the need for conventional monitoring systems such as differential pressure measurement by pressure sensors. With PID input, the volume flow can be controlled by means of a less expensive pressure measuring technique.

A further benefit of using a frequency inverter is the lower starting current, enabling smaller fuses and cables to be used. The drives run at reduced speed under partial load, leading to a marked reduction in noise.

More building management on page 26