HVAC applications saving energy

Using ABB variable speed drives is helping industrial and commercial HVAC applications saving energy and money. The way motors consume power (cube law) means that a 20% drop in speed of centrifugal pumps and fans can save as much as 50% in energy.

Electric motors installed in new buildings are optimised energy-saving. This is not the case in existing buildings. Here, many still use traditional mechanical devices to control system flow.

The design of an HVAC system must cover a range conditions. To achieve this, the fans and pump motors run at full speed. The conventional response to meeting the changing demand for heating and cooling within a building is to restrict flow to individual rooms. Control is by regulating the output using inefficient throttling devices such as vanes or valves.

HVAC applications saving energy

This approach, requires more energy and reduces equipment life. A much better approach is to use a variable speed drive on HVAC pumps and fans to vary air or water flow to meet more precisely changing load demands. This gives the stakeholders considerable potential for saving energy.

Pumps and fans offer the best energy savings potential of any equipment in the building services industry. A fan running at 80% speed only uses 50% of the energy, compared to one running at full speed. Yet far too many pumps and fans run continuously at full speed, with the output regulated by inefficient throttling devices such as vanes or valves. A 20% reduction in fan speed can reduce energy consumption by up to 50%. Applied to a 75 kW motor in continuous duty, means nearly £15,000 per year in saved energy, every year.

Automatic energy savings with variable speed drives

The design of variable speed drives (VSDs) is to provide optimal energy efficiency through speed control. Without a variable speed drive, an A.C. motor runs at full speed all the time. A variable speed drives allows the speed of pump and fan motors to be infinitely variable to match demand.

Drives operate by switching the fixed mains supply voltage to a variable voltage and frequency in response to an electrical control signal. When coupled to a fan or pump motor, the change in frequency will result in a corresponding change in motor speed.

Automatic control

In most cases, motors maintain a constant pressure within air ducts or water pipes. A pressure sensor in the pipe or duct is uses to measure changes in the system pressure. This sends a signal to the building automation system, which in turn sends a speed demand signal to the drive. Thus, as valves and dampers close, the pressure rises in the ducts or pipes, this automatically reduces the speed of the fan or motor to save energy.

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