38 n BUILDING SERVICES March 2025 www.drivesncontrols.com PM motors deliver a boost to HVAC efficiency One of the key drivers behind the rising demand for energy-efficient technologies lies in regulatory standards designed to enhance building energy efficiency being implemented around the world. California’s Title 24 Building Code, for example, has stringent requirements for HVAC systems, mandating the use of fans that can operate at multiple speeds. This allows systems to vary their output based on actual need rather than running continuously at full capacity. This regulation is stricter than most, but reflects a broader shift towards energy conservation. Similar trends can be seen globally, such as Europe's eco-design regulations which impose minimum efficiency standards for motor and drive systems. As more of these mandates come into force, they are shifting the way that HVAC systems are designed, operated, and maintained, putting greater emphasis on powerful energy-saving technologies. One of the key elements in meeting these regulations is the use of VSDs, which play a crucial role in enhancing the efficiency of HVAC systems by optimising the performance of components such as fans, compressors and pumps. When it comes to fans, for example, VSDs can control the airflow to match specific heating or cooling needs. For compressors, they can adjust cooling capacity to accommodate varying thermal loads, ensuring efficient energy use and maintaining ideal indoor climates even in fluctuating conditions. Similarly, in hydronic systems, VSDs fine-tune pump flow rates based on real-time demands, enhancing system efficiency and contributing to significant energy savings. By adopting VSDs, HVAC systems can operate more efficiently, cost-effectively, and reliably, aligning with modern environmental and energy standards. This only improves when they also make use of PM motors. In traditional induction motors, a proportion of the power supplied to the motor produces a magnetic field to provide torque to make the motor turn. PM motors use permanent magnets on the rotor to create a permanent magnetic field, therefore saving the energy that goes into this task in an induction machine. This means they can offer high efficiencies and good performance across a variety of speeds and loads. When paired with the enhanced control offered by VSDs, this results in a synergy that greatly enhances system efficiencies, thanks to the “affinity laws”. An affinity for efficiency These laws are fluid dynamics principles that describe how changes in the speed of a pump or fan affect flow rate, pressure, and power usage. Specifically, the flow rate of a fluid is directly proportional to the speed of the device, while the pressure or head created increases with the square of the speed. Most significantly, the power consumption is proportional to the cube of the speed ratio – and rises exponentially. This relationship means that even modest reductions in speed can result in substantial decreases in power usage. For instance, A PM motor costs fall, they are becoming a more practical option for HVAC applications. In its quest for sustainable and energy-ecient technologies to help it cope with uctuating energy prices and stringent environmental regulations, the HVAC sector is turning to PM (permanent magnet) motors paired with VSDs (variable-speed drives).
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