42 n BUILDING SERVICES March 2025 www.drivesncontrols.com Dealing with VSD issues in HVAC installations HVAC (heating, ventilation and airconditioning) systems are essential for maintaining indoor air quality and comfort in residential, commercial, and industrial environments. According to Grand View Research, the UK HVAC market is growing signicantly. In 2024, it was worth around $6.68bn and is projected to reach $10.28bn by 2030, driven by increased urbanisation, climate change, a growth in construction, and the focus on energy eciency. Modern HVAC systems often use VSDs (variable-speed drives) to drive and control fans and pumps. However, VSDs introduce electrical harmonics, voltage spikes and electromagnetic interference (EMI), which can reduce reliability and increase running and maintenance costs. Using external harmonic reduction chokes, motor chokes, and sinewave lters can help reduce the eects of these problems, and help comply with EN 61800-3 – the standard concerned with EMC (electromagnetic compatibility) for power drive systems, while improving energy eciency and system longevity. Using harmonic reduction chokes for energy e ciency and EMC compliance Harmonic currents from VSDs can cause excessive heating in transformers, motors, cabling and switchgear, and can interfere with electrical equipment in the installation. Harmonic reduction reactors – or line chokes – mitigate these issues by smoothing the input current, reducing total harmonic distortion (THD) and with standards conformity. Motor and sinewave lters The highfrequency switching circuitry in a VSD can lead to motor insulation failures and accelerated wear, resulting in costly downtime. To solve this, motor chokes can be placed between the VSD and motor. Sinewave lters provide superior protection by converting the PWM (pulse-width modulation) output of a VSD into a near-sinusoidal waveform. This reduces electrical stress on motors and minimises EMI emissions, making them ideal for long cable runs. The key advantages of using motor chokes and sinewave lters include: n extended motor lifespans, reducing voltage peaks that degrade the insulation; n reduced bearing currents, helping to prevent premature motor failures; n improved EMC compliance as a result of lower EMI emissions; n enhanced motor eciency, lowering power losses and heating; and n lower acoustic noise – essential for hospitals, oces and residential spaces. Challenges with IP65/66 drives and chokes The increasing use of IP65/66-protected drives in HVAC installations introduces challenges when looking for suitable chokes. These drives, built for potentially dusty and moisture-laden environments, often lack space for extra chokes, requiring additional enclosures with appropriate thermal management and cost. HVAC installers need to select compact, high-IP-rated chokes designed for these environments that can be connected directly to the VSD to maintain compliance with EMC standards, while ensuring reliable system performance. Long cable runs and compliance issues Most VSD manufacturers design drives for use with short runs of motor cable – often less than 5m. By contrast, HVAC systems often need much longer cable runs to connect VSDs to motors across long distances in large buildings. Longer cable runs increase the likelihood of dV/dt stress and EMI, making compliance with EN 618003 more challenging. To mitigate these issues: n Sinewave lters should be used to smooth the voltage waveform and reduce Using VSDs in HVAC installations can introduce electrical harmonics, voltage spikes and EMI, aecting reliability and increasing running and maintenance costs. But as Steve Hughes, director of REO UK, explains, these are eective ways to tackle these issues. Test results of VSD current and voltages for various motor cable lengths, without (top) and with (bottom) sinewave lters
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