Dealing with VSD issues in HVAC installations
25 February 2025 
Using VSDs in HVAC installations can introduce electrical harmonics, voltage spikes and EMI, affecting reliability and increasing running and maintenance costs. But as Steve Hughes, director of REO UK, explains, these are effective ways to tackle these issues.
HVAC (heating, ventilation and air-conditioning) 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 significantly. 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 efficiency.
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 filters can help reduce the effects of these problems, and help comply with EN 61800-3 – the standard concerned with EMC (electromagnetic compatibility) for power drive systems, while improving energy efficiency and system longevity.
Using harmonic reduction chokes for energy efficiency 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 filters The high-frequency 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 filters 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 filters include:
- extended motor lifespans, reducing voltage peaks that degrade the insulation;
- reduced bearing currents, helping to prevent premature motor failures;
- improved EMC compliance as a result of lower EMI emissions;
- enhanced motor efficiency, lowering power losses and heating; and
- lower acoustic noise – essential for hospitals, offices and residential spaces.
Harmonic reduction chokes (left) can help to improve energy efficiency and ensure EMC compliance in HVAC installations. IP65-protected motor chokes (right) can be connected to VSDs in damp or dusty environmentsChallenges 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 61800-3 more challenging.
To mitigate these issues:
- Sinewave filters should be used to smooth the voltage waveform and reduce stress on motor windings. These filters often negate the need for shielded cables, reducing installation costs.
- Proper grounding techniques must be implemented to ensure low-impedance earthing.
- Chokes or line reactors can minimise transient voltage spikes along longer cable lengths.
Other issues
Additional operational issues that HVAC installers face include:
- energy inefficiency from voltage harmonics – this can be mitigated using line reactors to reduce input rms current;
- EMI – this affects sensitive equipment and can be reduced using chokes and sinewave filters;
- voltage reflections in long cable runs – these can be reduced using sinewave filters, which smooth voltage waveforms and attenuate high-frequency noise;
- audible motor noise – sinewave filters can convert the VSDs PWM output into a smooth sinusoidal waveform, improving workplace comfort and reducing noise pollution.
Some choke and filter manufacturers provide test data for various VSDs and cable lengths to ensure compliance with EN 61800-3, allowing HVAC installers to choose the most effective systems for their applications.
Input chokes, motor chokes, and sinewave filters are important in HVAC applications for energy savings, equipment longevity and regulatory compliance. These components enhance system reliability by mitigating harmonic currents, voltage spikes and EMI. VSDs used in HVAC systems – particularly IP65/66 versions using longer cable runs – pose integration challenges, requiring compact, application-specific components. Choke and filter manufacturers should be challenged to provide appropriate technologies.
