Optimising MVHR systems for health, efficiency, and comfort

Mechanical ventilation with heat recovery (MVHR) systems have emerged as a cornerstone technology in the realm of sustainable living and superior indoor comfort. However, to ensure their efficacy, it’s essential the specifics of MVHR design have been carefully considered in relation to the building they’re to be installed in. Sizing considerations, ductwork design, and the selection of the right type and size of components are crucial factors. Oversized systems can lead to energy wastage, while undersized systems may fail to adequately ventilate the space. 

Here, we delve into the intricacies of MVHR system design, offering insights into key considerations, component specifications, and optimisation tips to ensure peak performance all year round.

How does an MVHR system work?

Let’s start with the basics: what is an MVHR system, and how does it work? MVHR systems are designed to provide controlled ventilation while simultaneously recovering heat from outgoing stale air, transferring it to incoming fresh air. This process not only ensures a constant supply of fresh air but also significantly reduces heating costs by capturing and reusing heat that would otherwise be lost. By balancing airflow and heat exchange, MVHR systems create a healthier and more comfortable indoor environment, free from pollutants and excessive humidity – both of which can have significant impact on health and comfort.

Ductwork design for energy efficiency and longevity

Optimal ductwork design minimises pressure losses and ensures efficient air distribution throughout the building. MVHR ductwork is embedded into the fabric of the building and would be very disruptive to have to replace, so it’s worth investing in a high-quality system from the outset. 

Wherever possible, we recommend rigid galvanised steel ducting, as this results in a robust system that can last the lifetime of the building. However, in instances where space is at a premium, a semi-rigid ducting system may be installed as the ducts are typically smaller in diameter. When well designed, a semi-rigid ducting system can be as efficient as a rigid option.

Specifying for indoor air quality

Indoor air quality goes hand in hand with energy efficiency. Filtration options, humidity control, and ventilation rates must be carefully considered to maintain a healthy environment. High-efficiency filters remove particulate matter and allergens from the air, while humidity control systems prevent airborne bacteria, viruses, mould growth, and buildup of dust mite numbers – all while maintaining comfort levels. Balancing ventilation rates ensures adequate air exchange without unnecessary energy consumption.

Air flow rates should be carefully calculated for each room, and MVHR units selected that have constant volume flow fans. Ductwork airtightness is important to ensure that the designed air flow is delivered to the rooms. Air leakage is designed out through use of high-quality ducting systems with airtight seals. By minimising air leakage, inefficiencies within the system are eliminated, helping ensure lower energy consumption and noise levels.

Enhancing occupant comfort

In any living space, comfort is paramount. Noise reduction strategies and air flow volumes are essential considerations to ensure comfort throughout the year.

To ensure MVHR systems run quietly, it's important to specify the right size of sound attenuator  for each duct run, as well as primary attenuators (silencers) to reduce noise generated by the MVHR unit fans, and secondary ‘cross talk’ attenuators, to reduce noise transmission between rooms. The cross talk attenuators also offer further sound suppression for duct-generated noise. 

Duct sizes in our designs are typically larger than those specified by other companies, helping to keep air speeds low. In turn, this minimises duct-generated noise and excessively high pressure loss across the ducting system. As a result, we’re able to design our MVHR systems to have noise levels of no more than 30 dB(A) at the extract valve and no more than 25 dB(A) at the supply valves.

Optimisation and maintenance

Commissioning plays a pivotal role in ensuring the optimal performance and efficiency of your MVHR system. Proper commissioning involves meticulously balancing ventilation terminals to precisely match the design’s intended airflow rates into and out of rooms. Additionally, it serves as a crucial quality control checkpoint, assessing the installation process and the system’s functionality.

Once the MVHR system has been installed, regular servicing and maintenance are critical for the long-term performance of MVHR systems, delivering lasting benefits to occupants and the environment. Thorough servicing should involve a professional check the system’s airflow rates are in accordance with design specifications, a clean of all MVHR unit components, filter and insulation replacement if required (usually at an additional cost), a diagnostic check, and a refresher lesson on controller usage.

Optimising MVHR systems is essential for achieving energy efficiency, indoor air quality, and occupant comfort in buildings. For further advice and specialist knowledge on specifying the best MVHR system for your project requirements, check out our MVHR design service. Alternatively, contact us to speak to a member of our expert team.