With the deadline looming for net-zero carbon, buildings are being designed to be ever more airtight. Richard Paine of Vent-Axia explains how MVHR combines energy efficient ventilation with good indoor air quality
The road to net zero carbon has led to a focus on reducing energy use in new homes. But we have all witnessed the consequences of ‘sealing up’ homes and insulating them to make them more energy efficient. It has resulted in indoor air pollution. The most visible sign of this has been condensation and mould, but this is only the tip of the iceberg since homes can contain over 900 chemical and biological contaminants in the air, including viruses. And now the pandemic has further highlighted the importance of indoor air quality (IAQ) and ventilation in buildings, due to the airborne transmission of Covid-19 and extra build-up of moisture and pollutants from greater occupancy.
Although the pandemic has catapulted ventilation into the limelight, IAQ and health were already rising up the agenda in building design. Where pollution levels are high, local planning conditions put the responsibility on developers to ensure air to dwellings is filtered to increasingly high standards. There has also been a raft of research connecting health issues with poor IAQ in the home. In January 2020 the National Institute of Health and Care Excellence (NICE) guidance ‘Indoor Air Quality at Home’ provided detailed information and advice on how to reduce exposure to indoor pollutants and so help protect health. This guidance set in stone the importance of good IAQ, highlighting the significant part effective ventilation plays in helping combat indoor air pollution in the home.
Ventilation is vital in new build homes. It has always been essential, but until recently the focus has been on building energy efficient and airtight homes. But the focus now needs to be on providing energy efficient and healthy homes.
Therefore, energy saving tech such as mechanical ventilation with heat recovery (MVHR) should be central to future homes. Anything that reduces energy loss while providing good IAQ and better ventilation rates has to be positive.
MVHR ticks all the boxes when it comes to balancing energy efficiency with good IAQ. It is energy efficient, recovers heat, and provides effective ventilation. MVHR extracts warm, moist air from ‘wet’ rooms and passes it through the heat exchanger to preheat fresh incoming air to improve home comfort. Furthermore, MVHR not only extracts harmful pollutants but also allows the air coming into the home to be filtered, taking out pollen and dangerous contaminants.
When specifying MVHR, architects should in the first instance look for a unit that offers high efficiency combined with low sound levels, good heat recovery and sufficient airflow. Architects should refer to the BRE’s Product Characteristics Database (PCDB) list for the best performing MVHR systems – some boast a specific fan power as low as 0.38 W/l/w with 93 per cent heat recovery and airflow of 100 l/s at 150 Pa, offering high pressure development. It’s also possible to achieve the ‘Holy Grail’ of high efficiency and low sound levels, with the latest MVHR being not only efficient but also extremely quiet – with trickle settings up to 40 per cent staying below 20 dBA. This sort of MVHR therefore provides housebuilders with the efficiency and performance they require, offering valuable reductions in Dwelling Emission Rates.
MVHR isn’t only suitable for larger homes either. For smaller dwellings where space is tight there are now units that combine a cooker hood with MVHR in one. This means there is no need for a loft or ceiling void since it fits discreetly within a 600 mm wide kitchen unit above a hob for a seamless finish with full accessibility for operation and maintenance.
Since it is vital that ventilation operates in the homes as set out in the original house design, MVHR systems are now being developed which are as simple as possible to install and commission. App-controlled functionality offers simplified installation and commissioning, saving time on site, reducing build length and improving build quality. It also encourages best practice, in turn ensuring efficient performance and adequate ventilation – minimising the chances of poor IAQ.
The threat of Covid-19 has brought renewed focus to filtration in buildings. Inside an MVHR unit, fresh incoming air passes through a filter to remove pollen, debris and products of pollution. This protects the heat exchanger from blocking and ensures the indoor air is cleaner and healthier than the air that would come in via a window. Filters up to ISO ePM2.5 70 per cent (F7 grade) ensure even homes in heavily urbanised areas can filter out most impurities, up to and including PM2.5 particles, for example diesel particulates. A filter check warning can alert households when filters need changing, thus helping to maintain the quality of incoming air. To go one step further to improve IAQ, there are filtration units now available that are fitted to MVHR unit’s intake airflow and incorporate two types of filtration – activated carbon and particulate filters to achieve even higher levels of filtration.
Meanwhile, in thermally efficient homes overheating can be an issue. Therefore, architects should consider MVHR units with 100 per cent Summer Bypass to help ensure thermal comfort, a significant issue in air-tight new build properties. Sophisticated summer bypass systems feature an evening or overnight purge, allowing occupiers to choose when to take advantage of cooler air during hot summer periods.
As buildings become more efficient, their air tightness will continue to improve making effective ventilation ever more important to help provide good IAQ for households, especially since Covid-19 could mean more home working from now on. MVHR not only provides good IAQ to make homes healthier, but as an energy efficient ventilation solution it is also the ideal choice for new build homes on the road to net-zero.
Richard Paine is marketing director at Vent-Axia