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Complete Eco-Retrofit


The link between air quality and health is nothing new. For decades ventilation systems, air conditioning units and even climate control systems in cars have included some level of air filtration.

As any hayfever sufferer will tell you, all it takes is a filter that stops pollen to make life immeasurably better. In terms of respiratory health, the technology that provides indoor air quality has moved forward significantly in recent years.

Studies have shown that adequate ventilation in a property will prevent damp, which leads to black mould, which in turn exacerbates and in some cases even triggers the first instance of asthma in children. Add the right air filtration too and the same ventilation can stop dust, pollen, microparticles and NOX gasses from vehicle emissions currently linked to around 40,000 deaths per year nationally, at the same time removing indoor pollutants like Formaldehyde and other VOC’s. But Since March there’s a new airborne problem people are keen to avoid, aerosolised Covid-19 droplets that cause Coronavirus. The question is will MVHR and other HVAC devices help to reduce the chances of the viral spread or are they counter-productive?

As the virus is airborne anything that moves air could theoretically spread contamination. However, if the direction of the air flow is managed correctly any contaminated air can be safely removed at or near to the source. For instance, with MVHR installed in an en-suite bedroom the air inside this ‘zone’ is kept inside this zone. Fresh air is supplied to the bedroom and stale air is removed from the adjacent bathroom. Keep the bedroom door shut and you’ve got the ideal space to self-isolate without spreading germs throughout the whole property. Use radial ducting that serves each room independently rather than branch ducting that connects rooms together, and you’ve eliminated the risk of cross contamination through the pipework. Incoming and outgoing air stream do not mix in the heat recovery cell, so provided you avoid the MVHR exhaust you should have the safest possible indoor environment. Unfortunately there are no domestic ‘virus filters’ at the moment.

In a recent statement, ASHRAE came to a similar conclusion (American Society of Heating, Refrigerating and Air-Conditioning Engineers) saying “Ventilation and filtration provided by HVAC systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air. Unconditioned spaces can cause thermal stress to people that may be directly life threatening and that may also lower resistance to infection. In general, disabling of HVAC systems is not a recommended measure to reduce the transmission of the virus”.

“HVAC filters, along with other strategies, help to reduce virus transmission while removing other air contaminants that may have health effects.”

Other variables such as temperature and humidity are believed to play a part in the infection rate of viral spread. Uganda for instance only has 145 confirmed cases and no deaths at the time of writing. According to ASHRAE the ‘sweet spot’ in terms of minimising the lifespan of viruses is between 50% and 70% relative humidity at 21 degrees centigrade, which is a range that can be reproduced in the home using an MVHR that both monitors and adjusts the air flow rate to suit your target %RH. While MVHR doesn’t kill bugs it can at least make life unpleasant for them and remove other known pollutants and allergens to make your home a healthy, fresh place to live.


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