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Mechanical Heat Recovery Ventilation

Today's modern apartment buildings offer challenges to the ventilation system designer. Limiting noise ingress, wind effects, aesthetics and installation limitation have to be taken into account in addition to regulatory compliance and cost. MEV has less dependency on background ventilators, requires only a single discharge grille for a whole apartment and very often has smaller, easier to install ducts than systems designer around intermittent operation extract fans and background vents. Such benefits make MEV an increasingly popular method of providing adequate ventilation in such homes.

How does it work?
Essentially the concept is to provide simultaneous, low level extraction from Kitchens, Bathrooms, Shower rooms, Utility rooms and WC's to a central extract fan via a system of ductwork and grilles. The extract air is then normally discharged to outside via a single duct and grille/cowl. Current Building Regulation guidance, in the form of BRE Digest 398, requires such systems be designed to provide background extraction at a rate equating approximately 0.5 air change per hour based on the whole dwelling volume with the ability to boost by 25-50% for times when increased ventilation is required e.g. during cooking.

Replacement air is normally able to be provided via structural air leakage with background ventilation openings like trickle vents not normally needed unless the home is built to extraordinarily airtight standards. This can be best demonstrated by referring to the table below which shows the very small building fabric air resistance an MEV system boosted extraction (0.625 ACH) would have to overcome in apartments of different levels of airtightness. As this type of system has to work 24 hours a day, 7 days a week, 365 days a year, low noise levels and reliability are critical.