Definition of MVHR
Mechanical Ventilation with Heat Recovery (MVHR) is a continuous source of ventilation that extracts stale, moisture-laden air from a building and resupplies fresh, filtered air back in, resulting in a comfortable and condensation free environment all year round. Mechanical ventilation with heat recovery (MVHR), heat recovery ventilation (HRV) or Comfort ventilation are all names for the same thing.
MVHR works quite simply by extracting the air from the polluted sources e.g. kitchen, bathroom, toilets and utility rooms and supplying air to the ‘living’ rooms e.g. bedrooms, living rooms, studies etc. The extracted air is taken through a central heat exchanger and the heat recovered into the supply air. This works both ways, if the air temperature inside the building is colder than the outside air temperature then the coolth is maintained in the building.
Why do I need MVHR?
As homes become increasingly airtight through efficiency measures such as insulation, draught-proofing and double-glazed windows, a lack of natural ventilation means that moisture created from everyday activities such as cooking, washing and even breathing remains in the home. With nowhere to go, this moisture collects on cold surfaces such as windows and outside walls and causes condensation, damp and mould growth, all of which contribute to poor indoor air quality (IAQ).
An MVHR unit is constantly ventilating a property, meaning that everyday moisture has no time to settle on surfaces as it is extracted to the outside, eliminating the risk of structural and cosmetic damage caused by condensation and mould. They are also extremely efficient, being able to recover up to 91% of heat lost through extraction and transferring it to incoming air.
The importance of good MVHR design
If you are intending to fit MVHR heat recovery ventilation into a new build or refurbishment then it should be considered from early in the planning stage. For any MVHR heat recovery ventilation system to give its best performance the devil is in the detail. System design will make the difference between a highly efficient system working un-noticed in the background and one that is constantly in the awareness of the inhabitants and wasting both heat and electrical energy. These systems necessarily require ducts to be run through the building and the routing is important both from the point of view of the building and the efficiency of the ventilation system. Indeed, layout of rooms can be influenced by ventilation needs.
The installation of MVHR in a building will also affect the heating system design. One of the effects of heat recovery ventilation is to equalise the temperature throughout the building. Therefore it is important to prioritise the heat supply to the rooms that should be warmer. If the building is of sufficiently high standard then it might be only necessary to put heat directly into certain rooms.
