Mechanical Ventilation & Heat Recovery

MVHR is a key design tool for a Passiv Haus. This system allows for the ventilation required for the occupants in a very airtight house. However, rather than just bring fresh air from outside, the MVHR system uses the warm stale air from inside the building to pre-heat the incoming air. This Heat Exchange / Recovery idea is well used across Europe and efficiencies are now over 90%. This means that the energy required to heat the house is seriously reduced.

Within the Cardiff Passiv Haus building there is also a fall back option where the MVHR system has an integral heating element, this means that if the house is unoccupied for a long period of time in the winter then the residents can use this to preheat the incoming air until a comfortable temperature is restored.

For the system to be effective the house must be very airtight. To test this a Pressure Test is used. This basically blows air into the property until a certain pressure is attained and then a measurement is taken to see how long it takes for this to equalise with the normal prevalent pressure. A photo of this test is shown below. It is then followed by a series of photos showing the MVHR system and its vents / extractors in the building.

It should be noted that any pressure test should take place twice during a build. Firstly once the main structure is completed. This allows for any remedial work to be undertaken if required, and secondly upon completion of the build. This allows you to ensure that the building has complied with the relevant standards.