Ventilation is critical for airtight buildings – we all know that. We also have heard from leading lights of indoor air quality research, such as Dr. Sterling Howieson, that the risk of black mould triples when dwellings are being insulated and made more airtight.

The difficult question is, how to implement energy efficient ventilation systems in smaller dwellings and properties that are being upgraded. In such dwellings, whole house MVHR is often quite difficult to fit in, due to the size of the equipment and due to the amount of ductwork.

In recent years a few companies have dedicated themselves in developing de-central MVHR systems, which work continuously and on higher ventilation levels (up to 100 m3/h), compared to smaller oscillating de-central units. BluMartin is the first one that achieved Passivhaus certification for their de-central MVHR unit.

The concept is simple, but stunning:

• A de-central MVHR unit is placed, e.g. in an external wall of a living room.
• Wet rooms and the kitchen are connected to the unit via extract ducts, connected to the MVHR, thus creating an air flow path through the dwelling.
• Bedrooms and other habitable rooms tap into the airflow through cascade fans within the internal bedroom wall. As stale air is expelled out of these rooms, fresh air is drawn in through door undercuts.
• The ventilation rate of both the MVHR and cascade fans is fully demand controlled according to CO₂, humidity and temperature.

Such setup comes with a number of advantages compared to the traditional whole house approach:

1. The ventilation adjusts to the use of the dwelling, ensuring that CO₂ and humidity levels do not exceed the recommended levels. It minimises user-interference, but also counteracts over-dehumidification, which can sometimes be an issue with conventional MVHR systems.
2. It follows the usage cycle between living spaces and bedrooms. Therefore and due to their demand controlled operation, they use a fraction of energy compared to a standard MVHR.
3. The need for ducting is minimal, as only extract ductwork is needed.
4. Advanced control technology allows monitoring of all air quality parameters, if so desired.

Each of these units can serve only about 70 m2 space and one story at a time. For two storey buildings, at least two of these MVHR units have to be implemented.

Personally, I believe that this innovative approach to whole house ventilation will shape the future of the domestic ventilation industry, as it combines the advantages of heat recovery with those of demand controlled extract systems.

Please do contact us if you would like to obtain more information about BluMartin cascade MVHR.

Stefan Huber, director of PAUL Heat Recovery Scotland