In many parts of the world, we take it for granted that we have access to clean air. Or at least we think we do. As we improve the quality of our homes and other buildings, we are starting to get a more realistic picture of what we are breathing in along with our supposed clean air.
Air pollution has a significant and pervasive impact on public health. According to the World Health Organization, it is now considered “the world’s largest single environmental health risk,” with more than three million people dying every year as a result. This is more than twice the number of people that die in vehicle accidents each year.
This is a Passivhaus Basics blog post that gives an overview of a specific aspect of the Passivhaus Standard.
The international Passivhaus Standard does not explicitly require mechanical ventilation. And yet almost every certified Passivhaus building includes a mechanical ventilation system with heat recovery.
What is mechanical ventilation with heat recovery (MVHR) and why is it needed in Passivhaus buildings?
Mechanical ventilation is familiar to most people. This leads to the assumption that a Passivhaus ventilation system is the same as other mechanical ventilation systems. It is not.
There are things that MVHR does not do. It is important to know what these are in order to understand the difference between Passivhaus MVHR and other types of ventilation.
And there are things that Passivhaus MVHR does do that other ventilation systems don’t, including ‘natural ventilation’. It is important to know what MVHR does do, as MVHR is vital to the consistent success of the passivhaus standard.
Mechanical ventilation with heat recovery (MVHR) is key to delivering the benefits the Passivhaus Standard promises – radical energy efficiency and exceptional comfort.
A passivhaus home in almost all climates across the world will include a mechanical ventilation system with heat recovery (MVHR*). This kind of ventilation system is required for both energy efficiency and for comfort. However, to many people this is an intimidating and misunderstood aspect of passivhaus. As a result, there are various concerns and misconceptions about what a passivhaus ventilation system is and how you use it.
To address some of these issues I have enlisted the help of Zehnder, a global supplier of Passivhaus Certified ventilation systems. In this post, we explore the following aspects of a residential passivhaus ventilation system:
How do I control the ventilation system?
What day-to-day interaction do I need to have with the ventilation system?
What is the boost function and when should I use it?
When should I switch the ventilation system off?
Rupert Kazlauciunas, Senior Technical Advisor at Zehnder Group UK, very kindly provided answers to my questions
In a residential passivhaus, the ventilation system can be simple to use. It will save energy and money, while ensuring comfort and excellent indoor air quality.
Passivhaus buildings are sometimes criticised by environmentally minded designers as being “hermetically sealed” boxes that can’t “breathe”. These designers have the best intentions of creating healthy and energy efficient buildings where people have direct control over their indoor environment and a close relationship with the outdoor environment. And they fear the passivhaus standard won’t allow a building to provide this. Luckily, their fear is unfounded. Let’s take a closer look at the two aspects of this criticism:
What does it mean for a building to be “hermetically sealed” and does the Passivhaus Standard require this?
What does it mean for a building to “breath” and does the Passivhaus Standard allow this?
I often read and hear people, including passivhaus experts, state that once a building is airtight it requires mechanical ventilation. This is not strictly true. And there are many examples of passivhaus buildings that operate using ‘natural ventilation’ during the summer months. An airtight building significantly reduces air movement through the building fabric: walls, floor, roof, window frames and junctions etc.. And we should never rely on this kind of air movement to provide the air that we breath inside a building, for ventilation, that is. (Fancy drinking the water that seeps through a leaking roof? It’s kind of similar.) A ventilation strategy and system that genuinely does work, and is used properly all year round, is needed in any building, airtight or not. Once you add comfort and energy efficiency into the equation, this almost always means mechanical ventilation with heat recovery will be required for some of the year. The comfort and energy efficiency benchmarks of the Passivhaus Standard certainly mean this is the case.
And this is where airtightness and mechanical ventilation converge – both are needed for comfort and energy efficiency.