Anyone who has read this column long enough knows I can’t resist a good pun or turn of phrase. Believe me I shall not “Air” on the side of caution anytime soon! No – we are not going to talk about me being full of hot air, we are going to look at something a bit more refreshing.
The air we breathe has lots of stuff floating in it. Anyone who has ever changed an air filter knows that. When we pop in the new filter and toss the old one we feel good knowing the air we are breathing will be cleaner… until the next time we need to change the filter. We don’t want to have to think about the air, yet we do need to make sure we plan for healthful air inside our homes. We can do that in a number of ways from choosing the materials and chemicals that we introduce into the indoor environment carefully and making sure we change those air filters.
Passive Houses, because of their very tight construction, could trap more stale air inside than regularly constructed houses if proper planning is not followed. This is why Passive Houses generally require a mechanical ventilation system to make sure the air quality is maintained. By using a Heat Recovery Ventilator (HRV) or an Energy Recovery Ventilator (ERV) and sizing it to meet the needs of the building, a Passive House provides its residents with a continual supply of fresh air.
So, how do we know that the mechanical units are up to snuff and will work well in our Passive Houses? Passive House Institute has a standard that these mechanical ventilation systems must meet in order to become certified. The testing covers everything from their energy use to their air handling ability as well as their noise output. (Indoor environmental quality extends beyond just air to include other factors such as noise pollution too!) The ventilation systems that are able to receive PHI Certification can be relied upon to work as claimed by the manufacturer. A Passive House project may use an uncertified ventilation unit, but the manufacturers reporting of its units effectiveness is reduced for consideration in the PHPP.
In Europe there are many companies that have received certification of their systems. As Passive House grows in popularity you will see manufacturers here also seeking certification of their units. I was impressed that the testing went beyond measuring just the electrical requirements of the unit. The manufacturers are also required to show such things as “The service life of the outdoor air filter should be limited to one year (to avoid endotoxins). The manufacturer must ensure that the proliferation of microorganisms and the entry of endotoxins is prevented permanently by providing either components or obligatory attachments for the apparatus” 
In researching this topic I came across something that was interesting. It isn’t related so much to Passive House as it is to air quality – after all, your outdoor air will be come your indoor air and this will give you just a hint at how good your outdoor air quality is to begin with. Check the lichen growth on the trees in your immediate area. A study showed that the better the air quality the better lichens grow and the more varieties you will find of them too.  Passive House and planning for fresh air – I’m lichen it!!!
 Requirements and testing procedures for energetic and acoustical assessment of Passive House ventilation systems for Certification as “Passive House suitable component” http://www.passiv.de/03_zer/Komp/Lueft/Requirements_L_EN.pdf
 “The Guide to Air Quality Monitoring with Lichens.” By William Denison. http://gis.nacse.org/lichenair/doc/Denison.pdf