Indoor Air Quality

I was reading Dr. Wolfgang Feist’s 8 secrets behind the success of Passivhaus, one of which is “Best indoor air quality”.

I think no one will dispute the importance of good indoor air quality (IAQ).  However, to what lengths do builders actually go to make the indoor air healthy for the occupants? In the industrialized world, people spend about 90% of their time indoors, but according to the EPA, indoor air quality can be 10 times worse than outdoor air on warm days in large smoggy cities.  What are the contaminates to our indoor air:

1. Biological contaminates:  these include pet dander, dust mites, mold and bacteria that originate either indoors or outdoors.

2. Chemical contaminates: these include formaldehyde, VOCs (Volatile Organic Compounds) both of which are ingredients in solvents and adhesives used in a whole dost of wood products, paint, caulk, carpets, finishes.

3. Radon: naturally occuring but carcinogenic gas

4. Combustion by-products: carbon monoxide and other gases caused by incomplete burning in gas appliances and car exhaust that migrate into living space from attached garages

Let’s not go into the nasty health problems we can get from all these and straight to the solutions that the Passivhaus approach provides.

A Certified Passivhause must have an air-infiltration rate of 0.6 ACH at 50 Pascal or less.  This means the house is virtually air-tight.  A conventional house breathes through the cracks in its walls and windows and doors frames, this is sort of like using your skin to breath without a filtration system for the air coming in (your air-handler typically has a filter but that only filters the airs that gets sucked into the duct work).

A Passivhaus actually has a respiratory system like us with a dedicated intake and exhaust and a lung (Energy Recovery Ventilator) with very good filters, to filter the air that gets into the indoor living space.  This is one of the reasons it is important to build the house air-tight, so no air is intruding into the house through an accidental pathway and even more important that when you build the duct system for the ERV, it be air-tight too.  In a Passivhaus, the air enters into the intake duct which is filtered through the ERV before it is taken to the living space, that same air is breathed by the humans and animals in the house goes through the ERV again and it is exhausted to the outside.  The process continues 24/7, which means fresh air all the time.  Like my friend David Peabody says, it is a “one way” path for the air to circulate.


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