Our Certified Passive House (‘CPH’) is quite well known in our neighbourhood. Last weekend whilst I was out in the garden battling with the latest weed invasion I heard a group of gents (members of a local shooting club) talking about my home. I downed-tools and strained to eavesdrop on their chatter. One of them proclaimed that whilst energy saving was all-very-well that he’d “still like to be able to open the windows once in a while”.
Humph.. put me right off my gardening for the rest of the day.
You see the problem is that many people associate Passive Houses as sealed-up boxes. That’s it – full stop! That’s true to a certain degree – they are indeed super sealed up (ten times tighter than local building regulations require). But they are also drenched with fresh air all day everyday through the heat recovery ventilator, or ‘HRV’ to those in the know. In the trade we chant ‘Build Tight, Ventilate Right’.
The air flow rate through the HRV is specifically sized to ensure really good indoor air quality. It needs to be not too low as to render the house stuffy, but also not too high as to lose all that valuable heat in the winter (or coolness in the summer). Those clever boffins at the Passive House Institute require that the flow rate at normal fan speed in Passive House projects delivers 23 cubic metres of fresh air per person per hour.
The ventilation design for a Passive House requires delivery of fresh air to all the living spaces (bedrooms, living room, study, home office) whilst simultaneously extracting air from all the wet and humid spaces (kitchen, bathrooms, mud-room, utility spaces). It’s on all day, every day, pumping fresh air around your home (or office, or classroom). Yummy freshness.
Taking our home with five persons, we receive an hourly dose of fresh air goodness equating to 115 cubic metres. Extrapolating this to a full year, we’re blessed with just over 1 million cubic metres of fresh air. Doesn’t sound so stuffy anymore, right?
So the next time you hear someone criticising Passive Houses on the issue of air quality, please do me a favour and proclaim ‘au-contraire, they’re fresh air millionaires’.