Passive House Course Day 6 - Ventilation
For me, this topic is a game-changer. Our minds are wired to get fresh air into a home by opening a window or a door. Not ideal when the outdoor temperature is freezing or roasting. So inefficient!
So, what does a passive house do to ventilate whilst maintaining a consistent indoor climate?
A Heat Recovery Ventilation (HRV) system is employed, constantly bringing into the home filtered fresh air and extracting stale air. The term ‘heat recovery’ means that it will transfer most of the extracted air temperature to the filtered incoming air, making it very effective ventilation without increasing load for the heating or cooling system.
Here is a brilliant video by Steele Associates on their Fern development in Sydney showing and explaining their HRV system.
Remembering that we are making the building more airtight to make it more efficient, 0.6ACH (air changes per hour at 50 pascals of pressure) versus 10-15ACH, the input of fresh air and extraction of stale air is going to be essential. This, as a result, is going to massively reduce the heating demand alone - for example, a modern house using space heating still uses on average 15x more energy than a passive house. If you live in an unrenovated old weatherboard house with ducted heating, chances are you consume 30x more heating energy than a passive house! (Ouch!)
So you are about to renovate or build a new house, this is what you’ve got to weigh up…
The installation cost of a HRV system + 24/7 running cost of a HRV system + very low heating and cooling requirements (installation and running costs) = healthy indoor air quality + comfortable indoor environment
Versus
Installation cost of complete heating and cooling system + 15x less airtight building envelope (taking your average new build compared to a passive house) + 15-30x more heating demand = uncomfortable indoor climate (inconsistent heat distribution) + mould risk + toxin / VOC risk + bigger utility bills + bigger health bills
This is where I sense hesitation…. “well what is the point?”
This is why I’d make a new building airtight and employ a HRV system;
Healthy indoor air quality - constant input of fresh air and removal of stale air & toxic particles
Low cost of running HRV compared to the high cost of heating and cooling demands
No mould or moisture issues
Get used to seeing the term HRV or MHRV. There is no doubt that buildings are becoming more airtight. We will witness problems arising if we do not employ mechanical ventilation. This is a fact. It has happened elsewhere and we should learn from their mistakes and not from our own.
Want to find out more….
Here are a few brands available in Australia. Like air conditioning specialists, they would design a suitable system for your home;
Here is a great article in Sanctuary magazine, (written far more elegantly than I could have put it) explaining HRV systems
And a recent article here, again in Sanctuary magazine, explaining the type of HRV system you would employ if you know the airtightness of your home.