The passive house pillar that raises the most eyebrows is probably the HRV system, the heat recovery ventilation system. It’s needed due to the house being super airtight (thanks to the membrane and double glazed windows) meaning we need a system to ensure fresh air inside the house.
The HRV will swap fresh air from outside the house with the air inside, but prevent heat being transferred with the air. Not only does it bring fresh air in, but it also filters the air before distributing it throughout the house. Pollen, dust, smoke and smog is filtered out before getting inside. Yay! Of course, those things can still get inside if we open the windows, but that is our choice. The HRV means we can have the windows closed (keeping the house airtight) and still get fresh air.
Each room has a vent connected to a duct that runs back to the HRV unit where the magic happens. Metal plates inside the unit work as heat exchangers picking up and dropping the heat as the air passes through. The unit is connected to the outside world via an inlet and an outlet duct. The inlet side has a filter on it to remove particles as the air comes in, the unit then pushes fresh filtered air into the house via the ducts, entering the bedrooms and living room via vents in the ceiling. The bathrooms and kitchen ducts take air away – think steam, burnt toast and bathroom smells being whisked away to the outside via the unit.
All this air change happens without the heat from outside coming inside during the summer, or the cold during winter coming inside our cosy house. The idea is that without mechanical heating and cooling the house will stay at a stable temperature (22 degrees) all year round and provide excellent indoor air quality. Even better quality indoor air than a home with all the windows open.
Fun fact – we won’t need extraction fans in the bathrooms as the HRV will take care of the steam and anything else.
Some quick HRV Q and A:
- Is the HRV unit noisy? The one we have purchased should be under 40 decibels.
- Is it expensive to run? We’ve calculated about $1.50/day
- How big is the unit? Ours hasn’t arrived yet, but we’re expecting it to be about 60cm wide, by 30cm deep and 80cm high, plus all the ducting.
- Is it like an air conditioner? No, it’s an air exchange system, it doesn’t ‘condition’ the air.
- Do you need an air conditioner as well? We are installing a small split system to use on extreme days, maybe 10 days of the year.
- Where do you install it? Ours has been installed in a small storage room. I will admit the unit is taking up quite a bit of space in our compact house’s only bit of storage, We also sadly lost a bit of ceiling height in some locations with the 90mm diameter ducts needing space. I guess it can take up the storage space we won’t need for winter doonas and blankets. With my allergies I’m looking forward to fresh filtered air (no pollen, no smoke), so it’s worth it.
I’m really excited about living in a house with fresh indoor air year round and not needing to stick close to the heater in winter or flick the AC everyday in summer.
For further reading see our suppliers website at energyrecovery.com.au
(Image credit for main image: energyrecovery.com.au)