Tiny Ventilation Systems Deliver Fresh Air to Apartments and Small Homes

Three men visible through a window cut into a wall of wood slats

Lloyd Alter / CC BY 2.0

I often say that homes and buildings designed to the tough Passivhaus or Passive House standards are "dumb buildings", because they do not rely on a bunch of smart stuff to save energy, just dumb old insulation, high-quality components, and careful design and detailing. But there is one smart and fancy device in every Passivhaus building: a mechanical ventilation system with a heat exchange system to bring in fresh air. These units are usually big and expensive and were originally designed for bigger houses or offices.

But as I noted in my post about coming to Munich for the International Passivhaus Conference, I am really interested in multifamily housing these days.

(Aside: For North Americans used to forced air furnaces and ducts running around their houses, I should explain that in Passivhaus designs, there is so much insulation that they do not need much of a heating system. If they have one, it is used very rarely. But they do need air, and not nearly as much as comes out of the ducts when they are delivering heat. So the heating and ventilation requirements and equipment are usually kept separate.)

Vallox HRV
Lloyd Alter

So it was exciting to see that there are all kinds of new systems actually designed for smaller spaces. Your typical heat recovery ventilator (HRV) looks like this one from Vallox, a box that gets mounted on the wall in a closet. You can see how they work conceptually: a stream of air comes from the home through the heat exchange core, warming fresh air coming from the outside. So there are usually two pairs of ducts coming out of the box, two that run outside, one from the bathroom and another supplying the living spaces. There are often little ducts flying around above the ceilings. This can be a problem in retrofits, and adds a bit of money for the drop ceiling.


Smartvent demonstration
Lloyd Alter / CC BY 2.0

One approach for getting rid of the box is this new Smartvent HRV system from window maker Smartwin; it is so new that it isn't in their catalog yet, and in fact was just certified to Passivhaus standards at 10AM ET on March 9. Exterior air is sucked in from a vent beside the window and delivered to the HRV to the left of the window, while exhaust air goes out through a grill below the window behind the slatted siding. It is interesting in that it gets rid of the big box, but is really a conventional HRV and seems a bit home-made, although this is really early days.


Fresh-r open side view
Lloyd Alter / CC BY 2.0

I kept taking long silly photos of this Fresh-R unit because they ran a steamroller over an HRV and squished it down so that it fits in an 18cm (7") wall. It is an incredible bit of engineering that would be terrific for small apartments. In the condo biz, every square foot of usable space matters, so this really pays for itself.

Fresh-r diagram of air movement

Air from the bathroom or the interior goes into the top of the unit and gives up its heat through a copper core; outside air picks up that heat and is released into the living space where the unit is mounted. They do have a strategy for multiple rooms called "cascaded ventilation" with special vents between rooms.

FreeAir 100 and FreeAir Plus

FreeAir device
Lloyd Alter/CC BY 2.0

But as with people, perhaps one can be too thin. The FreeAir 100 is a little less svelt but still is tiny and would only need a small box-out rather than a closet.

Here you can see how the air circulates through the unit. Watch the video (in German) here.

Free Air Plus demonstration
FreeAir Plus/ Lloyd Alter/CC BY 2.0

But what really differentiates this unit is the FreeAir Plus, this little unit that goes through the wall from living spaces to bedroom. It has sensors that measure CO2, humidity and temperature, and re-routes the air through those spaces as required.

FreeAir flow chart diagram
Lloyd Alter/CC BY 2.0

"This ensures precise, demand-based ventilation." If one is doing a retrofit and it is hard or expensive to do a full set of ducts for the heat recovery ventilation, this might be an acceptable alternative.

Tiny units are not the only approach to the problem; when The Heights was built in Vancouver, they used mechanical rooms on the top floor and a big mess of ducts down to all the units. When I asked Passive House expert Monte Paulsen about these individual units, he noted that filters had to be changed regularly and that meant either the people in the apartments had to do it, or management had to gain access on a regular basis. Both are problematic.

But another expert noted that in condominiums, where the owners have a stake in the building, it is more likely that they would change the filters, and the less common and areas and equipment that that there is, the lower the common area charges are, so there is a real benefit to putting the units in each suite.

Perhaps each approach has its place. Still, it is wonderful to see that the manufacturers are really trying to address the problem of delivering fresh air to small spaces. This is progress.