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Posted: 2018-12-05 18:36:23

This BluMartin freeAir unit has almost no ductwork.

One of the big selling points of Passivhaus design is the air quality. There is almost no air leakage through the walls, so most Passivhaus buildings have a heat recovery ventilator where exhaust air pre-warms or pre-cools incoming air, because in an energy efficient building you don't want people opening the windows when they need fresh air, which is responsible for as much as 50 percent of heat loss.

In apartment buildings, air quality is particularly problematic. Most apartments have ducted bathroom exhausts and actually get the replacement fresh air from under the entry door from the pressurized corridor, along with dust and whatever else people have tracked into the carpet. So a Passivhaus style HRV is a huge plus for comfort, health and air quality.

Minden HRVLloyd Alter/CC BY 2.0

But getting that air around a house or an apartment can often mean a mess of ducts, and that can be a particular problem in retrofits, requiring boxing or drop ceilings. Here's an extreme example from a house in Minden, Ontario.

FreeAir unitsfreeAir units/CC BY 2.0

That's why this FreeAir system from German company BluMartin is so interesting.

section through unit© BluMartin

It's designed for apartments up to 750 square feet, and has almost no ductwork – just the exhaust from the bathroom, which feeds into the top of the FreeAir unit. It seems straightforward in a studio apartment; a loop is created where bathroom exhaust air is replaced by fresh outside air through the heat exchanger.

FreeAir PlusfreeAir Plus/ Lloyd Alter/CC BY 2.0

Where it gets really interesting is where there are multiple bedrooms. The little FreeAir plus unit gets installed in the wall over the bedroom door. It has built-in temperature, CO2 and humidity sensors; when anything gets above the set threshold, it diverts air from the hall into the bedroom.

Blumartin© BluMartin

Because the unit is in the actual suite, it can be "demand dependent" and deliver fresh air when actually required, rather than running all the time like most HRVs.

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