The three most important things about passive houses are comfort, comfort and comfort.
When people talk about the Passivhaus, or Passive House system of design, the first thing anyone mentions is energy efficiency: the fact that they use hardly any energy at all. That's obviously important, but as I say every time we talk about green building, energy efficiency is only one part of the story. In fact there is another side to the Passivhaus that might make people pay more attention: they are really comfortable to live in.
British architect Elrond Burrell notes in his post, Passivhaus; Comfort, Comfort, Comfort, Energy Efficiency that the standard for airtightness (0.6 air changes per hour) makes the house completely draft-free. Since the windows are so good, designed to have interior surfaces that are within 5°F of interior temperature, there are no drafts off the glass like there are in most conventional houses. (That's why the radiators and duct vents are placed under windows, to counteract this). It also means there are no cold spots.
Windows that are much colder than the room temperature are also uncomfortable because we experience them as cold spots. The glass acts like a radiator in reverse, drawing warmth away from our body. And the reverse is true in summer; the glass acts like a radiator adding unwanted heat into the room.
There is less overheating as well, and less need for air conditioning when heat gain is controlled by careful shading and control of window size. This was a problem in early solar and passive designs.
It's great that the building is sealed so tightly, but people need fresh air. So notwithstanding the name Passive House, there is a very active mechanical ventilation system with heat recovery, bringing in fresh air all the time. There is also that other active system: opening windows.
A byproduct of designing a building that is so comfortable, without drafts or cold spots, is that is that the Passive House sips energy.
It sets extremely ambitious yet achievable targets, provides the methodology and toolkit to accurately model predicted building performance and it has an outstanding track record of delivering. And it does this simply by design.
This is why Passivhaus is so interesting. Anyone can build a net zero house by slapping enough solar panels on the roof; it can still be drafty, have too much glass and too little insulation. Alternatively, anyone can build a sort of comfortable house by throwing enough radiant flooring and ground source heat pump air conditioning and other high tech gizmo green at it. What Elrond shows here is that comfort can also be achieved simply by design.
It is a really important point that is often overlooked. ( I did myself when I cherrypicked from 11 great reasons why Passive House is such a great green building standard However it might just be a great way to sell the Passivhaus to a larger audience.
Read more at Elrond Burrell's blog