So you want to build a Passive House. Where to start? What's the secret?
Passive means that the energy required to heat the house is collected from such sources as the sun (direct sun radiation into the house), household appliances and inhabitants. The passive heat generated in the house is carefully calculated using software (PHPP). In order to avoid adding cost and making the building uneconomic by adding other heat sources, such as electric baseboards, hydronic heating (hot water) or heat pumps, one can ad energy directly into the air stream of the already required ventilation system (heat/energy recovery ventilator). Many in the industry refer to this as the "toaster" or the "hair blower", because that's about all it needs to heat a Passive House. (BTW *hint*hint*, Zehnder makes some great products with the "toaster" built right in)
Here is the key: the air can only be heated to a maximum of 52°C/125°F in the ventilation system. Above that temperature, dust pyrolysis starts to happen, which is when dust particles start to burn, manifested as a "burnt dust smell". It is the same smell you get when you fire up a little space heater that has sat for a while. Through some calculations - which I'll spare most of you, unless you really want to know* - one can determine that a Passive House can only be supplied with a maximum of 10W/m² of heating power through the ventilation system, which keeps the house comfy cozy even on the coldest day of the year. So this is the magical threshold for your Passive House (certified):
Maximum heat load: 10W/m²
If the building requires more than 10W/m² on the coldest day of the heating season, some sort of additional heating has to be aded to be able to keep the house from getting too cold. And who would want that?
*So, you really want to know: Here's how 10W/m² is calculated:
Easiest to transfer to a white board.
photo credit: "shhh..." by Val.Pearl