Can you open windows in a Passive House?
Yes, without a doubt. A Passive House must be built to a high level of airtightness, meaning no air leakages through the windows, but of course these specially designed windows can open. People usually open windows in their homes to let fresh air in and foul smells out, although there is no need to do so in a Passive House.
A Passive House is fitted with a heat recovery ventilation system that provides an abundance of fresh air, much more than opening a few windows and more constant with no drafts or chills.
Be sure to note that leaving windows open in colder seasons, such as winter, will mean a higher use of energy needed to heat the house, just as you would in a normal house.
Can you only build a Passive House on a sunny south site?
It is ideal to have south facing windows to make plentiful use of the free energy provided by the sun. However it is possible to achieve the Passive House standard if your site does not have south facing windows (more insulation may be needed to compensate). All designs have to be tested and verified in the PHPP software to ensure that they will indeed meet the Passive House Standard, north facing or south. This standard is not as strict as people think.