Today I Learned

Pfft you'll never get accepted into journalism school with that attitude

They literally need to meet airtightness requirements to meet the Passive House standard. It's tested with a blower door test to check the air exchange rate at a prescribed negative pressure. You may be referring to a loose definition of passive house, instead of the standard, though. Airtightness is not "awful" as you suggested - mechanical ventilation provides fresh air

I'd bet money that won't work well here in the southwest USA where it's been above 110F (43C) for almost 60 days in a row and above 115F (46C) for almost 30 days in a row.

I moved into one of these buildings about 1.5 years ago and it's indeed awesome. We also have no gas and tons of solar panels on the roof so last year with the insane energy prices in the whole of Europe I spend €2,83 for all my energy including heating for 8 months, and I'm easily cold so I always have the heating on. The only problem is as you say to get rid of heat in summer, but they opted for smaller windows than is standard so less heat is getting in in the first place. And because of the great insulation you also have pretty much no traffic noise from outside. The only complaint I have is that the mechanical ventilation can get quite loud when it's windy outside, but the benefits are so overwhelming I can't be that bothered by it.

So from the article it seems that when the passive air vents are closed the total flow of air is supposed to be less than 10m³/hm². The air flow that occurs during the test is from cracks and leaks in the fixtures and doors. Calling it airtight might be confusing since people assume that would mean zero net flow.

Genuine question: if they're airtight, how do oxygen and CO2 levels remain livable? Spacecraft and submersibles require oxygen supply and CO2 scrubbers to keep occupants alive.

At least In NL, what you can do for cooling is to have cold water run through your in-floor heating. Brings things down to about 2-3C under ambient, so not perfect by any means, but a lot more pleasant than without it.

Unfortunately it's considered an optional upgrade that you can only really get when buying a newly built home and most people skip it in favour of things like a fancier kitchen.

Can you address any of the intuitive concerns around the air freshness and getting enough O~2~ and removing enough CO~2~ ?

How much is the air exchange process a complex active process that you need to monitor and maintain, or is it pretty basic and "just works"?

Do you find yourself having to think about "optimal use" of the house? Or can you just live your life as you would have prior to ownership and reap the benefits of the engineering?

Does being airtight mean it's significantly easier to keep out pests (rodents, insects)?
Ever since I'd first heard of airtight houses (and figured I'd fit nets on all the windows) my arachnophobic ass has been fantasising about a spider-free house..

Most passive houses I've seen have windows that open, but they are typically double/triple glazed (depending on climate) and are casement style instead of the more typical (and inefficient) double hung. They also typically feature a ventilation system to manage air movement precisely to prevent the issues you're concerned about.

According to the article the windows do open.

And of course they do. The building is designed to be well insulated, not to make you comfortable.

If the owner wants to let air in or out, of course they should be allowed to do that.

If there is a fire in in a air tight room and you close the door and stop the ventilation, wouldn't the fire die out because of the lack of oxygen?