[avianlyric]

In modern planes, advanced HVAC systems end up being cheaper than older air management methods.

The old way of keeping a planes air “fresh” was to bleed air from the compression stage of each engine, because the air there will be at high pressure, and also reasonably high temperature (outdoor air temps at cruising altitude is -40C to -57C). You then just inject that air into the cabin, and let the old air bleed out.

But it turns out, pulling air like that from the compression stage of a turbine has a material impact on efficiency (you badly disrupt the airflow through the engine), and engine efficiency is so high these days, that removing those air bleeds, and replacing them with sophisticated HVAC systems with dedicated compressors, heaters and filters ends up being cheaper, at least from a total cost of ownership perspective. As a consequence, modern planes from the past 5-10 years have had some pretty capable air management systems. Of course there’s a much larger stock of older planes out there, which you’re more likely to be travelling on. But the claims regarding plane HVAC aren’t crazy when looking at modern planes.

[mapt]

The dubious claims made were about how aggressive and effective internal filtration was, not about actual fresh air circulation.