"The POLAR test chamber is much bigger than a CADR chambler, and more representative of real-world environments than existing standards dictate with a 81m3 footprint and no external fan to support air circulation – the purifier itself must do this."[1]

ie: dyson has written POLAR to exclude external fans into their new "standard". Honestly they also don't clarify what they mean by external fans. Since they compare to a box fan/filter in the CADR example above... one is left to either guess or assume that they are either talking about traditional fanned purifiers or are assuming that no hvac exists in "real-world" environments.

[1]https://www.dyson.com/newsroom/overview/update/december-2020...