A centrifugal compressor

A centrifugal compressor with an impeller (201, fig. 2b), a diffuser passage 401 and a volute 213, wherein the volute extends radially over the impeller, i.e. there is a radial overlap between the two in the sense that the volute's inner radius is shorter than the impeller's outer radius along at least part of the volute's circumference. The compressor becomes thereby dimensionally more compact and is suitable for application in ventilation systems for vehicles' passenger cabins, where installation space is limited. A vehicle with a ventilation system comprising such a compressor and suitable air ducts is also claimed. Preferably the volute has a flat radially outer side wall 404 and a curved radially inner side wall 405 and the impeller has an upper shroud 207. A lower wall 406 of the volute may be continuous with a lower wall 403 of the diffuser passage. Preferably the ratio D5/D3 of the diffuser's outer diameter to the impeller's outer diameter is at least 105%, more preferably at least 110%, whereas the ratio D6/D3, D6 being the volute's outer diameter, does not exceed 140%. The diffuser's maximum height H2 may be up to 110% of the impeller's height at its outlet.