VDI Guideline 6022, one of the most popular Guidelines published by VDI. Since 1998, more than 10.000 copies of VDI Guidebooks have been printed and thousands of people went to the training described in the guidebook. As the result the hygiene standard in air-conditioning systems today is much better than 10 years ago. REHVA´s Swiss member SWKI accepted the VDI 6022 Guideline as SWKI-2003-5, in 2003. The REHVA working group revised and updated the German Guidebook with some new ideas and procedures.