Maintenance of HVAC-Systems and components, definition of cleanliness

Maintenance of air-conditioning systems is acknowledged as an important means to run HVAC-systems properly. Although several maintenance programs and standards exist, not many systems are maintained in a proper way. Most standards and programs are not concerned with the indoor environment, they are only concerned with repair and failure-response of system components. Just now, some new guidelines come out in Europe, which contains first definition of cleanliness. These levels normally define dust concentration, or microorganism on the surface of components or the microorganism concentration in the water of humidifiers. Levels for microorganism in the air are not defined. One question that is not precise answered jet is: Is it good enough to define cleanliness levels for surfaces, or do we need concrete definitions