What does the term 'cleanness' refer to in the context of air conditioning?

The term 'cleanness' in the context of air conditioning pertains to the cleanliness of the air quality. This concept is crucial because, in indoor environments, maintaining high air quality is vital for health and comfort. Clean air is free from pollutants, allergens, and other harmful particles, which can affect respiratory health and overall well-being.

Air conditioning systems play a pivotal role in filtering and purifying the air, thus improving its cleanness. This includes the removal of dust, pollen, mold, and other contaminants. A system designed for effective air filtration will not only regulate temperature and humidity but will also ensure that the air quality remains high, making cleanness a key aspect of overall system function.

The other options pertain to different parameters of air conditioning, such as temperature and humidity, which, while important, do not specifically relate to the concept of cleanness.