O2, CO, CO2, NO, NH3           

The main function of the ventilation and air conditioning is to provide the oxygen required for the human breathing, to dilute the indoor pollutants or odors, to exclude the harmful toxic substances and other pollutants produced by the indoor process, to remove the indoor heat or residual humidity, and to provide the indoor air required, mainly in the factory, conference room, and other building rooms. Environment and so on.

In recent years, CO poisoning and ammonia explosion related to ventilation and air conditioning systems are frequently reported in newspapers. Many green building design standards stipulate that the underground garage with mechanical ventilation should be monitored and controlled in real time for the CO concentration, and the refrigeration machine room pays more attention to the monitoring of the leakage of ammonia gas. More attention is paid to personal health, and more oxygen and carbon dioxide concentrations in indoor air become more important.