Species Identification And Thermal Response Analysis Of Microbial Contaminants In Accumulated Dust In Air-conditioned Wind Systems

Air conditioning ventilating ducts are the important part of the air-conditioning system, which also is the most polluted and the most easily overlooked department in the air conditioning system. Under the appropriate temperature and humidity, the airborne microorganisms with dust will adhere to the components of air-conditioning. During the long running process a large number of microorganisms would grow, reproduction, and will release toxins, anaphylactic materials and several metabolites which will exacerbate air microbial contamination of indoor.The dust in the air conditioning system of the supermarket was selected to be researched, and the amount of dust, the total number of bacteria and fungi in the dust, the total number of bacteria and fungi in the air supply and other health indexes were used to revaluating the cleaning effect. The dust-associated microbial species were identified to make sure the dominant microflora during the last spring and early summer. The influence of different temperature and humidity to the microorganisms’ growth characteristic were researched to find out the unsuit temperature and humidity to the microbial.The results show that after cleaning of air conditioning ventilating ducts, the dust quantity, the total number of bacteria and fungi, the total number of bacteria and fungi in the air supply was decreased significantly, the effect of cleaning was remarkable, which has obvious effect on improving indoor air quality and the operation of air conditioning; The Gram-positive bacteria were the main bacteria in the dust, they are Staphylococcus epidermidis, Micrococcus luteus, Bacillus cereus and E. coli. The main fungal species were penicillium, aspergillus, alternaria, cladosporium, and yeast, and the dominant fungi were penicillium and aspergillus.The optimum environment of dust associated bacteria was35℃to37℃, the relative humidity is30%～90%, and the number of the colony has a significant positive correlation with the humidity,specially the relative humidity above the60%. The optimum growth temperature of dust associated fungi was25℃～30℃, the relative humidity range was30%-90%, and the number of the colony has a significant positive correlation with the humidity too, especially the relative humidity above70%.In non-running process of air conditioning, the influence of the treatment for30min at45℃～65℃and the relative humidity between60%-10%to the dust associated microorganisms inactivated effect were tested separately. As the temperature increased or the relative humidity decreased, the number of colony decrease gradually. The negative trend of the number of the colony was low until the temperature between60℃～65℃, and when the relative humidity below20%, the microorganisms were killed. The further optimization of the temperature and humidity conditions were the time of treatment was40min, the temperature and relative humidity was65℃and10%. Under this condition the concentration of the microorganisms remarkably decreased, but the number of the microbial species had little change. During the operation of air conditioning, temperature maintained at16℃～24℃and relative humidity generally maintained at range of60%～90%, the lower the relative humidity, the less colony.