Study On The Formation Mechanism Of Secondary Pollution Of Microbial Aerosol Deposited On Air Conditioning Heat Exchanger

Air conditioning system is indispensable in contemporary architectural environment.While air conditioning brings comfortable living environment to human beings,its internal parts can also provide places for the deposition and enrichment of microbial aerosols in the air.These settled microorganisms can have metabolism,reproduction and other behaviors in the air conditioning system,and produce secondary pollutants in these processes,leading to the deterioration of indoor air quality and affecting human health.However,at present,there is a lack of systematic research on the sedimentation and distribution of microbial aerosols on the air conditioning system,especially on the surface of heat exchangers,and the types and concentration characteristics of secondary pollutants produced by microbial metabolism on the surface of heat exchangers are not clear.In this study,a set of air conditioning experimental device with parallel air ducts is created.Through high-power temperature control equipment,stable and variable inlet air temperature,humidity,wind speed and other conditions are achieved in the operation stage of the air conditioning.A detachable heat exchanger is designed to realize the sample collection and monitoring between the fin gaps.Specifically,this study collected the condensate production of each row of fins and the culturable microorganisms in the condensate in different periods,and clarified the scouring effect of condensate on the surface of heat exchanger and the reproduction of microorganisms on the surface under different conditions;Secondly,ultrasonic cleaning equipment is used to collect the particles between the fins on the windward side and leeward side of the fins,explore the deposition amount of particles on the surface of the heat exchanger at different positions,determine the relative content of bacteria and fungi in the particles at different positions,and determine the deposition distribution and community evolution law of microorganisms on the surface of the heat exchanger by studying the change of unit mass of fine bacteria and fungi in different periods;Finally,we studied the particle size distribution of particles and microorganisms in the air before and after the heat exchanger,evaluated the possible human health risks caused by microorganisms,allergens and VOCs,and revealed the sources and change trends of harmful substances.Through experimental research methods,this subject comprehensively adopts a variety of sample collection methods and analysis methods to study the microbial deposition on the surface of heat exchanger and the release mechanism of secondary pollutants caused by surface microorganisms.The results show that the operating conditions of air conditioning(inlet air temperature and humidity,wind speed,condensate,operating time)will affect the distribution of particulate matter settling mass on the surface of heat exchanger,and the distribution of microorganisms on the surface of heat exchanger is not consistent with the distribution of particulate matter settling mass.The secondary pollutants produced by microbial aerosol deposition on the surface of air conditioning heat exchanger include offspring microorganisms,allergens and volatile organic compounds,which are closely related to the amount and types of surface microbial deposition.This topic provides a more comprehensive theoretical basis and research methods for the study of the impact mechanism of air conditioning and ventilation system on indoor air,and provides an important reference for the source analysis and optimal control of microorganisms,allergens and MVOCs in indoor air.