Design of Purification Air Conditioning for Microbial Laboratory

       The microbiology laboratory is mainly used for experiments and research on microbial isolation, cultivation, identification, morphology, utilization, variation, and harm. What functional rooms are required for its construction? How to design the air conditioning system? This article will reveal the answer.
       The main functional rooms of the microbiology laboratory include preparation room, buffer room, sterile room, culture room including bacterial culture room, fungal culture room, tuberculosis (TB) culture room, identification room, disinfection room, reagent room, strain storage room, etc. According to the functional nature of the work field (testing, teaching, research, monitoring), the composition and scale of the laboratory can be adjusted and merged accordingly.

       （一）Biosafety level
       The microbiological laboratory is mainly engaged in the inspection of pathogenic microorganisms, focusing on the research of infectious diseases, and plays an important role in the monitoring of hospital infection. Clinical microbiological inspection is the guarantee for the rational and standardized application of antibacterial drugs. The microbiological laboratory carries out corresponding protection according to the biosafety classification of its operating objects. The conventional microbiological laboratory is a biosafety class II (BSL-2) medical laboratory BSL-2 laboratory, which can also be divided into ordinary BSL-2 laboratory and enhanced BSL-2 laboratory. The main technical requirements and indicators of both are shown in the table.

       The design requirements for a regular BSL-2 laboratory are relatively simple, and there are no special requirements for air conditioning and ventilation. Mechanical ventilation or natural ventilation can be used.
       The enhanced BSL-2 laboratory requires mechanical ventilation, and the core workspace should not have openable external windows. A buffer room should be set up at the entrance, and the core workspace should maintain negative pressure on the atmosphere and install a pressure display device in a prominent position at the entrance. An efficient filter should be installed at the exhaust end; In addition, the enhanced BSL-2 laboratory also recommends using a brand new air system to control humidity and pressure gradients.
       （二）Air conditioning load calculation
       The air conditioning load includes the load of the enclosure structure, fresh air load, lighting load, equipment load, personnel load, and other loads. For biosafety laboratories, the air conditioning load is much larger than that of general office air conditioning loads and requires additional consideration.
       The heat dissipation of experimental equipment. In addition to the heat dissipation of office equipment, the laboratory also needs to consider the high heat dissipation of laboratory equipment, such as (ultra-low) temperature refrigerators, centrifuges, CO2 incubators, high-pressure sterilizers, etc., which can affect the sensible heat load of the laboratory compared to general office rooms.
       The amount of fresh air added to maintain the balance of room airflow. Due to the presence of local exhaust equipment such as biosafety cabinets in the laboratory, in order to maintain the balance of laboratory airflow, in addition to personnel fresh air, additional fresh air load needs to be considered.
       （三）Ventilation and air conditioning system
       The air conditioning system design of ordinary BSL-2 laboratories is relatively flexible. Based on the owner's needs and technical and economic analysis, various forms such as all air system, "air-water" system, variable refrigerant flow multi split (VRF) system, or split air conditioning can be selected. Reinforced BSL-2 laboratories generally adopt all air system (fresh air system), and it is recommended that the air exchange rate during use be 6-12 times/h. The specific air exchange rate of the laboratory should be determined according to the laboratory air conditioning load, experimental operation process, and the hazardous level of the materials used.
       When using an external exhaust type biosafety cabinet, it should be discharged through a pipeline independent of other public ventilation systems in the building. When the biosafety cabinet ventilation system is used in conjunction with the laboratory ventilation system, the exhaust fan pressure head should consider the local resistance of the biosafety cabinet to the design and construction of the medical laboratory (generally about 500Pa). When the laboratory exhaust and biosafety cabinet exhaust are separately equipped with exhaust systems, attention should be paid to the interlocking control of the biosafety cabinet exhaust and laboratory exhaust. The exhaust of the biosafety cabinet should always be started first and then stopped to ensure that the exhaust inside the biosafety cabinet is not sucked back into the indoor environment. The reinforced BSL-2 laboratory should also be equipped with high-efficiency filters on the exhaust side, and the exhaust fan should be equipped with backup air as needed. Machine.
       In order to prevent the disorderly or reverse diffusion of harmful biological factors, all types of laboratories should pay attention to indoor airflow organization. The arrangement of air supply and exhaust outlets in biosafety laboratories should form inward directional airflow, flowing from low pollution areas to high pollution areas, avoiding the formation of large blind spots or eddies in the room, and not affecting the performance of biosafety cabinets. GB50346-2011 "Building Technical Specification for Biosafety Laboratories" clearly states that air supply outlets should not be installed near the operating surface of biosafety cabinets or other locations where aerosols are generated; when the airflow organization is arranged for upward and downward discharge, the lower edge of the high-efficiency filter exhaust outlet should not be less than 0.1m and not more than 0.15m from the ground, and the upper edge height should not exceed 0.6m above the ground; the exhaust outlet should not be higher than 0.6m above the ground. The exhaust speed should not exceed 1m/s.