How to disinfect the clean area with HVAC

2020-05-14 08:17:54
1. Disinfection of clean area with central air conditioning purification system (HVAC)            In pharmaceutical plants, generally speaking, the clean area is large, and the central air conditioning purification system is used to complete the purification and disinfection of each clean area. The method is that the ozone generator is directly installed in the main air supply and return pipes of the central air conditioning purification system or the back end of the medium efficiency filter in the purification air conditioning box, and the power control box is placed in the machine room. During disinfection, close about 90% of the fresh air inlet valves and external discharge valves, so that the HVAC system and the clean area form an internal circulation state. It only takes about 1-1.5 hours for air sterilization every day, and 2-2.5 hours for fumigation instead of chemical reagent. The advantages of the scheme are as follows: using the purified air as the carrier of ozone (about 60m3 air volume per minute can pass through the ozone generator), the ozone can quickly spread to the clean room controlled by the HVAC system, and the ozone concentration is evenly distributed. The sterilization purpose of the clean room can be achieved without adding any disinfection equipment in the clean area; at the same time, the HVAC system can be killed Effect of mixed bacteria and mould. In practice, it is found that ozone can also play a role in dissolving bacteria and extending the service life of high efficiency filter.            2. Concentration standard of ozone applied in central air conditioning system of pharmaceutical industry            According to Section 8.2 of section 4.12 ozone application of technical specifications for disinfection issued by the Ministry of health in December 1991, "ozone with concentration of 5-10mg / m3 (equivalent to 2.5-5ppm) is used for 30 minutes for airtight air; 20-30mg / m3 is required for settling colonies on the surface of objects , (equivalent to 10-15 ppm). The purpose of ozone application in pharmaceutical industry is to replace ultraviolet rays and chemical fumigation to disinfect the settling colonies on the surface of air, mechanical equipment and medium materials in the whole clean area. The required ozone concentration is 10-15 ppm, which is equivalent to 20-30 mg of ozone per cubic meter of air.            3. Calculation method of ozone application in air conditioning system            Let V1 be the space volume of the clean area, V2 be the space volume of the HVAC system, and V3 be the loss of ozone caused by the fresh air supplemented by maintaining the positive pressure of the clean area            Then the total volume of sterilization space (V) is calculated as: v = V1 + V2 + V3            Determination of V3: according to the practice, the more reliable empirical formula is summarized as follows: V3 ≈ total circulating air volume of HVAC system m3 / h * 25% (replacement rate of conventional fresh air) × 10-20% (fresh air volume supplemented by maintaining positive pressure in clean area) × 39% (budget value of ozone half-life when ozone is applied), that is, V3 = total circulating air volume of HVAC system × 1-2%.            Selection of ozone generator: firstly, determine the concentration of ozone sterilization according to the efficiency of ozone sterilization, i.e. according to the standard of technical specifications for disinfection (c): for the floating bacteria in the air, the concentration of ozone sterilization is 2-4ppm; for the settling colonies on the surface, the concentration is 10-15ppm (refer to technical specifications for disinfection). The natural half-life (s) of ozone is about 23 minutes in reference state, and the decline rate of one hour is 61%. Design: when ozone sterilization is applied for 60min and reaches the required concentration, it can be kept for a period of time (1-1.5H) to get the effect of complete killing of settling colonies on the surface of mechanical equipment and building objects, so as to achieve the effect of chemical fumigation.            For example, the total volume of sterilization space (V) is 1000m3, and the sterilization requirement is to replace chemical fumigation for large-scale disinfection, and sterilize the settling colony on the surface of equipment and building objects. According to the above requirements, the ozone concentration (c) in the air shall be more than 10 ppm (converted to 19.63 mg / m3 in the working state). The ozone natural decline rate (s) after one hour of operation of the ozone generator is 61%. The ozone generation of the machine to be selected is g / h (W): w = CV / (1-s) = 19.63 × 1000 / (1-61%) ≈ 50.33 (g / h)            An ozone generator with an hourly output of 50g can be selected.