Copper has broad application prospects in air conditioning systems
Since some parts of the air conditioning system will produce condensation during operation, it often creates conditions for the reproduction of microorganisms. For example, in the fan coil of the terminal device of the central air conditioning system and the room air conditioner, microorganisms will reproduce in large numbers in the filter, heat exchanger and condensate tray, causing secondary pollution of the indoor environment.
According to the survey on the actual use of room air conditioners by the International Copper Association and relevant public health departments, bacteria and molds grow to varying degrees in the air conditioning system. Regardless of the central air conditioning terminal, split wall-mounted unit and split cabinet air conditioner, their total bacteria and mold can be detected, indicating that there is a certain degree of pollution. Especially after SARS, the hygiene of the entire public place has been fully valued. Under the premise that people's hygiene awareness has gradually increased, a large number of bacteria are still detected, including Staphylococcus aureus, Bacillus and Legionella.
Among them, Staphylococcus aureus, which produces toxins in Staphylococcus aureus, is a pathogenic bacterium that can cause infection and inflammatory response. The average detection level of Staphylococcus aureus in the air conditioning system is about 10%, which should attract our attention. Bacillus is a conditionally pathogenic bacterium with an extremely high detection rate of more than 88%. The detection rate of Legionella in fan coil units was 1.72% (1/58), while the detection rate in household air conditioners was 9.38% (3/67). Legionella can cause Legionnaires' disease, which is a type of pneumonia.
The main components of a room air conditioner are fans, heat exchangers, filters, and condensate pans. During energy exchange in summer, the temperature of the indoor heat exchanger surface is usually 5~20℃, which is the best temperature zone for bacterial reproduction; coupled with the humid micro-environment caused by condensed water, it constitutes an ideal place for various microorganisms to breed. Therefore, filters, heat exchangers, and condensate pans become places where dirt and filth are hidden in the living room, causing secondary indoor pollution and threatening human health. At the same time, in terms of microbial hazards, indoor air is more dangerous than outdoor air.
Antibacterial properties of copper
Antibacterial generally has the following meanings: (1) It targets bacteria living in the living environment, and its effect can last for years or even decades; (2) The bactericidal ability is below the normal bactericidal level and above the bacteriostatic level; (3) It can maintain the hygiene of the living environment for a long time. According to the different ingredients, antimicrobial agents can be divided into three types: natural, organic and inorganic. Copper is an excellent inorganic antimicrobial agent with an atomic weight of 63.54 and a specific gravity of 8.92. The main antimicrobial mechanisms of copper are: (1) contact reaction, that is, after the copper ions in the antimicrobial product come into contact with bacteria, the inherent components of the microorganisms are destroyed or functional disorders occur. (2) photocatalytic reaction, under the action of light, copper ions can act as catalytic active centers, activate oxygen in water and air, produce hydroxyl radicals (.0H) and active oxygen ions (O-2), destroy the proliferation ability of bacteria in a short time and cause cell death, thereby achieving the purpose of antibacterial.
Copper ions have a unique antibacterial effect. The use of copper structural parts in public places can prevent the spread of bacteria. From the perspective of environmental hygiene, copper foil is the best antibacterial material for air conditioner heat exchanger fins; at the same time, it is recommended that the water tray and filter screen also use copper or copper plating technology.
Prospects for the use of copper in air conditioning systems
At present, the relevant national standards of the General Rules for Sterilization and Disinfection of Household and Similar Electrical Appliances have entered the stage of soliciting opinions. In the post-SARS period, people have further reflected on the microbial breeding conditions of air conditioning systems. In order to prevent the spread of microorganisms through air conditioning systems and strengthen the sanitation management of air conditioning systems in public places, the filters, surface coolers, heaters (humidifiers), condensate trays, etc. of air conditioning systems should use antibacterial materials or antibacterial treatment on the surface, and the antibacterial performance and durability of the antibacterial materials used should be consistent with the effective life of the corresponding air conditioning system components.
Recently, Japan has developed new filter materials such as air conditioning copper filter cotton for the antibacterial effect of copper. The relevant antibacterial properties and excellent heat transfer properties of the new copper tube copper fin heat exchanger are also under study. For example, according to the computer simulation analysis of the heat transfer performance of room air conditioner heat exchangers jointly conducted by the International Copper Association and Shanghai Jiaotong University, when copper fins are used instead of aluminum fins, the heat transfer coefficient of the heat exchanger increases; when the fin thickness is smaller, the fin height is larger, and the air-side heat transfer coefficient is larger, the heat transfer enhancement effect of the all-copper heat exchanger relative to the copper tube aluminum fin heat exchanger is more obvious. Under typical working conditions, when the fin thickness is 0.1mm, the fin height is 15.0mm, the refrigerant side heat transfer coefficient is 4000W/m2/K, the air side heat transfer coefficient is 80 W/m2/K, and the fin spacing is 1.6 mm, the relative percentage of the total heat transfer coefficient enhancement is 9.88%. In the range of working conditions tested, when the fin thickness is 0.02 mm, the fin height is 30.0 mm, the heat transfer coefficient on the refrigerant side is 5000 W/m2/K, the heat transfer coefficient on the air side is 60 W/m2/K, and the fin spacing is 1.6 mm, the relative percentage of the total heat transfer coefficient enhancement can reach 23.276%.
The heat transfer increase effect when calculating the actual heat exchanger is significantly lower than the possible change in the heat transfer coefficient on the outside of the tube. For example, the heat transfer of the heat exchanger in Conclusion 3) only increased by 3.03%, while the heat transfer coefficient under similar conditions can increase by 9.88% (see Conclusion 2). This is because the inlet state of the refrigerant and air sides is fixed when calculating the actual heat exchanger. This shows that if the actual air conditioner is not well matched, the benefits of replacing its fins with copper sheets cannot be clearly reflected.
Looking forward to the future, if the heat exchange fins, filters and condensate trays of air conditioning systems can reasonably use copper with antibacterial effects, it will contribute to protecting people's health.
