Summer is coming, and air conditioning has become a "life-sustaining artifact" for many people.
But unexpectedly, the problem also followed, many netizens posted on social platforms that when the air conditioner in their home is turned on to 26 °C, there will be an unpleasant smell, "just like the smell of stinky socks that have not been washed for many years soaked in yogurt and fermented", but if the temperature is adjusted below 26 °C, this odor will disappear again.
Is it true or false that the air conditioner smells at 26°C? Why is it 26°C?
Where does the air conditioning smell come from
Let's start with the conclusion, it is true that the air conditioner may have an odor at a certain temperature, but it does not have to be 26°C.
Xie Wei, an intermediate engineer of Gree Electric Appliances (Zhengzhou) Co., Ltd., and others have published a study entitled "Research on the Causes and Prevention Methods of Air Conditioning Heat Exchangers", which systematically analyzes the odor of air conditioners at specific temperatures.
According to the researchers, the complaints from users about the peculiar smell of air conditioners can be traced back to before 2010. At that time, the odor of the air conditioner was mainly due to dirty filters, mold accumulation, improper installation of the drainage system or odors emitted by non-metallic materials, which could be eliminated after normal cleaning and maintenance. But in recent years, a large number of complaints have been about "three new users": new air conditioners, new installations, and new houses. The air conditioner did not produce dirt and other problems, but it still produced three peculiar smells: fishy, sour, and smelly.
The researchers also tested it with a prototype. They set the temperature of the air conditioner to run at 16~23°C for 30 minutes, and then adjusted it to the "air supply" mode, running at 25~28°C for 5~20 minutes. It is worth noting that there is no odor in the heating state, as well as during the conversion of different temperatures and modes.
Eventually, the researchers targeted hydrophilic aluminum foil.
Hydrophilic aluminum foil is a material aluminum foil with a thickness of 0.1mm that is coated with anticorrosive coating and hydrophilic coating - also known as primer and top coat - also known as primer and top coat after degreasing, washing and drying treatment, and is mainly used for air conditioning radiator fins. The surface of hydrophilic aluminum foil has strong hydrophilicity, which can make the water in the hot air of the air conditioner condense on the heat exchanger sheet flow down the sheet, so as to avoid the "bridging" of water droplets between the heat exchanger sheets and affect the ventilation effect of the heat exchanger.
The coating used in hydrophilic aluminum foil is an organic paint, and the main component is acrylic resin. The acrylic resin solution is mixed with curing agent and additive water to form the coating, and the coating is formed after the curing of the paint is completed.
Acrylic resin is synthesized from different acrylic monomers, acrylic monomers are substances with a larger odor, but they contain carbon-carbon double bonds, and the double bonds have reacted in the resin emulsion synthesis stage, and the monomers are polymerized to form polymer resin. Generally speaking, paint manufacturers will monitor the monomer content when synthesizing resins to ensure that there is almost no acrylic monomer residue in the resin, even if there is a small amount of residue, if the coating process is set up reasonably, these residual monomers will also react or directly volatilize in the process of baking and curing.
After the coating is applied to the surface of the aluminum foil, it is baked at high temperatures for a period of time for a cross-linking curing reaction to form the coating. In this process, some small molecule volatiles and coating decomposition products are produced. These substances have their own odor, and if they remain on the surface of aluminum foil, they will produce a special odor, and the size of the odor is greatly affected by the coating process.
In other words, if the coating process is set up reasonably, for example, the coating film is thoroughly dried, and the hydrophilic aluminum foil will not produce peculiar smells. If the coating process is not set up properly and the coating film is not fully cured, the hydrophilic aluminum foil coating will absorb moisture from the air and release a sour odor.
It is worth mentioning that this paper, which analyzed the causes of the sour smell of air conditioners, was later no longer publicly available. Combined with the experience of netizens contacting after-sales replacement parts and cleaning air conditioners, it can be said that hydrophilic aluminum foil is one of the factors that cause air conditioning odor.
Nowadays, the relevant process has been improved, and now the air conditioner has a peculiar smell, most of which is because the air conditioner is too dirty.
In the air-conditioning industry for more than ten years, Yang Xiaopeng (pseudonym), who is currently an agent of air-conditioning brands such as Midea and Gree, told Yiyu that the main reason for the odor of air-conditioning is that many microorganisms (fungi), dust, etc., are attached to the evaporator, wind wheel and water tray and other components during the operation of the air conditioner, and the air conditioner will produce condensate in the process of refrigeration operation.
Yang Xiaopeng said that low temperature will reduce the activity of microorganisms, so there is no obvious odor when the air conditioner is running at low temperature, and there will be obvious odor when the temperature is high. In addition, the humidity in the southern region is higher than that in the northern region, which is more suitable for the breeding of various fungi, so air conditioners in the southern region are more likely to produce peculiar smells.
As for why 26°C is the "watershed" of air conditioning odor, it is still related to the air conditioning temperature set by people. Yang Xiaopeng explained that the air outlet temperature of the air conditioner is not equal to the temperature we set for the air conditioner, generally speaking, the air outlet temperature of the air conditioner will be lower than the ambient temperature of more than 7 °C, when the ambient temperature reaches the temperature set for the air conditioner, the air conditioner is no longer refrigerated, and the natural wind begins to blow, at this time the odor is more likely to appear.
"For example, if it's 31°C indoors, you set the air conditioning temperature to 26°C. The air temperature of the air conditioner is below 24°C, and when the indoor temperature reaches 26°C, the air conditioner will start to blow natural wind, and the smell may appear. Therefore, it is not that 26 °C is easy to have peculiar smell, but many people set the temperature of the air conditioner at 26 °C, and after the indoor temperature reaches 26 °C, the air conditioner blows natural wind, and the odor appears. ”
Moreover, the odor has nothing to do with the form of air conditioning, whether it is a central air conditioner, a cabinet unit or an air conditioner hanging on the wall, it is the same situation.
"If you find after-sales service and say that the air conditioner has a peculiar smell, after the maintenance personnel arrive, basically the first reaction is to suggest cleaning the air conditioner." Yang Xiaopeng said.
In the final analysis, it is the air conditioner that is to blame. But can an air conditioner really be that dirty? How dirty can it really be?
How dirty is the air conditioner
One of the main reasons why an air conditioner gets dirty is that there are so many places where it can hide dirt.
When you open the air conditioner shell, the first thing you see is the filter, which is one of the hardest hit areas for dirty things. Dense dust, flocculents, pet hair, etc. are easily adsorbed on the filter screen, and the original white transparent mesh becomes a black, fluffy bacterial petri dish.
Air vents and water troughs of air conditioners are also prone to dirt accumulation.
The air outlets of many air conditioners are covered with mold, and the water in some of the water tanks is also muddy, and there are mold stains all around.
These are visible dirty things, and some invisible dirty things are also very lethal.
Daddy Evaluation has conducted a control experiment on an air conditioner that has been used for more than 10 years before and after cleaning. The researchers placed the preservative-free bread slices in the air outlet for 10 minutes before and after the air conditioner cleaning, prepared an additional untreated bread slice as a control group, and then placed the three slices of bread in a sterile sealed bag for seven days.
The results showed that the slices of bread blown by the unwashed air conditioner were covered with colonies.
A paper published in Modern Preventive Medicine also studied the current status of microbial pollution and the cleaning and disinfection effect of household air conditioners.
In the experiment, 15 household air conditioners were sampled, and 120 samples were sampled, and the four important parts of the household air conditioner air outlet, filter, radiator and water sink before and after cleaning and disinfection were aseptically sampled. The results showed that both bacterial and fungal contamination was severe before cleaning and disinfection of household air conditioners.
家用空调出风口、过滤网、散热片和接水槽的细菌总数平均值分别为2.51×10⁴CFU/cm²、6.79×10⁴CFU/cm²、3.16×10⁴CFU/cm²、1.40×10⁵CFU/cm²,真菌总数平均值分别为534CFU/cm²、948CFU/cm²、465CFU/cm²、2042CFU/cm²。
Since there is no sanitary standard for household air conditioning at home and abroad, the total number of bacteria and fungi on the inner surface of the centralized air conditioning duct specified in the "Hygienic Code for Centralized Air Conditioning and Ventilation System in Public Places" (WS394-2012) needs to be ≤ 100 CFU/cm², and it can be seen that the total number of bacteria and fungi in the four parts of the household air conditioner in the study exceeds the standard value by 1.5~2810 times.
But this is not difficult to solve, as long as you do a good job of cleaning, the situation can be greatly improved. The above studies show that after professional cleaning and disinfection, the total number of bacteria and fungi in each part of the household air conditioner has decreased significantly, and the bacterial removal rates of air outlets, filters, radiators and water tanks are as high as 99.88%, 99.93%, 99.92% and 99.93%, respectively, and the fungal removal rates are 99.57%, 99.53%, 98.96% and 97.97% respectively.
Taking a step back, even if someone can tolerate the smell of air conditioning, the health hazards brought by "dirty air conditioning" to the human body should not be taken lightly.
According to Guangdong TV Electrocution News, in May this year, a citizen in Guangzhou was admitted to the ICU because he was infected with germs after using an air conditioner that had not been cleaned for a long time. The doctor then said that the patient was infected with a germ called "Legionella pneumophila", and it happened that the cooling water in the cooling tower of the air conditioner and the condensate in the fan coil unit were suitable for the survival of this germ.
So, how do you clean an air conditioner?
The most effective and thorough way is to remove the filter and other parts of the air conditioner for cleaning, or use cleaning spray, in addition, the current air conditioner also has a certain cleaning function. Yang Xiaopeng said that in response to the problem of peculiar smell, various air conditioning manufacturers currently have some of their own ways to deal with it, and the air conditioners on the market basically use bacteriostatic fins to reduce the attachment of bacteria, or add self-cleaning operating procedures to the air conditioner.
However, Yang Xiaopeng also admitted frankly that the problem of air conditioning odor is still a problem in the industry, and there is no measure to completely eliminate odor.
In the final analysis, it is still up to the users themselves to be diligent and clean the air conditioner, or find a professional to do the cleaning work. It's really not good, when it's not so hot, let's return to the wisdom of our ancestors and shake the fan more......
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