Abstract: In recent years, the number of complaints about air-conditioning odors has been increasing. Through the investigation, it can be seen that the peculiar smell appears when the refrigerant is switched from the “cooling” mode to the “air supply” mode when the refrigerant is turned on, and it does not disappear after a period of time, and the peculiar smell cannot be eliminated after normal cleaning.
Therefore, this article mainly discusses the reasons for the peculiar smell of the air-conditioning heat exchanger and proposes targeted prevention methods.
Keywords: air-conditioning heat exchanger; peculiar smell; hydrophilic aluminum foil
1 Research background
In recent years, the problem of odors from the wind has continued to arise during the use of air conditioners. According to market research, this problem mainly occurs after running in the “cooling” mode for a period of time, or in the inverter air conditioner, when the indoor temperature reaches the set temperature, the outdoor unit stops running and the indoor unit switches to air supply mode.
The peculiar smell of the air conditioner was complained by users, and the earliest can be traced back to before 2010. At that time, the odor of air conditioners was mainly caused by dirty filters, accumulation of mold, improper installation of the drainage system, or odors from non-metallic materials. The odor can be completely eliminated after normal cleaning and maintenance. In recent years, a large number of odor complaints have been concentrated on the “three new users”, namely new air conditioners, new installations, and new houses. The peculiar smell appears when the refrigerant is switched from the “cooling” mode to the “air supply” mode when the refrigerant is turned on, and it does not disappear after a period of time, and the peculiar smell cannot be eliminated after normal cleaning. Through investigation, it can be known that the air conditioner did not produce dirt and other problems. Therefore, this article mainly discusses the reasons for the peculiar smell of the air-conditioning heat exchanger, and proposes specific prevention and treatment suggestions.
2 Causes of odor from heat exchanger
2.1 Summary of odor
Through customer feedback and the survey of the maintenance master, it can be found that the odor is mainly generated after a period of operation in the “refrigeration” mode, or in the inverter air conditioner, when the indoor temperature reaches the set temperature, the outdoor unit stops running and the indoor unit turns to air supply Appears during mode. Different groups of people have different descriptions of peculiar smell. Through investigation and evidence collection, it can be attributed to the three types of “fishy, sour, and smelly”. The specific manifestations are fishy, fishy acid, salty fishy acid, tomato acid, stuffy acid, unclean smell similar to stuffy air, moist and musty smell, sweaty feet, sweaty feet, dead mouse smell, smoke smell, plastic smell .
2.2 Causes of odor
First of all, through the analysis of the “problem prototype” parts of different reasons, the multi-person team sniffed them separately, and found no obvious unpleasant smell. Secondly, the original “problem prototypes” were cleaned routinely and then assembled again for power-on verification. The prototypes were placed at a temperature that simulates the actual use of the customer. After adjusting the temperature at 16 to 23 °C for 30 minutes, adjust to the “air supply” mode. , Operate at 25～28°C, after running for 5～20min, different groups of different machines feedback different wind odors and reproduce the situation reported by customers.
Through investigation, it can be seen that in the heating state, there is no peculiar smell during the conversion of different temperatures and modes. The original prototype verification did not find any abnormality in this mode. Therefore, the locked peculiar smell appeared in the “refrigeration” mode and transfer Wind” mode. Combining the operation logic of the air conditioner and the elimination of odors after a large number of customers replace the heat exchangers for analysis. After low-temperature cooling operation, the surface of the hydrophilic aluminum foil of the exchanger will be enriched with a large amount of condensate. When the indoor temperature reaches the temperature set by the air conditioner, the outdoor When the unit stops working, the indoor unit switches to “air supply” mode, and the condensed water evaporates continuously and diffuses into the air. If the hydrophilic aluminum foil has an “odor”, at this time, the water vapor will bring the “odor” into the air during the volatilization process.
2.3 Reasons for the peculiar smell of hydrophilic aluminum foil
Hydrophilic aluminum foil is composed of a layer of organic paint attached to the surface of the substrate aluminum product. The hydrophilic aluminum foil used in air conditioners usually has the characteristics of high corrosion resistance and high hydrophilicity. The outer coating of hydrophilic aluminum foil substrate is divided into anti-corrosion coating layer and hydrophilic coating layer, also called primer (HD) and top coating (HW). Most organic coatings in the industry are provided by Guangzhou companies. The coating is a water-soluble thermal organic resin, and the main component of the coating is acrylic resin. Acrylic resin is synthesized from different acrylic monomers, which are more odorous substances. Acrylic resin emulsion is mixed with curing agent, auxiliary agent and water to prepare coating; after coating, the coating undergoes cross-linking and curing reaction after being baked at high temperature to produce small molecular volatiles, decomposition products and water. After the coating is cured, a coating is formed. Acrylic monomers are odorous substances, but they contain carbon-carbon double bonds. The double bonds have reacted during the synthesis of the resin emulsion, and the monomers polymerize to form a polymer resin.
The coating manufacturer will monitor the monomer content when synthesizing the resin to ensure that there is almost no acrylic monomer residue in the resin. Even if there is a small amount of unreacted monomer remaining, if the coating process is set properly, it will happen during the baking and curing process. React or volatilize. After the base coat and top coat are applied to the surface of the aluminum foil, they must be baked for a period of time under high temperature conditions to carry out the crosslinking and curing reaction to form a coating with certain functions. During this process, some small molecule volatiles and coating decomposition products will be produced. These substances have a certain odor. If these substances remain or adsorb on the surface of the aluminum foil, they will produce a special odor. The size of the odor is affected by the coating process (such as coating). Layer thickness, drying temperature, drying time, production line speed, ventilation conditions). The process setting is reasonable, the coating film is completely dry, and the hydrophilic aluminum foil coating will not produce peculiar smell; the coating process is not set properly, the coating film cannot be completely cured, and the hydrophilic aluminum foil coating absorbs moisture in the air and releases acid odor . The most suitable curing temperature for the coating is 150-200°C. Too low a temperature will cause incomplete curing, and too high a temperature will cause the molecules that have been cross-linked into a network to decompose, and both will produce peculiar smell.
3 Preventive measures for heat exchanger odor
3.1 Hydrophilic aluminum foil odor improvement plan
①Choose odorless or less odorous paints, and use different brands of paint for indoor and outdoor units.
② Strictly control the baking temperature, and prevent excessive baking and incomplete curing under the premise of ensuring sufficient curing.
③Strictly control the coating accuracy of the coating to reduce the unevenness of the coating film thickness. The thick coating film causes insufficient curing and produces odor.
④ Strengthen the ventilation of the coating line during the coating curing process to reduce the odor residue generated by high-temperature baking.
⑤The storage of the paint is strictly in accordance with constant temperature and humidity, and the paint should be used within the shelf life as far as possible.
⑥The packaging layer should be made of odorless material, and the finished aluminum foil should be fully cooled before packaging.
3.2 Improvement plan for heat exchanger manufacturing process
①Choose aluminum fins with good volatility to make volatile oil;
②Strengthen the monitoring of the peculiar smell of the fin before heat exchange molding;
③ Strengthen the real-time monitoring of the temperature of the fin drying line, and strictly set the upper limit of the drying temperature to prevent excessive baking;
④Strengthen the monitoring of peculiar smell of heat exchanger finished products.
This article is from Henan Science and Technology. In response to the air-conditioning odor problem, the author determined that the odor occurs in the “cooling” mode and the “air supply” mode. Based on this, the selection of the coating process of the hydrophilic aluminum foil, the coating control temperature, the coating thickness, and the ventilation The packaging is optimized to effectively prevent and control odor.