Is the nominal temperature of high temperature resistant HEPA the continuous operating temperature?
When purchasing high-temperature resistant HEPA, you often see a temperature value written on the product information, such as 'temperature resistant 250°C'. What this number refers to is directly related to whether the selection is correct.
It may refer to continuous operating temperature, it may refer to short-term peak values, or it may be a tolerance value under specific test conditions. The meanings of the three are very different, and you need to confirm with the supplier before using them in the project. Placing an order just by looking at a number may cause problems in actual operation.
One temperature number, three possible meanings
The temperature values on the product information are as follows:
Continuous operating temperature : The filter can operate at this temperature for a long time, and the material performance and sealing state remain stable. This is the strictest definition and the one that requires the most confirmation.
Short-term peak temperature : The filter can withstand this temperature, but it is only allowed to last for a limited time, such as a short-term high temperature during the start-up and shutdown stages of equipment or process abnormalities. Beyond the duration, the material may begin to deteriorate.
Test condition temperature : Some test items are conducted at a specific temperature. This temperature value describes the test environment and does not mean that the product can work at this temperature for a long time.
If you do not distinguish between these three when purchasing and use the peak value as a continuous value, the life of the filter element may be far lower than expected.
The temperature resistance boundaries of filter materials, glue and gaskets are different
HEPA is an assembly, and each part has different temperature resistance capabilities.
Filter material : Glass fiber filter material usually has better temperature resistance, but there are differences in products with different processes and coatings. The temperature resistance range of PTFE filter material is different. The selection should be based on the actual applicable temperature of the filter material.
Sealant : The glue line between the filter material and the frame is a relatively sensitive part under high temperature conditions. If the temperature exceeds the applicable range of the glue, softening, cracking or aging may occur, causing leakage points. This kind of problem may not be found by leak detection at normal temperature and needs to be evaluated under hot conditions.
Frame and gasket : Metal frames expand at high temperatures, and dimensional changes may affect assembly and sealing. The resilience performance of the gasket material will also change at high temperatures, and the pressing force may decrease after long-term use.
These items should be checked separately, and the lowest item should be used as the overall temperature resistance boundary. Looking only at the temperature resistance data of the filter material may overestimate the applicability of the entire machine.
The heating and cooling process should also be considered
High-temperature working conditions are not just 'running at a certain temperature', the heating and cooling processes also affect the filter status.
The heating rate is too fast, and the expansion rates of the outer frame and filter material are inconsistent, which may cause stress. If condensation is accompanied by high humidity and high temperature during the cooling process, the requirements for sealing materials will be higher.
These dynamic processes will occur during equipment startup and shutdown, process switching, and maintenance shutdowns. Providing the temperature curve when selecting a model - including normal operating temperature, heating rate, peak duration and cooling method - is more valuable than just giving a temperature value.
Thermal performance is to be independently verified
Efficiency and resistance data at room temperature cannot directly represent performance at high temperatures.
Temperature changes will affect gas density and viscosity, which in turn affects filter resistance and air volume. For matching FFU fan filter unit or In the EFU equipment-end fan filter unit system, the fan operating point will also shift under high temperatures, and the air supply volume needs to be recalculated.
Therefore, for high-temperature working condition projects, it is recommended to clearly define the verification time points: after installation, after temperature rise, and after stable operation, which items should be tested respectively. The conditions and methods of thermal leak detection must also be agreed in the project document, and the normal temperature solution cannot be directly applied.
Maintenance records should be marked with actual temperatures
The actual temperature curve during operation is recommended to be included in the maintenance ledger.
The temperature in some working conditions is not constant. The temperature may be different during the day and night, during production and standby. Recording the actual temperature changes can help determine whether the status changes of the filter element are caused by normal aging or abnormal working conditions. When replacing, it can also be judged whether the selection needs to be adjusted based on the actual operating conditions.
Sealing materials under high temperature conditions usually age faster than at normal temperatures, and the replacement cycle may be shorter than under normal conditions. This should be taken into consideration when formulating the maintenance plan, and the specific period shall be based on the actual operation data of the project.
About Aili Industrial’s high-temperature working condition supporting equipment
Aili Industrial can discuss the material and structural configuration of high temperature resistant filters based on complete working condition information. Filters, fans, motors, control systems and sheet metal are in the same manufacturing system.Complete machine solutions such as FFU fan filter units can be confirmed together with the temperature resistance conditions of the filter element, instead of purchasing them separately and then matching them on site.
For high-temperature projects, it is recommended to provide the continuous temperature, peak temperature and duration, heating and cooling methods, whether there is condensation, as well as the installation location and operating time, so as to facilitate the determination of the applicable boundaries of filter materials, sealants and outer frame materials. Specific performance is subject to technical confirmation documents and project test results, involving The grade and testing requirements of HEPA/ULPA air filters should also be stated separately in the document.
