In trying to improve indoor air quality (IAQ), air handling units (AHUs) with advanced filters are very important. These systems are crucial for maintaining the purity of air in residential, commercial, and industrial spaces. This article explores the recommended filtration stages and practices for air handling units to achieve the best air quality and save energy.
The Placement of Filters
The journey to clean air begins with the placement of filters within the AHU. The first filtration stage is designed to capture large particulate matter and is positioned as close as possible to the outdoor air intake. This setup acts as the first line of defense, ensuring that the air handling components remain clean, thereby extending their operational lifespan and maintaining efficiency. The addition of coarse filters at this stage is also a common practice to enhance particulate capture.
Going further into the system, the second filtration stage is very important for keeping the duct system clean. It is placed at the end of the supply duct to stop any particles that got past the first stage from getting into the indoor area.
Filtration Efficiency Selection
The efficiency of the filtration system is paramount. For supply air systems utilizing a single-stage filter, the minimum requirement is an ISO ePM1 50% filter. This standard ensures that a significant portion of fine particulates is captured before the air is distributed indoors.
In more advanced configurations where two-stage filtration is employed, the positioning of the supply air fan between the first and second filtration stages is critical for maintaining airflow and filter effectiveness. Furthermore, to combat the potential for microbial growth within the filter media, it is imperative to control the relative humidity in the filter area, keeping it below 90% and ensuring that conditions never reach the dew point.
Please review this detailed post about Filter Selection;
https://ferhatgurer.com/2023/04/07/optimizing-hvac-systems-and-ahus-a-guide-to-filter-selection/
Considerations for Filter Selection and Maintenance
The choice of filters, such as bag filters, demands careful consideration of the filter area, which is recommended to be at least 10 square meters per square meter of equipment cross-section. The integrity of the sealing elements is also crucial; they must be of a closed-cell type to prevent moisture absorption and resist becoming a breeding ground for microorganisms.
Moreover, the filter chamber should be outfitted with an inspection window and lighting to facilitate easy maintenance and inspection, ensuring that filters can be monitored and replaced as necessary without compromising the system’s integrity.
Performance and Compliance
For fans and filters, the calculated pressure drop across the filter at nominal flow rates provides a benchmark for selecting components that balance air quality with energy efficiency. This pressure drop should reflect an average of the initial and final pressure drops across clean and dust-laden filters, respectively.
Air handling units designed for human occupancy should adhere to EN ISO 16890 standards, undergoing rigorous testing and classification to ensure they meet the necessary air quality and performance criteria.
Recommended Final Pressure Drop for Filters
A critical aspect of filter selection involves understanding the final pressure drop. According to EN 13053 standard;
*For ISO Coarse filters, the maximum final pressure drop is calculated by adding 50 Pa to the clean filter initial pressure drop or up to three times the clean filter initial pressure drop, whichever is lower.
*For ISO ePM1, ISO ePM2.5, and ISO ePM10 filters, this value is determined by adding 100 Pa to the clean filter initial pressure drop or up to three times the clean filter pressure drop, whichever is smaller.
These recommended values represent the highest typical values for air handling units in operation, lower than those used in EN ISO 16890 for classification purposes and energy savings. The performance obtained from tests conducted according to EN ISO 16890 does not need to be met at these pressure drop. According to ISO 16890 standards, the final pressure drop should be 200 Pa for ISO Coarse and 300 Pa for ISO ePM1, ISO ePM2.5, and ISO ePM10.
Transparent and Informative Labeling
To aid in the maintenance and longevity of the filtration system, each filter section should display critical information such as filter class, filter material type, and final pressure difference. This practice empowers users to make informed decisions when replacing filters, ensuring the system remains efficient and effective in maintaining indoor air quality.
Conclusion
The incorporation of advanced filtration techniques in air handling units represents a significant step forward in the pursuit of healthier indoor environments. Through filter placement, adherence to efficiency selections, diligent maintenance practices, and understanding the final pressure drop for filters, it is possible to significantly reduce indoor air pollutants and enhance the wellbeing of occupants across various settings. As technology advances, so too will the strategies for air purification, promising cleaner, safer indoor air for future generations.