ANSI/ASHRAE 52.2 General Ventilation Air Purifier Removal Efficiency Testing Method Based on Particle Size

The standard “ANSI/ASHRAE 52.2 Method for testing the removal efficiency of general ventilation air purifiers according to particle size,” developed jointly by the American National Standards Institute (ANSI) and the American Society of Heating, Cooling and Air Conditioning Engineers (ASHRAE), describes a test method for evaluating the performance of air purifiers based on particle size.

The test method measures the performance of air purifiers in removing particles of specific diameters when loaded with a standardized loading powder fed intermittently to simulate particle accumulation over the service life of the devices. This standard defines the procedures for generating the aerosols required for the test. It also provides a method for counting airborne particles with diameters ranging from 0,30 to 10 μm in front of and behind the air purifier to calculate removal efficiency based on particle size.

This standard also specifies performance characteristics for the equipment required to conduct the tests, defines methods for calculating and reporting results obtained from test data, and establishes a minimum efficient reporting system applicable to air purification devices within the scope of this standard.

The ANSI/ASHRAE 52.2 standard is one of the most important standards in the HVAC and air filtration industry. It provides a laboratory-standard test method for evaluating how effectively general ventilation air purification devices (primarily air filters) remove particles of varying sizes from the airflow. This standard is widely used to compare filter performance, specify products in building projects, and support indoor air quality requirements in codes and standards.

This standard was initially published to address the limitations of the ASHRAE 52.1 standard (which used dust spot and gravimetric methods). It later replaced general efficiency ratings with particle size-specific measurements focusing on fractional efficiency over a particle diameter range. ASHRAE 52.1 was subsequently discontinued, and some elements (such as average retention and dust retention capacity for low MERV filters) were incorporated into ASHRAE 52.2. This standard is continuously updated.

The ANSI/ASHRAE 52.2 standard establishes a reproducible laboratory procedure for the following purposes:

• Measuring removal efficiency depending on particle size (from 0,3 μm to 10 μm).
• Testing the filter's performance both when clean and when loaded with dust (simulating real-world use).
• The results are reported in a way that helps users select appropriate filters for applications such as commercial buildings, hospitals, industrial facilities, and residential buildings.

This applies to general ventilation air purification devices (e.g., panel filters, pleated filters, bag filters, rigid cell filters), but not to ultra-high efficiency filters such as HEPA/ULPA (different standards such as EN 1822 or IEST-RP-CC001 apply to these filters).

The basic testing method includes the following:

• Test setup: A standardized duct arrangement with controlled airflow, particle counters before and after the filter.
• Forced aerosol: Dry potassium chloride particles that form a highly dispersed aerosol, produced from an aqueous solution.
• Particle size range: Efficiency is measured across 12 distinct size channels (0,30–10,0 μm) divided into three broad categories:
• E1: 0,3-1,0 μm (fine particles, e.g., smoke, bacteria)
• E2: 1,0-3,0 μm
• E3: 3,0-10,0 μm (larger particles, e.g. dust, pollen)
• Loading procedure: The filter is progressively loaded with ASHRAE synthetic test powder until the specified final resistance (pressure drop) is reached. Efficiency is measured in six stages: clean + five loading steps.
• Composite minimum efficiency curve: The lowest efficiency in each size range across all loading phases is used to create a conservative performance curve.
• Additional measurements: Initial and final resistance to airflow, and (optionally) average retention and dust holding capacity for low MERV filters.

The most well-known output is the Minimum Efficiency Reporting Value (MERV) rating, a single number between 1 and 16 that summarizes the filter's performance based on the combined efficiencies in groups E1, E2, and E3.

• MERV 1-4: Basic protection (mostly large particles at least 10 μm), low efficiency for fine particles.
• MERV 5-8: Suitable for general commercial/residential use (3-10 μm particles).
• MERV 9-12: Improved filtration (1-3 μm) for superior residential/commercial use.
• MERV 13-16: High efficiency (0,3-1 μm) for smoke control in hospitals and clean rooms.

Higher MERV values ​​indicate better capture of smaller particles. MERV 17-20 has been discontinued as it overlaps with HEPA test protocols.

Here is a simplified summary of typical MERV implementations:

• MERV 8: Common pleated filters for offices and schools. Captures pollen and dust mites.
• MERV 13: Recommended for improved indoor air quality, hospitals, and post-COVID building standards. Strong against fine particles.
• MERV 16: Very high efficiency for critical environments.

The ANSI/ASHRAE 52.2 standard is referenced in building codes. It is particularly critical for indoor air quality in reducing airborne viruses, allergens, PM2.5, and other pollutants. It helps designers balance filtration performance with energy use (higher MERV generally means higher fan energy due to pressure drop).

In short, the ANSI/ASHRAE 52.2 standard arose because previous methods used to evaluate air filters were insufficient for modern needs regarding indoor air quality, health protection, energy efficiency, and fair product comparison. The main reasons why this standard is considered important are as follows:

• Particle size-specific performance
• A repeatable, controlled laboratory method.
• MERV rating system
• Real-world simulation
• Regulations, standards, and certification support.
• The importance of health and pandemics.
• A practical necessity in today's world.

For many years, our organization, with its competent and experienced team, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the ANSI/ASHRAE 52.2 standard to businesses.