About the Calculator

Adaptation of the original calculator created by: Joseph Allen , Jose Cedeno-Laurent of the Harvard T.H. Chan Y Shelly Miller and the University of Colorado Boulder:
https://docs.google.com/spreadsheets/d/1NEhk1IEdbEi_b3wa6gI_zNs8uBJjlSS-86d4b7bW098/edit#gid=1882881703

* Read all the scientific assumptions on the calculator's ReadMe page.

Before you start, read this:

Frequently asked questions about how to protect yourself from COVID-19 aerosol transmission (see section 9 for Air Filtering and Cleaning)
https://translate.google.com/translate?hl=en&sl=en&tl=es&u=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2Fe%2F2PACX-1vTgVkamic82Ux90zCWb5NFC6gYcDSWKYxKgh2y49uHQ5OJfGBAuQXs8igbmOaGqODI9wJ0UUnpo1dZu%2Fpub

Thread about HEPA filters and other alternative filtration systems written by José Luis Jiménez (world aerosol expert), translated and expanded by Pablo Fuentes: https://threader.app/thread/1292140276467802117

Thread about Hoaxes on HEPA filters written by José Luis Jiménez (world aerosol expert): https://threader.app/thread/1313133739036217348

3 things to keep in mind when buying a HEPA filter that is effective against SARS-CoV-2

• That complies with EN 1822-1: 2009 (see below)
• Ensure that they are filters H13 or higher: retention efficiency 99.95% or higher: H14, U15, U16 (being strict, the HEPA filter only includes two degrees of classification: H13 99.95% MPPS and H14 99.995% MPPS)
• Ensure that it is adapted to the space where we are going to use it (use CADR rate calculator)

Additional Information

Ensure the quality of HEPA and ULPA filters

The European filter test standard EN 1822-1: 2009 is the most important base for testing and classifying absolute filters. The standard is based on state-of-the-art particle measurement technology and authorized procedures for determining energy efficiency. It consists of five parts. The filter is assigned the corresponding filter class using the results of Sections 4 (local efficiency) and 5 (integral efficiency).

An individual test report and a serial number are generated for filters of classes H13 and higher. Therefore, each filter from H13 can be assigned its individual test.

Part 1: Classification, Performance, Testing, and Identification

EN 1822-1: 2009 establishes three groups:

• Group E: EPA Filter – Efficient particulate air
• Group H: HEPA Filter – High efficiency-particular air
• Group U: ULPA Filter – Ultra low penetration air

Absolute filters are rated based on integral and local efficiency values that are determined during testing.

Part 2: Aerosol Production, Measurement Equipment, Particle Count Statistics

This part describes test conditions and aerosol generators, particle measurement technology, and statistical procedures to evaluate counts.

* Integral efficiency is the average value of all the local efficiencies on the front area of the filter, In the first phase of this EN 1822 standard, fractional yield will be evaluated for the filter measurements ready at the same speed as the filter. The purpose is to determine the particle size which the average offers the lowest retention efficiency, called: Highest Penetration Particle Size (MPPS).

Part 3: Flat Sheet Filter Media Test (Determines MMPS)

Part 3 describes the determination of the fractional efficiency and the determination of the most penetrating particle size (MMPS) of the flat sheet filter medium.

A test aerosol is applied to the filter medium at the specified nominal flow rate for later use of the filter. The partial flows of the test aerosol are directed up and down in the filter sample. The particle counting method determines particle concentrations and calculates the fractional efficiency curve. The particle size at which the fractional efficiency curve reaches its lowest point is called the MPPS. In simplest terms, this is the particle size with which a filter medium works worst for a defined flow rate.

Part 4: Filter Element Leak Test (Scanner Method)

This section is about how to test if your filters are not leaking. Leaks can occur due to filter medium failure, improper seal between pleat assembly and frame, or component handling irregularities. Due to the high filtration efficiency estimated for absolute filters, even the smallest leak (only visible to the human eye) can produce higher concentrations of local particles.

For the automated process (scanner test), the filter element is placed on a test bench and then a DEHS (di-2-ethylhexyl sebacate) test aerosol is applied. The average aerosol particle size should be in the MPPS range. The flow side of the filter is approached using probes with a computer-controlled linear axis. At each point on the clean air side, local aerosol concentrations are measured to determine the degree of local penetration. If the aerosol concentration does not exceed the established limit at any point, the filter is considered not to be leaking.

The need to determine local efficiencies also implies the need to carry out individual tests for each filter element of filter classes above H13.

Part 5: Determining the efficiency of filter elements

Part 5 describes the determination of the integral filter efficiency. This value is usually calculated as the average of the individual local efficiencies included in part 4. Alternatively, individual measurement with fixed sampling probes is also allowed.