The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE)
https://www.ashrae.org is an organization whose mission is “To serve humanity by advancing the arts and sciences of heating, ventilation, air conditioning, refrigeration and their allied fields.”
They do scientific research to help develop standards that can than be adopted as code. While most of the standards developed are for the refrigeration, heating and cooling industries some are important for dust collection system design.
When designing your dust collection system, we will evaluate and consider the type of dust we are collecting. We want to know
- Is the dust explosive?
- Is the dust hydroscopic (will it adsorb moisture)?
- Is the dust abrasive?
- What is the size and shape of the dust particle measured in microns (um)?
These questions will help us determine the right filter media for your dust collector. The ASHRAE 52 Standard gives us guidelines for how efficient a filter is, based on a range of particle sizes. The efficiency of the filter is given a Minimum Efficiency Rating Value (MERV) based on how it performs during the ASHRAE test. MERV ratings go from 1 – 20 with 20 being the most efficient at removing particles in the submicron range – .3 um.
For example, if we are designing a wood dust collection system, we know that wood dust is explosive and the average size of wood dust particles is between 5 – 30 microns (um). The particle size will vary based on the tool creating the dust. Routers generate larger particles than sanding operations and smaller particles, which tend to be more explosive. If we have a small operation generating larger size dust particles, we may want to use a cyclone collector to remove the larger particles to ensure there is no filter replacement cost and exhaust directly outdoors. However, a large woodshop may be expensive to exhaust the air outside regularly.
We use a dust collector that has filter media tested by ASHRA Standard 52 to remove 90% of the dust particle in the size range of 5 – 30 microns. With that said, we would select a filter with a MERV rating of 15. We also know that the codes states if we are returning the air back into the building, the air must be 99.9% free of dust particles 10um or larger. This means we need a secondary filter with a minimum MERV rating of 17. Based on the ASHRAE test protocol, we now know the filters are capable of achieving our design criteria.
Filter manufacturers receive a certificate, after they have submitted their filters to a testing laboratory, stating the test results of their filter and what MERV rating it receives. This is import for engineers and end users to have this certificate as part of the verification of the design. The data on this sheet also indicates the air volume the filter is rated for. Over loading a filter, or increasing the air to cloth ratio, can lead to design problems with your dust collection system.
Other ASHRAE standards useful in our industry include Standard 41.2 for measuring airflow and air velocity. Testing procedures to validate air flows are important to ensure material does not accumulate in the duct system. Clean Air Company recommends using a company certified in air balancing to verify our system designs. Companies certified in air balancing will comply with the ASHREA standard.