HVAC School - For Techs, By Techs
The MERV 15 Filtration Physics - Short #300
· Summarized
Key takeaways
- Effective filtration is crucial for both protecting HVAC equipment and improving indoor air quality, especially when dealing with microbial spores and other small particles.
- Higher MERV ratings (such as MERV 13-16) are more effective at capturing ultra-fine and fine particles, including mold spores and bacteria.
- Filters must be properly sealed and fitted to prevent bypass, which can significantly reduce filtration effectiveness.
- Understanding particle sizes and their behaviors, such as Brownian motion, helps in selecting the right filters for specific needs.
- Bringing outdoor air into homes can improve air quality but also introduces pollutants; therefore, outdoor air should be filtered and assessed carefully.
- Regular maintenance and proper system placement (like outdoor air intakes) are essential to maximize filtration benefits and prevent contamination.
Summary
Introduction and Podcast Context
The hosts introduce the podcast episode, emphasizing a friendly tone and humor while setting the stage for a discussion on indoor air quality, filtration, and microbial control. They mention the episode's focus on MERV ratings and outdoor air filtration, mentioning recent personal experiences and the importance of understanding filtration in HVAC systems.
Importance of Filtration in Indoor Air Quality
This section discusses the vital role of filtration in maintaining indoor air quality. The hosts highlight how filters protect equipment and occupants from dust, particles, and microbial growth. The conversation emphasizes the need to filter both indoor air particles and outdoor air entering the home, especially due to the potential pollutants and spores present outside.
Particle Size and Filtration Ratings (MERV and ASHRAE 52.2 Standards)
The hosts explain particle sizes and how MERV ratings correspond to filtration efficiency for different particle sizes. They detail the classifications of particles into ultra-fine, fine, and coarse categories, and how higher MERV ratings (like MERV 15) can capture more of these particles, including fungal spores and bacteria. The discussion underscores the importance of selecting appropriate filters based on particle size and system compatibility.
Nuanced Approach to Outdoor Air Filtration and Quality Assessment
The hosts explore the complexity of bringing outdoor air into homes, including challenges like assessing outdoor air quality, the impact of location and environmental factors, and how filtration can mitigate risks. They discuss how outside air can carry pollutants such as spores, pollen, and chemicals, and the significance of efficient filtration to prevent these from contaminating indoor environments.
Technical Insights on Particle Capture and Filter Design
This section covers the physics of particle capture, including how small particles (like bacteria and spores) move via Brownian motion, making them easier to filter at certain sizes. The hosts also consider practical aspects like filter fit, bypass issues, and the impact of filter media and design on filtration effectiveness, advicing the use of filters with high MERV ratings like MERV 13 or 16.
Practical Considerations and Personal Experiences
The hosts share experiential insights, such as adjusting filters in dehumidifiers and the importance of proper placement and sealing to maximize filtration. They highlight the importance of maintenance and system design choices, including location of outdoor air intakes to avoid pollutants like smoke or dust, and reflect on personal mishaps to illustrate real-world challenges.
Conclusion and Final Recommendations
In closing, the hosts reiterate the importance of good filtration for controlling biological growth and improving indoor air quality. They stress understanding particle sizes, ensuring proper filter fit, and choosing appropriate filtration levels for different environments. The episode ends with a call for ongoing education and awareness about indoor air filtration.
Sponsors
- Refrigeration Technologies · Refrigeration Technologies and specifically Viper wipes, the all purpose wipe that is really amazing what it can cut through. It’s nice on the hands, makes them soft afterward, and good for cleaning various surfaces.
- Carrier · Carrier offers the 21d64c-843, a 2-in-1 deal with a universal hot surface igniter and flame sensor, each replacing over 150 OEM parts, providing a reliable upgrade for furnaces.
- Santa Fe Dehumidifiers · Santa Fe offers dehumidifiers with a new total peace of mind warranty program that provides five years of complete replacement coverage plus an extra year for parts—one of the most comprehensive warranties in the market.
- TruTechTools · TruTechTools supplies a broad catalog of over 90 brands, with industry experts and support team members who are tradespeople themselves, providing practical tools and resources including downloadable worksheets.
- Filtrete (implied as a sponsor during the discussion, if applicable)
Show notes
In this short podcast episode, Bryan and Roman Baugh talk about indoor air quality and microbial control, specifically MERV 15 filter physics and how it all works when bringing in outdoor air.
We filter indoor air to keep dust and particles off the equipment and keep them from circulating through the air. However, we also need to filter fresh air. While indoor air has several pollutants, including dust and VOCs, that make outdoor air dilution a sensible solution, outdoor air also has spores and other pollutants we want to filter out, and its quality can be hard to evaluate. Roman had an ERV that fed his VRF system, and it had significant microbial growth inside; he had some MERV 6 filtration on it, but that didn't capture particles effectively enough. MERV ratings measure the ability to filter particles out, and we use a unit called microns to measure particle size; higher ratings indicate a greater filter surface area and a better ability to filter out smaller particles.
ASHRAE 52.2 divides particles into three categories: E1 (ultra-fine particles between 0.3 and 1 micron in diameter), E2 (fine particles between 1 and 3 microns), and E3 (coarse particles between 3 and 10 microns in diameter). MERV 15 filters have a 90% capture rate of E2 particles and a 90%+ capture rate of E3 particles. Fungal spores tend to fall in the E2 or E3 category, and filtration can keep those from coming into the home with fresh air; bringing in fresh air to dilute indoor pollutants is good, but we need a nuanced approach, and good filtration (without bypass) is part of that equation. Filters can also capture much smaller particles due to the way those particles move. Smaller particles move via Brownian motion, which makes them move erratically and more likely to collide with filter media.
However, filter use and design, as well as fresh air intake location, can also affect filter efficacy. Filters that don't fit well in the slot enable bypass, and some filters might be restrictive. Exhaust ventilation outlets also play a role, as wind can bring those pollutants back to fresh air intakes.
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