Clearing The Air
Air filtration is your first line of defense in achieving indoor air health, but it is often overlooked. This is reflected in minimal provision for air cleaning in design and a legacy of indoor air quality (IAQ) issues. Hvac manufacturers, ventilation system designers, and mechanical contractors need to raise the specter of filtration as an equal partner in the delivery of air for the comfort and health of people who occupy the spaces entrusted to their care.
The problems associated with poor IAQ are well documented, but you may be surprised to learn how simplistic and cost-effective the solutions can be through understanding the role that better filtration design, application, and maintenance plays. This article attempts to ask the IAQ stakeholders to give equal space, time, and thought to air filtration for the delivery of acceptable indoor air health.
Planned Obsolescence?In deference to a sensitized society becoming ever more paranoid about the quality of the air in homes, schools and the workplace, an inexpensive (less than $1) air filter continues to dominate the filtration products marketplace. The standard filtration installation in today's high-efficiency furnaces, heat pumps, and room air conditioners affords, at best, a 1-in. slide rail track for an air filter.
Failure to provide space for adequate filtration is exacerbated by reducing the amount of fresh air to occupied spaces in the drive towards energy cost savings. Cynical as it may appear, inadequate filters, by design, have created market opportunities for hvac service companies, duct cleaners, and IAQ remediation companies in the months and years following initial installation and commissioning.
Each year, furnace and air conditioner manufacturers deliver thousands of units to their distributors and contractors for new projects and replacements. They build a range of capacities and sizes to handle a variety of heating fuels in a variety of ambient conditions from Alaska to Quebec to Florida. Energy-smart designs reflect the desire for quiet, heated or cooled, comfortable air for breathing. But what about clean?
Oh, yes. There is an air cleaner. It is, invariably, a 1-in. panel filter. The two most popular sizes are 20- by 25- by 1-in. or 16- by 25- by 1-in. models. A colleague once shared with me why they are called furnace filters: "Simply put, these filters are efficient at stopping particles the size of a furnace."
Welcome to the World of MicronsThe lack of understanding or concern for what role filtration plays in providing indoor air health in homes, schools, and workplaces is rooted in one solitary piece of flawed thinking: "What you cannot see cannot hurt you."
In fact, what you can see, at the optic threshold, is a particle larger than 10 microns1 in size. Even a particle that large needs a sharp eye and a bright beam of light to be seen. Unseen to the naked eye are billions of smaller particles that blow right through the standard 1-in. filters in most furnaces, passing into homes and workplaces. These particles mass over time and become part of our world. They can be annoying, irritating, infectious, and to some people, quite toxic. With only a 1-in. access rail provided for a flat panel filter, the long-suffering consumer has only one place to turn for relief.
And that place is, naturally, the local home hardware store. There, you will be dazzled by point-of-sale marketing sleeves on more 1-in. panel filters. There, you can browse through a maze of products that work mostly in the mind and wordsmithing of marketers who know only too well that people suffering with allergies and other respiratory problems will pay dearly for a breath of clean air.
The hottest item on the shelf is a passive electrostatic air filter that claims to stop up to 95% of allergy-causing pollen, dust, smoke, dander, flies, mites, hair, lint, loam, bacteria, viruses, mold, and fungi down to 0.1 microns, and they have ASHRAE testing2 to prove it. If consumers could visualize how really small a 0.1-micron particle is and how many thousands of these particles occupy a moment's breath, they would soon marvel at the mystical electrostatic powers claimed by the manufacturer's literature. Our testing, using laser-based particle counters and sophisticated flow rate instruments, raises serious doubts about many of these claims, especially with respect to allergen-size particles and resistance to airflow for a clean filter.
Consumers should research the full story about what contaminants are in the indoor air, their size and concentration, and the technologies available to treat and remove them. Of course, we know that this is not likely to happen.
"I don't want to own a filter factory. I just want a filter that works in my home or office," is a common attitude. So the responsibility lies with us, the experts.
Ask The ExpertsWhether you are designing a better filter to include in your ventilation apparatus or trying to improve the cleanliness of the air in your own home, here are some simple questions you need to ask.
What about that 1-in. slide rail filter access?
Why not provide a 2-in. or 4-in. track? More media area usually means better performance and longer life.
Why not provide an access door on the filter plenum to prevent chronic bypass around the filter frame?
An integral filter-holding sleeve or channel can be field designed and installed. Low-cost, self-adhering neoprene gaskets work wonders. Duct tape also works.
Why not specify a quality commercial-industrial treated filter media just like the big buildings use?
There are quality filtering materials out there. They are not expensive, and they actually last a lot longer than a 1-in. filter without significant reduction in airflows.
Can you really stop 0.1-micron particles with a passive electrostatic filter or any flat panel filter?
This is the same target particle that needs to be controlled in nuclear environments.
How many particles can be found in the unseen world inside?
Assume that your furnace or air conditioner operated 12 hrs per day, the flat panel filter sees 1,000 cu ft of air every minute, and each cu ft of air contains 200,000 particles3, all 0.3 microns and larger (that's on a good day).
Here's the math:
(1,000 cu ft of air) x (200,000 particles) x (60 minutes) x (12 hrs) x (365 days) = 52,560,000,000,000 particles.
The Truth Is Out ThereWe-the purveyors, designers, and manufacturers-need to better understand air filtration dynamics, the simple facts about small particles, and how they affect human health and safety. This information is out there. NSF International writes standards for and certifies legions of filter integrity technicians.
We can deliver air for critical care medical and biohazard environments at efficiencies of 99.99% on 0.3-micron size particles. We need to apply some of this wisdom to the ventilation appliances we deliver to homes, schools, and the workplace. While it may not always be practical to install a HEPA filter with 200 sq ft of filtering media capable of stopping everything but dirty thoughts, we can surely do better than a 1-in. flat panel or a 1-in. pleated throwaway.
As you deliberate on the root causes of poor IAQ and search for lasting solutions, take a very close look at the design, installation, accessibility, and performance of the filtration system. This often-overlooked, maligned, and least-understood strategy may be the key to better indoor air health. ES