Air Purifiers

[zappy]

What is the general consensus on the stand alone air purifier hardware? Can they really clean the air for the room they are located in (assuming you buy one that is rated for the sq/ft of the room)?

[Kevin O'Neill]

Performance varies widely.

[Kevin O'Neill]

Consumer Reports had a good article in the October 2003 issue.

[genesis]

Performance varies widely.

ditto

[zappy]

Any suggestions on units that perform well?

I checked the Consumer Reports article but the top suggestions have been discontinued.

[Kevin O'Neill]

Trane Clean Effects (ducted mounted)

Carrier Infinity (ducted mounted)

Honeywell Enviracare room HEPA

[pmeunier]

Any suggestions on units that perform well?

I checked the Consumer Reports article but the top suggestions have been discontinued.

I think you looked at an old report. The one you want is the December 2007 one:

http://www.arb.ca.gov/research/indoor/cr-12-2007.pdf

[breathe easy]

Stand alone air purifiers work very well as long as they are sized properly. You should have a minimum of 4 air changes per hour. They work best in a one room environment - for example in the bedroom of an allergic and/or asthmatic person.

Three brands we have tested and found to be very effective are IQ Air, Amaircare and Austin Air.

[pmeunier]

A major consideration for portable ones is the noise level. It doesn't matter how efficient it is if you won't turn it on. Stay clear of the small ones, they're too noisy. You want the biggest one you can afford that you will run at the lowest speed. Even IQ Air ones are noisy.

Also, an air purifier can be completely ineffective if there is much infiltration of dusty air, like trying to collect water in a sieve. For example, poor windows, or average windows on a windy day, may make running an air purifier pointless. The only way to be sure if an air purifier is effective is to own a particle counter like the Dylos. You may have to seal the windows in a room (tape, caulking, etc...)

[breathe easy]

pm
It is not just the efficiency of the filter that makes for effective air cleaning. Air changes per hour have a much bigger role than one assumes.

For example, I have been testing a Vornado Air Purifier. It is very quiet. In fact, I can hear the Dylos particle counter vacuum over the air purifier. At the normal speed it is producing 386 cfm. This means that it is getting 17 air changes per hour in my office. We are using MERV 11 filters in the unit.

The Dylos particle count on the 5 micron size particles is zero. The particle count on the 1 micron size particles is 2,800. Particle counts at 0.3 microns are 282,000. In an office down the hall the 5 micron particle size count is 800. The 1 micron size count is 23,200. And the 0.3 micron size particle count is 840,000.

Even though the one pass counts through a HEPA filter are much better, the cumulative effect of multiple passes through a MERV 11 filter give comparable results in room particle counts.

[pmeunier]

pm
It is not just the efficiency of the filter that makes for effective air cleaning. Air changes per hour have a much bigger role than one assumes.

For example, I have been testing a Vornado Air Purifier. It is very quiet. In fact, I can hear the Dylos particle counter vacuum over the air purifier. At the normal speed it is producing 386 cfm. This means that it is getting 17 air changes per hour in my office. We are using MERV 11 filters in the unit.

The Dylos particle count on the 5 micron size particles is zero. The particle count on the 1 micron size particles is 2,800. Particle counts at 0.3 microns are 282,000. In an office down the hall the 5 micron particle size count is 800. The 1 micron size count is 23,200. And the 0.3 micron size particle count is 840,000.

Even though the one pass counts through a HEPA filter are much better, the cumulative effect of multiple passes through a MERV 11 filter give comparable results in room particle counts.

That's a lot of air delivered quietly, I'm impressed. However, the air changes is only one factor. Your filter is in a contest with the infiltration of new dust. So if (air changes) X efficiency@size <= 100x (new dust infiltration rate in air changes) does not hold, the filter is not good enough.
Even at these very high "air changes", per your own measurements, the MERV 11 is ineffective on 0.3 uM particles. A reduction of 3-4x is not enough to matter, and is completely negligible for strong allergies. Typically you want 100x fewer particles or better to be able to get below the "detection level" of the allergic person. In practice a MERV 11 filter only works at that level on coarse particles like pollen.

[pmeunier]

For example, with moderate activity in my house the particle counts at 0.5 and 2.5 microns are respectively 10 and 2 (1000 and 200 particles per cubic foot), without a portable filter running in the room. A frenetic ruffling of papers and moving about will increase it to about 60 and 15. While just sitting and typing it will go down to 8 and 0 (800 and <50). This is what I need for my allergies to quiet down. I believe that I'd be uncomfortable in your office (and possibly cold from the wind, although I imagine it may feel nice in Texas ). I suppose that means I need to be in a class 1000 clean room for my allergies to go away (according to a graph I saw, class 1000 means 1000 particles or fewer per cubic feet at 0.5 microns http://www.ee.byu.edu/cleanroom/particlecount.phtml).

Can you make a *livable* class 1000 clean room out of an ordinary office with just MERV 11 filters? If so I'll be impressed.

[pmeunier]

the removal of dust is
dC/dt = -C (E F/V)
where
C is the concentration of particles (particles/cubic feet)
E is the efficiency of the filter @ size
F is the cfm of the device
V is the volume of the room

At equilibrium this is equal to the infiltration rate:
dCi/dt = D (L/V)
where D is the dusty (outside) concentration of particles (particles/cubic feet)
L is the flow in cfm through openings
V is the volume of the room

C (E F/V) = D (L/V)
we want C= D/100 so
E F/V = 100 D L/V
or in air changes,
A = 100 I/E
where A is the number of air changes of the device and I is the number of air changes due to infiltration. E is the efficiency of the filter @ size.
So for a MERV 11 filter with an efficiency at 0.5 microns of about 1% (?) and an infiltration rate of 0.1 (tight building), the number of air changes needed would be 100*0.1/0.01 = 1000 air changes.

So, you would need 50 of those vornado devices in your office before my allergies would be OK, considering a 0.5 uM allergen.

[breathe easy]

pm
I am leaving in five minutes to go to a ballgame - Rangers vs. Yankees.

Just some quick thoughts. I will respond with more information later.

We have had this discussion before on particle size vs. allergic reactions. I have to admit that you have convinced me that sub-micron allergen fragments can cause an allergic reaction in some people. However, you need to be careful not to generalize your reaction to allergens as the reaction of the standard allergic person. Different people have different thresholds.

You are dealing with a particularly nasty allergen - cat dander. This can cause a major reaction in sensitive people with just a few grains of exposure. I don't think it is realistic or necessary for most allergic people to need a 1000 Cleanroom to be comfortable.

MERV 11 filters pull out about 30% of the particles at 0.3 microns and about 35% of the particles at 0.5 microns. Frankly, I was surprised that the particle counts at 0.3 microns were so low in my office. I think a 60% reduction at this particle size is pretty good and I would contend adequate for most allergic individuals.

Have a great Memorial Day! Wish me luck.

[pmeunier]

Good point, it's true that different people have very different thresholds. Also, the threshold for a single person can vary as well depending on many things. That's why I try to consistently qualify my statements as being for "strongly allergic" people. Also, the simultaneous presence of several different allergens seems to add up. I believe that the more things you are allergic to and that are present in the contaminated air infiltrating into your location, the more filtration air changes you need. I'm allergic to many things at this time of year that produce sub-micron particles (indirectly), not just cats. I'm not alone, I have a friend for who even strong antihistamines provide insufficient relief.

You are dealing with a particularly nasty allergen - cat dander. This can cause a major reaction in sensitive people with just a few grains of exposure. ...

I hope you had a great game!

According to the figures you quote, you would have around 2.4 air changes/hour (17x0.35/2.5) in your office with dirty air.

-I think some of the studies on cat allergens are silly. There's this one in particular "Air Cleaners for Cat Allergy: Effective, but Not Useful" (Am J Resp Crit Care Med. 1998;158:115–120). The whole conclusion is based on the absence of improvement of symptoms after a 33% reduction in cat allergen levels. All it proves is that if you're drowning under 100 feet of water, bringing you 33 feet up isn't going to save you.

-I'm surprised that you would settle on a specific figure as adequate given your previous caution about making claims of health benefits from operating an air purifier, and the statement about varying sensitivities. I would think one goes with the other -- if you can prove a specific figure as adequate then you can make health claims. Searching the web, I think people have no idea how many air changes/hour will provide relief; quoted figures vary from 6 to 40. A lot of these statements sound to me like wishful thinking, especially because the infiltration rate of dusty air, or sources, isn't discussed. If you have 0 infiltration and 0 sources then any filtration (>0 air changes/hour) will work . However, if a ventilation system is constantly pushing contaminated air in your office, you will have a hard time. The math says that if a particular person needs 10 filtration air changes with an infiltration rate of 0.1, then you need 25 if the infiltration rate is 0.25, to maintain the same particle levels.

-The same way you may install a 4-Ton A/C system in a house based on maximum likely need, you may want a 1000 clean room capability. Replace 1000 by X depending on the individual and local conditions. I submit to you that nobody knows how many people would need a 1000 clean room level to remove allergy symptoms without medication, and that any guesses would grossly underestimate it. At this point it's a matter of opinion based on anecdotal evidence. Studies on the health benefits of air purifiers would probably find greater effects if they attempted to attain 1000 clean room levels... I find it interesting that there's one air purifier claiming an effect similar to 1200 air changes by creating a localized clean zone over the head of your bed. It might be a good one to use in such a study...

I'm looking forward to your post.

[pmeunier]

Zappy, sorry for hijacking your thread. However I have a conclusion which may help or give you a sense of perspective. I'm thinking... If you are a strongly allergic person living in a home with more than 1 ACH infiltration, move to a better constructed house or be prepared to invest considerable time and effort tightening it. I'm convinced that operating an air purifier in a loose home is ineffective and a waste of money.

Regards

[breathe easy]

pm
Game was a romp. Unfortunately, the Rangers were the rompee.

You are absolutely correct about allergies being additive or cummulative. Once your body encounters an allergic substance it goes into defense mode and creates a chemical called IgE. This stays in your system for quite some time. The more allergens you encounter the higher the IgE. IgE is what sets off the runny nose, watery eyes, inflammation, etc. of the allergy sufferer.

The idea of allergen avoidance is to reduce the levels of IgE in the system and thereby decrease the chances of feeling miserable. On the other hand people do not want to live in a bubble.

I am not quite sure how you did the ACH math. I guess you are subtracting the air infiltration. Otherwise I would come up a figure more like 5.1 ACH at 0.3 microns. (.3X17)

Again I am pressed for time. So let me respond to some of your points with some quotes from an article I wrote last year for an indoor air publication on the subject of air cleaners and health effects.

On the cat allergen study:

A commonly cited medical study on the effectiveness of air cleaners on allergies and asthma was conducted by R. A. Wood, et. al. entitled “A Placebo Controlled Trial of a HEPA Air Cleaner in the Treatment of Cat Allergy,” published in the American Journal of Respiratory Care Medicine (Vol. 158, pp 115-120, 1998). In this study the researchers used a double-blind, placebo controlled protocol to determine the effects of a HEPA air cleaner in the bedroom of cat-allergic patients who kept one or more cats in their homes. This 3-month study included 35 subjects with allergies to cat dander. (All patients had positive skin tests to at least one other allergen.) A stand-alone HEPA air purifier was placed in the bedroom of all subjects. The “active” test group had a filter in their air cleaner while the placebo group used their air cleaner with no filter. All patients encased their pillows and beds in allergen proof encasements. Even though the allergy and asthma symptoms when measured by respiratory function and markers of allergic reactions decreased in all subjects, there was no measurable difference between the active group with the functioning HEPA air purifier and the placebo control group.
What is very interesting is that we know that products like HEPA air purifiers will reduce particle counts and exposure to airborne allergens and irritants. In fact, the researchers in the above mentioned study found significant decreases in cat allergen in the active HEPA air filter group. In tests we have conducted we have found that a HEPA air filter in a room with the door closed can reduce particle counts by up to 90%.
So why do we see this phenomenon – significantly decreased particle counts and no measurable improvement in allergy and asthma symptoms? To answer this question we talked with Allergist Dr. Robert Rogers, MD of Fort Worth, Texas.
“There are several things that can account for the fact that despite a decrease in allergens in the air in their bedrooms the patients in the study found no decrease in their allergy and asthma markers.
First, people are often allergic to more than one substance. Dealing with just cat allergen may not produce any measurable results when these people might also be allergic to dust mite, cockroach, rodent and other allergens.
Secondly, many people with allergies to cat dander have very low allergen thresholds. Even very significant decreases in exposure may not be sufficient to produce the desired outcomes.
Thirdly, cat allergen is very pervasive. It is relatively small and light. Consequently it stays in the air for an extended period of time. It is also ‘sticky’ so it adheres to walls, carpets and furniture. While the exposure to cat allergen in the air in the bedroom was significant, these patients were also receiving contact with cat allergen in other areas of their houses.
Fourthly, cat allergen stays around for a long time. We have seen high levels of cat allergen in homes 6 months after all cats have been removed. In this study almost all of the bedrooms were carpeted and no special cleaning was conducted to remove cat allergen from the bedrooms before the start of the tests. It is likely that there was a significant amount of residual cat allergen stirred up by vacuuming, walking on the carpeting and using the furniture in the bedrooms.”

Dr. Roger’s first point is very important. Very few people are allergic to just one substance. For example, most people with allergies are allergic to dust mite proteins. Dust mites are found in beds, pillows, upholstered furniture and carpeting. Dust mite allergens (feces) are relatively big (over 10 micrometers) so they settle out of the air quickly. The chances of pulling dust mite feces from the air with an air cleaner or air filter are very small. They just do not stay in the air long enough. More importantly, air cleaners and air filters are very inefficient at stopping dust mite allergen from going from a pillow or bed to the breathing zone of the allergic person.
Dr. James Sublett, MD of Louisville, Kentucky in a recent presentation at the Healthy Indoor Environment Conference of the American College of Allergy, Asthma and Immunology said that the above study as well as others that were designed to assess the effectiveness of “cleaner air” on improving allergy and asthma symptoms had similar limitations. All used small study populations and limited environmental interventions. Most did not use sufficient clinical measurements such as bronchial hyperreactivity and inflammatory markers. All were of insufficient duration. According to Dr. Sublett a few months is not long enough. These types of studies should be conducted for 12 months to 24 months or longer.


On the need for a comprehensive allergen avoidance approach:

This brings us to some major recent research on controlling asthma and allergies through environmental interventions (including HEPA air cleaners). In September of 2004 a paper was published in the New England Journal of Medicine entitled “Results of a home-based environmental intervention among urban children with asthma. Inner-City Asthma Study Group (Morgan WJ, Crain EF, Gruchalla RS, et. al.) In this paper the authors summarize the results of their well designed, multi-year study on allergen avoidance.
The study, co-funded by the National Institute of Allergy and Infectious Diseases (NIAID) and the National Institute of Environmental Health Sciences (NIEHS), involved over 900 children between the ages of 5 and 11 in seven major metropolitan areas. Study participants had suffered at least one asthma-related hospitalization or two asthma-related unscheduled doctor visits the six months prior to enrollment in the study. They also had a positive allergy skin test to at least one of 11 indoor allergens such as dust mites, molds, cockroaches, pets or rodents.
The patients were given an initial evaluation through questionnaires on asthma symptoms, medication use and an analysis of the home environment. The “active” families were then taught how to reduce allergens in their homes, told why it was necessary and given the needed tools to accomplish the task. These tools consisted of allergen impermeable encasements for their beds and pillows, a vacuum cleaner with a HEPA filter, professional extermination of cockroaches and rodents, repair of any water leaks or infiltration and a HEPA air purifier for the child’s bedroom. The study was conducted for one intervention year and one additional year. Researchers followed up by phone and collected information about the child's asthma every few months during the study. The “control” group was given standard medical care without specific home environmental interventions.
The results of this study were remarkable. The children living in homes with these simple environmental controls had an average of 21 fewer days of symptoms in the first year and an average of 16 fewer days during the follow-up year. In addition, the benefits of the intervention occurred rapidly. Investigators noted significant reductions in symptoms just 2 months after the study began.
While it is true that air cleaners alone have not been shown to be effective at reducing allergy and asthma symptoms, this study confirms that HEPA air cleaners, when used as a part of a comprehensive program of environmental controls, are very beneficial. In fact, the improvement in symptoms of the asthmatic children in the study was comparable to the use of inhaled corticosteroids. It not only worked. It worked as effectively as the most advanced medications - with no side-effects!

By the way I participated in the Dallas component of the Inner City Asthma Study by supplying the mattress and pillow encasements. I also trained the workers who visited the homes of the asthmatic children.

Another point about sub-micron sized allergen fragments. I have talked with a number of allergists on this point. The consensus is that they could have an effect on the allergic person. However, the reaction to allergens is dose responsive ie. the greater the mass of the allergen particle the greater the allergic reaction. Thus by eliminating the larger particles one may be achieving close to the same results for the moderately allergic person.

[pmeunier]

Thanks BE. Great point about the goal being the removal of the mass of allergens, and not directly the number of particles carrying them. OK, so we are referencing the same study. Dr. Rogers' explanation is helpful and makes sense. Perhaps the low allergen thresholds can be explained without invoking a different biological response or a special property of the protein itself, but simply because more of the cat allergen makes it into the lungs and sinuses, as it is more readily airborne than others -- it's mostly the delivery mechanism.

For the air changes I simply transformed A = F I/E into I = AE/F where F is the reduction in particle counts@size (2.5), I is the infiltration rate in air changes and E is the efficiency of the filter @size (0.35) and A is the filtered air changes (17).

It's very cool that you participated in the Inner City Asthma Study!

Edit: You are calculating the filtered air changes. I was calculating the "equivalent dirty air changes" you're fighting (converting all sources in your office to an equivalent influx of dirty air):
I = 17 * 0.3 * 282/840 = 1.7 @0.3 microns (earlier I was attempting to calculate at 0.5 microns)

[zappy]

Wow, so glad you guys joined this thread. I have learned a ton!

I did purchase a Honeywell air purifier (like the following although my model is a 50300)

http://www.amazon.com/Honeywell-Perm...ref=pd_sbs_k_1

It was about $150 and I didn't expect much so I was happy to find that after a couple days of running 24/7 (high speed all day and then low during the night) the bedroom is now a place of comfort. On the 3rd morning there was very little allergy symptom present on waking. This is a HUGE win!

The main downside is the noise when the unit is on high (where it moves some major air).

Do air purifiers make rooms a bit warmer when run 24/7?

If anyone has any specific models they like please suggest them as we'll be considering units for a few more rooms.

Also, what is this particle counting device mentioned above? Where can I gett one?

[zappy]

I think you looked at an old report. The one you want is the December 2007 one:

http://www.arb.ca.gov/research/indoor/cr-12-2007.pdf

That that is the same report with the top 2 rated units that have been discontinued (at least as far as I can tell by searching for them).