http://particlecounting.tumblr.com/post/55...iy-air-purifier



Comments?

An air purifier is basically just a fan + HEPA filter (and sometimes particle counter) right?

Thanks. Didn't of that.
But those are easy problems to solve. Stronger and bigger fans. Trap.
Anything else?

I am wondering because my Sharp is about 3 years old. I've used it very little, but it's a consumer grade device. And we all know about the models changing frequently, resulting in the needed HEPA fiilters no longer being available. If the current haze do not let up, the filter will soon get all clogged up, and I may have to hack and modify a filter that does not fit, to force it to go into an existing machine.

But really, I want 3 or 4 additional machines, and just can't afford to buy them all.

It's much worse than that. Even the same brand, wouldn't always fit different models. For consumer level air purifiers, they like the change the model every few years. Nothing wrong with that, if they want their machines up-to-date so as to better compete against other brands, it's perfectly fine. The problem is that they then stop making the filters for the older models. After a while, you have a perfectly working machine, except that you need to change the filter, and can't buy it anywhere.

As for compatible third party manufacturers ... there's probably just too much variety in shapes. What with all those different models, and the constant change of models and shapes.

This isn't my personal experience. Just what I read on the www. Our own machine is still on the original filter. But we're probably well past the 50% mark by now.

Some of the better machines sell for RM2k. At that level, there's plenty left over to get a good powerful fan.

They're big enough to clean an entire house? (500-1000 cubic meter).

I've seen suggestion of 4-6x per hour for light duty, and 8x per hour for medium duty. That equates to a space of 14-28 cubic meters at the most. Only one room.

Definitely not large enough for the whole house. And how many of us can afford to buy multiple units of this thing?

No HEPA filter = clean only large particulates.
With HEPA filter = even smell is also removed (eg finish eating nasi lemak, turn on filter, after a few minutes, there's no smell at all).

The cheap cheap ones will not have built in detectors.
Without the built in detector, you don't know if it is actually cleaning the air or not.
With the detector, it is easy to tell. Open the door, dirty outside air comes in, and you can see it on the panel. Stir fry some chili dish, and the detector indicate it.
Without the detector, you turn on the power, and the fan starts. Turn off the power, and the fan stops.
With the detector, I turn it on when I get home and the fan starts. When the air is clean, the fan stops automatically. If I open the outside door and dirty air comes in, the fan automatically starts up, and stops again when the air is clean. I only turn it off when I leave for work the next day.

The one I have also have this humidifier function as well. Which now that I have it, I don't think I need it. Only makes the machine more expensive. I never use it. The air isn't that dry because I do not run the air conditioner 24/7.

They generate ozone as a byproduct, correct?

"... all of the ESPs and ionizers tested produced ozone at levels that are below health-based standards for all the tests conducted. None of the devices produced ozone concentrations above 45 ppb during the face tests, and all produced room concentrations below 16 ppb in the room test. All of the devices examined produced less than 3 mg/hr of ozone. ...

Caution also is warranted because introduction of any amount of ozone into indoor spaces may result in increased levels of formaldehyde, ultrafine particles, and other pollutants due to the reaction of ozone with terpenes (fragrance compounds such as pinene and limonene) and other chemicals emitted from modern consumer products and building materials. Additionally, operation and maintenance practices of air cleaner owners have the potential to significantly impact the amount of ozone produced. Recent survey results indicate that most California air cleaner owners operate their indoor air cleaning devices continuously and year round; however, owners typically do not maintain their devices as instructed by the manufacturer. This can lead to excess ozone generation and greater ozone emissions than observed in the tests reported here. "

http://www.arb.ca.gov/research/indoor/esp_report.pdf
Evaluation of Ozone Emissions
From Portable Indoor Air Cleaners:
Electrostatic Precipitators and Ionizers

Isn't HPP an electrostatic device? Electrostatic air cleaners generate small amount of ozones as a byproduct. Does their literature mention some special mechanism to prevent the generation of ozone?

"Electrostatic air cleaners (sometimes known as electrostatic precipitators) are highly efficient filtration devices that use electrostatic attraction to remove fine particulate matter such as dust and cigarette smoke from the air. Electrostatic air cleaners ionize (or electrically charge) particles as incoming air is drawn over an electronic cell. The charged particles are then attracted to and trapped by a series of flat collector plates that are oppositely charged, with the particles literally “sticking” to the collection plates until they are manually removed.

Electrostatic air cleaners have two main drawbacks. First, they can produce ozone – a known lung irritant and asthma trigger. While many units produce negligible levels of ozone, there are some brands and models on the market that exceed government safety standards. They may also produce ultra-fine particles from the reaction of the ozone with indoor chemicals (e.g., those from household cleaning products, paints, flooring or carpeting) that some people are sensitive to."

http://www.modernalchemyair.com/technology/electrostatic/

Clean dust : look for HEPA filter
Fresh air : no such thing. Air purifiers only filter stuff from the air in the room. It cannot generate new air. For fresh air, either open a window or add an exhaust fan installed in reverse blowing fresh air in. But the air will only be as fresh as the air outside your window. If you're living next to a busy road, it wouldn't be very nice. No purifier can remove CO, NO, or whatever poison pumped out by vehicle exhausts. They only remove particulate matter, not gases. The only way to get fresh air is to live so high that you're actually above the city smog (which my own house used to be but isn't anymore, 12km from KL city center, and atop a small hill) or you relocate to a geographic position far enough in the countryside that you have fresh air outside your window.