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re: do air purifiers/ionizers work?
14 apr 2002
lvs2write   wrote:

>from what i've read online, hepa filters are great, but only filter
>down to a level that still allows pollen and most allergens to get
>through. so then i read about negative ion purifiers
>( which claim to work better, cost less money to
>operate and take care of those things that are too small for hepa filters. 

negative ion generators have an unfortunate habit of blackening room
walls as they deposit particles. we might overcome this by mounting
one near the bottom of a 2' length of 12" grounded stovepipe, with
a small light bulb below to ensure an updraft. 

the essa electronic filter made by aqua-air technologies, (410) 489-5288,
comes in 14 standard sizes and slips in place of a normal air filter in
a forced air heating system. it has a retail price of about $200. it's an
inch thick, and it uses three metal screens with two filter pads between
the screens. the center screen has a potential of 7,000 vdc, and the outer
two are grounded. the filter pads cost about a dollar, and need replacing
about every two months. the device comes with a small 110-24v transformer
which plugs into a wall socket, and the power consumption is listed as
24vac at 1.6 va, i. e. less than 2 watts. 

here is the basic filter performance:

typical ambient particle                
size distribution (in microns) per m^3       particle removal rates 
                       % by    % by          electrostatic   essa
size (um.)   count     count   weight        ($800-1200)     ($200)

10+          1,000     .005%   28%  xxx x    99%             99+%
5-10        35,000     .175%   52%    x x    95%             99+%
1-5        264,000    1.32%    17%    x x    85%             99+%
.5-1     1,352,000    6.78%     2%    xxx    60%             90+%
.01-.5  18,280,000   91.72%     1%    xxx    40%             65%

                                    |||||_ bacteria/viruses/spores
                                    ||||_ cooking/tobacco smoke
                                    |||_ household dust
                                    ||_ pollen/mold/spores
                                    |_ dander/hair

average synthetic dust weight arrestance: 79%.

single pass efficiency: 33% @0.3 um, 75% @0.5 um, 95% @1 um, 99% @3 um.

pressure drop: 0.05" @150 lfm, 0.1" @225 lfm, 0.15" @300 lfm, 0.22" @375 lfm.

ashrae dust holding capacity: 20 gm/ft^2.

it does not produce ozone, and never zaps.

aqua air also make a stand-alone console model with built-in fan,
prefilter and charcoal filter. one lower-cost way to do this is
to buy a $15 20" box fan and mount their 20" essa filter on the
suction side with some aluminum channel or duct tape...


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