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re: envirosept furnace filter
5 jun 2005
stretch  wrote:

>...the envirosept uses a power supply and media,

yes. less than 2 watts at 7 kv...

>therefore produces o-zone as well high resistance media.

it does not produce ozone. i'm not sure what you mean by the rest.

>the electrostatic filters typically used arrestance test for
>efficiency, which has a large particle size dust for testing.

here's a basic comparison. "electrostatic" below means honeywell
types with fine wires with a high voltage and no charged media: 

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

>the media filters typically use dust spot test as opposed to arrestance
>test used by electrostatic filters.

i think we are comparing apples to apples above.

>electrostatic filters don't work well below about 300 feet per minute
>air velocity, because they don't develope a charge below that air speed.

i think those "electrostatic filters" are different animals, with no
power supplies. the expensive honeywell types above work better with 
lower flow rates and longer residence times. 

>the combination filters like envirosept and dynamic are the worst of
>both worlfs.  they have media which has high resistance to air flow
>needs and replaced periodically $$$, and they produce ozone.

the envirosept doesn't. iirc, the filters cost about $1. i wish they made
a washable filter. that would be a better worlf.

> should get a flow hood and a differential pressure gauge and
>test the results before you recommend them to anyone.

again, here's the envirosept spec:

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

it's designed to slip into the same space as a passive filter. how do these
pressure drops compare to passive filters and typical duct pressure losses?

>as an option, put two filter grilles side by side, due to the fan laws,
>since the velocity is 1/2, the pressure drop will be only 1/4 (the square
>of the change).  then the envirosept becomes a more interesting concept.

from the spec above, the fan laws may fit fans better than filters. for
instance, 300 lfm is 2x 150, but dp = 3 vs 4x.

and maybe most blowers can handle higher pressures, or the duct and register 
losses are a lot larger than filter losses, so the filter loss doesn't matter
much. i know envirosept's father mike putro, who is one smart cookie, and
honest as well. he's been selling these filters for about 10 years. a larger
housing might be difficult to make, as well as unnecessary.

>...half of the systems that i measure have air flow of 200 cfm/ ton
>instead of the 400 cfm/ton they should have.  hence my dislike of high
>efficiency/high resistance filters that reduce air flow another 10% to 20%.

which bodily orifice produced your 10-20%? :-) imo, most modern acs cool
too much and dehum too little, wasting too much electrical energy in the
blower and too much heat energy through the walls. a fountain or mister
or perspiring human can help distribute coolth to occupied rooms more
dynamically, with less heat gain from the outdoors...


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