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re: envirosept furnace filter
6 jun 2005
stretch  wrote:

>some clarifications, using industry standard nomenclature, so that we
>are speaking the same language:

good. the first 3 rules of philosophy are "clarify, clarify, clarify."

>"here's a basic comparison. "electrostatic" below means honeywell
>types with fine wires with a high voltage and no charged media:"
>the filters that use electricity to charge plates or media are normally
>called electronic air filters in the trade.

i also think "electrostatic precipitator."

>while they don't use much electricity, the power output is usually several
>thousand to as high as ten thousand volts.

maybe higher. i built one years ago with a 1b3 and a tv flyback transformer.

>...the electronic air cleaners have very low resistance to air flow.
>if you want a high efficiency air filter, this is the way to go.

except for the price, cleaning task, zappy noises, and ozone... i'm not
sure they all produce ozone. the ionic breeze doesn't, altho it puts all
the dirt on the walls of the room :-) i put one inside a 12" grounded
stovepipe with a light bulb below to make some airflow, and it worked
as an electrostatic precipitator.
>...a 20 x 20 fiberglass filter at 800 cfm has a pressure drop of .08"wg.


>the net opening of that filter is 18" x 18", or 2.25 sq. ft...
>800 cfm/2.25 sq. ft. = 355 linear feet per minute (fpm).  compare this
>to the envirosept pressure drop of .22" at 375 fpm.  at very close
>velocities, the envirosept filter has a pressure drop of just under 3
>times that of the fiberglass filter.

i wonder how important that is, given some blower overcapacity and
the rest of the pressure losses in the duct/register/plenum system.
what's a typical total?

grainger's 5c092 direct drive furnace blower (with a 9.5" 1075 rpm wheel
and a 1/4 hp motor) is rated 1529 cfm at 0.3" sp, 1517 at 0.4, 1483 at 0.5,
1416 at 0.6, 1326 at 0.7, 926 at 0.8, and 397 at 0.9. adding 0.22-0.08
= 0.14" wouldn't make much difference over the low part of that range. 

>the fan laws apply to fans, duct systems and coils.  i have also found
>it to be very close with air filters that i have tested.

not the envirosept, with 3x vs the fan-law 4x pressure drop at 2x flow.
we also need to consider the operating point on the blower curve, imo.

>i am not pulling these numbers out of any body oriface as you suggest.

they don't seem unreasonable. if the blower above is working in the middle
of its range at 0.6" and 1416 cfm and we add 0.14", the output might drop
to 1326-(0.74-0.7)/0.1(1326-926) = 1166 vs 1416 cfm... 18% less.

>as to ac systems cooling too much and dehumidifying too little, i agree
>there.  paying attention to load calculations and proper air flow would
>help tremendously.  most ac systems dehumidify best at air flows of 350
>to 400 cubic feet per minute (cfm) per ton.

seems to me they could dehumidify better and better at lower velocities.

>...the vs blower will speed up as the filter loads up, producing nearly
>the same air flow at different filter pressure drops.

sounds like a fix for the perils of pressure drop. 

>...i would not recomment using a "mister"... here in south carolina.

i might, in conjuction with a low-flow ac that mainly dehumidifies.
you might think of this as an alternative to variable air volume, or
"dynamic balancing," with less blower power and duct and house heat
losses. why cool a room if nobody's in it? a little misting can lower
the air temp in an occupied room while the rest of the house air is
warmer and drier, with less coolth moving out through the walls. 

>it might work wellin your climate up in mass though.

i'm near phila. we only need home ac for 1-2 weeks per year mostly in our
tropical august climate when night temps and rhs stay over 70 f and 70%. 
even then, ceiling fans are a good alternative.

>by the way #2:  what the heck is coolth??

the opposite of heat. it's equally ambiguous, since it can mean a flow
(heat power in btu/h) or a quantity of energy (stored heat in btu). 
coolth flows from cooler to warmer objects. google shows lots of use.


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