When I was teenager I developed really bad allergies.
My post about protecting a LCD monitor screen from
heavy dust, started me thinking again about all these
residential air filtration devices.
The dust collection system I have in my own shop
is big, noisy, and just plain ugly! If you visit an
attractive wood shop, they often hide the collector
behind a partition or in a closet. The one thing they
all have in common is tremendous power. The bigger
ones could tear the skin off your body, or fracture
a bone if you are unfortunate enough to come in
direct contact with the suction end of the motor.
During my years as an HVAC contractor I was always
on the lookout for really effective dust trappers for
the home. (With my dust allergies, I had a very personal
interest in this subject.) If my customers were concerned
about dust control, I would usually install an electrostatic
filter in the central heating and ac duct. The filter itself
was a woven metal grid. It looked a lot like those woven
sisal door mats. A 5000 volt transfromer created the
static charge across the mat. I put one in my own home
too. They lasted about five years, if you were lucky. The
transformer would fail or the filter would short out.
In my master bedroom (with attached bathroom) I've tried
a Honeywell drum style HEPA machine, and one of those
tower or vertical units that passes high voltage (miniscule
amperage) through a series of thin metal plates. When
charged up, a small convection current causes air to flow
through the plates. Both units claimed they could handle
a room with square footage greater than my bedroom. I
gave each unit a one week test. They ran continuously
with the bedroom door and windows shut. When I checked
the HEPA filter or metal stack you could barely see any
dust. In other words, they simply do not work. Incredibly,
millions of allergy sufferers swear they work great.
As far as I know, there are only two ways to drastically
reduce the amount of dust in a room. Use a commercial
dust collector that sounds like a small jet engine, or drop
the room pressure a fraction below the normal 14.7 psi
and pump in fresh filtered air from the outside. The latter
is usually found in "clean rooms" or chip foundries where
the slightest amount of dust could cost millions.
I know allergists recommend the HEPA type machine to
their patients. Mine did. I'd own ten of these HEPA units
if I felt the slightest reduction in my allergy symptoms!
If you take a cup of sawdust and sprinkle it in front of
a powerful shopvac you'd be lucky if half the dust got
sucked into the drum. To me, this is the staggering
contradiction about all residential dust collection. These
devices are wowfully under powered. The manufacturers
have no choice. A loud (and powerful) blower, or a massive
high voltage device that buzzed like a shorted lamp cord
would not work in a residential setting!
I have to admit I haven't kept up with any new technology
that might be employed to collect household dust. If you
know about something new and wonderful, for goodness
sakes tell me right away!
Why Don't HEPA & Electrostatic Dust Trappers Work?
-
Robert Reed
- Posts: 2277
- Joined: Wed Nov 24, 2004 1:01 am
- Location: ASHTABULA,OHIO
- Contact:
You might try different types of filters in series, and check for good seals to keep air where it is supposed to be. Regular filter, Hepa filter, then Ulpa filter; maybe even a Sulpa.
http://ateam.lbl.gov/Design-Guide/DGHtm ... ilters.htm
http://ateam.lbl.gov/Design-Guide/DGHtm ... ilters.htm
I inherited an "Ionic Breeze" air purifier. It's in a room about 16'X20', and has to be cleaned every 2 weeks or so. It shuts down when overloaded. I run it while I'm out, 8-10 hours/day, and the room does "smell" different-clean as in ozonated.
Perhaps the unit you tried was defective?
As for a HEPA unit, you have to move all of the room air through it to filter, and that takes a large air mover.
Any consideration of "conditioning" the air in a room has to take into account the rate at which particles are being generated. An empty room will eventually become clean, but the more activity, the more generated particles.
Perhaps the unit you tried was defective?
As for a HEPA unit, you have to move all of the room air through it to filter, and that takes a large air mover.
Any consideration of "conditioning" the air in a room has to take into account the rate at which particles are being generated. An empty room will eventually become clean, but the more activity, the more generated particles.
WA2RBA
Well, since moving air is the nature of sound, its natural to expect that any appliance that moves more air will have more noise. Unfortunately if you want cleanest air you have to move a lot of air through a small hole (or a bunch of tiny holes rather).
A shop vac or shop dust collection system has somewhat of a different job than an air purifier. They operate under similar principals but at drastically different operating points. A shop collection system is designed to move dense collections of dust (and sometimes larger chunks of cuttings) from specific locations while an air purifier has to remove miniscule amounts of dust from a huge volume. Some dust collection systems use a vortex to separate the air from derbris but this is inefficient and very noisy for general air purification (think Dysan). Add to that that sawdust is much larger than house dust on average.
A clean room is under positive pressure. Air handlers with HEPA filters clean a mix or recirculated and fresh air and inject it into the room. The positive pressure prevents any unfiltered outside air from entering the space. Clean air along with any would be dust are blown out continuously. That plus strict rules about what can enter the room keep it clean. Unless you plan to don a bunny suit, paint everything glossy and prohibit most everything from the house, this is impractical.
A fume hood is under negative pressure, the chimney sucks air up and through the hood area evacuating fumes out of the room. A clean room bench is just the opposite with filtered air coming down over the work area and blowing dust out of the hood and back into the room.
Clean room workers often suffer allergy like symptoms outside the workplace due to not being used to allergins and loosing their resistance
I would suggest a mix of electrostatic cleaner and bulk filtering with carbon inserts for the best air (I like the Oreck because it has both and several fan speeds from silent to roaring). Preventative maintenance in the form of replacement filters and cleaning collector plates is essential. An electrostatic filter should not be left until it fails but cleaned or replaced yearly according to its instructions.
Ozone alone does not clean the air but it kills anything living in it like dust mites and mold spores. In many cases, it shatters the cells and DNA. It still may allow protiens to exist so allergies are not totally eliminated
Can only speculate on why a HEPA would not work well for your allergies. Anything from inadequate maintenance to wrong cure comes to mind. It's usually just not any old dust that causes allergies, most dust is essentially inert but dust from living things which contains protiens is what treiggers histimine reactions. Otherwise its just usually mucosal irritation. Position of a filter can effect its efficiency too, its possible to create an eddie of air which mixes little with the rest of the room.
A good (subjective) way to count particles in the air is to observe a photo flash perpendicular to the beam. Could probably actually photograph the dust in 1 square meter and use S/W to count the dots as a way to objectively gauge air quality. This of course says little of the composition of the dust.
A shop vac or shop dust collection system has somewhat of a different job than an air purifier. They operate under similar principals but at drastically different operating points. A shop collection system is designed to move dense collections of dust (and sometimes larger chunks of cuttings) from specific locations while an air purifier has to remove miniscule amounts of dust from a huge volume. Some dust collection systems use a vortex to separate the air from derbris but this is inefficient and very noisy for general air purification (think Dysan). Add to that that sawdust is much larger than house dust on average.
A clean room is under positive pressure. Air handlers with HEPA filters clean a mix or recirculated and fresh air and inject it into the room. The positive pressure prevents any unfiltered outside air from entering the space. Clean air along with any would be dust are blown out continuously. That plus strict rules about what can enter the room keep it clean. Unless you plan to don a bunny suit, paint everything glossy and prohibit most everything from the house, this is impractical.
A fume hood is under negative pressure, the chimney sucks air up and through the hood area evacuating fumes out of the room. A clean room bench is just the opposite with filtered air coming down over the work area and blowing dust out of the hood and back into the room.
Clean room workers often suffer allergy like symptoms outside the workplace due to not being used to allergins and loosing their resistance
I would suggest a mix of electrostatic cleaner and bulk filtering with carbon inserts for the best air (I like the Oreck because it has both and several fan speeds from silent to roaring). Preventative maintenance in the form of replacement filters and cleaning collector plates is essential. An electrostatic filter should not be left until it fails but cleaned or replaced yearly according to its instructions.
Ozone alone does not clean the air but it kills anything living in it like dust mites and mold spores. In many cases, it shatters the cells and DNA. It still may allow protiens to exist so allergies are not totally eliminated
Can only speculate on why a HEPA would not work well for your allergies. Anything from inadequate maintenance to wrong cure comes to mind. It's usually just not any old dust that causes allergies, most dust is essentially inert but dust from living things which contains protiens is what treiggers histimine reactions. Otherwise its just usually mucosal irritation. Position of a filter can effect its efficiency too, its possible to create an eddie of air which mixes little with the rest of the room.
A good (subjective) way to count particles in the air is to observe a photo flash perpendicular to the beam. Could probably actually photograph the dust in 1 square meter and use S/W to count the dots as a way to objectively gauge air quality. This of course says little of the composition of the dust.
Re: Why Don't HEPA & Electrostatic Dust Trappers Work?
Semi fabs and film processors, PCB shops, and otherrotatepod wrote: In my master bedroom (with attached bathroom) I've tried
a Honeywell drum style HEPA machine, and one of those
tower or vertical units that passes high voltage (miniscule
amperage) through a series of thin metal plates.
...
I gave each unit a one week test. They ran continuously
with the bedroom door and windows shut. When I checked
the HEPA filter or metal stack you could barely see any
dust.
...
Use a commercial
dust collector that sounds like a small jet engine, or drop
the room pressure a fraction below the normal 14.7 psi
and pump in fresh filtered air from the outside. The latter
is usually found in "clean rooms" or chip foundries
...
If you know about something new and wonderful, for
goodness sakes tell me right away!
low pollution areas use *positive* air pressure to force
the debris out of the clean room. The incoming air is
filtered to the desired class (particle size) first.
All materials (including humans) are cleared of dust
in an airlock and/or air shower. All visitors and inmates
wear "bunny suits" to keep personal debris out of the
clean room.
There are two types; Turbulent and laminar flow.
Turbulent causes small eddies to swirl pollutents,
laminar flow has a parallel down flow to force
pollutents from work areas to the lower exit vents.
Once established the clean room requires a period of
adjustment, while native debris is blown out. Only by
testing and regular monitoring can a clean room
remain clean.
By definition a clean room is only clean by ratio
of the particles of pollution to a reference (outside
space for example). Besides particles a clean
room also removes moisture and vapours. This
low humidy environment is a new problem, requiring
ESD handling or ionic 'anti-static' measures.
The debris is particulates. The cleaners are mechanical
(filter papers) not ionic breezes that may smell clean,
or electrostatic chargers that may attract and retain
insulator particles.
For relieve of a medical condition you should first
identify the irritant. It may not be necessary to filter
below a certain size, or the target might be a
chemical or specific material that can be delt with
by other means (trapping, ventilation, electrostatic
scrubbing).
To convert a bedroom to a clean room would be
somewhat difficult without a separate positive air
handler, filter, and air lock to the rest of the home.
Plus, most of the materials in a bedroom produce
pollutants (fibres, fabrics, naked humans).
Here's some of what I have done along these lines.
In my early 20s I started to be allergic to dust / pollen. I bought a real electronic air cleaner. Something like Grainger 5C417. It was almost 30 years ago, so it wasn't this exact unit. It has a stack of aluminum plates, set up with opposite charge polarity on every other one, and a set of corona wires that charge the air on it's way in. It has a very quiet fan.
It made enough Ozone to smell, like after a thunderstorm. This is bad. It's the same as smog. I modified the power supply to reduce the voltage, and the fan to run at a slower RPM (with a more efficient motor also). I had to wash (dishwasher) the dust collector plates about once per month.
It helped. So does air conditioning. I also set up a central vac system. I got an Ametek Bypass Vacuum Motor/Blower. This has an output for the dust, not just let it blow through the motor like 99% of regular vacuume cleaner blowers. The output of the blower goes through a short pipe to the outside, returning the dust to where it came from. On the intake side, I made a cyclonic seperator to trap the bigger dust, hair, etc. The seperator is made from 2 metal 5 gallon pails. I've used it to clean the ash from my coal stove (even hot) dust collection from radial arm saw, sanders, routers, etc. With the radial arm, it doesn't get all of the dust, mostly due to the gaurds, etc. not enclosed enough. My router table is pretty dust free. The sander is very good - it probably gets 95% of the dust. I can sand sheetrock all day, never loose suction power. With an extra 5 gallon pail set up as a water trap, I've vacuumed up water. It is more powerful that many shop vacs. If I remeber correctly, the motor is rated at 12Amps, and it can lift 110" of water.
For many years, the combination of all that was all i needed. About half way through building our house, I got so alergic to pollen I coud barely work outside. I got a prescription for Nasonex. No problems any more.
In my early 20s I started to be allergic to dust / pollen. I bought a real electronic air cleaner. Something like Grainger 5C417. It was almost 30 years ago, so it wasn't this exact unit. It has a stack of aluminum plates, set up with opposite charge polarity on every other one, and a set of corona wires that charge the air on it's way in. It has a very quiet fan.
It made enough Ozone to smell, like after a thunderstorm. This is bad. It's the same as smog. I modified the power supply to reduce the voltage, and the fan to run at a slower RPM (with a more efficient motor also). I had to wash (dishwasher) the dust collector plates about once per month.
It helped. So does air conditioning. I also set up a central vac system. I got an Ametek Bypass Vacuum Motor/Blower. This has an output for the dust, not just let it blow through the motor like 99% of regular vacuume cleaner blowers. The output of the blower goes through a short pipe to the outside, returning the dust to where it came from. On the intake side, I made a cyclonic seperator to trap the bigger dust, hair, etc. The seperator is made from 2 metal 5 gallon pails. I've used it to clean the ash from my coal stove (even hot) dust collection from radial arm saw, sanders, routers, etc. With the radial arm, it doesn't get all of the dust, mostly due to the gaurds, etc. not enclosed enough. My router table is pretty dust free. The sander is very good - it probably gets 95% of the dust. I can sand sheetrock all day, never loose suction power. With an extra 5 gallon pail set up as a water trap, I've vacuumed up water. It is more powerful that many shop vacs. If I remeber correctly, the motor is rated at 12Amps, and it can lift 110" of water.
For many years, the combination of all that was all i needed. About half way through building our house, I got so alergic to pollen I coud barely work outside. I got a prescription for Nasonex. No problems any more.
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