On Fri, 10 Feb 2012 21:07:17 -0800, mike wrote:

On 2/10/2012 6:23 PM, wrote:
On Fri, 10 Feb 2012 13:41:57 -0800, wrote:

On 2/10/2012 11:31 AM, radiotom wrote:
Tony Hwang;2799305 Wrote:
mike wrote:-
My 95.5% Gas furnace came with a fiberglass air filter
with little restriction and no filtering action.

I substituted a Filtrete allergy reduction filter and went
about my business. Been running that way for 2 years.

In my filter search today, I found a gauge that tells you when
to change the filter by monitoring negative pressure
near the blower inlet. It says it can be calibrated
for 0-.4"WC.

I did some measurements on my system.
With the filter removed and the filter door open,
I measured -0.1"WC.
I measured with my Filtrete installed and with a
lesser MERV9, I think, filter then a washable
permanent electrostatic filter.
All measured -.55"WC.
With the filter access door closed, it goes up
to -0.6"WC.
That's outside the calibration range of the filter
monitor gauge, so it got me thinking.
I don't have a fiberglass filter to compare.

I also measured some temperatures.
With indoor temperature at 65F, the air coming out
of the closest vent stabilizes at 119F. It's about
12' from the furnace and the ducts are insulated,
so it should be somewhere near the furnace output
temperature.

Looks like I'm getting 60F rise across the furnace.
That's near the max claimed in the spec.

Another thing is that I don't heat part of the house.
Three registers are closed. Last time I did the experiment,
heating the whole house cost me almost 50% more in gas.

So,
I don't want to heat the whole house.
I need the better air filters.
Should I worry about overheating the furnace?
Is there anything simple I can to about it?
Like turn up the blower speed?

I do have an electronic filter that's designed to replace
the 1" paper filter. I'd have to cut it down to fit.
Looks like it has about as much material as the original
fiberglass filter, so should have lower pressure drop.

Is that a viable alternative?
It's not clear how they compare at removing pollen.
It's hard to decide based on the vague marketing hype.

Thanks mike.-
Hi,
I think you should do the measurement with all the registers open.
I use EAC only on our furnace. I clean the elements twice a year.

I can't really comment on your questions but you've got me thinking. I
too use Filtrete filters. I think maybe I should get one of those
gauges. Never even occurred to me. Wonder how much I'm wasting.

Those gauges can be useful for people who don't have a calendar and a
pencil.
You can do the same measurement with some plastic tubing and water.
Google "manometer". Once you figure out how long a filter lasts
in your situation, just mark the calendar to change it.

While there's no question that moving air costs money and friction
adds to that, I've never seen any apples-to apples numbers that
support how much.

In any given situation, you have the ratio of the BTU's in the
gas supply to the BTU's that end up as heat in the dwelling.
For small changes in back pressure, I don't expect that ratio
to change much. The blower may use more power...I'd like to hear
some real numbers on that. Next time I have the cabinet open, I'm gonna
stick a current meter on the blower power and try it with and without
the air filter installed. Just gotta figure out how to read the meter
through the metal door.

The vendors for low restriction filters and gauges use all sorts
of marketing speak and misdirection to induce you to buy their stuff.
They throw the apples and oranges into the mix and claim it's proof.

Here's what I think I know about filters. I'm sure people won't
be shy about correcting my misconceptions.

For a simple, passive filter, the size of the particles that can be
trapped is determined by the pore size of the filter. As the pores
get smaller, you can put more pores in the same space. But the filter
material has some minimum fiber dimension. At some point, you're
down to one fiber width between pores and you can't fit any more in.
And there are significant friction effects as the pores get smaller.

Pressure goes up for smaller pores, so you have to have more surface area.
Pleating is the first thing to do, but even that has it's limits.
You can make the filter as large as will fit in the cabinet, but
that has limits too. Smaller pores plug up faster.

Making the media thicker doesn't help. To reduce pressure, you'd
have to make the pores even bigger and not be able to trap the small stuff.
Thicker filters can accommodate bigger pleats of the thin media
resulting in larger surface area.

The solution to this diminishing returns situation is to use
technology that traps particles in a way unrelated to their size.
Electronic filters use an electric field to force particles to displace
out of the air stream and collect on a plate.
The electric field has little effect on the air stream, so pressure
rise is minimal.
This also has tradeoffs, so you usually end up with a passive filter
for the big stuff and the electric field for the stuff that gets thru.

Now, back to the question that I started in another thread.
There is a technology that uses an electric field that does not require
external power.
I thought the field was created by the triboelectric effect of air
passing through insulating media. The only response to that was
the rude statement that, "my education was faulty," but no real
useful help was provided.
The other theory presented was that the electric field was permanently
installed
at the time of manufacture. That was debunked.


They are called ELECTROSTATIC filters. They are not electronic - and
they DO work on the electrostatic charge built up by the air flowing
through them.. Don't know if triboelectric is the correct term or not
- but the darn things work pretty well and are quite low resistance.
And they fit directly in place of the 1 inch cheap folded paper or the
even cheaper tangled string filters.

What measurement techniques did you use to determine that "they work
pretty well"? I'm interested in pollen capture.
I cut one down to 64 square inches and stuck it on an experimental Heat
recovery ventilator. Put about 20 CFM through it. Velocity is pretty low,
so I'd like some info on performance vs air velocity that's creating the
electrostatic field. Also wonder how humidity affects it.
If you have any links to actual, unbiased engineering tests, I'd like
them. If there's an electric field in there, I should be able to detect it.
So far, I've not been able to do that. Exactly where is the field
supposed to be?

A particle counter ought to be able to verify performance instantly.
If that could show that they work, you'd think the vendors would publish
that video alongside their flashy videos of marketing speak.

I can't give you any quantitative data, but there is a LOT less fine
dust in the house and I hardly ever need my athsma medication any
more.. When I wash the filter there is a lot of REAL FINE dirt.