measuring air duct static pressure with a digital manometer

[rundawg]

Well... it seems to depend which way one learned TESP... I have heard it both ways.
I think we had this discussion somewhere before, I have forgotten the name of the thread though...

I sent you an email of a presentation I put together awhile back on TESP testing.

I would post it here, but I don't post technical info or manuals, in this "OPEN" forum.

If anyone else wants it, send me an email (address is in my profile).

Footnote:

Using a pitot tube in a residential application not only requires you to do math in public, but will require alot of straight duct, before and after the pitot tube, to get an accurate reading.

Even using the smaller static probes can give inaccurate readings because of turbulent airflow.

[cuervo]

I sent you an email of a presentation I put together awhile back on TESP testing.

I would post it here, but I don't post technical info or manuals, in this "OPEN" forum.

If anyone else wants it, send me an email (address is in my profile).

Footnote:

Using a pitot tube in a residential application not only requires you to do math in public, but will require alot of straight duct, before and after the pitot tube, to get an accurate reading.

Even using the smaller static probes can give inaccurate readings because of turbulent airflow.

Hey Rundawg, would you be able to send me this info also? Thanks!

[air1]

Has anyone tried to build their own flow hood and use a digital manometer with fpm display to measure airflow? I was thinking of a testo 510 and a 1'x1' square by 6" long piece of sheet metal duct with a pressure sensing grid. The grid would be 1/4" tubing with holes drilled to measure the velocity pressure and a second grid underneath the upper grid to measure the static pressure. Then attaching a homemade hood to the measuring assembly. You could even make the hood from cardboard to funnel the supply air.

[mark beiser]

Has anyone tried to build their own flow hood and use a digital manometer with fpm display to measure airflow? I was thinking of a testo 510 and a 1'x1' square by 6" long piece of sheet metal duct with a pressure sensing grid. The grid would be 1/4" tubing with holes drilled to measure the velocity pressure and a second grid underneath the upper grid to measure the static pressure. Then attaching a homemade hood to the measuring assembly. You could even make the hood from cardboard to funnel the supply air.

Old trick, works best with a vane anemometer.
Set the dimensions of the outlet of the box, and do an average velocity reading, the anemometer calculates the CFM.

On residential grills it can be quite accurate if you use a rectangular box, long enough for the turbulence to mostly settle, and are not choking the airflow down with the box.

If you look into how shockingly inaccurate the results from expensive flow hoods can be, you may come to a similar conclusion as other people have.
The anemometer traversing the outlet of a box method is at least as accurate as a $2000+ flow hood, probably more so if done properly.

[air1]

Old trick, works best with a vane anemometer.
Set the dimensions of the outlet of the box, and do an average velocity reading, the anemometer calculates the CFM.

On residential grills it can be quite accurate if you use a rectangular box, long enough for the turbulence to mostly settle, and are not choking the airflow down with the box.

If you look into how shockingly inaccurate the results from expensive flow hoods can be, you may come to a similar conclusion as other people have.
The anemometer traversing the outlet of a box method is at least as accurate as a $2000+ flow hood, probably more so if done properly.

So an anemometer would be better than a average of the velocity pressure?

[Hvac216]

Hey run dawg would you be able to send that to me too? Thanks.

[mark beiser]

So an anemometer would be better than a average of the velocity pressure?

Absolutely, because a traverse with an anemometer is a direct measurement of the average air velocity, so there is only one step to calculating the CFM.
With a vane anemometer, no corrections for air density are needed either.

You can do it with a pitot tube and manometer, but then you have to convert velocity pressure to velocity, with associated air density corrections, for each measurement point, average them, then calculate CFM.
The measurements are also MUCH more subject to error due to turbulence than using a vane anemometer.

[air1]

Absolutely, because a traverse with an anemometer is a direct measurement of the average air velocity, so there is only one step to calculating the CFM.
With a vane anemometer, no corrections for air density are needed either.

You can do it with a pitot tube and manometer, but then you have to convert velocity pressure to velocity, with associated air density corrections, for each measurement point, average them, then calculate CFM.
The measurements are also MUCH more subject to error due to turbulence than using a vane anemometer.

I was thinking of using a "velogrid" arrangement. A velogrid is effectively a pitot tube that mesures velocity pressures at multiple locations simultaneously. The result is an average velocity pressure of the area being measured. Connecting the velogrid to a Testo 510 would convert the velocity pressure to fpm and if the area is 1 sq. ft. the fpm would equal cfm. The testo 510 has air density compensation capabilities although I'm not sure how one would go about setting it.
I don't mean to be argumentative. I'm just trying to understand the why a anemometer is better. Personally, I've never trusted vane anemometers. Seems to me that a vane anemometer would be affected by friction caused by wear over time.

[rundawg]

Hey Rundawg, would you be able to send me this info also? Thanks!

I would need an email to do that.

Put an address in your profile, or send me an email (address is in my profile), and I will get it off to you.

[rundawg]

Hey Rundawg, would you be able to send me this info also? Thanks!

double post - sorry

[rundawg]

Hey run dawg would you be able to send that to me too? Thanks.

Check your email.

[cuervo]

I would need an email to do that.

Put an address in your profile, or send me an email (address is in my profile), and I will get it off to you.

Thanks for the info!

Here's a question............
If there's no way to pop a hole in the back of a residential furnace (walls or other restrictions) and evaporator coil is right above the furnace, is the limit hole (if centered) an option to take the TESP or is it still too much turbulence from the blower to get an accurate reading? I've never tried this myself.
Leaving the only choice to popping a hole into the evaporator coil casing.

[jrbenny]

I only drill a hole in the plenum above the coil. I use holes already in the furnace.

NCI has found that the average difference in pressure between the limit hole and bottom of the coil to be 0.04 IWC.

I measure return pressure in the thermostat wire hole or the fault code peep hole. Slide the filter out for filter pressure drop.

Easy breezy.