Static pressure testing

[ch4man]

thx for the kind remarks. but trained and experienced are two different things. i took NCI class to better understand airflow issues, not to go and balace commercially...

as with most things, the more i learn the dumber i get......as in i really learn how much i dont know.

since my last post i went and measured air flow again on high speed and med low. tesp/blower curve= 950 cfm est( off chart, hi tesp) and 650 cfm.

return drop traverse with testo 416 on high and med low however= 1150 cfm and 960 cfm respectfully.... hmmm.

also checked face velocity at most supply registers, again very little change.


whiskey tango foxtrot

[DeHeatify]

I have also been playing with my system in taking measurements trying to learn.
I'm using a testo 410 and so far have been taking measurements at the returns and through an old humidifier hole in the return plenum.
I have a question about taking face velocity readings at the registers. what sizing should we be using for the grills? the measured size of the grill or the measured size of the whole assembly including the border around the grill. If I measure 6/ 13.5 grill area, should that really be 8/14. Also what if the holes aren't cut out well? And how do we know the free area of the grills? I have a house built in the 70's with old return grills. same goes for supply readings?
I guess it's always more accurate to do the readings at the plenums but I don't have $600 for a testo 416.
I have also found my readings way off from the blower performance charts.
I'll post some later.
Thanks, love the info on this site! Also finding that old saying true the more I learn the dumber I get.

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[DeHeatify]

Ok on my set cooling fan spd:
RABF: 0.19" RAAF: 0.55"
SABAC: 0.31" SAAAC: 0.15"
TESP: 0.86" Filter PD: 0.36" Coil PD: 0.16" dry coil.
Total area of returns:1.498sqft Total air flow at registers: 688 fpm Total CFM: 1030.624

Blower performance data for TESP @ 0.80" = 800CFM TESP @ 0.90" = 605CFM

Right now I feel like I must be doing something wrong....
I measured the airflow on low spd at the return drop and got 503FPM @ 2.014sqft = 1013.042CFM

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[rundawg]

Total area of returns:1.498sqft Total air flow at registers: 688 fpm Total CFM: 1030.624

Right now I feel like I must be doing something wrong....

Is this the area of the entire return grill, or the "Effective AREA" of the return air grill derived from manufacturer data?


Effective area, given the abbreviation Ak, is the area of the register, grille, or diffuser in square feet that is utilized by the air flowing through it.

[DeHeatify]

Is this the area of the entire return grill, or the "Effective AREA" of the return air grill derived from manufacturer data?


Effective area, given the abbreviation Ak, is the area of the register, grille, or diffuser in square feet that is utilized by the air flowing through it.

this was measured area of grill only * 0.70 as I have no idea how to obtain the grill data for these old grills and the holes arnt well cut out either. For example 8/31.5 is total grill size (edge to edge) I used [(5.25*29)/144]*0.70 = 0.739sqft (I rounded to 3 decimal places during calcs)

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[rundawg]

this was measured area of grill only * 0.70 as I have no idea how to obtain the grill data for these old grills and the holes arnt well cut out either. For example 8/31.5 is total grill size (edge to edge) I used [(5.25*29)/144]*0.70 = 0.739sqft (I rounded to 3 decimal places during calcs)

You might not be exact by using .70, but at least you got close to what the Effective Area might be.

As many have said, the blower performance data from the manufacture is usually a computer generation based on ideal conditions.

Static pressure tests can be inaccurate if there is turbulent airflow around the probe.

We usually place our probes near bends in the return drop/plenum, and very near the blower where laminar airflow is less than ideal, causing less than accurate results.

Then when we throw these TESP tests into a blower performance chart and come up with results that some times make us scratch our heads.

All I can say is that sometimes taking 2-3 tests in each location (moving the static probe to a slightly different location), then averaging the results, will result in a slightly more accurate test.

Yes I know, what a pain in the a**! But if one wants to use a blower chart, it will yield the best results.

[beenthere]

I don't see how that could be BT.

Because different size units sometimes share the same cabinet.

So it would seem that the PD would vary based on Cfm.

PD would be based on CFM through the filter. I think they use to test it at one CFM, and then extrapolate from there using fan laws without actually testing.

[beenthere]

thx for the kind remarks. but trained and experienced are two different things. i took NCI class to better understand airflow issues, not to go and balace commercially...

as with most things, the more i learn the dumber i get......as in i really learn how much i dont know.

since my last post i went and measured air flow again on high speed and med low. tesp/blower curve= 950 cfm est( off chart, hi tesp) and 650 cfm.

return drop traverse with testo 416 on high and med low however= 1150 cfm and 960 cfm respectfully.... hmmm.

also checked face velocity at most supply registers, again very little change.


whiskey tango foxtrot

Do you have section of the supply you can traverse.

You may have too much turbulence in the return area your traversing.

[Nytefog]

I checked the TESP of a two year system in a Toll Bro house today during a PM. I found the Supply SP 0.38" and the Return SP .77"! TESP was taken in heat mode. It's a five ton blower, 60kbtu condenser, and they only took the return from the right side (16X25). They put a box on the left side but never cut the return into it. It's installed in a small mech room with another furnace. They are going to have to remove the entire furnace to either install a return plenum or some how connect the return to the box on the left. These systems were installed so poorly it's a shame. Venting incorrect size, drains installed improperly, humidistat in the air stream on the return after the bypass humidifer...ect..

I'm surprised the limit is still functioning after two years of tripping on high temp....They called Tolls and they are sending someone to take care of it. I'm anxious to return to see whats been done.

[ch4man]

Do you have section of the supply you can traverse.

You may have too much turbulence in the return area your traversing.

maybe but right now my ductwork looks like swiss cheese the all the "learning" im doing

[beenthere]

maybe but right now my ductwork looks like swiss cheese the all the "learning" im doing

LOL, just another price tag of continuing education.

[energy star]

NCI classes are not recognized by the Air Balance Council. Not saying you need that, but if you want to be an actual independent balancer certified to submit reports to clients requested by the state, or a commercial project by a builder, NCI is meaningless. Too many classes and companies in our industry creating these certifications with the only goal being a new source of revenue for them.

[tipsrfine]

By CH4MAN:
the factor blower curve claims on low speed tap at 0.88" tesp to deliver approx 650 CFM. ok sounds about right?. well a return drop traverse with a testo 416 claimed 1100 CFM ,, huh! a 3 ton blower on low at 0.88 tesp. cant be.

but the capacity check showed terrible cooling numbers with no dehumidifcation. and this was just after i did a clean and check of my AC. SH &SC numbers right on. if i use 650 CFM in the total heat formula made no sense, yet if i plugged in 1100 CFM my capacity check results fell into place..

Please help me understand this. My understanding of restricted ductwork would mean LESS CFM airflow at the same static pressure, rather than an INCREASE in airflow. How is it your system is delivering more airflow with restricted ductwork than what the blower performance chart says it will move under perfect laboratory conditions?