Static pressure testing

[jtrammel]

i am also learning about TESP and ESP so I will ask.... is the problem in the return, ie: a blockage? may be a silly question but will solidify my assumptions.Thanks.

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Dirty filter and/or blower wheel probably, or some type of return blockage

[beenthere]

i am also learning about TESP and ESP so I will ask.... is the problem in the return, ie: a blockage? may be a silly question but will solidify my assumptions.Thanks.

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Return. Half of them blocked off.

[dsprice]

I always check esp. Based on blower performance, I know what the unit is moving and use this as a starting point. I don't see how you can charge a system without it.

[tipsrfine]

Let me tell you why static tests aren't that important.
A fan curve is plotted from laboratory test data under ideal conditions with NO inlet restrictions.
Not every fan is tested. Similar fans have curves developed by interpreting
test data.
Sometimes they are useful as a design tool
They represent laboratory data and do not represent measurable performance under field conditions.
They can be useful in trying to get a probable performance of a fan type.
You cannot predict the CFM of a fan from lab data because it'd difficult to predict system effect.

This information was gleaned from T&B data of the Sheet Metal and Air Conditioning Industry.
I've always thought that too much emphasis has been placed recently on static testing to the point of replacing real T&B instrument testing.
On T&B reports, static tests were made to inform the engineer but the numbers that really matter are the actual real world performance measurments.

It is good to see someone mention system effect. The way so many residential duct systems are designed... I would love to see a field study of actual measured air flow of a large amount of systems to see how far off most of them are as compared to their blower performance charts.

[dsprice]

We design our systems to deliver 350 cfm's at .5 esp. After setting the blower speed and verifying our static, we do the air balance. As it turns out, we do deliver what we designed better than 95% of the time. This includes multi system houses, damper systems, upflows, horizontals, and any combination of.

The company I work for does 80% of RNC in our area. Good enough for a field test?

I don't want to come across as being a know-it-all but anyone who says static pressures don't matter is wrong. Air flow is probably more important than mechanics in our industry. It's also the most difficult to understand.

If your static pressures aren't right, than nothing else about your system will be right.

[SBKold]

The qualm I have with blower charts is that liitle subnote....."air filter included ". Ok well without publishing the Pd it leaves it to interpretation.

[DeHeatify]

The qualm I have with blower charts is that liitle subnote....."air filter included ". Ok well without publishing the Pd it leaves it to interpretation.

So if it's included am I to be taking the measurement from upstream or downstream of the filter? I have wondered this before...

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[SBKold]

This is what I mean .... a lot is left to interpretation.

From the manufactures standpoint they say to take reading upstream. But without publishing the Pd across that factory included filter it is hit or miss IMO.

With that said they are usually talking about a very loose weaved fiberglass. And a Pd of .1 - .2 at the most.

Carrier does do a good job of publishing their data for those metal framed blues but those let a lot of dirt through also.

[beenthere]

This is what I mean .... a lot is left to interpretation.

From the manufactures standpoint they say to take reading upstream. But without publishing the Pd across that factory included filter it is hit or miss IMO.

With that said they are usually talking about a very loose weaved fiberglass. And a Pd of .1 - .2 at the most.

Carrier does do a good job of publishing their data for those metal framed blues but those let a lot of dirt through also.

When York includes filter, its a .07" PD filter.

[gasser65]

The number one thing that checking static pressure has helped me with is fixing condensation problems. Almost all the horizontal attic units that I've seen with a pan full of water under them have shown to be off on static pressure. Some have a hole in the primary pan of course, but on the ones that didn't have a hole and that I've taken whatever measures to get the static right on, have dried up and not had condensate leaks again.

[ch4man]

It is good to see someone mention system effect. The way so many residential duct systems are designed... I would love to see a field study of actual measured air flow of a large amount of systems to see how far off most of them are as compared to their blower performance charts.

i took NCIs air diagnostic and balance class last year and this past summer was living and breathing capacity checks.
it seemed to me that blower curve are more of a guideling than actual numbers. too much imterpolation ( although what does that say to a TAB guy who uses fan laws regularly?). way more times than i ever expected the capacity checks reveiled something amiss with my calculations and always pointed to the CFM number i plugged into the total and sensbile formulas,

my own furnace is a mid eff amana with a 3 ton blower package. horrible ductwork with the most restriction on the return ( yeah i know, and doctors make the worst patients).

the following numbers are approx as i didnt record them but close enough to make my point,

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..

this is only one example. most times wile doing rebate data collection cap checks show way less airflow than ecm dipswitchs lead you to believe..

Tips, you sound like a TAB guy, any thoughts?

We design our systems to deliver 350 cfm's at .5 esp. After setting the blower speed and verifying our static, we do the air balance. As it turns out, we do deliver what we designed better than 95% of the time. This includes multi system houses, damper systems, upflows, horizontals, and any combination of.

The company I work for does 80% of RNC in our area. Good enough for a field test?

I don't want to come across as being a know-it-all but anyone who says static pressures don't matter is wrong. Air flow is probably more important than mechanics in our industry. It's also the most difficult to understand.

If your static pressures aren't right, than nothing else about your system will be right.

you are correct, airflow is the most important check to do. but static presure doesnt alway mean airflow

[SBKold]

When York includes filter, its a .07" PD filter.

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.

[tipsrfine]

Tips, you sound like a TAB guy, any thoughts?

Not officially trained in it. I'm a bit of a AUTODIDACTIC POLYMATH. I have tried to get people talking about system effect whenever I've seen threads regarding air flow & how to check it, but havn't had much luck. You being trained in TAB maybe will be better able to help get this knowledge out more than it is. Thanks for sharing your story about your own system. I hope that gets peoples attention.