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[hvacker]

technocratic, Was my coil write-up written well enough to get the message across without turning off someone with minimal knowledge of the subject? If not criticize it and I will try to improve. Don't be afraid to ask questions. Someone here will know the answer.

Personally, I like your writing style. A question is addressed and the answer gets more technical as one reads further. Probably a person with less tech experience can stop reading anytime they feel a bit on overload.
I had problems when attempting teaching some years ago. I lacked the patience to go from point A to B. I juts jumped to B.
When performance problems come up on a job it's often because some little bit of knowledge is missing in a tech's toolbox. Addressing job problems and solutions that allow learning was what a boss I had called "Osmosis" learning by exposure. A limiting factor when on a job problem is leaving w/o an answer. Reading of what happens from the inside of a coil or duct, when well written will stick in some heads.
In troubleshooting, mostly it's going from the known and through logic to the unknown. The answer to the unknown is more likely if a tech has exposed themselves to solutions others have discovered.
The next time a tech sees tabulators in a boiler tube they might not ask "what are these things?" but bounce back to what they remember reading.

[hvacker]

About a duct traverse:
They often can't be done with accuracy because of the wrong instrument, or a turbulent duct.
The tech that says he stuck his Fieldpiece ( or whatever ) in the duct and read the velocity doesn't know duct. The instrument I had to reach all the necessary places on a duct was a Dwyer incline manometer. Kind of old school but never needed calibration. My longest probe was 3 feet. Try that with a FieldPiece.

Not being able to find the nice straight duct needed to arrive at something even close is not uncommon. So often the equipment, especially on R/T units, hook directly to the supply duct w/o any reasonable place or distance to do a traverse.
My report often would explane why the traverses were missing. No straight runs long enough. In that situation about all that could be used to determine total air flow were the terminal readings. Because of that duct leakage and system effect couldn't be determined except by probability.
For techs that don't do T&B or have the right instruments can benefit from learning how it should be done and scrap a previous approach.
Answers to the question, how should a problem system be approached regarding what comes first can answer some problems by itself.

[tridiumtech]

Wayne3298

We used the company Alnor 9535A VelociCalc air velocity meter ($XXXX). The NEBB guy used the 'equal spacing' method - 3" from the sides and a reading every 6". We used a black sharpie to mark off the reading lines (on frame of the cooling coil) - I guess that created a 'grid' - very useful.

So for my own personal tool kit, I'm thinking buying a vane anemometer - prices do vary ($xx to $XXX). Did see a decent one at Davis Instruments (their own brand) - about the 1/8 the cost of the Alnor unit. Davis does provide NIST calibration (pricey). What's your take on vane anemometers? My use is to get a general 'snapshot' of the CFM.

[WAYNE3298]

Thanks hvacker I have had clients that said they didn't understand what I was saying. The only object is to communicate and maybe help those with less experience and if that doesn't happen nobody gains. I understand why there is a desire to short cut the pitot traverse and hope to convey here why it shouldn't be done. Your comments help do that. The Duct traverse as you know is universally recognized as the baseline for measuring airflow and overrides any other method. AMCA rates the accuracy of the traverse at from 1.5 to 7.5 % and is calculated to two standard deviations. That does not include variations in the duct system (varied velocity profiles and continuity of mass). The combined overall accuracy can only be calculated after the traverse has been done and the error of velocity pressure measurement is included. Nobody I know does that calculation but it changes the overall expectation of error to between 5 and 10 % which is why NEBB and others expect verification readings to be within 5 % of that recorded. If you need to hang your hat on airflow readings and/or design around them you need the best information you can get. Even when I had an ideal velocity profile I traversed the duct at least two times to make sure the readings if challenged would stand up to scrutiny.

[WAYNE3298]

tridiumtech,
Glad you did a pitot traverse which is different than the vel-grid. The vel-grid is essentially the same as the velocity grid that has been taken out of a flow hood. Shortridge designed it to measure airflow at the inlet of AHU air filters. The vel-grid for every use has to have a correction multiplier applied which is arrived at by comparing the readings to a pitot traverse. Originally Shortdidge provided a multiplier for Kitchen hood exhaust measurements at the filters of 1.2 but eventually told us not to use it due to complaints from the hood manufacturers. Without the multiplier the vel-grid is useless and frankly the rotating vane anemometer is even worse. I have two rotating vane anemometers and never was able figure out how to get reliable readings with them. The cheapest and believe it or not the most accurate is the inclined manometer. It is a pain to use but when done properly is more accurate than the digital meters. That may raise some eyebrows but the reason is that with unstable airflows you can easily mentally average individual readings which is required by AMCA.

[hvacker]

I don't find a vane anemometer all that useful. There are places where a hood can't be used and an Alnor Velometer might not have the grill information at hand so I might use a vane.
For just a snapshot that no one will hold you to there is always TESP. The fastest for sure but with a built in error factor due to how fan curves are developed. You might adjust the reading by 10% less delivery due to duct leakage but if you just need an idea of CFM there ya go.
For all of the measurements taken or needed there is going to be one instrument that does it best. Before Shortridge developed the flow hood the instrument of choice was an Alnor Velometer. The measurements had to be taken a certain way for a certain grill/diffuser . The right tip placed in just the right place. Make the little pins were right. What a time consuming pain they were.
For a traverse I'd use an incline manometer. They have gotten pricey. Built in shock absorber.
For terminals a flow hood.
TESP an Alnor velometer #2 a magnehelic.

Early on before flow hoods the Alnor was recommended because the one instrument could do the whole job. It just would take three times longer.
Except for the incline because there is no calibration requirement the rest all cost $$$ for calibration. Last time I looked calibration for an Alnor flow hood was near $300 plus shipping. Shortridge wanted to upgrade the boards first.
My Problem with NEBB was even though Alnor suggested calibration once/year NEBB wanted it done twice/year. That's a lot of money if a company has several.

Wayne, what's your take on instrument of choice.

[WAYNE3298]

NEBB revised their calibration requirements a few years back (actually due to electronics) and now require it yearly. You may be aware of this but Shortridge according to reliable sources did not manufacture their own instruments early on. I don't know about now. One big reason the certifying agencies were formed was to assure the proper instrument was used in the right place. There were a lot of other reasons but the time consuming yet inaccurate method you mentioned for reading diffusers was part of it. My take on that thing was a stick with a rag on the end was just as good. Instrument calibration is very expensive and should be required every 2 years unless you have reason to believe there is a problem. They should trust the balancers more because the last thing a balancer wants is an instrument that lies to him. NEBB also dropped the requirement to have the entire digital hood calibrated if you had the meter calibration checked. They also relaxed requirements on pressure reading instruments.
My instrument of choice for pitot traverse is the electronic micro-anemometer in all cases except if the system has serious pressure fluctuations then the expensive inclined manometer. I prefer the mag for pressure readings because the digital bounces around too much and the mag is easy to carry around. For diffuser readings the analog flow hood because the digital is too unstable and reads high in low pressure systems. Back pressure compensation is not relevant until 500 CFM and is easy to calculate and the calculation is more accurate. The backpressure compensation feature on the digital was often in left field partly because it is vulnerable to significant changes in building pressure.. For slot diffusers pitot of the duct because many times the flow hood reads them wrong even when you use the closed flaps trick. I pitot traversed the duct and proportioned with the flow hood.

[Cagey57]

First of all Dad, Thanks for the New T & B Forum.

Secondly, all you T & B types get technical real fast, I can follow but it takes 2 readings some times.

Thirdly, hvacker on your comments about my "who do you trust". I agree with you 100% on the 'poor balancer' part. There are 3 TAB contractors that I have worked with over the past 20 plus years that are straight up reliable and honest. I have watched all of them get royally pissed when the equipment would not perform to the "Spec's" but the DOR demanded a report that meets the +/- percentage limits. On the other side of the coin, I had to teach a "Balancer" (I know just enough to not say or do stupid stuff in that area (BTW, Stupid should hurt!)) that he could not change the 4005 constant in the flow calculation but that he had to change the K_Factor (gain) to correctly do the balance. He had values (in place of the 4005) that ranged from 3800 to 8300. I don't remember for sure but I think the altitude correction value was supposed to be something like 4350 on that job (4600').

Fourthly, I vote for open for now and Pro after while so when you balance types get real technical I can stick to the "Easy" forum. ;-)

[WAYNE3298]

Cagey57,
I was asked to clean up one mess in particular where the balancer didn't know how to calibrate a pneumatic VAV box. He got caught because the owner knew the RTU airflow was short and more than half of the boxes didn't even have controllers and were full open or closed. When I told the owner I had to check the RTU because it was short on airflow he said according to the balance report the other balancer didn't have that problem. He then told me the RTU is maxed out but can you balance the system so it works right. When I told him no because a lot of the boxes don't have controllers he got a lot more friendly because he already knew that too and knew I was being honest. He actually watched me do the balance and was happy when the balance was finished. This guy had been lied to before and wasn't going to put up with it anymore. I wished many times there were more owners like him.

[BBeerme]

Heh heh, reminds me of another story. Think I mentioned it on here once before.

Six story building. New account. Complaints of no cooling. Fellow tech went out and the mechanical seemed to be good, but couldn't get a cold enough supply air temp or supply air static pressure. We were in there checking superheat, and the air was howling.

Told him we needed to check a VAV or two.

Come to find out, the previous contractor had stripped out ALL of the minimum maximum controls on all of the VAV boxes.

Cagey57,
I was asked to clean up one mess in particular where the balancer didn't know how to calibrate a pneumatic VAV box. He got caught because the owner knew the RTU airflow was short and more than half of the boxes didn't even have controllers and were full open or closed. When I told the owner I had to check the RTU because it was short on airflow he said according to the balance report the other balancer didn't have that problem. He then told me the RTU is maxed out but can you balance the system so it works right. When I told him no because a lot of the boxes don't have controllers he got a lot more friendly because he already knew that too and knew I was being honest. He actually watched me do the balance and was happy when the balance was finished. This guy had been lied to before and wasn't going to put up with it anymore. I wished many times there were more owners like him.

[WAYNE3298]

BBeerme,
I assume you are referring to the max & min adjustment screws on the pneumatic controllers. I always carried controllers in case that happened and occasionally it did. Bet you had a real mess to fix and also expensive!!

[BBeerme]

It was quite a long time ago, but if memory serves, it was electronic.

Which might be why 'the guy' ripped them out.

We restored them one floor at a time.

Wasn't too difficult. I mean, after the first couple, it just gets sort of boring. Easy money. And everyone was happy after it was done.

And yes, it was pricey for the building owner.

BBeerme,
I assume you are referring to the max & min adjustment screws on the pneumatic controllers. I always carried controllers in case that happened and occasionally it did. Bet you had a real mess to fix and also expensive!!

[hvacker]

Cagey57: There is a technical component to T&B but I think that's what makes it interesting.
I know when I want to baffle my self I can just open ASHRAE Fundamentals book. Things get thick real fast.
A good book on T&B is NEBB's HVAC Testing Adjusting and Balancing Manual. A very long title. McGraw Hill Pub. I think I saw SMACNA had some too.
I did T&B but more often I used what I learned to analyze systems when called for other problems. Example of a system having poor performance, a look at the total system can often give answers. If the mechanical part seems ok but the ducts look like a hack job, system effect might be the culprit. Knowing how to test for that is one up on companies that can't.
When I mentioned about the contractor that only cared about the NEBB report, a balancing company knows the report will never be questioned. Another T&B company will charge to retest and a lot of these guys are friends often subbing to each other when they are on overload. Human nature or good business pick one.
The nature of the business is often to get the report done and lets get paid. Mechanical contractors heads are already on the next job and some attitudes are the T&B is just a necessary inconvenience.
But on the positive side a knowledge of T&B is an excellent help for problems. Even if a tech is not doing a full tilt T&B using what they know on the job will be worth it.

[timebuilder]

You guys do realize the new T&B forum is open, right?

[WAYNE3298]

Cagey57,
Believe it or not one controls manufacturer uses 4005 for all VAV sizes and alters it's effect by changing the gain. All others I can think of off hand have different values for each size box and some of them automatically change that value when you input the measured airflow. One manufacturer has a default control that corresponds to the design airflow of that size box with a velocity pressure of 1.0 inches measured at the VAV flow ring. On VAV's that change the value if it isn't right, which often is wrong, the box will not calibrate and some boxes will bomb out giving an error message that the flow at 1.0 can't be as calculated by your input. When that happens the VAV will not work at all until you get a better number installed.