I have an Acubalance by TSI in like new condition for sale. I goes to 2 ft x 2 ft. I am retiring. Digital, measures supply and returns. $900.00

 

Having a flow hood is a good idea. You need to learn how to use it because for some applications they are useless. For your use the old analog hood would be best. Digital hoods have more problems with low pressure systems than the analog.
Analog hoods are both simple and reliable. You should also consider having pitot traverse capability. Use an inclined manometer for that. Again simple and reliable.

 

Do you recommend any books, literature or any on-line reading to get properly trained on this equipment ? I was always interested in this field because some of the problems I come across is not the equipment, it is the water or air flow issue. Understanding this better helps to put everything into perspective.




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I respect your opinion Artrose. I suggested the incline because there is no calibration expense and because they are not as easily fooled as any other gage. When doing a traverse the biggest potential for error is "reversed flow". That is in quotation marks because the tricky ones are best seen to identify. I agree with most of what you said but I hated my hot wire. Nothing wrong with it I just didn't like it.
One caution with the inclined manometer is in extreme weather let it reach room temperature before using it.
I double and triple your advice concerning learn what you are doing.

On one job the engineer insisted that one of the duct systems was static regain design and didn't need balanced. I tried to tell him it wasn't properly designed for regain but if that was his intent I couldn't put money in the job to balance it or read all the diffusers. He agreed but it didn't work. The contractor called and insisted I read the diffusers with a flow hood. I told him I didn't have money in for that but they couldn't be read with the hood anyway. The mechanical contractor read the diffusers and gave them to a consulting engineer (not the system designer). The consultant knew the flow hood wouldn't work and rejected the readings. They then ask me to obtain the airflows and I did by pitot traverse ahead of each diffuser. The consultant redesigned from those readings and the system was modified accordingly. Had he redesigned using the bogus readings there would have been another disaster.

 

How/why, were the flowhood readings not acceptable Wayne?
I think one can see different flows at times, dependent on how air exits the diffusers ,but is that what you are refering to?

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The diffuser design airflows exceeded the hood capacity. They tried to read half the diffuser at a time. That was bad enough but they had to cut a cardboard and install it on the hood to fit the hood to the diffuser. The system was also low pressure and they read the diffusers with a digital hood. The airflow readouts were unstable. Before they took readings I traversed the duct and their total wasn't close to the traverse.

 

There are situations where a flow hood just doesn't work so well, despite the different size canopy's, and your ability to customize the canopy with cardboard and tape.

I had been working with a hood for a few years, and thought I had it down pretty good. Was even starting to develop a little carpal tunnel in my right hand, and was already wearing old people work shoes because my feet were pretty screwed up from all the ladder time.

We were balancing a small shotgun style auditorium unit with the air handler centered on one end, with the air handler discharge being sent up through a splitter, then out and down each side the length of the structure. There were 1x4 sidewall diffusers about 14 feet off the floor tapped directly off the duct, equally spaced the length of the room.

We took multiple flow hood readings, and no total was the same, and none of the readings came close to design.

There was some serious head scratching that day. Never encountered this before. Turns out the hood was creating too much backpressure, and the air simply stayed in the very large supply duct, and moved over to another discharge where there was less resistance to flow.

We traversed the unit, and walked away. Another lesson learned.

Don't forget to zero your analog meter before you take sidewall readings.

Learning. It's not confined to the classroom.

 

Your post Artrose demonstrates my point about low pressure systems especially when read with digital flow hoods. High airflows in a low pressure system will make you pull out your hair. You can't even establish a flow factor to correct the readings.
To be totally up front I have never seen that problem addressed by TAB certifiers.

 

szw21 By powered I assume you mean digital. If so in this situation they are worse. One of my competitors read a railroad signal house airflow with a digital hood and the controls overheated when tested due to the lack of air. The digital hood readings indicated there was enough air. I was ask to drive the 70 or 80 miles to read the airflows when there was a TAB company about 5 to 8 miles from them. That made me curious so when I got there I read the airflow with the analog and digital hood. The digital indicated enough airflow but the analog indicated the flow was short. The engineer designing the system said the airflow indicated by the analog was close to his calcs. He redesigned using the analog flows and all was well.

 

Wayne - no I don't mean digital vs analog. There are digital passive and powered flowhoods. A powered flowhood has a fan to compensate for the backpressure of having a flowhood and supposedly has far better accuracy than the passive. The only thing is that I believe the powered flowhood is only good for measuring lower airflows so they are good for supply measurements. For return measurements you would need the larger flowhood like the Alnor EBT731.

This is based on a talk I attend a while ago by the CEO of one of companies that makes airflow measurement stuff including flowhoods.I cannot recall which company it was offhand - I think it was The Energy Conservatory.

Here is an example. https://retrotec.com/flow-finder-mk2.html

 

I have never seen a powered flow hood and didn't know there was such a thing. It will be interesting to see if anyone here has used one.

 

The talk I attend presented results of tests of various flowhoods for supply measurement. They took us through the test setup and then the results. For lower supply airflows the larger flowhood were off by as much as 30%. The smaller passive flowhood were off by about 15% and the powered flowhoods about 5%. One thing they did not do in the test was to test the large flowhood with a smaller hood designed for smaller registers. If they did I suspect the accuracy would be closer to 15%.

Analog was not mentioned. I think the digital instruments of today are probably way more accurate than when they first came out.

 

How often are you taking supply air measurements that are over 500cfm?
Most high volume hoods are highly accurate with returns, they just suffer accuracy on supply air.

 

Forgot to add that the digital passive large flowhood - EBT731 - does have a backpressure compensated measurement mode to account for the insertion loss of the flowhood. I have used it on return air measurements but on larger flows it did not make much difference. I will see if I can get a hold of a powered flowhood for experiments and also measure some supplies in BP compensated mode with the 731.

 

Good book on the subject for a service guy is called “Start, Test, and Balance”

Tools I find most useful for service work is a hot-wire (I have a fieldpiece)

A pitot with a micro-manometer (fluke makes a nice one, which I have)

An rpm meter, and static pressure probes for use with any manometer.

Static pressure measurements across fittings and dampers is by far the fastest way to pinpoint a problem.

I rarely use a flow hood, but they definitely have a place

Im a service guy.

Before you start doing anything system side though beyond initial readings, make sure the mechanicals are in good order. Number one issues are lack of maintenance: worn pulleys, wrong pulleys, dirty coils, fan rotation wrong, return fan not running, too low of setting for the vfd, etc…


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You are absolutely correct. Performing a static pressure profile on a unit can save hours of head scratching and guessing.

Performing one can help you pinpoint clogged coils, closed fire dampers, leaking or broken ductwork, closed dampers, on and on.

Just another diagnostic that should be in every service person's trick bag.

As well as those basic tools that you've listed.

 

For service most times I just take static pressure pressure and use that with blower tables to get the airflow to see if there are any issues with airflow. This of course requires access to the AH manual. I don't take the flowhood (too big and cumbersome to setup) and don't have time doing a traverse with the anemometer. I don't have a hot-wire - just the vane type.

 

A good book. NEBB's Hvac Testing Adjusting and Balancing Manual. John Gladstone & W. Bevert.McGraw Hill pub.