Airflow capture hoof

[szw21]

How often are you taking supply air measurements that are over 500cfm?

Never. It probably means one needs 2 flowhoods - since return airflow exceed the capacity of the smaller flowhoods. Only downside is more $ since flowhoods are not cheap.

Our local utility has a lending library of tools which include flowhoods - that's a good option to try out before purchasing but they have been shut since the start of Covid. Not sure when they are going to reopen.

My own testing based on return airflow measurement using the larger flowhood and then cross checked against a duct traverse, static pressure measurements with blower tables and measuring supplies individually show that it is overestimating supplies by about 15% - this is in line with the test results from the talk using the smaller passive flowhood. My supply measurements were with the larger flowhood but with the smaller (16 x 16) hood. I think the 30% error was based on using the 24 x 24 hood.

[mgenius33]

Never. It probably means one needs 2 flowhoods - since return airflow exceed the capacity of the smaller flowhoods. Only downside is more $ since flowhoods are not cheap.

Our local utility has a lending library of tools which include flowhoods - that's a good option to try out before purchasing but they have been shut since the start of Covid. Not sure when they are going to reopen.

My own testing based on return airflow measurement using the larger flowhood and then cross checked against a duct traverse, static pressure measurements with blower tables and measuring supplies individually show that it is overestimating supplies by about 15% - this is in line with the test results from the talk using the smaller passive flowhood. My supply measurements were with the larger flowhood but with the smaller (16 x 16) hood. I think the 30% error was based on using the 24 x 24 hood.

My Alnor LoFlo is pretty good at supply air. I do need to figure an ak factor for certain types of grilles to gain a bit more accuracy. The Alnor LoFlo seems to read a bit low compared to larger hoods which read significantly high like you stated. This is necessary for different style and size grilles. The Alnor is programmable and can store several different grille factors. There may be more accurate low flow hoods out there, and certainly the powered hood is most accurate.
I have the benefit of having essentially a powered hood with my Retrotec duct tester, in order to get a good test reading. I need to get some time to play around with this again, it’s definitely interesting.

[szw21]

My Alnor LoFlo is pretty good at supply air. I do need to figure an ak factor for certain types of grilles to gain a bit more accuracy. The Alnor LoFlo seems to read a bit low compared to larger hoods which read significantly high like you stated. This is necessary for different style and size grilles. The Alnor is programmable and can store several different grille factors. There may be more accurate low flow hoods out there, and certainly the powered hood is most accurate.
I have the benefit of having essentially a powered hood with my Retrotec duct tester, in order to get a good test reading. I need to get some time to play around with this again, it’s definitely interesting.

It would be interesting to compare the EBT731 with the LoFlo side by side. According to the specs the EBT731 can measure a lower airflow than the LoFlo if my memory serves me correctly.

It does sound like a powered flowhood is the most accurate for measuring supplies.

[heatingman]

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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[Artrose]

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.

[mgenius33]

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

Im a service guy.

That’s the reason I like the Alnor LoFlo 1600. It’s small, quick and easy to set up. Also it’s far more accurate I believe than that CPS thing-a-ma-bob wanna be flow hood.
My larger Testo 420 is great on returns, but it’s a chore to assemble, lug around and store in the van.

I think that is what keeps most of us from using them.

[szw21]

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.

[hvacker]

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