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Thread: Alnor LoFlo Flow Hood

  1. #21
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    Quote Originally Posted by mgenius33 View Post
    I’ll preface this post by stating, I have nowhere near the air balancing experience as Wayne, but I have done my fair share of testing, taking notes, and comparing different methods for “residential applications.”

    I trust the Alnor Lo-Flo as my #1 for residential supply air diffuser readings so far. It seems to read slightly low, but it’s linear and repeatable. I’ve compared it to high volume flow hoods, high end large vanes, small vanes, hot wires, pitot with auto zeroing digital dual ports, analog magnehelic and red oil tubes, Retrotec powered duct leakage tester configured for air measurements, and probably a few others I’ve forgotten about. I even set up a lab test with a small sealed return and supply ducting system.

    So, when comparing several diffusers, you can weight them. When balancing a residential system, your trying to get a certain % of the total volume to certain spaces. The actual cfm doesn’t really matter much if the meter reading is repeatable and linear, because you’re simply comparing it to the other vents. Basically “robbing Peter to pay Paul”. As long as your static isn’t affected that much.

    The total volume is more accurately read by the fewer return vents. Of course there’s leakage to be considered. Unfortunately, the Lo-Flo is not capable of reading return air volumes above 500cfm. I have found flow hoods to be extremely accurate with return air readings. Larger cfm flow hoods are less accurate for residential supply air readings.

    I found:

    the hot-wire to be accurate at higher velocity without a grille (less turbulence).

    The vanes to be ok most of the time with a grille but less so without a grille. I find the expensive large vane to be a waste of money for small residential supply air vents. It works well with the larger return air vents, but the small vane is probably a better buy for small supplies. Just don’t get a cheap off brand one from e-Bay.

    Pitot only good for in duct, Magnehelic most accurate other than very expensive auto zeroing manometer. Cheaper digital manometers under $400 are not worth connecting to a Pitot. The Magnehelic works very well and is relatively inexpensive.

    High flow hood very good at large return air measurements. Probably good with high volume large supplies, I don’t know.
    Not good with small supply measurements.

    Lo-Flo Alnor very good with small return air, and small supply air.
    Again, it reads a little low on supplies I think, but it’s very reliable IMO. I don’t even bother reaching for anything else when taking residential supply air readings. It has the small 16”x16” short hood.

    For more accurate readings I made a cardboard box with a hyperbola shaped insert. This made both the high flow and low flow hoods read very close to one another.
    Thanks for your feedback on this. Yes I realize that the LoFlo cannot used for returns. I guess I could use my rotating vane assuming it is accurate. The correct technique is to traverse the return grill about 1" away, average the velocity readings and then multiply by the Ak of the grill correct?

    I might try creating a ductboard test fixture with a pitot traverse to see how far off the other tools are - based on a previous post that a pitot traverse wound be the most accurate out of all the techniques.

  2. #22
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    Quote Originally Posted by szw21 View Post
    Thanks for your feedback on this. Yes I realize that the LoFlo cannot used for returns. I guess I could use my rotating vane assuming it is accurate. The correct technique is to traverse the return grill about 1" away, average the velocity readings and then multiply by the Ak of the grill correct? yes

    I might try creating a ductboard test fixture with a pitot traverse to see how far off the other tools are - based on a previous post that a pitot traverse wound be the most accurate out of all the techniques. Be sure to radius the inlet side of the box. Straight edges on the inlet side will not create laminar flow in a short section of straight duct. This is why flow hoods do so well on return air readings. (Or my theory anyway)
    ..

    I’ll likely be doing more testing this year. I’ve added a Testo 416 mini-vane to my arsenal.
    "The only true wisdom is in knowing you know nothing" Socrates

  3. #23
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    Old thread but...I thought I saw a couple of new posts - I got email notification and I also viewed the posts a day or two ago. Now when I look the posts are missing. I think there were 2 that are gone.

  4. #24
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    szw21 my last post is missing. Concerning your post #21 Pitot traverse of the duct does not use AK factors. I may have misunderstood your post because I don't know how you intend to traverse a diffuser other than the duct. If you meant the velocity grid it was not designed for air supply measurement.
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  5. #25
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    Quote Originally Posted by WAYNE3298 View Post
    szw21 my last post is missing. Concerning your post #21 Pitot traverse of the duct does not use AK factors. I may have misunderstood your post because I don't know how you intend to traverse a diffuser other than the duct. If you meant the velocity grid it was not designed for air supply measurement.
    Yes Dad confirmed that some of the posts and threads in a certain timeframe have disappeared and that would include the 2 posts on this thread. The other guy who posted also had some useful suggestions but that's gone.

    Regarding post #21 I was not talking about a duct traverse when referring to Ak in that post. What I was saying is that if I traversed the return air grille with a rotating vane anemometer I assumed the correct technique would be to take the readings 1" away from the grille and using the Ak of the grille (rather than the full open theoretical area) to compute the cfm from the velocity reading.

  6. #26
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    I spent a lot of money on a rotating vane and was bitterly disappointed in it. I wanted to use it on diffusers I couldn't get a hood on. If There were say 6 diffusers alike I thought I could hood one then read it with the rotating vane to establish the multiplier. That didn't work because the vane wouldn't repeat.
    If you have found a way to get good results good for you.
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  7. #27
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    Quote Originally Posted by WAYNE3298 View Post
    I spent a lot of money on a rotating vane and was bitterly disappointed in it. I wanted to use it on diffusers I couldn't get a hood on. If There were say 6 diffusers alike I thought I could hood one then read it with the rotating vane to establish the multiplier. That didn't work because the vane wouldn't repeat.
    If you have found a way to get good results good for you.
    Did you have differing results on the same one each time you measured - or was it on different diffuses. I get consistent results on the same one for each measurement - whether the actual value is correct or not I have no idea since I do not have a flow hood or some other kind of setup to cross check. It would be interesting to actually try with a duct setup and a pitot traverse and see if the correction factor is consistent. I plan on doing that sometime in the future.

  8. #28
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    The biggest problem I had was on different diffusers. I finally concluded that the distribution of the air across the diffuser was the biggest problem. If there was an elbow close to the diffuser it made a big difference. I had to certify my readings so the rotating vane for me was a bust. You may have a better use for it than me.
    I compared the vane readings with hood and pitot traverse of the duct.
    No man can be both ignorant and free.
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  9. #29
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    I will try my own setup and see if I can get consistent readings from my vane anemometer. I understand that it cannot be used for low velocities due to the effects of friction on the spinning wheel and also a larger wheel is going to be more accurate than a smaller wheel. But I have never had to means to verify it against a better setup or instrument.

  10. #30
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    Reviving an old thread - after much thought I decided to purchase the Alnor EBT731 flow hood. One of the downsides of the LoFlo was the inability to measure the return airflows due to the 500 cfm limit. I did also get the smaller (16 x 16) hood kit which is more suitable for residential registers.

    Been playing around with it and getting familiar with its operation.

  11. #31
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    Quote Originally Posted by szw21 View Post
    Reviving an old thread - after much thought I decided to purchase the Alnor EBT731 flow hood. One of the downsides of the LoFlo was the inability to measure the return airflows due to the 500 cfm limit. I did also get the smaller (16 x 16) hood kit which is more suitable for residential registers.

    Been playing around with it and getting familiar with its operation.
    Cool. Please let us know how well it works on supply air. I'm quite sure it will perform excellent on all return air, but lower volume supplies may be an issue. I hope I'm wrong for your sake, and I hope that hood works well.
    "The only true wisdom is in knowing you know nothing" Socrates

  12. #32
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    Quote Originally Posted by mgenius33 View Post
    Cool. Please let us know how well it works on supply air. I'm quite sure it will perform excellent on all return air, but lower volume supplies may be an issue. I hope I'm wrong for your sake, and I hope that hood works well.
    Reviving this but I wanted to update on the EBT731 and low flows. Yes it turns out the flowhood is not very good at measuring supply airflows in a residential setting. I found that it gave much higher readings when added to give the total system airflow compared to the total system airflow values obtained using 3 other methods - return airflow using the flowhood, static pressure measurements with blower tables as well as doing a duct traverse using the micro-manometer that came with the flow hood. So I was not able to trust the supply airflow readings from the hood

    More recently I purchased a Retrotec duct leakage tester in order to conduct my own duct leakage tests required by the permitting process here. I found out that the leakage tester could be used a powered flowhood which apparently is way more accurate than any passive flowhood. Using this I got much lower values for the supply airflow. I found that the error for a given type of register is consistent so this allowed me to apply a correction factor to the flowhood. Now the total supply values are in line and correlate with the other airflows arrived by the other 3 methods.

    Setting up the duct leakage tester as a powered flowhood is very cumbersome so my plan is to come up with correction factors for different types of residential supply registers and then use the flowhood with the correct correction factor applied.

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  14. #33
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    One piece of advice sw21 keep calibration of your equipment up to date. I'm not saying you haven't just a reminder.
    No man can be both ignorant and free.
    Thomas Jefferson

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  16. #34
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    Here is a link to the paper I used as a basis for setting up the duct tester as a reference active flowhood in order to calibrate the passive flowhood.

    https://www.aceee.org/files/proceedi...l1_Paper27.pdf

    Right now Retroctec has one model of active flowhood on the market but the hood size I believe i 10" x 10" which is okay for things like bathroom fans but still too small for some residential registers. I believe that is the only one on the market.

    Retrotec did present a paper similar to the one I linked which also showed experiments done by them on powered vs passive flowhoods at the HVAC Excellence conference a year or two ago. Unfortunately I don't think there is a copy online. Unlike the paper above although they did not name the passive flowhoods there were diagrams of them of enough detail so that one could pretty well guess what they were. The big flowhoods were the worst for this application followed by the smaller passive flowhoods and then then the active flowhood which were accurate with within a few parentage points.

    I plan to also use the active flowhood setup to calibrate and verify the accuracy of my vane anemometer. I have comes across registers in residential applications where they are really small and next to a door jamb making the use of a flowhood impossible. The only thing that one can use in this situation is a vane anemometer.

  17. #35
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    Maybe someone knows the answer to this. I was doing some controls. The duct system had a number of horizontal outlets.
    I watched the T&B guys holding their flow hoods sideways to get readings. I know it's done often like this and I've also done this.

    I couldn't find information from either of my hoods, Shortridge or Alnor that this was accurate procedure.

    The T&B guys said they would just zero the meter(analog) while in the horizontal position.
    Anyone ever see procedures for this? I guess the question is if the meter can be read on it's side accurately. I've never compared readings with another type of instrument.
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  18. #36
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    Quote Originally Posted by hvacker View Post
    Maybe someone knows the answer to this. I was doing some controls. The duct system had a number of horizontal outlets.
    I watched the T&B guys holding their flow hoods sideways to get readings. I know it's done often like this and I've also done this.

    I couldn't find information from either of my hoods, Shortridge or Alnor that this was accurate procedure.

    The T&B guys said they would just zero the meter(analog) while in the horizontal position.
    Anyone ever see procedures for this? I guess the question is if the meter can be read on it's side accurately. I've never compared readings with another type of instrument.
    I cannot comment on analog flowhoods. It's possible that the meter itself will be affected by orientation due to gravity and other effects.

    For digital ones the two references I have showing that would be fine would be.

    1. The manual for the one I have shows photos of the flowhood measuring airflow in biological safety cabinets in the horizontal orientation.

    2. The NCI training I've attended on duct optimization and airflow balancing show that the flowhood can be used in any orientation.

    Both these are for digital hoods.

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