Measuring Airflow with the Fieldpiece STA2
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  1. #1
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    Measuring Airflow with the Fieldpiece STA2

    Did a video this afternoon on how the Fieldpiece STA2 works, how to layout a traverse and how to make a correct airflow measurement in a residential system.

    http://youtu.be/6mWOnU9rT_g

    Any feedback would be appreciated.

    Jim Bergmann
    JLB,

  2. #2
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    That is an excellent video Jim!

    I have had the STA2 for about 3 months now and really like it. Quick accurate airflow measurements. Thanks for the explanation of the Tchebycheff method, I posted a thread here a while ago asking about it and didn't really get a good answer.

    One question, is it less accurate to take readings in the supply air when the equipment is heating or cooling? Or should I just use fan on the respective heat or cool taps without the heat or cooling on?

    I really like that magnetic tape measure, where can I get one of those?

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    Yes it is less accurate as the RH in a cold air stream is approaching 100% while in a hot air stream approaching 0%RH. Also the hot-wire in a hot air stream may not respond if the air gets hotter then the wire. I always recommend checking in the return, or testing the blower speed that you want to check without conditioning the air. If you are measuring in the supply, pull the disconnect with the A/C on, the blower will never know.
    JLB,

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    Jim,

    Your dedication to the trade is admirable. The videos have assisted many in their work performance. An observation I would like to make is in the video you say you have a three ton system, and stated 1200 cfm. Your measurement of 1700+ is a quite a bit over that, what is the temp of the supply air? You mention you could slow the blower down some in the video, do you know that instrument to be accurate? That is like 40% over design. What is the static? The duct size certainly looks large enough, actually looks larger than the stated size you mention. Just thought I would ask.......
    Always here

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    Quote Originally Posted by energy star View Post
    Jim,

    Your dedication to the trade is admirable. The videos have assisted many in their work performance. An observation I would like to make is in the video you say you have a three ton system, and stated 1200 cfm. Your measurement of 1700+ is a quite a bit over that, what is the temp of the supply air? You mention you could slow the blower down some in the video, do you know that instrument to be accurate? That is like 40% over design. What is the static? The duct size certainly looks large enough, actually looks larger than the stated size you mention. Just thought I would ask.......
    I did not compare it to another instrument, nor did I check the split. I will do that. I was just trying to show how to use the instrument. It caught me by surprise also. I am getting an error on my ECM code that say non compatible motor data. It is not in the book. Also it is a 16 SEER so it does run higher then normal airflow at full capacity but it should only be at 10% over. It has a 5 ton drive, so 1740 is possible, but I have not checked the configuration settings. I was in it this winter when I did another video, I may have flipped a wrong DIP switch. I will have to figure it out later.
    JLB,

  6. #6
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    Thats a good video and thanks for posting.

    Im not an expert on traversing ducts, but guys I consider experts only trust traverses that are in long straight sections of duct. At least 3 duct diameters of straight into the spot and one or two after it. I know you rarely have this in residential, and you just do the best you can. I would just not consider the reading you take that close to an ahu extremely accurate.

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    Quote Originally Posted by bigtime View Post
    Thats a good video and thanks for posting.

    Im not an expert on traversing ducts, but guys I consider experts only trust traverses that are in long straight sections of duct. At least 3 duct diameters of straight into the spot and one or two after it. I know you rarely have this in residential, and you just do the best you can. I would just not consider the reading you take that close to an ahu extremely accurate.
    Bigtime,
    That is exactly the reason we perform a traverse and use the averaging mode of measurement. The meter makes 2-3 readings per second, we did a 5 point traverse that overall took 60 seconds to complete. The meter made between 120 and 180 readings that were recorded in the time average mode. Additionally because we use the Tchebycheff method, we accounted for the profile of the duct and the airflow through it. While you are correct that the measurement point was not ideal, based of my experience, it was the best point to make the measurement. Taking all of this into consideration, the reading was likely very close to the actual CFM moving through the system. The more turbulent the airflow the more measurements you need to take. Also because of the design of the hot-wire probe, it is not as subject to eddies currents in the duct that would impact the reading. Remember a raw micro glass bead thermistor is not a position sensitive device so if air is swirling in a duct and hits the probe from multiple directions it will interpret a higher velocity than is actually present. Fieldpiece has engineered the STA2 probe so the sensor is mounted in a position sensitive housing to further increase accuracy and to limit the impact of turbulent air present in residential systems.
    JLB,

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    The averaging a lot of points makes sense to me. But I know several NEEB certified guys with 30 plus years of experience that will not really trust a traverse in a location like you checked.

    I have often thought about setting up a system to "test" the test and balance stuff. A small system with 100% sealed duct so you know there is no leakage. A long straight section of duct to be the baseline. Then traverse the duct in the less than ideal, but normal locations of the real world, and compare these to the baseline. Also compare the baseline to the totals with a hood at the diffusers.

    A different subject, but I dont really trust the hoods with small exhaust flows on grilles.

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    Quote Originally Posted by bigtime View Post
    The averaging a lot of points makes sense to me. But I know several NEEB certified guys with 30 plus years of experience that will not really trust a traverse in a location like you checked.

    I have often thought about setting up a system to "test" the test and balance stuff. A small system with 100% sealed duct so you know there is no leakage. A long straight section of duct to be the baseline. Then traverse the duct in the less than ideal, but normal locations of the real world, and compare these to the baseline. Also compare the baseline to the totals with a hood at the diffusers.

    A different subject, but I dont really trust the hoods with small exhaust flows on grilles.
    I agree 100% with you, the problem is the entire duct system is a continuous transition. I picked the best of the bad locations my duct system had to offer.
    JLB,

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    Quote Originally Posted by jim bergmann View Post
    Did a video this afternoon on how the Fieldpiece STA2 works, how to layout a traverse and how to make a correct airflow measurement in a residential system.

    http://youtu.be/6mWOnU9rT_g

    Any feedback would be appreciated.

    Jim Bergmann
    I would love to see a comparison between the Fieldpiece and the Testo 425 and other appropriate comparisons.

    Note to Fieldpiece, imo they should incorporate the built in slide protector for the hotwire that I have seen on Dwyers'.
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    They do have a slip on cover, but an integrated cover would be cool.
    JLB,

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    Quote Originally Posted by pageyjim View Post
    I would love to see a comparison between the Fieldpiece and the Testo 425 and other appropriate comparisons.

    Note to Fieldpiece, imo they should incorporate the built in slide protector for the hotwire that I have seen on Dwyers'.
    I'd like to see that comparison, too.

    I've been shopping anemometers and the price difference makes the FP almost "too good to be true" which makes me question it's quality and accuracy. I was burned a looooong time ago by a FP meter and I'm VERY hesitant to buy another.

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    Quote Originally Posted by jpsmith1cm View Post
    I'd like to see that comparison, too.

    I've been shopping anemometers and the price difference makes the FP almost "too good to be true" which makes me question it's quality and accuracy. I was burned a looooong time ago by a FP meter and I'm VERY hesitant to buy another.
    OK,
    Here is a comparison of the accuracy of the Fieldpiece STA 2 compared to my furnace ECM.

    http://youtu.be/-iddwdcr3Ps
    JLB,

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