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  1. #1
    Join Date
    May 2009
    Location
    Savannah, Ga/H.H. Island, S.C.
    Posts
    1,489

    2 Fieldpiece tools + 10 mins = 1 easy BTUH calculations.

    2 Fieldpiece tools + 10 mins = 1 easy BTUH calculations.

    I just wanted to make a post explaining how easy an actual output BTU calculation is using only two of Fieldpiece's tools. FP really has simplified some of the hardest HVAC calculations with the introduction of these tools.

    What I used:

    Fieldpiece SDP2 Dual In-duct psychrometer
    Fieldpiece STA2 In-duct hot wire anemometer
    Drill w/ 1/2" step bit.
    Tape measure.

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    Step 1:

    Operate your system in cooling mode. Drill one 1/2" hole in the supply and one 1/2" hole in the return. Using the SDP2, insert the probe marked with red in the return and the unmarked probe in the supply. After the system has ran for a bit and settled down, record the enthalpy. The SDP2 will display supply enthalpy and return enthalpy. Subtract the supply from return.

    My system.
    Return Enthalpy: 26.04
    Supply Enthalpy: 19.50
    Enthalpy change (Δh): 6.54


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    Step 2:

    Using the tape measure - measure your return duct. Using the STA2, input your square duct measurements or round duct diameter. Refer to the table in the STA2 manual; mark and drill 1/2" holes in appropriate traverse locations. Take timed measurements.

    My system:
    Feet per minute: 556
    Cubic feet per minute: 988.4


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    Step 3:

    Calculate.
    CFM x 4.5 x Enthalpy change (Δh) = BTUH

    My system:
    988.4 x 4.5 x 6.54 = 29,088 BTUH.


    I have a 2.5 ton (30,000) system. Not to bad. I would like to make a few adjustments and maybe get a little closer to the nominal tonnage. This whole process took no time at all. I stated 10 minutes and that is only due letting the system run and settle down. By performing this calculation on each system I service, I can tell exactly what changes need to be made produce more output BTU's.

    Hope this helps!

    Thanks.

    Brent A. Ridley

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,046
    Thanks Brent, can't wait for my tool stash $$$ to build back up so I can add some more stuff to the arsenal. The sdp2 is definitely towards the top of the list.

  3. #3
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    You can run your return and supply air DB and WB readings, along with the CFM, through a psychrometric process calculator, several phone apps available, and get the full psychrometrics breakdown, including sensible and latent cooling being done.

    I'd like to see a future firmware update to the HG3 to allow it to do the calculations based on data received from the SDP2 and the hot wire anemometer accessory head, or better yet, a wireless version of the STA2 anemometer, as I'd like to have a stand alone meter instead of the accessory head.

    Kind of a poor man's Testo 435 HVAC kit.

    I "should" be purchasing the HG3, hot wire anemometer head, and vane anemometer head within the next 2-4 weeks.

    The way systems are installed around here, the "system effect" often precludes getting reasonably accurate readings with an in duct anemometer probe, so I'm not sure how useful the hotwire prob will be to me.
    If more government is the answer, then it's a really stupid question.

  4. #4
    I have the hot wire head and its great.

    I'm sure u know the HG 3 has a CFM program init.

    Been using the STA 2 along with a 510 manometer to get air flow but am confused about a procedure the Boss taught me.

    That is: Take a static reading and then go to each register with the vane anemometer (all dampers open)
    then add up the sum of all the registers. Total cfm should equal the blower chart at the static measured.

    Sometimes it does not equal out. The method is a dealer school procedure taught at Heil training seminars ...very old school late '80s stuff. I've read the manual my self.

  5. #5
    Join Date
    Aug 2007
    Location
    Southern,Ca
    Posts
    544
    great post Brent

  6. #6
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,121
    Quote Originally Posted by hvac5646 View Post
    I have the hot wire head and its great.

    I'm sure u know the HG 3 has a CFM program init.

    Been using the STA 2 along with a 510 manometer to get air flow but am confused about a procedure the Boss taught me.

    That is: Take a static reading and then go to each register with the vane anemometer (all dampers open)
    then add up the sum of all the registers. Total cfm should equal the blower chart at the static measured.

    Sometimes it does not equal out. The method is a dealer school procedure taught at Heil training seminars ...very old school late '80s stuff. I've read the manual my self.
    Two or three scenarios can cause it to not come out equal. The first and most likely is duct leakage. The next is the fact that anything between the two static measuring points that is dirty, blower wheel, coil, heat exchanger etc can give you an invalid cfm reading. Also if you don't know the AK or effective area of each grill you can get inaccurate readings.

    I use the STA2 and get very consistent results, it was money well spent.

  7. #7
    Join Date
    May 2009
    Location
    Savannah, Ga/H.H. Island, S.C.
    Posts
    1,489
    I agree. An updated version of the HG3 and STA2 with wireless capabilities are high on my wish list.

    Note to anyone using the STA2: I suggest taking measurements in the return. The air is less turbulent and you will get better results.

  8. #8
    Quote Originally Posted by Brent Ridley View Post
    I agree. An updated version of the HG3 and STA2 with wireless capabilities are high on my wish list.

    Note to anyone using the STA2: I suggest taking measurements in the return. The air is less turbulent and you will get better results.
    Thee was another way to do it?

  9. #9
    Quote Originally Posted by chuckcrj View Post
    Two or three scenarios can cause it to not come out equal. The first and most likely is duct leakage. The next is the fact that anything between the two static measuring points that is dirty, blower wheel, coil, heat exchanger etc can give you an invalid cfm reading. Also if you don't know the AK or effective area of each grill you can get inaccurate readings.

    I use the STA2 and get very consistent results, it was money well spent.
    Thanks a lot. That's more helpful to me than you know.

  10. #10
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,121
    Quote Originally Posted by hvac5646 View Post
    Thanks a lot. That's more helpful to me than you know.
    Here's a great blog post on the subject. http://ncidavid.********.com/2013/05...-your.html?m=1

  11. #11
    Join Date
    Jun 2009
    Location
    South Carolina
    Posts
    484
    Ya it would be nice to have a wireless STA2 that is a stand alone like the sdp2.

    Looks like i will be purchasing the STA2 or some equivalent

    but first i have to pay off my paypal account for the spd2 and hg3

  12. #12
    Quote Originally Posted by klee7013 View Post
    Ya it would be nice to have a wireless STA2 that is a stand alone like the sdp2.

    Looks like i will be purchasing the STA2 or some equivalent

    but first i have to pay off my paypal account for the spd2 and hg3
    Aw, Dude...did you get hooked wit that 19.9% APR credit plan?

  13. #13
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,046
    Quote Originally Posted by hvac5646 View Post
    Aw, Dude...did you get hooked wit that 19.9% APR credit plan?
    Bill me later is 6 months same as cash.

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