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Thread: SHR and ADP

  1. #1

    SHR and ADP

    Hi again guys

    I know my room air specs, outside air specs and mixed air specs. How do I figure out the ADP or SHR of a cooling unit? Are those given values for a specif unit?

  2. #2
    I was told that most of the time for standard units we simply use a SHR of .70.

    Is this correct?

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,098
    Most mfrs. give you SHR of a given unit/coil match at ARI rating conditions of 95 out, 80/67 in. Pretty rare to be as low as .70 except Rheem & Trane. Could be a few others, but most tend to be .73 to .75.

    Of course this is at extreme conditions. A cool, dry house on a warm day could be running mostly sensible since the system adjusts to conditions. A steamy house could run a high latent til it dries out.

  4. #4
    Is there a way to acculate calculate the SHR if I don't have the unit's spec sheet?

  5. #5
    Join Date
    Apr 2004
    Posts
    7,680
    If you want to know a snap shot then yes but it is not easy as you'd think

    First you would need to know the airflow, not a guess but the real airflow.

    Once you have that, you can do a simple temp drop sensible calculation.

    Then you would do a wet bulb drop, plot the readings on a phycometric chart to get the enthalpy and do the math to determine total capacity and subtract the sensible from the total. The divide the sensible by the total. IE Sensible 26,239/ Total 35,837= 0.732...

    Total Heat Formula:
    BTUH=CFM*4.5*(H1-H2) where H is enthalpy.

    Sensible Heat Formula
    BTUH= CFM*(T1-T2)*1.08 where T is temperature

    Of course that's at sea level to 2000 feet you would have to adjust the constants (4.5 and 1.08) at higher altitudes.

    Remember this calculation is just a snap shot not an indication of the system's potential and the accuracy of your instruments and readings are crucial. I would take multiple readings, especially on the enthalpy and average them.

  6. #6
    Join Date
    Apr 2002
    Posts
    11,808
    you need the entering and leaving air condition as a minimum, plot them on a pyschrometric chart

    you connect the two points with a line then extend the line all the way to the 'far left' of the page

    you can get the SHR from the slope of the line, you get the ADP by reading off where it cuts the "100% RH" line and it is a snap shot as doc said

    if the room is cooler or dryer than 80F at 51% RH the numbers will be different than any mfg rating
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  7. #7
    In other words it’s easier and more precise to get the SHR from the manufacturer of the unit.

    Next question is the temperature of Freon inside the cooling coil, SST and TD… what is the relation to the ADP. And If I know that info I can determine the SHR.

  8. #8
    Join Date
    Apr 2002
    Posts
    11,808
    I view ADP as the average coil surface temperature, and average of the tube and fin temperature. The refrigerant will be boiling at a lower temperature than the ADP
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  9. #9
    Join Date
    Apr 2004
    Posts
    7,680
    Carnak... Werent you working in Aruba? I was just there and didnt see you anywhere

    Then again, I wasnt looking, I was too busy sipping Mimosa's. (Was at the Rennisance).

  10. #10
    Join Date
    Apr 2002
    Posts
    11,808
    caymans
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

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