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negative coil bypass factor calculated

asked 2020-09-04 16:53:39 -0600

Wooyoung's avatar

updated 2022-07-14 13:51:23 -0600


I have an err file saying the following.

 ** Warning ** The Standard Ratings is calculated for Coil:Cooling:DX:SingleSpeed = SPLIT MNW COOLING COIL but not at the AHRI test condition due to curve out of bound.
   **   ~~~   **  Review the Standard Ratings calculations in the Engineering Reference for this coil type. Also, use Output:Diagnostics, DisplayExtraWarnings for further guidance.
   **   ~~~   ** CheckCurveLimitsForStandardRatings: The max and/or min limits specified in the corresponding curve objects
   **   ~~~   **  do not include the AHRI test conditions required to calculate one or more of the Standard Rating values.
   **   ~~~   ** Coil:Cooling:DX:SingleSpeed=SPLIT MNW COOLING COIL:  Integrated Energy Efficiency Ratio (IEER) calculated is not at the AHRI test condition.
   **   ~~~   **  Check limits in Total Cooling Capacity Function of Temperature Curve, Curve Type = Curve:Biquadratic, Curve Name = SPLIT DX COIL CAP-FT
   **   ~~~   **  Check limits in EIR Function of Temperature Curve, Curve Type = Curve:Biquadratic, Curve Name = SPLIT DX COIL EIR-FT
   ** Severe  ** Coil:Cooling:DX:SingleSpeed "SPLIT MNW COOLING COIL" -- negative coil bypass factor calculated.
   **   ~~~   **  During Warmup, Environment=NEW.YORK-JOHN.F.KENNEDY.INTL.AP_NY_USA ANN HTG 99.6% CONDNS DB, at Simulation time=01/21 00:00 - 00:10
   **  Fatal  ** Coil:Cooling:DX:SingleSpeed "SPLIT MNW COOLING COIL" Errors found in calculating coil bypass factors

I think this is related to weather data (as when I feed another NewYork weather data, although I get warnings, the simulation never fail) and the minimum/maximum X and Y values (according to this answer (

Any clue for this issue would be highly appreciated. Thanks.

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Any clue for soving this severe error?

Keigo's avatar Keigo  ( 2022-07-13 23:06:25 -0600 )edit

1 Answer

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answered 2022-07-14 07:24:06 -0600

updated 2022-07-14 08:06:47 -0600

The first sentance of the warning is the clue. It says the standard ratings calculation is not at the AHRI test condition due to curve out of bound. The standard ratings calculation looks at each of the performance curve objects min/max limit (Minimum/Maximum Value of x or y). If these limits exceed the values required for the calculations, this warning is printed. So this warning directly relates to the performance curves. Look at each curves limits and compare to the values shown below.

The Minimum Value of y in your performance curve is 23.88889 C while the F1 test requires 19.44 C. I assume this is the trigger for the warning.

IndoorCoilInletAirWetBulbTempRated(19.44);   // 19.44C (67F)  Tests A2, B2, B1, and F1
OutdoorCoilInletAirDryBulbTempRated(35.0);   // 35.00C (95F)  Tests A2, B2, B1, and F1
OutdoorCoilInletAirDryBulbTempTestA2(35.0);  // 35.00C (95F)  Test A2 (high speed)
OutdoorCoilInletAirDryBulbTempTestB2(27.78); // 27.78C (82F)  Test B2 (high speed)
OutdoorCoilInletAirDryBulbTempTestB1(27.78); // 27.78C (82F)  Test B1 (Low speed)
OutdoorCoilInletAirDryBulbTempTestF1(19.44); // 19.44C (67F)  Test F1 (Low speed)

  DXCoolCapFT,            !- Name
  0.942587793,             !- Coefficient1 Constant
  0.009543347,             !- Coefficient2 x
  0.000683770,             !- Coefficient3 x**2
  -0.011042676,            !- Coefficient4 y
  0.000005249,             !- Coefficient5 y**2
  -0.000009720,            !- Coefficient6 x*y
  12.77778,                !- Minimum Value of x  <---
  23.88889,                !- Maximum Value of x  <---
  18.0,                    !- Minimum Value of y  <---
  46.11111,                !- Maximum Value of y  <---
  ,                        !- Minimum Curve Output
  ,                        !- Maximum Curve Output
  Temperature,             !- Input Unit Type for X
  Temperature,             !- Input Unit Type for Y
  Dimensionless;           !- Output Unit Type
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Asked: 2020-09-04 16:53:39 -0600

Seen: 10,235 times

Last updated: Jul 14