#2735 EnergyPlus Crash - Coil:Cooling:DX:SingleSpeed Capacity Out of Range

[Felicia Lee]

We had resolved this issue last year, the main issue was I had set the wrong streams in the HX. We resolved all the errors and the model passed, after that we had another design iteration where we went ahead and made some changes to our building. I incorporated all those changes and made a new model, but I am experiencing the same error this time, I went through all the communications from last time and implemented those files, went through SourceForge forums and implemented any applicable fixes. I still seem to get the same error again, please explain the cause.

[Nikhil Kapur]

5/8/18 RH - I reviewed the ap error file (eplusout.err in the LADOMH - run\ap\EnergyPlus folder) and found the following:

** Severe ** Sizing: Coil:Cooling:DX:SingleSpeed "COOLING COIL C1": Rated air volume flow rate per watt of rated total cooling capacity is out of range.
** ~~~ ** Min Rated Vol Flow Per Watt=[4.027E-005], Rated Vol Flow Per Watt=[3.622E-005], Max Rated Vol Flow Per Watt=[6.041E-005]. See Input Output Reference Manual for valid range.
** Severe ** For object = Coil:Cooling:DX:SingleSpeed, name = "COOLING COIL C1"
** ~~~ ** Calculated outlet air relative humidity greater than 1. The combination of
** ~~~ ** rated air volume flow rate, total cooling capacity and sensible heat ratio yields coil exiting
** ~~~ ** air conditions above the saturation curve. Possible fixes are to reduce the rated total cooling
** ~~~ ** capacity, increase the rated air volume flow rate, or reduce the rated sensible heat ratio for this coil.
** ~~~ ** If autosizing, it is recommended that all three of these values be autosized.
** ~~~ ** ...Inputs used for calculating cooling coil bypass factor.
** ~~~ ** ...Inlet Air Temperature = 26.67 C
** ~~~ ** ...Outlet Air Temperature = 10.81 C
** ~~~ ** ...Inlet Air Humidity Ratio = 1.125000E-002 kgWater/kgDryAir
** ~~~ ** ...Outlet Air Humidity Ratio = 8.142148E-003 kgWater/kgDryAir
** ~~~ ** ...Total Cooling Capacity used in calculation = 5198.00 W
** ~~~ ** ...Air Mass Flow Rate used in calculation = 0.215692 kg/s
** ~~~ ** ...Air Volume Flow Rate used in calculation = 0.188307 m3/s
** ~~~ ** ...Air Volume Flow Rate per Watt of Rated Cooling Capacity is also out of bounds at = 3.6226849E-005 m3/s/W
** ~~~ ** During Warmup, Environment=LOS-ANGELES-DOWNTOWN-USC ANN CLG 0.4% CONDNS DB=>MCWB, at Simulation time=07/21 00:00 - 00:15
** Fatal ** Check and revise the input data for this coil before rerunning the simulation.
...Summary of Errors that led to program termination:
..... Reference severe error count=13
..... Last severe error=For object = Coil:Cooling:DX:SingleSpeed, name = "COOLING COIL C1"
*** Warning: Node connection errors not checked - most system input has not been read (see previous warning).
***** Fatal error -- final processing. Program exited before simulations began. See previous error messages.

The zone system “IDF1 CU1” had a fan flow of 399 cfm with a cooling capacity of 17,000 Btu/hr. This gives an airflow of 282 cfm/ton which is low enough to trigger the error above. The exact lower limit on cfm/ton is not known, but anytime it is less than 300 to 350 you might run into problems like this. I would suggest revising the airflow or cooling capacity to increase the cfm/ton to 350 or 400 and rerunning.

There were other SEVERE errors of the same type for coils “COOLING COIL G1”, “COOLING COIL CME”, “COOLING COIL MSG”, and “COOLING COIL CMDF”, so you might look at the cfm/ton for those systems as well. Finally, there was a SEVERE error on the heat pump heating coil “HEATING COIL MSG.” The limits on this type of coil are from 0.025 cfm/Btuh to 0.0375 cfm/Btuh. Inverting these give limits of 40 to 26.7 Btuh/cfm.

Let me know if those changes do not resolve the problem.

[Nikhil Kapur]

5/9/18 User - Thank you so much for your help, the model ran to completion. Due to the modeling limitations you indicated, we had to oversize some fans to run, which in turn is making us fail. But the model is running as of now, thanks for the quick responses.