Maximum capacity of Coil:Cooling:DX:SingleSpeed

asked 2017-05-05 10:19:13 -0600

HI, I am working on a LEED energy model for a data center. The design case model ran through fine but my baseline model crashes with the following error:

 ** Severe  ** Temperature (high) out of bounds (202.78] for zone="FLR3_WHITESPACE_A4.03.WS", for surface="6892E3"
   **   ~~~   **  During Warmup, Environment=AMSTERDAM ANN HTG 99.6% CONDNS DB HVAC Sizing Pass 1, at Simulation time=01/21 15:30 - 15:40
   ** Severe  ** Temperature (low) out of bounds [-101.84] for zone="FLR3_WHITESPACE_A4.03.WS", for surface="DAFECC"
   **   ~~~   **  During Warmup, Environment=AMSTERDAM ANN HTG 99.6% CONDNS DB HVAC Sizing Pass 1, at Simulation time=01/21 15:30 - 15:40
   ** Severe  ** Temperature (low) out of bounds [-111.87] for zone="FLR3_WHITESPACE_A4.03.WS", for surface="6892E3"
   **   ~~~   **  During Warmup, Environment=AMSTERDAM ANN HTG 99.6% CONDNS DB HVAC Sizing Pass 1, at Simulation time=01/21 15:30 - 15:40
   ** Severe  ** Temperature (high) out of bounds (210.03] for zone="FLR4_WHITESPACE_A4.04.WS", for surface="B02EB9"
   **   ~~~   **  During Warmup, Environment=AMSTERDAM ANN HTG 99.6% CONDNS DB HVAC Sizing Pass 1, at Simulation time=01/21 15:50 - 16:00
   **   ~~~   ** Zone="FLR4_WHITESPACE_A4.04.WS", Diagnostic Details:
   **   ~~~   ** ...Internal Heat Gain [2114.971] W/m2
   **   ~~~   ** ...Infiltration/Ventilation [0.224] m3/s
   **   ~~~   ** ...Mixing/Cross Mixing [0.000] m3/s
   **   ~~~   ** ...Zone is part of HVAC controlled system.

The IT and electrical rooms have very high internal loads as it is a datacenter. These spaces are conditioned by system 4 - PTHP with single speed DX cooling, single speed DX Heating coils and constant flow fan. Based on my sizing calculations, the rated air flow per watt for the zones is 0.000075 m³/s per watt. According to the idd file, I see that this value should be between 0.00004027 m3/s and .00006041 m3/s per watt of rated total cooling capacity. Here is the error that I get:

   ** Severe  ** Sizing: Coil:Cooling:DX:SingleSpeed "FLR10_TECHSPACE_A4.10.11_PTHP-CCDX": 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=[7.500E-005], Max Rated Vol Flow Per Watt=[6.041E-005]. See Input Output Reference Manual for valid range.
   ************* SizeDXCoil: Potential issue with equipment sizing for Coil:Heating:DX:SingleSpeed FLR10_TECHSPACE_A4.10.11_PTHP-HCDX
   **   ~~~   ** User-Specified Rated Air Flow Rate [m3/s] = 7.12000
   **   ~~~   ** differs from Design Size Rated Air Flow Rate [m3/s] = 13.25438
   **   ~~~   ** This may, or may not, indicate mismatched component sizes.
   **   ~~~   ** Verify that the value entered is intended and is consistent with other components.

Is there a work around to get this Coil:Cooling:DX:SIngleSpeed component used with ZoneHVAC:PackagedTerminalHeatPump to work?

Thank you, Raghu

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answered 2017-05-05 10:39:38 -0600

rraustad

13804 ●79 ●12 http://www.fsec.ucf.edu/

For the DX cooling coil, the rated air flow rate ratio has a limit of 0.00004027 m3/s (300 cfm/ton) - 0.00006041 m3/s (450 cfm/ton). The operating air flow rate ratio has a wider range at 0.00002684 m3/s (200 cfm/ton) - 0.00006713 m3/s (500 cfm/ton).

The best outcome at this point would be to size the coil near the top end of the rated air flow range (air flow rate used in the DX coil object), and operate that coil (air flow rate used in the parent object) near the top end of the operating air flow rate ratio range.

You could also use the Total Cooling Capacity Function of Flow Fraction Curve and Energy Input Ratio Function of Flow Fraction Curve to adjust the performance of this coil such that you get what you would have at the higher air flow rate ratio.