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DX Single Speed Cooling Coil

asked 2016-01-07 11:51:43 -0600

Dustin gravatar image

updated 2016-01-07 13:17:59 -0600

Having troubles modelled some basic ACs that are in some of my centre zones. I have the following errors that occur at the beginning of my simulation.

   ** Warning ** CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed="CC AC 6" - Air volume flow rate per watt of rated total cooling capacity is out of range at 1.523E-005 m3/s/W.
   **   ~~~   **  Environment=RUN PERIOD 1, at Simulation time=01/01 00:00 - 00:15
   **   ~~~   ** Expected range for VolumeFlowPerRatedTotalCapacity=[2.684E-005--6.713E-005]
   **   ~~~   ** Possible causes include inconsistent air flow rates in system components,
   **   ~~~   ** or variable air volume [VAV] system using incorrect coil type.

   ** Warning ** CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed "CC AC 6" - Full load outlet air dry-bulb temperature < 2C. This indicates the possibility of coil frost/freeze. Outlet temperature = -37.38 C.
   **   ~~~   **  ...Occurrence info = RUN PERIOD 1, 01/01 00:00 - 00:03
   **   ~~~   ** ... Possible reasons for low outlet air dry-bulb temperatures are: This DX coil
   **   ~~~   **    1) may have a low inlet air dry-bulb temperature. Inlet air temperature = 16.268 C.
   **   ~~~   **    2) may have a low air flow rate per watt of cooling capacity. Check inputs.
   **   ~~~   **    3) is used as part of a HX assisted cooling coil which uses a high sensible effectiveness. Check inputs.

I have auto sized the ACs and these errors still seem to be occurring. Not sure how to go about fixing them. To create the ACs I used an empty air loop and threw a fan and dx single speed cooling coil on the supply side and the zone with a VAV on the demand side. If there is something wrong with how I modelled this or if anyone has any suggestions that would be greatly appreciated.


Edit: Not sure if this will help determine the problem but here is a screenshot of the loop I am using for the ACs.

image description

I was not sure if I should be adding the outdoor air handler or not.

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I can translate the icons for @rraustad (and everyone else) because the types are not obvious unless your life revolves around OS like mine sadly does.

This is most likely AirTerminalSingleDuctVAVNoReheat, CoilCoolingDXSingleSpeed (already mentioned), FanVariableVolume, and a SetpointManagerScheduled.

Kyle Benne gravatar image Kyle Benne  ( 2016-01-07 20:34:47 -0600 )edit

@Dustin, the example file 5ZoneAutoDXVAV uses this system type. I suggest running that file and reviewing the configuration.

rraustad gravatar image rraustad  ( 2016-01-08 08:49:43 -0600 )edit

2 Answers

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answered 2016-01-07 12:27:35 -0600

If you check the eio file for sizing results, you will find that this coil has a design flow to capacity ratio within the limits used for sizing, 0.00004026 and 0.00006041 m3/s/W (look at the eio results and do the math, air flow divided by capacity).

This warning shows that the "operating" flow to capacity ratio, which as stated in the warning, must be between the values shown in the warning. The question is what is causing the air flow rate to be lower than expected during the simulation.

  • What system type is used
  • What type of terminal units are used
  • Is the overall simulation completely autosized
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answered 2016-01-07 20:39:50 -0600

updated 2016-01-08 09:05:43 -0600

I'd say the VAV terminal is allowing turndown below where the single speed coil can operate. I suggest that you try CoilCoolingDXTwoSpeed.

You should also click on the center line and double check that the SystemSizing object's field "Central Cooling Design Supply Air Temperature" is aligned with the temperature defined by the SetpointManagerScheduled schedule. That is you want to make sure the sizing parameters in SizingSystem are reasonably close to how you are trying to operate the system.

If you stick with the single speed coil, consider the terminal inputs for the zone minimum air flow fields. You can set it up so that the terminal does not reduce air flow below the ratio accepted by the coil.

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Asked: 2016-01-07 11:51:43 -0600

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Last updated: Jan 08 '16