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Adding a Heat Pump Water Heater causing many new out of range errors

asked 2016-08-19 14:19:45 -0500

jugonzal07 gravatar image

updated 2017-08-07 13:46:00 -0500

Coming back to you with another exciting heat pump water heater (HPWH) question.

I've been testing an OpenStudio measure I wrote to add HPWHs on a few test buildings and am running into errors I haven't seen before. In particular, it is causing errors in this building that has 5 rooftop AC units and wanted to hear what you all thought.

Below are the error logs of the buildings before and after adding the HPWH. :

Lines in HPWH error file that are cause for concern:

   *************  ** Warning ** Enthalpy out of range (PsyTsatFnHPb)
   *************  **   ~~~   **   This error occurred 7144 total times;
   *************  **   ~~~   **   during Warmup 0 times;
   *************  **   ~~~   **   during Sizing 0 times.
   *************  **   ~~~   **   Max=-56493.273821 J/kg  Min=-11888262.758062 J/kg
   *************  ** Warning ** Temperature out of range [-100. to 200.] (PsyPsatFnTemp)
   *************  **   ~~~   **   This error occurred 728 total times;
   *************  **   ~~~   **   during Warmup 0 times;
   *************  **   ~~~   **   during Sizing 0 times.
   *************  **   ~~~   **   Max=-600.530182 C  Min=-11848.583984 C

Full error logs

You'll see I get some very alarming temperature and enthalpy values. Any thoughts on what I should check or how to think through these types of errors? I'm stumped on why adding a HPWH would cause this.

I got E+ to report the inlet node temperatures for the cooling coil on the HVAC side as well as the inlet and outlet nodes for the SHW and not seeing anything near the ranges reported in the error files. All temperatures there seem reasonable.

TL;DR - Adding a HPWH caused strange errors with respect to temperature and enthalpy. Why would adding a HPWH cause such drastic temperature ranges? How would one check WHERE the temperatures reported in the error file come from?

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answered 2016-08-23 20:42:48 -0500

updated 2017-03-09 02:16:41 -0500

It's hard to say exactly what is causing this without seeing the input file (idf). The psyc routines have been evolving to show what routine was executing when the error occurred, but all the calls to the psyc routines have not yet been updated. I would suspect something to do with air flow control for DX coils given this warning:

** Warning ** CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed="COIL COOLING DX SINGLE SPEED 5" - Air volume flow rate per watt of rated total cooling capacity is out of range at 1.299E-006 m3/s/W.
**   ~~~   ** Expected range for VolumeFlowPerRatedTotalCapacity=[2.684E-005--6.713E-005]

I did not see this warning in the baseline error file. Is this a HPWH coil? Regardless, check the inputs to see if there is a reason for the air flow to capacity ratio being an order of magnitude lower than expected. You can also send your input file to the help desk at

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Hi rraustad,

Thanks for the reply. I sent them something yesterday and hope to hear back from them soon!

As for that coil, that appears to be Zone 5's cooling coil on the rooftop unit. Zone 5 is the zone with the HPWH however so maybe there's something there. Overall, my concern is whether or not I should accept the results (OS throws warnings on nearly all files I run) or if these errors warrant more investigation.

jugonzal07 gravatar image jugonzal07  ( 2016-08-24 16:55:37 -0500 )edit

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Asked: 2016-08-19 14:19:45 -0500

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Last updated: Mar 09 '17