Fatal error for autosizing when using WaterHeater:Mixed

[CarlosOchoaIERC]

Issue overview

Similar to #10464 , there is a fatal error when forward translating an old file and asking to autosize the WaterHeater:Mixed

** Severe ** DualSetPointWithDeadBand: Unanticipated combination of heating and cooling loads - report to EnergyPlus Development Team
** ~~~ ** occurs in Zone=BLOCK1:ZONE1 During Warmup, Environment=DUBLIN ANN HTG 99.6% CONDNS DB, at Simulation time=02/21 00:00 - 00:10
** ~~~ ** LoadToHeatingSetPoint=NAN, LoadToCoolingSetPoint=NAN
** ~~~ ** Zone Heating Set-point=20.00
** ~~~ ** Zone Cooling Set-point=20.00
** ~~~ ** Zone TempDepZnLd=2367.13
** ~~~ ** Zone TempIndZnLd=NAN
** ~~~ ** Zone ThermostatSetPoint=20.00

The issue disappears if the water tank is provided with a fixed volume. All the schedules cover the relevant DesignDays.

Details

Some additional details for this issue (if relevant):

• Platform: Windows 11
• Version of EnergyPlus (if using an intermediate build, include SHA): 24.1
• File was originally generated by DesignBuilder (E+ v8.0)

[jmarrec]

@CarlosOchoaIERC Can you attach the IDF file to reproduce please?

[CarlosOchoaIERC]

Solar Colector 10 m2 - PV 20 m2-Customized.zip
Hi, I'm attaching the file as zip since GitHub says it does not support .idf

[jmarrec]

@CarlosOchoaIERC so this file runs fine, and has no WaterHeater:Mixed that has an autosized volume. It has 4 Waterheater:Mixed objects, which one am I supposed to set to autosized volume?

Trial and error: setting Solar Loop Water Heater to autosize is sufficient to produce the NaNs.

[CarlosOchoaIERC]

@CarlosOchoaIERC so this file runs fine, and has no WaterHeater:Mixed that has an autosized volume. It has 4 Waterheater:Mixed objects, which one am I supposed to set to autosized volume?

Trial and error: setting Solar Loop Water Heater to autosize is sufficient to produce the NaNs.

Hi Julien, they were all supposed to be initially in autosize. Hope this helps.

[jmarrec]

The issue is specific to the Solar Loop Water Heater. It's really a very specific combination of factors that lead to the issue:

• Tank sizing uses the PerSolarCollectorArea
• The solar collectors in the model are PhotovoltaicThermal ones (BIPVT), not the regular FlatPlatWater ones
  • This is currently not handled by the routine for calculating the area
• Tank has "Ambient Temperature Indicator" set to "Zone"

As a result the collector area is found to be 0.0, there are zero warnings/errors reported.

The tank volume becomes zero, so the mass of the fluid is also 0, and in CalcTankTemp, you end up with a NaN due to a divide by zero.

This tank has "Ambient Temperature Indicator" set to "Zone", and that NaN propagates to the zone internal gains, and you end up with a DualSetPointWithDeadBand error due to that.

PR that fixes it:

• Fix #10574 - Deal with BIPVT for WaterHeater sizing and throw error if Total Collector area found is zero #10577

[CarlosOchoaIERC]

Thanks a lot for the thorough analysis!