ForwardTranslator writes an uninitialized/garbage value into "DX Heating Coil Sizing Ratio" for ZoneHVAC:PackagedTerminalHeatPump, at scale, in the pip openstudio 3.11.0 SDK

[macumber]

Description

See openstudiocoalition/OpenStudioApplication#890 filed by @jmcaamanog for details

When openstudio.energyplus.ForwardTranslator translates an .osm model containing a large
number (~49, confirmed) of ZoneHVAC:PackagedTerminalHeatPump objects, it writes an invalid,
apparently-uninitialized value (4.94065645841247e-324, i.e. std::numeric_limits<double>::denorm_min()
— a classic "read of unset/garbage memory" pattern) into the optional field "DX Heating Coil
Sizing Ratio" of the resulting IDF ZoneHVAC:PackagedTerminalHeatPump object. EnergyPlus then
rejects the value outright ("is not a valid Object Type") and the simulation terminates with a
Fatal Error before running.

This reproduces consistently and only with the pip openstudio 3.11.0 wheel
(pip install openstudio==3.11.0). It does not reproduce with the openstudio-3.10.0 CLI
(openstudio.exe, bundled EnergyPlus 25.1.0) translating the exact same model. Both environments
bundle the same EnergyPlus release (25.1.0), so the difference is in the OpenStudio
ForwardTranslator/model library itself between these two builds, not in EnergyPlus.

Current Behavior

During ForwardTranslator.translateModel(model) (pip 3.11.0), repeated for every affected PTHP
object:

[BOOST_ASSERT] <2> Assertion value failed on line 362 of double __cdecl
openstudio::model::detail::ZoneHVACPackagedTerminalHeatPump_Impl::dXHeatingCoilSizingRatio(void)
const in file D:\a\OpenStudio\OpenStudio\src\model\ZoneHVACPackagedTerminalHeatPump.cpp.

The resulting IDF ZoneHVAC:PackagedTerminalHeatPump object then contains:

  ,                                       !- Capacity Control Method
  ,                                       !- Minimum Supply Air Temperature in Cooling Mode {C}
  ,                                       !- Maximum Supply Air Temperature in Heating Mode {C}
  4.94065645841247e-324;                  !- DX Heating Coil Sizing Ratio

EnergyPlus then fails at the GetSurfaceData/IDD-parsing stage (or later, depending on which tool
wrote the file) with:

** Severe  ** Object contains more field values than maximum number of IDD fields and is not extensible.
** Severe  ** Error parsing "ZoneHVAC:PackagedTerminalHeatPump". Error in following line.
** Severe  ** ~~~   4.94065645841247e-324;                  !- DX Heating Coil Sizing Ratio
** Severe  ** "4.94065645841247e-324" is not a valid Object Type.

repeated once per affected PTHP object (49 times in our case), followed by:

EnergyPlus Terminated--Error(s) Detected.

Confirmed NOT autosize-related: the source .osm template had this field genuinely
unset/blank (isEmpty on the underlying IDF field is True, confirmed via
ZoneHVACPackagedTerminalHeatPump.getString(<field index>)), and the bug reproduces identically
whether the heating/cooling coil capacities are left in Autosize or explicitly hard-sized (we
tried both, to rule out an autosizing-calculation code path as the trigger — same failure either
way, same garbage value).

Expected Behavior

ForwardTranslator should either (a) correctly omit the "DX Heating Coil Sizing Ratio" field when
it is unset on the model object (as it already does correctly for models with few PTHP objects),
or (b) if some internal autosizing-related computation needs a value for it, fall back to the IDD
default (1.0) instead of writing whatever uninitialized memory the getter happens to return.

Steps to reproduce

We don't have a small, shareable, from-scratch repro script yet (our case involves a real building
model we can't publish), but the pattern that triggers it reliably is:

1. Build (or load) an OpenStudio model with a genuinely large number (order of 40-50+) of
   ThermalZones, each with its own ZoneHVAC:PackagedTerminalHeatPump (Fan:SystemModel supply
   fan, Coil:Heating:DX:SingleSpeed, Coil:Cooling:DX:SingleSpeed, Coil:Heating:Electric
   supplemental heater) — in our case, all 49 were .clone()-d from a single real template PTHP
   object (with populated schedules/curves) into the target model, once per zone.
2. Leave the "DX Heating Coil Sizing Ratio" field unset (its default state after cloning from a
   template that also never had it explicitly set).
3. Translate the model with openstudio.energyplus.ForwardTranslator under the pip openstudio
   3.11.0 wheel.
4. Observe the repeated BOOST_ASSERT on dXHeatingCoilSizingRatio() and the garbage value
   written into the IDF.

If someone from the OpenStudio team wants to build a minimal repro: a loop that creates N
ZoneHVACPackagedTerminalHeatPump objects (with real Fan:SystemModel + DX coils + electric
backup coil, not defaults) attached to N zones, then runs ForwardTranslator, scaling N up from a
handful to 40-50, would likely find the exact threshold.

Possible Solution

No response

Operating System affected

Windows 11

Environment

• Failing: openstudio 3.11.0 installed via pip on Windows 11, Python 3.11.
• Not failing (same model, same EnergyPlus release): C:\openstudio-3.10.0\bin\openstudio.exe
  (the official 3.10.0 CLI distribution), which bundles EnergyPlus 25.1.0-1c11a3d85f — the
  exact same EnergyPlus version string reported by the pip 3.11.0 install when it does run.
• OS: Windows 11.

Version of OpenStudio

3.11.0

Context

• This was found while building a tool that merges real building materials/HVAC (ZoneHVAC:PackagedTerminalHeatPump,
  cloned from a real reference model of the building) onto a much finer-grained geometry (73
  thermal zones) exported from a Revit BIM model — a legitimate, real-world use case for having
  many PTHP-equipped zones in one model.
• Happy to provide more detail, the exact IDF fragment (without the real building's proprietary
  geometry), or test further scale thresholds if useful for triage.