Merge pull request #2092 from NREL/gshp_sizing_error

Fix possible GSHP sizing error

Author: shorowit

Changelog.md

@@ -30,6 +30,7 @@ __Bugfixes__
 - Fixes zero mech vent fan energy when CFIS system w/ `AdditionalRuntimeOperatingMode="air handler fan"` has the airflow rate set to zero.
 - Fixes requested EnergyPlus timeseries output variables/meters not displayed in DView if they don't have units.
 - Fixes possible errors when small water flow rates for variable-speed experimental ground-source heat pump model.
+- Fixes possible ground-source heat pump sizing error if the heating or cooling design temperature differences are zero.
 
 ## OpenStudio-HPXML v1.10.0
 

HPXMLtoOpenStudio/measure.xml

@@ -3,8 +3,8 @@
   <schema_version>3.1</schema_version>
   <name>hpxm_lto_openstudio</name>
   <uid>b1543b30-9465-45ff-ba04-1d1f85e763bc</uid>
-  <version_id>ebf347a8-a3b8-4096-a72c-078aa24e7d59</version_id>
-  <version_modified>2025-10-31T18:46:56Z</version_modified>
+  <version_id>136fac64-f9c0-4cbd-b9ef-18324d2691c6</version_id>
+  <version_modified>2025-10-31T22:09:18Z</version_modified>
   <xml_checksum>D8922A73</xml_checksum>
   <class_name>HPXMLtoOpenStudio</class_name>
   <display_name>HPXML to OpenStudio Translator</display_name>
@@ -420,7 +420,7 @@
       <filename>hvac_sizing.rb</filename>
       <filetype>rb</filetype>
       <usage_type>resource</usage_type>
-      <checksum>AFA48130</checksum>
+      <checksum>AE488BAC</checksum>
     </file>
     <file>
       <filename>internal_gains.rb</filename>
@@ -768,7 +768,7 @@
       <filename>test_hvac_sizing.rb</filename>
       <filetype>rb</filetype>
       <usage_type>test</usage_type>
-      <checksum>3E300829</checksum>
+      <checksum>8F446353</checksum>
     </file>
     <file>
       <filename>test_lighting.rb</filename>

HPXMLtoOpenStudio/resources/hvac_sizing.rb

@@ -3409,11 +3409,22 @@ def self.get_geothermal_loop_borefield_ft_per_ton(mj, hpxml_bldg, geothermal_loo
       cooling_month = 6 # July
     end
 
-    rtf_DesignMon_Heat = [0.25, (71.0 - weather.data.MonthlyAvgDrybulbs[heating_month]) / mj.htd].max
-    rtf_DesignMon_Cool = [0.25, (weather.data.MonthlyAvgDrybulbs[cooling_month] - 76.0) / mj.ctd].max
+    # Runtime fraction average in heating/cooling months, assumed
+    if mj.htd > 0
+      rtf_design_mon_heat = (mj.heat_setpoint - weather.data.MonthlyAvgDrybulbs[heating_month]) / mj.htd
+    else
+      rtf_design_mon_heat = 0
+    end
+    if mj.ctd > 0
+      rtf_design_mon_cool = (weather.data.MonthlyAvgDrybulbs[cooling_month] - mj.cool_setpoint) / mj.ctd
+    else
+      rtf_design_mon_cool = 0
+    end
+    rtf_design_mon_heat = [[rtf_design_mon_heat, 0.25].max, 1.0].min
+    rtf_design_mon_cool = [[rtf_design_mon_cool, 0.25].max, 1.0].min
 
-    nom_length_heat = (1.0 - 1.0 / clg_ap.heat_rated_cops[0]) * (r_value_bore + r_value_ground * rtf_DesignMon_Heat) / (weather.data.DeepGroundAnnualTemp - (2.0 * clg_ap.design_hw - clg_ap.design_delta_t) / 2.0) * UnitConversions.convert(1.0, 'ton', 'Btu/hr')
-    nom_length_cool = (1.0 + 1.0 / clg_ap.cool_rated_cops[0]) * (r_value_bore + r_value_ground * rtf_DesignMon_Cool) / ((2.0 * clg_ap.design_chw + clg_ap.design_delta_t) / 2.0 - weather.data.DeepGroundAnnualTemp) * UnitConversions.convert(1.0, 'ton', 'Btu/hr')
+    nom_length_heat = (1.0 - 1.0 / clg_ap.heat_rated_cops[0]) * (r_value_bore + r_value_ground * rtf_design_mon_heat) / (weather.data.DeepGroundAnnualTemp - (2.0 * clg_ap.design_hw - clg_ap.design_delta_t) / 2.0) * UnitConversions.convert(1.0, 'ton', 'Btu/hr')
+    nom_length_cool = (1.0 + 1.0 / clg_ap.cool_rated_cops[0]) * (r_value_bore + r_value_ground * rtf_design_mon_cool) / ((2.0 * clg_ap.design_chw + clg_ap.design_delta_t) / 2.0 - weather.data.DeepGroundAnnualTemp) * UnitConversions.convert(1.0, 'ton', 'Btu/hr')
 
     return nom_length_heat, nom_length_cool
   end

HPXMLtoOpenStudio/tests/test_hvac_sizing.rb

@@ -1784,15 +1784,15 @@ def test_gshp_geothermal_loop
       XMLHelper.write_file(hpxml.to_doc, @tmp_hpxml_path)
       _model, _test_hpxml, test_hpxml_bldg = _test_measure(args_hash)
       assert_equal(3, test_hpxml_bldg.geothermal_loops[0].num_bore_holes)
-      assert_in_delta(194.0, test_hpxml_bldg.geothermal_loops[0].bore_length, 1.0)
+      assert_in_delta(190.0, test_hpxml_bldg.geothermal_loops[0].bore_length, 1.0)
 
       # Bore depth greater than the max -> increase number of boreholes
       hpxml, hpxml_bldg = _create_hpxml(ghp_filename)
       hpxml_bldg.site.ground_conductivity = 0.18
       XMLHelper.write_file(hpxml.to_doc, @tmp_hpxml_path)
       _model, _test_hpxml, test_hpxml_bldg = _test_measure(args_hash)
       assert_equal(5, test_hpxml_bldg.geothermal_loops[0].num_bore_holes)
-      assert_in_delta(442.0, test_hpxml_bldg.geothermal_loops[0].bore_length, 1.0)
+      assert_in_delta(431.0, test_hpxml_bldg.geothermal_loops[0].bore_length, 1.0)
 
       # Bore depth greater than the max -> increase number of boreholes until the max, set depth to the max, and issue warning
       hpxml, hpxml_bldg = _create_hpxml(ghp_filename)