Improve MaxLoad sizing methodology by shorowit · Pull Request #2235 · NatLabRockies/OpenStudio-HPXML

shorowit · 2026-07-07T23:18:28Z

Pull Request Description

Closes #2226.

This also fixes the case where HeatPumpSizingMethodology="HERS" and HeatPumpBackupSizingMethodology="supplemental" are used together. If the HP heating capacity was increased due to the HERS methodology, the supplemental heating capacity is now reduced accordingly.

Checklist

Not all may apply:

Schematron validator (EPvalidator.sch) has been updated
Sample files have been added/updated (openstudio tasks.rb update_hpxmls)
Tests have been added/updated (e.g., HPXMLtoOpenStudio/tests/test*.rb and/or workflow/tests/test*.rb)
Documentation has been updated
Changelog has been updated
openstudio tasks.rb update_measures has been run
No unexpected changes to simulation results of sample files

…HPXML into maxload_sizing # Conflicts: # HPXMLtoOpenStudio/measure.xml

…HPXML into maxload_sizing # Conflicts: # HPXMLtoOpenStudio/measure.xml # workflow/tests/base_results/results_simulations_bills.csv # workflow/tests/base_results/results_simulations_energy.csv # workflow/tests/base_results/results_simulations_loads.csv # workflow/tests/base_results/results_simulations_misc.csv

Copilot

Pull request overview

Refactors air-source heat-pump sizing to improve MaxLoad calculations and account for HERS-adjusted capacity when sizing supplemental backup heat.

Changes:

Selects MaxLoad capacity from independently calculated heating and cooling capacities.
Applies HERS capacity adjustments before supplemental backup sizing.
Updates documentation, tests, metadata, and simulation baselines.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
`HPXMLtoOpenStudio/resources/hvac_sizing.rb`	Refactors heat-pump capacity sizing.
`HPXMLtoOpenStudio/tests/test_hvac_sizing.rb`	Adjusts sizing methodology test coverage.
`HPXMLtoOpenStudio/measure.xml`	Updates measure metadata and checksums.
`docs/source/workflow_inputs.rst`	Clarifies air-source applicability.
`Changelog.md`	Records the MaxLoad fix.
`workflow/tests/base_results/results_hers_hvac.csv`	Updates HERS HVAC baselines.
`workflow/tests/base_results/results_simulations_misc.csv`	Updates miscellaneous simulation baselines.
`workflow/tests/base_results/results_simulations_loads.csv`	Updates load baselines.
`workflow/tests/base_results/results_simulations_energy.csv`	Updates energy baselines.
`workflow/tests/base_results/results_simulations_bills.csv`	Updates utility-bill baselines.

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…HPXML into maxload_sizing # Conflicts: # HPXMLtoOpenStudio/measure.xml # workflow/tests/base_results/results_simulations_bills.csv # workflow/tests/base_results/results_simulations_energy.csv # workflow/tests/base_results/results_simulations_misc.csv

shorowit · 2026-07-09T23:07:21Z

+    if hpxml_bldg.header.heat_pump_sizing_methodology == HPXML::HeatPumpSizingMaxLoad
+      # MaxLoad sizing methodology: autosized heat pumps have their nominal capacity
+      # sized based on the larger of heating/cooling design loads, while taking into
+      # account the heat pump's reduced capacity at the design temperature, such that
+      # no backup heating should be necessary.
+      hp_capacities = []
+      hp_capacities << hvac_sizings.Cool_Capacity if hvac_heating.fraction_cool_load_served > 0
+      hp_capacities << heat_cap_rated if hvac_heating.fraction_heat_load_served > 0
+      hp_capacity = hp_capacities.max
+      if hvac_heating.fraction_cool_load_served > 0
+        scaling_factor = hp_capacity / hvac_sizings.Cool_Capacity
+        hvac_sizings.Cool_Capacity = hp_capacity
+        hvac_sizings.Cool_Capacity_Sens *= scaling_factor
+        hvac_sizings.Cool_Airflow *= scaling_factor
      end
+      if hvac_heating.fraction_heat_load_served > 0
+        hvac_sizings.Heat_Capacity = hp_capacity
+      end


All MaxLoad code moved to here (which only applies to air-source HPs). At this point, we have the autosized cooling capacity as determined by Manual J/S. Then we compare that to the heating capacity needed to meet the full heating load, choose the larger of the two, and bump up capacities/airflows as needed.

shorowit · 2026-07-09T23:08:33Z

    end

-    return heating_load
+    if hpxml_bldg.header.heat_pump_sizing_methodology == HPXML::HeatPumpSizingHERS


Moved the existing HERS code to here so that it applies before we determine the backup heating capacity (needed when HeatPumpBackupSizingMethodology="supplemental"). This fixes a small unrelated bug.

shorowit · 2026-07-14T17:49:41Z

+      end
+    elsif cool_cap_adj_factor.nil? # Heat pump has no cooling
+      # Size equal to heating design load (arbitrary)
+      hvac_sizings.Heat_Capacity = hvac_sizings.Heat_Load


Should this be heating_load instead of hvac_sizings.Heat_Load (here and elsewhere)?

Or maybe we should remove this path and make sure that cool_cap_adj_factor is always defined?

shorowit · 2026-07-14T18:14:05Z

-denver-hvac-autosize-air-to-air-heat-pump-var-speed-backup-boiler-hvac-seasons-sizing-methodology-MaxLoad-backup-emergency.xml,53765.0,53765.0,23884.0,1613.0,1613.0
-denver-hvac-autosize-air-to-air-heat-pump-var-speed-backup-boiler-hvac-seasons-sizing-methodology-MaxLoad-backup-supplemental.xml,53765.0,53765.0,23884.0,1613.0,1613.0
+denver-hvac-autosize-air-to-air-heat-pump-var-speed-backup-boiler-hvac-seasons-sizing-methodology-MaxLoad-backup-emergency.xml,38589.0,38589.0,23884.0,1158.0,1158.0
+denver-hvac-autosize-air-to-air-heat-pump-var-speed-backup-boiler-hvac-seasons-sizing-methodology-MaxLoad-backup-supplemental.xml,38589.0,38589.0,23884.0,1158.0,1158.0


Consider adding another sample file (for simulation results).

shorowit · 2026-07-14T18:22:37Z

-      if hpxml_bldg.header.heat_pump_sizing_methodology == HPXML::HeatPumpSizingMaxLoad
-        # Size based on heating, taking into account reduced heat pump capacity at the design temperature
-        hvac_sizings.Cool_Capacity = heat_cap_rated
+      # Size based on cooling, but with ACCA oversizing allowances for heating
+      load_shr = hvac_sizings.Cool_Load_Sens / hvac_sizings.Cool_Load_Tot
+      if ((weather.data.HDD65F / weather.data.CDD50F) < 2.0) || (load_shr < 0.95)
+        # Mild winter or has a latent cooling load
+        hvac_sizings.Cool_Capacity = [(oversize_limit * hvac_sizings.Cool_Load_Tot) / cool_cap_adj_factor, heat_cap_rated].min
      else
-        # Size based on cooling, but with ACCA oversizing allowances for heating
-        load_shr = hvac_sizings.Cool_Load_Sens / hvac_sizings.Cool_Load_Tot
-        if ((weather.data.HDD65F / weather.data.CDD50F) < 2.0) || (load_shr < 0.95)
-          # Mild winter or has a latent cooling load
-          hvac_sizings.Cool_Capacity = [(oversize_limit * hvac_sizings.Cool_Load_Tot) / cool_cap_adj_factor, heat_cap_rated].min
-        else
-          # Cold winter and no latent cooling load (add a ton rule applies)
-          hvac_sizings.Cool_Capacity = [(hvac_sizings.Cool_Load_Tot + oversize_delta) / cool_cap_adj_factor, heat_cap_rated].min
-        end
+        # Cold winter and no latent cooling load (add a ton rule applies)
+        hvac_sizings.Cool_Capacity = [(hvac_sizings.Cool_Load_Tot + oversize_delta) / cool_cap_adj_factor, heat_cap_rated].min


Looks like a lot of changes but really just removed any if hpxml_bldg.header.heat_pump_sizing_methodology == HPXML::HeatPumpSizingMaxLoad branches.

shorowit · 2026-07-14T18:23:10Z

+    # Test that the supplemental heating capacity is reduced when we switch
+    # from ACCA to HERS sizing methodology (which increases the HP capacity)


Found this unrelated bug and added a test to show it now works as expected.

shorowit added 2 commits July 7, 2026 17:13

First pass on fixing MaxLoad sizing algorithm.

609eb3a

Clarify docs.

d76808c

shorowit self-assigned this Jul 7, 2026

github-project-automation Bot moved this to Triage in OpenStudio-HPXML Jul 7, 2026

github-project-automation Bot added this to OpenStudio-HPXML Jul 7, 2026

Merge branch 'master' of https://github.com/NatLabRockies/OpenStudio-…

f2fabf3

…HPXML into maxload_sizing # Conflicts: # HPXMLtoOpenStudio/measure.xml

shorowit removed this from OpenStudio-HPXML Jul 7, 2026

GitHub Action and others added 5 commits July 8, 2026 00:41

Latest results. [skip ci]

6e18328

Latest results. [skip ci]

fdd100c

A little code refactor.

8808347

Skip assignment of HP sizing methodology to GSHP test runs.

ca53863

github-project-automation Bot added this to OpenStudio-HPXML Jul 9, 2026

github-project-automation Bot moved this to Triage in OpenStudio-HPXML Jul 9, 2026

Latest results. [skip ci]

de223a7

shorowit marked this pull request as ready for review July 10, 2026 23:08

Update Changelog.md [ci skip]

5600990

shorowit requested a review from Copilot July 10, 2026 23:12

Copilot started reviewing on behalf of shorowit July 10, 2026 23:13 View session

Copilot AI reviewed Jul 10, 2026

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Comment thread HPXMLtoOpenStudio/resources/hvac_sizing.rb Outdated

Comment thread HPXMLtoOpenStudio/tests/test_hvac_sizing.rb

shorowit force-pushed the maxload_sizing branch from a562b3c to 5600990 Compare July 10, 2026 23:34

shorowit and others added 3 commits July 13, 2026 16:39

Address review feedback

473a0c6

Latest results. [skip ci]

c09c42d

shorowit commented Jul 14, 2026

View reviewed changes

Small refactor. Shouldn't change results.

35d007f

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