Writing OpenStudio Model Measures

Expert guidance for creating OpenStudio ModelMeasures - Ruby scripts that programmatically modify building energy models (.osm files).

Target Version: OpenStudio 3.9 Measure Type: ModelMeasure (modifies OSM files) Measure Directory: C:\Users\mcoalson\OpenStudio\Measures Reference: https://nrel.github.io/OpenStudio-user-documentation/reference/measure_writing_guide/

When to Use This Skill

Invoke when you need to:

• Write a new OpenStudio measure from scratch
• Modify existing measure.rb files
• Create measure test files
• Understand OpenStudio measure structure and best practices
• Scaffold a complete measure directory with boilerplate code

Quick Start: Creating a New Measure

Use the Node.js scaffolding script to generate a complete measure structure in your measures directory:

cd "C:\Users\mcoalson\OpenStudio\Measures"
node "C:\Users\mcoalson\Documents\WorkPath\.claude\skills\writing-openstudio-model-measures\scripts\scaffold-measure.js" "Your Measure Name"

This creates:

• Measure directory with snake_case name
• measure.rb with complete boilerplate
• measure.xml (auto-generated by OpenStudio)
• tests/ directory with MiniTest template
• resources/ directory for helpers
• README.md stub

Measure Structure

Every ModelMeasure requires:

Required Files:

• measure.rb - Main Ruby script (see ./templates/model-measure-template.rb)
• measure.xml - Metadata (auto-generated when measure runs)

Recommended Files:

• tests/measure_test.rb - MiniTest unit tests (see ./templates/measure-test-template.rb)
• README.md - Documentation
• resources/ - Helper Ruby files
• LICENSE.md - Distribution license

Core Implementation Pattern

Every ModelMeasure must:

1. Inherit from base class:

   class YourMeasure < OpenStudio::Measure::ModelMeasure
   

2. Implement five required methods:

   • name() - User-visible title
   • description() - General audience explanation
   • modeler_description() - Technical details for modelers
   • arguments(model) - Define user inputs
   • run(model, runner, user_arguments) - Main logic

3. Return boolean from run():

   • true if measure succeeds
   • false if measure fails (after logging error)

Required Methods Details

1. name()

def name
  return "Add Window Overhangs"
end

• Short, descriptive, general
• User-visible in OpenStudio Application

2. description()

def description
  return "Adds overhangs to all exterior windows based on user-specified projection factor. Improves solar control and reduces cooling loads."
end

• General audience explanation
• Include what measure does and benefits

3. modeler_description()

def modeler_description
  return "Iterates through all SubSurfaces with 'Window' type, creates ShadingSurfaceGroup and ShadingSurface objects with projection calculated as window height × projection factor. Assumes windows face outward from building."
end

• Technical implementation details
• Assumptions, algorithms, references

4. arguments(model)

def arguments(model)
  args = OpenStudio::Measure::OSArgumentVector.new

  # Double argument
  projection_factor = OpenStudio::Measure::OSArgument.makeDoubleArgument('projection_factor', true)
  projection_factor.setDisplayName('Projection Factor')
  projection_factor.setDescription('Overhang depth as multiple of window height')
  projection_factor.setDefaultValue(0.5)
  args << projection_factor

  # Boolean argument
  apply_to_north = OpenStudio::Measure::OSArgument.makeBoolArgument('apply_to_north', true)
  apply_to_north.setDisplayName('Apply to North-Facing Windows?')
  apply_to_north.setDefaultValue(false)
  args << apply_to_north

  # Choice argument
  choices = OpenStudio::StringVector.new
  choices << "All Windows"
  choices << "South-Facing Only"
  choices << "East and West Only"
  orientation = OpenStudio::Measure::OSArgument.makeChoiceArgument('orientation', choices, true)
  orientation.setDisplayName('Window Orientation Filter')
  orientation.setDefaultValue("All Windows")
  args << orientation

  return args
end

Argument Types:

• makeDoubleArgument(name, required) - Real numbers
• makeIntegerArgument(name, required) - Whole numbers
• makeBoolArgument(name, required) - True/false
• makeStringArgument(name, required) - Text input
• makeChoiceArgument(name, choices_vector, required) - Dropdown selection

5. run(model, runner, user_arguments)

def run(model, runner, user_arguments)
  super(model, runner, user_arguments)

  # 1. Validate and extract arguments
  if !runner.validateUserArguments(arguments(model), user_arguments)
    return false
  end

  projection_factor = runner.getDoubleArgumentValue('projection_factor', user_arguments)
  apply_to_north = runner.getBoolArgumentValue('apply_to_north', user_arguments)
  orientation = runner.getStringArgumentValue('orientation', user_arguments)

  # 2. Additional validation
  if projection_factor < 0 || projection_factor > 5
    runner.registerError("Projection factor must be between 0 and 5, got #{projection_factor}")
    return false
  end

  # 3. Register initial condition
  initial_overhang_count = model.getShadingSurfaces.length
  runner.registerInitialCondition("Model has #{initial_overhang_count} shading surfaces.")

  # 4. Main measure logic
  windows_modified = 0

  model.getSubSurfaces.each do |sub_surface|
    next unless sub_surface.subSurfaceType == "FixedWindow" || sub_surface.subSurfaceType == "OperableWindow"

    # Your logic here
    windows_modified += 1
    runner.registerInfo("Added overhang to window: #{sub_surface.name}")
  end

  # 5. Handle not applicable case
  if windows_modified == 0
    runner.registerAsNotApplicable("No windows found in model.")
    return true
  end

  # 6. Register final condition
  final_overhang_count = model.getShadingSurfaces.length
  runner.registerFinalCondition("Added #{final_overhang_count - initial_overhang_count} overhangs to #{windows_modified} windows.")

  return true
end

Logging and User Communication

Use runner methods to communicate:

Info Messages (measure continues):

runner.registerInfo("Processing 42 windows...")

Warning Messages (measure continues):

runner.registerWarning("Window '#{name}' has no parent surface, skipping.")

Error Messages (measure stops):

runner.registerError("Invalid projection factor: #{value}")
return false

Condition Tracking:

runner.registerInitialCondition("Before: #{count} objects")
runner.registerFinalCondition("After: #{count} objects, added #{delta}")

Not Applicable:

runner.registerAsNotApplicable("No HVAC systems found in model.")
return true  # Still return true!

OpenStudio API Patterns

Getting Objects from Model

Non-unique objects (can have multiple instances):

# Get all instances
spaces = model.getSpaces
thermal_zones = model.getThermalZones

# Get by name
space = model.getSpaceByName("Office 101")
if space.is_initialized
  space_obj = space.get
  # Use space_obj
end

Unique objects (only one instance):

# Get the single instance
building = model.getBuilding
site = model.getSite

Safe Optional Handling

OpenStudio uses boost::optional types extensively. Always check before using .get():

# UNSAFE - will crash if empty
zone = space.thermalZone.get  # BAD!

# SAFE - check first
if !space.thermalZone.empty?
  zone = space.thermalZone.get
  runner.registerInfo("Space is in zone: #{zone.name}")
else
  runner.registerWarning("Space has no thermal zone assigned.")
end

# Alternative safe pattern
if space.thermalZone.is_initialized
  zone = space.thermalZone.get
  # Use zone
end

Common Model Queries

# Spaces and Zones
model.getSpaces.each do |space|
  puts space.name
end

model.getThermalZones.each do |zone|
  puts zone.name
end

# Surfaces
model.getSurfaces.each do |surface|
  puts "#{surface.name}: #{surface.surfaceType}"
end

# SubSurfaces (windows, doors)
model.getSubSurfaces.each do |sub_surface|
  puts "#{sub_surface.name}: #{sub_surface.subSurfaceType}"
end

# HVAC Equipment
model.getAirLoopHVACs.each do |air_loop|
  puts air_loop.name
end

model.getPlantLoops.each do |plant_loop|
  puts plant_loop.name
end

# Constructions and Materials
model.getConstructions.each do |construction|
  puts construction.name
end

# Schedules
model.getScheduleRulesets.each do |schedule|
  puts schedule.name
end

Testing with MiniTest

Every measure should include tests in tests/measure_test.rb.

Run tests:

cd /path/to/your_measure
ruby tests/measure_test.rb

See ./templates/measure-test-template.rb for complete test structure.

Basic test pattern:

def test_valid_arguments
  # Load test model
  model = load_test_model

  # Create measure instance
  measure = YourMeasure.new

  # Get arguments
  arguments = measure.arguments(model)

  # Set argument values
  argument_map = OpenStudio::Measure.convertOSArgumentVectorToMap(arguments)
  projection_factor = arguments[0].clone
  assert(projection_factor.setValue(0.5))
  argument_map['projection_factor'] = projection_factor

  # Run measure
  measure.run(model, runner, argument_map)
  result = runner.result

  # Assertions
  assert_equal('Success', result.value.valueName)
  assert(result.info.size > 0)
  assert_equal(0, result.warnings.size)
end

Best Practices

Code Quality

• Follow Ruby Style Guide
• Use 2-space indentation
• Keep methods focused and concise
• Add comments for complex logic

Input Validation

• Always validate user arguments
• Check value ranges and logical constraints
• Provide clear error messages
• Use runner.validateUserArguments() first

Error Handling

• Check for empty optionals before calling .get()
• Handle edge cases (empty model, missing objects)
• Use registerAsNotApplicable() when measure doesn't apply
• Return false only after logging error with registerError()

Performance

• Avoid nested loops when possible
• Cache frequently accessed values
• Use model.getObjectsByType() for specific object types

User Experience

• Use clear, descriptive argument names
• Set sensible default values
• Log progress for long-running operations
• Report initial and final conditions

OpenStudio 3.9 Specific Notes

Ruby Version: OpenStudio 3.9 uses Ruby 2.7.2 API Documentation: https://openstudio-sdk-documentation.s3.amazonaws.com/index.html

Common gotchas:

• Method names are camelCase (OpenStudio convention), not snake_case (Ruby convention)
• Units matter - always check if arguments need IP or SI units
• measure.xml auto-regenerates - don't manually edit structure, only metadata
• Test with multiple model types (residential, commercial, different HVAC systems)

Common Measure Patterns

Iterating Through Spaces

model.getSpaces.each do |space|
  runner.registerInfo("Processing space: #{space.name}")

  # Get space properties
  floor_area = space.floorArea  # m²

  # Get thermal zone
  if space.thermalZone.is_initialized
    zone = space.thermalZone.get
    runner.registerInfo("  Zone: #{zone.name}")
  end

  # Get space type
  if space.spaceType.is_initialized
    space_type = space.spaceType.get
    runner.registerInfo("  Type: #{space_type.name}")
  end
end

Modifying Constructions

model.getSurfaces.each do |surface|
  next unless surface.surfaceType == "RoofCeiling"
  next unless surface.outsideBoundaryCondition == "Outdoors"

  # Create or get construction
  new_construction = model.getConstructionByName("High Performance Roof")
  if new_construction.is_initialized
    surface.setConstruction(new_construction.get)
    runner.registerInfo("Updated roof construction: #{surface.name}")
  end
end

Working with Schedules

# Get schedule by name
schedule = model.getScheduleRulesetByName("Office Occupancy")
if schedule.is_initialized
  sched = schedule.get
  # Modify schedule rules
end

# Create new schedule
new_schedule = OpenStudio::Model::ScheduleRuleset.new(model)
new_schedule.setName("Custom Schedule")
new_schedule.defaultDaySchedule.setName("Custom Default")
# Add time-value pairs
new_schedule.defaultDaySchedule.addValue(OpenStudio::Time.new(0,8,0,0), 0)
new_schedule.defaultDaySchedule.addValue(OpenStudio::Time.new(0,18,0,0), 1)

Upgrading to OpenStudio 3.10 (Future)

When ready to upgrade, note these areas that may require changes:

• API method deprecations
• Ruby version changes
• New object types or properties
• Updated testing frameworks

Document upgrade process in ./upgrading-to-310.md when that time comes.

Additional Resources

Templates:

• ./templates/model-measure-template.rb - Complete ModelMeasure boilerplate
• ./templates/measure-test-template.rb - MiniTest template

Scripts:

• ./scripts/scaffold-measure.js - Node.js script to create measure directory structure

External References:

• NREL Measure Writing Guide
• OpenStudio API Documentation
• Ruby Style Guide
• OpenStudio Common Measures - Example implementations

Workflow Summary

1. Scaffold measure using Node.js script or manually create directory
2. Write measure.rb using template as starting point
3. Implement five required methods (name, description, modeler_description, arguments, run)
4. Add input validation and error handling
5. Test with MiniTest - create tests in tests/ directory
6. Run in OpenStudio Application to generate/update measure.xml
7. Iterate and refine based on testing with various models

---

Last Updated: 2025-11-18 Target OpenStudio Version: 3.9.0 Ruby Version: 2.7.2