OpenStudio-ERI documentation

Introduction

The OpenStudio-ERI project allows calculating an Energy Rating Index (ERI) using the Department of Energy’s open-source OpenStudio/EnergyPlus simulation platform. The building description is provided in an HPXML file format.

ERI is defined by ANSI/RESNET/ICC 301-2014© “Standard for the Calculation and Labeling of the Energy Performance of Low-Rise Residential Buildings using an Energy Rating Index”.

License

This workflow is available under a BSD-3-like license, which is a free, open-source, and permissive license. For more information, check out the license file.

Disclaimer

Downloading and using this software from this website does not constitute accreditation of the final software product by RESNET. If you are seeking to develop RESNET Accredited Rating Software, you will need to submit your final software product to RESNET for accreditation.

Any reference herein to RESNET, its activities, products, or services, or any linkages from this website to RESNET’s website, does not constitute or imply the endorsement, recommendation, or favoring of the U.S. Government, the Alliance for Sustainable Energy, or any of their employees or contractors acting on their behalf.

Capabilities

ERI Capabilities

The following ERI Standards and Addenda are currently available:

• ANSI/RESNET/ICC 301-2014© “Standard for the Calculation and Labeling of the Energy Performance of Low-Rise Residential Buildings using an Energy Rating Index”.
• ANSI/RESNET/ICC 301-2014 Addendum A-2015, Domestic Hot Water Systems, January 15, 2016
• ANSI/RESNET/ICC 301-2014 Addendum D-2017, Duct Leakage to Outside Test Exception, January 1, 2018
• ANSI/RESNET/ICC 301-2014 Addendum E-2018, House Size Index Adjustment Factors, February 1, 2018
• ANSI/RESNET/ICC 301-2014 Addendum G-2018, Solid State Lighting, February 2, 2018
• ANSI/RESNET/ICC 301-2014 Addendum L-2018, Duct Leakage to Outside Test Exception, July 1, 2019
• ANSI/RESNET/ICC 301-2019 “Standard for the Calculation and Labeling of the Energy Performance of Dwelling and Sleeping Units using an Energy Rating Index”.
• ANSI/RESNET/ICC 301-2019 Addendum A-2019, Clothes Washers and Dryers and Dishwashers, July 1, 2020

Modeling Capabilities

The following building features/technologies are available for modeling:

• Enclosure
  • Attics
    • Vented
    • Unvented
    • Conditioned
    • Radiant Barriers
  • Foundations
    • Slab
    • Unconditioned Basement
    • Conditioned Basement
    • Vented Crawlspace
    • Unvented Crawlspace
    • Ambient
  • Garages
  • Windows & Overhangs
  • Skylights
  • Doors
• HVAC
  • Heating Systems
    • Electric Resistance
    • Furnaces
    • Wall/Floor Furnaces
    • Stoves & Portable Heaters
    • Boilers
  • Cooling Systems
    • Central Air Conditioners
    • Room Air Conditioners
    • Evaporative Coolers
  • Heat Pumps
    • Air Source Heat Pumps
    • Mini Split Heat Pumps
    • Ground Source Heat Pumps
    • Dual-Fuel Heat Pumps
  • Thermostat Type
  • Ducts
• Water Heating
  • Water Heaters
    • Storage Tank
    • Instantaneous Tankless
    • Heat Pump Water Heater
    • Indirect Water Heater (Combination Boiler)
    • Tankless Coil (Combination Boiler)
  • Solar Hot Water
  • Desuperheaters
  • Hot Water Distribution
    • Recirculation
  • Drain Water Heat Recovery
  • Low-Flow Fixtures
• Mechanical Ventilation
  • Exhaust Only
  • Supply Only
  • Balanced
  • Energy Recovery Ventilator
  • Heat Recovery Ventilator
  • Central Fan Integrated Supply
• Whole House Fan
• Photovoltaics
• Appliances
  • Clothes Washer
  • Clothes Dryer
  • Dishwasher
  • Refrigerator
  • Cooking Range/Oven
• Lighting
• Ceiling Fans

Accuracy vs Speed

The EnergyPlus simulation engine is like a Swiss army knife. There are often multiple models available for the same building technology with varying trade-offs between accuracy and speed. This workflow standardizes the use of EnergyPlus (e.g., the choice of models appropriate for residential buildings) to provide a fast and easy to use solution.

The workflow is continuously being evaluated for ways to reduce runtime without significant impact on accuracy. A number of such enhancements have been made to date.

There are additional ways that software developers using this workflow can reduce runtime:

• Run on Linux/Mac platform, which is significantly faster by taking advantage of the POSIX fork call.
• Do not use the --hourly flag unless hourly output is required. If required, limit requests to hourly variables of interest.
• Run on computing environments with 1) fast CPUs, 2) sufficient memory, and 3) enough processors to allow all simulations to run in parallel.

Getting Started

Here is a brief overview on getting setup, running an ERI calculation, and obtaining outputs.

Setup

To get started:

1. Either download OpenStudio 3.0.0 and install the Command Line Interface/EnergyPlus components, or use the nrel/openstudio docker image.
2. Download the OpenStudio-ERI v0.10.0 Beta release.
3. To obtain all available weather files, run: openstudio workflow/energy_rating_index.rb --download-weather

Note

If the openstudio command is not found, it’s because the executable is not in your PATH. Either add the executable to your PATH or point directly to the executable found in the openstudio-X.X.X/bin directory.

Running

Run the ERI calculation on a provided sample HPXML file as follows: openstudio workflow/energy_rating_index.rb -x workflow/sample_files/base.xml

Note that the Reference Home, Rated Home and Index Adjustment Home (if applicable) simulations will be executed in parallel on the local machine.

This will generate output as shown below:

You can also request generation of hourly output CSV files as part of the calculation by providing one or more --hourly flags.

To request all possible hourly outputs: openstudio workflow/energy_rating_index.rb -x workflow/sample_files/base.xml --hourly ALL

Or one or more specific hourly output types can be requested, e.g.: openstudio workflow/energy_rating_index.rb -x workflow/sample_files/base.xml --hourly fuels --hourly temperatures

Run openstudio workflow/energy_rating_index.rb -h to see all available commands/arguments.

Output

Upon completion, ERI is provided in the console (stdout) as well as available in some of the summary output files. See the Outputs section for a description of all available outputs.

ERI Use Case for HPXML

HPXML is an flexible and extensible format, where nearly all elements in the schema are optional and custom elements can be included. Because of this, an ERI Use Case for HPXML has been developed that specifies the HPXML elements or enumeration choices required to run the workflow.

Software developers should use the ERI Use Case (defined as a set of conditional XPath expressions) as well as the HPXML schema to construct valid HPXML files for ERI calculations.

ERI Version

The version of the ERI calculation to be run is specified inside the HPXML file itself at /HPXML/SoftwareInfo/extension/ERICalculation/Version. For example, a value of “2014AE” tells the workflow to use ANSI/RESNET/ICC© 301-2014 with both Addendum A (Amendment on Domestic Hot Water Systems) and Addendum E (House Size Index Adjustment Factors) included. A value of “latest” can be used to always point to the latest version available.

Note

Valid choices for ERI version can be looked up in the ERI Use Case.

Building Details

The building description is entered in HPXML’s /HPXML/Building/BuildingDetails.

Building Summary

This section describes elements specified in HPXML’s BuildingSummary. It is used for high-level building information needed for an ERI calculation including conditioned floor area, number of bedrooms, number of conditioned floors, residential facility type, etc. Note that a walkout basement should be included in NumberofConditionedFloorsAboveGrade.

The BuildingSummary/Site/FuelTypesAvailable element is used to determine whether the home has access to natural gas or fossil fuel delivery (specified by any value other than “electricity”). This information may be used for determining the heating system, as specified by the ERI 301 Standard.

Climate and Weather

This section describes elements specified in HPXML’s ClimateandRiskZones.

The ClimateandRiskZones/ClimateZoneIECC element specifies the IECC climate zone(s) for years required by the ERI 301 Standard.

The ClimateandRiskZones/WeatherStation element specifies the EnergyPlus weather file (EPW) to be used in the simulation. The weather file can be entered in one of two ways:

1. Using WeatherStation/WMO, which must be one of the acceptable TMY3 WMO station numbers found in the weather/data.csv file. The full set of U.S. TMY3 weather files can be downloaded here.
2. Using WeatherStation/extension/EPWFilePath.

In addition to using the TMY3 weather files that are provided, custom weather files can be used if they are in EPW file format. To use custom weather files, first ensure that all weather files have a unique WMO station number (as provided in the first header line of the EPW file). Then place them in the weather directory and call openstudio energy_rating_index.rb --cache-weather. After processing is complete, each EPW file will have a corresponding *.csv cache file and the WMO station numbers of these weather files will be available in the weather/data.csv` file.

Note

In the future, we hope to provide an automated weather file selector based on a building’s address/zipcode or similar information. But for now, each software tool is responsible for providing this information.

Enclosure

This section describes elements specified in HPXML’s Enclosure.

All surfaces that bound different space types in the building (i.e., not just thermal boundary surfaces) must be specified in the HPXML file. For example, an attached garage would generally be defined by walls adjacent to conditioned space, walls adjacent to outdoors, a slab, and a roof or ceiling. For software tools that do not collect sufficient inputs for every required surface, the software developers will need to make assumptions about these surfaces or collect additional input.

The space types used in the HPXML building description are:

Space Type	Description	Temperature
living space	Above-grade conditioned floor area	EnergyPlus calculation
attic - vented		EnergyPlus calculation
attic - unvented		EnergyPlus calculation
basement - conditioned	Below-grade conditioned floor area	EnergyPlus calculation
basement - unconditioned		EnergyPlus calculation
crawlspace - vented		EnergyPlus calculation
crawlspace - unvented		EnergyPlus calculation
garage		EnergyPlus calculation
other housing unit	Conditioned space of an adjacent housing unit	Same as conditioned space
other heated space	E.g., shared laundry/equipment space	Average of conditioned space and outside; minimum of 68F
other multifamily buffer space	E.g., enclosed unconditioned stairwell	Average of conditioned space and outside; minimum of 50F
other non-freezing space	E.g., parking garage ceiling	Floats with outside; minimum of 40F

Warning

It is the software tool’s responsibility to provide the appropriate building surfaces. While some error-checking is in place, it is not possible to know whether some surfaces are incorrectly missing.

Also note that wall and roof surfaces do not require an azimuth to be specified. Rather, only the windows/skylights themselves require an azimuth. Thus, software tools can choose to use a single wall (or roof) surface to represent multiple wall (or roof) surfaces for the entire building if all their other properties (construction type, interior/exterior adjacency, etc.) are identical.

Air Leakage

Building air leakage is entered using Enclosure/AirInfiltration/AirInfiltrationMeasurement. Air leakage can be provided in one of three ways:

1. nACH (natural air changes per hour): Use BuildingAirLeakage/UnitofMeasure='ACHnatural'
2. ACH50 (air changes per hour at 50Pa): Use BuildingAirLeakage/UnitofMeasure='ACH' and HousePressure='50'
3. CFM50 (cubic feet per minute at 50Pa): Use BuildingAirLeakage/UnitofMeasure='CFM' and HousePressure='50'

In addition, the building’s volume associated with the air leakage measurement is provided in HPXML’s AirInfiltrationMeasurement/InfiltrationVolume.

Attics

If the building has an unvented attic, an Enclosure/Attics/Attic/AtticType/Attic[Vented='false'] element must be defined. It must have the WithinInfiltrationVolume element specified in accordance with ANSI/RESNET/ICC Standard 380.

If the building has a vented attic, an Enclosure/Attics/Attic/AtticType/Attic[Vented='true'] element may be defined in order to specify the ventilation rate. The ventilation rate can be entered as a specific leakage area using VentilationRate[UnitofMeasure='SLA']/Value or as natural air changes per hour using VentilationRate[UnitofMeasure='ACHnatural']/Value. If the ventilation rate is not provided, the ERI 301 Standard Reference Home defaults will be used.

Foundations

If the building has an unconditioned basement, an Enclosure/Foundations/Foundation/FoundationType/Basement[Conditioned='false'] element must be defined. It must have the WithinInfiltrationVolume element specified in accordance with ANSI/RESNET/ICC Standard 380. In addition, the ThermalBoundary element must be specified as either “foundation wall” or “frame floor”.

If the building has an unvented crawlspace, an Enclosure/Foundations/Foundation/FoundationType/Crawlspace[Vented='false'] element must be defined. It must have the WithinInfiltrationVolume element specified in accordance with ANSI/RESNET/ICC Standard 380.

If the building has a vented crawlspace, an Enclosure/Foundations/Foundation/FoundationType/Crawlspace[Vented='true'] element may be defined in order to specify the ventilation rate. The ventilation rate can be entered as a specific leakage area using VentilationRate[UnitofMeasure='SLA']/Value. If the ventilation rate is not provided, the ERI 301 Standard Reference Home defaults will be used.

Roofs

Pitched or flat roof surfaces that are exposed to ambient conditions should be specified as an Enclosure/Roofs/Roof. For a multifamily building where the dwelling unit has another dwelling unit above it, the surface between the two dwelling units should be considered a FrameFloor and not a Roof.

Beyond the specification of typical heat transfer properties (insulation R-value, solar absorptance, emittance, etc.), note that roofs can be defined as having a radiant barrier.

Walls

Any wall that has no contact with the ground and bounds a space type should be specified as an Enclosure/Walls/Wall. Interior walls (for example, walls solely within the conditioned space of the building) are not required.

Walls are primarily defined by their Insulation/AssemblyEffectiveRValue. The choice of WallType has a secondary effect on heat transfer in that it informs the assumption of wall thermal mass.

Rim Joists

Rim joists, the perimeter of floor joists typically found between stories of a building or on top of a foundation wall, are specified as an Enclosure//RimJoists/RimJoist.

The InteriorAdjacentTo element should typically be “living space” for rim joists between stories of a building and “basement - conditioned”, “basement - unconditioned”, “crawlspace - vented”, or “crawlspace - unvented” for rim joists on top of a foundation wall.

Foundation Walls

Any wall that is in contact with the ground should be specified as an Enclosure/FoundationWalls/FoundationWall. Other walls (e.g., wood framed walls) that are connected to a below-grade space but have no contact with the ground should be specified as Walls and not FoundationWalls.

Exterior foundation walls (i.e., those that fall along the perimeter of the building’s footprint) should use “ground” for ExteriorAdjacentTo and the appropriate space type (e.g., “basement - unconditioned”) for InteriorAdjacentTo.

Interior foundation walls should be specified with two appropriate space types (e.g., “crawlspace - vented” and “garage”, or “basement - unconditioned” and “crawlspace - unvented”) for InteriorAdjacentTo and ExteriorAdjacentTo. Interior foundation walls should never use “ground” for ExteriorAdjacentTo even if the foundation wall has some contact with the ground due to the difference in below-grade depths of the two adjacent space types.

Foundations must include a Height as well as a DepthBelowGrade. For exterior foundation walls, the depth below grade is relative to the ground plane. For interior foundation walls, the depth below grade should not be thought of as relative to the ground plane, but rather as the depth of foundation wall in contact with the ground. For example, an interior foundation wall between an 8 ft conditioned basement and a 3 ft crawlspace has a height of 8 ft and a depth below grade of 5 ft. Alternatively, an interior foundation wall between an 8 ft conditioned basement and an 8 ft unconditioned basement has a height of 8 ft and a depth below grade of 0 ft.

Foundation wall insulation can be described in two ways:

Option 1. Both interior and exterior continuous insulation layers with NominalRValue, extension/DistanceToTopOfInsulation, and extension/DistanceToBottomOfInsulation. Insulation layers are particularly useful for describing foundation wall insulation that doesn’t span the entire height (e.g., 4 ft of insulation for an 8 ft conditioned basement). If there is not insulation on the interior and/or exterior of the foundation wall, the continuous insulation layer must still be provided – with the nominal R-value, etc., set to zero. When insulation is specified with option 1, it is modeled with a concrete wall (whose Thickness is provided) as well as air film resistances as appropriate.

Option 2. An AssemblyEffectiveRValue. The assembly effective R-value should include the concrete wall and an interior air film resistance. The exterior air film resistance (for any above-grade exposure) or any soil thermal resistance should not be included.

Frame Floors

Any horizontal floor/ceiling surface that is not in contact with the ground (Slab) nor adjacent to ambient conditions above (Roof) should be specified as an Enclosure/FrameFloors/FrameFloor. Frame floors in an attached/multifamily building that are adjacent to “other housing unit”, “other heated space”, “other multifamily buffer space”, or “other non-freezing space” must have the extension/OtherSpaceAboveOrBelow property set to signify whether the other space is “above” or “below”.

Frame floors are primarily defined by their Insulation/AssemblyEffectiveRValue.

Slabs

Any space type that borders the ground should include an Enclosure/Slabs/Slab surface with the appropriate InteriorAdjacentTo. This includes basements, crawlspaces (even when there are dirt floors – use zero for the Thickness), garages, and slab-on-grade foundations.

A primary input for a slab is its ExposedPerimeter. The exposed perimeter should include any slab length that falls along the perimeter of the building’s footprint (i.e., is exposed to ambient conditions). So, a basement slab edge adjacent to a garage or crawlspace, for example, should not be included.

Vertical insulation adjacent to the slab can be described by a PerimeterInsulation/Layer/NominalRValue and a PerimeterInsulationDepth.

Horizontal insulation under the slab can be described by a UnderSlabInsulation/Layer/NominalRValue. The insulation can either have a fixed width (UnderSlabInsulationWidth) or can span the entire slab (UnderSlabInsulationSpansEntireSlab).

For foundation types without walls, the DepthBelowGrade element must be provided. For foundation types with walls, the DepthBelowGrade element is not used; instead the slab’s position relative to grade is determined by the FoundationWall/DepthBelowGrade values.

Windows

Any window or glass door area should be specified as an Enclosure/Windows/Window.

Windows are defined by full-assembly NFRC UFactor and SHGC, as well as Area. Windows must reference a HPXML Enclosures/Walls/Wall element via the AttachedToWall. Windows must also have an Azimuth specified, even if the attached wall does not.

Finally, windows must have the FractionOperable property specified for determining natural ventilation. The input should solely reflect whether the windows are operable (can be opened), not how they are used by the occupants. If a Window represents a single window, the value should be 0 or 1. If a Window represents multiple windows (e.g., 4), the value should be between 0 and 1 (e.g., 0, 0.25, 0.5, 0.75, or 1).

Overhangs (e.g., a roof eave) can optionally be defined for a window by specifying a Window/Overhangs element. Overhangs are defined by the vertical distance between the overhang and the top of the window (DistanceToTopOfWindow), and the vertical distance between the overhang and the bottom of the window (DistanceToBottomOfWindow). The difference between these two values equals the height of the window.

Skylights

Any skylight should be specified as an Enclosure/Skylights/Skylight.

Skylights are defined by full-assembly NFRC UFactor and SHGC, as well as Area. Skylights must reference a HPXML Enclosures/Roofs/Roof element via the AttachedToRoof. Skylights must also have an Azimuth specified, even if the attached roof does not.

Doors

Any opaque doors should be specified as an Enclosure/Doors/Door.

Doors are defined by RValue and Area. Doors must reference a HPXML Enclosures/Walls/Wall element via the AttachedToWall. Doors must also have an Azimuth specified, even if the attached wall does not.

Systems

This section describes elements specified in HPXML’s Systems.

If any HVAC systems are entered that provide heating (or cooling), the sum of all their FractionHeatLoadServed (or FractionCoolLoadServed) values must be less than or equal to 1.

If any water heating systems are entered, the sum of all their FractionDHWLoadServed values must be equal to 1.

Heating Systems

Each heating system (other than heat pumps) should be entered as a Systems/HVAC/HVACPlant/HeatingSystem. Inputs including HeatingSystemType, HeatingCapacity, and FractionHeatLoadServed must be provided.

Depending on the type of heating system specified, additional elements are required:

HeatingSystemType	DistributionSystem	HeatingSystemFuel	AnnualHeatingEfficiency
ElectricResistance		electricity	Percent
Furnace	AirDistribution or DSE	<any>	AFUE
WallFurnace		<any>	AFUE
FloorFurnace		<any>	AFUE
Boiler	HydronicDistribution or DSE	<any>	AFUE
Stove		<any>	Percent
PortableHeater		<any>	Percent
Fireplace		<any>	Percent

If a non-electric heating system is specified, the ElectricAuxiliaryEnergy element may be provided if available.

Cooling Systems

Each cooling system (other than heat pumps) should be entered as a Systems/HVAC/HVACPlant/CoolingSystem. Inputs including CoolingSystemType and FractionCoolLoadServed must be provided. CoolingCapacity must also be provided for all systems other than evaporative coolers.

Depending on the type of cooling system specified, additional elements are required/available:

CoolingSystemType	DistributionSystem	CoolingSystemFuel	AnnualCoolingEfficiency	SensibleHeatFraction
central air conditioner	AirDistribution or DSE	electricity	SEER	(optional)
room air conditioner		electricity	EER	(optional)
evaporative cooler	AirDistribution or DSE (optional)	electricity

Central air conditioners can also have the CompressorType specified; if not provided, it is assumed as follows:

• “single stage”: SEER <= 15
• “two stage”: 15 < SEER <= 21
• “variable speed”: SEER > 21

Heat Pumps

Each heat pump should be entered as a Systems/HVAC/HVACPlant/HeatPump. Inputs including HeatPumpType, CoolingCapacity, HeatingCapacity, FractionHeatLoadServed, and FractionCoolLoadServed must be provided. Note that heat pumps are allowed to provide only heating (FractionCoolLoadServed = 0) or cooling (FractionHeatLoadServed = 0) if appropriate.

Depending on the type of heat pump specified, additional elements are required/available:

HeatPumpType	DistributionSystem	HeatPumpFuel	AnnualCoolingEfficiency	AnnualHeatingEfficiency	CoolingSensibleHeatFraction	HeatingCapacity17F
air-to-air	AirDistribution or DSE	electricity	SEER	HSPF	(optional)	(optional)
mini-split	AirDistribution or DSE (optional)	electricity	SEER	HSPF	(optional)	(optional)
ground-to-air	AirDistribution or DSE	electricity	EER	COP	(optional)

Air-to-air heat pumps can also have the CompressorType specified; if not provided, it is assumed as follows:

• “single stage”: SEER <= 15
• “two stage”: 15 < SEER <= 21
• “variable speed”: SEER > 21

If the heat pump has backup heating, it can be specified with BackupSystemFuel, BackupAnnualHeatingEfficiency, and BackupHeatingCapacity. If the heat pump has a switchover temperature (e.g., dual-fuel heat pump) where the heat pump stops operating and the backup heating system starts running, it can be specified with BackupHeatingSwitchoverTemperature. If the BackupHeatingSwitchoverTemperature is not provided, the backup heating system will operate as needed when the heat pump has insufficient capacity.

Thermostat

A Systems/HVAC/HVACControl must be provided if any HVAC systems are specified. Its ControlType specifies whether there is a manual or programmable thermostat.

HVAC Distribution

Each separate HVAC distribution system should be specified as a Systems/HVAC/HVACDistribution. The three types of HVAC distribution systems allowed are AirDistribution, HydronicDistribution, and DSE. There should be at most one heating system and one cooling system attached to a distribution system. See the sections on Heating Systems, Cooling Systems, and Heat Pumps for information on which DistributionSystemType is allowed for which HVAC system. Also note that some HVAC systems (e.g., room air conditioners) are not allowed to be attached to a distribution system.

AirDistribution systems are defined by: - ConditionedFloorAreaServed - Optional supply ducts (Ducts[DuctType='supply']) - Optional return ducts (Ducts[DuctType='return'])

Each duct must have DuctInsulationRValue, DuctLocation, and DuctSurfaceArea provided.

DuctLocation must be one of the following:

Location	Description	Temperature
living space	Above-grade conditioned floor area	EnergyPlus calculation
basement - conditioned	Below-grade conditioned floor area	EnergyPlus calculation
basement - unconditioned		EnergyPlus calculation
crawlspace - unvented		EnergyPlus calculation
crawlspace - vented		EnergyPlus calculation
attic - unvented		EnergyPlus calculation
attic - vented		EnergyPlus calculation
garage		EnergyPlus calculation
exterior wall		Average of conditioned space and outside
under slab		Ground
roof deck		Outside
outside		Outside
other housing unit	Conditioned space of an adjacent housing unit	Same as conditioned space
other heated space	E.g., shared laundry/equipment space	Average of conditioned space and outside; minimum of 68F
other multifamily buffer space	E.g., enclosed unconditioned stairwell	Average of conditioned space and outside; minimum of 50F
other non-freezing space	E.g., parking garage ceiling	Floats with outside; minimum of 40F

AirDistribution systems must also have duct leakage testing provided in one of three ways:

1. Supply (and optionally return) leakage to the outside: DuctLeakageMeasurement[DuctType="supply" or DuctType="return"]/DuctLeakage[Units="CFM25"][TotalOrToOutside="to outside"]/Value
2. Total leakage: extension/DuctLeakageTestingExemption="true" (Version 2014ADEGL or newer)
3. Leakage testing exemption: DuctLeakageMeasurement/DuctLeakage[Units="CFM25"][TotalOrToOutside="total"]/Value (Version 2014AD or newer)

Note

When the leakage testing exemption is used with Addendum L or newer, it effectively overrides the Addendum D specification such that the leakage testing exemption reflects solely the Addendum L specification.

Warning

Total leakage and leakage testing exemption should only be used if the conditions specified in ANSI/RESNET/ICC© 301 have been appropriately met.

HydronicDistribution systems do not require any additional inputs.

DSE systems are defined by AnnualHeatingDistributionSystemEfficiency and AnnualCoolingDistributionSystemEfficiency elements.

Mechanical Ventilation

A single whole-house mechanical ventilation system may be specified as a Systems/MechanicalVentilation/VentilationFans/VentilationFan with UsedForWholeBuildingVentilation='true'. Inputs including FanType and HoursInOperation must be provided.

The measured airflow rate should be entered as TestedFlowRate; if unmeasured, it should not be provided and the airflow rate will be defaulted. Likewise the fan power for the highest airflow setting should be entered as FanPower; if unknown, it should not be provided and the fan power will be defaulted.

Depending on the type of mechanical ventilation specified, additional elements are required:

FanType	SensibleRecoveryEfficiency	TotalRecoveryEfficiency	AttachedToHVACDistributionSystem
energy recovery ventilator	required	required
heat recovery ventilator	required
exhaust only
supply only
balanced
central fan integrated supply (CFIS)			required

Note that AdjustedSensibleRecoveryEfficiency/AdjustedTotalRecoveryEfficiency can be provided instead of SensibleRecoveryEfficiency/TotalRecoveryEfficiency.

In many situations, the rated flow rate should be the value derived from actual testing of the system. For a CFIS system, the rated flow rate should equal the amount of outdoor air provided to the distribution system.

Whole House Fan

A single whole house fan may be specified as a Systems/MechanicalVentilation/VentilationFans/VentilationFan with UsedForSeasonalCoolingLoadReduction='true'. Required elements include RatedFlowRate and FanPower.

Water Heaters

Each water heater should be entered as a Systems/WaterHeating/WaterHeatingSystem. Inputs including WaterHeaterType, Location, and FractionDHWLoadServed must be provided. The Location must be one of the following:

Location	Description	Temperature
living space	Above-grade conditioned floor area	EnergyPlus calculation
basement - conditioned	Below-grade conditioned floor area	EnergyPlus calculation
basement - unconditioned		EnergyPlus calculation
attic - unvented		EnergyPlus calculation
attic - vented		EnergyPlus calculation
garage		EnergyPlus calculation
crawlspace - unvented		EnergyPlus calculation
crawlspace - vented		EnergyPlus calculation
other exterior	Outside	Outside
other housing unit	Conditioned space of an adjacent housing unit	Same as conditioned space
other heated space	E.g., shared laundry/equipment space	Average of conditioned space and outside; minimum of 68F
other multifamily buffer space	E.g., enclosed unconditioned stairwell	Average of conditioned space and outside; minimum of 50F
other non-freezing space	E.g., parking garage ceiling	Floats with outside; minimum of 40F

Depending on the type of water heater specified, additional elements are required/available:

WaterHeaterType	UniformEnergyFactor or EnergyFactor	FuelType	TankVolume	HeatingCapacity	RecoveryEfficiency	UsesDesuperheater	WaterHeaterInsulation/Jacket/JacketRValue	RelatedHVACSystem
storage water heater	required	<any>	required	<optional>	required if non-electric	<optional>	<optional>	required if uses desuperheater
instantaneous water heater	required	<any>				<optional>		required if uses desuperheater
heat pump water heater	required	electricity	required			<optional>	<optional>	required if uses desuperheater
space-heating boiler with storage tank			required				<optional>	required
space-heating boiler with tankless coil								required

For combi boiler systems, the RelatedHVACSystem must point to a HeatingSystem of type “Boiler”. For combi boiler systems with a storage tank, the storage tank losses (deg-F/hr) can be entered as StandbyLoss; if not provided, a default value based on the AHRI Directory of Certified Product Performance will be calculated.

For water heaters that are connected to a desuperheater, the RelatedHVACSystem must either point to a HeatPump or a CoolingSystem.

Hot Water Distribution

A Systems/WaterHeating/HotWaterDistribution must be provided if any water heating systems are specified. Inputs including SystemType and PipeInsulation/PipeRValue must be provided.

For a SystemType/Standard (non-recirculating) system, the following element is required:

• PipingLength: Measured length of hot water piping from the hot water heater to the farthest hot water fixture, measured longitudinally from plans, assuming the hot water piping does not run diagonally, plus 10 feet of piping for each floor level, plus 5 feet of piping for unconditioned basements (if any)

For a SystemType/Recirculation system, the following elements are required:

• ControlType
• RecirculationPipingLoopLength: Measured recirculation loop length including both supply and return sides, measured longitudinally from plans, assuming the hot water piping does not run diagonally, plus 20 feet of piping for each floor level greater than one plus 10 feet of piping for unconditioned basements
• BranchPipingLoopLength: Measured length of the branch hot water piping from the recirculation loop to the farthest hot water fixture from the recirculation loop, measured longitudinally from plans, assuming the branch hot water piping does not run diagonally
• PumpPower

In addition, a HotWaterDistribution/DrainWaterHeatRecovery (DWHR) may be specified. The DWHR system is defined by:

• FacilitiesConnected: ‘one’ if there are multiple showers and only one of them is connected to a DWHR; ‘all’ if there is one shower and it’s connected to a DWHR or there are two or more showers connected to a DWHR
• EqualFlow: ‘true’ if the DWHR supplies pre-heated water to both the fixture cold water piping and the hot water heater potable supply piping
• Efficiency: As rated and labeled in accordance with CSA 55.1

Water Fixtures

Water fixtures should be entered as Systems/WaterHeating/WaterFixture elements. Each fixture must have WaterFixtureType and LowFlow elements provided. Fixtures should be specified as low flow if they are <= 2.0 gpm.

Solar Thermal

A solar hot water system can be entered as a Systems/SolarThermal/SolarThermalSystem. The SystemType element must be ‘hot water’.

Solar hot water systems can be described with either simple or detailed inputs.

If using simple inputs, the following elements are used:

• SolarFraction: Portion of total conventional hot water heating load (delivered energy and tank standby losses). Can be obtained from Directory of SRCC OG-300 Solar Water Heating System Ratings or NREL’s System Advisor Model or equivalent.
• ConnectedTo: Optional. If not specified, applies to all water heaters in the building. If specified, must point to a WaterHeatingSystem.

If using detailed inputs, the following elements are used:

• CollectorArea
• CollectorLoopType: ‘liquid indirect’ or ‘liquid direct’ or ‘passive thermosyphon’
• CollectorType: ‘single glazing black’ or ‘double glazing black’ or ‘evacuated tube’ or ‘integrated collector storage’
• CollectorAzimuth
• CollectorTilt
• CollectorRatedOpticalEfficiency: FRTA (y-intercept); see Directory of SRCC OG-100 Certified Solar Collector Ratings
• CollectorRatedThermalLosses: FRUL (slope, in units of Btu/hr-ft^2-R); see Directory of SRCC OG-100 Certified Solar Collector Ratings
• StorageVolume
• ConnectedTo: Must point to a WaterHeatingSystem. The connected water heater cannot be of type space-heating boiler or attached to a desuperheater.

Photovoltaics

Each solar electric (photovoltaic) system should be entered as a Systems/Photovoltaics/PVSystem. The following elements, some adopted from the PVWatts model, are required for each PV system:

• Location: ‘ground’ or ‘roof’ mounted
• ModuleType: ‘standard’, ‘premium’, or ‘thin film’
• Tracking: ‘fixed’ or ‘1-axis’ or ‘1-axis backtracked’ or ‘2-axis’
• ArrayAzimuth
• ArrayTilt
• MaxPowerOutput
• InverterEfficiency: Default is 0.96.
• SystemLossesFraction: Default is 0.14. System losses include soiling, shading, snow, mismatch, wiring, degradation, etc.

Appliances

This section describes elements specified in HPXML’s Appliances. Many of the appliances’ inputs are derived from EnergyGuide labels.

The Location for each appliance must be provided as one of the following:

Location	Description
living space	Above-grade conditioned floor area
basement - conditioned	Below-grade conditioned floor area
basement - unconditioned
garage
other	Any attached/multifamily space outside the unit, in which internal gains are neglected

Clothes Washer

An Appliances/ClothesWasher element must be specified. The efficiency of the clothes washer can either be entered as an IntegratedModifiedEnergyFactor or a ModifiedEnergyFactor. Several other inputs from the EnergyGuide label must be provided as well.

Clothes Dryer

An Appliances/ClothesDryer element must be specified. The dryer’s FuelType and ControlType (“timer” or “moisture”) must be provided. The efficiency of the clothes dryer can either be entered as a CombinedEnergyFactor or an EnergyFactor.

Dishwasher

An Appliances/Dishwasher element must be specified. The efficiency of the dishwasher can either be entered as a RatedAnnualkWh or an EnergyFactor. The dishwasher’s PlaceSettingCapacity also must be provided as well as other inputs from the EnergyGuide label.

Refrigerator

An Appliances/Refrigerator element must be specified. The efficiency of the refrigerator must be entered as RatedAnnualkWh.

Cooking Range/Oven

Appliances/CookingRange and Appliances/Oven elements must be specified. The FuelType of the range and whether it IsInduction, as well as whether the oven IsConvection, must be provided.

Lighting

The building’s lighting is described by nine Lighting/LightingGroup elements, each of which is the combination of:

• LightingType: LightEmittingDiode, CompactFluorescent, and FluorescentTube
• LightingGroup/Location: ‘interior’, ‘garage’, and ‘exterior’

Use LightEmittingDiode for Tier II qualifying light fixtures; use CompactFluorescent and/or FluorescentTube for Tier I qualifying light fixtures.

The fraction of lamps of the given type in the given location are provided as the LightingGroup/FractionofUnitsInLocation. The fractions for a given location cannot sum to greater than 1. If the fractions sum to less than 1, the remainder is assumed to be incandescent lighting. Garage lighting values are ignored if the building has no garage.

Ceiling Fans

Each ceiling fan (or set of identical ceiling fans) should be entered as a Lighting/CeilingFan. The Airflow/Efficiency (at medium speed) and Quantity must be provided.

Validating & Debugging Errors

When running HPXML files, errors may occur because:

1. An HPXML file provided is invalid (either relative to the HPXML schema or the ERI Use Case).
2. An unexpected error occurred in the workflow (e.g., applying the ERI 301 ruleset).
3. An unexpected EnergyPlus simulation error occurred.

If, for example, the Rated Home is unsuccessful, first look in the ERIRatedHome/run.log for details. If there are no errors in that log file, then the error may be in the EnergyPlus simulation – see ERIRatedHome/eplusout.err.

Contact us if you can’t figure out the cause of an error.

Sample Files

Dozens of sample HPXML files are included in the workflow/sample_files directory. The sample files help to illustrate how different building components are described in HPXML.

Each sample file generally makes one isolated change relative to the base HPXML (base.xml) building. For example, the base-dhw-dwhr.xml file adds a DrainWaterHeatRecovery element to the building.

You may find it useful to search through the files for certain HPXML elements or compare (diff) a sample file to the base.xml file.

Outputs

Upon completion of the ERI calculation, summary output files and simulation files are available. See the sample_results directory for examples of these outputs.

Summary Files

Several summary files described below are found in the results directory.

ERI_Results.csv

The ERI_Results.csv file includes the ERI result as well as the high-level components (e.g., REUL, EC_r, EC_x, IAD_Save) that comprise the ERI calculation. The file reflects the format of the Results tab of the HERS Method Test spreadsheet.

Note that multiple comma-separated values will be reported for many of these outputs if there are multiple heating, cooling, or hot water systems.

See the example ERI_Results.csv.

ERI_Worksheet.csv

The ERI_Worksheet.csv file includes more detailed components that feed into the ERI_Results.csv values. The file reflects the formate of the Worksheet tab of the HERS Method Test spreadsheet.

Note that multiple comma-separated values will be reported for many of these outputs if there are multiple heating, cooling, or hot water systems.

See the example ERI_Worksheet.csv.

ERI______Home.csv

A CSV file is written for each of the homes simulated (e.g., ERIReferenceHome.csv for the Reference home). The CSV file includes the following sections of output.

See the example ERIRatedHome.csv.

Annual Energy Consumption by Fuel Type

Current fuel types are:

Type	Notes
Electricity: Total (MBtu)
Electricity: Net (MBtu)	Excludes any PV generation.
Natural Gas: Total (MBtu)
Fuel Oil: Total (MBtu)
Propane: Total (MBtu)
Wood: Total (MBtu)	Currently unused for ERI.
Wood Pellets: Total (MBtu)	Currently unused for ERI.

Annual Energy Consumption By Fuel Type and End Use

Current end use/fuel type combinations are:

Type	Notes	Type (cont’d)	Notes
Electricity: Heating (MBtu)		Natural Gas: Heating (MBtu)
Electricity: Heating Fans/Pumps (MBtu)		Natural Gas: Hot Water (MBtu)
Electricity: Cooling (MBtu)		Natural Gas: Clothes Dryer (MBtu)
Electricity: Cooling Fans/Pumps (MBtu)		Natural Gas: Range/Oven (MBtu)
Electricity: Hot Water (MBtu)		Fuel Oil: Heating (MBtu)
Electricity: Hot Water Recirc Pump (MBtu)		Fuel Oil: Hot Water (MBtu)
Electricity: Hot Water Solar Thermal Pump (MBtu)		Fuel Oil: Clothes Dryer (MBtu)
Electricity: Lighting Interior (MBtu)		Fuel Oil: Range/Oven (MBtu)
Electricity: Lighting Garage (MBtu)		Propane: Heating (MBtu)
Electricity: Lighting Exterior (MBtu)		Propane: Hot Water (MBtu)
Electricity: Mech Vent (MBtu)		Propane: Clothes Dryer (MBtu)
Electricity: Whole House Fan (MBtu)		Propane: Range/Oven (MBtu)
Electricity: Refrigerator (MBtu)		Wood: Heating (MBtu)	Currently unused for ERI.
Electricity: Dehumidifier (MBtu)	Currently unused for ERI.	Wood: Hot Water (MBtu)	Currently unused for ERI.
Electricity: Dishwasher (MBtu)		Wood: Clothes Dryer (MBtu)	Currently unused for ERI.
Electricity: Clothes Washer (MBtu)		Wood: Range/Oven (MBtu)	Currently unused for ERI.
Electricity: Clothes Dryer (MBtu)		Wood Pellets: Heating (MBtu)	Currently unused for ERI.
Electricity: Range/Oven (MBtu)
Electricity: Ceiling Fan (MBtu)
Electricity: Television (MBtu)
Electricity: Plug Loads (MBtu)
Electricity: PV (MBtu)

Annual Building Loads

Current annual building loads are:

Type	Notes
Load: Heating (MBtu)	Includes HVAC distribution losses.
Load: Cooling (MBtu)	Includes HVAC distribution losses.
Load: Hot Water: Delivered (MBtu)	Includes contributions by desuperheaters or solar thermal systems.
Load: Hot Water: Tank Losses (MBtu)
Load: Hot Water: Desuperheater (MBtu)	Load served by the desuperheater.
Load: Hot Water: Solar Thermal (MBtu)	Load served by the solar thermal system.

Annual Unmet Building Loads

Current annual unmet building loads are:

Type	Notes
Unmet Load: Heating (MBtu)
Unmet Load: Cooling (MBtu)

These numbers reflect the amount of heating/cooling load that is not met by the HVAC system, indicating the degree to which the HVAC system is undersized. An HVAC system with sufficient capacity to perfectly maintain the thermostat setpoints will report an unmet load of zero.

Peak Building Electricity

Current peak building electricity outputs are:

Type	Notes
Peak Electricity: Winter Total (W)	Winter season defined by operation of the heating system.
Peak Electricity: Summer Total (W)	Summer season defined by operation of the cooling system.

Peak Building Loads

Current peak building loads are:

Type	Notes
Peak Load: Heating (kBtu)	Includes HVAC distribution losses.
Peak Load: Cooling (kBtu)	Includes HVAC distribution losses.

Annual Component Building Loads

Component loads represent the estimated contribution of different building components to the annual heating/cooling building loads. The sum of component loads for heating (or cooling) will roughly equal the annual heating (or cooling) building load reported above. Current component loads disaggregated by Heating/Cooling are:

Type	Notes
Component Load: *: Roofs (MBtu)	Heat gain/loss through HPXML Roof elements adjacent to conditioned space
Component Load: *: Ceilings (MBtu)	Heat gain/loss through HPXML FrameFloor elements (inferred to be ceilings) adjacent to conditioned space
Component Load: *: Walls (MBtu)	Heat gain/loss through HPXML Wall elements adjacent to conditioned space
Component Load: *: Rim Joists (MBtu)	Heat gain/loss through HPXML RimJoist elements adjacent to conditioned space
Component Load: *: Foundation Walls (MBtu)	Heat gain/loss through HPXML FoundationWall elements adjacent to conditioned space
Component Load: *: Doors (MBtu)	Heat gain/loss through HPXML Door elements adjacent to conditioned space
Component Load: *: Windows (MBtu)	Heat gain/loss through HPXML Window elements adjacent to conditioned space, including solar
Component Load: *: Skylights (MBtu)	Heat gain/loss through HPXML Skylight elements adjacent to conditioned space, including solar
Component Load: *: Floors (MBtu)	Heat gain/loss through HPXML FrameFloor elements (inferred to be floors) adjacent to conditioned space
Component Load: *: Slabs (MBtu)	Heat gain/loss through HPXML Slab elements adjacent to conditioned space
Component Load: *: Internal Mass (MBtu)	Heat gain/loss from internal mass (e.g., furniture, interior walls/floors) in conditioned space
Component Load: *: Infiltration (MBtu)	Heat gain/loss from airflow induced by stack and wind effects
Component Load: *: Natural Ventilation (MBtu)	Heat gain/loss from airflow through operable windows
Component Load: *: Mechanical Ventilation (MBtu)	Heat gain/loss from airflow/fan energy from a whole house mechanical ventilation system
Component Load: *: Whole House Fan (MBtu)	Heat gain/loss from airflow due to a whole house fan
Component Load: *: Ducts (MBtu)	Heat gain/loss from conduction and leakage losses through supply/return ducts outside conditioned space
Component Load: *: Internal Gains (MBtu)	Heat gain/loss from appliances, lighting, plug loads, water heater tank losses, etc. in the conditioned space

Annual Hot Water Uses

Current annual hot water uses are:

Type	Notes
Hot Water: Clothes Washer (gal)
Hot Water: Dishwasher (gal)
Hot Water: Fixtures (gal)	Showers and faucets.
Hot Water: Distribution Waste (gal)

ERI______Home_Hourly.csv

See the Running section for requesting hourly outputs. When requested, a CSV file of hourly outputs is written for the Reference/Rated Homes (e.g., ERIReferenceHome_Hourly.csv for the Reference home).

Depending on the outputs requested, CSV files may include:

Type	Notes
Fuel Consumptions	Energy use for each fuel type (in kBtu for fossil fuels and kWh for electricity).
End Use Consumptions	Energy use for each end use type (in kBtu for fossil fuels and kWh for electricity).
Hot Water Uses	Water use for each end use type (in gallons).
Total Loads	Heating and cooling loads (in kBtu) for the building.
Component Loads	Heating and cooling loads (in kBtu) disaggregated by component (e.g., Walls, Windows, Infiltration, Ducts, etc.).
Zone Temperatures	Average temperatures (in deg-F) for each space modeled (e.g., living space, attic, garage, basement, crawlspace, etc.).
Airflows	Airflow rates (in cfm) for infiltration, mechanical ventilation, natural ventilation, and whole house fans.
Weather	Weather file data including outdoor temperatures, relative humidity, wind speed, and solar.

See the example ERIRatedHome_Hourly.csv.

ERI______Home.xml

A HPXML file is written for each of the homes simulated (e.g., ERIReferenceHome.xml for the Reference home). The file reflects the configuration of the home after applying the ERI 301 ruleset.

See the example ERIRatedHome.xml.

Simulation Files

In addition, raw EnergyPlus simulation input/output files are available for each simulation (e.g., ERIRatedHome, ERIReferenceHome, etc. directories).

Warning

It is highly discouraged for software tools to read the raw EnergyPlus output files. The EnergyPlus input/output files are made available for inspection, but the outputs for certain situations can be misleading if one does not know how the model was created. If there are additional outputs of interest that are not available in our summary output files, please send us a request.

See the example ERIRatedHome directory.

Testing Framework

A large number of tests are automatically run for every code change in the GitHub repository.

The current set of tests include:

• Successful ERI calculations for all sample files
• RESNET® ANSI/ASHRAE Standard 140-2011, Class II, Tier 1 Tests
• RESNET HERS® Reference Home auto-generation tests
• RESNET HERS Index Adjustment Design auto-generation tests
• RESNET HERS method tests
• RESNET HVAC tests
• RESNET Duct distribution system efficiency tests
• RESNET Hot water system performance tests

If you are seeking to develop RESNET Accredited Rating Software, you will need to submit your final software product to RESNET for accreditation.

Running Tests Locally

All tests can be run locally using: openstudio energy_rating_index_test.rb

Individual tests (any method in workflow/tests/energy_rating_index_test.rb that begins with “test_”) can also be run. For example: openstudio energy_rating_index_test.rb --name=test_resnet_hers_method

Test results in CSV format are created at workflow/tests/test_results. For many RESNET tests, the Excel spreadsheet test criteria are also implemented in code to automate the process of checking for test failures. All simulation/HPXML/etc. files generated from running the tests can be found inside the workflow/tests/test_files directory.

At the completion of the test, there will also be output that denotes the number of failures/errors like so:

Finished in 36.067116s, 0.0277 runs/s, 0.9704 assertions/s. 1 runs, 35 assertions, 0 failures, 0 errors, 0 skips

Software developers may find it convenient to export HPXML files with the same name as the test files included in the repository. This allows issuing the same commands above to generate test results.

Packaging

The OpenStudio-ERI workflow is cross-platform and can be used in web or desktop applications.

Web Applications

Using the OpenStudio-ERI workflow in a web application is very straightforward.

First, OpenStudio must be available. Web applications may wish to use the nrel/openstudio docker image. Alternatively, the OpenStudio installer can be executed on the web server – only the EnergyPlus and Command Line Interface (CLI) components are required.

Then grab the latest OpenStudio-ERI release.

Desktop Applications

The OpenStudio-ERI workflow can also be packaged into a third-party software installer for distribution to desktop users.

First, OpenStudio must be bundled – only the EnergyPlus and Command Line Interface (CLI) components are required. Either the OpenStudio setup file can be automatically run as part of your install, or the OpenStudio application can be installed to a local computer and its contents can be re-bundled in your installer (there are no external dependencies required). The only required OpenStudio contents are the openstudio/bin and openstudio/EnergyPlus directories.

Then grab the latest OpenStudio-ERI release.

Indices and tables

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