Software Connection

Introduction

OpenStudio-ERI requires a building description in an HPXML file format. HPXML is an open data standard for collecting and transferring home energy data. Using HPXML files reduces the complexity and effort for software developers to leverage the EnergyPlus simulation engine.

HPXML Inputs

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, a stricter set of requirements for the HPXML file have been developed for purposes of running an Energy Rating Index calculation.

HPXML files submitted to OpenStudio-ERI should undergo a two step validation process:

  1. Validation against the HPXML Schema

The HPXML XSD Schema can be found at hpxml-measures/HPXMLtoOpenStudio/resources/HPXML.xsd. It should be used by the software developer to validate their HPXML file prior to running the workflow. XSD Schemas are used to validate what elements/attributes/enumerations are available, data types for elements/attributes, the number/order of children elements, etc.

OpenStudio-ERI does not validate the HPXML file against the XSD Schema and assumes the file submitted is valid. However, OpenStudio-ERI does automatically check for valid data types (e.g., integer vs string), enumeration choices, and numeric values within min/max.

  1. Validation using Schematron

The Schematron document for the ERI use case can be found at rulesets/301EnergyRatingIndexRuleset/resources/301validator.xml. Schematron is a rule-based validation language, expressed in XML using XPath expressions, for validating the presence or absence of inputs in XML files. As opposed to an XSD Schema, a Schematron document validates constraints and requirements based on conditionals and other logical statements. For example, if an element is specified with a particular value, the applicable enumerations of another element may change.

OpenStudio-ERI automatically validates the HPXML file against the Schematron document and reports any validation errors, but software developers may find it beneficial to also integrate Schematron validation into their software.

Important

Usage of both validation approaches (XSD and Schematron) is recommended for developers actively working on creating HPXML files for Energy Rating Index calculations:

  • Validation against XSD for general correctness and usage of HPXML
  • Validation against Schematron for understanding XML document requirements specific to running ERI calculations

HPXML Software Info

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 “2019AB” tells the workflow to use ANSI/RESNET/ICC© 301-2019 with both Addendum A and Addendum B 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 Schematron document (rulesets/301EnergyRatingIndexRuleset/resources/301validator.xml).

HPXML Building Details

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

HPXML 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.

HPXML Weather Station

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/extension/EPWFilePath element specifies the path to the EnergyPlus weather file (EPW) to be used by the simulation. The full set of U.S. TMY3 weather files can be downloaded here.

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.

HPXML 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 Building Type
living space Above-grade conditioned floor area EnergyPlus calculation Any
attic - vented   EnergyPlus calculation Any
attic - unvented   EnergyPlus calculation Any
basement - conditioned Below-grade conditioned floor area EnergyPlus calculation Any
basement - unconditioned   EnergyPlus calculation Any
crawlspace - vented   EnergyPlus calculation Any
crawlspace - unvented   EnergyPlus calculation Any
garage Single-family (not shared parking) EnergyPlus calculation Any
other housing unit Unrated Conditioned Space Same as conditioned space Attached/Multifamily only
other heated space Unrated Heated Space Average of conditioned space and outside; minimum of 68F Attached/Multifamily only
other multifamily buffer space Multifamily Buffer Boundary Average of conditioned space and outside; minimum of 50F Attached/Multifamily only
other non-freezing space Non-Freezing Space Floats with outside; minimum of 40F Attached/Multifamily only

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.

HPXML Air Infiltration

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.

HPXML 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.

HPXML 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.

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.

HPXML 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. If RadiantBarrier is provided, RadiantBarrierGrade must also be provided.

HPXML 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.

HPXML 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.

HPXML 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.

HPXML 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.

HPXML 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.

HPXML 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.

HPXML 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.

HPXML 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.

HPXML 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.

HPXML Heating Systems

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

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

HeatingSystemType IsSharedSystem DistributionSystem HeatingSystemFuel AnnualHeatingEfficiency HeatingCapacity extension/FanPowerWatts extension/FanPowerWattsPerCFM
ElectricResistance     electricity Percent (required)    
Furnace   AirDistribution or DSE <any> AFUE (required)   (optional)
WallFurnace     <any> AFUE (required) (optional)  
FloorFurnace     <any> AFUE (required) (optional)  
Boiler false HydronicDistribution or DSE <any> AFUE (required)    
Boiler true HydronicDistribution or HydronicAndAirDistribution <any> AFUE      
Stove     <any> Percent (required) (optional)  
PortableHeater     <any> Percent (required) (optional)  
FixedHeater     <any> Percent (required) (optional)  
Fireplace     <any> Percent (required) (optional)  

For a furnace connected to an air conditioner, if fan powers are provided for both systems, they must be equal.

For boilers, the ElectricAuxiliaryEnergy element may be provided if available. For shared boilers (i.e., serving multiple dwelling units), the electric auxiliary energy can alternatively be calculated using the following inputs:

  • extension/SharedLoopWatts: Shared pump power [W]
  • NumberofUnitsServed: Number of units served by the shared system
  • extension/FanCoilWatts: In-unit fan coil power [W]

If electric auxiliary energy is not provided (nor calculated for shared boilers), it is defaulted per ANSI/RESNET/ICC 301-2019.

For shared boilers connected to a water loop heat pump, an additional element is required:

  • extension/WaterLoopHeatPump/AnnualHeatingEfficiency[Units="COP"]/Value: WLHP rated heating efficiency

HPXML 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.

Depending on the type of cooling system specified, additional elements are used:

CoolingSystemType IsSharedSystem DistributionSystem CoolingSystemFuel AnnualCoolingEfficiency SensibleHeatFraction CoolingCapacity extension/FanPowerWattsPerCFM
central air conditioner   AirDistribution or DSE electricity SEER (optional) (required) (optional)
room air conditioner     electricity EER (optional) (required)  
evaporative cooler   AirDistribution or DSE (optional) electricity       (optional)
chiller true HydronicDistribution or HydronicAndAirDistribution electricity kW/ton   (required)  
cooling tower true HydronicAndAirDistribution electricity        

For an air conditioner connected to a furnace, if fan powers are provided for both systems they must be equal.

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

For shared chillers (i.e., serving multiple dwelling units), additional elements are required:

  • NumberofUnitsServed: Number of units served by the shared system
  • AnnualCoolingEfficiency[Units="kW/ton"]/Value: Chiller efficiency
  • extension/SharedLoopWatts: Total of the pumping and fan power serving the system [W]

For shared chillers connected to a fan coil, additional elements are required:

  • extension/FanCoilWatts: Total of the in-unit cooling equipment power serving the unit [W]

For shared chillers connected to a water loop heat pump, additional elements are required:

  • extension/WaterLoopHeatPump/CoolingCapacity: WLHP cooling capacity [Btu/hr]
  • extension/WaterLoopHeatPump/AnnualCoolingEfficiency[Units="EER"]/Value: WLHP rated cooling efficiency

For shared cooling towers (which must always be connected to a water loop heat pump), additional elements are required:

  • NumberofUnitsServed: Number of units served by the shared system
  • extension/SharedLoopWatts: Total of the pumping and fan power serving the system [W]
  • extension/WaterLoopHeatPump/CoolingCapacity: WLHP cooling capacity [Btu/hr]
  • extension/WaterLoopHeatPump/AnnualCoolingEfficiency[Units="EER"]/Value: WLHP rated cooling efficiency

HPXML 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 used:

HeatPumpType IsSharedSystem DistributionSystem HeatPumpFuel AnnualCoolingEfficiency AnnualHeatingEfficiency CoolingSensibleHeatFraction HeatingCapacity17F extension/FanPowerWattsPerCFM extension/PumpPowerWattsPerTon
air-to-air   AirDistribution or DSE electricity SEER HSPF (optional) (optional) (optional)  
mini-split   AirDistribution or DSE (optional) electricity SEER HSPF (optional) (optional) (optional)  
ground-to-air false AirDistribution or DSE electricity EER COP (optional)   (optional) (optional)
ground-to-air true AirDistribution or DSE electricity EER COP (optional)   (optional) (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 BackupHeatingSwitchoverTemperature is not provided, the backup heating system will operate as needed when the heat pump has insufficient capacity.

For multiple ground source heat pumps on a shared hydronic circulation loop (IsSharedSystem="true"), additional elements are required:

  • NumberofUnitsServed: Number of units served by the shared system
  • extension/SharedLoopWatts: Shared pump power [W]

HPXML HVAC Control

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

HPXML HVAC Distribution

Each separate HVAC distribution system should be specified as a Systems/HVAC/HVACDistribution. The four types of HVAC distribution systems allowed are AirDistribution, HydronicDistribution, HydronicAndAirDistribution, 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.

Air Distribution

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 Building Type
living space Above-grade conditioned floor area EnergyPlus calculation Any
basement - conditioned Below-grade conditioned floor area EnergyPlus calculation Any
basement - unconditioned   EnergyPlus calculation Any
crawlspace - unvented   EnergyPlus calculation Any
crawlspace - vented   EnergyPlus calculation Any
attic - unvented   EnergyPlus calculation Any
attic - vented   EnergyPlus calculation Any
garage Single-family (not shared parking) EnergyPlus calculation Any
exterior wall   Average of conditioned space and outside Any
under slab   Ground Any
roof deck   Outside Any
outside   Outside Any
other housing unit Unrated Conditioned Space Same as conditioned space Attached/Multifamily only
other heated space Unrated Heated Space Average of conditioned space and outside; minimum of 68F Attached/Multifamily only
other multifamily buffer space Multifamily Buffer Boundary Average of conditioned space and outside; minimum of 50F Attached/Multifamily only
other non-freezing space Non-Freezing Space Floats with outside; minimum of 40F Attached/Multifamily only

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

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

Note

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

Warning

Total leakage and leakage to outside testing exemption should only be used if the conditions specified in ANSI/RESNET/ICC 301 have been appropriately met. OpenStudio-ERI does not assess the validity of the duct test exemption claim.

Hydronic Distribution

HydronicDistribution systems are defined by:

  • HydronicDistributionType: “radiator” or “baseboard” or “radiant floor” or “radiant ceiling”

Hydronic And Air Distribution

HydronicAndAirDistribution systems are defined by:

  • HydronicAndAirDistributionType: “fan coil” or “water loop heat pump”

as well as all of the elements described above for an AirDistribution system.

Distribution System Efficiency

DSE systems are defined by AnnualHeatingDistributionSystemEfficiency and AnnualCoolingDistributionSystemEfficiency elements.

HPXML Mechanical Ventilation

This section describes elements specified in HPXML’s Systems/MechanicalVentilation. Systems/MechanicalVentilation/VentilationFans/VentilationFan elements can be used to specify whole home ventilation systems and/or cooling load reduction.

Whole Home Ventilation

Mechanical ventilation systems that provide whole home ventilation may each be specified as a Systems/MechanicalVentilation/VentilationFans/VentilationFan with UsedForWholeBuildingVentilation='true'. Inputs including FanType, HoursInOperation, and IsSharedSystem must be provided.

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 and AdjustedTotalRecoveryEfficiency can be provided instead of SensibleRecoveryEfficiency and TotalRecoveryEfficiency.

If the ventilation system is not shared, the following inputs are available:

  • TestedFlowRate: The measured airflow rate. If unmeasured, provide extension/FlowRateNotTested[text()="true"] instead. For a CFIS system, the flow rate should equal the amount of outdoor air provided to the distribution system.
  • FanPower: The fan power for the highest airflow setting. If unknown, provide extension/FanPowerDefaulted[text()="true"] instead.

If the ventilation system is shared (i.e., serving multiple dwelling units), the following inputs are available:

  • RatedFlowRate: The rated airflow rate of the entire system.
  • FanPower: The fan power for the entire system at highest airflow setting. If unknown, provide extension/FanPowerDefaulted[text()="true"] instead.
  • FractionRecirculation: Fraction of the total supply air that is recirculated, with the remainder assumed to be outdoor air. The value must be 0 for exhaust only systems.
  • extension/InUnitFlowRate: The flow rate delivered to the dwelling unit. If unmeasured, provide extension/FlowRateNotTested[text()="true"] instead.
  • extension/PreHeating: Optional. Element to specify if the supply air is preconditioned by heating equipment. It is not allowed for exhaust only systems. If provided, there are additional child elements required:
    • Fuel: Fuel type of the preconditioning heating equipment.
    • AnnualHeatingEfficiency[Units="COP"]/Value: Efficiency of the preconditioning heating equipment.
    • FractionVentilationHeatLoadServed: Fraction of heating load introduced by the shared ventilation system that is met by the preconditioning heating equipment.
  • extension/PreCooling: Optional. Element to specify if the supply air is preconditioned by cooling equipment. It is not allowed for exhaust only systems. If provided, there are additional child elements required:
    • Fuel: Fuel type of the preconditioning cooling equipment.
    • AnnualCoolingEfficiency[Units="COP"]/Value: Efficiency of the preconditioning cooling equipment.
    • FractionVentilationCoolLoadServed: Fraction of cooling load introduced by the shared ventilation system that is met by the preconditioning cooling equipment.

Cooling Load Reduction

Whole house fans that provide cooling load reduction may each be specified as a Systems/MechanicalVentilation/VentilationFans/VentilationFan with UsedForSeasonalCoolingLoadReduction='true'. Required elements include RatedFlowRate and FanPower.

The whole house fan is assumed to operate during hours of favorable outdoor conditions and will take priority over operable windows (natural ventilation).

HPXML Water Heating Systems

Each water heater should be entered as a Systems/WaterHeating/WaterHeatingSystem. Inputs including WaterHeaterType, IsSharedSystem, Location, and FractionDHWLoadServed must be provided.

Warning

FractionDHWLoadServed represents only the fraction of the hot water load associated with the hot water fixtures. Additional hot water load from the clothes washer/dishwasher will be automatically assigned to the appropriate water heater(s).

The Location must be one of the following:

Location Description Temperature Building Type
living space Above-grade conditioned floor area EnergyPlus calculation Any
basement - conditioned Below-grade conditioned floor area EnergyPlus calculation Any
basement - unconditioned   EnergyPlus calculation Any
attic - unvented   EnergyPlus calculation Any
attic - vented   EnergyPlus calculation Any
garage Single-family (not shared parking) EnergyPlus calculation Any
crawlspace - unvented   EnergyPlus calculation Any
crawlspace - vented   EnergyPlus calculation Any
other exterior Outside Outside Any
other housing unit Unrated Conditioned Space Same as conditioned space Attached/Multifamily only
other heated space Unrated Heated Space Average of conditioned space and outside; minimum of 68F Attached/Multifamily only
other multifamily buffer space Multifamily Buffer Boundary Average of conditioned space and outside; minimum of 50F Attached/Multifamily only
other non-freezing space Non-Freezing Space Floats with outside; minimum of 40F Attached/Multifamily only

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

WaterHeaterType UniformEnergyFactor or EnergyFactor FirstHourRating FuelType TankVolume HeatingCapacity RecoveryEfficiency UsesDesuperheater WaterHeaterInsulation/Jacket/JacketRValue RelatedHVACSystem
storage water heater required required if UEF <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 required if UEF 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.

If the water heater is a shared system (i.e., serving multiple dwelling units or a shared laundry room), it should be described using IsSharedSystem='true'. In addition, the NumberofUnitsServed must be specified, where the value is the number of dwelling units served either indirectly (e.g., via shared laundry room) or directly.

HPXML Hot Water Distribution

A single Systems/WaterHeating/HotWaterDistribution must be provided if any water heating systems are specified. Inputs including SystemType and PipeInsulation/PipeRValue must be provided. Note: Any hot water distribution associated with a shared laundry room in attached/multifamily buildings should not be defined.

Standard

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

  • PipingLength: Measured length of hot water piping from the hot water heater (or from a shared recirculation loop serving multiple dwelling units) 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)

Recirculation

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

  • ControlType: One of “manual demand control”, “presence sensor demand control”, “temperature”, “timer”, or “no control”.
  • 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: Pump power in Watts.

Shared Recirculation

In addition to the hot water distribution systems within the dwelling unit, the pump energy use of a shared recirculation system in an Attached/Multifamily building can also be described using the following elements:

  • extension/SharedRecirculation/NumberofUnitsServed: Number of dwelling units served by the shared pump.
  • extension/SharedRecirculation/PumpPower: Shared pump power in Watts.
  • extension/SharedRecirculation/ControlType: One of “manual demand control”, “presence sensor demand control”, “timer”, or “no control”.

Note that when defining a shared recirculation system, the hot water distribution system type within the dwelling unit must be standard (SystemType/Standard). This is because a stacked recirculation system (i.e., shared recirculation loop plus an additional recirculation system within the dwelling unit) is more likely to indicate input errors than reflect an actual real-world scenario.

Drain Water Heat Recovery

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

HPXML 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.

HPXML 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.

Simple Model

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.

Detailed Model

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.

HPXML 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:

  • IsSharedSystem: true or false
  • 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.

If the PV system is a shared system (i.e., serving multiple dwelling units), it should be described using IsSharedSystem='true'. In addition, the total number of bedrooms across all dwelling units served by the system must be entered as extension/NumberofBedroomsServed. PV generation will be apportioned to the dwelling unit using its number of bedrooms divided by the total number of bedrooms in the building.

HPXML 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 Building Type
living space Above-grade conditioned floor area Any
basement - conditioned Below-grade conditioned floor area Any
basement - unconditioned   Any
garage Single-family (not shared parking) Any
other housing unit Unrated Conditioned Space Attached/Multifamily only
other heated space Unrated Heated Space Attached/Multifamily only
other multifamily buffer space Multifamily Buffer Boundary Attached/Multifamily only
other non-freezing space Non-Freezing Space Attached/Multifamily only

HPXML Clothes Washer

A single Appliances/ClothesWasher element may be specified. The IsSharedAppliance element must be provided.

If no clothes washer is located within the Rated Home, a clothes washer in the nearest shared laundry room on the project site shall be used if available for daily use by the occupants of the Rated Home. If there are multiple clothes washers, the clothes washer with the highest Label Energy Rating (kWh/yr) shall be used.

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.

If the clothes washer is a shared appliance (i.e., in a shared laundry room), it should be described using IsSharedAppliance='true'. In addition, the following elements must be provided:

  • AttachedToWaterHeatingSystem: Reference a shared water heater.
  • NumberofUnitsServed: The number of dwelling units served by the shared laundry room.
  • NumberofUnits: The number of clothes washers in the shared laundry room.

HPXML Clothes Dryer

A single Appliances/ClothesDryer element may be specified. The IsSharedAppliance element must be provided.

If no clothes dryer is located within the Rated Home, a clothes dryer in the nearest shared laundry room on the project site shall be used if available for daily use by the occupants of the Rated Home. If there are multiple clothes dryers, the clothes dryer with the lowest Energy Factor or Combined Energy Factor shall be used.

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.

If the clothes dryer is a shared appliance (i.e., in a shared laundry room), it should be described using IsSharedAppliance='true'. In addition, the following elements must be provided:

  • NumberofUnitsServed: The number of dwelling units served by the shared laundry room.
  • NumberofUnits: The number of clothes dryers in the shared laundry room.

HPXML Dishwasher

A single Appliances/Dishwasher element may be specified. The IsSharedAppliance element must be provided.

If no dishwasher is located within the Rated Home, a dishwasher in the nearest shared kitchen in the building shall be used only if available for daily use by the occupants of the Rated Home. If there are multiple dishwashers, the dishwasher with the lowest Energy Factor (highest kWh/yr) shall be used.

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.

If the dishwasher is a shared appliance (i.e., in a shared laundry room), it should be described using IsSharedAppliance='true'. In addition, the following elements must be provided:

  • AttachedToWaterHeatingSystem: Reference a shared water heater.

HPXML Refrigerator

A single Appliances/Refrigerator element may be specified.

If there are multiple refrigerators, the total energy consumption of all refrigerators/freezers shall be used along with the location that represents the majority of power consumption.

The efficiency of the refrigerator must be entered as RatedAnnualkWh.

HPXML Cooking Range/Oven

A single pair of Appliances/CookingRange and Appliances/Oven elements may be specified.

The FuelType of the range and whether it IsInduction, as well as whether the oven IsConvection, must be provided.

HPXML Dehumidifier

A single Appliance/Dehumidifier element may be specified. The Capacity (pints/day) and FractionDehumidificationLoadServed (0-1) must be provided. The efficiency of the dehumidifier can either be entered as an IntegratedEnergyFactor or EnergyFactor.

Note

Dehumidifiers only affect ERI scores if Version 2019AB or newer is used, as dehumidifiers were incorporated into the ERI calculation as of 301-2019 Addendum B.

HPXML Lighting

This section describes elements specified in HPXML’s Lighting.

HPXML Lighting Groups

The building’s lighting is described by nine 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.

HPXML 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.