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Residential building energy models in URBANopt are created using the OpenStudio-HPXML workflow. For every residential building feature found in the geojson file, an HPXML file is built to represent each living unit of the building. In the case of a single-family detached building (which is the only type of low-rise residential building supported at this time), one HPXML file is built to represent the single unit. HPXML files are built based on feature information contained in the geojson file as well as on sets of default assumptions contained in:

  • clothes_dryer.tsv
  • clothes_washer.tsv
  • cooling_system.tsv
  • dishwasher.tsv
  • enclosure.tsv
  • heat_pump.tsv
  • heating_system.tsv
  • mechanical_ventilation.tsv
  • refrigerator.tsv
  • water_heater.tsv

(See below for more information on controlling how these assumptions are made.) A translator measure is then applied to the HPXML file to constuct an OpenStudio(R) building model.

Supported Building Types

Currently, Single-Family Detached is the only low-rise residential building type supported (mid-rise and high-rise multifamily building prototypes can be found in the commercial building workflows). Additionally, on the Baseline Scenario is supported at this time. Single-Family Attached and low-rise Multifamily capabilities will be included in future releases of the URBANopt SDK.

1. Single-Family Detached

The 3D building surfaces stored in HPXML and OSM models represent the area and orientation of ground and exterior exposure of surfaces, but do not represent their position relative to each other. An example geometry rendering for a translated HPXML file is given below.


Modeling Notes

  • Single-Family Detached home models may contain unconditioned non-living spaces that are included as part of the total building area, such as a garage. As a result energy use intensities (EUIs) for homes, often calculated in units of kBtu/sqft/yr, will vary based on the unconditioned floor area if total building area is used for the calculation. Alternatively, conditioned floor area can be used for such calculations. EUIs are not currently used as part of the URBANopt reporting.
  • Single-Family Detached home models may be heated only, air conditioned only, or both heated and cooled.
    • Partial Conditioning: heating and cooling may be applied to just a portion of the living space of the home or to the entire living space. Representation of partial conditioning of the living space of a home is accomplished by adding ideal air load system to heat and cool the un-conditioned portion of the living area. In this situation, district heating or cooling loads may show up in end uses for the home.
    • Undersized Mechanical System: District heating or cooling loads may also show up in end uses when a designed mechanical system cannot meet the load required to maintain thermostat temperatures. An example would be an evaporative cooling system in a hot humid climate.
    • For both the partially conditioned and undersized examples, it is possible for reporting or post processing to filter out these unintended district heating and cooling loads.
  • It is important to know, that unlike the commercial models that will result in unmet heating or cooling hours, the residential models will not have any unmet heating or cooling hours. To understand how the HVAC system is conditioning for Single-Family Detached home models, users should look at district heating and cooling loads.

GeoJSON Schema

The URBANopt geojson schema differentiates between sets of required and optional fields for Single-Family Detached residential buildings:

  • Required fields:

    1. floor_area (i.e., conditioned floor area)
    2. number_of_stories_above_ground
    3. number_of_stories (includes foundation stories)
    4. number_of_bedrooms
    5. foundation_type: slab, crawlspace - vented, crawlspace - unvented, basement - unconditioned, basement - conditioned, ambient
    6. attic_type: attic - vented, attic - unvented, attic - conditioned, flat roof
  • Optional fields:

    1. system_type: combinations of electric resistance, furnace, boiler, central air conditioner, room air conditioner, evaporative cooler, air-to-air heat pump, mini-split heat pump, ground-to-air heat pump
    2. heating_system_fuel_type: electricity, natural gas, fuel oil, propane, wood
    3. template (see below)

An example “Single-Family Detached” building feature snippet is shown below.

    "type": "Feature",
    "properties": {
      "id": "1",
      "geometryType": "Rectangle",
      "name": "New Building_1",
      "type": "Building",
      "floor_area": 3000,
      "building_type": "Single-Family Detached",
      "number_of_stories_above_grade": 1,
      "number_of_stories": 1,
      "number_of_bedrooms": 4,
      "foundation_type": "slab",
      "attic_type": "attic - vented",
      "system_type": "Residential - furnace and central air conditioner",
      "heating_system_fuel_type": "natural gas"

2. Single-Family Attached

The current plan is for this capability to become available in a future release.

3. Low-Rise Multifamily

The current plan is for this capability to become available in a future release.

Customizable Template

An optional template enumeration may be specified for each feature in the geojson. Enumerations that are applicable to residential buildings:

  • Residential IECC 2006 - Customizable Template Sep 2020
  • Residential IECC 2009 - Customizable Template Sep 2020
  • Residential IECC 2012 - Customizable Template Sep 2020
  • Residential IECC 2015 - Customizable Template Sep 2020
  • Residential IECC 2018 - Customizable Template Sep 2020

If no template enumeration is specified, argument values will be defaulted according to the documentation for the HPXMLtoOpenStudio translator measure. In general, these defaults are based on ANSI / RESNET / ICC Std. 301 (2006).

Otherwise, argument values will be set according to these lookup files that span across the following categories:

  • enclosure (insulation levels, air leakage, etc.)
  • HVAC systems (heating/cooling types, efficiencies, etc.)
  • appliances (refrigerator, clothes washer, etc.)
  • mechanical ventilation
  • water heater

All argument values for the previous categories may be customized by manually adjusting values in the lookup files. The enumeration names include “Residential IECC 20XX” because a variety of enclosure, window, duct insulation, and whole-home air leakage assumptions are based on the different IECC model code years to illustrate how templates can be used to approximate different levels of efficiency. Note that not all possible assumptions have been aligned with IECC requirements (e.g., see above regarding defaults), but the users can further customize these templates as needed for specific projects.

URBANopt, Copyright (c) 2019-2020, Alliance for Sustainable Energy, LLC, and other contributors. All rights reserved.