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Matthew Dahlhausen edited this page Sep 21, 2020 · 3 revisions

Why we care about weather

  • Appropriate design and HVAC system selection
  • Right-sizing HVAC equipment
  • Comfort, both indoors and outdoors
  • Accounting for climate change and future weather conditions
  • Accounting for urban environments
  • Design for resiliency

Types of weather files

  • Design Days (.ddy) Design weather days used for sizing HVAC equipment.
  • TMY, TMY2, TMY3 (.epw) Typical Meteorological Year weather files. TMY3 is the most common, and represents an average of 30 years of weather for a given location. Used for energy simulations for energy efficiency improvements.
  • TMY3, TMY5, TMY7, TMY10 (.epw) Typical Meteorological Year weather files, but from the last 3, 5, 7, or 10 years. The '3' in TMY3 has a different meaning in this case. Useful for near term design and localized energy efficiency estimates.
  • XMY (.epw) Extreme Meteorological Year weather files, similar to TMY but taking extreme weather instead of average or representative weather. Useful for resiliency simulation and guaranteeing net zero energy operation even in extreme years.
  • AMY (.epw) Annual Meteorological Year weather files. Weather from a specific year, used for calibrating an energy model.

Design Day Weather

Future weather files

Climate change is moving fast enough that TMY3 datasets will no longer be valid for loads or energy modeling several decades out. Future weather is predicted by using a global circulation model (GCM) at fine resolution, and simulating future weather.

There are two ways to generate future weather files. Morphing approaches use an existing weather file and shift each hourly temperature up by a fixed amount, and then adjust humidity accordingly properties . Probabilistic approaches use a weather simulator to generate an ensemble of future weather files and then pick representative ones from the ensemble. Probabilistic approaches capture how climate change influences the length and severity of heat waves, droughts, cold spells, and other weather and is the preferred approach.

  • ($, Free if you provide data) Indra Create synthetic weather time series from a short weather record of at least one year.

  • ($) WeatherShift Generates future weather files for 250 cities at 2020, 2050, and 2080, and will soon have design days as well. It makes these files from the TMY3 file by a scaling factor derived from 14 GCM models running the RCP 8.5 scenario of the IPCC.

  • (Free) CCWorldWeatherGen The climate change world weather file generator (CCWorldWeatherGen) allows you to generate climate change weather files for world-wide locations ready for use in building performance simulation programs.

  • (Free, Data only*) NARCCAP Future weather data for different climate scenarios. Need to translate into .epw format.

  • From ASHRAE HOF 2013:

    • The results, averaged over all locations,are as follows:
      • The 99.6% annual dry-bulb temperature increased 2.74°F
      • The 0.4% annual dry-bulb increased 1.42°F
      • Annual dew point increased by 0.99°F
      • Heating degree-days (base 65°F) decreased by 427°F-days
      • Cooling degree-days (base 50°F) increased by 245°F-days

Urban climate weather adjustments

Weather file sources

Weather analysis tools

  • (Free) epwvis Visualization and analysis tool for .epw files.
  • (Free) epwvis-compare epwvis, but compares weather files.
  • (Free) WeatherSpark Wonderful site for graphical and textual climate summaries.
  • (Free) ClimaPlus An early design tool with graphics for outdoor and indoor conditions for naturally-ventilated and mixed-mode buildings.
  • (Free) Ladybug Ladybug is a free and open source environmental plugin for Grasshopper to help designers create an environmentally-conscious architectural design. The first step is weather data analysis.
  • (Free) Dragonfly Warp climate files based on either satellite data, urban morphology parameters, or future climate change scenarios.
  • (Free) DView A tool that can view and run basic statistics on weather files. Developed by NREL as part of BeOpt library.
  • (Free) ClimateConsultant - standalone software for generating many design options for weather files. Architects seem to really like the design strategies overlay on the psychrometric chart.
  • (Free) Elements Elements is a free, open-source, cross-platform software tool for creating and editing custom weather files for building energy modeling.
  • (Free) klimmat - pdf report based on .epw weather files across the globe.
  • (Free) DegreeDays - online tool for generating heating and cooling degree days. Only goes back 36 months for monthly data. If you want to go back farther, go to the source:
  • (Free) Weather Underground - Despite the name, this site has lots of above-ground weather data for lots of hyper-local locations, extending back for as long as a station has existed. Good visualizations too.
  • (Free) LMNts architects parallel coordinates for analyzing components of weather data.
  • (Free) ODS Wind Rose Generates wind roses from an .epw file and generates a downloadable .pdf report.
  • ($) Climate Tool Lots of cool tools for climate analysis, similar to ClimateConsultant, but with some more features. Calculate potential for heating/cooling strategies, including: natural ventilation, night cooling, evaporative cooling, passive solar heating, and passive solar cooling.
  • ($) IES excel macro

Types of weather analysis and graphics

  • line chart
  • heat map
  • psychrometric chart
  • area plot (cold, comfortable)
  • solar stereogram
  • windrose
  • Mahoney analysis
  • universal thermal comfort index (UTCI)
  • thermal autonomy

Relevant reports and articles

Relevant Unmet Hours posts

Relevant code resources

Tips for using weather data

  • Always plot it to make sure the data is clean. There are some known issues with TMY3 files, e.g. Minneapolis
  • Prioritize data that is most recent, then the nearest location.
  • Simulation weather that contains days that are substantially more extreme than the design days may lead to undersized equipment and unmet hours.
  • Use annual design conditions for both heating and cooling from the .ddy files and add monthly cooling design conditions as well. This is important for buildings that have peak cooling driven by solar heat gain rather than dry bulb temperature, occurring in shoulder season months with a lower solar angle.

Workshops, coursework, and additional resources

Contributors

  • Matthew Dahlhausen
  • Stefan Gracik
  • Ken Takahashi
  • Neil Bulger
  • Parag Rastogi

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