> For the complete documentation index, see [llms.txt](https://docs.betterbuilding.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.betterbuilding.io/support-and-training/other-support/faqs/energyplus/energyplus-environment-data.md). # EnergyPlus Environment Data EnergyPlus environment data represents real-time weather and outdoor conditions that drive building energy simulations. These variables capture the external environmental factors that influence heating, cooling, lighting, and other building energy demands. ## Key Characteristics ### **Weather-Driven Simulation** Environment data comes from weather files (EPW format) or user-defined conditions that provide hourly outdoor conditions for an entire year. ### **Boundary Conditions** These variables define the external boundary conditions that affect heat transfer, solar gains, natural ventilation, and HVAC system operation. ### **Solar Calculations** EnergyPlus automatically calculates solar position (altitude and azimuth angles) based on location, date, and time, which drives daylighting and solar heat gain calculations. ### **Dynamic Response** Building energy systems respond dynamically to these changing environmental conditions throughout the simulation period. ## Common Applications * **Climate analysis** - Understanding local weather patterns * **Solar energy assessment** - Evaluating solar radiation availability * **Natural ventilation studies** - Using wind data for ventilation strategies * **Seasonal energy patterns** - Correlating energy use with outdoor conditions * **Comfort analysis** - Understanding outdoor conditions for natural conditioning strategies These environment variables form the foundation for realistic building energy modeling by providing the external driving forces that determine building energy performance. ## Environment Data Variables * **Site Day Type Index** - Numerical index indicating day type (weekday, weekend, holiday, etc.) * **Site Diffuse Solar Radiation Rate per Area** - Solar radiation intensity from scattered sunlight (not direct beam) * **Site Direct Solar Radiation Rate per Area** - Solar radiation intensity from direct sunlight beam * **Site Ground Temperature** - Temperature of the ground surface at the building site * **Site Outdoor Air Drybulb Temperature** - Ambient air temperature measured in shade * **Site Outdoor Air Relative Humidity** - Percentage of moisture in outdoor air relative to saturation * **Site Precipitation Depth** - Amount of rainfall or precipitation accumulated * **Site Solar Altitude Angle** - Vertical angle of the sun above the horizon * **Site Solar Azimuth Angle** - Horizontal angle of the sun's position (compass direction) * **Site Wind Direction** - Compass direction from which the wind is blowing * **Site Wind Speed** - Velocity of outdoor air movement --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://docs.betterbuilding.io/support-and-training/other-support/faqs/energyplus/energyplus-environment-data.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.