TMY (Typical Meteorological Year) data is a 12-month synthetic weather dataset composed of actual monthly weather observations from the most statistically typical years in a 20-30 year historical record for a specific location. TMY files provide representative weather patterns for annual energy simulations and building performance analysis, balancing realism with typical operating conditions.
Data Structure and Sources
TMY files contain hourly values for 8,760 hours including dry bulb temperature, wet bulb temperature, relative humidity, atmospheric pressure, wind speed, wind direction, and solar radiation components. The National Renewable Energy Laboratory (NREL) develops and maintains TMY3 datasets for 1,020 U.S. locations using 1991-2005 weather records, recently expanding to TMY4 with 2017-2021 data reflecting climate changes. Each month in a TMY dataset represents the most typical month from the available historical years, creating a composite year that avoids extreme seasonal biases.
Energy Modeling Applications
Energy simulation software uses TMY data to calculate annual HVAC loads, equipment run time, and utility consumption under typical weather conditions rather than design extremes. TMY-based simulations typically overestimate energy consumption compared to design day peak loads, allowing engineers to evaluate equipment part-load efficiency and seasonal performance. Solar thermal and photovoltaic system sizing heavily relies on TMY solar radiation data for accurate yield predictions.