Sources of data - EPW files

The Energy Plus site Weather Data for Simulation provide, for free, the data for more than 3 thousand sites. They can be downloaded in a zip file for each site contain:
  1. .txt file, specifying a disclaimer about the origin of data and their copyright and a warranty about their us.
  2. .stat text file, CSV formatted, presenting some statistics about the following data.
  3. .ddy file, containing few basic Design Day of the year data or the typical extreme days
  4. An .epw text file, CSV (comma separated values) formatted, hourly data series to record EnergyPlus-ready data, for building energy simulation. The format is widely used but not the only one. This format has become a standard and many other softwares use and read it without problems.
Our main interest refer to the you open the EPW file with a text editor or in a spreadsheet (sometime it is better to change its extension to .txt, just take care to set the proper numerical format, i.e. the the Decimal separator and Thousands separator - see also the excel support page about) you will find a strange file.
First, you will see that it has a long “header” (not necessarily filled).  In the header we find some interesting data \cite{file}:
  1. In the first row of the header we can recognize few fundamental information: it begins with the name of the city and ends with four numbers: (1) the Latitude (North when positive, South when negative), (2) the Longitude (East of Greenwich when positive, West of Greenwich when negative), (3) the Time Zone (Greenwich Mean Time - GMT) and (4) the Elevation above the sea level.
  2. the second row of the header is about Design Conditions Header/Data (CSV)
  3. the third row reports the typical Extreme Periods
  4. the fourth row reports the Ground Temperatures, typically for 3 depths, the assumed soil conductivity, density and specific heat) and the monthly “undisturbed” ground temperatures.
  5. the fifth row is related to Holiday/Daylight Saving Time Data: default weather processing contains no holidays or daylight saving period.
  6. other rows are available for comments and other technical information.
After the header rows, eventually, Data Records come: usually hourly data. Their structure is the following (35, comma separated, columns):

Morphic transformations of the reference year 

Attachments

Glossary

  1. DDY: it is the extension for Climatic Data files and it means Design Day Year)
  2. STAT: it is the extension for Climatic Data files and it means "statistics" and it is referred to EnergyPlus weather data
  3. EPW: means EnergyPlus weather file
  4. TRY: Test Reference Year
  5. CSV: comma separated values" format
  6. TMY (TMY2): Typical Meteorological Year
  7. WYEC2: Weather Year for Energy Calculations
  8. FTMY: future Typical Meteorological Year