Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
These are design conditions read from the ASHRAE 2009 (now 2013) Handbook of Fundamentals, e.g., 99.6% and 99% heating dry-bulb temperatures, 0.4%, 1%, and 2% cooling dry-bulb and mean coincident wet-bulb temperatures, etc., when the EnergyPlus Weather Converter is used to convert the source weather file to the epw format. You can look at the ASHRAE design conditions data base in files like ASHRAE_2009_Yearly_DesignConditions.csv located in the subdirectory PreProcess\WeatherConverter. under the main EnergyPlus directory on your PC. As far as I know, what each number represents in this long string of numbers is not in the EnergyPlus documentation (although I think it should be), so if you're interested to know you have to compare them to the ASHRAE Handbook of Fundamentals Chapter 14 (2009 version) Appendix and write them down. I've never had the urge to do that, because frankly I don't even know how or whether these numbers are even used by EnergyPlus, since there's also a companion DDY file with the same ASHRAE Design Conditions expanded into IDF that can be used to do design calculations, which makes it all rather confusing, even to me.
As a final comment, these ASHRAE design conditions are not related to the weather file itself. They were derived independently by ASHRAE and are linked by the EnergyPlus WeatherConverter based on their WMO Weather Station number. I say this to warn people that regardless whether you're running an old file, e.g., TMY2, or a newer file, e.g., TMY3, the design calculations do not change.
