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Re: [EnergyPlus_Support] What exactly is a Design Day?



There are others on this forum that know better- and I sometimes do use extreme weather for design conditions-- but to answer your question as simply as I think is possible---

Design days are the aggregate of weather data that when used for HVAC sizing they will cover a desired amount of conditions by percent.
For instance: LEED requires the use of 99.6%  for heating and 1% for cooling. Translated this means that the heating design day will cover  99.6% of the cold weather conditions from the weather file and only 1% of the time will hot conditions from the weather file surpass the design day.
It is also noteworthy that design day's can be generated from weather files by using the weather utility packaged with E+.  
The only times I choose to not use design day's is when I do a climate study that involves many weather files (and even then I am just being lazy as there is reportedly a way to use Ep Macro to get the design day info) this type of use makes since when the modeling goal is proportional rather then precise. 

If I where you I would either use 99.6%  for heating and 1% for cooling blindly, or get a copy of the ASHRAE handbook and read up on the design day concept then use the days appropriate for your use.  

Best of luck


Jeremiah D. Crossett  | Senior Analyst  |  Phase Change Energy Solutions
120 E. Pritchard St.  | Asheboro, NC 27203  | Mobile 503-688-8951
  





On Mon, Jan 7, 2013 at 5:13 PM, gabrieljew1990 <gjew@xxxxxxxxxx> wrote:
 

I am confused by the definition.
"the DesignDay input syntax
defines a single day of weather
information"

What is the purpose of this?
If I am using a weather file, do I need to worry about a Design Day?




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