Are typical/extreme periods from EPW used if a DDY file is provided?

I'm curious if its necessary to recalculate the typical/extreme periods for historical weather data if the model is using a DDY file? Are these dates used in the E+ sizing methods?

The periods I'm referring to are located in the header rows of an EPW file: TYPICAL/EXTREME PERIODS,6,Summer - Week Nearest Max Temperature For Period,Extreme,6/22,6/28,Summer - Week Nearest Average Temperature For Period,Typical,6/ 8,6/14,Winter - Week Nearest Min Temperature For Period,Extreme,1/27,2/ 2,Winter - Week Nearest Average Temperature For Period,Typical,1/ 6,1/12,Autumn - Week Nearest Average Temperature For Period,Typical,10/13,10/19,Spring - Week Nearest Average Temperature For Period,Typical,4/26,5/ 2

Unless you are hardsizing equipment, equipment sizing is based of the sizing run which uses the design days (.ddy files). The TYPICAL/EXTREME PERIODS field is ignored in the simulation. If your .epw file has more extreme conditions, the equipment may not have enough capacity to meet the full load, depending on the oversizing factor.

I recommend sizing based off of the ASHRAE climate design conditions. If you are using TMY3 files, the bundled .ddy files use the 2009 values. I recommend the 2017 values, which you can find at the link above. You can choose a more stringent sizing criteria (e.g. 0.4% instead of 1%) or use the "extreme annual design conditions".

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mdahlhausen

answered 2019-12-20 10:15:50 -0500, updated 2019-12-20 13:36:16 -0500

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Oh the perpetual debate over right-sizing and safety factors.

Luis Lara (2019-12-20 10:32:16 -0500) edit

Thanks, I'm really just wondering about how the TYPICAL/EXTREME PERIODS header gets used within an EPW file and if it even impacts a simulation which has the DDYs included