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

asked 2019-12-19 20:00:17 -0500

updated 2020-01-15 18:25:23 -0500

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

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answered 2019-12-20 10:15:50 -0500

updated 2019-12-20 13:36:16 -0500

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

Luis Lara gravatar image 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

Sam Currie gravatar image Sam Currie  ( 2019-12-20 10:54:51 -0500 )edit
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That field in the .epw isn't used in the simulation.

mdahlhausen gravatar image mdahlhausen  ( 2019-12-20 12:14:35 -0500 )edit

I had a feeling that was the case; if you edit your answer to include that bit I will mark it as accepted, thanks!

Sam Currie gravatar image Sam Currie  ( 2019-12-20 13:01:10 -0500 )edit

Can I use the *.epw to size the equipment?

enriquesissa gravatar image enriquesissa  ( 2021-05-30 04:53:38 -0500 )edit

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Asked: 2019-12-19 20:00:17 -0500

Seen: 157 times

Last updated: Dec 20 '19