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Why doesn't the EnergyPlus Environment:Site Wind Speed correspond to the wind speed in the epw weather file if the boundary conditions are the same?

asked 2015-07-16 06:54:30 -0600

updated 2017-05-29 17:44:16 -0600

If I compare the EnergyPlus output variable "Environment: Site Wind Speed" to the corresponding epw weather file, the windspeeds don't always correspond ( although δmet, αmet, zmet = δsite, αsite, zsite in the formula Usite=Vmet(δmet/zmet)^αmet * (zsite/δsite)^αsite ) (Formula extracted from: "Local Wind Speeds Calculations" in the Engineering Reference) Does anybody know why? Sometimes the windspeeds do correspond. Sometimes the difference is bigger than 1,5m/s.

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Is your building tall? Might be adjustments for higher speeds on upper floors?

David Goldwasser gravatar image David Goldwasser  ( 2015-07-16 08:54:37 -0600 )edit

If you aren't using hourly time steps, the adjustment to sub-hourly timesteps can affect the output results. Try running again with one timestep per hour and see if you are still getting different outputs.

Neal Kruis gravatar image Neal Kruis  ( 2015-07-16 09:35:20 -0600 )edit

You are correct. It has to do with the sub-hourly timesteps. If I run with one timestep per hour the values correspond. Thank you.

BBel gravatar image BBel  ( 2015-07-16 10:59:07 -0600 )edit

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answered 2015-07-16 09:31:43 -0600

Bear in mind that environment variables are interpolated so output variable do not match epw hourly value. Could that be the reason? Take a look at

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Asked: 2015-07-16 06:54:30 -0600

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Last updated: Jul 16 '15