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