Air Density Calculated Column

In any dataset that contains wind speed data, Windographer automatically creates a calculated data column containing the air density in every time step. You can change the properties of this data column in the Configure Dataset window, but you cannot delete it. The air density calculations will incorporate measured air temperature, air pressure and relative humidity data as described below.

Measured Temperature and Pressure

If the dataset includes a temperature column, Windographer will use that temperature data in the above equations. If the dataset contains multiple temperature data columns, Windographer will use the one with the highest measurement height to calculate air density. Similarly, if the dataset includes an air pressure data column, Windographer will use that pressure data in the air density equation.

If the dataset does not contain temperature and pressure data, or if they have different measurement heights, or if there are time steps where these columns contain no data or are flagged to exclude, Windographer will use the International Standard Atmosphere to adjust the pressure to the same height as the temperature reading, and estimate either or both values when they are missing. For a full description of this process, please see the article Calculating Air Density.

Measured Relative Humidity

If the dataset includes one or more relative humidity columns, and you have chosen (in the properties of the air density column) to use measured RH to calculate air density, Windographer will use in the above equations the measured RH column nearest in height to the height of the air density column. If the dataset lacks an RH column, or in time steps in which the nearest RH column lacks valid data, Windographer will use the constant RH that you enter.

Windographer uses the air density data column to calculate wind power density, wind turbine power output, and wind energy content.