LB1.8 Outdoor Solar MRT - Sky Temperature?

remyweather · October 14, 2025, 7:16pm

Hi @chris or @mostapha I am wondering if you guys have any documentation or can tell me how you calculate, if at all, or handle, the sky temperature in this component in LB1.8. We are trying to redo our outdoor thermal comfort scripts and were wondering:

chris · February 11, 2026, 10:41pm

Sorry for the late response, @remyweather

The component definitely accounts for long-wave sky temperature (that is what the _horiz_infrared input is for). To see the exact equation that we use to convert the infrared radiation to degrees C, see this function in ladybug-core:

github.com

ladybug-tools/ladybug/blob/27393f667bba19380f42e508ecfa93eb6fe91c2e/ladybug/skymodel.py#L418-L436


      
          def calc_sky_temperature(horiz_ir, source_emissivity=1):
              """Calculate sky temperature in Celsius.
          
              See EnergyPlus Engineering Reference for more information:
              https://bigladdersoftware.com/epx/docs/8-9/engineering-reference/
              climate-calculations.html#energyplus-sky-temperature-calculation
          
              Args:
                  horiz_ir: A float value that represents horizontal infrared radiation
                      intensity in W/m2.
                  source_emissivity: A float value between 0 and 1 indicating the emissivity
                       of the heat source that is radiating to the sky. Default is 1 for
                       most outdoor surfaces.
          
              Returns:
                  sky_temp -- A sky temperature value in C.
              """
              sigma = 5.6697e-8  # stefan-boltzmann constant
              return ((horiz_ir / (source_emissivity * sigma)) ** 0.25) - 273.15

remyweather · February 12, 2026, 4:41pm

Thank you @chris I think this will satisfy Carlos