About the equivalent radiative temperature for clear skies

The cold sky radiation constitutes a heat sink mainly used for passive cooling systems. The usefulness of this resource is commonly expressed in terms of the equivalent sky temperature T_c, whose accurate determination still remains as an interesting problem. Increasing the number and the diversity of the observations is necessary. An inexpensive pyrradiometer, made for that purpose, is described here. In addition, analysis of five years of observations with the Carpentras pyrradiometer (National Meteorology) lead us to propose a formulation for T_c which points out the influence of the boundary layer.