Clothing convective heat exchange--proposal for improved prediction in standards and models

Convection is an important determinant for both sensible and evaporative heat exchange. Heat transfer by convection for normal boundary conditions is readily described by simple power functions. Clothing affects convection in various ways and existing characterisation of clothing by its static insulation values produces inaccurate prediction of sensible heat exchange, eventually leading to erroneous risk assessment. The present paper reviews various methods for evaluation of clothing convective (sensible) heat exchange. Based on available data, two equations are proposed for determination of the reduction of the total insulation values obtained under static, still wind conditions as a consequence of wind and walking effects. The equations apply from 0 to 1.84 clo, from 0.2 to 3 m/s and for walking speeds up to 1.2 m/s. The equations are incorporated in ISO 7933 to provide a more realistic and accurate prediction of sensible heat transfer through clothing.