Prediction of wind effects on cold protective clothing

Abstract : Cold protective clothing is characterized by its thermal insulation and wind-proof properties. Standard insulation is measured for complete ensembles under static and wind still conditions (ENV-342) Air permeability is measured on the material of the outer layer (ISO-EN-9237). Limited information is available on the interaction of air permeability and thermal insulation under the influence of wind and walking. Ten ensembles comprising 2 to 3-layer combinations with a range of insulation values from 1.49-3.46 clo (0.23-0.54 sq m per deg C/W) air permeability between I and 1000 l/sq m/s were measured with a standing and walking thermal manikin. The manikin was placed in a wind tunnel at wind speeds between 0.2-18 m/s. Walking speeds ranged from standing to 1.2 m/s. One equation was derived for prediction of the reduction in thermal insulation value as function of wind, walking and air permeability. The deviation between measured and predicted value was mostly less than 5% and below 10%! Air permeability has limited influence in wind speeds below 3 m/s, but becomes progressively important at higher wind speeds. Typically a three layer ensemble with low air permeability will loose 60-70 0% of its total insulation in winds of 12 m/s and higher. The new algorithm for collection of clothing insulation has been incorporated in (ISO/CD-1179) and subsequently, allows more realistic prediction of heat balance in cold environments and operational capabilities; analysis of the risks associated with extreme cold and wind conditions; assessment of the protective function of available cold weather ensembles.