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C-value â Thermal Conductance. Thermal conductance is the time rate of steady state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces, in W/m2âK. C-value, hence, is the reciprocal of the R-value and can be expressed as Equation (3).
Therefore the thermal conductance from the collector surface to the water is 0.4 W/mm/degreeC * 19504 mm2 / 38 mm = 205W/degreeC. In other words, a 1 degreeC temperature difference between the water and the fin will result in 205W of heat transfer.