θ is set to 0° for all collector types.
K b ( )
θ
is set to 1 for all collector types.
If wind speed dependence of the heat losses and the zero loss efficiency are used in the collector model for glazed collectors (c3 > 0 and c6 > 0) as outlined in 25.1.4.3, the wind speed u = 3 m/s should be used in the formula. If sky temperature dependence of the heat loss coefficient is used in the collector model (c4 > 0), then (EL-σ·Ta4) = - 100 W/m2 should be used in the formula.