<< Calculus`VectorAnalysis`

Off[General::"spell1"]

hl = 100;
nhl = 400;
t = 8*3600;
cp = 4186;
T1 = 5. ;
T2 = 80;
Tp = 105;
vykon = ((nhl*hl*cp*(T2 - T1))/t);
Print["vykon je ", (vykon/1000), " kW"];

Δ1 = Tp - T1;
Δ2 = Tp - T2;
reskS = Solve[
            vykon == 
              kS*((Δ1 - Δ2)/Log)[Δ(1/Δ)2]][[1]];
KS = kS /. reskS;
\(\(Print["kS je ", 
        KS, \*"" W.\!\(K\^\(-1\)\)""];\)\)