If you increase the Subcooling, the deltaH increases, then the fluid flow decreases, then the Power decreases from formula Q=W*deltaH
with Q=power (KW); W=fluid flow (m3/h); H=enthalpy (KJ/Kg)
The power in the cases is little different because the global exchange coefficient (K) is little different, from formula Q=K*A*deltaT
with Q=power (KW); K= global exchange coefficient (W/m2K); A=exchange surface (m2); T= temperature (°C).
In fact K=1/(1/he*Ea)+(s/se)/hi+…
with K= global exchange coefficient; he= exchange coefficient to external tube; Ea= efficiency finned surface; s=total surface; se= secondary surface; hi= exchange coefficient to internal tube.
Because the K is least of (1/he*Ea) and (s/se)/hi, if one of these factors change little, K changes little or for nothing.
An example with numbers: if “(1/he*Ea)” is 60 and “(s/se)/hi” is 4000, K will be 40.
Then, if you change “(s/se)/hi”, K will change little (for example 39) and then, also, the power will change little.