Not a good design anyway. The red parts are just a substitute for an adjustable Zener voltage but without any feedback it wouldn't produce a very stable output and with 3V more than it's rating on C1 it probably wouldn't last long either.
There are more issues with this poor man's voltage regulator design. When output voltage is set to minimum (Rp = 0), R1 has to dissipate 5-6W. Besides missing feedback and respective bad load regulation, the output voltage is also strongly temperature dependend.
nowadys we use integrated parts.
* linear regulators, which need about 2 or 4 additionaly parts only .. while giving exact output voltage and additional features like overcurrent limit, overtemperature shutdown...
* switch mode regulators with high efficiency. = less wasted power, less generated heat, no need for a big heatsink.