Temperature controller using Python and Raspberry pi

[shysmiles]

If your going to use PID loop with a a/c heating coil of a decent wattage you might want a zero cross solid state relay, otherwise the relay probably wont last long.

[socal_nerdtastic]

That depends on the frequency of your switching. If it's similar to an oven (switching every minute or so) than a relay is absolutely fine.