I'm not a physicist so the details may be shaky, but I think this correctly describes the situation:
A highly technological society with a large industrial base is going to produce and use up a lot of energy as part of its daily existence.
Even assuming maximal efficiency throughout, and devices in place to reuse as much of the waste energy as is possible, there is a theoretical limit beyond which it's not possible to improve efficiency or recover energy. Check out http://en.wikipedia.org/wiki/Carnot%27s_theorem_(thermodynamics) for an idea.
Due to conversion costs, it's most likely that unusable, unrecoverable energy will end up radiated as heat. It's cheaper to convert energy into heat energy, than to go back, especially if you're looking at an already hot planet.
So it's entirely reasonable that a very efficient, highly optimized society, will be producing high quantities of excess heat.
This is not a problem, yet. It's actually, in general, easier to be energy efficient - especially for mechanical processes - at higher temperatures. Hotter engines are more efficient - mostly since their environment can't absorb as much waste if it's warmer. The real problems with heat are for survival of living organisms, and for proper functioning of advanced tech devices - the more advanced they are, the more likely they to be sensitive to energy differences. Look at your computer internals as an example.
So, if I had to guess, the puppeteers, despite being as energy efficient as possible, produced too much heat that the balance between efficiency and function was skewed, and they had to take extreme measures to dispose of the excess.