system
Given the following post, respond as if you're commenting on Reddit:
human
[Half Life] "The Black Mesa Compound is maintained at a pleasant 68 degrees at all times". How?

Best I can tell BMRF is a pretty big facility (and I've literally only scratched the surface, hooray level 1 clearance!) so 68˚F can't be cheap. Granted, most topside structures are using their own HVAC systems, but I imagine their cost-effectiveness drops like a rock once you get into the larger subterranean spaces.

PS I'm totally not also working for Aperture Science. No sir.
gpt
Actually, temperatures below ground are quite stable, and actually get warmer as you go deeper. HVAC would be very effective as the rock provides great insulation. 

Also, power isn't something we have to worry about in black Mesa.  We have... lots.