Not to be a jerk, but that's a discipline matter - you need to do what you need to do to maintain attention. Too much heating in my car in the winter and I get drowsy as well; and that's a situation where I need to be VERY engaged! If I fall asleep at the wheel, I can't blame it on the car, that was my fault. I do try to practice mindfulness, so I never let myself fall into "auto-pilot".
Breaks help and are definitely needed, the classes I've taught have been anywhere from 1 to 2 hours. I'd typically do a 1 hour block, 10 minutes and finish (or 50 min then break depending on room vibe and natural progression of material).
However, I cannot control things like AC or number of people. AC in a large-scale building is an unsolved problem as-is, I have no control over every person's thermal comfort level (plus everyone's different). In that situation, I view it more internally as "What can I do to stay engaged?" rather than "What can they do to keep me engaged?"
With more students enrolling, all you can do is offer ways to let them receive the material outside the prescribed time. No one has a photographic memory and can remember literally everything - that's why I make Khan Academy-style videos of my lectures.
I'd love to mirror a martial art class, where I can rely on more experienced students to help others, as they may be able to offer another viewpoint I skipped over (since, I already understand the material, they just figured it out). However, in a college setting, it's a harder thing to do, given its hard to convince TAs attend the class again and act as an assistant.
Repetition is a very important tool for learning, but current Western education philosophy dislikes it. I could go on, but I'm starting to ramble on a tangent...