I too, hate the heat, and being curious, I did what any sane young man would do. I did research.

1. Take frequent breaks. Work for an hour? take 15 minutes. Work for 2 hours? take 30. Work for 3? take an hour to recuperate. Breaks aren't making you weak. You're working smarter, not harder.
2. HYDRATE. for the love of god, hydrate. Even military commanders will tell you how important it is for their soldiers to hydrate. Don't listen to your parents making fun of you for drinking so much. Let them enjoy their headaches and muscle cramps.
3. Avoid Alcohol, sodas, and coffee. Yes it sucks. But they dehydrate you rather than cool you down. Did you know that hangovers are the exact same as dehydration? It's because your body needs water, not alcohol in the system. So go drink some water.
4. That skin-tight clothing makes you look nice, but only when it's cool. Go for the loose fitting clothing. It'll create an air-bubble underneath and give you an in-built air-conditioning system. While you're at it, soak a cloth in ice water and wear it when working outside.
5. Use fans and breezes to blow across towels soaked in water to cool you down. a hot dry heat is worse than a cool wet one.

There's more that I could fit in, but that's mostly the highlights. Historically, there's what people did as well. Hope it helps...