Personally, training hard in the heat equals a zen experience I can't really explain but I love it. When most cyclists would be indoors I'd be out on the baking asphalt using that time to understand how the heat would affect me and how I would deal with it. I've always acclimated well to those conditions but I always allowed myself to do it gradually.
The process starts in the first few days you’re exposed to higher temperatures, so long as you're training in hotter conditions for at least an hour a day over the duration of 3 to 5 days strait. Be sure your workout intensity and duration is gradually increased over those 3 or 5 days, gradual is the key here. Increased sodium intake may be necessary during the first 3 to 5 days since initially you'll experience more sodium loss. After 7 to 14 days positive adaptations should have your sweat rate up, sodium loss down, blood plasma or volume level up and your perceived exertion level should feel easier. As your sweat rate goes up after 7 to14 days of being exposed to the heat, higher fluid intake is needed after you acclimate. Don’t' forget, pre - hydrating is a must due to the increased sweat rates you'll experience if your training for over a few hours. Even though sweat rates are up sodium absorption into the cells becomes higher.
Calories in the heat
As your body works harder due to the heat you burn more calories and calorie absorption is lessened so forcing yourself to eat enough becomes essential. From my own experience my appetite decreases in the heat while my fluid intake increases. Sweet tasting calories are less appealing in very hot conditions than in milder temperatures. In high temps combined with a high heart rate sweet stuff is just tough getting down. This seems to be a general theme with most endurance athletes. Many athletes will alter the foods they consume in very hot conditions so if you’re going to change your foods in hotter weather you need to experiment prior to any racing.