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They still produce heat, quite a lot of it, both accelerating and braking. Also, don't underestimate the heat produced by people - even in the dead of winter large concert halls will be running air conditioning, not heating.

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A common rule-of-thumb is "100W per person" I think that's probably slightly high, but it's in the right ballpark. If you're standing in a crowd, you should expect that it'll be as hot as if every person was replaced with a 100W lightbulb.

If you assume a 2000 (kilo)calorie per day diet, you get:

2000 Kcal/day * (4.18 Joules/calorie) * (1 day/86400 seconds) = 96.75 Watts

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