The temperatures in winter wouldn't matter to me. The temperatures in summer are crucial! Training in an uncooled room at 30°C is hell. Even for the circulatory system...
But a simple air conditioner should be enough for a garden house, running during sports, right? In the Maldives or similar places, they don't cool any differently and the construction of the huts is probably not much different.
I find "irresponsible" a bit exaggerated. It could be electricity from the own photovoltaic system. And for about 1 hour a day, the power consumption won't be that high. It is not supposed to run 24 hours continuously.