Usually we're standing still in the hall so there is probably less breeze as we do the standing meditation around the hottest time of the day. But standing still requires a lot of effort and it does also build a lot of energy. Keeping the body still is sometimes very difficult, whereas in the walking meditation you can move the body and avoid some of the unpleasant physical sensations.
When we're trying to stand still it is often difficult to observe some of the tendencies that arise such as wishing to move and escape from the restlessness in the mind. It may require more energy but it also, as I said before, does build energy by increasing body awareness. Some people may think that it uses up energy, but that is not the case if we're able to actually get that body awareness going. That is why it is so useful when we're sleepy because the extra awareness needed to stop falling down is energy building.