The calorific value refers to the energy within the fuel that gets released as heat upon its combustion.

热值是指燃料燃烧时以热量形式释放的能量。

It offers a better calorific value than coal and is easier to transport than gas.

蒸馏油比煤炭具有更高的热值， 并且比天然气更易于运输。

And of course, leaves have little calorific value, so sloths have evolved to spend as little energy as possible.

当然， 树叶的热值很小，所以树懒已经进化到尽可能少地消耗能量。