[selcuka]

Actually reverse cycle air conditioners are said to have a heating efficiency of over 100%, but what they really do is to move the heat from one point to another. It's all about definitions; if you define the system as your room, it will be more than 100% efficient. If your system is the universe, then it's always 100%.

By the same logic, yes, your hypothetical statement can be rephrased as "if you already have boiling water, cooking pasta doesn't require any energy".

[hn_throwaway_99]

But the whole point is that Barilla's definition is ludicrous. The only definition that really makes sense is how much energy did it take to get the pasta from the box to my plate, and Barilla is excluding the vast majority of that energy in their 80% number for the sole purpose of inflating it to make it look better.

[selcuka]

Barilla's definition is ludicrous, and I'm playing the Devil's advocate.

> The only definition that really makes sense is how much energy did it take to get the pasta from the box to my plate

Including the energy required (and the carbon footprint) to manufacture the pasta in the first place, yes? Or no?

[harg]

no, because we're only comparing the energy required to cook the pasta; not the whole lifecycle.

[simondotau]

If your definition of efficiency encompasses change within the entire universe, you could say that everything has an efficiency of 0% because matter and energy cannot be created or destroyed.

Back in reality, the purpose of a heat pump is to heat/cool an enclosed space. Its efficiency is rated by comparing it to a direct conversion from electricity to heat. So long as what occurs outside doesn't affect what occurs inside, it isn't relevant to the question of efficiency.