3 ms·
It's only >100% efficient because % efficiency is defined in a goofy way: benefit/cost, instead of benefit/(cost+benefit). (Moving 3n requires moving 4n and wa
by alisonkisk 5y ago
It's only >100% efficient because % efficiency is defined in a goofy way: benefit/cost, instead of benefit/(cost+benefit). (Moving 3n requires moving 4n and wasting n: 75% real efficiency).
This difference only matters for A/C, when cost is not much larger than benefit.
- mjmahone17 5y agoThis doesn’t make sense to me. You’re saying a water heater that uses N joules to heat water by 0.5N joules is 33% efficient? That would be difficult for most people to translate: I use 100 wh to get 50 wh of heat, which should imply 50% efficiency. As the cost to gain the end state I want is what I care about.
- quickthrowman 5y agoThe poster you are responding to was referring to heat pumps, not a resistive electric water heater like you assumed.
- johncolanduoni 5y agoBut only n has to be low-entropy energy, while the 3n is ambient heat that you’re trying to get rid of. There’s no scarcity of ambient heat when you’re just trying to move it anywhere else but inside.