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Comment by OJFord | Hacker News Reader

Just because you pay a positive non-zero amount for less than a quarter of the energy in, it does not mean that a device has greater than 100% efficiency, which is not possible.

If heat pumps are 400% efficient then log burners in cabins in the woods are even better.

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A heat pump warms a home more efficiently than using the same amount of electricity for resistive heating. It can do this because it's not generating the heat from scratch; it's moving heat from outside to inside.

https://en.wikipedia.org/wiki/Heat_pump#Performance

I know. It's only >100% 'efficient' if you ignore the input of 'outside heat'. That is not a normal calculation, and not really called 'efficiency'.

It's desirable for multiple reasons, of course, but it's not efficiency.

Unfortunately by that metric other electrical heaters tend to 0% efficiency because they are not making use of the virtually unlimited energy outside the buildings.

The 400% metric let's you compare with other heaters, the 100% is kind of useless.

They're not using them as an input, so.. obviously they're not included in the input/output calculation?

A local company has developed a heat pump with a thermal energy storage system. Not sure how they do this, but I imagine there is some sort of insulated cinder blocks on a secondary loop that shuttles heat/cold to where it needs to go.

(1) https://stash.energy/en/product/

They try very hard not to be specific, but the industrial heat accumulators are usually just water.

> … heat accumulator

Thank you for helping me learn a new HVAC term!

All energy from log burners comes from the fuel, and some ashes remain unburnt. They're under 100% efficient at converting fuel to heat. You put in x fuel and <x heat.

A heat pump takes heat from outside the system. You put in x fuel and you get >x heat. Getting more energy than you put in makes the efficiency over 100%.

I know. You can't just ignore the bulk of the input and still call it 'efficiency' though.

Even manufacturers call this 'coefficient of performance', not efficiency.

Since precise use of language is so important to you:

> "You can't [...]"

He did, so obviously he can. You mean shouldn't, not can't.

An implied qualification of "you can't [while remaining logically consistent]" is common usage.

Sure, a slightly irritating turn of phrase, not accurate. I didn't think it would be so controversial to hold terms of art/words with actual scientific meaning to a higher standard though.

If we're willing to be so blasé with 'efficiency' then why not, say, 'functional programming'? If it works it's functional right?

> They're under 100% efficient at converting fuel to heat

I think only matter-antimatter reaction comes close to 100%. Burning fuels isn't even 1% of that.

Impossible in a closed system. Extremely common elsewhere.

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