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by gpm 2105 days ago
No, it's way worse than that.

At the location of the hvac it puts 130% of the source heat into the environment.

But 30% of that heat put into the environment came from electricity generated in a power plant. Power plants are typically less than 50% efficient, so it put's out as much heat into the environment at the source of the electricity. Bumping the value to 160% (130% + 30%).

However waste heat is a small fraction of the heating that electricity generation produces. Very roughly 10 times as much heat is trapped via the CO2 released than heat is released by the power plant. Bumping that value up to 460% (160% + 30% * 10).

I.e. 4.6 units of heat are put into the environment for every unit of heat removed from a closed system.

(Obviously the details of this depend dramatically on the environment. Heat pump efficiency depends on the degree of temperature gradient, CO2 release and power plant efficiency depends dramatically on where the power is coming from, which changes with where you are located.)
2 comments
mlyle 2105 days ago
Fair points. IMO, the 460% metric is a bit of a wacky number, though, because of not counting the carbon and efficiency involved in the original 100%. Assuming the 100% comes from the same power source, it's still only 25-30% "worse".

Also I think you're a bit pessimistic about modern power plant efficiency-- combined cycle plants do better than 50%, and that's before we're considering any benefit from renewables.

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gpm 2105 days ago
> Assuming the 100% comes from the same power source, it's still only 25-30% "worse".

Fair point, I guess my argument makes more sense if we were discussing moving naturally occurring heat out (i.e. household ac) than with respect to cooling a datacenter.

Nitpicking the numbers used in the estimate... is probably not worth it. Every bit of it is a very rough order of magnitude number. If you're somewhere with 95% renewable energy it should be an order of magnitude better, if you're somewhere where energy production is dominated by an inefficient coal plant it should be an order of magnitude worse.

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pavanky 2105 days ago
Isnt this assuming coal / gas powerplants ?

Wouldnt solar / Wind have a smaller CO2 foot print and hydro electric be more efficient ?

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