Hacker News Reader

Comment by satya71 | Hacker News Reader

I don't have the numbers. But intuitively, AC should be less energy as it's energy transfer. Heating is usually directly adding energy to the living environment. You can get heating using heat pumps (some southern US homes have this type) but it doesn't work very well when it's too cold outside. Europe should have more heating than US, with it's more northern location.

View on HN

Indeed. Heat pumps routinely have efficiencies[0] around 400%-500%, because they're not really "producing cold", they just move energy from one inside to outside (or the other way around).

[0] - of course that's a specific meaning of "efficiency"; they're still less than 100% efficient in terms of energy expended on moving other energy around vs. theoretical minimum.

Electric heaters are more efficient than traditional air conditioning units. Transferring heat from inside a 80F house to the 110F air outside is not very efficient, only about 30-60%. On the hand, an incandescent light bulb is a ~99% efficient heater. The only energy that is "lost" is the light which is radiated out the window. Space heaters and electric radiators are 100% efficient.

Additionally, heat pumps are can be spectacularly efficient when it's warm outside (in which case, who needs a heater) but are still more than 100% efficient when it's cold outside. Waste heat is still heat, after all. The problem with heat pumps is that the quantity of thermal they can put into a house drops dramatically when it's cold outside. When it's extremely cold outside, the only heat you're added to the place you're trying to heat is the waste heat from the unit itself.

Swamp coolers can be very efficient "air conditioners" but they only work in extremely dry environments. Heat exchangers that pull cold water from a nearby cold lake (for instance, there are data centers in Chicago that use the lakewater from Lake Michigan) can be highly efficient, but there's a lot of infrastructure involved, and they only work on warm land near cold water.

> Transferring heat from inside a 80F house to the 110F air outside is not very efficient, only about 30-60%.

This is wrong. Modern heat pumps can easily have efficiency over 400%.

> Transferring heat from inside a 80F house to the 110F air outside is not very efficient, only about 30-60%.

Where did you get this number from?

The coefficient of performance (efficiency) of an AC at that temperature range would still be well over 1. Probably around 3-4 depending on the unit and refrigerant. [0] ACs are very efficient for the same reason heat pumps are efficient. They are just moving energy around.

[0] https://www.researchgate.net/publication/242172797_A_Compari...

Reply on news.ycombinator.com