Sure thing. Heating (space + water) represents nearly 80% of EU household energy use[1], compared to 60% in the US[2]. I have no clue what you mean by "heating is efficient compared to AC". In fact, opposite is true -- unless you use some kind of heat pump, which are very uncommon in Europe, you only get exactly one unit of heating per unit of energy consumed. On the other hand, with AC (which _is_ a heat pump), you get something on the order of 5 units of heat (energy) removed per unit of energy consumed.

[1] - https://ec.europa.eu/eurostat/statistics-explained/index.php... [2] - https://www.eia.gov/energyexplained/index.php?page=us_energy...

This way of thinking about efficiency doesn't take into account gains from insulation and/or reducing unnecessary heating. An electric blanket is more efficient than heating a room, which in turn is more efficient than heating a house.

Here is a study from 2013 in Environmental Research Letters. Comparing Minneapolis and Miami, the coldest and the warmest metropolitan areas in the US. Minneapolis uses (per capita) 3.5 times more energy for heating and AC (mainly heating) than Miami (mainly AC).

"This finding suggests that, in the US, living in cold climates is more energy demanding than living in hot climates."

http://iopscience.iop.org/article/10.1088/1748-9326/8/1/0140...

Part of the difference is that, heating is usually directly burning oil or gas, so the efficiency is 1:1, whereas cooling can have efficiency 4:1 because heat pumps just move heat. But you need electricity to run a heat pump, and generating the electricity is at about 0.5:1 efficiency. So if all Minneapolis switched to heating with heat pumps, they could bring the difference down from 3.5 to 1.8. But still living in Miami is more energy efficient.

Miami can only be considered "hottest" because it never gets cold and you consider the average. It actually spends a long time near room temperature. Somewhere like Las Vegas or Phoenix gets both hotter and colder.

If we arbitrarily pick 70F as room temperature, Miami has a typical annual high/low spread of approximately 60F-90F or -10 to +20 degrees relative to room temperature. Meanwhile, Minneapolis has a typical annual spread of approximately 10F-85F or -80 to +15 degrees relative to room temperature.

You should look at section 2.2 in the article. Miami has more cooling degree days (2423) per year than Phoenix (2327) or Las Vegas (1786).

My main intention when I started responding was to point out the much larger winter heating differential in the north, in response to the discussion about heating versus cooling costs and efficiency. I am not sure why I got distracted about Miami versus Phoenix and inserted that before posting.

My experience living for a few years in a tropical country was that locals acclimate and do not cool nor dehumidify their living spaces nearly as much as many Americans seem to do. Much like in Florida, you will see people running around in jackets or even knit hats on slightly cooler days when someone from a colder climate would already think it is warm and time for shorts.

I think it is difficult to compare different regions with different climates and cultures. It seems impossible to me to choose a metric that isn't inherently biasing the analysis towards one arbitrary normative standard. Compare similar regions or one region year-to-year to evaluate the efficiency of local practices.

Edit: another issue is the daily cycle. You can use thermal mass to smooth out daily temperature extremes but that doesn't work when you spend weeks or months with temperature differentials that remain offset from comfortable.

Heat transfer, though, is based on temperature differentials - if Miami is +7degrees every day of the year, and Phoenix is +20degrees only 117 days per year, the energy demands of Phoenix for cooling could very easily be much higher (energy lost through walls, roof would be much higher, as would mass transfer of energy when doors open.) This is irrespective of local construction. Add to this, radiative gain (insolation through windows) is not captured in the degree-days statistic, nor is humidity related cooling (condensing water takes a lot of energy!)

No. No no.

Heat conduction rate is linear in response to the temperature difference [1], so 1 day of 20 degrees difference should give the same total heat loss as 2 days of 10 degrees difference. They also both give 20 degree days, so degree days is the correct measure and should correlate linearly with the energy needed for heating or cooling. The same goes for the heat content in the air that is exchanged due to draft, opening doors etc.

You might have a little bit of a point with sunlight, and humidity. But my guess is that they don't dominate, compared to the conductive and convective heat exchanges.

[1] https://en.wikipedia.org/wiki/Thermal_conduction#Fourier's_l...

Right, thank you for the correction. I was mistaken about the conduction. I'm not sure why I was thinking it was something other than linear. So degree days should account fairly closely for the conductive heat transfer through walls.

I think my comment about mass transfer when opening doors could maaaybe be defensible but I'll leave it alone :)

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.

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.

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...

> 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?

> 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%.

It may have to do with where the heat comes from? I live in southern most areas of US, but from what I understand it's common for heating to use Gas/etc. instead of electricity.

Therefore they use less "energy" (i.e. Electrical energy)

All just a theory

The most efficient way to heat would still be generating electricity from gas. You lose 50% of the energy (well, you can still use part of the residual heat for heating, too), but with the electricity, you can run a heat pump that heats with about 400% efficiency. 50% × 400% is still 200%, so twice as good as burning gas for heat.