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Comment by teuobk | Hacker News Reader

This article ignores the fact that it takes less energy to cool a home in a hot climate than it does to heat a home in a cold climate. Since people have been able to more easily move to hot climates thanks to air conditioning, the net effect has been a reduction in energy use.

A somewhat more balanced article is this one from the Economist:

http://www.economist.com/news/international/21569017-artific...

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I too doubted the assertion that it's easier to cool in a warm climate than it is to heat in a cool climate. So I compared Stockholm, Sweden to Phoenix, Arizona USA. Sweden averages about 4,000 heating degree days, while Phoenix averages slightly more cooling degree days (4,600). Therefore, takes about 15% more heating/cooling power to live in Phoenix than in Stockholm.

Of course, a gas furnace is quite efficient at turning hydrocarbons into heat and CO2. Some furnaces turn 96% [1] of their input gas into heated air, but average is probably closer to 80%. This number could be tempered somewhat by gas transmission loss, in some cities as high as 10% [2]. So, overall, gas furnace heating is maybe 72% efficient.

On the other hand, using the same gas, a combined-cycle gas turbine generate is at most 62% efficent [3]. Then there are electricity transmission losses (pretty minor at 6.5%) [4]. However, an A/C unit uses the electricity as a heat pump, which can actually move MORE heat energy than is used to operate the pump. Impressive! A reasonably-efficient A/C unit has a SEER rating above 10, which gives it a Coefficient of Performance (ratio of heat energy pumped to heat energy used) of around 3. [5]

This means that it's at least twice as energy-efficient to cool your house in Phoenix as it is to heat your house in Stockholm, if you insulate your house equivalently. I suspect many in Phoenix (or LA, or other hot climates) don't insulate thoroughly, though.

[1] https://www.angieslist.com/articles/what-do-furnace-efficien...

[2] http://www.sourcewatch.org/index.php/Natural_gas_transmissio...

[3] https://en.wikipedia.org/wiki/Combined_cycle#Efficiency_of_C...

[4] https://en.wikipedia.org/wiki/Electric_power_transmission#Lo...

[5] http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatpump.h...

I guess one difference between heating and cooling is that heating can be very, very efficient by just burning whatever. With cooling you're burning whatever, and then turning that into electricity at about 60% efficiency (at best) then losing some efficiency through transmission and then some more turning that electricity back into mechanical energy.

I'm not saying it's a wash by any stretch of the imagination.

I was surprised at how efficient a heat pump can be! Research SEER. A new A/C unit has a greater-than-300% efficiency.

Heat pumps can be used for heating, too, but they're expensive and commonly involve drilling wells for geothermal loops.

Air source heat pumps are about as costly to operate as natural gas in mild climates (where it's generally above freezing most of the time). If you do dig up your yard and lay underground pipe, that heat pump system will cost a fraction of natural gas to operate, even in Minnesota. And that's with natural gas prices at historic lows. Heat pumps are amazing.

Not to mention that AC is so easily powered by solar. Offsetting heat with solar requires batteries, an electric grid hookup, or some other energy storage system.

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