4 ms·

I'm not sure. Many of the countries with the largest emissions per capita are in regions where houses are heated in the winter and cooled in the summer. Given

I'm not sure. Many of the countries with the largest emissions per capita are in regions where houses are heated in the winter and cooled in the summer. Given that indoor temperature is ~ 20C, the ∆T for heating can be much greater than for cooling, since cold outdoor temp can easily go as low as -20C, while really hot weather won't go much above 40C. Thus, in a warmer climate where you need less heating in winter and more cooling in summer, you might actually end up using less total power for AC.

throwanem 10y ago
That assumes power consumption is constant for a given ∆T regardless of the method used to produce it, which seems optimistic.
- sevenless 10y ago
  Yeah. I don't think thermodynamics works like that.
  - VLM 10y ago
    Shockingly that is pretty much how heat pumps work to a first degree (oh the pun), they don't much care which side is the evaporator and which side is the condenser. There are minor details in size of fan and design of coil vs tolerable noise level vs quality of insulation on connecting pipes. Also the pressure vs temp graphs are a little non-linear which does show up at the extremes (and the extremes are a small fraction of total operational time) In the west most cooling is done with a heat pump permanently wired into refrigeration mode aka a conventional air conditioner. There's a widely held belief that the entire system coefficient of performance is exactly 1 with somewhat less popular urban legends claiming a small fraction of 1 or only analyzing 100% efficient theoretical gas table cycles of 30 or whatever. However real world deployed average systems including air handler (aka fan) power and a realistic depreciation or embedded energy of manufacture etc results in about 3. So in the real world the total cost to the environment is about a kilowatt/hr to move about 3 kilowatt/hr of heat out of a building. It scales better than linear with size, something to do with moving air being expensive and larger AC being connected to larger buildings having a better surface area to volume ratio. Anyway for better or worse a kilowatt into an electric heater costs 3 KW of burned coal or uranium down at the plant and generates about 1 KW of heating in a typical building, whereas a kilowatt into an AC or heat pump costs 3 KW of burned coal or uranium down at the plant and moves about 3 KW of heat out of the building. In practice it takes less energy to cool than to heat although in theory a heat pump has difficulty telling the difference between 90F outdoor and 50F outdoor temps.
madaxe_again 10y ago
Heating is far more efficient than cooling, however, given that the former is a direct process, and the latter uses heat pumps.
- semi-extrinsic 10y ago
  That seems very backwards. Heat pumps for heating can have a COP of as much as 4.5 at an external temperature of 7C, i.e. deliver 4500 W of heating using only 1000 W of electricity. An electric heater has a COP of 1.
manarth 10y ago
Global warming also increases the number of extreme weather events, so we can't necessarily extrapolate winter => winter + 1ºC, so therefore we need less heating.
ZenoArrow 10y ago
I'm not sure there's a 'need' for AC in homes, at least not for new builds. Would recommend taking a look at the work of the Passivhaus Institute: http://www.passivhaus.org.uk/ http://www.passivhaus.org.uk/ https://en.wikipedia.org/wiki/Passive_house https://en.wikipedia.org/wiki/Passive_house
- neuromancer2701 10y ago
  Compressed earth brick is pretty amazing. The whole house become a water vapor trap and the house cools itself as the heat of the day increases. Granted then you need to cool the house at night to refresh the thermal mass. https://www.youtube.com/watch?v=IuQB3x4ZNeA https://www.youtube.com/watch?v=IuQB3x4ZNeA

throwanem 10y ago

That assumes power consumption is constant for a given ∆T regardless of the method used to produce it, which seems optimistic.

sevenless 10y ago
Yeah. I don't think thermodynamics works like that.
- VLM 10y ago
  Shockingly that is pretty much how heat pumps work to a first degree (oh the pun), they don't much care which side is the evaporator and which side is the condenser. There are minor details in size of fan and design of coil vs tolerable noise level vs quality of insulation on connecting pipes. Also the pressure vs temp graphs are a little non-linear which does show up at the extremes (and the extremes are a small fraction of total operational time) In the west most cooling is done with a heat pump permanently wired into refrigeration mode aka a conventional air conditioner. There's a widely held belief that the entire system coefficient of performance is exactly 1 with somewhat less popular urban legends claiming a small fraction of 1 or only analyzing 100% efficient theoretical gas table cycles of 30 or whatever. However real world deployed average systems including air handler (aka fan) power and a realistic depreciation or embedded energy of manufacture etc results in about 3. So in the real world the total cost to the environment is about a kilowatt/hr to move about 3 kilowatt/hr of heat out of a building. It scales better than linear with size, something to do with moving air being expensive and larger AC being connected to larger buildings having a better surface area to volume ratio. Anyway for better or worse a kilowatt into an electric heater costs 3 KW of burned coal or uranium down at the plant and generates about 1 KW of heating in a typical building, whereas a kilowatt into an AC or heat pump costs 3 KW of burned coal or uranium down at the plant and moves about 3 KW of heat out of the building. In practice it takes less energy to cool than to heat although in theory a heat pump has difficulty telling the difference between 90F outdoor and 50F outdoor temps.

madaxe_again 10y ago

Heating is far more efficient than cooling, however, given that the former is a direct process, and the latter uses heat pumps.

semi-extrinsic 10y ago
That seems very backwards. Heat pumps for heating can have a COP of as much as 4.5 at an external temperature of 7C, i.e. deliver 4500 W of heating using only 1000 W of electricity. An electric heater has a COP of 1.

manarth 10y ago

Global warming also increases the number of extreme weather events, so we can't necessarily extrapolate winter => winter + 1ºC, so therefore we need less heating.

ZenoArrow 10y ago

I'm not sure there's a 'need' for AC in homes, at least not for new builds. Would recommend taking a look at the work of the Passivhaus Institute: http://www.passivhaus.org.uk/ http://www.passivhaus.org.uk/ https://en.wikipedia.org/wiki/Passive_house https://en.wikipedia.org/wiki/Passive_house

neuromancer2701 10y ago
Compressed earth brick is pretty amazing. The whole house become a water vapor trap and the house cools itself as the heat of the day increases. Granted then you need to cool the house at night to refresh the thermal mass. https://www.youtube.com/watch?v=IuQB3x4ZNeA https://www.youtube.com/watch?v=IuQB3x4ZNeA