9 ms·

All electricity used in a city ends up as waste heat - AC is no different. If AC is using (as claimed in the article) 10% of a city's electricity, then it is re

by emtel 3y ago

All electricity used in a city ends up as waste heat - AC is no different. If AC is using (as claimed in the article) 10% of a city's electricity, then it is responsible for 10% of the waste heat in that city. There could be a short term spike as the AC rejects interior heat from buildings to the outside, but that will be balanced out later as outside heat is absorbed by the cooler buildings, or as cool air leaks to the outside.

pjerem 3y ago
The issue IS the short term span. Nobody is complaining about ACs making cities hotter in winter. The issues comes from the fact that AC rejects heat from buildings when it’s already hot outside. It renders the city unbreathable in summer.
- emtel 3y ago
  Time of year is not the issue. As soon as the system is in equilibrium, the contribution of AC is just the waste heat of the energy consumed. This is just thermodynamics / conservation of energy
- _3u10 3y ago
  So summer is caused by AC rather than AC being turned on in summer?
adammarples 3y ago
This sounds wrong, lots of electricity does useful work that doesn't turn into heat (moving an electric vehicle, making plastic items) or escapes as other waste (light, sound, etc)
- BytesAndGears 3y ago
  Those are actually all converted to heat eventually, just with more steps. Moving an electric vehicle causes motion, but that motion is absorbed by the air and ground via friction with both, aka heat. Light is just energy in a photon — when it hits a surface that absorbs it, it becomes heat. And it can be quite a lot actually! If you put your hand in front of a really bright flashlight, you’ll notice a warm feeling. If you turn off the flashlight, it goes away immediately, proving that is the light itself causing the heat. Approximately all of the energy we use as electricity is just changing something into heat with some useful work in between
- hinkley 3y ago
  Moving an electric vehicle turns into heat. Because routes are cyclical all of the potential energy turns into heat in the end. You buy a book case and haul it to the top of a hill, eventually that book case is going to the dump, which will be downhill. Manufacturing products via endothermic processes does not turn all of the energy into heat, but then again exothermic processes can exceed the energy used.
- SirMaster 3y ago
  Sound and light are heat. Heat is movement of atmos. When the sound or light physically hit a surface, they cause the surface to heat up a bit. It's all heat in the end.
- dgacmu 3y ago
  In the case of the car: when you accelerate, it turns most of that electric energy into kinetic energy (and turns some of it into heat). As you cruise along at a constant velocity, it's turning most of that electricity into heat: It's overcoming air and road friction, aka, rubbing against things and producing heat. Etc. Waste light and sound get absorbed by surfaces, thus, turned into heat (unless the waste light is in the right IR band to pass out through the atmosphere).
  - rcme 3y ago
    What about flipping bits in a processor? Current processors do produce waste heat, but I don't think all of the energy in a processor gets converted to heat and it's not a requirement for computation that heat be generated, e.g. if we had superconducting processors.
    - wardedVibe 3y ago
      Actually, it is a physical requirement that erasing information generates waste heat. https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle We're still pretty far from that limit, but unless your plan is to never erase bits, you're going to waste energy.
      - rcme 3y ago
        > On the other hand, recent advances in non-equilibrium statistical physics have established that there is no a priori relationship between logical and thermodynamic reversibility.[19] It is possible that a physical process is logically reversible but thermodynamically irreversible. It is also possible that a physical process is logically irreversible but thermodynamically reversible. At best, the benefits of implementing a computation with a logically reversible system are nuanced.[20]
    - dgacmu 3y ago
      It's not necessarily a requirement (see reversible computing), but we're very far from knowing how to do it if indeed it's possible at all. current processors do convert all of the energy they use into heat. To set a transistor one way, you put a bunch of charge onto its gate. To set it the other way, you take those electrons and dump them to ground. All of that current flowing is converted to heat.
- _3u10 3y ago
  Think of heat as like nature's income tax, every energy transaction you do is subject to a heat tax. Eventually almost all energy is converted into heat. Even the sun converts every chemical into its lowest energy state and releases all that energy in the atoms as heat. The primary thing the universe currently does is turn matter into heat, and tries to distribute that heat evenly. Eventually most of the energy for earth either becomes heat in the earth, gets radiated into space, or slows the earths rotation around the sun, or spin. Of all of these things the dominant two are heat radiating into space (this is by far the largest), and heating the earth, with a few things like the tides slowing the rotation of the earth. A little bit of it gets stored as chemical energy through plants and animals, but eventually those get burned either through fire, or chemical decomposition. To give you an idea of how much heat escapes, if the sun stopped, and we used our nuclear arsenal to replace it, we'd have about 30 minutes of sunlight. The idea that AC causes heat in cities to any real extent is laughable, if AC was capable of changing the temperature of the earth to any meaningful degree we'd just water cool the heat exchanger and solve global warming by dumping the heat into the ocean.
hinkley 3y ago
Heat pumps don't work that way. If it's using 10% of the electricity it could be 25-35% of the waste heat in the city.
- contravariant 3y ago
  Heat that is moved from a dwelling onto the street shouldn't really count as 'waste' heat.
  - hinkley 3y ago
    If you're talking about the heat island effect? The hotter it is outside compared to the desired inside temperature, the less efficient heat pumps get. Also the hotter you make it outside the harder it is for your neighbors to eschew AC in the first place. In a part of town where some critical mass of people have AC, the remainder will be forced to flip. And when that happens, there goes your 10% of all power is used for air conditioning.

by emtel 3y ago

pjerem 3y ago

The issue IS the short term span. Nobody is complaining about ACs making cities hotter in winter. The issues comes from the fact that AC rejects heat from buildings when it’s already hot outside. It renders the city unbreathable in summer.

emtel 3y ago
Time of year is not the issue. As soon as the system is in equilibrium, the contribution of AC is just the waste heat of the energy consumed. This is just thermodynamics / conservation of energy
_3u10 3y ago
So summer is caused by AC rather than AC being turned on in summer?

adammarples 3y ago

This sounds wrong, lots of electricity does useful work that doesn't turn into heat (moving an electric vehicle, making plastic items) or escapes as other waste (light, sound, etc)

BytesAndGears 3y ago
Those are actually all converted to heat eventually, just with more steps. Moving an electric vehicle causes motion, but that motion is absorbed by the air and ground via friction with both, aka heat. Light is just energy in a photon — when it hits a surface that absorbs it, it becomes heat. And it can be quite a lot actually! If you put your hand in front of a really bright flashlight, you’ll notice a warm feeling. If you turn off the flashlight, it goes away immediately, proving that is the light itself causing the heat. Approximately all of the energy we use as electricity is just changing something into heat with some useful work in between
hinkley 3y ago
Moving an electric vehicle turns into heat. Because routes are cyclical all of the potential energy turns into heat in the end. You buy a book case and haul it to the top of a hill, eventually that book case is going to the dump, which will be downhill. Manufacturing products via endothermic processes does not turn all of the energy into heat, but then again exothermic processes can exceed the energy used.
SirMaster 3y ago
Sound and light are heat. Heat is movement of atmos. When the sound or light physically hit a surface, they cause the surface to heat up a bit. It's all heat in the end.
dgacmu 3y ago
In the case of the car: when you accelerate, it turns most of that electric energy into kinetic energy (and turns some of it into heat). As you cruise along at a constant velocity, it's turning most of that electricity into heat: It's overcoming air and road friction, aka, rubbing against things and producing heat. Etc. Waste light and sound get absorbed by surfaces, thus, turned into heat (unless the waste light is in the right IR band to pass out through the atmosphere).
- rcme 3y ago
  What about flipping bits in a processor? Current processors do produce waste heat, but I don't think all of the energy in a processor gets converted to heat and it's not a requirement for computation that heat be generated, e.g. if we had superconducting processors.
  - wardedVibe 3y ago
    Actually, it is a physical requirement that erasing information generates waste heat. https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle We're still pretty far from that limit, but unless your plan is to never erase bits, you're going to waste energy.
    - rcme 3y ago
      > On the other hand, recent advances in non-equilibrium statistical physics have established that there is no a priori relationship between logical and thermodynamic reversibility.[19] It is possible that a physical process is logically reversible but thermodynamically irreversible. It is also possible that a physical process is logically irreversible but thermodynamically reversible. At best, the benefits of implementing a computation with a logically reversible system are nuanced.[20]
  - dgacmu 3y ago
    It's not necessarily a requirement (see reversible computing), but we're very far from knowing how to do it if indeed it's possible at all. current processors do convert all of the energy they use into heat. To set a transistor one way, you put a bunch of charge onto its gate. To set it the other way, you take those electrons and dump them to ground. All of that current flowing is converted to heat.
_3u10 3y ago
Think of heat as like nature's income tax, every energy transaction you do is subject to a heat tax. Eventually almost all energy is converted into heat. Even the sun converts every chemical into its lowest energy state and releases all that energy in the atoms as heat. The primary thing the universe currently does is turn matter into heat, and tries to distribute that heat evenly. Eventually most of the energy for earth either becomes heat in the earth, gets radiated into space, or slows the earths rotation around the sun, or spin. Of all of these things the dominant two are heat radiating into space (this is by far the largest), and heating the earth, with a few things like the tides slowing the rotation of the earth. A little bit of it gets stored as chemical energy through plants and animals, but eventually those get burned either through fire, or chemical decomposition. To give you an idea of how much heat escapes, if the sun stopped, and we used our nuclear arsenal to replace it, we'd have about 30 minutes of sunlight. The idea that AC causes heat in cities to any real extent is laughable, if AC was capable of changing the temperature of the earth to any meaningful degree we'd just water cool the heat exchanger and solve global warming by dumping the heat into the ocean.

hinkley 3y ago

Heat pumps don't work that way. If it's using 10% of the electricity it could be 25-35% of the waste heat in the city.

contravariant 3y ago
Heat that is moved from a dwelling onto the street shouldn't really count as 'waste' heat.
- hinkley 3y ago
  If you're talking about the heat island effect? The hotter it is outside compared to the desired inside temperature, the less efficient heat pumps get. Also the hotter you make it outside the harder it is for your neighbors to eschew AC in the first place. In a part of town where some critical mass of people have AC, the remainder will be forced to flip. And when that happens, there goes your 10% of all power is used for air conditioning.