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Wait what? An AC does not simply turn hot air into cold air. It "moves energy" from one place to another. Indeed it would be nice to power the AC with solar po

by y42 3y ago

Wait what? An AC does not simply turn hot air into cold air. It "moves energy" from one place to another. Indeed it would be nice to power the AC with solar power, but how does this help the city to cool down? You would cool down the houses, but the heat from the houses would remain in the city, it would even get hotter.

robotresearcher 3y ago
The argument is that you aren’t moving additional energy into the city from power stations to run the AC, which ends up as heat. Instead you’re using energy that’s already radiated into the city from the sky. As others have pointed out, you might do better bouncing the incoming radiation back out of the city with white roofs. And still others say you can do a bit of both.
- reportingsjr 3y ago
  Exactly correct! Also, you could definitely do well to reduce your roof albedo by switching to white/reflective roofs. This point has been made endlessly over the last 30-40 years. No one actually does it. People are actually installing solar panels.
  - crazygringo 3y ago
    > No one actually does it. To the contrary -- at least in NYC it's extremely common. The vast majority of "tenement" apartment buildings have silver roofs, for this reason. Just fire up Google Maps in satellite view over Manhattan and see for yourself. White-looking roofs everywhere (but silver in reality). New construction with roof decks tends to use things like white-ish floor squares as well. They're obviously much cooler to walk on in the summer. (While, sadly, contrary to your assertion, virtually nobody is installing solar panels in NYC. Landlords don't seem very interested so far.)
    - wolverine876 3y ago
      Why silver and not white?
      - crazygringo 3y ago
        Good question. I can't easily find an answer, but this page at least seems to describes the type of silver roof common on old NYC buildings: https://flatroofdoc.com/silver-coating-protecting-a-rubber-roof/amp/ https://flatroofdoc.com/silver-coating-protecting-a-rubber-r... Elsewhere I find a claim that the aluminum paint used was a 20th century thing, but now white paint is preferred as being more reflective.
  - andsoitis 3y ago
    > No one actually does it. Los Angeles has building codes for cool roofs: https://www.ladbs.org/docs/default-source/publications/ordinances/cool-roof-fact-sheet-and-faq.pdf?sfvrsn=10 https://www.ladbs.org/docs/default-source/publications/ordin...

by y42 3y ago

robotresearcher 3y ago

The argument is that you aren’t moving additional energy into the city from power stations to run the AC, which ends up as heat. Instead you’re using energy that’s already radiated into the city from the sky. As others have pointed out, you might do better bouncing the incoming radiation back out of the city with white roofs. And still others say you can do a bit of both.

reportingsjr 3y ago
Exactly correct! Also, you could definitely do well to reduce your roof albedo by switching to white/reflective roofs. This point has been made endlessly over the last 30-40 years. No one actually does it. People are actually installing solar panels.
- crazygringo 3y ago
  > No one actually does it. To the contrary -- at least in NYC it's extremely common. The vast majority of "tenement" apartment buildings have silver roofs, for this reason. Just fire up Google Maps in satellite view over Manhattan and see for yourself. White-looking roofs everywhere (but silver in reality). New construction with roof decks tends to use things like white-ish floor squares as well. They're obviously much cooler to walk on in the summer. (While, sadly, contrary to your assertion, virtually nobody is installing solar panels in NYC. Landlords don't seem very interested so far.)
  - wolverine876 3y ago
    Why silver and not white?
    - crazygringo 3y ago
      Good question. I can't easily find an answer, but this page at least seems to describes the type of silver roof common on old NYC buildings: https://flatroofdoc.com/silver-coating-protecting-a-rubber-roof/amp/ https://flatroofdoc.com/silver-coating-protecting-a-rubber-r... Elsewhere I find a claim that the aluminum paint used was a 20th century thing, but now white paint is preferred as being more reflective.
- andsoitis 3y ago
  > No one actually does it. Los Angeles has building codes for cool roofs: https://www.ladbs.org/docs/default-source/publications/ordinances/cool-roof-fact-sheet-and-faq.pdf?sfvrsn=10 https://www.ladbs.org/docs/default-source/publications/ordin...