[HN Gopher] Is air conditioning making cities hotter?
___________________________________________________________________
Is air conditioning making cities hotter?
Author : elorant
Score : 94 points
Date : 2023-09-10 12:51 UTC (10 hours ago)
(HTM) web link (www.euronews.com)
(TXT) w3m dump (www.euronews.com)
| SavageBeast wrote:
| So lets look at how the refrigeration cycle works here and make
| some conjectures. If I understand correctly, this kind of system
| removes heat from one side and moves that heat out the other
| side. An AC unit with a structure as a barrier is a machine that
| removes heat from the confined structure and vents it to the
| outside. So, with enough AC units removing heat from sealed
| structures and outputting it into the atmosphere, seems plausible
| that getting enough of them together would behave like a kind of
| heater.
|
| Now, how did the air inside these structures get warmed up in the
| first place? Under normal conditions, is the air inside the
| structures WARMER than the ambient air? Does the structure itself
| somehow more efficiently harness the suns energy to warm the
| structure more than the ambient outside air?
|
| If the same energy source is heating the ambient air and the air
| inside the structures - and it is - its the sun here, don't we
| have a constant amount of energy warming the area? Some of that
| energy warms outside, some of it warms inside, but the amount is
| constant.
|
| So how could a device that removes heat from structures to vent
| it outside be responsible for a warming of the outside air?
| Unless the AC itself added some extra heat energy in the process
| OR the structures somehow more efficiently turned solar energy
| into heat, how could moving heat around cause a temperature
| increase?
|
| For example - on a warm day in a little European village,
| everyone lights a gigantic fire and adds non-solar heat to their
| homes. The devices that remove the heat would then be adding new
| energy to constant solar energy heating the town. Ambient
| temperatures would likely rise. But did the AC cause the
| temperature increase? Didn't the AC unit just move heat from
| structure to ambient? The AC added no heat in this case.
| labster wrote:
| Just look at inputs and outputs. Electrical energy goes in;
| heat, noise (heat), and moving air (heat) come out. Nearly 100%
| of the energy going into an air conditioner produces heat.
| anticrymactic wrote:
| > Now, how did the air inside these structures get warmed up in
| the first place? Under normal conditions, is the air inside the
| structures WARMER than the ambient air?
|
| Greenhouse effect + no wind.
|
| The infrared emitted by heated objects are reflected by the
| glass, heating the room even more
| coda_ wrote:
| As someone said in a another comment:
|
| "There is the heat being removed plus some heat from the
| compressor and fan."
| jiofj wrote:
| [flagged]
| arnaudsm wrote:
| Great example that systemic problems require systemic solutions.
|
| AC is an individual solution to global warming, and actually
| making things worse. And deincentivizes us from fixing the actual
| problem.
| megaman821 wrote:
| Well if AC is your cutoff line for the amount of energy use and
| carbon intensity making things worse, I have really bad news
| for everyone using heating.
| whynotmaybe wrote:
| Like this?
|
| https://www.theonion.com/addressing-climate-crisis-bush-call...
| reportingsjr wrote:
| This is one reason I heavily push for roof top solar, even if it
| is a bit more expensive than utility scale. In many areas air
| conditioning is pretty much a given at this point.
|
| A typical solar panel absorbs ~20% of the sun's energy blasted on
| to a city rooftop. If that's used to power air conditioning it's
| doubly effective. You're reducing the heat urban heat island
| effect from the sun's energy, and you're also not adding
| additional heat from external power sources in to the city.
|
| On a large scale this would really help make cities more livable.
| On a hot summer day here in northern Kentucky I noticed a massive
| difference (I've roughly measured it at a 5-7F difference) going
| from less developed areas to the more urban areas.
| chiefalchemist wrote:
| Trees also "capture" heat. Whether urban or suburban, we'd be
| wise to plant more anywhere we can.
| slt2021 wrote:
| just wanted to add illustration
| https://creativelyunited.org/wp-
| content/uploads/2019/02/temp...
| 7e wrote:
| What is the effect of this approach in winter? The opposite?
| Losing heat from the sun that would otherwise help heat the
| building?
| zdragnar wrote:
| Depends on how much snow you get.
| hinkley wrote:
| You've heard of blackbody radiation?
|
| Black is hotter in the day and colder at night. In the desert
| you want light colors, which do the opposite.
| slt2021 wrote:
| Trees are a much better solution to urban heating. Proven with
| millennia, eco friendly, and makes cities beautiful and
| desirable to live
|
| https://creativelyunited.org/wp-content/uploads/2019/02/temp...
| demandingturtle wrote:
| [dead]
| jjoonathan wrote:
| Trees are swamp coolers. Consuming freshwater for outdoor air
| conditioning isn't necessarily a bad idea, but you aren't
| cheating thermodynamics.
| ComputerGuru wrote:
| Native, grown trees need no watering, even in a (one- or
| two-off) drought.
| jjoonathan wrote:
| Sure, but less evapotranspiration = less cooling. You
| aren't cheating thermodynamics.
| kgermino wrote:
| Trees are so much more than swamp coolers.
|
| Leaves block the Sun relatively high off the ground,
| meaning people are in the shade during the hottest part of
| the day and feeling as much radiation off buildings and
| streets in the evening.
|
| Beyond cooling they're also good for water management. Most
| street trees don't need any watering (at least in the
| Midwest) they live off rainwater. When it rains, water
| pools on the leaves and evaporates from there, reducing the
| amount of run off and keeping the street dryer and less
| humid on days with light rain.
|
| In cooler months (and places where this is relevant) the
| leaves fall and you can still get the warming benefit of
| sunlight.
| andsoitis wrote:
| We can do both.
| distant_hat wrote:
| My neighbors cut down trees around their house so that the
| solar panels could have unobstructed Sun.
| hinkley wrote:
| This is why we can't have nice things.
| ProfessorLayton wrote:
| I have mixed feelings about this. My neighbor cut down
| their tree, and now my living room enjoys a lot more sun
| throughout the day, and my yard has a lot less trash to
| cleanup.
| hinkley wrote:
| There's an art to growing and tending trees that leave
| visibility and air at ground level.
| psunavy03 wrote:
| Grinds my gears when people just hack down something that
| took 20-100 years to grow without even thinking of
| consulting an arborist.
| m463 wrote:
| I think an interesting way of doing this would be to have
| tree-like solar panels. they would be somewhat wasteful in
| some ways, but would organically gather solar energy at a
| variety of times from a variety of directions. They could
| also provide a % of light through in all directions to give
| partial shade and coexist with trees.
| zdragnar wrote:
| I can't- the solar company I talked to said there's too
| much shade on my roof for too much of the day, there's no
| way to place the panels to make financial sense before the
| panels need to be replaced.
|
| It seemed a bit odd, because my roof is fully lit up, but
| only for a few hours a day- one half is covered most of the
| morning, and the other half most of the evening.
|
| Sadly, it's not even really nice trees, just gigantic
| cottonwoods that litter leaves and twigs and sticky leaf
| pods like crazy.
| hinkley wrote:
| Wait a couple years and check again. With micro inverters
| you can deal better with partial shade. They're probably
| right that it makes no financial sense now, but that
| changes over time.
|
| The problem with solar is that unlit panels behave like a
| diode and no current flows. Chain together a lit and
| unlit panel and you get nothing. Put the inverter ahead
| of the interconnects and that's not a problem.
| 10u152 wrote:
| Micro inverters don't solve everything. Installing panels
| where they'll be in full sun for an hour a day isn't a
| good use of resources.
| cassepipe wrote:
| Don't worry, a sizeable part of the tree population we
| are used to live by are going to die because of climate
| change. Problem (soon to be) solved.
| rowanG077 wrote:
| I disagree. No amount of trees will take my 30 degree indoor
| temp down to 22.
| lionkor wrote:
| Have you lived in a house covered entirely in tree shade?
| jeffchien wrote:
| With regards to temperature, there are more levers to pull,
| like the aspect ratio of the street (narrower = cooler).
| Architects in Taiwan and southern China have been studying
| arcaded streets (qilou/Qi Lou ), which seem to be as good as
| trees for shielding pedestrians [1], except in situations
| where the sun might shine through the sides or ends.
|
| Of course, trees are great for many other reasons like air
| quality, but for temperature fundamentally they're just big
| evaporative coolers. I wish cities in more water-stressed
| areas would consider arcades + rooftop solar.
|
| [2] https://www.mdpi.com/2071-1050/11/5/1355/htm
| guerrilla wrote:
| What % do trees and other plants absorb?
| reportingsjr wrote:
| Below 10%. The most efficient plants are food crops we've
| genetically modified. I believe corn absorbs around 10%.
|
| However, plants also reflect a lot of energy, unlike
| black/asphalt roofs that most people in the US install.
| guerrilla wrote:
| When you say efficient it makes me suspicious. Just because
| a plant doesn't absorb the energy for conversion doesn't
| mean it doesn't absorb it as heat. Remember, they're quite
| connected to the ground so they could be good heat
| dissipation (I have no idea, just speculating.)
| tonfa wrote:
| One thing trees/plant help with (instead of
| concrete/asphalt in cities) is with the added impact of
| evapotranspiration (besides providing shade).
| ars wrote:
| Plants also evaporate water from the extra light energy,
| which further cools things.
| Ekaros wrote:
| Wouldn't it be more effective to surface the roof tops with
| some reflective material?
| slt2021 wrote:
| Trees, trees are a much better solution. Very simple yet
| effective solution to urban heating problem
|
| https://creativelyunited.org/wp-
| content/uploads/2019/02/temp...
| Dylan16807 wrote:
| Yes but not on roofs. They're so heavy.
| sgu999 wrote:
| Aren't grass-like plants working reasonably well? It's
| quite common on new build where I am
| Dylan16807 wrote:
| "white" and "mirror" are equally good at bouncing light, and
| the exact effectiveness is based on the specific design.
| _vertigo wrote:
| Not if you want to use the sun's energy for power
| amelius wrote:
| Thermal radiation is just EM waves, which you can reflect.
|
| So just put the PV panels on top, and a reflective layer
| below.
| stephen_g wrote:
| You can do both - having solar panels over a reflective
| white roof (like the fancy newly discovered passive
| radiative cooling paints) helps increase PV output by
| cooling the panel.
|
| The solar panels will still absorb and radiate heat back so
| you won't get as much cooling as you would have just with
| passive radiative cooling paint, but it'd be better than
| just solar on a regular roof in both ways (solar output and
| thermally).
| gamerDude wrote:
| Yes! In fact there is a new paint that was developed with
| exactly this in mind.
| https://www.purdue.edu/newsroom/releases/2021/Q2/the-
| whitest...
|
| Reflects 98.1% of the suns rays.
| artursapek wrote:
| is that dangerous to aircraft?
| mitthrowaway2 wrote:
| Aircraft can safely fly over snow, which has albedo if
| 90%, so it's probably ok.
| hinkley wrote:
| If the roof scatters the light, probably not.
|
| However if an entire downtown or subdivision does it?
| Possibly.
| ars wrote:
| Only if the roof has a lens shape, otherwise it's the
| same light as what's coming from above which isn't
| harmful.
| dylan604 wrote:
| well, it's 98.1% of the same light, so technically, less
| harmful
| _Algernon_ wrote:
| Considering that solar panels are close to perfectly black,
| they will also close to perfectly absorb the remaining 80%. The
| 20% of solar electricity that is then used for AC, will be
| released as heat as well.
|
| You've just made a ~100% efficient heat capturing machine. The
| 98.1% reflecting paint will be much more efficient, with the
| added bonus of not being dependent on the grid.
| hinkley wrote:
| The solar panels are not quite in contact with the roof
| though, and that air gap does reduce absorption.
| contravariant wrote:
| For the heat island effect the distinction is immaterial.
| The city itself is still absorbing more heat, this heat
| must go somewhere.
|
| Your reasoning is a bit like assuming solar panels stop
| flooding because they prevent the roof from getting wet.
| hinkley wrote:
| My point was that a carbon black shingle would result in
| a much higher amount of work required to cool the inside
| of the house because you'd be baking yourself alive. The
| standoffs for solar prevent that. Which at 20% efficiency
| panels, back of the envelope says that could end up
| cancelling out the benefit of the panels entirely, for
| more than half the year.
| pfdietz wrote:
| Are PV cells really that black for photon energies below
| their bandgap?
|
| It would be nice if the cells were highly reflective at a
| range of wavelengths between the range they can actually use
| and the range where they radiate waste heat.
| MichaelZuo wrote:
| Yes they are very black in the visible spectrum. Like the
| parent said a highly reflecting white paint for rooftops
| would certainly be the smarter choice.
| aeternum wrote:
| You can do both, typical rooftop solar installations
| typically don't cover the majority of the roof. Make the
| rest reflective and/or make it a space for people.
| Rooftop area has some of the greatest views in any city.
| Kinda crazy that we don't use it as space for humans and
| greenery in most cases.
| esel2k wrote:
| Rooftops are great, we have a 100m2 rooftop terrace and
| kids love it. But I had no idea how hot it gets. To the
| point where I don't even step outside during those
| heatwaves. When the offical temperature was 36C we had in
| fullsun above 46C and the concrete panel was too hut to
| wall barefoot. So my take is that in dry/hot areas
| rooftops are just unliveable.
| pfdietz wrote:
| I want to point out that to optimize for temperature
| reduction, you want to minimize absorption while
| maximizing thermal radiation. This says you want the
| surface to be reflective at wavelengths below some
| cutoff, but perfectly emissive (that is, black) above
| that wavelength. (Actually it's a bit more complex,
| because the atmosphere emits IR in some bands.)
|
| Some work on surfaces of this kind have shown promising
| results, being able to fall below ambient temperature
| even in full sunlight.
|
| Do it yourself:
| https://www.youtube.com/watch?v=KDRnEm-B3AI
| chris_va wrote:
| They are usually reflective out of band, for unifacial
| (ito on semiconductor on a metallic backing), so ~40% of
| the radiation is heading back to space, vs 10-20% for a
| typical roof.
|
| However... that means they don't radiate well at night
| (they have low emissivity and are not well thermally
| coupled to the roof). Painting the roof white is ideal.
| pfdietz wrote:
| Hmm. I wonder if the glass can have a coating that would
| make them more emissive in the atmospheric transparent
| bands of the mid- and far-IR.
| zbrozek wrote:
| Roof reflectivity higher than 40% is illegal by zoning
| code in my city.
| pfdietz wrote:
| White roofs are being pushed in NY City.
|
| (shared link, readable even without a sub)
|
| https://www.nytimes.com/2021/11/10/realestate/cool-roofs-
| cli...
| crtified wrote:
| I wonder, would that make for some interesting (or
| potentially problematic) visual side effects in an urban
| environment? With the variety of roof angles and sun
| angles, suddenly all manner of observation points (e.g.
| on roads) would potentially be subject to blinding
| reflections at different times of day and year.
| sethhochberg wrote:
| These concerns already come up with things like glass and
| metal clad buildings - plenty of urban zoning codes
| already account for the light that reflects off new or
| modified structures (or at least try to).
|
| It tends to be newsworthy when it goes wrong, because the
| results can be things like buildings cooking nearby
| objects at certain times of day. Spicy stuff.
|
| https://www.upi.com/Odd_News/2013/09/03/Skyscraper-
| melting-c...
| pfdietz wrote:
| I wasn't talking about the visible spectrum, I was
| talking about near IR below the bandgap (which is just
| below visible for Si cells.) This light does not
| contribute to the output of the cells, so reflecting it
| back into space would reduce heat generation at no loss
| of efficiency. If anything, by keeping the cells cooler
| it would slightly boost efficiency.
| perihelions wrote:
| There were HN threads about this (?)
|
| https://news.ycombinator.com/item?id=27782370 ( _"
| Passive radiative cooling below ambient airtemperature
| under direct sun"_)
| raverbashing wrote:
| There's one other minor factor that helps even if the solar
| panel did nothing:
|
| By making the sun hit at a layer above the ceiling (and
| assuming you have proper air circulation below), your attic
| area will heat less, hence your house will get less hot.
|
| (This is similar to the effect you get by staying under a tree
| shadow)
|
| As per the article, yes, if everybody had air conditioners city
| wide that would increase the city temperature. But that would
| require everyone to blast it at the same time
| vbezhenar wrote:
| You can also insulate roof and it'll just heat air and radiate
| energy in cosmos. Heating air is not a problem because it's
| already somewhat high and will only move higher.
| sidewndr46 wrote:
| It can't be "doubly effective". The energy cannot simply
| disappear into the void. If it is used to run something
| electrical in the house, that energy is still there. If you
| ship it into the grid and across the country, less of the
| heating is localized. But it is still heating as it travels
| through the wires.
|
| As it turns out, solar panels are often more reflective than
| the typical roof of a house in North America. So solar panels
| can actually reduce the heat island effect. But it is mostly
| independent of whether they are hooked up at all.
| y42 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| > _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.)
| andsoitis wrote:
| > No one actually does it.
|
| Los Angeles has building codes for cool roofs:
|
| https://www.ladbs.org/docs/default-
| source/publications/ordin...
| tonfa wrote:
| > Air conditioners [...] leak harmful planet-warming gases into
| the atmosphere.
|
| Anyone has a reference about that? Last time I tried to research
| it, it seems like it was mostly fixed at least in Europe with the
| most harmful gases being banned for new sales.
| housemusicfan wrote:
| Sounds like FUD. A properly installed AC leaks _nothing_
| because it is by design a sealed system. I wonder if they feel
| the same about refrigerators.
|
| These same smooth-brains are probably extolling the benefits of
| heat pump water heaters not realizing they have the equivalent
| of an AC attached to them.
| aa_is_op wrote:
| They do leak. That's why you have to replenish their gas
| reserves every 2-3-4 years (based on brand). Had to do mine
| two years ago.
| callalex wrote:
| You are being fleeced by some shady repair business. Can
| you point me to the user manual of your machine where it
| calls for such frequent recharging?
| housemusicfan wrote:
| This is false. They're not supposed to leak. "Replenish gas
| reserves" is not a regularly scheduled maintenance item. In
| fact it's illegal for a technician to add refrigerant more
| than once without identifying and repairing the source of
| the leak. Unless you did something stupid like tried to
| install a split system yourself.
|
| If your unit leaks refrigerant it needs to be repaired.
| This is _not_ normal.
| Finnucane wrote:
| "Not supposed to" is a very weak condition in
| manufacturing these days.
| housemusicfan wrote:
| ICE cars aren't supposed to explode nor are EVs supposed
| to burst into flames via inextinguishable battery fires.
|
| But sometimes they do.
|
| We don't use this outlier data to refer to them as
| conflagrations-on-wheels and assert it's a normal
| function of the device just to strengthen our biased
| case.
| Finnucane wrote:
| Sure but battery fires are still a problem that needs to
| be fixed and not ignored. Also, even though it doesn't
| happen often, when it does the results can be
| catastrophic. So it is a reasonable concern.
| networkchad wrote:
| [dead]
| WheatMillington wrote:
| If you're replacing your gas every 2-4 years, something is
| terribly wrong.
| stephen_g wrote:
| What? I've never heard of a system that (with proper
| installation etc.) needs to be replenished _anything like_
| that often! Where are these brands you're talking about
| from?!
|
| Car air conditioners maybe, but it seems unbelievable for
| fixed systems of any reasonable quality...
| userbinator wrote:
| Find the leak and fix it. They're not supposed to leak.
|
| AC should be as sealed as a fridge, and you don't hear
| people having to recharge their fridges every few years.
|
| Even ignoring the environmental concerns of refrigerant
| leaks, it's wasteful of your money too.
| SirMaster wrote:
| I've been using my window AC unit for 10 years now. Have
| not had to replenish any gas...
|
| They definitely aren't supposed to leak.
| moritz wrote:
| The phase-out under the Montreal protocol is an ongoing
| process, but we are far from there. The HFCs that replaced
| (H)CFCs in the 90s quickly turned out to be fastes growing
| category of short-term climate pollutants in many countries in
| the world [1]. The Kigali Amendment to the Montreal protocol
| from 2019 now covers HFCs too, and the EU limits them since
| 2015, but these things take time...
|
| R-410A, commonly used in Europe, has a GWP of 2088. Worldwide,
| R-22 still is the most common refrigerant. That's a HCFC, so
| stratospheric ozone depleting, and with a GWP of 1960.
|
| [1]: https://www.science.org/doi/10.1126/science.1216414
| stephen_g wrote:
| R-410A is being phased out in major markets including the US
| too over the next few years (R-22 has been banned for new
| equipment most places for more than a decade, and is banned
| entirely in the EU since 2015 for recharging existing units).
| My Mitsubishi air to air heat pumps (one from 2015 and one
| from 2018) were already R-32 (GWP 675, Ozone depletion
| potential 0) and my air to water (Sanden, installed 2022) is
| R-744 (which is CO2 - obviously GWP 1)
| tonfa wrote:
| Thanks both for the pointers (it's easier to google if you
| know what to search for).
|
| https://climate.ec.europa.eu/eu-action/fluorinated-
| greenhous... is the list of alternatives with corresponding
| GWP for EU.
| moritz wrote:
| In so-called developing countries, the full ban of R-22
| will be 2030, which is a full ban with an asterisk to 2040.
|
| Not saying the phase-out isn't happening, but there are,
| and there will be for quite some time, millions of units
| leaking climate pollutants (which was the question).
| emtel wrote:
| 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.
| hinkley wrote:
| 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 wrote:
| Heat that is moved from a dwelling onto the street shouldn't
| really count as 'waste' heat.
| hinkley wrote:
| 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.
| pjerem wrote:
| 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 wrote:
| 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
| adammarples wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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).
| a_square_peg wrote:
| I really hope people don't take this result at its face value -
| the model used and the approach is extremely simplistic, which is
| essentially a pseudo 2-D simplification of urban canyon geometry,
| a street with buildings on either sides. I worked with the
| referenced model as part of my master's thesis.
|
| The bulk of urban heat island effect is driven by the radiative
| absorption of non-porous materials of the built-environment.
| Other heat waste put into the area accounts for less than
| something like 5% of the additional heat added when compared to
| rural areas.
| tasogare wrote:
| [dead]
| Etrnl_President wrote:
| Cities are made of houses. Houses are made of rooms. If rooms are
| hot, aren't cities hot? If room heat is pumped outside, did the
| city temperature really change? What is the heat-island effect?
| lowbloodsugar wrote:
| The asphalt and concrete is doing far more than the AC. But the
| city would have to pay for that and the poor need roads, so not
| as useful for lefties to incite riots against the "rich".
| Aeolun wrote:
| Kinda weird. Of course air conditioning makes cities hotter, but
| the point is kinda to cool down the insides of the house, not the
| outsides. Small enclosed areas are a lot easier to cool.
|
| Heating up the 40 square kilometers of city outside by 2.4
| degrees reduces 1 sqkm of inside temperature from a sweltering 30
| to 23 degrees (note, made up numbers).
| crazygringo wrote:
| Question: is there a huge difference based on whether units are
| placed in windows vs. on roofs?
|
| Obviously for a window unit or split where the compressor is on
| the building's wall -- those are going to heat the air in the
| street. Ground level units most of all.
|
| But a lot of buildings place all their compressors on the roofs.
| And since hot air rises, does that produce any noticeable effect
| at ground level?
| agumonkey wrote:
| Where's research on passive thermal management (materials acting
| as heat phasors kinda) ?
| lucb1e wrote:
| Would it help to have an IR-reflective dish below hot AC units,
| to reflect more of the heat they put out back into space?
| contravariant wrote:
| Most of the heat is probably spreading by convecting hot air,
| not as thermal radiation. A good chimney seems like it should
| be more effective, though it fundamentally still can't stop the
| fact that you're converting quite a bit of electricity into
| heat.
| lucb1e wrote:
| There will be some loss, but the heat trapped in houses
| wasn't going anywhere anyway. By putting it outside the home,
| there is a more direct pathway for it to be leaving the city.
| Though I wouldn't know how to quantify this by any sort of
| approximation, I assume it's less than the heat added from
| inefficiencies yeah
| kkfx wrote:
| Honestly? That's just bullshit to try pushing people against A/C.
|
| Cities are hotter than outside because:
|
| - they absorb more heat :: concrete, asphalt absorb much more
| than grass or trees and disperse far more slowly. Just go walking
| in a bush, measure temperature at 1.5 m from soil, do the same in
| grass covered area and the same over a road. You'll see and feel
| the difference;
|
| - in cities there are MANY ICE vehicles whose engine produce much
| heat, much more than any electrical motor;
|
| - in cities there is less air circulation than in the open nature
| due to the high and heat-absorbing buildings;
|
| - in many cities glass coated skyscraper works like any other
| glass keeping much of Sun IR radiation inside.
|
| These are the reason why cities are hotter. Another proof? They
| are ALSO hotter in winter, not just in summer. In winter you can
| count extra heat from badly insulated heated buildings, little
| cold pushed outside by the so far limited percentage of people
| heating with some heat pumps that have air on their exterior
| side, but look at the numbers and you'll see they are more hotter
| than mere heats spread outside by badly insulated heated
| buildings.
|
| People should learn two things:
|
| - cities WAS a necessity to evolve in the past, but with the '80
| logistic revolution they lost one of their last reasons to
| exists, manufacturing became cheaper to do far from customers, so
| far from cities. With the remote work the last remaining reasons
| vanish as well. As a result dense cities and high rise buildings
| have NO REASONS TO EXISTS anymore. Try to keep them and sell them
| as green, good for the future etc is just a push toward intensive
| human farming to keep people dependent on service they don't own,
| living to operate them so they can pay them. Since in the modern
| era cities can't be sustained the push needs to makes people
| accept bad living condition as a new normal;
|
| - we need to switch from a high density model, too dense for
| today state of tech and society, climate etc to a new less dense
| one, that's hard and that's means MANY will be simply
| "overflowing humans" to be put somewhere, since no one like that
| role, if told in such a crude way, some try to advertise such
| role with various "bells and whistles" but that's simply
| BULLSHIT.
|
| If you try reasoning about the above you'll understand a thing:
| such move to put aside a significant percentage of humans can't
| really work, never worked in history. It does work if the set
| aside cohort is very limited, the poorest, very isolated and very
| dependent, but at modern scale can't work.
| crooked-v wrote:
| > we need to switch from a high density model, too dense for
| today state of tech and society, climate etc
|
| The populations of dense cities use _fewer_ resources than the
| same population spread out in low-density settlements,
| especially when those cities are laid out to be properly
| walkable. It 's just basic economy of scale.
|
| > in cities there are MANY ICE vehicles whose engine produce
| much heat, much more than any electrical motor;
|
| In cities, not having a vehicle is an option. Outside of them,
| it's basically required in most places.
| mschuster91 wrote:
| > It's just basic economy of scale.
|
| Economies of scale aren't a goal on their own. Scaling
| something up will always have side effects... in the case of
| too dense urban areas, it's for example the sheer amount of
| traffic. For example, a quarter full of high-rises, no way
| you can get away without expensive high-capacity subterranian
| trains to handle commuters, and surface traffic is going to
| be a hot mess even with just shuttling the basic supplies for
| supermarkets, restaurants and the likes in one direction and
| waste on the other direction. In contrast, even a standard
| European mid-sized city can get away with cheap bus and tram
| lines. And it's harder to provide other essentials to
| meaningful life in a city as well, particularly where
| children are involved - land is too valuable to leave it as a
| park, and children can't have outdoor places to play either
| in kindergarten because it's too expensive, so you have _even
| more_ traffic just from parents bringing their kids to
| kindergarten /school/playgrounds/whatnot.
|
| Another effect of urban over-density that's often neglected
| is human health, both physical (we've seen that with COVID,
| just how fast pathogens can spread in urban areas) and
| mental. I mean, even here in Munich or Berlin we're not at
| the US levels of mental health and housing issues with people
| defecating on the sidewalk, but still it's noticeable how
| cities tend to have more anti-social behavior, as poverty and
| boredom are definitely contagious especially when not backed
| by the implicit social control that life even in smaller
| cities brings.
| bigbacaloa wrote:
| [dead]
| kraig911 wrote:
| A lot of things are making everything including cities hotter.
| Here in Texas it was 110 at my house yesterday in September. I
| live way way way outside of a large city. I personally think
| concrete/asphalt absorbs and retains a lot of heat keeping things
| hotter. If we could just reflect more back I think it'd help much
| more. I have solar on my house and it practically pays for my AC
| Bill.
| SavageBeast wrote:
| Greetings Fellow Texan - I live in the downtown Austin area and
| I can second your conjecture that concrete and asphalt absorb
| heat.
|
| Here is a downtown weather station:
| https://www.wunderground.com/weather/us/tx/austin/KTXAUSTI18...
|
| This site allows you to check various weather stations and see
| temps as recorded at the location.
|
| You can compare your location to others less or more urban and
| see this while its happening. Next time you're awake at 3AM
| with nothing to do check it out! Compare downtown Austin to the
| suburban area of your choice. I saw a 2-3 degree difference
| pretty regularly last I looked.
| stephen_g wrote:
| Concrete and asphalt definitely do absorb huge amounts of heat
| - it's well studied and called the _urban heat island effect_.
| zo1 wrote:
| Do we know how much of that is causing global warming?
| s0rce wrote:
| https://www.nature.com/articles/s41467-022-31558-z
| Solvency wrote:
| Yeah. Read a book.
|
| https://www.amazon.com/Kiss-Ground-Reverse-Climate-
| Ultimatel...
| aaomidi wrote:
| City wide geothermal cooling pls thanks
|
| You can use huge water mains to transfer the heat
| thatwasunusual wrote:
| Isn't this well known, and not limited to AC, based on the Urban
| heat island effect?
|
| https://en.wikipedia.org/wiki/Urban_heat_island
| rapnie wrote:
| 14 trackers after "reject all" is also making me hotter.
| [deleted]
| merth wrote:
| install "ublock origin" and enable "annoyances" from settings.
| SoftTalker wrote:
| Didn't know about "Annoyances" thanks -- giving that a try
| now (these are under the "Filter lists" tab in settings, for
| anyone looking for them).
| MaKey wrote:
| Thanks for the hint!
| Arn_Thor wrote:
| By coincidence I was walking around Paris today in 30+ degree
| heat. It was only really bearable in the shade, which the city
| has a lot of thanks to a good amount of trees lining the
| sidewalks. It was quite pleasant until we passed a convenience
| store and the heat and humidity of that part of the street
| immediately rose to oppressive levels. This was because an air
| conditioner for the store was venting into the street.
|
| The effect is stark and incontrovertible. There is the heat being
| removed plus some heat from the compressor and fan. Everyone in
| public and private spaces will be better off if we reduce AC
| usage as much as possible in favor of other solutions
| 6502nerdface wrote:
| In Las Vegas they solve this by blowing cold air onto the
| sidewalk through an always-open door, thereby cooling
| passersby, and perhaps enticing a few to enter for a game of
| slots.
| alistairSH wrote:
| That doesn't really solve the problem. They're just dumping
| the waste heat on the back of the building where tourists
| aren't walking. And producing more of that waste heat because
| they're trying to condition a leakier building.
| mertd wrote:
| 99% sure the parent post is sarcastic
| wavemode wrote:
| No, I've personally witnessed this practice. Wide open
| doors pouring out cold air on a sweltering day really
| gets people to stop and shop.
| baud147258 wrote:
| Living near Paris, it annoys me whenever I look through my
| window and see the exit pipes of mobile AC units (like this one
| https://www.emoqui.fr/wp-
| content/uploads/2019/06/climatiseur...) running through the
| open windows of the opposite flat.
| jefftk wrote:
| Why does this annoy you?
| SirMaster wrote:
| It annoys me whenever I see a single hose AC unit period.
|
| It just makes no sense to me.
|
| First, you are now pumping air from inside the building to
| outside. You aren't creating a vacuum inside, so all that
| means is somewhere else in the building the air is being
| replaced from the only place it can... from outside...
|
| Second, the air you are pumping outside contains some of the
| air from the inside space that you just spent electricity
| cooling...
|
| I use a mobile AC unit like this because it's really the only
| type of unit that will work in my apartment, but I use a dual
| hose unit. The unit has 2 air loops. Air from the room is
| drawn in from the back of the unit, heat is absorbed by the
| heatsink, and then cool air is blown out the front of the
| unit into the room.
|
| Then to dissipate the absorbed heat as well as the heat from
| the electricity being consumed, air from outside is sucked in
| through 1 hose, runs through the other heatsink, and then is
| expelled back outside again from the other hose.
|
| It just makes so much more sense, and if you can stick 1 hose
| in your window, it's really not that hard to stick 2.
| mikhailfranco wrote:
| It's not (just) the a/c in the store, it also has huge
| refrigeration units.
|
| In Asia, 7-Eleven is famous for its chilled air, but also has
| the walls covered with refrigerators for cool drinks, and there
| may be freezers for meat, seafood and ice cream.
| jimnotgym wrote:
| TLDR; YES
| guerrilla wrote:
| That would seem inevitable, so the only real question was how
| much (+2C.) So, how much cooler does the city with many heat
| pumps get in the winter then?
| stephen_g wrote:
| The opposite effect I expect should be less for heating, since
| the heat is constantly leaking out of buildings at some rate
| back into the environment (insulation, double glazing etc.
| reduces this but all the added heat eventually leaks out), and
| additional energy is being put in which turns into heat too
| (e.g. COP 4 means 1 unit heat from electricity and 3 units
| shifted from the outside environment).
|
| So whether there is temporary localised cooling depends on the
| quality of the insulation but overall and over time there is no
| cooling due to the additional input.
| guerrilla wrote:
| The heat is constantly leaking _into_ the buildings too. I 'd
| be more concerned with differences in efficiency with
| direction that you mention at the end. In any case, the net
| result is still negative, so how much negative is still the
| question that stands.
| Ozzie_osman wrote:
| Effect must be less. For AC, you're transferring indoor heat
| outdoor AND generating excess heat from running the AC itself.
| For heating, the excess heat generation presumably works
| counter to the heat transfer.
| raverbashing wrote:
| Good question, some aspects make it different:
|
| - you're always getting some "free warmth" through the sun, so
| on average you need to pump less energy to heat than to cool
| (for same temp difference)
|
| - Hot air rises, cold air sinks, not sure how that works in a
| city environment, probably concentrates the cold more
| superq wrote:
| Temp differentials are still differentials, though, so sun
| warmth would be already accounted for.
| raverbashing wrote:
| Kind of, because your house will always be warmer than the
| outside at thermal equilibrium, both in summer and winter
| (with heating/ac off)
|
| So, yes if you consider the differential in-house current-
| target temperature yes, but difference of outside/inside
| temperature no.
| grey-area wrote:
| For the curious, the answer is yes, by 2.4 degrees C.
| aaron695 wrote:
| > by 2.4 degrees C.
|
| For the curious this is not correct.
|
| The article cited by the fake news 'fact check' doesn't agree -
| https://iopscience.iop.org/article/10.1088/1748-9326/ab6a24/...
|
| Nor do multiple other studies.
|
| Minimal during the day, maybe 1 degree at night in certain
| locations.
|
| Urban heat islands need to be fought, while the environment-
| industrial complex pumps out fake news like this it's not going
| to happen.
| matthewmacleod wrote:
| The article you have linked to literally contains the phrase
| "Air temperature is increased by up to 2.4degC" citing the
| conditions under which this was observed. Have I completely
| misunderstood what you are trying to say?
| pierat wrote:
| "Up to" is Comcast weasel words language, in which -10c is
| also in that set.
|
| It's at best garbage science reporting.
|
| Best answer: give GIS heatmaps that show variance of temp
| from in-city to nearby large green space. Then we can talk.
|
| (I see the urban heatisland effect locally. But 1 instance
| isn't science. Doing the math AND displaying it correctly
| is.)
| enraged_camel wrote:
| Check their comment history. It's mostly flagged comments
| for a reason.
| ajb wrote:
| I've been looking at getting shutters on my windows; They're not
| common in the UK but are common in more southern European
| countries. Unfortunately UK windows are designed without the
| expectation that shutters might be installed. Also it seems to
| require planning permission to install them on street facing
| windows too, as they are not currently one of the exceptions. But
| installing air conditioning (and heat pumps) does have an
| exception. This needs to be fixed.
| jdjdjdjdjduuuu wrote:
| Why do you need window gutters? Your roof has no overhang?
| ajb wrote:
| I don't know if that is a joke, but shutter != gutter. A
| shutter covers the window during hot weather to keep the sun
| out and keep the building cool, and can be opened during
| cooler weather.
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