Comment on Is air conditioning making cities hotter?
Mojojojo1993@lemmy.world 2 years agoHeat from the device working?
We know trees cool areas. We know concrete retains heat. We know humans produce/generate 1 bar of heat per adult.
Less trees more concrete and more people with less airflow plus a bunch of electrical devices. Everything is heating is including us and very little is dissipating that wasted heat.
Probably could argue all our fridges also cause heat, computers, laptops, phones and tvs.
Pretty much every electrical device is creating wasted heated. Are AC units doing more or less than any other appliances?
I’m sure a clever engineer can work out which device is the least efficient and is creating the most excess heat vs it’s ability to cool
Haui@discuss.tchncs.de 2 years ago
No engineer but technically adept. A computer consumes roughly 500W (some do more) of electricity which is mostly converted to heat while the work is done. This heat is then dissipated over the heatspreader/s and dumped into the room air.
A one apartment air conditioner can easily use 2kw to work or more (which is also converted into heat) plus it also pulls 10 degrees celsius (35 to 25 c for example) out of the apartments air and dumps it into the open. That means a continoous stream of hot air while the device is working.
As I said, no engineer and it is 6 am so excuse the missing numbers. The formula would be amount of energy pulled out of the air plus working energy times devices in a city. Then you have the wattage of dumped heat just for the air conditioning of said city.
Mojojojo1993@lemmy.world 2 years ago
Ok that’s very helpful. So are AC units the biggest offender ? Depending on their power and efficiency?
Haui@discuss.tchncs.de 2 years ago
I would be hardly a qualified person to tell you if they are the biggest offenders but I think it makes sense to ask this question. If they have a significant impact on temps worldwide or citywide.
Mojojojo1993@lemmy.world 2 years ago
I’m guessing they are if they use power to cool and pull out hot air as well. No other appliances really move heated air around. Except fridges and freezers.
mvirts@lemmy.world 2 years ago
All power ends up as heat. Blender: electric -> kinetic -> heat. Toaster: electric-> heat. Computer: see toaster. Hydropower storage pump: heat + potential now -> heat + electricity later. Chemical battery: heat + potential now -> heat+ electricity later. Whatever work gets done electrically or otherwise, the result of that work eventually dissipates its excess energy as heat. How much energy is required to drive 2000 miles at 60 mph? Ideally the same as driving 20 miles at 60 mph, the difference is lost to heat in the air, tires, road, engine components.
Not to mention the power grid bleeds heat as well, a lot of it.
Air conditioners are just icing on the cake because they extract heat from tiny boxes and boot it out into the environment, burning excess power in the process. Heat pumps are a miracle of thermodynamics that actually use less power than the heat they add to a tiny box. Heat pumps cool the city, air conditioners heat it up. Both do work that evaporates almost immediately after it is done, so they have to always run.
Basically the hobbits had it right all along, just build a few feet underground and you’re good
Haui@discuss.tchncs.de 2 years ago
Thanks for this elaborate explanation. It was fun to read. :)
Mojojojo1993@lemmy.world 2 years ago
So AC is bad but heat pumps are better ? Can waste heat be used for something else ? Heating greenhouses ? Pumped into water to dissipate the excess heat or used to create steam for turbines ?
Any other good use for excess heat ?
mvirts@lemmy.world 2 years ago
Yes! There are plenty of uses for excess heat, especially if you like having hot water on tap, but it’s really difficult to capture or store waste heat, mostly because if the heat is available where it is needed, like the heater of a car in a cool day, it’s not waste heat at all. There is a point where the difference in temperature between the waste heat source and the environment is large enough that it could be used to create electricity, but usually it’s not worthwhile and the equipment needed would would be better used with a dedicated heat source or not at all. I dream of a day when we develop ways to harvest energy from heat more efficiently and can use waste heat for power.