this post was submitted on 24 Jul 2023
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Mildly Interesting
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This isn't just mildly interesting. We should be considering methods of air cooling that do not use any carbon in order to avoid aircon usage becoming a contributor to the climate problem as things get hotter and hotter.
I agree with you that we should be exploring alternatives, but aircon is extremely energy efficient for how much thermal energy it moves (reaching 400% efficiency in some cases) . The problem isn't aircon itself, but what is being used to power it (coal/natural gas power plants)
In fact the technology behind aircon can be expanded into a heat pump to both heat and cool, being more efficient than electro-resistive or gas heating. There's even water heaters that will actually cool the area they're in and use the heat they gather from the space to heat the water.
Technology Connections has a great series of videos that go in depth on both heat pumps and aircon.
Yeah, "air conditioning powered by solar/wind/hydro" can feel like it's one big Rube Goldberg machine to make air cool, but the reality is that it comes together to make something that can scale really easily. I can't imagine coming up with a design like what's in OP for an apartment complex or condo building.
Source: just made it up, but also a Technology Connections fan. All that's to say, feel free to correct me with a little data
They actively use this design in large buildings (with a modern twist). Its known as a chilled water system: https://hvactrainingshop.com/how-a-chilled-water-system-works/
Or you have ones that do not run at all during the day, and only chill/freeze the water at night on excess power/cheap power: https://www.buildinggreen.com/news-article/making-ice-night-cool-buildings
The second system I linked would then let the ice slow melt over the day as its way of actively chilling air passing through its exchanger.
These systems work by chilling water instead of air, which has a much higher heat capacity. Meaning, it can accept much more thermal energy per unit mass before raising its temperature by 1 kelvin. You are able to build a single, very well designed, and efficient refridgeration unit that can provide HVAC services to up to multiple high rise buildings. This reduces waste and reduces the usage of coolant/refridgerant.
This system can be reversed in the winter (heating the water instead of chilling) with geothermal heat, solar heat, or if no "green" options are readily available, natural gas direct fire heat can be extremely efficient compared to electric coil
The #hvactrainingshop.com link is dead to me (it’s in an exclusive walled garden not openly available to all people [#Cloudflare]). I could not find a replacement link. If anyone has a better source, plz mention it.
Does this one work: https://web.archive.org/web/20230521234645/https://hvactrainingshop.com/how-a-chilled-water-system-works/
400% efficiency is good, but it's not better than the ∞% efficiency you get from something that doesn't require fuel input to begin with. (I'm pretty sure the Technology Connections guy would agree on that point.)
If nothing else, think of it this way: even if you still want to use air conditioning to make sure you get all the way down to comfortable room temperature or whatever your target is (which a Qanat, although able to achieve a >15°C ΔT, might or might not be able to do reliably), it'll still give you a big head start and greatly reduce the amount of energy needed. It's a lot like using a ground-source heat pump instead of an air-source one. What's not to like‽
Sorry my point wasn't that we shouldn't explore other options to use instead of/in tandem with A/C. I was entirely pointing out that the use of an AC/heatpump is by itself, in absence of the context of what is used to power it, a non issue as its one of the most efficient electric heating/cooling technologies we have.
Wind catchers could be, and likely are a great technology to adapt for wider use, though I can't speak to that, I'm not an HVAC engineer.
Can you explain 400% efficiency?
Sorry, my notifications have been messed up because of the lemmy.world issues! Some other people have already answered but I'll still reply :)
A heat pump's efficiency is measured differently than that of a gas furnace.
The actual unit for heat pumps is the Coefficient of Performance (CoP). This measures the power input (electricity) VS the power output (heat). A "400% efficiency" as I put it, is a CoP of 4, meaning that for every watt of power used, 4 watts of heat energy are moved. As some other people pointed out, depending on the quality and technology of the heat pump and the interior/exterior temperature, the actual range of a heat pump is a CoP of anywhere from 2-5.5 (the theoretical, perfect maximum is 8.8). The efficiency of the heat pump does dip as the temperature of the region it's pulling heat energy from lowers, there's less energy available to move, so it has to work harder. This is why heat pumps in regions with especially cold winters have what's usually called "emergency heat" which brings us to...
Electrical heating. This works by pushing electricity through a wire to heat it up. Directly turning electricity into heat. Electrical heating always has a CoP of 1 (terms and conditions apply). For each watt of electrical power consumed, 1 Watt of heat energy is produced.
Finally we have gas heating, which is still the only option for some areas for various reasons. Gas heating efficiency is not measured with CoP but instead with Annual Fuel Utilization Efficiency, simply a number that represents what % of the fuel burned is actually turned into useful heat energy. I'm finding AFUE ranges of 76-97% as a general range for modern furnaces. If a furnace has an AFUE of 90%, that means that when it burns an amount of fuel representing 100 units of heat potential (I'm not using a unit, BTUs confuse and terrify me) then 90 of those units will be turned into usable heat, and 10 of them will be waste, whether that is heat that leaves via the chimney or is simply unburnt fuel.
TLDR: 400% means 4x more energy is moved than is used, I apologize for the wordiness, I find this stuff rather interesting
This would be a great idea if you want everyone in that building to file humidity complaints every single day. Air conditioners work by using mechanical work (compressor) to exploit evaporation in order to pull heat from one location to another and exhaust it away, in turn cooling the first location (this could be air, water, etc.)
This system works by using ground temp water as a heatsink to suck heat out of the air passing over it. When it does this, it humidifies the air. In the desert...who cares? In an office building...who cares? Every single worker who is stuck there all day
If you're saying we need better systems than the AC unit you grew up with, fear not! Many office buildings have been moving away from it (same with other large venues) they use a chilled water system. They use the best of both these systems to get WAY more performance out of way less wattage. You only need a fraction of the cooling power with a chilled water system because the water can absorb much more heat per unit mass than air and can be sized to never run during the day, but only at night when the grid is least in use
Lmao grew up with? Most of us have never used AC at all in europe. Here in the UK no homes have AC. The issue is that people are installing it now because of climate change and the result is massively higher energy use.
Not necessarily in your house. I'm talking about the design of the units from when you were a child (Many public buildings in the EU have AC regardless of houses not having it). AC was invented in 1901, and has come a very long way since then, and we have begun combining it with old principles to extract the best of both solutions
Combining modern refrigeration/cooling techniques with well designed passive systems that exploit material properties (Heat capacities, transfer coefficients, etc.) to their advantage is the future of HVAC. It started with CFCs and knowing we could exploit their boiling point with mechanical force to chill air beyond the outside air temperature. Who knows where science and engineering may take us next!