1905
Ancient Iran had air conditioning (lemmy.world)
submitted 3 years ago by to c/mildlyinteresting@lemmy.world
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[–] 149 points 3 years ago (32 children)

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.

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  • [–] 111 points 3 years ago* (14 children)

    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.

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  • [–] 18 points 3 years ago (5 children)

    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

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  • [–] 11 points 3 years ago* (last edited 3 years ago) (3 children)

    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

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  • [–] 1 point 3 years ago* (1 child)

    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.

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  • [–] 7 points 3 years ago (1 child)

    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‽

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  • [–] 8 points 3 years ago

    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.

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  • [–] 2 points 3 years ago (5 children)

    Can you explain 400% efficiency?

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  • [–] 2 points 3 years ago (2 children)

    What the other guy said. It's down to the fact that you aren't actually heating/cooling down a room, you're just moving the heat already there around. E.g. in winter, instead of producing your own heat with electricity, which is 100% efficient, you take heat from the outside and put it inside, using a lot less energy in the process than if you were to create the heat inside of your home.

    Though I'm not sure if it's that efficient, I think I heard it's more around the 150-200% mark, but I'm not sure.

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  • [–] 3 points 3 years ago* (last edited 3 years ago) (1 child)

    I think I heard it's more around the 150-200% mark

    Most cheap air conditioners have COPs (coefficients of performance) around 3.2-3.5, which means 320-350% efficiency. In real world conditions, the best systems reach 4.5, though the theoretical limit is about 8.0.

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  • [–] 1 point 3 years ago

    3.2-3.5 is also on a good day. It might not be as efficient when the outside temperature differences are further away from your thermostat setting inside, though if you have a geothermal setup, then you've got peak efficiency year round.

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  • [–] 2 points 3 years ago*

    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

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  • [–] 17 points 3 years ago (8 children)

    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

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  • [–] 20 points 3 years ago (6 children)

    AC unit you grew up with

    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.

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  • [–] 10 points 3 years ago (1 child)

    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!

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  • [–] 2 points 3 years ago

    Cooling a ware house, lecture hall or mall is very different from cooling an apaprtement building. In particular because most of the former have been designed with AC in mind.

    Who knows where science and engineering may take us next!

    Not beyond the hard limits of physics. You are not going to retrofit an appartement building built in 1900 or 1970 or 2000 for that matter with an efficent heating/cooling system without major rebuilding.

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  • [–] 1 point 3 years ago (3 children)

    People in the UK are installing air cons, because most houses are very bad and have no insulation.

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  • [–] 4 points 3 years ago (2 children)

    This is not true? L1A, L1B, L2A, and L2B exceed american insulation regulations by a huge amount, and they exceed the EU regulations as well. I did some roofing once upon a time.

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  • [–] 4 points 3 years ago* (4 children)

    I had a crazy thought. What if you used depressurization to cool interiors?

    Not as in depressurize the room and potentially kill the people inside, but in a way similar to soundproofing where you create an airtight gap in your walls, depressurize it to create a partial vacuum and effectively restrict both heat and sound transfer. That way it would be much easier to control internal temperature.

    The only two problems I can see with it is expense (pumping air out of the gaps between your walls could be pricey), and the potential of explosive repressurization if something were to break the wall.

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  • [–] 7 points 3 years ago

    Wall isolation is pretty fine as it is, main weaknesses are windows and thermal bridging.

    We still have the issue that a perfectly isolated house will need to lose the heat created by humans and electric systems, so actual cooling is required.

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  • [–] 2 points 3 years ago

    And how do you get fresh air in? Also the problem of heat transfer is never by gaps in the walls, at least not for buildings in western and central Europe. The problem is heat conduction through the window panes. And that is with isolated windows already. Also it is impossible to get a brick wall air tight. Leave alone you create a great environment for water to leak in and damage everything.

    A building needs to be able to "breathe" in order to get rid of the humidity that is generated inside.

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  • [–] 1 point 6 months ago* (last edited 6 months ago)

    I agree we should have more passive forms of cooling/heating.

    But I think the problem is that often these are highly dependent on the environment and are very situational.

    Places that are dry and hot benefit from water and internal ventilation like this, because the perspiration and water evaporation naturally cools things down, just like our sweat does (same principle that refrigerates water in clay pots like Spanish botijo, or what makes central gardens inside buildings very common in some areas). But they need to stay dry and hot for systems like this to make sense... a cold and humid year would make this whole design pointless at best, counter productive at worst.

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