> The notoriously bad energy efficiency of air conditioners
Air conditioners are actually pretty fantastically efficient for what they do. The problem with air conditioners is that there's no way to move a ton of heat without using a lot of energy. So, they do use a lot, but they make the most of it.
What's truly bad are our buildings that have the minimal insulation and sealing possible, leaking all that cold air right back out into the environment.
New buildings are rather efficient in US. The problem is old buildings that use 5X the energy for HVAC.
I echo that AC is quite efficient. Far more efficient than traditional heating. There's a misconception that hot areas are less environmentally friendly due to AC. The opposite is true.
Hot areas are only 25 freedom units hotter than humans prefer. Cold areas have months of 50+ temperature difference.
The misconception persists because heat uses gas, which is 5-10X less expensive per BTU of energy than electricity. So it might be cheaper to heat cold areas than run AC in hot ones, but its much more damaging to the environment. Plus, hot climates are using a lot of renewables these days which impacts the environmental friendliness of electric but not gas.
I expect migration to the sun belt to accelerate, at least in the US. It makes a lot of sense from environmental perspectives. In some southern cities there's already long stretches every summer where daytime AC use runs on 70%+ renewable energy.
> What's truly bad are our buildings that have the minimal insulation and sealing possible, leaking all that cold air right back out into the environment.
In the case of the house I'm currently at, it is pretty good at retaining heat in "winter" (in quotes, because it's Bay Area winter). However, in the summer it will be quite warm late at night. So sometimes I want it the other way around, I want it to radiate excess heat away as fast as possible, but I can't control that. We should be able to deploy "heatsinks" at night.
That's for a house. Modern office buildings are built like greenhouses, even when they are otherwise insulated.
We can't really roll out solar panels fast enough. They would help offsetting the cooling energy costs by a lot. After all, it's during warm sunny days where the air-conditioning needs are the greatest. They also provide shade.
The author doesn't really explain it well because his explanation breaks some physics laws, so it doesn't "suck" your body heat away.
Instead, it lowers the amount of heat radiating onto you from your environment by replacing hot walls with cold walls, which will lower the temperature of your skin.
It's efficient specifically because it doesn't cool by convection (like every other cooler). This allows the designers to insulate it so they only have to offset temperature gained by incoming heat radiation when keeping it cool. That also means it won't cool the air, just the objects near it.
Thermal radiative coupling is bidirectional. Sucking away is appropriate and important as you do actually have to displace the energy somewhere. It works the same way when sucking air.
A simpler non-radiating equivalent would be a reflective foil, or a polished metal - you could enclose yourself within it, get no radiating heat from environment, yet it wouldn't help cool you, because your radiation has no place to go.
An idea I was told about relatively recently that kind of blew my mind:
- Space is cold (~3K)
- The atmosphere is really quite transparent in the wavelegth 8-13 μm
- If one can construct an optical filter (e.g. grating) which is highly reflective except for a bandpass at 8-13μm, it is possible to reflect most solar energy but still "see" the cold of deep space
- It's possible to build a box with sufficiently low thermal conduction, and this 'magic mirror' on top, to effectively refrigerate its contents by radiation to space. This uses no power, and works in direct sunlight [^1].
So weird, probably not very practical (what about cloudy days?), but very cool!
[^1] in fact, if you put it in the shade then it would warm up because it could no longer radiate to space.
> [^1] in fact, if you put it in the shade then it would warm up because it could no longer radiate to space.
If I understand correctly, this isn't quite right. If it's in the shade, then whatever is shading it is radiating more heat onto it (because the shading object is hotter than space) and possibly reflecting its own radiated heat back. If it's under a clear sky then it's receiving less heat, so what it loses by radiating has more effect. Does that sound right?
Temperature is an attribute of things, space is a lack of things.
What you're referring to is the temperature of cosmic background radiation, which is akin to how you emit infrared radiation at your body temperature. But you certainly don't classify the space where this radiation move through as having your body temperature. The two things are not the same imo.
This sounds pretty neat, but their description of cold things sucking thermal radiation doesn't jive with my freshman-physics understanding of thermodynamics. AFAICT they've got cold water circulating in a moisture-repellent membrane, so they're able to absorb heat by chilling the water in the pipes instead of fussing with the humidity in the air like most AC does. So it sounds like trading inefficiency of standard AC units for an inefficient thermal interface -- you need to stand next to it to feel cooled?
It's the cooling equivalent of a radiant heater, and you need line-of-sight to the walls to feel cooled. The thermal interface is deliberately inefficient for convection (to avoid wasting power chilling the air), but efficient for radiation.
Radiation is proportional to absolute temperature T^4. So compared to a glowing radiant patio heater, I'd expect to need maybe (1000^4 - 300^4)/(300^4 - 270^4) ~ 350x the area for the same heat transfer in the opposite direction, thus their big tunnel instead of a little filament. Even with their cold source at absolute zero, they'd still need >100x.
It might be better to think of it as creating an environment where you are not surrounded by warm objects radiating at you. So it should not matter where you are in the space or how large it is. The effect should be the same.
About 60% of human body heat is lost through radiation. The cooling you would feel would be proportional to the percentage of the area around you that is covered by these cooling walls. Distance wouldn't cause that much loss because the air doesn't absorb much radiation in blackbody range of humans over distances less than 50 meters.(Infrared range with intensity peaking at 93 thousand angstroms)
Gaining or losing heat via radiation isn't as easy as conduction, but it does work.
It's possible to make ice at night in temperate climates by taking the equivalent of a solar concentrator, putting water at the focus and pointing it at a dark patch of clear sky.
You know, probably standing in the sun vs shade is probably the opposite analogy. In the sun you get radiative heating from the sun, in the shade you just get heating from the nearby air.
> but their description of cold things sucking thermal radiation doesn't jive with my freshman-physics understanding of thermodynamics.
Pseudoscience alarms started to sound in my head, until I read the comments.
If I understood this correctly - you will still radiate heat as normal. But, since the thermal radiation you emit will reach these things (assuming line of sight), you won't have much reflected back at you (or at nearby objects, which would heat them up). And so, you feel colder, even though the air is not being chilled.
That would make sense, similar to how we can make ice during the night even in a desert. You can radiate heat into space(as not all thermal radiation will be absorbed by the air)
From a freshman physics point of view, “sucking” is also not a pull-from-low process but a push-from-high process. There is some nuance there but simply, a straw doesn’t work right in a vacuum.
I saw a very promising AC technology at CES in january that people may find interesting: https://www.oxicool.com/
I don't have the material science or chemistry background to know how effective it is, but I hope everything they claim holds water, it sounds pretty good.
There's also a DIY water based AC with pipes and a cheap pump you can find widely on the internet, but I haven't done it yet. Here's an example https://www.instructables.com/id/Hollis-homemade-AC/ ... In the comments one poster suggested a toilet tank as a reservoir, that sounds promising.
That's neat and I'm going to keep an eye on it. The -15° F ambient differential somewhat limits its usefulness, and I'd like to see an induction-powered heater as an option instead of conduction-based heating. I'm guessing the 10-year lifespan is due to the fan bearings and the molecular sieve lifetime, and I'd like to see the overall system lifespan increased by 10X.
Would be interested in the papers behind this tech, as I think there are a lot of caveats they're glossing over.
[1] seems to be a paper on adjacent technology.
[2] seems to indicate the service lifetime of the molecular sieve is the controlling factor in the estimated lifecycle. 10 years sounds like the upper range.
"The primary energy for HomeCool™ is derived from clean open flame burn of natural gas. This can be converted with an optional kit to propane and also hydrogen* (*once commercially available)."
Burning gas isn't exactly a clean energy source. In fact, we need to be aggressively exploring ways to stop burning gas for heating - not starting to burn more for cooling!
This is just a regular hydronic radiant system which is very efficient because it doesn’t need to heat the air. The thing is, hydronic systems have been around for 70 years or more but they typically are not used for cooling because of the humidity issues that arise which are damaging to the building. So this can only be implemented in buildings with materials resistant to water damage. Hydronic radiant systems are the best around it terms of heating efficiency but very expensive to install. This article seems like hype and bs.
It does say that there is a Novel membrane to prevent humidity build up, but there isn’t a lot of information about the membrane and what conditions it will work in. For instance, Will it work in a wooden structure with drywall?
This is a bit different. A cooled ceiling cools the air through convection, but this isn't supposed to. Instead, it basically just "removes" the warm walls you'd experience in any other setting.
A cooled ceiling would cool more effectively but possibly not as efficiently.
I'm not an expert, if one is available please comment.
Human perception of temperature is mostly based on 5 things: Ambient air temperature, Radiant Heat (infrared radiation), humidity, direct conduction of heat, and air movement.
It seems like this addresses Radiant Heat. Another way to address this is to add more insulation, install low-emissivity windows, plant shade trees in your yard.
Half of my house feels much warmer in the afternoon because it lacks shade. I used a thermometer to see the difference between the ambient air temperature in the two halves; the hot side was only 2 degrees F hotter. I don't have an IR thermometer, but I imagine that the walls in the hot side are at least 10 degrees F hotter.
This is pretty neat. It lets you (somewhat) decouple the temperature and humidity of the air from how cool it feels to be in the room, by only removing radiative heat coming from inside the room. You could choose to exchange air with the outside more rapidly without losing efficiency because you aren't putting as much energy into conditioning the air itself. I wonder if there are any infrared-transparent wall paints.
This is just a geothermal unit with the evaporator built around the load and instead of air to air transfer through convection it is air to air transfer through radiation... nothing but smoke and mirrors. The problem with efficiency and A/C is the excess heat generated by the compression element of the Refrigeration Cycle. The closest thing to 100% efficiency is achieved through absorption chillers that utilize an internal chemical reaction based off of external heat to produce compression through a metered system... neat idea though. Heating systems that utilize the same process are different though - you can achieve greater than 100% efficiency with the use of flash gas bypass designs that will say for example produce 1.5 tons of heat in a 1 ton system.
My new rule is upvote anyone who segues into anti-global warming statements on articles that don't mention Global Warming.
Because I'm sick to death of every time an efficiency is mentioned people have to bring out their favourite religion because we all forgot about Global Warming since a hour ago.
This confused me for a bit. The point of the system is to prevent energy from being reflected or radiated from a surface. Systems like this have been around for a while (https://www.energy.gov/energysaver/home-cooling-systems/radi...), the news here is that this works with temperatures below the dew point because they have solved the condensation issues.
The cold air will contribute, but this is an accurate description. A person constantly radiates a blackbody spectrum determined by temperature, as does the surrounding room. We perceive ourselves as in equilibrium when we radiate as much as we receive. If a wall is cooler than the rest of the room, the person receives less infrared from that direction and perceives cold, even in the absence of convection.
[+] [-] sparker72678|5 years ago|reply
Air conditioners are actually pretty fantastically efficient for what they do. The problem with air conditioners is that there's no way to move a ton of heat without using a lot of energy. So, they do use a lot, but they make the most of it.
What's truly bad are our buildings that have the minimal insulation and sealing possible, leaking all that cold air right back out into the environment.
[+] [-] eggsnbacon1|5 years ago|reply
I echo that AC is quite efficient. Far more efficient than traditional heating. There's a misconception that hot areas are less environmentally friendly due to AC. The opposite is true.
Hot areas are only 25 freedom units hotter than humans prefer. Cold areas have months of 50+ temperature difference.
The misconception persists because heat uses gas, which is 5-10X less expensive per BTU of energy than electricity. So it might be cheaper to heat cold areas than run AC in hot ones, but its much more damaging to the environment. Plus, hot climates are using a lot of renewables these days which impacts the environmental friendliness of electric but not gas.
I expect migration to the sun belt to accelerate, at least in the US. It makes a lot of sense from environmental perspectives. In some southern cities there's already long stretches every summer where daytime AC use runs on 70%+ renewable energy.
[+] [-] outworlder|5 years ago|reply
In the case of the house I'm currently at, it is pretty good at retaining heat in "winter" (in quotes, because it's Bay Area winter). However, in the summer it will be quite warm late at night. So sometimes I want it the other way around, I want it to radiate excess heat away as fast as possible, but I can't control that. We should be able to deploy "heatsinks" at night.
That's for a house. Modern office buildings are built like greenhouses, even when they are otherwise insulated.
We can't really roll out solar panels fast enough. They would help offsetting the cooling energy costs by a lot. After all, it's during warm sunny days where the air-conditioning needs are the greatest. They also provide shade.
[+] [-] dghughes|5 years ago|reply
Technology Connections has a good video about this: https://youtu.be/_-mBeYC2KGc?t=355
[+] [-] ianai|5 years ago|reply
[+] [-] ekianjo|5 years ago|reply
Their efficiency is based on thermodynamics, so there's not much you can do to break the physical barriers.
[+] [-] ladberg|5 years ago|reply
Instead, it lowers the amount of heat radiating onto you from your environment by replacing hot walls with cold walls, which will lower the temperature of your skin.
It's efficient specifically because it doesn't cool by convection (like every other cooler). This allows the designers to insulate it so they only have to offset temperature gained by incoming heat radiation when keeping it cool. That also means it won't cool the air, just the objects near it.
[+] [-] labawi|5 years ago|reply
A simpler non-radiating equivalent would be a reflective foil, or a polished metal - you could enclose yourself within it, get no radiating heat from environment, yet it wouldn't help cool you, because your radiation has no place to go.
[+] [-] heisenzombie|5 years ago|reply
- Space is cold (~3K)
- The atmosphere is really quite transparent in the wavelegth 8-13 μm
- If one can construct an optical filter (e.g. grating) which is highly reflective except for a bandpass at 8-13μm, it is possible to reflect most solar energy but still "see" the cold of deep space
- It's possible to build a box with sufficiently low thermal conduction, and this 'magic mirror' on top, to effectively refrigerate its contents by radiation to space. This uses no power, and works in direct sunlight [^1].
So weird, probably not very practical (what about cloudy days?), but very cool!
[^1] in fact, if you put it in the shade then it would warm up because it could no longer radiate to space.
[+] [-] MengerSponge|5 years ago|reply
[+] [-] Tade0|5 years ago|reply
https://mse.umd.edu/news/story/cooling-wood-an-ecofriendly-b...
[+] [-] mkl|5 years ago|reply
If I understand correctly, this isn't quite right. If it's in the shade, then whatever is shading it is radiating more heat onto it (because the shading object is hotter than space) and possibly reflecting its own radiated heat back. If it's under a clear sky then it's receiving less heat, so what it loses by radiating has more effect. Does that sound right?
[+] [-] hoseja|5 years ago|reply
[+] [-] Aperocky|5 years ago|reply
Temperature is an attribute of things, space is a lack of things.
What you're referring to is the temperature of cosmic background radiation, which is akin to how you emit infrared radiation at your body temperature. But you certainly don't classify the space where this radiation move through as having your body temperature. The two things are not the same imo.
[+] [-] klyrs|5 years ago|reply
[+] [-] tripletao|5 years ago|reply
Radiation is proportional to absolute temperature T^4. So compared to a glowing radiant patio heater, I'd expect to need maybe (1000^4 - 300^4)/(300^4 - 270^4) ~ 350x the area for the same heat transfer in the opposite direction, thus their big tunnel instead of a little filament. Even with their cold source at absolute zero, they'd still need >100x.
[+] [-] upofadown|5 years ago|reply
[+] [-] foxyv|5 years ago|reply
[+] [-] m463|5 years ago|reply
It's possible to make ice at night in temperate climates by taking the equivalent of a solar concentrator, putting water at the focus and pointing it at a dark patch of clear sky.
You know, probably standing in the sun vs shade is probably the opposite analogy. In the sun you get radiative heating from the sun, in the shade you just get heating from the nearby air.
[+] [-] outworlder|5 years ago|reply
Pseudoscience alarms started to sound in my head, until I read the comments.
If I understood this correctly - you will still radiate heat as normal. But, since the thermal radiation you emit will reach these things (assuming line of sight), you won't have much reflected back at you (or at nearby objects, which would heat them up). And so, you feel colder, even though the air is not being chilled.
That would make sense, similar to how we can make ice during the night even in a desert. You can radiate heat into space(as not all thermal radiation will be absorbed by the air)
https://tecped.com/process-of-freezing-ice-in-the-desert-acc...
[+] [-] colechristensen|5 years ago|reply
[+] [-] alacombe|5 years ago|reply
Humidity will have to be dealt with no matter what, either by the AC system, or though condensation, as cold air holds less water vapour as warm air.
[+] [-] kristopolous|5 years ago|reply
I don't have the material science or chemistry background to know how effective it is, but I hope everything they claim holds water, it sounds pretty good.
There's also a DIY water based AC with pipes and a cheap pump you can find widely on the internet, but I haven't done it yet. Here's an example https://www.instructables.com/id/Hollis-homemade-AC/ ... In the comments one poster suggested a toilet tank as a reservoir, that sounds promising.
[+] [-] yourapostasy|5 years ago|reply
Would be interested in the papers behind this tech, as I think there are a lot of caveats they're glossing over.
[1] seems to be a paper on adjacent technology.
[2] seems to indicate the service lifetime of the molecular sieve is the controlling factor in the estimated lifecycle. 10 years sounds like the upper range.
[1] https://aip.scitation.org/doi/abs/10.1063/1.4822041?journalC...
[2] http://www.yyindustry.com/news_show.asp?id=28
[+] [-] leoedin|5 years ago|reply
"The primary energy for HomeCool™ is derived from clean open flame burn of natural gas. This can be converted with an optional kit to propane and also hydrogen* (*once commercially available)."
It burns gas. It may work in a similar manner to absorption refrigerators often found in RVs. https://en.wikipedia.org/wiki/Absorption_refrigerator
Burning gas isn't exactly a clean energy source. In fact, we need to be aggressively exploring ways to stop burning gas for heating - not starting to burn more for cooling!
[+] [-] abrowne0|5 years ago|reply
[+] [-] abrowne0|5 years ago|reply
[+] [-] andor|5 years ago|reply
https://de.wikipedia.org/wiki/K%C3%BChldecke
[+] [-] justinclift|5 years ago|reply
https://en.wikipedia.org/wiki/Chilled_beam
[+] [-] ladberg|5 years ago|reply
A cooled ceiling would cool more effectively but possibly not as efficiently.
[+] [-] ac42|5 years ago|reply
[+] [-] csours|5 years ago|reply
Human perception of temperature is mostly based on 5 things: Ambient air temperature, Radiant Heat (infrared radiation), humidity, direct conduction of heat, and air movement.
It seems like this addresses Radiant Heat. Another way to address this is to add more insulation, install low-emissivity windows, plant shade trees in your yard.
Half of my house feels much warmer in the afternoon because it lacks shade. I used a thermometer to see the difference between the ambient air temperature in the two halves; the hot side was only 2 degrees F hotter. I don't have an IR thermometer, but I imagine that the walls in the hot side are at least 10 degrees F hotter.
[+] [-] zbyte64|5 years ago|reply
Also, one currently ensures there is a stud or lack of electrical when putting nails in a wall. I guess you gotta hang things up differently.
[+] [-] sparker72678|5 years ago|reply
[+] [-] alacombe|5 years ago|reply
Pretty costly in water damages for sure, people tends to drive nails in pipes all the time already, just imagine this * 100x.
[+] [-] infogulch|5 years ago|reply
[+] [-] b0rsuk|5 years ago|reply
The Revenge of the Circulating Fan https://www.lowtechmagazine.com/2014/09/circulating-fans-air...
[+] [-] username505|5 years ago|reply
[+] [-] adrianmonk|5 years ago|reply
[+] [-] finphil|5 years ago|reply
[+] [-] tobyhinloopen|5 years ago|reply
[+] [-] OminousWeapons|5 years ago|reply
[+] [-] pengaru|5 years ago|reply
[+] [-] LifeIsThermal|5 years ago|reply
[deleted]
[+] [-] ladberg|5 years ago|reply
This has nothing to do with the greenhouse effect (which occurs when you have two bodies of drastically different temperatures with an air barrier).
[+] [-] aaron695|5 years ago|reply
Because I'm sick to death of every time an efficiency is mentioned people have to bring out their favourite religion because we all forgot about Global Warming since a hour ago.
I'm also impressed you waited 3 years to comment.
[+] [-] growlist|5 years ago|reply
(sorry)
[+] [-] Stierlitz|5 years ago|reply
I'm not sure that is an accurate description of the physics. Maybe the air next to the panel is cooler, accounting for the cooling sensation.
[+] [-] thefiregecko|5 years ago|reply
[+] [-] yummypaint|5 years ago|reply