[HN Gopher] New 'mirror' fabric can cool wearers by nearly 5degC
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New 'mirror' fabric can cool wearers by nearly 5degC
Author : jnord
Score : 326 points
Date : 2021-07-09 08:22 UTC (14 hours ago)
(HTM) web link (www.sciencemag.org)
(TXT) w3m dump (www.sciencemag.org)
| smusamashah wrote:
| Can it be used in reverse to keep the body heat in instead? If
| the body is producing the radiation, it should be usable in
| reverse.
| mark-r wrote:
| I think you just described a space blanket. In fact based on
| the title, I expected this to be one of those used backwards.
| Kichererbsen wrote:
| you mean like a woolen jumper?
| franferri wrote:
| BootStrap website really needs this in the documentation for its
| components
| amelius wrote:
| Can I put this around my CPU?
| rwmj wrote:
| In Japan they have these portable AC jackets. I believe they are
| mainly used by people working on building sites where it gets
| very hot in summer. While these are actively cooled rather than
| passively (as in the article), they seem like a better idea than
| air conditioning whole rooms.
|
| https://wonderfulengineering.com/japanese-invent-a-jacket-wi...
| https://www.dailymail.co.uk/sciencetech/article-2016513/Japa...
|
| (Sorry can't find any good links - the jackets aren't a fad and
| seem to be popular with builders)
|
| Edit: The company website (Japanese) https://kuchoufuku.com
| 123pie123 wrote:
| they have something like this but full body - for those people
| who wear the full body mascot outfits eg games/ Disney etc..
| LeoPanthera wrote:
| > they seem like a better idea than air conditioning whole
| rooms
|
| Is that really true? It's more efficient to cool larger rooms,
| because their surface area to the outside world is lower
| relative to the volume of the room.
|
| Keeping entire factories or warehouses cool uses surprisingly
| little energy. Once they reach the desired temperature they
| stay there with only minor additional cooling.
| bonzini wrote:
| House cooling doesn't really need A/C most of the time. Most
| countries in Europe and North America (exceptions are mostly
| Mediterranean countries) aren't even using blinds that
| prevent sunrays from reaching the glass of the windows.
| People are living in greenhouses, not houses, and the
| ridiculous part is that they are not even in there most of
| the time during the day, so the light is unused and the heat
| accumulates so much that you get home to an unbearable
| 30C/80F temperature.
|
| If the heat was kept out of the house properly during the
| day, you could just keep the house cool enough by opening the
| windows during the night, without any A/C at all.
| KingMachiavelli wrote:
| Most people do use blinds to keep the sun out but they are
| on the inside of the glass. Blinds on the inside of the
| glass are sufficient since we are only talking about
| blocking/reflecting infrared heat. In the US at least,
| modern windows in the last 20 years can have an inferred
| reflective coating meaning you don't need blinds at all.
|
| The big issue is humidity. Attic fans work great in low
| humidity places but by their nature they pull in exterior
| air. If it's 70F but very humid, then you will not have a
| great time opening windows even at night. The scenarios in
| which you don't need AC also work really well with AC; the
| efficiency (COPR) of a heat pump depends on the temperature
| difference that you pump heat across. If the exterior
| temperature is lower at night then the heat pump is going
| to have great efficiency anyway. Also AC has to condense
| water (cooler air holds less water), letting in (humid) air
| at night only to run AC during the day is not as efficient
| as looks.
|
| I big part of people saving money on cooling when using an
| attic fan or opening windows is they are probably also just
| letting the interior reach a higher temperature.
|
| To keep this somewhat on topic, in is more efficient for
| heat pumps to cool a room than to cool individual
| people/things inside that room _typically_ because when you
| are cooling the room you are moving the heat to the
| _outside_ of an insulated area.
| bonzini wrote:
| > Most people do use blinds to keep the sun out but they
| are on the inside of the glass.
|
| That's exactly my point, in Southern Europe blinds are on
| the outside of the glass, not inside. Reflective coating
| and insulating double glass is good but not the same as
| they're not 100% efficient (with outside blinds, they
| absorb the heat and insulating glass is very good at
| keeping conduction at bay).
|
| I can come home in the evening and barely notice the
| difference in temperature from when I left (25C-26C in
| the morning, 26C-27.5C in the evening, so about 1.5C
| difference); that's even with 33-36C highs outside. By
| 5PM it's possible to open blinds because I don't get
| direct sunlight anymore (my house faces South and East
| and has other buildings towards west), and I open the
| windows from 10PM till dawn at 5-6AM.
| olivermarks wrote:
| Air conditioning removes heat and moisture from indoor air,
| which has a big impact on your breathing comfort. This is
| very different to the cool suits racing drivers and others
| wear, who also have cooled breathing air piped into their
| helmets.
| clairity wrote:
| > "...they seem like a better idea than air conditioning whole
| rooms."
|
| in the same vein, most people's behavior around heating/cooling
| is comically misguided and inefficient. most people believe
| temperature is what we're trying to control, and that's driven
| by how weather reports, climate controls, and even our language
| ("it's hot!") emphasize temperature (which isn't nefarious, and
| makes sense in their separate, respective domains) rather than
| heat transfer, which is what we're really after.
|
| this is most evident in cars, where folks point air vents away
| from themselves while running the a/c (or heat) full blast,
| rather than pointing the vents at themselves and running at a
| lower speed. the former is based on the idea that the whole
| car's interior temperature needs to be lowered (or raised) for
| effective heat transfer away from (or to) the body, which is
| incorrect and inefficient. pointing the vents at you (on bare
| skin ideally) promotes heat transfer immediately instead of
| waiting to create a big enough temperature differential to do
| the same work.
| robscallsign wrote:
| Your pithy analysis seems to entirely discount having
| passengers in the back seat, or multiple rows of seating like
| minivans.
| Broken_Hippo wrote:
| You can point them at you if you only have front seat
| passengers - if that is comfortable for you. If you have
| folks in the back seat or want to keep your groceries
| coolish, whole cabin cooling is much better.
| cjohansson wrote:
| I think what is evident for all parents is the importance of
| cooling down the entire car, not just the driver or front
| passenger but all kids in the back, sometimes with a lot of
| stuff in the way of the vents
| dan_quixote wrote:
| If the vehicle's air conditioner compressor only runs at one
| stage, does it even matter? Are there any automotive air
| compressors with multiple stages/speeds?
| Unklejoe wrote:
| I suspect they use something like a TXV (thermostatic
| expansion valve) that is found on newer household AC units.
|
| This acts as sort of a regulator for the system, which
| ultimately ends up reducing the load on the compressor as
| the evaporator is colder.
|
| So while the compressor runs at one stage in the sense of
| it being directly driven by the engine, the resistance to
| spin the compressor varies based on the load of the AC
| system.
| clairity wrote:
| that's valid, but even then, there's also the efficiency of
| whisking away heat from your body to consider, which is the
| more direct/relevant efficiency concern here.
| throwaway284534 wrote:
| Personally I don't enjoy the sensation of the air blowing
| against my skin. It's distracting and usually moves my hair
| around when I'm trying to focus on the road.
| kebman wrote:
| I think you're giving them too little credit. I'd rather have
| even and comfortable warmth through-out the cabin, than
| having to sit in front of a hot draft the entire ride,
| despite what might be more effective. That is a matter of
| comfort, and not physics.
| echlebek wrote:
| People sit in the back seat of cars too.
| wolverine876 wrote:
| I could not agree more: People don't wear insulation (e.g.,
| sweaters) in winter, the heat escapes from their body, and
| then they heat the entire house/office in order to warm
| themselves up again. You already have the heat! It's getting
| away!
|
| Summer has similar situations. Point a small fan at yourself
| and you can save a lot on cooling the entire unit. A fan is
| blowing a gentle breeze across my hands right now (tip: aim
| it across the keyboard; it cools the laptop and you, and it
| doesn't dehydrate me). As long as the ambient temperature is
| below about 85, I'm fine. Think of it: 80 degrees, in the
| shade, with a breeze. That's pretty nice.
| ARandomerDude wrote:
| I use a 3-step approach: point the vents at me while I'm very
| warm, then away from me when I start to get comfortable. If I
| actually get cold, I then turn the blower speed down.
| porphyra wrote:
| But having the whole cabin be at a cooler temperature allows
| the heat transfer to happen uniformly across your whole body,
| which is a lot more comfortable than having a vent pointed at
| yourself.
| easygenes wrote:
| I find having a vent on my hands or face MUCH more
| comfortable. I've lived in some of the hottest places on
| earth and indeed on the worst days there would never be a
| point where you'd feel cool enough without blowing the
| vents directly at you. Even in more temperate climates the
| airflow over my face is just refreshing, and helps keep my
| hands completely dry for a better grip.
| IgorPartola wrote:
| That's because you have good blood circulation. Blood
| acts as your body's coolant and transfers heat to your
| hands. Lots of people don't have this so what they would
| get is the sensation of being very hot except their hands
| which will get very cold. Not a pleasant combo.
| comex wrote:
| > I've lived in some of the hottest places on earth and
| indeed on the worst days there would never be a point
| where you'd feel cool enough without blowing the vents
| directly at you.
|
| Surely if an air conditioner brings an indoor area to a
| given temperature (and humidity), it doesn't matter what
| the temperature is outside. So what gives? Is the air
| conditioner not powerful enough? Do people not want the
| inside to be as cold as in other locales, since they're
| used to the heat? The latter would make sense, but then I
| don't understand why you'd need to be blowing the vents
| directly at you.
| clairity wrote:
| no, that's just rationalizing. you're sitting uncomfortably
| for 10-15 minutes waiting for that temperature to be
| reached[0], and even then, heat transfer is maximized by
| having the air flow over you. the edge case might be when
| there are like 4+ people in a car for which there are not
| enough vents, but even then, pointing the vents at people,
| even somewhat indirectly, is better.
|
| heat transfer is what makes you feel cool/warm, _not
| temperature_ , and air flow promotes convection (as well as
| conduction). it's why metal feels cooler (or warmer) than
| plastic at the same temperature (e.g., differing heat
| transfer coefficients).
|
| [0]: note that most car trips are less than ~15 minutes, at
| which point, all that heating/cooling is wasted as you
| flush it out the door.
| chmod600 wrote:
| You are arguing too technically here. How people feel and
| what they like is very subjective. If people don't like
| air blowing unnaturally at them, no amount of arguing
| will change that.
| clairity wrote:
| you're implying that there is something incorrigible
| about such feelings, and that it's useless to point out
| other, objective factors that can impact decision-making
| (and habits). if that were true, we'd be a way more
| predictable, and boring, species than we are.
| drdeca wrote:
| I don't think they are implying that. If someone's
| preferences are based on metric A, and another method
| provides better results with regards to metric B, even if
| metrics A and B are correlated, this needn't be a reason
| for the person to prefer the proposed alternate method,
| because the current method may still provide results with
| regards to metric A.
|
| Telling someone that tomato is a more vibrant red than
| chicken, will not compel them to prefer the taste of a
| tomato to the taste of chicken. (In this example the
| "correlation" bit doesn't apply, but, whatever.)
| wvenable wrote:
| The purpose of air conditioning in comfort -- so arguing
| that people can make themselves slightly less comfortable
| by doing something different is moot. It's even more
| energy efficient to not run the AC at all so why argue
| about vent position?
| nicoburns wrote:
| > note that most car trips are less than ~15 minutes, at
| which point, all that heating/cooling is wasted as you
| flush it out the door.
|
| Talking about energy efficiency: if your car trip is <15
| minutes, then ideally you shouldn't be using a car at
| all!
| lotsofpulp wrote:
| In the US, that frequently involves crossing 6 to 8 lane
| roads with 40mph+ speed limits, and 200ft setbacks to
| allow for huge parking lots. Or an actual highway where
| only motorized vehicles are allowed.
| clairity wrote:
| if only we could collectively realize this and
| reconfigure our urban spaces according to that
| consideration! for instance, adding many, many more
| street trees everywhere, replacing street parking with
| protected bike lanes, and converting a lane on major
| streets to dedicated bus lanes with synchronized/sensored
| lights.
|
| but yes, for those majority short trips, the wind in your
| hair on a (electric) bike/scooter is likely just as
| cooling, and the trip likely no longer.
| oblib wrote:
| > Talking about energy efficiency: if your car trip is
| <15 minutes, then ideally you shouldn't be using a car at
| all!
|
| That depends on where you live. It take me about 5-7
| minutes to drive to the nearest store (a "Dollar General"
| store). That store is about 2.5 miles away, so about a 5
| mile round trip. Average walking speed is about 3.2 mph,
| so a +2 hour trip walking it.
|
| The next nearest store is about 10-12 miles away (a
| grocery store). Most of those miles are on a road with a
| 55mph limit but these are curvy hilly roads so probably
| closer to a 40-45 mph average. That's a +6 hour walk.
|
| Riding a bicycle is akin to death wish on those 2 lane
| roads with no shoulder.
| nicoburns wrote:
| > It take me about 5-7 minutes to drive to the nearest
| store (a "Dollar General" store)
|
| Assuming you live in an urban area, this seem like
| absolute madness to me. Does this not represent a huge
| opportunity for someone to start a local grocery store
| business?
|
| I have never lived further than 15 minutes walk to the
| local grocery store (and I considered that a pretty
| inconvenient location). Where I live now I have a 2 local
| shops ~1 minute walk away, with a small high street with
| a small supermarket ~10 minutes walk away. And I would
| say this is pretty typical across the entirety of
| urban/suburban UK.
| kube-system wrote:
| US post-war neighborhoods built after the advent of cars,
| were mostly designed for them. It's not madness, as much
| as it is the inevitable result of consumer demands for
| what was at the time, new housing.
|
| > Does this not represent a huge opportunity for someone
| to start a local grocery store business?
|
| Those stores do mostly exist where they are viable. The
| limiting factors are:
|
| 1. many of those neighborhoods don't have commercial
| space, and are filled with people who live there
| specifically because they do not want to live by
| commercial property, and support zoning regulations to
| keep grocery stores from being built besides their
| property.
|
| 2. because many people do have cars, neighborhood grocery
| stores are sometimes at a commercial disadvantage,
| because many of their potential customers can easily
| drive to stores with greater selection.
|
| I do like living in more lively neighborhoods, and I
| picked one where I do have two small grocery stores
| within 15 minutes walking distance. The thing is, they're
| both ethnic grocery stores with limited selections. I try
| to support them when I can but to get everything that I
| want to buy in one shopping trip, it's much quicker and
| easier to drive out of my neighborhood to a much larger
| store.
| ajuc wrote:
| This sounds so weird. Like a place that has no general
| store in walking distance implies end of the world but
| then you say it has bad traffic too. And 2-lane road with
| no shoulder implies it's not a highway in the middle of
| nowhere but a place where people live. Why has nobody
| opened a shop closer? Seems like easy money.
| URSpider94 wrote:
| He didn't say it has bad traffic, he said it's dangerous.
| I grew up in a place like this - isolated houses along a
| 2-lane road through the countryside with no shoulder.
| It's a local road, but the speed limit is typically 55
| mph because the housing density is very low. There's not
| much traffic, but the traffic that is there is flying
| down the curvy road just trying to hang on. All of the
| stores are centralized in small towns and villages spaced
| 20 miles apart or so.
| ajuc wrote:
| Yeah I just have no reference. Here villages spaced 30 km
| from each other doesn't happen. It's usually walking
| distance.
| crooked-v wrote:
| To get a better idea of that sort of context, look at
| Texas or Montana in Google Maps and zoom in on one of the
| low-population areas. You'll see plenty of little towns
| with no public transit that would be literally days away
| from each other if walking.
| [deleted]
| rpenm wrote:
| Likely restrictive zoning. In much of North America,
| commercial and mixed-use buildings are not permitted in
| areas zoned for single-family residences.
| Tarsul wrote:
| I wonder how improved traffic could be if we somehow had
| managed that people driving alone would be driving in a
| vehicle that is suited for exactly 1 person. (although
| now I'm having pictures in my head of the insane traffic
| in India's cities... :))
|
| Maybe electric vehicles could be an incentive to downsize
| vehicles?
| clairity wrote:
| for sure. on top of energy taxes, we could assess
| escalating maintenance fees on cars by size and weight,
| to encourage right-sized vehicles, especially in metro
| areas where it really matters.
| conk wrote:
| There are several studies on the relationship between
| vehicle weight and road wear and tear. 1 fully loaded
| semi does more damage than nearly 10,000 cars. The
| reality is if costs were assigned appropriately large
| aspects of life would become unworkable.
| datameta wrote:
| One method optimizes for energy efficiency and the other
| for comfort.
|
| This material is a passive method that I think rather soon
| recoups any extra energy expended during manufacturing.
| klysm wrote:
| I think people absolutely understand that pointing the vent
| at their face will cool them faster. The problem is it's not
| uniform and uncomfortable to have your left mid arm freezing
| while the rest of you is hot.
| clairity wrote:
| sure, but that's why there are multiple vents? and you can
| run the a/c at a lower speed to boot.
| usefulcat wrote:
| Two cold spots are not better than one. If you're
| claiming that the approach you describe is more
| efficient, then I agree with you. But for me the 'vents
| pointed away' approach is still subjectively more
| comfortable, though it does take longer.
| clairity wrote:
| there are controls for both speed and temperature, as
| well as vent direction. it's not difficult to find a
| comfortable combination.
| sedatk wrote:
| Basically, any fan/temp setting with vents directed at
| you either feels too uncomfortable or not cooling enough
| due to the direct impact. It's easier to fine tune
| ambient cooling with vents directed away from you. I
| wonder how these jackets work in that regard.
| [deleted]
| MetaWhirledPeas wrote:
| I understand what you're getting at, but having 1-4 vents
| pointed at the front of your body is _not_ the same as
| having the cabin air at a particular temperature. Neither
| is having air blowing on your front side the same as
| having air swirling about your entire body.
| wolverine876 wrote:
| That is a problem that people can solve if they want to.
| But if you insist that you need help: I find that aiming
| fans across extremities, arms/hands and legs, is very
| pleasant and effective (a higher surface area : volume
| ratio?).
| IgorPartola wrote:
| God this is such an engineer response. Yes every body is
| the same and everyone should always do the most optimal
| thing regardless of the actual outcome or goal.
|
| Some people have poor blood circulation. Pointing a small
| fast fan at their arms will not cool their core.
|
| Some people get dry eyes easily. Pointing a fan at their
| face will make them extremely uncomfortable.
|
| Some people are extremely sensitive to temperature
| changes. They don't want to be hot but pointing a 40
| degree F stream of air at their chest will give them
| physical pain.
|
| No, this isn't a one size fits all problem/solution. The
| correct solution is actually to cool the whole car while
| allowing the user control over how to cool themselves by
| adjusting the fans/doors. It would be much better however
| if car manufacturers included better PID controllers as
| well as moisture sensors inside and outside the cabin to
| create better climate control. In a car that really
| shouldn't be difficult, at least with the windows closed.
| It's not like a house with multiple rooms that have
| different exposure to heating and cooling as well as
| sunlight.
| bootlooped wrote:
| Ever since I got lasik my eyes get dry and uncomfortable if I
| have dry air moving over my face for too long. This is what
| happens if the vent is pointed anywhere around my upper body
| sadly.
| tqi wrote:
| You really think people point vents away from themselves
| because they don't understand how heat transfer works, rather
| than because they dislike having the air blowing directly on
| them?
| droopyEyelids wrote:
| Not many people know it, but blasting detainees with air
| conditioning for prolonged periods is one of the Enhanced
| Interrogation techniques we use on detainees in Guantanamo
| Bay
| [deleted]
| oseityphelysiol wrote:
| Also, a ridiculous review of these by AvE (a channel I
| recommend to anyone who's mechanically inclined):
| https://youtu.be/ySw0IHIwQ3s
| btbuildem wrote:
| Wow, I find his manner so disagreeable.
| ansible wrote:
| He affects an overly exaggerated Canukistan patois that I
| find endlessly amusing, but I can see why it would grate on
| others.
|
| Some of the other "vidjaeos" are quite interesting when he
| is tearing down power tools to see how well they are
| constructed, and which ones are really worth the money.
| SamBam wrote:
| Agreed. Quite a bit of casual racism, among other things.
| ansible wrote:
| If you're just going by that video, I can see why you
| might think so.
|
| But he has a lot of respect for Japanese products in
| general, because they are well engineered and
| manufactured. And a lot of the stuff for sale these days
| in Norte America is very cheaply made, and he really
| doesn't like that.
| CharlesW wrote:
| > _If you 're just going by that video, I can see why you
| might think so._
|
| That video isn't unique in that way. I do enjoy his
| channel, but he's not afraid to let his racist/sexist
| flag fly.
| ansible wrote:
| Now you're making me question how much I should tolerate
| that sort of thing. Where is the line between "he's just
| joking around, he's not really serious" vs. "deep down he
| really believes this". Am I just too complacent? I'll
| have to think about that.
| cecilpl2 wrote:
| People who don't believe those kinds of thing deep down
| tend not to make jokes like that.
| CharlesW wrote:
| Same! If you figure it it, please let me know.
| ciupicri wrote:
| There are also cooling vests packed with ice or other
| substances e.g. PureTemp from Glacier Tek [1], although I
| wonder how good are these compared to the traditional ice.
|
| [1]: https://glaciertek.com/
| fy20 wrote:
| It looks like it's more of an air "cooler" than an air
| conditioner. It probably works somewhat depending on the
| climate, but air conditioning actively cools the air (it
| produces colder air than the exterior air temperature) and
| reduces humidity.
| rwmj wrote:
| This page explains (not very clearly) how it works:
| https://kuchoufuku.com/?mode=f1
| Aachen wrote:
| (In Japanese)
| SapporoChris wrote:
| I have seen these and pondered if it is rude to wear them.
| While it is actively cooling your body, you are aggressively
| blowing your heat to those around you. In a crowded subway
| train I would not want to be next to someone wearing this.
| However, perhaps I overestimate their effects.
| ezconnect wrote:
| They are usually worn by workers with long sleeve jacket
| uniforms. They need to cool down during summer when it gets
| really hot and they need to wear their uniforms. Ordinary
| people do wear them and remove the sleeves and they are not
| that loud. You wont even notice them unless you see the fan.
| The DIY jackets with fan are the loud one, I've seen a couple
| them.
| fpoling wrote:
| While it does not actively cool your body, it transfers the
| heat to any surface that absorbs MIR. So in a crowded space
| the wearer will indeed dump the heat on other people.
| kalleboo wrote:
| I've only seen these in use by construction workers and
| parcel delivery/mail people
| manwe150 wrote:
| I wonder if that would be true at steady-state (e.g. when the
| train is effectively empty), but for a train at rush hour,
| whether much of the capacity of the AC system is already
| being used to remove heat generated from the humans, and if
| that means the temperature difference to the outside is
| actually mostly unimportant.
|
| That is to say, the person next to you is generating and
| dissipating a fixed rate of heating onto you (equal to their
| basal metabolic rate consumption), so all that the jacket can
| have changed is their steady-state perception of the local
| temperature.
| teruakohatu wrote:
| They appear to just circulate air around the body, which
| makes sweat evaporate cooling the body. If they were actual
| air conditioners they would be indeed moving heat from the
| body into the surrounding air.
|
| Edit: to be clear I am not suggesting heat/energy disappears.
| In this case they are cooling the air and the body using
| evaporation. The system appears to suck in hot air on one
| side and ejects cooler humid air on the other. More or less
| human swamp coolers.
|
| https://en.m.wikipedia.org/wiki/Evaporative_cooler#Physical_.
| ..
| noctune wrote:
| It's the same dilemma though. Now you are raising the
| humidity around you, making other peoples' sweat less
| effective at cooling them.
|
| Although lowering humidity can be more easily done with
| just ventilation.
| rini17 wrote:
| Only in poorly ventilated enclosed spaces. But the sweat
| usually gets evaporated anyway only slower.
|
| And when they are used outside, the added humidity is
| negligible compared to volume of surrounding air.
| usrusr wrote:
| Not really, because the body self-regulates temperature
| by pushing out as much sweat as it needs to reach target
| temperature. A tool that facilitates evaporation allows
| the body to get by with less sweating. The amount
| evaporated will be the same, but the carrier won't be
| drenched. (PS: roughly the same, additional heat
| transfered from air to dry skin will need to be shed by
| sweating, but I doubt that this would make much
| difference compared to all the watts resulting from
| metabolistic base load, even in absence of physical
| activity)
|
| Mandatory slightly related anecdote: on a summer drive
| through Morocco back when car air conditioners where a
| thing exclusive to America and the one percent I never
| felt sweaty as long as the car was moving.
| treeman79 wrote:
| A few years ago I stopped sweating, almost completely.
| Trying to cool off is nearly impossible now.
|
| I have an ice vest if I really want to go outside for
| then a few minutes.
|
| Mirror clothing sounds like a dream.
| bin_bash wrote:
| Yeah I rarely ever feel sweat on my body when I run. It's
| when I _stop_ running that I get drenched and need to put
| a headband on.
|
| (I live in a dry climate and generally don't sweat much
| anyways, YMMV)
| easygenes wrote:
| Evaporative cooling also moves heat from the body into the
| surrounding air, just encapsulated in water droplets.
| rwmj wrote:
| Isn't that just the same thing, but using a natural process
| (sweating) rather than phase change in a refrigerant?
| louthy wrote:
| Evaporated sweat only cools the body if it leaves the area
| where the body is. So presumably they would be radiating
| warm air away from them.
| contravariant wrote:
| Not necessarily, they might just be radiating humid air.
| It's the evaporation itself that leads to the cooling.
| Razengan wrote:
| Hey as long as I feel cool and look cool I don't care
| what it does.
| gruez wrote:
| But the humid air makes it harder for people around you
| to cool evaporatively (eg. sweating)
| contravariant wrote:
| Well yes, you must (irreversibly) increase entropy
| somehow. The air itself won't be warmer though.
| StrictDabbler wrote:
| This is why we have wet and dry bulb temperatures.
|
| Your intuition about temperature is focused on the dry-
| bulb temperature that a simple probe gives you.
|
| A wet-bulb is literally a probe with a wet cloth or
| tissue around it.
|
| As the humidity in the air increases the wet-bulb
| temperature approaches the dry bulb temperature.
|
| This is absolutely "warming". The latent heat of the air
| increases. The sensible heat remains the same.
| Retric wrote:
| Without the jacket the person will emit the same heat.
| The jacket fans do generate a trivial amount of heat, but
| it's likely less than a desktop fan.
| gmadsen wrote:
| ventilation is a lot cheaper than AC though
| faeyanpiraat wrote:
| So heat goes poof?
| deregulateMed wrote:
| I can't remember the exact situation, but it's better to keep a
| gigantic house at temperature than to let it get far out of
| temperature only to be recooled.
|
| With something like this you'd need near constant cooling.
| Although still you are only cooling a small volume, so it could
| be better.
| rwmj wrote:
| These jackets are powered for hours from a rechargeable
| battery about as big as a fist. I don't know of any house-
| sized AC unit that could run from such a battery for more
| than a few seconds. So that doesn't make intuitive sense.
| tzs wrote:
| I find that a bit hard to believe.
|
| The rate of heat flow across an insulator is proportional to
| the temperature difference across the insulator, if I recall
| correctly.
|
| Suppose you want the inside of you house to be at temperature
| Tin when occupied and the temperature outside is Tout.
|
| The rate of heat flow across the boundary between inside and
| outside will be k|Tin-Tout|.
|
| Imagine two identical houses.
|
| In house #1 we keep it at a constant Tin. In house #2 we keep
| it at Tin while occupied but when empty we let it move toward
| Tout, turning on heating or cooling when it is going to be
| occupied again to get it back to Tin when the people return.
|
| For each house, if we plot |Tin-Tout| over time, the total
| energy used over a given interval will be proportional to the
| area under that |Tin-Tout| curve.
|
| For house #1, that curve is simply a horizontal straight
| line.
|
| For house #2, that curve matches the curve of #1 while the
| house is occupied, but during the unoccupied times falls
| toward zero until it is time to get it back to Tin in
| anticipation of people returning home. It then rises back up
| to Tin.
|
| The area under house #2's curve will be less than the area
| under house #1's curve.
|
| Thus, in terms of energy required to produce the desired
| temperature curve, house #2 uses less than house #1.
|
| There are inefficiencies in producing and applying that
| energy, though, and so getting a given amount of energy
| applied to heating or cooling the house from your heating or
| cooling system will take more energy, and that extra energy
| might depend on Tin or Tout, so it is possible that this
| might be a big enough effect to counter the savings from
| letting the unoccupied temperature move toward Tout.
| codingdave wrote:
| Much of the energy drain when heating/cooling a home is the
| fan to blow the air. These days, keeping the fan running is
| quite efficient. Turning it off, then putting in a large
| draw to get it moving again is expensive.
|
| So at least part of the efficiency comes from not
| restarting the fan repeatedly.
| pjerem wrote:
| What fan are you talking about ?
| dTal wrote:
| This is wrong on several levels. The energy expended by a
| fan is proportional to the mass flow. The energy required
| to accelerate the rotor is negligible compared to the
| ongoing energy required to keep it turning and doing
| work. Also, I'm pretty sure that the energy use of the
| fan is itself negligible compared to the heat pump.
| codingdave wrote:
| Hm - everything people are saying makes sense. I was
| repeating what I've been told by literally every HVAC guy
| I've had work on multiple houses over the last 10+ years.
| If the professionals are all wrong, I suppose it could
| just be one of those tropes that persists in an industry?
| Johnny555 wrote:
| My furnace has an 80,000 BTU burner (equivalent to 23,000
| watts), and a 1/2 horsepower blower, which would use
| around 600W.
|
| So the blower uses less than 3% of the energy used by the
| burner. Some of the waste heat from the blower motor
| probably helps heat the home, so in reality it's probably
| less than that.
|
| While startup current is significant (for a very short
| time), starting the fan up in the morning and again in
| the evening after work doesn't add that much to the total
| power drain, or even cycling it on/off a few times an
| hour to maintain temperature. Starting wattage on that
| motor is around 1800W, but only lasts for a few seconds.
| deregulateMed wrote:
| Isn't it harder to heat 32 degree air 1 degree than heat 70
| degree air?
|
| This was my 400 level thermo 2 class, we calculated
| everything, inefficiency, convection, conduction.
| aw1621107 wrote:
| > Isn't it harder to heat 32 degree air 1 degree than
| heat 70 degree air?
|
| From a pure heat capacity viewpoint, heating cooler air
| is very slightly easier (on the order of a few
| thousandths at most for realistic temperatures) [0].
| Don't think it'll be noticeable for the average heating
| system, though.
|
| > we calculated everything, inefficiency, convection,
| conduction.
|
| I'd be curious to how those calculations affect things.
| If the heating element is the same temperature, I'd think
| heating cooler air would be faster because heat
| conduction is faster across a larger temperature
| differential and you'd get "faster" convective mixing for
| air with bigger temperature differences. Have to admit
| I'm not sure what inefficiencies might come into play,
| and I haven't taken classes at that level so I wouldn't
| be surprised if I missed something.
|
| [0]: https://www.engineeringtoolbox.com/air-specific-
| heat-capacit...
| deregulateMed wrote:
| I could not find the problem I was referencing. I'm
| either wrong, or the problem wasn't in the book and was
| in the professors notes. I'm leaning on the later, but
| unless I reply with something else, assume I'm wrong.
| aw1621107 wrote:
| Sorry to hear that you couldn't find the problem. Was
| hoping that I'd get to learn something new
| Aachen wrote:
| That sounds like a convenient thing to believe, similar to
| family telling me to just leave the heater on all day on a
| base level heat to supposedly save energy because it doesn't
| have to do a lot of heating when I come home from work. But,
| obviously, a lower temperature differential between inside
| and outside is going to lose less heat/cold, so unless the
| heater/AC is more efficient at lower power levels (they're
| not) it cannot possibly make sense to leave the heater/AC on
| when you're not making use of it to save energy. Sure it'll
| have to work harder when you get home, but that's better than
| it trying to maintain that temperature all the time. I guess
| people want to believe this though because you'll have a
| higher thermal comfort if you don't come home to a hot/cold
| house.
| manwe150 wrote:
| I tried to find the source for this claim too in the past.
| The nearest I can find is that it implies the HVAC system
| is sized correctly: if the system is optimally sized, it
| should need to run most of the time to stay at the desired
| temperature. If it changes the temperature too fast, then
| it may end up with wild temperature swings that overshoot
| the desired comfort level and waste energy that way. In
| certain situations, with good insulation and building
| design, this waste can apparently exceed the savings from a
| few percent lower degrees for part of the day. If I
| understand correctly, this is a bigger problem for heat
| pumps that take a long time to spool up/down so simple
| bang-bang hysteresis control has poor performance in this
| scenario.
|
| Edit: as another poster mentioned, for heat pumps (like AC,
| but frequently not furnaces), it is also much more
| efficient to run them when it is cool outside (the
| morning), and then maintain that temperature through the
| day as a cold reservoir, than to try to expel the heat when
| it is hot outside. Which is probably a better explanation
| for the effect.
| lotsofpulp wrote:
| This seems like it would heavily depend on how well insulated
| the house is, and for how long it will be unoccupied.
|
| Based on my experience with most houses' insulation,
| especially bigger ones, I cannot imagine it being economical
| to cool it for 8+ hours when no one is there (for work and
| school), rather than letting it warm and then starting the AC
| 30min before people start coming back home.
| deregulateMed wrote:
| I remember this problem being absurd, like bigger than a
| mansion.
|
| Gosh I wish I could find it. I've referenced this problem a
| few times, I need to find it. I might have the book, if I
| can find it I'll update this post.
| deregulateMed wrote:
| I could not find the example problem I was referencing in
| my textbook, consider me either incorrect or ambiguous
| until I do. I'm going to look through my notes next. I
| believe it was a problem from my professor.
| rootusrootus wrote:
| The short answer is that you should keep the house
| relatively cool, but maybe above your comfort level while
| you're not there, and well insulated. The details of when
| it's best to run the AC for maximum efficiency pales in
| comparison.
|
| The AC will be more efficient in the morning, for one, than
| during the heat of the day. And if you let the entire house
| get truly hot inside, it will take a lot longer than 30
| minutes to bring the temperature down (it's not just air
| that has to get cool, it's all the solid objects as well).
| And when it's fairly hot outside, it may not actually be
| possible to get it cooled down if you wait until the heat
| of the day. E.g. my AC will keep my house at 70F when the
| temperature outside is over 110F, but if I let it drift up
| to 80F inside and then try to bring it down to 70F in the
| mid-afternoon, it won't get any lower than maybe 75F until
| the ambient temperature outside drops into the 90s.
| Retric wrote:
| The same effect works in reverse though, maintaining
| temperature through the heat of the day is wasteful if
| the temperature drops before you get home. If you're
| dealing with significant solar gain then running a fan
| before turning on the AC becomes even more efficient.
| starlust2 wrote:
| Only if it's already cooler outside than inside the
| house. On a day where it's only 90 out during the day,
| it's not dropping to 75 until 8-9pm at the earliest.
|
| Also can't use a fan on the west coast in the later parts
| of the summer when the air is full of wildfire smoke.
| Retric wrote:
| An example of significant solar gain would be a car
| sitting outside in sunlight. A surprising amount of
| modern architecture would work just fine as a greenhouse.
| Assuming a 9 hour workday it's going to get well above
| ambient before you get home.
| dragontamer wrote:
| The only device that gets that small is a Peltier cooler, and
| those have far less efficiency than a proper Air Conditioner /
| Refrigerant based pump.
|
| You can experiment with Peltiers yourself: they're widely
| available on Digikey and are extremely small and effective at
| "air conditioning" like tasks (moving heat to the hot side,
| while cooling the cold side).
|
| But due to their lack of efficiency, they can never properly
| compete against a large scale central air conditioner: be it a
| proper dehumidifier, refrigerator, or actual AC / HVAC unit.
|
| -------
|
| A 100W Peltier might be able to move 50W (meaning the hot-side
| is 150W of heat, while the cold side is -50W of cooling).
| Perfect efficiency (50W heat hot side / -50W of cooling cold
| side) is impossible, much like perpetual motion machines.
|
| In contrast, a proper air conditioner might be closer to 100W
| of power delivering 300W of cooling (Emit 400W of heat on the
| hot side, and provide -300W cooling on the cold side).
|
| Furthermore, the temperature difference from a Peltier is
| small, maybe 10C or 20C (and the bigger the delta, the less
| efficient a Peltier gets). A proper compressor / refrigerator
| can handle much larger temperature differences at much higher
| efficiency.
|
| -------
|
| So the key for Peltier is to find low temperature differences
| (maybe keep it to 10C to minimize the efficiency loss), at low-
| wattages (so that the inefficiency won't generate too much
| heat). Maybe 10W to provide -5W of cooling (cold side) and 15W
| of heating (hot side) which won't raise the temperature of the
| room too much, and still provide some degree of comfort to the
| people wearing the jacket.
|
| But its clear to me that "air conditioning" is one of those
| "bigger is better" deals. You'd rather more centralize the hot-
| side vs cold-side (ex: make sure the hot side is outside,
| rather than having many hot-sides inside fighting each other,
| raising the temperature of the room you're working in)
| f6v wrote:
| Is that shirt effective when it's 40 degrees outside? I have
| noticed that the fan stops working for me after certain
| temperature.
| [deleted]
| cghendrix wrote:
| Funny seeing all of the comments span multiple years asking to
| buy or distribute this product.
| Tepix wrote:
| The headline is somewhat inaccurate, the fabric reduces the
| heating by the sun by 5degC, which is still useful of course.
| tmvphil wrote:
| I'm not sure about this particular fabric, but there are
| materials which will reduce temperature below ambient (i.e.
| below air temperature), not just reduce radiative heating from
| the sun. You do this by exploiting the "cold resource" of
| space! See
| https://advances.sciencemag.org/content/5/10/eaat9480?intcmp...
| dwighttk wrote:
| Wonder how it holds up to laundering/drying.
|
| Remember those shirts that changed color based on temperature but
| couldn't be put in the dryer?
| jeffkeen wrote:
| Hypercolor! God yeah I remember those. I wanted one so badly
| when I was a kid but it never happened.
| dwighttk wrote:
| I listened to a podcast about their history... didn't realize
| the fad didn't last more than a year:
|
| https://www.omnibusproject.com/42
| lurtbancaster wrote:
| Honestly, you shouldn't have to wonder. The article is of poor
| quality. Given the concerns regarding microplastics release
| from the fabrics we wear causing environmental pollution in
| recent years, it would behoove any respectable science
| journalist/publication to press for answers to these "common
| sense" questions.
|
| Especially when they also seem so eager to mention
|
| >"Ma and Tao are now reaching out to textile manufacturers and
| clothing companies to try to get their fabric on shelves. They
| say the nanomaterial-infused fabric should add only about 10%
| to typical clothing manufacturing costs. "We can make it with
| mass production, which means everybody can get a T-shirt ...
| and the cost is basically the same as their old stuff," Ma
| says. "It can benefit everybody.""
|
| Sure...and that's why stuff like PVC - one of the worst
| offenders of releasing microplastics into the water when washed
| - which was previously only used sparingly by professionals
| because human life depended on their using it but has sadly now
| come to be worn by a lot more people as a "fashion piece" way
| more frequently.
|
| The full paper appears to be paywalled?
| https://science.sciencemag.org/content/early/2021/07/07/scie...
| . Here's the Abstract - "Incorporating passive radiative
| cooling structures into personal thermal management
| technologies could effectively defend human against the
| intensifying global climate change. We show that large scale
| woven metafabrics can provide high emissivity (94.5%) in the
| atmospheric window and reflectivity (92.4%) in the solar
| spectrum because the hierarchical-morphology design of the
| randomly dispersed scatterers throughout the metafabric.
| Through scalable industrial textile manufacturing routes, our
| metafabrics exhibit excellent mechanical strength,
| waterproofness, and breathability for commercial clothing while
| maintaining efficient radiative cooling ability. Practical
| application tests demonstrated the human body covered by our
| metafabric could be cooled down ~4.8degC lower than that
| covered by commercial cotton fabric. The cost-effectiveness and
| high-performance of our metafabrics present great advantages
| for intelligent garments, smart textiles, and passive radiative
| cooling applications."
|
| Again, no mention of environmental impact.
|
| Also I don't know if this common is material sciences or not,
| so bear that in mind; but that Abstract reads like a pitch to
| VC firms to fund their startup. Am I wrong?
| elric wrote:
| Or those coats coated in water-repellant stuff .. which washes
| off and is apparently rather toxic.
| thebean11 wrote:
| Can't you just spray that stuff on anything? I've seen it
| sold for hats and shoes
| leke wrote:
| I need a pair of boxers made from this stuff.
| giantg2 wrote:
| I can honestly say this is the most exciting article I've read in
| a long time. Can't wait for this to be commercially available.
| irjustin wrote:
| Okay heat map is cool, but what does it look like? any different?
|
| Also how does it breath? Natural cotton shirts still feel the
| best to me. I hate Rayon.
|
| I'm interested in this because I currently live in Singapore
| where it's sunny, annoyingly hot and humid all year round. I'd
| welcome something like this when I'm outdoors.
|
| Just too light on the details.
| TaylorAlexander wrote:
| Yeah the lack of even a regular color photo is weird.
| afterburner wrote:
| One thing I noticed is that their control was a cotton shirt
| "about the same thickness" as the new one. But the new shirt is
| "550 micrometers" thick, which is about twice as thick as a
| regular T-shirt. So maybe they're tilting the scales a bit to
| make the cooling effect seem a little better?
| cptskippy wrote:
| What constitutes a "regular T-shirt"?
|
| I have t-shirts that are quite thin, but I also have t-shirts
| that are quite thick. Both I would consider regular t-shirts.
|
| At least for me, undershirts and blended material t-shirts
| tend to be on the thinner side while graphic t-shirts are
| usually heavier.
|
| I also have some t-shirts that are ridiculously thin that I
| think are mostly synthetics but there's no tag so I'm unsure.
| rob74 wrote:
| Unfortunately this new fabric only helps with the "sunny" part
| (it keeps you cooler when you are exposed to direct sunlight),
| but not with the "hot" and "humid" part...
| Cthulhu_ wrote:
| If it can more effectively radiate body heat away from you it
| would be somewhat effective. Plus, radiant heat doesn't have
| to be from direct sunlight.
| gattilorenz wrote:
| Looking at the pictures in the scientific article it doesn't
| look particularly weird, just a white cloth:
| https://science.sciencemag.org/content/early/2021/07/07/scie...
| bruce343434 wrote:
| You link to what I assumed to be a picture, got a paywall
| instead.
| gattilorenz wrote:
| Sorry, being under the IP address of a university removes a
| lot of paywalls :)
|
| Here's the images from that article https://ibb.co/1fBT3RZ
| https://ibb.co/tQRVqS2
| bruce343434 wrote:
| thanks!
| a_f wrote:
| Cool. I wonder if you could turn it inside out, such that
| it dumps heat inwards to have the opposite effect and
| warm you?
| ars wrote:
| It probably reflects sunlight, not heat. So unless you
| shine very brightly it won't work in reverse :)
| enjikaka wrote:
| Or just use linnen...
| bamboozled wrote:
| How does linnen compare to this at all?
| elric wrote:
| I love linen in summer, it's nice and breezy, but sunlight gets
| through and will actively heat you up all the same. This seems
| to be about reflecting the sunlight away from your body, so I
| don't think the two compare all that favourably in terms of
| cooling capacity.
| [deleted]
| ur-whale wrote:
| All that's needed now is to produce enough of it wrap it around
| the earth.
| mrfusion wrote:
| If this sends the heat into space, what happens if you're
| indoors? Would it still cool you?
| pjerem wrote:
| It reflects radiant heat, that is, the form of heat that is
| sent by the sun rays. There is no radiant heat indoors, only
| convective (the form of heat that is transferred through
| matter). So it would not cool you inside, no.
| mark-r wrote:
| Not true, anything above 0 degrees K will radiate. The
| problem is that indoors it will get absorbed and re-radiated
| right back at you. The only way to lose the heat entirely is
| to have it radiate all the way to space.
| jschwartzi wrote:
| The need for the material to be tight fitting isn't actually a
| problem for athletic wear. If you're wearing a wicking shirt you
| would also want it to be tight fitting. And a lot of rash guards
| will be tight because they wick in addition to providing uv
| protection. So I'm skeptical that the researchers really
| understand the applications for their material. There's also no
| discussion of how it performs when it gets wet.
| [deleted]
| dkdbejwi383 wrote:
| I wonder if it would be useful for things like curtains or
| overhead canopies, adding some passive cooling to spaces to
| reduce the need for mechanical cooling
| fpoling wrote:
| This only works if MIR radiation can escape, like happens
| outdoors unless the air is very humid. As the glass and walls
| reflects/absorbs MIR, curtains that emit that type of infrared
| will do nothing unless you hang them outside the window.
| roywiggins wrote:
| Yeah, they've looked into using this tech for roofs and
| things:
|
| https://www.sciencemag.org/news/2014/11/new-way-cool
| TuringNYC wrote:
| I see how this would be useful in always-warm/hot
| environments. But I'm curious -- would this be useful at
| locations with major seasonal changes? For example, in
| northeastern USA, the temperature varies from 100F to 0F
| through the year. So this would be great in the summer, but
| do I just "pay" for it in the winter via more heating? I
| imagine it depends on the cost of heating vs cost of
| cooling depending on the location.
| peteradio wrote:
| Where it gets cold, a single family home would tend to
| have snow cover anyway.
| mrfusion wrote:
| I think the idea is that the attic tries to maintain
| ambient outdoor temperature and the house is then
| insulated from the attic.
|
| So you may not get much heating from your roof in the
| winter anyway.
|
| Someone correct me if I'm wrong.
| ricardobeat wrote:
| I wonder why they haven't tested a full model? They say the cost
| is low and production is easy, so why not do that to prove it
| works before going to manufacturers?
| bostonsre wrote:
| The military will love that stuff. Could you drape it over
| vehicles as well to hide from infrared optics?
| spockz wrote:
| Wouldn't these shirts be extra easy to spot as they are
| essentially reflectors? It not really be helpful for hiding.
| rcarmo wrote:
| Great to see the academic tradition of roasting graduate students
| as an experiment is being carried on. :)
|
| Seriously now, as someone who occasionally spends a good while
| walking about in direct sunlight, I'm really interested in this,
| especially since I have noticed a marked increase in temperatures
| over the last few years and my Summer walks have become quite
| arduous...
| chrisweekly wrote:
| Try Patagonia "Capilene cool daily" t-shirts.
| beebeepka wrote:
| I've been waiting for something like this my entire life. I hope
| that fabric is good enough for producing underwear.
|
| Not even remotely overweight but I produce a considerable amount
| of extra heat. Seriously, whoever starts selling panties that
| cool my junk is going to be rewarded handsomely
| float4 wrote:
| Same. Very healthy weight, very active lifestyle. In the summer
| my junk often gets so warm that I actually feel like it isn't
| good for my fertility.
| beebeepka wrote:
| Believe me, it isn't. Don't ask how I know :/
| moomin wrote:
| Just to point out the obvious: this ain't gonna make a blind bit
| of difference if wet bulb temperatures enter the kill zone, so do
| not rely on this to protect you from the effects of climate
| change.
| yosito wrote:
| IANAS, but I'm puzzled by the use of the word "cooling". This
| fabric doesn't actively cool the wearer, or reduce the
| temperature, it simply prevents temperature from rising, keeping
| things up to 5 degrees cooler, if they were already cool to begin
| with.
| roywiggins wrote:
| I think if you started with a regular shirt, and then put this
| one on instead, you would eventually start cooling down. The
| article says that human skin radiates in MIR but that's blocked
| by normal fabric. So if you take off your shirt, you will
| radiate more, and possibly cool down a bit. This fancy shirt is
| similar to not wearing any shirt, except it can also reflect
| visible light a bit better because it's whiter. It might even
| be more efficient at radiating MIR than skin? I'm not sure, but
| if it's better than normal fabric it should help.
|
| Obviously the physiology here complicates things, but it really
| could cool you down- your body is always attempting to radiate
| way heat, and this is supposed to make that process faster.
| It's like carrying around your own shade.
| [deleted]
| reissbaker wrote:
| It sounds like it cools the wearer by absorbing body heat and
| emitting it as mid-infrared radiation. It also prevents
| temperature from rising by being reflective against UV,
| visible, and near-infrared radiation.
| chrisweekly wrote:
| PSA: Patagonia makes these fantastic lightweight "Capilene cool
| daily" short- and long-sleeved t-shirts that feel like they must
| have some magical active cooling built in along with their SPF 50
| protection. I don't know how they did it, but I own half a dozen
| and will continue to gift and recommend them as the greatest
| t-shirts ever made.
| bootlooped wrote:
| The Uniqlo Airism line has some extremely light and breathable
| shirts. The "micro mesh" ones are insane. But the style is not
| going to be everybody's taste, unlike the Capilene shirts which
| pretty much just look like a normal t-shirt.
| vincentmarle wrote:
| Thanks for the suggestion, I've been looking for a shirt that
| keeps me cool for a while, I just ordered one!
| sjm wrote:
| Never thought I'd read about Patagonia clothing on HN of all
| places. /s
| carabiner wrote:
| Various manufacturers make UPF clothing, Outdoor Research,
| Kuhl, and Black Diamond are some. REI's house brand has worked
| well for me, though the fit is baggy.
|
| A white cotton t-shirt is said to be SPF 15.
| oehtXRwMkIs wrote:
| They are UPF not SPF and recently they announced a voluntary
| recall because they weren't actually UPF 50.
| iAm25626 wrote:
| Older Patagonia "Capilene" material have undesirable "odor
| retention" feature. Patagonia claim the updated version does
| much better. Do you have any experience between the new vs old
| (circa ~2000-2005 version)?
| chrisweekly wrote:
| Only w the new ones which def do not have this (or any other)
| problem. Note "Capilene cool *daily*" in particular. I tried
| one "capilene cool runner" which was... ok I guess, but much
| heavier fabric, not as soft, etc.
| AntiqueFig wrote:
| Merinos ftw though.
| culopatin wrote:
| What's the difference? I'm looking at some now. I hate heat
| but I like working in my non conditioned garage, so I'll
| take anything that may help
| cowmoo728 wrote:
| I like the feel of polyester shirts better in hot
| weather. But I don't buy polyester or polyester blends
| anymore because they stink after just an hour or two of
| sweating in the sun. Merino doesn't have the same
| "cooling" feel but is good at wicking away and
| evaporating sweat, which helps your body keep a
| consistent temperature as long as you're hydrated. And
| merino doesn't reek like polyester clothing.
| fouc wrote:
| No idea if it will help, but I've found regularly adding a
| capful of bleach to my laundry of polyester shirts eliminates
| all odors for me.
| poorjohnmacafee wrote:
| They are talking about the atmospheric window - the band of
| EM/heat that can be freely radiated out to space unblocked by our
| atmosphere.
|
| This is an important concept in global warming/ghg that you
| almost never see discussed. The band that CO2 absorbs (15 microns
| mainly) is not in the atmospheric window. The 15 microns band is
| already absorbed by water vapor, and is almost 99% saturated as
| is.
|
| (This is where some particle physics students stop talking so
| they don't upset people)
| goodcanadian wrote:
| If you are a particle physics student, you will understand the
| concept of mean free path. Adding more greenhouse gases
| (including water vapour) decreases the distance a photon can
| travel before being absorbed again, and thus increases the
| amount of time it takes IR radiation to escape the atmosphere.
| The fact that basically no photons manage it in one go is sort
| of irrelevant.
| poorjohnmacafee wrote:
| There is nil escape to space from that band with today's
| water vapor level which is why it's not considered part of
| the atmospheric window.
|
| Do you have any research you can link to about your opinions
| on the 15 micron band?
|
| An ivy league physics professor was the one who insisted in
| discussion adding CO2 will only increase warming by some
| minuscule overall amount due to the band saturation. This was
| over 15 years ago when the academic climate was a little
| different.
| goodcanadian wrote:
| You are correct that 15um radiation will not escape
| directly to space from the ground. It will be absorbed by
| by the atmosphere. The atmosphere heats up and re-radiates
| the energy. Some of that energy ultimately escapes to
| space. The atmosphere warms up until the energy escaping to
| space equals the energy input by the sun. By adding more
| greenhouse gases, you are decreasing the distance a photon
| in the 15um band can travel before it is reabsorbed. This
| causes the atmosphere to heat up more than it would
| otherwise. Sure, water dominates the greenhouse effect. If
| it weren't there, the Earth would be frozen. That doesn't
| meant that adding more greenhouse gas has no effect. It
| most certainly does. It sounds like your professor was
| simply wrong.
|
| This is not a bad article, but I am mainly linking it for
| the graph which shows that the Earth does indeed radiate at
| 15um:
|
| https://www.giss.nasa.gov/research/briefs/2010_schmidt_05/
|
| Though, again, that is a little irrelevant. What matters is
| at what temperature the total energy escaping balances the
| incoming energy regardless of the wavelength.
| avsteele wrote:
| This is only 'not discussed' in the popular literature.
|
| The scientists and modelers are definitely take this into
| account. But its _is_ a tricky thing to get right.
|
| https://www.acs.org/content/acs/en/climatescience/climatesci...
| [deleted]
| chris_va wrote:
| The paper: https://advances.sciencemag.org/content/3/11/e1700895
|
| And the paper for nanoPE:
| https://science.sciencemag.org/content/353/6303/1019
|
| ... TLDR, they sandwiched a reflective and emissive surface
| inside of a thermally transparent material. Body heat convects to
| the surface (so it needs to be tight fitting), and the surface is
| radiatively coupled to the environment (emissive surface), but
| not to the body (reflective surface). You lose out on directly
| radiating body heat through the nanoPE, but that doesn't work
| well anyway.
|
| Anyway... it probably wouldn't work very well if the ambient
| temperature was high since it is absorbing LWIR from the
| environment. The article does mention MIR (MWIR) a few times,
| though. There isn't anything MWIR specific with this fabric, but
| the atmosphere is generally very cold in that band, so maybe LWIR
| can be reradiated in the MWIR by the fabric even when the ground
| temperature is at/above body temperature. The blackbody power in
| the MWIR at 98.6F is pretty poor, so it can't be much.
|
| They used an ambient temperature of 22.0C in the paper, which is
| kind of cheating (why bother with a cooling shirt at that
| temperature?). The LWIR coupling will help a lot at that
| temperature. Once the ambient gets close to human body temp,
| though, it'll not work nearly as well. One could run the numbers
| to see, the thermal model is pretty simple.
| at_a_remove wrote:
| I wonder how they do against UVA and UVB.
| ivan_gammel wrote:
| The interesting part is how big are the environmental costs of
| the production?
| DiffEq wrote:
| If it is like a mirror then what about people around you getting
| all that light reflected back into their eye - light which they
| can't really "see"? Seems like if you are around something like
| that all day where multiple people are wearing such clothes that
| it could possibly be damaging?
| drak0n1c wrote:
| If it is a cloth with a cloth's texture it wouldn't be bad
| since it would be reflected in such a diffuse pattern. Besides
| getting it directly from the sun anyways, you're already
| getting harsher glare reflections off of water, glass
| buildings, and metallic surfaces (cars) all around you.
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