8 ms·

> "...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 a

> "...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.

porphyra 5y ago
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.
- datameta 5y ago
  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.
- clairity 5y ago
  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.
  - nicoburns 5y ago
    > 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!
    - clairity 5y ago
      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 5y ago
      > 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.
      - ajuc 5y ago
        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 5y ago
- easygenes 5y ago
  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.
  - comex 5y ago
    > 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.
    - galangalalgol 5y ago
      It happens in houses too. People will run their heater warmer than they cool their house to in summer. My theory is that the wall temperature is causing more or less radiant heating and the thermostat gets adjusted to compensate. So if the car body is much hotter it will feel hotter even with the same air temp.
    - easygenes 5y ago
      Well the topic is car A/C and indeed if the outside temperature is 45C (113F), and the air conditioner only produces a difference of 20C, and your target is 22C then you’ll fall short of that by a few degrees. Also with car A/C (or indoor spaces which take in a lot of direct sunlight), hotter days tend to be the result of greater insolation. If direct sunlight is hitting your skin on a clear summer day it has a significant warming effect which you would want to offset with more ambient or active cooling.
  - IgorPartola 5y ago
    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.
Broken_Hippo 5y ago
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.
ARandomerDude 5y ago
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.
dan_quixote 5y ago
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?
- clairity 5y ago
  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.
- Unklejoe 5y ago
  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.
klysm 5y ago
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 5y ago
  sure, but that's why there are multiple vents? and you can run the a/c at a lower speed to boot.
  - usefulcat 5y ago
    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 5y ago
      there are controls for both speed and temperature, as well as vent direction. it's not difficult to find a comfortable combination.
      - deleted 5y ago
        [deleted]
      - MetaWhirledPeas 5y ago
        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.
      - sedatk 5y ago
        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.
throwaway284534 5y ago
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.
deleted 5y ago
[deleted]
robscallsign 5y ago
Your pithy analysis seems to entirely discount having passengers in the back seat, or multiple rows of seating like minivans.
tqi 5y ago
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 5y ago
  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
cjohansson 5y ago
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
kebman 5y ago
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.
wolverine876 5y ago
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.
bootlooped 5y ago
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.
echlebek 5y ago
People sit in the back seat of cars too.

porphyra 5y ago

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.

datameta 5y ago
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.
clairity 5y ago
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.
- nicoburns 5y ago
  > 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!
  - clairity 5y ago
    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 5y ago
    > 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.
    - ajuc 5y ago
      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 5y ago
easygenes 5y ago
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.
- comex 5y ago
  > 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.
  - galangalalgol 5y ago
    It happens in houses too. People will run their heater warmer than they cool their house to in summer. My theory is that the wall temperature is causing more or less radiant heating and the thermostat gets adjusted to compensate. So if the car body is much hotter it will feel hotter even with the same air temp.
  - easygenes 5y ago
    Well the topic is car A/C and indeed if the outside temperature is 45C (113F), and the air conditioner only produces a difference of 20C, and your target is 22C then you’ll fall short of that by a few degrees. Also with car A/C (or indoor spaces which take in a lot of direct sunlight), hotter days tend to be the result of greater insolation. If direct sunlight is hitting your skin on a clear summer day it has a significant warming effect which you would want to offset with more ambient or active cooling.
- IgorPartola 5y ago
  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.

Broken_Hippo 5y ago

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.

ARandomerDude 5y ago

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.

dan_quixote 5y ago

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?

clairity 5y ago
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.
Unklejoe 5y ago
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.

klysm 5y ago

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 5y ago
sure, but that's why there are multiple vents? and you can run the a/c at a lower speed to boot.
- usefulcat 5y ago
  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 5y ago
    there are controls for both speed and temperature, as well as vent direction. it's not difficult to find a comfortable combination.
    - deleted 5y ago
      [deleted]
    - MetaWhirledPeas 5y ago
      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.
    - sedatk 5y ago
      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.

throwaway284534 5y ago

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.

deleted 5y ago

[deleted]

robscallsign 5y ago

Your pithy analysis seems to entirely discount having passengers in the back seat, or multiple rows of seating like minivans.

tqi 5y ago

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 5y ago
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

cjohansson 5y ago

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

kebman 5y ago

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.

wolverine876 5y ago

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.

bootlooped 5y ago

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.

echlebek 5y ago

People sit in the back seat of cars too.