6 ms·

A hot day, a fan provides little benefit when the temperature exceeds 35°C

deleted 2y ago
[deleted]
exabrial 2y ago
35c = 95freedom units btw. I agree. The article mentions all of this... when it gets that hot, especially with US-Midwest humidity levels, you need evaporative cooling with "just a fan". The phase change absorbs energy and can provide relief to higher temps.
- PaulHoule 2y ago
  When I lived in New Mexico people frequently used a "swamp cooler" https://en.wikipedia.org/wiki/Evaporative_cooler https://en.wikipedia.org/wiki/Evaporative_cooler which gives excellent cooling with small amounts of water and electricity. Good luck trying that in New York!
  - SoftTalker 2y ago
    Or anywhere in the southeast or midwest. Techniques for staying cool (or at least not dying) in hot weather will vary by region.
- pengaru 2y ago
  aka sweat
- mmooss 2y ago
  > freedom units Is that a typo or a real term?
  - exabrial 2y ago
    yes
  - Izkata 2y ago
    20 year old meme that still comes up occasionally as a joke: https://en.wikipedia.org/wiki/Freedom_fries https://en.wikipedia.org/wiki/Freedom_fries
pstrateman 2y ago
Have they not heard of wet bulb temperature? The chart in this wiki article is really good at showing the various effects. https://en.m.wikipedia.org/wiki/Psychrometrics https://en.m.wikipedia.org/wiki/Psychrometrics
- schiffern 2y ago
  For a surprising application of this chart, check out Indirect-Direct evaporative cooling. More cooling but (paradoxically) lower water consumption. Summary: https://www.youtube.com/watch?v=sJl-NIgGDL8#t=89 https://www.youtube.com/watch?v=sJl-NIgGDL8#t=89 Long-form (chart @29:30): https://www.youtube.com/watch?v=aVgB557bz0I https://www.youtube.com/watch?v=aVgB557bz0I
- xattt 2y ago
  Not many people have wet-bulb setups.
- deleted 2y ago
  [deleted]
- thehours 2y ago
  I first learned about this from a recent (and excellent) Practical Engineering video [1] on the shape of cooling towers. [1] https://www.youtube.com/watch?v=tmbZVmXyOXM https://www.youtube.com/watch?v=tmbZVmXyOXM
- mmooss 2y ago
  In theory, wet bulb should be used by weather reports on hot days, but for some reason it's not. IIRC it's hard to measure or to universalize - that is, it's hard to produce a consistent, meaningful, clear metric.
  - pstrateman 2y ago
    The "feels like" temperature weather reports use is an approximation of wet bulb.
    - 2y ago
technothrasher 2y ago
https://www.youtube.com/watch?v=WhtKkl0L7Ek https://www.youtube.com/watch?v=WhtKkl0L7Ek
quantadev 2y ago
Thermodynamics dude here. :) All moving air does is increase the rate of the heat transfer from the higher temp substance to the lower temp one. If the air outside is hotter than your body temperature then a fan will be heating you UP not cooling you DOWN. Without electricity or chemical reactions the only way to stay cool in high heats is to use evaporative effects. Evaporation is endothermic (takes in heat) and actually cools down the thing being evaporated off of. So you can basically soak your shirt and as it evaporates it cools you down. There are things called 'evaporative vests' which can cool you off for hours.
- loeg 2y ago
  > So you can basically soak your shirt and as it evaporates it cools you down. There are things called 'evaporative vests' which can cool you off for hours. Or like, sweat? Which is something people who aren't dehydrated tend to do at or above 95F (35C).
  - thrw42A8N 2y ago
    Have you ever spent hours sweating (working) in humid 35 degrees? You wish you'd rather die. Any help is appreciated.
    - crop_rotation 2y ago
      While this is an exaggeration, it really is very very bad. I have stayed for short amount in very hot and humid areas where sadly electricity was rare and yes you just want to get out of there as soon as you can.
      - rimunroe 2y ago
        It makes a huge difference if you get introduced to high temperatures and humidities over a period of weeks or months rather than all of a sudden. People live in hot climates year round without feeling miserable all the time. Most bodies are able to do a surprisingly good job of adapting to high temperatures if the transition is done very gradually.
chrismorgan 2y ago
> CDC recommends not using a fan at temperatures above 32.2°C I don't know quite how to put this, but are they idiots? I don't quite mean that, but at the very least there's something weird going on. I double down on this as they double down on their recommendation at the end of the article. Go to places like India, and see how people use fans, in the humid places like Kolkata and the dry places like Hyderabad. Fans obviously provide great relief at far higher temperatures than their 90°F. The very idea of suggesting not to use fans from such a low temperature is, to me who grew up in Melbourne, Australia and now lives in Hyderabad: ludicrous. Even when they talk about "people who are less able to cope with heat", it sounds like they may be giving advice very harmful to normal people, for the possible but highly contested safety of a few. —— When talking about ineffectiveness of fans in high temperature low humidity (which is Hyderabad summer to a tee—it barely gets below CDC's 90°F, and is very dry), the details mentioned make me sceptical of the entire approach of the studies. I know each time I've come to India, it's taken me well over a week to adjust to the temperature. (I still sweat more than most Indians do, but not as much as a day or two after I come.) And hydration is a rather important factor too, likely not accounted for adequately. We're talking definite heat stress circumstances, you can't expect to get accurate results from an unacclimated body. Yes, I am a layman casting doubt on the work of experts without investigating carefully. I imagine they've been at least somewhat careful about these things, none of these people will be idiots. It's probably not all as bad as the vibes I'm getting. Do treat my scepticism with scepticism of your own.
- Clubber 2y ago
  >> CDC recommends not using a fan at temperatures above 32.2°C >I don't know quite how to put this, but are they idiots? I can't believe they said that. They need to move anywhere in the US Southern region. 32.2C is a cool day reprieve in a Southern summer and fans are a necessity. https://baltimoreaircoil.com/evaporative-cooling#:~:text=As%20perspiration%20evaporates%20it%20absorbs,resulting%20in%20a%20cooler%20liquid https://baltimoreaircoil.com/evaporative-cooling#:~:text=As%....
  - chrismorgan 2y ago
    Follow the link in the article. They do actually say explicitly that, with no tempering statements.
thecleaner 2y ago
Its because of thermodynamics. When you use fans in an area that doesn't have other external circulation, you introduce more energy into the system. This will increase increase temperature. From personal experience for a closed room, fans don't help if temperature even reaches 27degC. If the temperature outside exceeds 35 degC or basically any comfortable temperature, the result will depend on humidity levels. If you are sweating, it will help because of evaporation - some energy is absorbed for the phase change. If its really dry, a fan will only make it worse.
- mmooss 2y ago
  > When you use fans in an area that doesn't have other external circulation, you introduce more energy into the system. This will increase increase temperature. From personal experience for a closed room, fans don't help if temperature even reaches 27degC. Why wouldn't blowing 27C air over your 37C body cool you off? The fan isn't adding 10C to the room temperature (or you need a new fan).
tonymet 2y ago
[flagged]
0xbadcafebee 2y ago
For those not reading the article: - The HN title is misleading. The real title is "When is it too hot to use a fan?" - The article explains: "The key point: Above 35°C, humidity matters a lot. In very dry conditions, a fan could be counterproductive, whereas in very humid ones it could continue to help at much higher temperatures." They quote two controlled studies that show the same results so there's no reason to debate this. It's just a bad title. There's nothing controversial here.
ch1kkenm4ss4 2y ago
[dead]
amluto 2y ago
This article is IMO quite a stretch based on the actual data. > New research from two different groups of thermal physiologists favors the higher temperature limits, especially in humid weather. But the groups don’t agree on a single temperature threshold. One study, published on 6 November in The New England Journal of Medicine (NEJM), reports that fans can relieve stress on the heart in elderly people in humid conditions at 38°C. The other, published on 17 October in JAMA, concluded there was little additional benefit from using a fan above 35°C. The NEJM article is pay-to-read. The JAMA article took older adults, had them sit in a room at 36C, for 8 hours, getting very occasional light exercise and tested three different air movement speeds. The body temperature of the subjects was 38C, independent of fan speed, from which IMO one can conclude approximately nothing other than that the subjects' bodies were warmer than ideal under those conditions. In my personal experience, the effect of air movement and body movement under conditions like this is dramatic. "Resting" (as the study had the subjects do) in the daytime (as the subjects did) is, for me, not so pleasant. Add a fan, and it's less unpleasant. Riding a bike can be very pleasant as long as there's plenty to drink. But I suspect that my rectal temperature would be more or less independent of any of this.
ourmandave 2y ago
But public health agencies warn that if it’s too hot, the blowing air can actually make things worse by acting like a convection oven—and they differ on that threshold. This is a real problem. A lot of people are found dead sitting in their closed apartments in front of a fan, thinking it would cool them off during a heat wave.
- mmooss 2y ago
  Yes, the CDC is trying to give advice that won't kill vulnerable people - if they get it wrong, people die. Imagine that's your job every day. Whether healthy young people are comfortable is very secondary. One might imagine the solution to that problem is, 'don't use fans', but that would result in people dying from heat illnesses. They need to find a threshold that minimizes those very bad outcomes.

deleted 2y ago

[deleted]

35c = 95freedom units btw. I agree. The article mentions all of this... when it gets that hot, especially with US-Midwest humidity levels, you need evaporative cooling with "just a fan". The phase change absorbs energy and can provide relief to higher temps.

PaulHoule 2y ago
When I lived in New Mexico people frequently used a "swamp cooler" https://en.wikipedia.org/wiki/Evaporative_cooler https://en.wikipedia.org/wiki/Evaporative_cooler which gives excellent cooling with small amounts of water and electricity. Good luck trying that in New York!
- SoftTalker 2y ago
  Or anywhere in the southeast or midwest. Techniques for staying cool (or at least not dying) in hot weather will vary by region.
pengaru 2y ago
aka sweat
mmooss 2y ago
> freedom units Is that a typo or a real term?
- exabrial 2y ago
  yes
- Izkata 2y ago
  20 year old meme that still comes up occasionally as a joke: https://en.wikipedia.org/wiki/Freedom_fries https://en.wikipedia.org/wiki/Freedom_fries

pstrateman 2y ago

Have they not heard of wet bulb temperature? The chart in this wiki article is really good at showing the various effects. https://en.m.wikipedia.org/wiki/Psychrometrics https://en.m.wikipedia.org/wiki/Psychrometrics

schiffern 2y ago
For a surprising application of this chart, check out Indirect-Direct evaporative cooling. More cooling but (paradoxically) lower water consumption. Summary: https://www.youtube.com/watch?v=sJl-NIgGDL8#t=89 https://www.youtube.com/watch?v=sJl-NIgGDL8#t=89 Long-form (chart @29:30): https://www.youtube.com/watch?v=aVgB557bz0I https://www.youtube.com/watch?v=aVgB557bz0I
xattt 2y ago
Not many people have wet-bulb setups.
deleted 2y ago
[deleted]
thehours 2y ago
I first learned about this from a recent (and excellent) Practical Engineering video [1] on the shape of cooling towers. [1] https://www.youtube.com/watch?v=tmbZVmXyOXM https://www.youtube.com/watch?v=tmbZVmXyOXM
mmooss 2y ago
In theory, wet bulb should be used by weather reports on hot days, but for some reason it's not. IIRC it's hard to measure or to universalize - that is, it's hard to produce a consistent, meaningful, clear metric.
- pstrateman 2y ago
  The "feels like" temperature weather reports use is an approximation of wet bulb.
  - 2y ago

technothrasher 2y ago

https://www.youtube.com/watch?v=WhtKkl0L7Ek https://www.youtube.com/watch?v=WhtKkl0L7Ek

quantadev 2y ago

Thermodynamics dude here. :) All moving air does is increase the rate of the heat transfer from the higher temp substance to the lower temp one. If the air outside is hotter than your body temperature then a fan will be heating you UP not cooling you DOWN. Without electricity or chemical reactions the only way to stay cool in high heats is to use evaporative effects. Evaporation is endothermic (takes in heat) and actually cools down the thing being evaporated off of. So you can basically soak your shirt and as it evaporates it cools you down. There are things called 'evaporative vests' which can cool you off for hours.

loeg 2y ago
> So you can basically soak your shirt and as it evaporates it cools you down. There are things called 'evaporative vests' which can cool you off for hours. Or like, sweat? Which is something people who aren't dehydrated tend to do at or above 95F (35C).
- thrw42A8N 2y ago
  Have you ever spent hours sweating (working) in humid 35 degrees? You wish you'd rather die. Any help is appreciated.
  - crop_rotation 2y ago
    While this is an exaggeration, it really is very very bad. I have stayed for short amount in very hot and humid areas where sadly electricity was rare and yes you just want to get out of there as soon as you can.
    - rimunroe 2y ago
      It makes a huge difference if you get introduced to high temperatures and humidities over a period of weeks or months rather than all of a sudden. People live in hot climates year round without feeling miserable all the time. Most bodies are able to do a surprisingly good job of adapting to high temperatures if the transition is done very gradually.

chrismorgan 2y ago

> CDC recommends not using a fan at temperatures above 32.2°C I don't know quite how to put this, but are they idiots? I don't quite mean that, but at the very least there's something weird going on. I double down on this as they double down on their recommendation at the end of the article. Go to places like India, and see how people use fans, in the humid places like Kolkata and the dry places like Hyderabad. Fans obviously provide great relief at far higher temperatures than their 90°F. The very idea of suggesting not to use fans from such a low temperature is, to me who grew up in Melbourne, Australia and now lives in Hyderabad: ludicrous. Even when they talk about "people who are less able to cope with heat", it sounds like they may be giving advice very harmful to normal people, for the possible but highly contested safety of a few. —— When talking about ineffectiveness of fans in high temperature low humidity (which is Hyderabad summer to a tee—it barely gets below CDC's 90°F, and is very dry), the details mentioned make me sceptical of the entire approach of the studies. I know each time I've come to India, it's taken me well over a week to adjust to the temperature. (I still sweat more than most Indians do, but not as much as a day or two after I come.) And hydration is a rather important factor too, likely not accounted for adequately. We're talking definite heat stress circumstances, you can't expect to get accurate results from an unacclimated body. Yes, I am a layman casting doubt on the work of experts without investigating carefully. I imagine they've been at least somewhat careful about these things, none of these people will be idiots. It's probably not all as bad as the vibes I'm getting. Do treat my scepticism with scepticism of your own.

Clubber 2y ago
>> CDC recommends not using a fan at temperatures above 32.2°C >I don't know quite how to put this, but are they idiots? I can't believe they said that. They need to move anywhere in the US Southern region. 32.2C is a cool day reprieve in a Southern summer and fans are a necessity. https://baltimoreaircoil.com/evaporative-cooling#:~:text=As%20perspiration%20evaporates%20it%20absorbs,resulting%20in%20a%20cooler%20liquid https://baltimoreaircoil.com/evaporative-cooling#:~:text=As%....
- chrismorgan 2y ago
  Follow the link in the article. They do actually say explicitly that, with no tempering statements.

thecleaner 2y ago

Its because of thermodynamics. When you use fans in an area that doesn't have other external circulation, you introduce more energy into the system. This will increase increase temperature. From personal experience for a closed room, fans don't help if temperature even reaches 27degC. If the temperature outside exceeds 35 degC or basically any comfortable temperature, the result will depend on humidity levels. If you are sweating, it will help because of evaporation - some energy is absorbed for the phase change. If its really dry, a fan will only make it worse.

mmooss 2y ago
> When you use fans in an area that doesn't have other external circulation, you introduce more energy into the system. This will increase increase temperature. From personal experience for a closed room, fans don't help if temperature even reaches 27degC. Why wouldn't blowing 27C air over your 37C body cool you off? The fan isn't adding 10C to the room temperature (or you need a new fan).

tonymet 2y ago

[flagged]

0xbadcafebee 2y ago

For those not reading the article: - The HN title is misleading. The real title is "When is it too hot to use a fan?" - The article explains: "The key point: Above 35°C, humidity matters a lot. In very dry conditions, a fan could be counterproductive, whereas in very humid ones it could continue to help at much higher temperatures." They quote two controlled studies that show the same results so there's no reason to debate this. It's just a bad title. There's nothing controversial here.

ch1kkenm4ss4 2y ago

[dead]

amluto 2y ago

This article is IMO quite a stretch based on the actual data. > New research from two different groups of thermal physiologists favors the higher temperature limits, especially in humid weather. But the groups don’t agree on a single temperature threshold. One study, published on 6 November in The New England Journal of Medicine (NEJM), reports that fans can relieve stress on the heart in elderly people in humid conditions at 38°C. The other, published on 17 October in JAMA, concluded there was little additional benefit from using a fan above 35°C. The NEJM article is pay-to-read. The JAMA article took older adults, had them sit in a room at 36C, for 8 hours, getting very occasional light exercise and tested three different air movement speeds. The body temperature of the subjects was 38C, independent of fan speed, from which IMO one can conclude approximately nothing other than that the subjects' bodies were warmer than ideal under those conditions. In my personal experience, the effect of air movement and body movement under conditions like this is dramatic. "Resting" (as the study had the subjects do) in the daytime (as the subjects did) is, for me, not so pleasant. Add a fan, and it's less unpleasant. Riding a bike can be very pleasant as long as there's plenty to drink. But I suspect that my rectal temperature would be more or less independent of any of this.

ourmandave 2y ago

But public health agencies warn that if it’s too hot, the blowing air can actually make things worse by acting like a convection oven—and they differ on that threshold. This is a real problem. A lot of people are found dead sitting in their closed apartments in front of a fan, thinking it would cool them off during a heat wave.

mmooss 2y ago
Yes, the CDC is trying to give advice that won't kill vulnerable people - if they get it wrong, people die. Imagine that's your job every day. Whether healthy young people are comfortable is very secondary. One might imagine the solution to that problem is, 'don't use fans', but that would result in people dying from heat illnesses. They need to find a threshold that minimizes those very bad outcomes.