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

50 点作者 giuliomagnifico6 个月前

9 条评论

chrismorgan6 个月前
&gt; <i>CDC recommends not using a fan at temperatures above 32.2°C</i><p>I don&#x27;t know quite how to put this, but are they <i>idiots</i>? I don&#x27;t quite mean that, but at the very least there&#x27;s <i>something</i> weird going on. I double down on this as they double down on their recommendation at the end of the article.<p>Go to places like India, and see how people use fans, in the humid places like Kolkata and the dry places like Hyderabad. Fans <i>obviously</i> provide <i>great</i> 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.<p>Even when they talk about &quot;people who are less able to cope with heat&quot;, it sounds like they may be giving advice very harmful to normal people, for the <i>possible but highly contested</i> safety of a few.<p>——<p>When talking about ineffectiveness of fans in high temperature low humidity (which is Hyderabad summer to a tee—it barely gets <i>below</i> CDC&#x27;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&#x27;ve come to India, it&#x27;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&#x27;re talking definite heat stress circumstances, you can&#x27;t expect to get accurate results from an unacclimated body.<p>Yes, I am a layman casting doubt on the work of experts without investigating carefully. I imagine they&#x27;ve been at least somewhat careful about these things, none of these people will be idiots. It&#x27;s probably not all as bad as the vibes I&#x27;m getting. Do treat my scepticism with scepticism of your own.
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amluto6 个月前
This article is IMO quite a stretch based on the actual data.<p>&gt; 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.<p>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&#x27; bodies were warmer than ideal under those conditions.<p>In my personal experience, the effect of air movement and body movement under conditions like this is <i>dramatic</i>. &quot;Resting&quot; (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&#x27;s less unpleasant. Riding a bike can be very pleasant as long as there&#x27;s plenty to drink. But I suspect that my rectal temperature would be more or less independent of any of this.
ourmandave6 个月前
<i>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.</i><p>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.
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pstrateman6 个月前
Have they not heard of wet bulb temperature?<p>The chart in this wiki article is really good at showing the various effects.<p><a href="https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Psychrometrics" rel="nofollow">https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Psychrometrics</a>
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exabrial6 个月前
35c = 95freedom units btw.<p>I agree. The article mentions all of this... when it gets that hot, especially with US-Midwest humidity levels, you need evaporative cooling with &quot;just a fan&quot;. The phase change absorbs energy and can provide relief to higher temps.
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quantadev6 个月前
Thermodynamics dude here. :)<p>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.<p>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 &#x27;evaporative vests&#x27; which can cool you off for hours.
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thecleaner6 个月前
Its because of thermodynamics. When you use fans in an area that doesn&#x27;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&#x27;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.
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technothrasher6 个月前
<a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=WhtKkl0L7Ek" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=WhtKkl0L7Ek</a>
0xbadcafebee6 个月前
For those not reading the article:<p>- The HN title is misleading. The real title is &quot;When is it too hot to use a fan?&quot;<p>- The article explains: <i>&quot;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.&quot;</i> They quote two controlled studies that show the same results so there&#x27;s no reason to debate this.<p>It&#x27;s just a bad title. There&#x27;s nothing controversial here.