Comment by kijin | Hacker News Reader

Comment by kijin | Hacker News Reader

Apart from a few isolated statements that suggest using fans together with ACs (which, of course, is a totally reasonable thing to do), the overall tone of the article is very much "AC = evil, fan = cool."

Unfortunately, fan-only cooling only works in a narrow range of climates.

> For instance, instead of cooling down a space to 24°C (75°F), the aircon can cool it to 29°C (84°F), which is a comfortable temperature if combined with fans.

Whether or not 29°C can be considered a "comfortable temperature", even with fans, depends a lot on other factors, the most important of which is humidity. 29°C at 30% humidity is very different from 29°C at 90% humidity. The former is common in Europe and the American West. The latter is much more common in the Southeast, as well as the majority of newly industrialized countries such as China and India.

Try installing a radiant cooling system in one of those hot & humid places. See all that condensation on the walls? That's a recipe for explosive mold growth. All the fans in the world will not make that pesky H2O go away, since the air is already oversaturated with it. People can tolerate a lot of heat with nothing but a paper fan, but there's no alternative to a good ol' electron-guzzling compressor when it comes to humidity control.

You might feel totally comfortable with a fan in your cool and dry Northern California summers, but be very careful before you try to generalize your energy-saving hack to different climates. There's a reason why millions of people won't give up their AC's for fans, and it's not because they don't know how to stay cool.

Exactly. There could be an alternative discussion about the sustainability of cities that are entirely AC dependent, but the suggestion that AC is simply a luxury that could be largely replaced by fans gives me the impression that the author hasn't spent much time in Houston, Atlanta or Washington DC in the summertime. I don't like AC all that much, but I don't think I could continue to live and work in NYC in the summer without it, nevermind somewhere further south, it's just too damn humid.

Also, the author suggests leaving the air conditioning at a too-warm setting and supplementing it with fans...having experienced this as friends and family try to save money on cooling, I can't recommend it. At least with a typical residential HVAC system, it seems to me to make the air feel very stale, to where I'd much rather open a window even if it's sweltering outside.

HVAC systems should only circulate dry air. When they circulate lukewarm (read: insufficiently dehumidified) air, various smelly and unhealthy substances tend to accumulate in the ducts and filters. Stale air is a telltale sign that you've got a mycotoxin factory in your house.

I have made it through a number of Washington summers simply on fans. Now, I was in a deeply shaded neighborhood, and to be sure I did not sleep that well on the hot nights. I wouldn't do it now: for one thing, my wife would regard it as insane.

The problem that occurs to from NYC is the noise that would come in through open windows.

I've lived in India for years, generally my experience has been that fans work much better in humid air than dry air. So 29 degrees with 90% humidity and fan would be much more comfortable than 29 degrees with 30% humidity and fan.

In Delhi (45 degrees in summer) we would manage with desert coolers + fan, which specifically work by increasing the humidity of the air and then using a fan.

I believe though that, AC vs. coolers vs. fans vs. any combination of them is really not at all as important as the way cities and the buildings within them are built. In Delhi it is estimated that 3-5 degrees local heating is caused by bad urban design. As an anecdote, I've been in mud-huts where despite 45 degree temperatures outside, insides felt like they were AC. Sure, mud-huts do have problems with mould and require a lot of maintenance, but it's illustrative that we've dug ourselves into a hole where AC is required because we build buildings of inappropriate materials.

> In Delhi (45 degrees in summer) ...

That's 113 degrees Fahrenheit for American readers. The rest of the world has wisely adopted more rational measurement units. Even Canada, a stone's throw away from the U.S., uses the Metric system.

Both temperature scales are (thankfully) rational. Some physicists have been dabbling in complex temperatures, but thankfully most of us don't need to know anything about them.

Sorry, mathematician joke.

Celsius used two very reproducible tresholds (freezing and boiling points of water), associated them to two very easy to remember values (0 and 100), and defined his scale according to them.

The way Farenheit got to his scale seems really less practical to me, from Wikipedia :

"Fahrenheit proposed his temperature scale in 1724, basing it on three reference points of temperature.[9] In his initial scale (which is not the final Fahrenheit scale), the zero point is determined by placing the thermometer in brine: he used a mixture of ice, water, and ammonium chloride, a salt, at a 1÷1÷1 ratio. This is a frigorific mixture which stabilizes its temperature automatically: that stable temperature was defined as 0 °F (−17.78 °C). The second point, at 32 degrees, was a mixture of ice and water without the ammonium chloride at a 1÷1 ratio. The third point, 96 degrees, was approximately the human body temperature, then called "blood-heat".[12]"

http://en.wikipedia.org/wiki/Rational_number

http://en.wikipedia.org/wiki/Complex_number

It was not a direct response to the "rational" bit.

> two very reproducible tresholds (freezing and boiling points of water)

Reproducible if you happen to be near sea level.

And have the appropriate "water".

Unfortunately in India it's generally Fahrenheit as well, independence from the British didn't remove that piece of the imperial system (in length it's even more confusing where shorter measures feet and inches are preferred while for longer once m and km...).

Indians generally use Fahrenheit only for body temperature... to know if we're running a fever. But off-hand, I'd have no idea what an air temperature of 113 degrees Fahrenheit would feel like. I understand 45C quite easily. Surely you've seen weather reports and forecasts in Indian newspapers and on Indian TV. Did you ever see them use Fahrenheit?

For distances, a person's height is measured in feet and inches, tailors prefer to use inches for their dimensions, plots of land are often measured in feet. But everything else is metric. (Listen to the local farmer speak, in your own vimeo video link.) Speedometer, odometer, fuel, grocery, produce, etc. all use the metric system. To say nothing of my entirely-metric work in engineering.

Yes, you're absolutely right and most Indians seem far more literate in converting between the two than I ever would be. My generalization was way too broad and wrong - thanks for pointing out the specific cases.

It seems like, as with the examples you give, that certain systems are used for certain purposes which was always fascinating to me come from outside. In construction, in rural areas I've found it varying between different parts of the country whether metric or imperial is preferred.

> Sure, mud-huts do have problems with mould

Yeah, mold tends to be the default trade-off when you choose any method of cooling other than AC.

As someone who is allergic to mold, I'd choose an air-conditioned glass-and-steel box any day over a moldy mud hut if they were equally cool. But I do wonder if, given better technology, we could come up with buildings and cities that have the best of both worlds.

Maybe we should look to ancient building materials and methods for new ideas. The Seokguram grotto in Korea, for example, had been dry for over a thousand years until modern "restoration" projects messed up the delicate balance of air and water. Now there are dehumidifiers running 24/7 to keep mold out of the grotto. It's really pathetic. If pre-modern Indian mud huts can reduce the temperature by 10 degrees without electricity, why can't modern science come up with structures that reduce the humidity by 30 percent, for instance?

Beyond energy use, allergies seem also to be a by-product of growing up sanitised & sealed glass-and-steel boxes. Not that it helps people like you and me who already have them, but in the long-run saner construction might help avoid even that.

Yes, I agree that the long-term solution lies somewhere in the middle. Certainly it would be unwise for mass-adoption of mud buildings (not least because they're a LOT of work to maintain), but if architects and builders would become more open to mixing and exploring with traditional techniques and materials (which, lets face it, has been honed over a long period to deal with humidity, heat and uncomfortable climate before electricity) we could probably get much more comfortable and energy efficient buildings and also cities.

An acquaintance of mine, Laurent, works on this in eastern India [1].

1. http://vimeo.com/68119509

"desert coolers + fan, which specifically work by increasing the humidity of the air and then using a fan"

Actually, evaporative coolers significantly reduce the air temperature[1], when used in dry climates.

[1] http://en.wikipedia.org/wiki/Evaporative_cooler#Performance

"At 32 °C (90 °F) and 50% relative humidity, air may be cooled to about 24 °C (75 °F). The dew point for these conditions is 20 °C (68 °F).

"At 40 °C (104 °F) and 15% relative humidity, air may be cooled to nearly 21 °C (70 °F). The dew point for these conditions is 8 °C (46 °F)."

False dichotomy. Fans can be used in conjunction with AC, greatly reducing the energy required by the AC, by making higher temperatures acceptable.

Of course it's a false dichotomy. Did you read the first sentence of my comment?

I did. The other 10 sentences then completely ignored the possibility, so I felt it was worth re-iterating. The article is pretty clear that you can dispense with air-con in many instances, and dramatically reduce it's use in the remaining cases, simply by using a fan. Nowhere does the article make the claim that air-con shouldn't be used, merely that it shouldn't be the first option when things get hot. You mis-characterised the article, and I just wanted to point that out.

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