AC myths 6: Metabolism doesn’t count, not really

Thursday 15 September 2011, 2.30pm HKT

<< Part 5 << || >> Part 7 >>

(Continued from Part 5)

In this sixth instalment of the series, we’ll blow the myth about metabolic differences between individuals being relevant to AC settings that people still fall for — unless you’re comparing yourself to a pet animal.

* * *

Bullshit #9
Room temperature should be in the range of 20°C to 26°C to best match human metabolism.

People love clutching at straws.

I happen to know something about metabolism. My first-ever job was a medical laboratory officer at a London hospital, and I quit after seven months because of the criminally poor pay — but that’s for another blogpost.

Mammals, my biology tutor once said, in many respects have a permanent fever. O rly? Mammalian metabolism always produce heat. The human body needs to maintain a constant 37°C (98.6°F). To dissipate the extra heat (generated by metabolism, movement, etc), the surrounding temperature needs to be lower.

FACT: Human body temperature is 37°C (98.6°F). As the ambient temperature rises to our body temperature or more, the less adaptable we become. The reason is that, as temperature rises, the protein molecules in our cells become increasingly denatured, thereby inhibiting our overall ability to produce somatic cells properly.

Sooner or later you’ll run into this kind of longwinded, scientific-sounding explanation (source forgotten):

“How much lower the environmental temperature needs to be for heat dissipation depends on the metabolic rate of each individual. Everybody has a different metabolic rate and these rates fluctuate according to the individual performing certain activities or under certain environmental conditions. Therefore, even people in the same room can feel differences of the same ambient temperature due to their different metabolic rates. That makes it very hard to find an optimal temperature in any given location. Body shape, height, weight, eating and drinking habits, etc, will affect thermal comfort, so generally the temperature for human thermal comfort is between 20°C and 26°C [68°F and 78°F].”

That’s a longwinded way of saying 20°C to 26°C is the temperature range for optimal human thermal comfort because human metabolic rates differ between individuals since each individual senses ambient temperatures differently.

Actually, that’s kind of crap. And coming from an online discussion board, you’ll know the person posting it was showing off.

You could churn out drivel like that only if you’re comparing yourself to a dog or a cat or gecko. Our metabolic rates are not wildly different between individuals — after all, we belong to the same species (although sometimes we must have wondered about that).

FACT: The human body works most comfortably with the least amount of physical stress at temperatures of 19°C to 21°C (66°F to 69°F).

You can check this fact against any university physiology textbook or lab manual.

These must be human beings … like you and me

Although my general appearance might suggest otherwise, I am in fact a highly consistent person in many things. One of my more highly consistent habits is about room temperature — 20°C (68°F) all year round, anywhere in the world, in hot or cold climes, come rain, shine and thunder, summer or winter.

Not only is 20°C something I’ve gotten used to, I’ve also seen with my own eyes (as an employer) that employees tend to work more efficiently at 20°C than at any other temperature.

Some might disagree, but they can go to hell and don’t come back — mainly because I don’t think people who say otherwise have actually taken the effort to check or test things out physically or information-wise, and just talk out of their backsides.

Human thermal comfort being 20°C to 26°C is nonsense and 10 degrees too wide. That’s only the temperature range in which human thermal comfort can tolerate; it’s not the same as actual human thermal comfort.

Now, we could get pretentiously scientific and talk about factors like air velocity, clothing, insulation, gender differences, thermal sensitivity, adjustment mechanisms of individuals, etc, also playing a part in thermal comfort. In the end, comparing human to human, the differences are of small enough scale that they don’t amount to a hill of beans.

FACT: Human metabolism operate within a rather narrow temperature range (± 2 degrees centigrade), otherwise our enzymes (the protein molecules that assist metabolic reactions) will start to become denatured and affect (or even halt) metabolism.

The pseudo-biologists forgot to tell you is this: Our bodies operate optimally when the surrounding temperature is 15 to 17 degrees lower than the body temperature (on the Celsius scale).

Then, our enzymes are more fully subject to internal body temperature (constant anyway) rather than be additionally influenced by high or low surrounding temperatures. At 15 to 17 degrees lower, that means the surrounding temperature has to be in the 3-degree band of 20°C to 22°C (68°F to 71°F). Please learn basic arithmetic, please.

And what coincidence: AC makers use 21/22°C as the preset temperature setting for ACs.

You can stand 20°C to 26°C pretty well and for a long time, but it doesn’t necessarily mean it’s comfortable. Of course, everyone considers comfort differently, but I would argue it’s more a psychological or psychosomatic preference — and nothing to do with metabolism.

But some people just can’t take ‘no’ for answer and argue endlessly. Then go bloody ask NASA for the figures — after all, they got the data from the Nazis, who got theirs from horrendous little experiments on innocent victims.

Like I said before, if 20°C/68°F is too cold, you must be one helluva effing physical wreck. You’re either not eating enough or not getting enough exercise or sex or something. In other words, you’re a dillweed.

* * *


Temperature vs. humidity vs. your propensity to be blindsided

<< Part 5 << || >> Part 7 >>

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© The Naked Listener’s Weblog, 2011.

Images: Right to Own Onion meme via c4c ♦ Guinea pigs on terracotta tiles via Coimbatore.

AC myths 5: Lower temperatures cost more?

Thursday 15 September 2011, 2.05pm HKT

<< Part 4 << || >> Part 6 >>

(Continued from Part 4)

Now the fifth part of the series, we’ll examine the myth that lower AC temperature settings will jack up your electricity bills.

* * *

Bullshit #8
Higher AC thermostat settings costs less and lower settings more in summer.

If you look around the Internet long enough, eventually you’ll encounter this bizarre statistic:

“Research on Florida homes showed that summer AC cost increases
12% for each degree the thermostat is lowered below 80°F [26.7°C].”

If this sounds idiotic to you, then you must already understand basic logic.

This sentence is found almost word for word all over the Internet. Origins unknown. Recyclability, very high. Usually found in any type of online discussion about air conditioning.

It’s crap — and here are the two dead giveaways:

  • the 80°F — the figure is too rounded and too high, even for Florida
  • the 12% — a wee high (and I live in one of the most energy-costly places on earth)

Everything you’ve read so far from me, have I ever given out temperatures in such completely rounded figures? No, you haven’t (not yet anyway). The percentage? Already explained. So someone, somewhere, is into crap invention and/or distribution.


Srsly, this is the idiocy that some of us still subscribe to — to equate lower temperature settings with more power use and higher bills. Or, conversely, less power use and cheaper bills with higher settings.

To restate from Part 2:

FACT: The AC runs at its rated power consumption level regardless of the thermostat setting.

To be 100% honest and objective in absolute terms, there is a difference in power consumption between different temperature settings. In relative terms, however, the difference is just under the threshold of significance in the context of billing.

A friend has this setup and cost bugger to run:

  • two 8½-kilowatt Mitsubishi splits (living and dining rooms, kitchen, study)
  • four 3½-kilowatt Mitsubishi inverter splits (3 bedrooms, office)
  • total load is (2 × 8.5) + (4 × 3.5) = 17 + 14 = 31 kilowatts an hour
  • basic domestic rate is 90¢ Hong Kong (11¢ US or 7 pence) per unit (1 kW/h)
  • therefore, billing at 31 kW/h × $0.90 = $27.9 × 8 hours = HK$223 a day

That’s roughly US$28.60 or £18.16 a day if everything was on full blast.

But of course the friend doesn’t have all six ACs on all the time. It’s mostly just one or two ACs at any given moment. And friend sets the ACs at 20°C (68°F), which basically cools the entire place well enough to around 24°C.

From that, you can see setting the AC to 20°C doesn’t cool the place down to 20°C — you have to take into account that cooled air gets heated up by the ambient temperature of the premises. And concrete jungles like Hong Kong retain a lot of heat.

As if by the laws of physics, for every vision there is an equal and opposite ‘revision’:

“I hate running the AC. Every way I look at it is a waste of energy. I lived in Nigeria [or Djibouti, Tanzania, the Amazon or whatever] for two years and never once used the AC. I was totally comfortable in the daytime when it’s never below 36°C with 100% humidity and the nights never lower than 32°C with 95% humidity. Your body just adapts.(Invented example)

Yeah, right. And some people find swimming with sharks totally comfortable too. I love swimming in leech-infested waters; your body just adapts. Gee, were you previously violated by a barnyard animal or something?

Most of us find living in a humid, semitropical country (like Hong Kong or Singapore) with almost year-round temperatures in the mid-30s centigrade and 90+% relative humidity annoyingly uncomfortable — just as you, prat, find ACs annoyingly cold. Your body adapts (true) but there’s a limit.

You obviously never lived in the Middle East. Summers there average over 50°C (112°F) with 100% humidity. (I once lived in Beirut, whose climate is a shagging lot nicer than, say, Cairo or Dubai.) If you don’t turn on the AC below 22°C, everything goes mouldy or otherwise disintegrate under the heat. Ever wondered why archaeological artefacts from the Middle East are generally in a distressed state?

These are the same livestock people who have no concept of even a test tube unless it’s got the words “environmentally friendly” written on it. They are also the kind who can’t tell you the difference between ‘element,’ ‘molecule,’ ‘compound,’ ‘alloy’ or even ‘substance’ — stuff that middleschoolers are expected to know from General Studies classes.

FACT: In practical terms, running the AC set at higher temperatures produces roughly the same amount of pollution as set at lower temperatures.

Listen, dimwit, if we’re deadset on polluting our planet, allow us to do it with some degree of comfort.

FACT: Human body temperature is 37°C (98.6°F). As the ambient temperature rises to our body temperature or more, the less adaptable we become. The reason is that, as temperature rises, the protein molecules in our cells become increasingly denatured, thereby inhibiting our overall ability to produce somatic cells properly.

Don’t you remember anything from school?

* * *


Metabolic differences between individuals counts for shite
— unless you’re comparing yourself to a gerbil.

<< Part 4 << || >> Part 6 >>

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© The Naked Listener’s Weblog, 2011.

Images: ‘Trust The Lies’ via irational ♦ Test tubes via Yancheng Rongkang Glassware Co. Ltd.

AC myths 4: Temperature is relatively relative

Thursday 15 September 2011, 1.35pm HKT

<< Part 3 << || >> Part 5 >>

(Continued from Part 3)

In this fourth instalment, we’ll bust the myth about official temperature recommendations being good for all and sundry because they were based on some kind of standard.

* * *

Bullshit #7
That the ‘recommended’ temperature setting is good for every situation.

recommend (vt) 1. to give in charge; commit; entrust 2. to suggest favorably as suited to some use, function, position, etc. 3. to make acceptable or pleasing 4. to advise; counsel; suggest
(Webster’s New World Dictionary of American English, Third College Edition (1988), p. 1121: Simon & Shuster Inc.)

Normally, we tend to think of a recommendation as in sense 2. In reality, it’s more like sense 3, especially if it comes from the government.

Anything that is recommended is not one-size-fits-all. Recognise that the recommended AC temperature setting (whatever it may be in your location) is just a guideline, not gospel.

But a guideline based on what? On lousy logic?

Getting used to getting used to

Bit chilly in ‘ere, innit?

Suppose I were to go from outside in the mid-30s Celsius (mid-90s Fahrenheit) and high humidity into indoors set for 21°C (69°F) or 22°C, it would feel absolutely freezing. Even 25°C (77°F) feels cold at first, but pleasant after a few minutes (or when the sweat isn’t there anymore).

It’s what you get used to, isn’t it?

But I also think the home is a lot different from the office. Somehow, notwithstanding that my workplace has no real dress code, it just doesn’t seem acceptable to turn up at most workplaces in a tee and shorts and sockless, whereas the same at home makes a lot of sense.

The point is, temperature is relative.

If your local climate is never likely to hit 25°C/77°F indoors for more than a couple of days a year, then of course the idea of setting the AC to 26° is a bit excessive. You might even question why you need AC installed at all. Such is the case for most of Canada, northern USA and northern Europe.

However, it’s a different ballgame if you live in equatorial, tropical, subtropical and desert climes, such as Hong Kong, India, Indonesia, North Africa, the Middle East, southern USA, Central America, etc. In those places, half to three-quarters of the year will be 29°C (84°F) or hotter. The higher AC temperature setting is wasteful of energy and prices up your bills. And adds to the general pollution and environmental damage of the planet.

Which is why the Hong Kong government recommendation for 25.5°C (78°F) is such bollocks. Since that recommendation is recycled from other countries, it means by extension American, Canadian, Australian and other Absurdistani recommendations are equally bollocks.

Stop destroying my planet, you sonofabitch.

Sodahead evangelism

Sooner or later in any discussion about ACs, you’ll encounter some fathead who contends nearly everything boils down to acclimatisation. Adapt or die! The typical attitude most likely would be:

“Yeah, people, keep turning your aircon to lower and lower temperatures. Every degree colder you make, your little indoor home bubble helps pollute our entire planet even more. Man up! Deal with whatever temperature you live at, unless you want your grandkids to be living in a world where the outdoor environment is too noxious for them to ever step outside.” (Invented example)

Cutting down on AC use is environmentally friendlier and better — it certainly feels intuitively right too. Actually, it’s shite-talk from an environmental sodahead.

(A sodahead is person who voices an orthodox opinion publicly but flames anyone with a different opinion, even if it’s still an orthodox one).

If you live in an essentially cold region, it doesn’t matter. But if you live in a hot and humid region, that’s another story.

There, you’re almost always hot — almost always dribbling away in sweat (as I am now while writing this). You take more showers. You do more laundry: your clothes are almost always sopping drenched. More showers, more laundries — more direct consumption of freshwater, power and detergents or polluting substances.

In the end, trying to adjust yourself to your essentially unadaptable-to surroundings actually contributes to even more damage to the environment than otherwise from AC use of energy. This idea is quite a bit lost even on the environmentally minded.

Unless and until there is a workable alternative to the AC, telling people to shut off the AC and adapt or die is really asking to be spat at.

Yeah, people, keep saying acclimatise, acclimatise, adapt or die. Every time you say it, your ignorant stupidness lights up like a Christmas tree, embarrassing us that you’re also in the same species as the rest of us.

Yeah, man, keep telling us to set temperatures higher in summer and lower in winter, helping to pollute our entire planet even more under the pretext of eco-friendliness.

Man up! Realise your temperate-zone crap don’t always work in the tropics, unless you want your grandkids to live like foulsome beggars in a sewer with skin rashes and boils all over their bodies and so much cockroach infestation in the home for them to ever step inside. Twerp.

* * *


It’s a myth that lower temperature settings will jack up your bills.

<< Part 3 << || >> Part 5 >>

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© The Naked Listener’s Weblog, 2011.

Images: Asian female in tube top by David Ewing via World of Stock ♦ Dickhead T-shirt via ♦ The Naked Listener blog icon by thenakedlistener.

AC myths 3: Not AC and fan together

Thursday 15 September 2011, 1.00pm HKT

<< Part 2 << || >> Part 4 >>

(Continued from Part 2)

In this third part, we continue our AC myth-busting by looking at why using the AC and fan together is all wrong, despite the strong temptation to do so.

* * *

Bullshit #6
If 25°C (77°F) is too warm for you, run an electric fan on high with the AC set no cooler than 25°C. This will provide optimal efficiency to augment AC cooling.

Rubbish! If you are ever concerned about maintaining a low carbon footprint (and who isn’t?), this is exactly the way to skyrocket your carbon footprint — and your electricity bill.

Running your fan like that is crazy. You can factualise all day long, calculationalise endlessly, citationise everything, statisticise all the time — but you’ll be no wiser about your expenses. Until the bills arrive.

FACT: The AC works at its rated power consumption level regardless of the thermostat setting.

Not strictly accurate in the absolute engineering sense, but true in a relative sense from a consumer point of view.

The garden-variety electric or ceiling fan uses around 60 watts an hour (just like a 60-watt lightbulb). The average split-type (wall) AC uses 650 watts an hour. That’s like 10 times the power consumption. Some people balk at this and use that ‘fact’ to talk trash.

Sure it’s 10 times greater. And it has to be.

THINK. The AC has to do several things — sucking in air, compressing, decompressing, cycling the refrigerant, cooling the air, running the fan motor, dehumidifying and other stuff. All the fan has to do is spin the propeller motor. Whaddaya expect, professah?

Be objective. Running a fan in addition to the AC is just adding on to your overall power usage whilst not making the ambient temperature appreciably cooler or more comfortable. As said already, modern ACs run at their manufactured power consumption level regardless of the temperature being set to.

The fact that a 650-watt AC uses 10 times the electricity of a 60-watt fan (and therefore higher running cost) is irrelevant. Running a high power-consuming appliance has to be more expensive than running a cheapo — that much should be obvious. It’s the number of hours you put the AC or fan to use that also determines the price of your electricity bills, dimwit.

If you want more, you use more, so you pay more. The AC is like your bitchy girlfriend: you like her cleavage, but you have to put up with her drama. Your mother never told you this?

FACT: ACs are designed to create their own air drafts for balanced cooling and dehumidification. Therefore, running a fan will throw the AC airflow out of whack.

Disrupting the AC airflow causes the AC to work that much harder. In effect, you’re driving your AC to early death.

It’s like the bathroom ventilation fan. What goes out, something must come in. Whenever you turn on the bathroom fan, you need to throw open at least one window for air inflow to balance out the air outflow. Since the air outflow is ‘assisted’ (by the fan), the air inflow must be of a greater margin than the outflow. Still with me?

Shut off all the windows or doors, and the bathroom fan causes a pressure difference between indoors and outdoors. Then, the fan labours against the lack of airflow (sometimes audibly so), and burns out sooner than usual.

The AC works roughly the same way, except that it does this by creating a closed system. Even my plumber knows this.

But why run another ‘cooling’ appliance (especially a fan) in conjunction with the AC? It makes no sense because of the above. Read some school-level physics, please.

FACT: The fan motor generates heat, and is counterproductive to the work of the AC.

You never thought of this, did you, genius?

For some people, a 25°C/77°F AC is sometimes unneeded altogether:—

“I find 25°C is a very comfortable temperature with [just] the fan on. And I grew up in Calgary [Canada] where 25°C is considered a hot summer day!” (Friend)

Use the AC as it was intended and it will do its job properly without using fans.

Trivia: American engineer Schuyler Skaats Wheeler (1860-1923) invented the electric fan in 1882 at age 22. A few years later, German-American inventor Philip Diehl (1847-1913) invented the electric ceiling fan by sticking blades to a sewing machine motor and attached it to the ceiling.

For that oh-so-environmentally friendly zero carbon footprint

* * *


Official recommendations on AC temperature settings
are only guidelines, not gospel.

<< Part 2 << || >> Part 4 >>

* * * 

© The Naked Listener’s Weblog, 2011.

Images: Electric fan from author’s collection ♦ Chinese fan via Freaking News.

AC myths 2: Thermostat at 25°C is all wrong

Thursday 15 September 2011, 12.30pm HKT

<< Back to Part 1<< || >> Forward to Part 3 >>

(Continued from Part 1)

This following piece of AC mythology is very widely believed and recommended, so it needs quite a bit of explaining to set the record straight.

* * *

Bullshit #5
The recommended AC thermostat setting is 25°C (77°F) and best balances the economy of running the AC and providing a comfortable temperature.

Wrong! See, that 25-degree crap is just wrong on all levels.

Say the outdoor temperature is 28°C (82°F). To run the AC at 25°C is just wasting energy and not maximising the capacity of the AC unit or its refrigerant. It leads to early degradation of the refrigerant (Freon, R-400 series or whatever). It also causes unwarranted heat buildup inside the AC unit.

You get this totally groundless assertion all over the place — and from not a few AC manufacturers, retailers, refrigeration engineers, power companies and governments.

You’ll also discover that well-meaning people develop a sudden high tendency to show off their supposed knowledgeability, usually by flooding the discussion with lots of facts and stats about ACs and optimal settings. In the end, it all confuses than enlightens.

But Bullshit #4 comes with several sub-bullshits — and the most usual is this one:—

Sub-Bullshit 4A:
Set the AC thermostat to a higher temperature in summer and a lower temperature in winter.

This is a rich one. The moron who churned out this drivel (and many continue to churn out this fine disgrace) didn’t even notice he/she slipped up (and neither did we) — why are you using the AC in winter? That instantly puts this recommendation in the bullshit category.

FACT:— The actual optimal AC thermostat setting is 20°C to 23°C (68°F to 73°F) because the internationally accepted (and year-round) normal temperature and pressure (n.t.p.) is 20°C at 101.3 kilopascals (68°F at 14.7 pounds per sq. inch).

Anyone who ever did O-level (secondary/high school) physics and certainly every university engineering student knows this — so why not you?

And you need to be slapped around if you were to quibble about this. Honestly, the behaviour of some people…

ASIDE:— N.t.p. is different from standard temperature and pressure (s.t.p.), which is 0°C (32°F) at 101.3 kPa/14.69 psi — but that’s another story altogether.

If you find 20°C (68°F) too cold, then you must be one helluva effing physical wreck.

I’m serious — I’m a scrawny, skinny small fry of 120 lbs and 5 feet 8½ (55 kg, 174 cm), and 20°C is nowhere near cool-feeling. And I live in a subtropical city where three-quarters of the year is 28°C to 33°C at 90% relative humidity.

Protip:— I learnt yonks ago the rule of thumb was to set the AC at 10 degrees below the outdoor temperature (using the Celsius scale).

A friend who actually works in the HVAC (heating, ventilation and AC) business confirms that this rule of thumb IS the optimum way to run air conditioning. Here’s what my friend had to say:—

“Setting the aircon to 10 degrees [on the Celsius scale] below the outside temperature is a good rule of thumb. Aircon in the home is a ‘comfort application’ rather than a ‘process application’ such as in industrial settings.

“It’s true that the dehumidifying effect of aircons means that you will feel cooler at 25°C [77°F] inside than standing in the same 25°C outside because of the lower humidity inside.

“Sure, if you set the aircon at 10 degrees below the outside temperature, you will feel a very big difference between inside and outside. But if you run your aircon generally 10 degrees below whatever is outside, you will find it pretty cost-effective in the long run and keep your bills low.”

Alright, you can argue till the cows come home that ‘normal room temperature’ will depend on the locale and the individual. I don’t dispute that. Ask and you’ll get a range of useless answers:—

  • North Americans will say 77°F (25°C)
  • most Europeans will say 20°C (68°F)
  • 20°C to 25°C for those who like to hedge their bets (gormless!)
  • grandparents would probably say 32°C (90°F) — then again, their lives are shutting down anyway so they’ll feel cold at any temperature

I don’t claim to be an engineer, or even any good in physics. I passed my O-level physics in a resit. But I’m not exactly ignorant of physics. If a bunch of boffins around the world agreed that n.t.p. is 20°C (68°F) at 1 atmosphere, there’s reason behind it, Einstein.

What we should do

Obviously, we must set the AC to the temperature we feel most comfortable with. The temperature value itself is not that important — the temperature sensor of the AC might be far away from you, or you could be closer to a heat/cold source (window, door, kitchen, etc), or you’re in an office environment or public place and don’t have much control.

Set thermostat on high, and this becomes of your home (click image for full story)

Use common sense:—

  • if you feel a bit chilly, put on an extra shirt or jumper (the only choice in the office)
  • if you feel warmish, strip
  • shut the AC for a while if it’s getting chilly (workable only at home)

I also think what needs to be considered also is whether you’re setting the AC to cool a larger or adjacent room or just a small room (like a bedroom). If your bed is in the AC’s direct line of fire set at 24°C (75°F), it’s bound to get freezing sooner or later. If you’re trying to cool the kitchen or dining room, perhaps with several people milling around or some sunlight streaming in, setting the AC a little cooler is only common sense.

Some people are so sensitive to temperature that more heroic efforts are needed:—

“Personally, I prefer to set the aircon to a degree or two more than thermal comfort during summer, and a degree or two less during winter — just the opposite of what others do to make up for inadequate thermal shielding [i.e. insulation] of the building — in order to achieve reduced thermal shock while leaving the building, and reduced mental shock while receiving the electricity bill.”

But the real question is, why the hell are you using the AC in winter? Throw open the bloody windows in winter, sport.

(BTW, I happen to feel that particular individual quoted just now was a liar and was trying just a bit too hard to lend believability to Bullshit 4A.)

Ultimately, for the sake of your AC lifespan and electricity bill, it would have been better just to do this:

Protip:— Keep the AC thermostat setting and room temperature constant at one fixed point all year round.

Just keep a thin cardigan around in the office or switch the unit off at home if things get a bit chilly. The more you mess with the AC, the quicker it effing breaks down.

Unless you bought a stupid Fortess AC like I did.

What about propaganda?

After a while of searching and asking around, you begin to notice like I did that virtually all governments around the world give out the same two recommendations:—

  • the optimum AC room temperature is 23°C to 26°C (73°F to 77°F)
  • for every 1° increase in indoor AC temperature, you can save 10% off your energy costs (e.g. Energy Rating website of the Australian government)

The U.S. and Canadian governments recommend 25°C (77°F). The Aussies recommend 23°C to 26°C. Our Hong Kong government recommends 25.5°C (78°F).

Every country has their own unique characteristics and develop standards most relevant to their situation. So how is it that almost all of the major AC-using countries could have almost identical recommendations for AC settings but physically different climate profiles?

That fact alone is a telling sign that there’s been quite a bit of statistical recycling going on — one country reduping the stats of another country — most probably because the civil servants in charge were bone idle to check or test things out for themselves, which is what I often find in my long experience of dealing with the bureaucracy.

Even at face value, both recommendations are lousy logic. You could just as easily argue that you would achieve zero energy cost if you set your room temperature to 30°C when the outside is also 30°C. See what I mean?

The upshot? Literally decades’ worth of collaboration by thousands of scientists to draw up international standards just go out the window when governments go it alone and decide to use completely different and variable sets of standards for making recommendations. Way to go.

Do your research properly

Let’s look at things:—

FACT:— Power companies have been promoting this 25°C (77°F) AC thermostat setting because they will have minimal brownouts (drops in voltage in the electricity supply) on their ageing grids — a plus for their bottom line. (Source: my HVAC friend)

I promise you, that’s why you’ll find nothing in the scientific literature on air conditioning that directly backs up the 25°C/77°F.

But look under the heading of ‘control engineering’ for prevention of power dips in legacy power grids and you’ll find plenty of references. Don’t take my word for it — check things out yourself.

FACT:— The human body operates most comfortably and with the least amount of physical stress at temperatures of 19°C to 22°C (66°F to 71°F).

You can look this up in any university human physiology textbook or lab manual. See later instalments of this article for details.

FACT:— All high-rises, shopping centres and public indoor spaces are set at 22°C (71°F) — because that is what building structures are designed to operate at.

Most likely you are an architect if you know this. I happen to know something about this because Dad was an architect — and I don’t think yours is one. I read Dad’s books too, y’know. And Dad passed his physics, qualified in engineering and surveying, qualified in architecture at the Bauhau (no less), passed his German and French, failed his Chinese, and not so hot in law. Unlike me, Dad never took Latin or Greek. So there. So screw you if you don’t think I know what I’m talking about for this bit.

FACT:— All climate control systems (for houses, cars, etc) have factory preset temperatures set at 22°C (71°F).

And you never thought to question why this is so.

Normal room temperature and pressure is 20°C (68°F) at 1 atmosphere, internationally agreed

Go and ask a power company what it sets ACs to in its own buildings. The ACs will be controlled by an environmental control system that sets ACs to 22°C (71°F) and 50% humidity — while they tell you to set yours at 25°C or 26°C. A bit contradictory, don’t you think? No, you didn’t think.

FACT:— The more times the AC compressor is running, the more moisture is removed from the air, therefore providing greater comfort. Conversely, the higher the set point temperature, the less moisture is removed from the air, and the more unpleasant or uncomfortable the air quality is.

Couple of protips:—

Protip:— If you have a remote for the AC, removing the batteries and reinstalling them should give you back the factory preset temperatures in each mode that the product was originally made for. For example, the Mitsubishi preset is 21°C (71°F). Think about that.

Protip:— The correct way to measure the AC air output temperature is use a thermometer 1 metre (3 feet 3 inches) from the air outlet. Don’t stick it right into the blowhole, like those two Laurel and Hardy repairmen did when they tried to fix my Fortress ACs.

* * *


Why running a fan with the AC on is counterproductive.

<< Part 1 << || >> Part 3 >>

* * *

© The Naked Listener’s Weblog, 2011.

Images: Hand setting a thermostat by Tom Grundy via 123RF ♦ Home AC on fire via ♦ Obey Our Recommendations by thenakedlistener ♦ Gridline brownout servicing via Little i-cay ♦ Office workspaces via Fashion Trends.

Air-conditioning myths exploded (Part 1)

Thursday 15 September 2011, 10.45am HKT

Updated 02 Aug 2013 with improved navigation links

>> To Part 2 >>

WE ARE MOSTLY MISLED about air conditioning.

I’m going to explode a few myths about ACs (air conditioners) because I’m angry and sick and tired of having to fix my two ACs year in, year out, every bloody summer.

At the time of this writing (12.55am), I’m drenched in sweat in a highly profuse way in 33°C (91°F) and 75% relative humidity in this toilet hellhole territory called Hong Kong (as if you didn’t know where I live already).

(By the way, don’t say “aircon” — it’s AC. Say it wrong and I’ll belt anyone around the mouth because I’m THAT upset from the heat.)

What happened?

Before my two present AC units, I’ve never had trouble with ACs. None ever needed anything more than general usual cleaning and usual upkeep.

Indeed, I’m generally very good with stuff. I used to have a Panasonic music centre (a ghetto blaster) from 1973 that was in daily use, and worked perfectly until it konked out in 1996 because of old age. Twenty-three years of service.

All my previous ACs worked and worked — until I bought those two Fortress brand ACs just 1½ years ago. Since then, they’ve broken down practically every bleeding quarter. Costing a cool HK$2,500 each (US$321 or £194), they ain’t exactly cheap either. So I’m namin’ names and kickin’ asses now.

One of the Fortress kicked the bucket in August (blown fan and compressor) — so that’s totalled. The other Fortress (still but barely functioning) probably has lost its refrigerant and is now spewing out more hot air than your favourite politician caught womanising. Fortress ACs are sodding hopeless machines.

Trust me, without the AC, life in Hong Kong in high summer just isn’t worth living. And to think that we’re officially in autumn (because of the Midautumn Festival).


More than 100 years of design and technology behind the AC — so how is it that the humble electric fan can work longer and more reliably than the AC?

Simply put, the AC is a more complicated piece of machinery. Complex engineering + bullshit propaganda = shite performance + needless expense.

Best AC that I ever bought was a Rasonic, made in Japan, and it worked and worked (just like Japanese cars tend to do) and gave out FREEZING air. I left the Rasonic at my old digs for the new tenants, and, sometimes, I have pangs of regret about that.

Back in the good ole’ days when my parents were still around, we had only “Made in USA” ACs. Dad preferred White-Westinghouse and Mum liked Polar — and they (parents and ACs) r-o-c-k-e-d, baby.

Trivia: Willis Haviland Carrier (1876-1950) invented modern air conditioning in 1902 one year after getting his engineering master’s degree from Cornell University. He’s the name behind the Carrier brand of ACs.

Off-topic: Mum and Dad also liked German TV sets (Saba, now Blaupunkt) and Grundig reel-to-reel tape recorders — but that’s another story.

Off-off-topic: Interestingly, Grandpa had the bizarre habit of using the long-defunct German words das Fernsehen or das Fernsehgerät for ‘television’ — that too is another story.

With over 100 years of history behind air conditioning, there’s really no reason for ACs to break down every bleeding quarter. Or ever.

So without further ado, let’s go straight to myth-busting.


Out there, there’s a lot of misconception, misinformation and plain old propaganda about air conditioning. Sniff around, and it really takes an effort of will to not see that most of the (mis)information and (mal)suggestions have been recycled around endlessly — particularly by those fine individuals with the words “sustainable living” hanging from the corners of their pursed lips.

I don’t claim my AC myth-debunking is any more complete than what you could find out there, but the myths that I recount are the main ones bandied about, at least here in Hong Kong.

* * *

Bullshit #1
Facts and figures speak for themselves.

We like to think of ourselves as reasonably scientific or logically minded. Truth is, we’re more into intuition — even that, our intuition mostly suck. The reason our intuition suck is precisely because we believe we’re reasonably logical.

Don’t be fooled by facts and figures. A lot of bullshit comes from burying things in a mass of numbers — supposed cost savings and general scientific-sounding lingo. Education have inured us to the idea that there is “austere beauty” in numbers — hogwash churned out by no less an idiot than Bertrand Russell.

We’re particularly (and peculiarly) fascinated with phrases like these:

“… reduce your energy use by 3% to 8% …”

“… save in the neighbourhood of $700/year …”

“… paying for itself in less than 6 years …”

Could be a lemon, though you wouldn’t think so from the way it looks

Facts and figures by themselves are fine. But it’s kind of silly too. Figures and stats used like that don’t necessarily tee in with your setup. It might not necessarily reduce your energy use by 3%, or save you $700 a year, or pay for itself in less than six years for you.

Of course, facts and figures put out by some organisation or whatnot are arguably just averages for general application.

But of course they are. We appreciate that, but please also explain the setup that the figures are derived from, or tell us how the averages were done — and that part is always conspicuously missing in any official recommendation.

I’m very sorry, but unless you do a better job at recommending, I just cannot take your word at face value. And that’s exactly what happened when I slipped up and bought those two lemons from Fortress.

* * *

Bullshit #2
Buying an energy-efficient AC will automatically reduce your electricity bills.

That will help, but even more important is buying a correctly sized AC. A small AC unit will struggle to keep your room cool. A big unit won’t cool your place down faster or remove moisture more thoroughly — it merely leaves your place cool but damp and clammy. Energy efficiency goes only so far.

Sizing an AC unit is using the correct capacity of AC for the size of the room.

Protip: To calculate the correct AC size to use, the professional rule of thumb is:

  • Temperate zone: 20 Btu’s per 1 sq. foot of living space (0.0063 kWh per 1 sq. metre)
  • Tropical zone: 25 Btu’s per 1 sq. foot  of living space (0.0072 kWh per 1 sq. metre)

Protip: Split the total Btu requirement over at least two AC units if over 10,000 Btu’s.

So, 500 square feet (46½ square metres) will require 500 × 25 = 12,500 Btu’s (2.93 kWh) of AC cooling capacity. That’s like two window ACs each of 6,000 Btu’s — because it’s better to have two or three AC units sharing the work than one gigantic AC handling it on its own. Remember Adam Smith, division of labour, no?

There is a more complicated way to size an AC unit [LINK].

Spit AC systems (a.k.a. central air conditioning) are measured by tonnage (not the same as weight tonnage). Splits provide overall climate control for the whole area. Very high initial installation cost if ductwork or electrical wiring are necessary. But splits have the highest savings potential compared with ductless or window units.

Protip: To convert Btu’s to tonnage, divide the total house Btu by 12,000.

So, 2,000 square feet (186 square metres) in the subtropics require 2,000 × 25 = 50,000 Btu ÷ 12000 = 4.1 tons. A 4½-ton AC unit would be the bare minimum size needed. That’s like eight or nine window AC units.

* * *

Bullshit #3
Your AC will perform the same no matter where you install it.

No, it does make a difference. A little planning goes a long way. Install in the right place and you’ll save energy and money.

The AC unit contains heat sensors. Install the unit at or near sources of heat, and you’ll make it work too hard. It’s common sense — you can’t expect the AC to cool if you put it in a hot place, right?

THINK! I used to know one idiot who installed the AC right next to the stoveworks and fridge, and then wondered why the AC kept breaking down. I wondered too, but more about why people like that idiot couldn’t spot the problem with that setup.

Protip: Install the AC unit in the shade because direct sunlight on the outdoor heat exchanger (backside) will reduce working efficiency. If no shaded area, then fix up a shade or canopy for it (especially important for window-type ACs).

Protip: Remove lamps, TV and any heat-emitting appliances near the AC thermostat — it senses their heat and can cause the AC to run too long or too much.

The truth is, optimal AC performance depends mostly on your geographical location and how you actually use the AC on a daily basis.

Some other factors:

  • engineering considerations
  • cost/efficiency considerations
  • effects of human metabolism
  • how your home as a whole uses energy
  • quality of your home insulation
  • prevailing weather conditions and general climate of your locale
  • your own perferred temperature range
* * *

Bullshit #4
Maintenance calls aren’t worth it.

O rly?

FACT: Preventative maintenance saves money.

Yearly maintenance agreements are more beneficial than most people think. Would you ignore changing the oil or filters in your car? Then why ignore maintenance on your AC?

  1. Failure to do something as easy as regular filter-changing can have drastic consequences. A dirty filter blocks proper airflow across the AC coils, making your unit less cooling, and eventually damages the coils and cost you hundreds or thousands of dollars to replace.
  2. Clogged drainlines cause mildew, mould and algal growth inside the unit. Water backs up inside and damages the unit. Excessive water buildup also causes safety switches to become activated (accordingly turning off the unit’s cooling parts) and requiring a thorough cleaning and draining of the system.

Repairs always cost more than preventative maintenance. Those two issues (and many others) can easily be avoided by proper and regular servicing.

* * *


Why the generally recommended AC thermostat setting for 25°C (77°F) is myth and propaganda all rolled into one.

>> To Part 2 >>

* * *

© The Naked Listener’s Weblog, 2011. Image of apple via Playerz Blog.

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