AC myths 9: Protips and hacks

Thursday 15 September 2011, 4.50pm HKT

<< Part 8 << || >> Part 10 >>

(Continued from Part 8)

Almost at the end of the series. We roll with some low-cost and no-cost ways of running your AC properly for summertime.

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First and foremost


1. Develop energy-saving habits. Savings come from little behaviour changes and habits. Strip down if you feel a bit warm, and put something on if a bit chilly. Stop running around the home in shirtsleeves in the middle of winter. Stop wearing dark suits and tie in the middle of summer unless at work.


2. Realise that using an AC is a relatively expensive undertaking, and if you’re that worried about cost, maybe you shouldn’t have AC installed at all.


3. For all practical purposes, the modern AC is designed to run at its rated power consumption level, regardless of the thermostat setting. It also produces the same amount of pollution at whatever the temperature setting. (Details in Part 5.)

AC-related tips

Relative temperature

4. Rule of thumb is set the AC at 10 degrees below the outdoor temperature (using the Celsius scale). For instance, if outdoors is 30°C (86°F), set the AC to 20°C (68°F) indoors. Professionals in the HVAC (heating, ventilation and AC) business use this rule of thumb, and it’s no mistake why they use it. (Details in Part 2.)

Thermostat habits

5. Handle the AC thermostat properly. Cool to 20°C to 23° (68°F to 73°F) and switch off when you feel chilly (instead of messing with the AC thermostat). At 20°C to 23°C, the extra cost is only marginal, but your AC will work more efficiently than at higher thermostat settings. (This tip contradicts the convention advice often given elsewhere: details in Part 2).


6. Don’t run fans while the AC is on. This is not a hard-and-fast rule — sometimes you have to make an exception. Fans disrupt the AC airflow, causing the AC to work harder, and therefore shortening its lifespan. A running fan motor also generates heat, therefore counteracting the work of the AC. Try to cut down on the number of electrical appliances running while the AC is on. (Details in Part 3.)

‘Auto fan’

7. Always use the ‘Auto fan’ thermostat setting, never just ‘On.’ On Auto, humidity is kept lower, so AC costs are much lower and comfort is higher.


8. Keep open the AC air-supply registers at all times (relevant for some AC models). It doesn’t save money, but closing off the registers may lead to costly problems.

Steady as she goes

9. Don’t try to speed-cool at max-low thermostat settings when you return home. Instead, choose a normal evening setting (20°C to 23°C, or 68°F to 73°F). The AC cools just as fast at 20°C as it does at any lower temperature.


No canopy? Wait till you see the bills

10. Block sunlight streaming into the premises when the AC is on.  Shut curtains and blinds in the direction of incoming sunlight. Close windows. Shut room doors to bigger rooms. Seal airleaks around doors (use caulking and weatherstripping). Check for airduct leaks or disconnected ducts around the house. Duct leaks can double your cooling cost. Rig up a canopy around the AC unit itself so sunlight won’t shine on it.

Bath time

11. Shut the AC off when you take baths and have the bathroom ventilation fan switched on. What goes out, something must come in. Open a window to let air flow in to balance the air outflow — it’s not the job of the AC to do that.


12. Change or wash the AC air filter screen once a month. It feels like a hassle, but it really isn’t. If you leave things untouched, the filter cakes up even more badly — then it becomes a real hassle. Clogged air filters restrict airflow, ups running costs, and often lead to expensive-to-fix compressor damage. Cleaning the filter screen is highly important in a polluted, concrete jungle or dusty place (like Hong Kong, the Middle East or southern USA) — you may have to clean the air filter once a week.

Microwave ovens

13. Use a microwave instead of the range (gas) oven when the AC is on. A microwave doesn’t heat up the kitchen. Shut the kitchen door when you’re cooking. A microwave pollutes less than a gas oven.

Water mist

14. If the AC is starting to go on the fritz, spray a fine mist of water at the rear end of the AC unit to keep it on the cool. This is a only stopgap measure.

Not in use

15. Cover the roomside and exterior ends of the AC unit when not in regular use (as in winter) to protect it from sunshine, rain and general debris landing on it or clogging it up.

Factory presets

What’s correct humidity?

16. If you have a remote for the AC unit, removing and reinstalling the batteries should give you back the factory preset temperatures in each mode the product was manufactured for. For instance, the Mitsubishi preset is 21°C (71°F).

Measuring temperature

17. The correct way to measure AC air output temperature is to use a thermometer 1 metre (3 feet 3 inches) from the cold-air outlet. Don’t stick it right into the blowhole, as some Laurel and Hardy repairmen are apt to do. (Story in Part 2.)


18. Set the indoor humidity level at 30% to 60% if your AC unit has humidity control settings. This is only a conventional wisdom, as there is no hard evidence to back up this recommendation. (Details in Part 7.)


19. Set the AC to blow cool air towards the middle of the roomspace. That allows for a more even distribution of cool air.

Hands in pockets

20. Stop messing around with the AC thermostat. You’ll make it break down quicker. Shut it off or put something on if you’re feeling chilly. Strip down if it’s a bit warm.

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General tips for keeping cool and saving energy.

<< Part 8 << || >> Part 10 >>

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© The Naked Listener’s Weblog, 2011.

Images: AC unit from author’s collection ♦ Thermostat setting by Tom Grundy via 123RF ♦ AC in the sunlight from author’s collection ♦ Sweaty Asian girls via c4c.

AC myths 8: Insulation can be daft

Thursday 15 September 2011, 4.15pm HKT

<< Part 7 << || >> Part 9 >>

(Continued from Part 7)

In this penultimate part of the series, the received wisdom about insulation might not be so wise for AC use.

* * *

Bullshit #11
Insulate your premises when you install an AC.

This is only a half-myth, because it is a legitimate factor to consider in some regions. In places like Hong Kong, though, it’s pretty stupid to see this recommendation for residential premises.

Hong Kong is a concrete jungle. Wait, not in real terms. Urban land use here only figures 15% of the total land availability. But the concrete parts of the place are seriously concrete. Srsly.

‘Visual impact’?

Many cities around the world make some abject effort to plant trees and other shrubbery on the sidewalks and generally around town.

Hong Kong makes no such effort. Here, plants are considered a ‘visual impact’ on property prices (I kid you not!) or bad feng shui or “noise-causing” (Shome mishtake here—Editor).

But if and when our municipal authorities do plant, they’re doin’ it wrong.

Many times you will see government contractors plant new trees along sidewalks — a good thing — but then they go all barmy and proceed to concrete over the base, so that the tree suffocates to death nearly always within 2 or 3 years of planting. And then the government arborialists wonder why.

(I can’t believe I’ve actually lived the day to have to write that.)

But Hong Kong IS a concrete jungle, practically speaking. (Singapore, too, although they won’t admit it.) Concrete jungles retain a lot of heat.

Concrete jungles retain a lot of heat: livable only with AC

When you’ve got something like cars, the underground train system, four million phonelines and 13 million mobile phones (for a population of 7½ million), 6,000 high-rises of 20-plus storeys, plus cable TV, Internet lines, etc, etc — that’s a lot of heat sources and a lot of heat retention. Living and working inside a concrete structure all the time, insulation is irrelevant here.

But insulation is highly relevant for some places — Australia, Canada, the UK and the USA being prominent examples.

In Australia, if there’s no roof insulation, the AC is working against the heat load on the roof, and that can be considerable. Bedrooms there tend to be downstairs and well-insulated from the floors above, and there is some insulation in the exterior walls.

For office buildings, Hong Kong forgoes much of the conventional Anglo-American-centric insulation wisdom and go straight into installing mirrored exterior glass panes to reflect away light and heat. We use specially formulated, man-made marble slabs for building exteriors and interiors. Porcelain tilework is nearly everywhere inside. We don’t have earthquakes, tornadoes or even tsunamis like some places do, so we can afford to use those building thingies.

We use 3M Panaflex Awning and Sign Facing 945 GPS material (a kind of flexible plastic tarpaulin) for hoardings and backlit signages — much more versatile than the woodboards, Sheetrock gypsum panels or Perspex sheeting often used in the West.

Shameless self-plug: The Naked Listener has the distinction of introducing Panaflex to Hong Kong in the 1980s. Got no money out of it, though.

Worst colour combo for any building

For residential buildings, we’re starting to use more reflective paint on rooftops and exterior walls than previously to reduce heat transfer. This is a costlier version of what Hong Kong did in the 1950s: whitewashing the outer walls.

FACT: Any normal white or light-coloured exterior wall paint will reflect light and heat off of a building structure.

Short of installing mirrors on the outside — not a bad idea, actually.

Protip: Whitewash your building’s exterior once a year. Every little bit helps, and white has the best heat/light reflectability than any other colour.

Think about why power stations and nuclear reactors are always painted white. Think why space rockets and spacesuits are in white. Think why there are no black or dark-coloured palaces.

Protip: Whatever you do, don’t paint your exteriors in dark pink (a.k.a. terracotta, burnt ochre, cemetery rose), brown or green — they’re the pits for heat/light reflection, they absorb heat and infrared radiation second only to all black, and they just look plain shite.

Which is why office buildings around the world almost never use those colours (except bloody Hong Kong and China).

Protip: When you use the AC, curtain off any incoming direct sunlight, which heats up the place. Even better, get those one-way mirror films and use them on window panes for general heat/light reflection.

Dakin Building, a.k.a. Luke Skywalker Building, in California

* * *


Low-cost and no-cost energy-saving protips for the home and office.

<< Part 7 << || >> Part 9 >>

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© The Naked Listener’s Weblog, 2011.

Images: Shrubbery and house via CurbedWire ♦ Hong Kong concrete jungle via TrekEarth ♦ Golden mirror window panes by Only2perCent via WallpaperWeb ♦ Green-white building in Hong Kong via Airconco ♦ Luke Skywalker Building via Wikipedia.

AC myths 7: Temperature and humidity for all and sundry

Thursday 15 September 2011, 3.05pm HKT

<< Part 6 << || >> Part 8 >>

(Continued from Part 6)

This is Part 7 of the series and we’ll look at the myth about correct temperature vs. correct humidity.

* * *

Bullshit # 10
Temperature and humidity apply to men and women alike.

Interesting, but wrong — on a level you’d probably not considered before (unless you’ve read Dad’s books on HVAC).

Wear a jumper if you’re cold

In the heated debate about air conditioning, the biggest problem is that women get cold quicker than men. Ladies are cold, gents get hot.

In the home, he (or she) who cries the loudest, wins. In an open office, we need to agree somehow.

I can’t answer for other people, but I find even fat ladies get cold quicker than skinny guys. Some bitches turn up the heat, but mostly they turn up your temper. Maybe it’s the crowd I run with. Your mileage may vary.

There’s almost no research on difference in temperature preferences between men and women.

What’s the correct humidity?

Humidity (or relative humidity) comes under the general heading of thermal comfort. It makes a big impact on our perceptions of temperature and thermal comfort.

The commonly recommended indoor humidity level is 30% to 60% — and that sounds about right.

But nothing’s correct, really. There are no hard statistics on optimal humidity.

If you live in a dryish city like Johannesburg (59% relative humidity generally), then a cold AC can dry out the air quite a bit more than people would have liked and people sometimes become ill because of it.

If you live in a region where temperatures are never likely to go higher than the mid- to high 20s Celsius (high 70s to low 80s Fahrenheit), the AC is an option, not an essential. Instead, you need a standalone dehumidifier, which does the job much more efficiently.

Protip: Just so you know, a standalone dehumidifier creates a lot of heat. Don’t use the AC together with a standalone dehumidifier, otherwise you’re busting your AC and bills.

But if you live in a high-heat, high-humidity region (such as Central America, the Middle East, and the equatorial, tropical and subtropical regions), you couldn’t get enough dehumidifiers and ‘dehum’ ACs to stop yourself from drowning in the wet air.

Okay, I gotcha, you don’t mind perspiration

Humidity in the sense of comfort is about how fast body perspiration evaporates and gives a cooling effect. Our perception of a dry or damp indoor environment comes from relative humidity (an objective fact) and how our body sensors detect humidity (a subjective fact, but a fact no less).

Evaporation requires energy for it to take place. Water evaporating from a body draws heat energy from that body. Which is why we feel cooler coming out of the swimming pool, and also why water in porous earthen pots is found to be cooler than water in non-porous metal vessels.

Relative humidity creates the perception in us of an dry or damp environment. High relative humidity (i.e. high moisture content in the surrounding air) prevents evaporation from taking place. Which is why you and everything else are sopping wet in the rainforest because the high relative humidity there (99% or 100%) just stops any evaporation from happening.

Protip: If you live in a nice, drowningly humid and hot place (as I do), wear home clothes that allow you to perspire. Forget T-shirts — they’re hot and bothering. Wear shirts, preferably a cheapo silk shirt from a stocklot outlet.

Or do what I do — a unisex-looking woman’s silk gown around the house. It’s for comfort, not kinkiness. C’mon, you’re at home! Who’s looking?

Sensors in our bodies are fairly efficient at sensing heat and cold, but crap at detecting relative humidity. Which is why there is so much more subjectivity (and arguments) about humidity preferences.

I’m over the moon when and wherever relative humidity is 50% or anything lower. Others think I’m insane because they think it’s like living in a dehydration chamber. I also like really cold environments, which makes friends think I should live inside a freeze-drying unit. It’s a shame that Hong Kong is so opposite of what I like.

* * *


Insulation is okay for some places, but kinda daft for others.

<< Part 6 << || >> Part 8 >>

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© The Naked Listener’s Weblog, 2011. All images via c4c.

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