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The Revenge of the Circulating Fan

Cooling people by increasing local airflow is at least ten times more energy efficient than refrigerating the air in a given space.


The 152 cm diameter Haiku ceiling fan from Big Ass Fans. Power consumption is 2-8 watts for normal range of use.

The steadfast rotating fan has been employed to keep people cool since the eighteenth century, and it remains highly effective, requiring much less energy and providing more comfort than air-conditioning. Cooling people by increasing local airflow is at least ten times more energy efficient than refrigerating the air in a given space, and it also adds the benefit of a personally controlled thermal environment.

If used in combination with air-conditioning, fans could lower energy use by 30-70%, even in incredibly hot climates or during heat waves. Circulating fans, which have become very energy efficient in their design, can be readily and cheaply applied in both new and existing buildings. Recent changes in international comfort standards have paved the way for their comeback.

The Rise of Air-Conditioning

Compressor-based cooling or air-conditioning (AC) puts increasing pressure on electric grids worldwide. In the USA, the birthplace of the technology, AC accounts for approximately 20% of year-round electricity consumption by American households, and 15% of total electricity use. 1

The widespread use of AC explains in large part why Americans use so much more electricity than Europeans: AC electricity use by an American household equals 60% of all electricity used by the average European household. 2

Except for the few temperate regions on the West Coast, air conditioners are now standard in most American homes. 3 While only 12% of American households had AC in 1960, this number increased to 87% in 2009. 1 Furthermore, the average air-conditioned home consumed 37% more energy for cooling in 2005 than it did in 1993 – in spite of a 28% increase in AC energy efficiency. Part of the increase in energy use is due to the switch from window units (which cool one room) to central air-conditioning (which cool the whole building), and in part to the growing cubic footage of houses and apartments. 1

Peak Power Demand

Even worse is the impact of air-conditioning on peak power demand. Obviously, the use of AC is not spread equally throughout the year, but concentrated in the summer months. On very hot days, many air-conditioning units are set to a maximum position, and as a consequence demand for electricity spikes. Hundreds of American power plants and a great many miles of transmission and distribution lines are needed on average only two or three days per year, while they sit idle for the rest of the time. Peak power demand is growing faster than average power demand, and compressor-based cooling is an important reason for this. 45

When we look at greenhouse gas emissions, another problem comes to light. AC not only produces emissions originating from electricity production. There is also the leakage of refrigerants, which are gases that—although they remain in the atmosphere for a shorter time — have a much higher global warming potential than CO2. The irony is that the substantial greenhouse gas emissions from air-conditioning bring us hotter summers, which in turn stimulates the use of air-conditioning. Another feedback loop is the “heat-canyon effect”: by blowing warm air out from buildings, AC heats up the streets, in its turn raising the need for more AC. 16

AC electricity use by an American household equals 60% of all electricity used by the average European household

While the USA remains the absolute champion of air-conditioning, the technology is also gaining importance in the rest of the world. For example, between 1997 and 2007, the number of Chinese households owning air-conditioning tripled, with the annual number sold reaching more than 20 million. 1 By 2020, energy consumption for air-conditioning in India is projected to grow almost tenfold compared to its 2005 level. 1 Even in the temperate climate of Europe, AC is advancing, especially in the commercial sector. For example, in the UK, based on currents trends, 40% of commercial floor space will have AC by 2020, compared to 10% in 1994. 6

The Historical Evolution of the Fan

Throughout history, humans have used energy to keep themselves warm during the winter months. The use of energy to keep cool in summer, however, is a relatively recent phenomenon. Before the advent of air-conditioning in the first half of the twentieth century, buildings in hot climates were designed for natural ventilation (see further), and people adapted to the heat by changing their routines. However, air-conditioning was not the first technology that used energy for cooling: circulating fans predate AC by decades.

For most of history, fans were human-powered. Hand-held fans were used by ancient Egyptians, Babylonians, Persians, Chinese, Greeks and Romans. Most often, fans were waved by servants in order to cool their masters and to scare away insects. The folding fan, which people used to cool themselves, was invented by the Japanese in the ninth century, and introduced to the west by Portuguese sailors during the Renaissance. 7


A remotely operated punkah, 1863.

The first remotely operated fans were “pankha” or “punkah”, developed in the 1500s in India and the Middle East. These rectangular canvas covered frames, suspended overhead, were waved back and forth by servants (called “pankwallah” or “punkawallah”), who pulled a rope against a counterweight while seated outside the room. 10

Rotating fans appeared in the eighteenth century, and these were initially human-powered, too. During the same century, however, clockwork fans appeared, driven by a wind-up mechanism. In the nineteenth century, fans were powered by waterwheels, steam engines, or small water turbines running on tap water from the town mains. The first electrically powered circulating fan appeared in the USA in 1882.

How to Keep People Cool?

The four environmental factors that determine human thermal comfort are air temperature, air velocity, air humidity, and radiant temperature. Each of these variables can be manipulated to cool (or heat) people.

Air-conditioning lowers air temperature and (if necessary) air humidity. A lower air temperature increases heat loss from the body through convection, while a lower air humidity increases heat loss from the body through evaporation of moisture from the skin (which also occurs when we are not sweating). Circulating fans increase air velocity, which accelerates heat loss from the skin through convection and evaporation. Heat loss through evaporation increases with the square of the air velocity. 8


Moving air. Image: Amancay Maahs.

Radiant cooling—another method of keeping humans comfortable—works by lowering the temperature of the surfaces in a space. This is achieved by circulating cool water through plastic tubes in building surfaces, such as walls, floors, ceilings, or in modular panels. Radiant systems cool people by increasing heat loss from the body through radiation, but there is also an indirect, limited, and delayed decrease of air temperature. This is not so in the case of circulating fans, which have no effect on air temperature. 8 Either way, both circulating fans and radiant cooling systems can provide thermal comfort at higher air temperatures during hot conditions.

Why AC is Inefficient

Air-conditioning is the least energy efficient way of cooling people, because it implies that all the air in an enclosed space needs to be refrigerated (and, if necessary, dehumidified) in order to cool the occupants. The larger the space and the fewer the people within it, the more energy it will take to cool each occupant. Like air-conditioning, circulating fans cool people by encouraging heat loss from the body through convection and evaporation. However, unlike air-conditioning, moving air around requires much less energy than refrigerating it.

Moving air around requires much less energy than refrigerating it. Moreover, the cooling effect of circulating fans can be applied locally and has immediate effect

Moreover, the cooling effect of circulating fans can be applied locally and has immediate effect. Fans circulate air around the body, while leaving the air in unoccupied parts of the space unaffected. Likewise, it is not necessary to keep the air circulating when nobody is around. Upon entering a room, turning on a fan has an immediate effect. Air-conditioning, on the other hand, needs time to cool down a space. As a consequence, a space will often be air-conditioned even when nobody is around, in order to provide immediate comfort when somebody enters it.


Vintage desk fan by Westinghouse. Wikipedia Commons.

Like circulating fans, radiant cooling is much more efficient than air-conditioning, because there is no need to refrigerate the air. Furthermore, radiation is often the primary method of heat exchange between the body and the indoor environment. 9

However, compared to circulating fans, radiant cooling has two disadvantages. Firstly, like air-conditioning, it’s slow acting, which means that it needs to be operated continuously in order to offer immediate comfort. Secondly, it’s considerably more expensive than fans and it’s not as easy to install in existing buildings.

Another disadvantage of air-conditioning is that it requires an airtight, enclosed space in order to keep the refrigerated air inside. Circulating fans and radiant cooling systems, on the other hand, work indoors as well as outdoors. They can be combined with natural ventilation, taking advantage of an additional, free cooling effect when it is available. Both cooling systems appear in nature: wind is the natural counterpart of a fan, while cold surfaces such as those of seas, lakes, or caves are the counterparts of radiant cooling surfaces in a building.

The Cooling Potential of Circulating Fans

The cooling effect of circulating fans is substantial. An air speed of roughly 1 m/s is capable of offsetting a 3°C (5.4°F) increase in indoor temperature, while an air speed of 3 m/s has a cooling effect of roughly 7°C (12.6°F). 10 For comparison, these modest air velocities correspond with an outdoor wind speed of Beaufort 1 and 2, respectively. The lower the air humidity, the higher the cooling effect of a given air speed. Fan configuration is another important variable, because the airflow from fans usually reaches only certain parts of the body surface.

Ceiling fans produce the least cooling for a given air speed, as they affect a smaller part of the body. However, they have other advantages: they don’t require floor or desk space and they can have very large diameters, which enables them to cool a larger area. Floor fans aimed at the back or the chest provide the most cooling, while the cooling effect of desk fans sits in between these extremes – the face appears to be very sensitive to the cooling effect of air movement. 12


Industrial ceiling fan. Image: Wikipedia Commons.

In recent years, several studies have calculated the cooling effect of different fan configurations at various air velocities and relative humidities. A 2013 study using ceiling fans found that subjects were comfortable up to 30°C (86°F) and 60% relative humidity with an air speed of 1.2 m/s, and up to 30°C and 80% relative humidity with an air speed of 1.6 m/s. At 60% relative humidity, subjects would be comfortable at temperatures higher than 30°C, but these conditions were not investigated. During the experiment, which took place in a climate chamber, subjects were wearing light clothing (0.5 clo) and performed light activity (for example, computer work at a desk). 12

Recent studies have shown that people can be comfortable at 30°C (86°F) and 80% relative humidity with an air speed of only 1.6 m/s

The same authors conducted a similar study with personally controlled floor fans. In this case, subjects were comfortable at a temperature of 30°C (86°F) and 60% relative humidity with an air speed of only 1 m/s. However, the maximum air speed of the floor fans was not sufficient to deliver thermal comfort at 30°C and 80% relative humidity, in which case only 60% of subjects felt comfortable (comfort standards require at least 80% of people to be comfortable in a given condition). The researchers concluded that increasing the maximum air speed could further improve the results. 12

Both studies also found that none of the subjects complained about noise or dry eyes as a consequence of the use of fans. Earlier experiments with personally controlled fans showed that thermal comfort could be maintained up to 31°C (88°F) and 50% relative humidity with an air speed of 1.6 m/s, while studies in Thailand and Hong Kong have shown that subjects were comfortable at temperatures well above 30°C (86°F) and a relative humidity up to 85% with air speeds up to 3 m/s. It must be noted, however, that these studies did not ask the subjects about possible discomfort due to noise or dry eyes. 12

Energy Savings of Circulating Fans

Circulating fans can save large amounts of energy, either by lowering the energy use of air-conditioning, or by completely obviating the need for it. International comfort standards dictate a very narrow comfort zone for air-conditioned buildings in summer, which is between 23°C and 26°C (73-79°F). 11 However, if air-conditioning is supplemented by the cooling effect of circulating fans, a building’s interior can be allowed to fluctuate within an expanded temperature range while maintaining the occupants’ thermal comfort.


The 126 cm diameter Aeratron E503, one of the ceiling fans tested, consumes only 4-8 watts for normal range of use.

Warmer thermostat temperatures can bring about large energy savings. For every rise in degree celsius above 25°C (77°F) in the thermostat setting in summer, a cooling energy saving of between 9 and 12% can be achieved (5% per degree F). Obviously, the energy consumption of fans should also be taken into account. For ceiling fans running at high speeds, energy use is approximately 2% of the air conditioning savings, leaving net savings from between 7-10% for every degree celsius of thermostat rise. Consequently, if fans allow a thermostat setpoint of, for example, 29°C (84°F) instead of 24°C (75°F), the net savings amount to 35-50%. 10

The new generation of fans with DC motors and magnetically levitated bearings have remarkably low energy consumption. In the earlier mentioned study, thermal comfort up to 30°C (86°F) could be provided by fans using less than 10 watts, increasing energy savings up to 70%. Even very low-wattage fans (3W) which produce an air speed of 1 m/s near each occupant are capable of offsetting a 3°C (5.4°F) temperature rise, saving around 30% of cooling energy. An additional benefit of the low energy use of these fans is that they can be easily operated via battery power during blackouts. 12

An additional benefit of the low energy use of these fans is that they can be easily operated via battery power during blackouts.

In more moderate climates, the use of circulating fans in combination with natural ventilation or radiant cooling systems could easily allow people to get rid of AC altogether. While natural ventilation can be very effective in a well-designed building, obviating the need for fans during most of the year, its effectiveness is dependent on outside wind conditions. Fans can therefore act as a backup during windless days. Furthermore, not all occupants might be close enough to a window to enjoy the cooling effect of natural ventilation.

Fans also work well alongside slow acting radiant cooling systems, because they can provide instant comfort in anticipation of the radiant cooling coming on stream, shortening pre-cooling times. 12 If circulating fans allowed people to ditch the AC entirely, cooling energy savings could reach above 90%. 10

The Limitations of Fans

The faster the air moves over the skin, the faster heat is lost from the body. Unfortunately, there is a fundamental limit to the cooling effect of circulating fans: they can only provide cooling at air temperatures below the mean skin temperature, which is about 35°C (95°F). Fans cannot cool people above that treshold, because moving air cannot reduce the skin temperature below the ambient temperature – no matter how high the air speed.

Despite this limitation, fans remain extremely useful at temperatures above 35°C (95°F), because they can be used in conjunction with air-conditioning. 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. When used in tandem, the energy savings during heat waves would be around 50% compared to using AC alone.


Under-desk fan for locally controlled airflow. Source: 11

Another limit to air speed is the possible disturbance of loose papers, which can become a problem in offices at fan speeds above 1 m/s. This can be solved by paper weights, or by locating fans below the desks, aimed at the midriff. Another solution would be the long-heralded paperless office. 10

Greater Comfort

The use of fans can increase thermal comfort in multiple ways. The main difference between air conditioning and circulating fans is that AC subjects all people in a space to the same thermal environment, while fans allow the creation of personal microclimates. People react differently to similar temperatures, and have different clothing and activity levels. Therefore, it is very unusual for people to reach unanimity on the AC thermostat settings. In offices, this problem is often exacerbated by the tendency to overcool the building, forcing some people to wear thick sweaters or even use electric heaters while outside temperatures are well above 30°C (86°F).

AC subjects all people in a space to the same thermal environment, while fans allow the creation of personal microclimates

Unlike air conditioning, fans can produce different thermal environments in a single space. If people have personal fans at their desks, they have control over their own thermal environment, greatly improving their relative comfort. Studies also show that circulating fans can significantly improve people’s perceived air quality, possibly by disrupting the body’s naturally-occuring thermal plume through which body odours and skin bioeffluents are carried to the breathing zone. 12 Like AC, fans offer a solution in regions plagued by flying insects, because these have trouble flying in the turbulent airflow of circulating fans. 10

Why are Fans Overlooked as a Cooling Option?

If fans are so effective and comfortable, why is their use not more widespread? Because until very recently, international comfort standards limited air movement indoors to a meagre 0.2 m/s in order to avoid drafts. 814 Obviously, avoiding drafts is very useful during the heating season, because in that case the powerful cooling effect of moving air is counter-productive. The fact that air speed was limited to the same level in summer, however, can only be explained by the fact that American comfort standards are written by the national branch organisation of the air cooling and heating industry (ASHRAE), protecting and promoting its own products. (Comfort standards outside the USA, such as ISO 7730 and EN 15251, are heavily influenced by ASHRAE). 11

Fortunately, these comfort standards have come increasingly under fire in recent years, as more and more studies show that higher air speeds can have a welcome cooling effect during the warm months. In 2010, the thermal comfort standard “ASHRAE 55” was revised to permit higher indoor air speeds: up to 0.8 m/s without local control of fan speed, and up to 1.2 m/s with local control of fan speed. Furthermore, at higher activity levels these limits do not apply at all.


The 30cm diameter Toshiba Sient, one of the tested floor fans. Power consumption is 2-8 watts for normal range of use.

In ASHRAE 55-2013, which was presented less than a year ago, a further step was taken by defining air speed not as a single-point maximum speed but as the “average air speed”, being the average air speed at ankle, midbody, and neck level. This allows the fan system to include higher maximum local airspeeds in the occupied zone, since flows from fans are rarely equally high at all three levels. 1213 Although it will take some time before architects, engineers and national building codes adopt the new guidelines, it looks likes the circulating fan is back on track.

AC has Produced AC-Architecture

Meanwhile, however, a lot of damage has been done. While a renewed interest in circulating fans could save large amounts of energy when cooling buildings, there are limits to what can be achieved because the widespread use of AC has had a profound influence on architecture. Before the advent of air-conditioning, buildings in hot climates were designed in such a way that they were comfortable during summer months without the use of energy. They encouraged natural ventilation by, among other things, large porches, high ceilings, roof vents, sash windows, ventilation shafts, transoms over interior doors, and courtyards. Some houses were even built on stilts to allow for more air circulation. 16911

Traditional buildings in hot climates kept solar radiation out by using heavy construction materials, big eaves, reflective tin roofs, and growing shade trees around the house. Air conditioning did away with all these building elements and stimulated the use of lighter and cheaper building materials. Office blocks with H, T, and L-shaped footprints, which facilitated cross-ventilation, were replaced by massive, square blocks with very deep floor plans. Completely new building types emerged, such as office towers with fully glazed facades or enclosed shopping centres, which would be simply uninhabitable without air-conditioning because of the greenhouse effect. While fans could somewhat lower the energy use of air-conditioning in such buildings, energy consumption would remain very high. 16911

Kris De Decker (edited by Jenna Collett


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Interesting article, as usual. The standards on indoor air speed was particularly new to me.

Counterpoints: Western Europe has more comfortable climate than most of the US; they’re further north, and on the west coast of a continent. I live near Boston, which is pretty far north for the US, and even so we’ve recently had A/C-only weather, temperatures of 33 C and humidity 60%, dew point 25 C (26+ is when some people start dying, according to wikipedia, and 24-26 is “oppressive”.) For a lot of the US, like the Southeast, I suspect good architecture and fans still just ameliorate the climate, as opposed to making it comfortable.

Architecture could be better, but often will have higher embedded energy costs, and of course it’d be expensive to simply replace what we have, flawed as it is.

Location could be better: the west coast and the southwest make cooling much easier (various mixes of moderate temperatures, ocean breezes, low humidity and cool nights) but then of course there’s the water problem. We could probably use a lot less energy if the US (or world!) lived in dense cities in the coastal west or southwest, but we’d need to be pumping in a lot of water or recirculating what we used much better.


Also: One thing I’ve wished for is a dual mode A/C or something. My window unit’s fan mode just recirculates indoor air, and I think that’s normal. Probably simplifies the design, but it makes hard to cool efficiently given erratic summers. Many days (or nights) a window fan would be fine, but I’m not going to wrestle the unit down and up, especially when that means redoing my makeshift plastic insulation on the sides. So I use the A/C all summer even though I’d like the option to not do so.

Expense: my default power bill is around $18 for electricity. Fridge, lights, computer, ceiling and window fans… I think the fridge dominates, really. But with just one 5000 BTU window unit, it’s $36 for the past month, and last year it went as high as $60 one month. Definitely a big difference! Maybe better insulation would help (I tape up bundles of plastic shopping bags on the sides), but still. The drawback of high mass wall buildings is that when they do heat up, they’ve got lots of heat to give back to you…


Great article again, thanks.

I think there’s a mistake under section ‘Why AC is Inefficient’

The larger the space and the fewer the people within it, the more energy it will take to cool the occupants.’

FEWER People should instead be MORE People right?

Kris De Decker

@ Dan

It should actually read “…the more energy it will take to cool EACH occupant.”

Thanks, corrected


Interesting comment about not being able to cool the skin with air that is warmer than it. The skin is cooled partly due to the evaporation of sweat (which coincidentally is similar to how aircon cools air by evaporating a coolant). This could happen with warm air too, in a similar way to how gas fridges burn gas to evaporate a coolant and cool down. I think you’re right though, as this happens on a small scale unless you apply more water to your skin. In central Europe, outdoor fans spray ‘mist’ to achieve this.


Another great article. I have acquired something of a distaste for AC for personal reasons. The ‘old man’ of the house(condo actually), is extremely OCD when it comes to AC. He runs it constantly and obsessed over single digit changes to the temp reported by the thermostat. For example, if the interior temp is 80F, and the AC is, or even if its 78, then the AC has to been turned on immediately to bring it down to the ‘required’ 75F. It doesn’t just run during the day, but 24/7 all summer long. Now hes the type of individual you cant say anything to, but once in a while, I am able to point out that humans will not melt into puddles of shapeless wax about 75F-files right over his head. I dont buy into the old people need to keep cool trope, but North Americans simply cant live w/o there AC, even in temperate Northern Canada! I often wonder what they do when AC is no longer widely available, melt?, die of heat stroke at 85F? Who knows? One side effect of this, there are tons of AC house bunnies that make zero effort acclimatize themselves to warmer summer temperatures-instead, like my old man, prefer to retreat indoors and stay there within their AC cooled shacks.Occasionally, they will forray outside to engage in something called ‘golf’, which is always generates endless talk of how ‘hot’ it was-but also how they managed to brave the harsh conditions on the golf course for several hours. Naturally the end goal of all this, was to return to an AC’d box as quickly as possible. I bike everywhere and acclimating myself to hot temperatures is not that a big a deal. If I stayed indoors all summer, Not only would would get nowhere-but I would also become (physiologically) dependant on artificial cooling-which is what I see happening in my own household-its bizarre to watch really. I dont if anyone has seen this, but I find, some peoples reaction to NOT being AC’d akin to withdrawal symptoms. They become quite irritable, and quickly.

A couple of other features that KdK didn’t specifically mention but also problem with AC, is the noise. Really, Our AC unit sits in a small enclosed room which is a TV room(I dont use it often), but when unit cycles, as it does constantly, its like a jet engine. Whether your watching the idiot box or even if you wanted to a read a book-you cant-not in that room. Nor can you enjoy the deck outside in the evening either. The exterior vents are so loud it reminds of the noise levels I am exposed to biking on the highway(No choice in that matter either).

Another issue that AC causes was a study I read that looked at how AC affects people physically. One conclusion was that AC makes, or helps, make you fat. The reason being, humans respond to cold temperatures by wanting to eat more-to store up food, whereas warm temperatures tend to have the opposite effect, and suppress the urge to eat endlessly. There is much truth in that observation. Our other condo has no AC and I remember clearly in the summer, our meals were small, light and everyone lost weight and on no one was constantly munching all the time. And everyone felt fine-if a little on warm side. In the current structure, with the AC going full tilt-its big meals constantly and I am always fighting down the (unnecessary) urge to snack and feed my face-as it were. Biking 20-40k a day is probably what’s saving my gut from expanding to North American standards, while the AC, OtOH, is telling me ‘eat more food’.

Another great article thank you-sorry if my comment is a little OT.

Richard Miller

It should be a requirement that A/C systems can only be installed in conjunction with Solar PV and that Solar PV is installed for all existing A/C systems above 1kW rating within a reasonable time. The problem with Solar in northern Europe is that it doesn’t generate during the peak demand in the evening and winter but it is ideal anywhere with peak electricity demand for A/C.

Mario Stoltz

Hello Kris, thanks for the great article, very useful food for thought, as always! An interesting aspect about the AC debate is integrated heating/cooling technology. Of course, this is (nearly) only relevant for new construction. In all the climates where you need to heat in winter, cooling in summer can help reduce the winter energy bill. Heating systems for new builds increasingly make use of heat pumps. Most run on air temperature exchange for their ventilation system, but more than just a few are using the ground as a heat buffer. Ground / often really groundwater a few meters below the immediate soil will have the average yearly temperature of your region of the world (in northern central Europe, about 8°C). This is easily “warm” enough to heat your home in winter with a heat pump system. In the same way and with the same equipment (if it has been set up for that mode), you can cool the house in summer. If the ground volume under your house is enclosed (like a water lens, rather than a groundwater “stream”), these two modes of operation will actually enhance each other. Cooling in summer will pump heat energy into the ground, which you can harvest back in winter, and vice versa. The energy required to run the system is far outweighed by the savings in heating/cooling energy.

In my own house (24 apartments) we have a forced ventilation system with central heat pump unit for energy recovery in winter. The heat pump is turned off in summers, but it is amazing how even the moderate airflow of the ventilation system makes you more comfortable. Compared to all the houses / apartments that I have lived in previously (none of these having a ventilation system), warm summer days are much more bearable.

Andre L.

I read the UC Berkeley study. I think there are a few caveats there in terms of it applicability to office environments, in no particular order of importance:

1) sandals and light t-shirts are not typical outfitting most people dress up on most office-jobs in the Western developed world

2) the article mentions discomfort after third break, and adaptation period. How much worse further sedentary work periods wound become, as most office jobs last much longer than the 2 hours the experimented involved

3) longer periods of light sweating that is evaporated leave the body with a salty sticky coat, which is uncomfortable and dirt in some sense.

4) silly as this might appear to be, hot air + wind + light evaporated sweat is bad for makeup on women and for hairstyles that involve anything besides natural form.

5) 80% humidity is a bad environment for computers, other electronics and furniture to being with.

6) the air flow on the experiment chamber is much higher than what is usually found on office buildings. This is positive for the experiment (facilitate creation of each controlled atmosphere), but it also increases the comfort of those in the chamber compared to the sticky and smelly air that would be created in an office full of people with their own smell-production and chemicals mixing up on a high-humidity environment with much more stagnant air.


One drawback of fans not mentioned in the article is the noise they generate, even if it is low level. The noise makes it very difficult for me to fall asleep in a room with a fan, and I’m probably not alone. Granted, AC units generate even more noise, but they are usually not adjacent to or in bedrooms. I suspect, though, that magnetic levitation bearings make ceiling fans much less noisy. Is this the case?

Kris De Decker

@ Ville (#10)

Indeed, the fans in the tests (which are also pictured in the article above) are the newest generation of fans with higher efficiency and lower noise generation than the average fan of yesteryear. None of the subjects in the tests said that the noise bothered them. However, people were doing office work, they were not sleeping or trying to sleep. So an answer to your question would require new research.

@ Andre L (#9)

1) Your point is only valid for men, not for women, and to your information women are also to be found in offices in the western developed world. The fact that men in offices wear inappropriate summer clothing (and usually are in charge) explains in large part the phenomenon of overcooling.

The main victims of overcooling in offices are women, because they usually wear appropriate clothes in summer — open shoes and clothes that expose more skin to the environment than just the hands and the face. If men want to keep their inappropriate costumes, let them use a fan. Japan has successfully lowered AC energy use in offices by promoting more appropriate summer clothing.

By the way, fans bring large energy savings even in combination with the typical business suit of 1 clo insulation.

2) Could you clarify this point?

3) Could you tell me where in the study you found a reference to “light sweating”? The skin also evaporates liquid when we are not sweating.

4) Now you are suddenly concerned about women! See 3

5) Since computers and other office equipment are usually tossed away after three years or so, most devices will work just fine during the operational life, even at 80% humidity. And the thought that people should subordinate themselves to AC for the benefit of office tools, strikes me as far-fetched. Maybe we could try to adapt the machines instead?

6) The study describes how in all experiments perceived air quality greatly increased with the use of fans compared to AC. So the situation would actually improve. By the way, if you read the study, you must have noticed that it includes several experiments in real office buildings, not just in climate chambers.


OTOH, there’s evidence that people get less productive above 25 or 26 C.

I don’t know if good fans change that much. I note “lazy heat” and “lazy tropicals” are common tropes, possibly for reason.

Kris De Decker

@ drs

That’s true. In the Berkeley study, the researchers note this as one of the topics for further research. They expect fans to have a positive influence on productivity, just like AC, but this has not been studied yet.

On a side note, us being so productive is probably one the main causes of resource depletion and other evils. I live in a country where people still have a siesta in afternoon during summer. Not very productive I guess, but we have the highest life expectancy and one of the happiest populations in Europe. And almost no AC.


This is good idea: He lets moisture into house at the lower level, moisture evaporates and absorbs heat, at the higher level is extractor which throws out humid air. claims low energy expense. The system could be improved to make more natural flow of moisture and air, hopefully eliminating the need for any extra energy input.


Evaporative coolers are ubiquitous in the high deserts of the Southwest US. Here in Denver I have rental properties with no A/C and @ 100F outside the inside temp never exceeds 78. I’ve seen different numbers, but Wikipedia pegs EC @ 1/8th the cost of compressor A/C. Plus the amount of water they use is trivial compared to other household water consumption.


Loved the article. Thanks. Just to highlight the “Peak Power Demand” aspect of a/c, in Australia where I live it is estimated that the installation of a 2 kilowatt reverse-cycle air conditioner can cost a consumer around $1500, but imposes costs on the energy system of up to $7000 by adding to peak demand. Costs that are spread across all customers. In other words, energy efficient households with fans are subsidizing energy-inefficient ones with a/c because the former pay the same for a kWh, but it’s the latter who raise that cost ($/kWh). “Cost reflective pricing” is the buzz term here nowadays. Make a/c users pay the real cost they impose on the energy system and fans (+ building standards) will have their day again. Real revenge.


Right on Kris.

I absolutely f**cking hate air conditioning.

Fair enough it has its uses in very hot countries as you have pointed out, but for example here in the UK we have it in our office, it is probably on about 6 months per year and centrally controlled so there is no getting away from it. I go to work in shorts and T-Shirt and then have to put a jumper on in the office… I mean… WTF!!!!???!! And this is at a company that champions its own “green agenda”. Idiotic to the max.

Apologies for the strong words but I would be happy to see the back of AC altogether, in the UK at least!

I don’t think I’ve posted a comment before but have to say I love your site, it has taught me so much and each article is very well researched and presented (Still got loads of back articles to read though!). Kudos to you sir.


I’ve been in movie theaters where I was too cold with t-shirt and long jeans. The theatre had their AC on max. I do not agree to banish AC altogether, just turn the central thermostat up a few degrees. I like the idea in a hot and dry climate to use AC to supplement a swamp cooler, and fans.

I try to maintain a balance with the outside world. I do not desire to take heaters and AC for granted, and I do want AC during the hottest days of the year and heat during the coldest nights of the year. What I am saying is, I consider my external temperature range to be around the 65 to 75 degree range in Fahrenheit.


This is all very well, but there are plenty of people who cannot tolerate ceiling fans at all. The beating motion of the blades is a migraine and seizure trigger, particularly bad when there’s lighting behind the fan or even just nearby. I have to turn right around and immediately leave any room that has a ceiling fan running. If I don’t get out quickly enough, I’m saddled with a migraine that lasts at least into the next day. I don’t love A/C, but I’m not alone in my inability to tolerate ceiling fans.

Sherwood Botsford

Peak demand can be reduced by adding a level of indirection: Cool water and store it for later use. This allows a cooling unit to be sized to the overall demand for the day, instead of being sized for the peak demand — a size reduction of about 60%. If the price differential between peak and non-peak time is sufficient, then sizing your unit to chill water during the lowest rate period makes sense.


You say “(circulating fan)can only provide cooling at air temperatures below the mean skin temperature, which is about 35°C”

Are you sure about that? Circulating fan stimulate sweat evaporation. This work at any temperature. I mean… if the suronding air could not cool our body down, then human would die within minutes if temperature get above 35°C. Of course we don’t rely on cool air to cool down our body!

The 35°C treshold might be true for 100% relative humidity


I’m curious how underground rooms can fit into a house’s cooling system. Our house is built on a hill, and the storage room is dug into the hill, so it the summer it is a couple degrees cooler than the rest of the house. If you had a fan/air circulation system that took advantage of underground rooms, I imagine you could somewhat simulate AC but with natural cooling.

Also, I wouldn’t write off glass completely. It helps light buildings naturally, and as glass insulation improves, it is less of a problem equalizing the indoor temp with the outdoor one, though it does still let the solar heat come through.


Much of this seems to ignore the fact that one of the biggest drivers of AC use, in certain environments, is in fact for humidity control more than temperature control. The textile industry, for example, was an early adopter to help control fabric properties during processing. In such cases I’m not certain there is any good replacement.

Additionally, you do your own arguments a disservice when you make seemingly petulant comments such as calling men’s clothing “costumes” and implying that posters such as Andre are somehow sexist. You should really leave such personal prejudices at the door if you want to be taken more seriously…

  1. “Cox, Stan. 2012. Losing our cool: uncomfortable truths about our air-conditioned world (and finding new ways to get through the summer). New York: New Press. 

  2. Home air conditioning in Europe – how much energy would we use if we became more like American households?” (PDF), George Henderson, 2005 

  3. While household air conditioners have become both more prevalent and more efficient, new data highlight opportunities to lower energy bills“, US Energy Information Administration, August 2011 

  4. Peak Demand Impacts of Residential Air-Conditioning Conservation Measures“, Burke Treidler and Mark Modera, Lawrence Berkeley Laboratory, 1994 

  5. The role of building technologies in reducing and controlling peak electricity demand” (PDF), Jonathan Koomey and Richard E. Brown, LBNL, 2003 

  6. “Growth in mobile air-conditioning: a socio-technical research agenda”, Graham Parkhurst & Richard Parnaby, in Comfort in a Lower Carbon Society (Building Research and Information), Elizabeth Shove, 2008. 


  8. Human Thermal Environments: The Effects of Hot, Moderate, and Cold Environments on Human Health, Comfort, and Performance, Third Edition, Ken Parsons, 2014 

  9. Thermally Active Surfaces in Architecture, Kiel Moe, 2010 

  10. Circulating fans for summer and winter comfort and indoor energy efficiency” (PDF), Richard Aynsley, 2007 

  11. Adaptive Thermal Comfort: Principles and Practice, Fergus Nicol, Michael Humphreys & Susan Roaf, 2012 

  12. Air movement as an energy efficient means toward occupant comfort“, Edward Arens, Hui Zhang, Wilmer Pasut, Yongchao Zhai, Tyler Hoyt, Li Huang, November 2013. Prepared for State of California Air Resources Board, Research Division. 

  13. ASHRAE Publishes 2013 Version of Thermal Comfort Standard“, December 2013 

  14. Moving Air for Comfort” (PDF), Edward Arens et al, ASHRAE Journal, May 2009