FLO-BRO LOGO by Radek Oborny

Living in warm countries is great!  But, just like life in the temperate regions requires heating, houses  in the tropical regions are often fitted with air-conditioning units, or simply just air coolers.

Air conditioning, an innovation that revolutionized living and working environments, has a rich history that spans over a century. It has evolved from a luxury to a near necessity in many parts of the world, impacting everything from architectural design to population movements, particularly in hotter climates. Since its invention at the start of the 20th century, the AC unit has conquered the world.

Carrier’s technology used a simple but effective mechanism that involved passing air through coils cooled by water, thereby controlling both temperature and humidity. Over the decades, this technology was refined and became more accessible to the public. By the late 20th century, air conditioning had become a staple in homes, businesses, and automobiles, especially in developed countries.

Today, it is estimated that there are over two billion air conditioning units in operation worldwide. This number is expected to grow significantly, particularly in developing countries with emerging middle classes and increasing urbanization.

However, the widespread use of air conditioners comes with significant energy demands. According to the International Energy Agency (IEA), air conditioning and electric fans account for about 10% of global electricity consumption. This figure is set to triple by 2050 due to rising demand and hotter temperatures due to climate change.

How did people survive without AC ?

Although the world is heating up, some places on the planet have been hot for thousands of years already, yet people managed to populate these areas and live there quite happily.

One of the ways, is to adapt to nature. Heat comes from the sun, so if you want to stay cool, stay out of the sun When it’s really hot, take a break. Spanish siestas presumably began when field workers took midday rests to escape the sun. The siestas allowed them to eat lunch and spend time with their family without the heat.

If you want to stay productive throughout the day, taking a midday break means, getting up earlier and staying up later. Actually, a habit I have adopted whilst living in Bali.

By 2026, let’s keep the AC set point at 26 degrees.

The siesta was predominantly meant for people working outside. Nowadays, we spend most of our time indoors. The indoors are therefore air-conditioned and keep a moreless constant temperature throughout the day.

Why is AC set to 16 degrees in so many places?

You have probably seen in in many places in tropical countries. The AC display shows a set temperature of 16 degrees Celsius, whilst it’s 30C outside. Inside it is certainly not 16 degeees, but nobody would enjoy that temperature either. This is the lowest setpoint of most Acs. By doing this,  the owners want to ensure, it’s always running on full power.  Usually, it has to, since the building design is poor, and lacks passive elements or insulation.

On a  sunny day the outside walls of the house receive a lot of heat energy. Up to 1000 W/m2 from the sun.  A roof can get easily above 80degrees Celsius. All the heat energy that gets absorbed, makes the material hot. The heat transfers to the surroundings by the three processes. Conduction, convection and radiation.

 

Conduction is particularly strong in metals, this means, that a metal roof will be as hot on the inside as on the outside. Other materials, for example a ceramic tile, will not get as hot on the inside, since its thermal conductivity is about 300-500x lower than that of a metal.

The convective heat transfer is caused by moving air currents around the hot object.  The hot roof will heat the air that it is in contact with it. Convective heat transfer is a function of the object temperature, geometry and surroundings.

Infra-red  radiation is a sort of long wavelength light, that transfers energy from hotter objects to colder objects. The object can also be our body.

So if you sit underneath a roof, during a mid-day sun, this roof gets 1000W of heat. A metal roof will absorb all that heat, get hot,  and transfer half of it to the underside and the other half to the upper side by convection and radiation.  A roof of 60 degrees Celsius in a 30 degree environment makes 300W  of convection and 200 W in radiation.

https://www.omnicalculator.com/physics/heat-transfer

Insulate & ventilate before cooling

Because AC’s are quite cheap, they allow even bad building design to be inhabitable. One of such modern design elements are large glass windows with curtains on the inside.  Glass windows are not a good design element in tropical buildings, since they are poorly insulated. When exposed to direct sunlight, most of the visible light goes in, heating the interior, causing a “greenhouse effect”.  Glass is in fact opaque to infrared radiation, so it keeps heat inside.

If you cover the windows with large curtains, you effectively turn these to large heaters. If you have windows present, always try shading them from the outside.

Second such bad design are flat roofs with poor or no insulation. Roofs made of corrugated metal sheet get hot quickly, this heat is radiated also on the underside of the roof, since the metal is such a great conductor.

In cases, where the roof is made of concrete, it does not get hot as quickly however, it has a large thermal inertia, so it will keep its heat for a long time.

If the roof is flat, make sure the upper side is not directly exposed to the underside, that there is a layer in between, ideally ventilated to the outside.

IMG ventilation.

Traditional tropical designs usually account for the natural conditions with plenty of shading , thick insulated roofs and wall openings ensure  ventilation.

IMG tropical design.

Heat comfort

What is the best temperature to have inside the house? I think, most people would say  25 degrees Celsius.  Temperature comfort is a matter of personal preference, of course. Some people like it cooler and some warmer.  But like with everything, there is a way to do things right, economically and  in environmentally sound fashion.

You have probably seen a “feels like” temperature, on a weather forecast. That is the product of the sensible temperature (what is shown on the thermometer) the humidity and wind.  Then another effect plays a role – that’s that of the sun. Even on a winter day, if it is sunny and with no wind, you can feel comfortable with short sleeves and shorts.

This applies also indoors. If you want to keep cool, stay away from sources of thermal radiation. That means any hot objects, such as direct sunlight, windows and roofs.

Provided the air around you is cooler than your body, improving convection also helps to keep cool. This is done by turning the fan on.

IMG – keeping cool without AC.

I want to feel really cool inside.

It’s alright to use an air cooler to keep the house cool, provided you took all the passive design measures.  AC is an active element.

It uses electricity to compress the cooling medium, thereby heating it up, then cooling it back to ambient outside temperature with a fan. This happens in the outside unit of a split AC. Then the gas passes through a tubing and valves, which allows it to expand. As the gas expands, it absorbs heat (or creates coolness?).  A second fan is used to move air around the heat exchanger in the indoor unit, removing the heat of the air.

As the indoor air cools, its capacity to bear moisture decreases. This condensing water is then dripping out of the AC units outside, but in fact this moisture comes from the inside of the house.

In humid climates, most of the energy, about 75%, consumed by an AC unit comes in fact from de-humidification, or the removal of latent heat, which is released as water condenses. For each temperature and humidity condition, this can be calculated on this handy tool.   https://www.mollier-diagram.com/.

As the humidity decreases, another way of keeping cool getsmore effective. Sweating. When we sweat, we release liquid on our skin. As that liquid turns to gas, it cools the body down.

What is a good temperature setting to put on an AC?

Before lowering the temperature setting take these steps first.

  1. Remove any sources of radiative heat onto your body
  2. Apply shading and insulation layer to the outside of the house, such as roofs or external shades.
  3. Use a fan to move the air around you.
  4. If using the AC, limit ventilation to sporadic and intense air changes.

Feel free to put any temperature on your AC you like. But always think about how to make the difference between outside and inside as small as possible. Not only it’s healthier for you, but also for the environment.

I try to keep the temperature in the house on 27 degrees, the room is quite well insulated, so putting 28 degrees on the AC makes the temperature in room about right. Let’s make a deal, though. In 2026, let’s not put the AC below 26 degrees. Keep the AC less cool will make the planet more cool.