Why does portable air conditioner blow warm air

Season tips

Contrary to popular belief, a fan does not cool the ambient temperature: it just creates a stream of air. And since its motor consumes electricity, it even gives off a bit of heat to the room - this is the reason why it should be switched off as soon as the moving air is no longer blowing directly on anyone in its vicinity.

Fans: There are many models, and some can do more than just fan air

In recent years, the market for fans has expanded to include many new devices that not only generate air flows, but also have other air conditioning functions: air fresheners, air purifiers, evaporators, fragrance atomizers, air humidifiers, fan heaters, etc., so that there is a tendency to Fans can be used all year round. The absolute top consumers when it comes to electricity are still the small mobile air conditioners, which consume a lot more electricity than the simple fans. Below you will find a small overview of the various commercially available devices that provide cooling - and we also recommend that you read our article Protection on hot days, which explains how you can protect yourself from heat without necessarily using up electricity.


Simple fans

A fan provides us with cooling in two ways. First, it waves away the warm air layer that lies like a small shell directly over our skin (because our body is constantly releasing heat and moisture) and replaces it with less warm and drier air (Cooling by convection). Second, it facilitates the evaporation of sweat, which is ours transpiration improved - this is the natural way our body protects itself from overheating.

In order for our body to live, it must always keep its temperature in the range of about 37 ° C. If we get too hot, our skin secretes droplets of sweat. However, it is not so much the moisture on the skin that provides us with cooling, but rather the evaporation of this moisture. When water - or in our case sweat on the skin - changes from the liquid to the gaseous state, the change of this aggregate state requires an enormous amount of energy, which is extracted from our skin surface in the form of heat (see at the end of the text under latent heat of evaporation *). A fan simplifies the evaporation of sweat by replacing the moist air that surrounds our skin with dry air. Even if the ambient temperature is very high - for example 38 ° C - a fan can cool very efficiently because it accelerates the evaporation of sweat on the skin.

Also consider power consumption and volume

There is no energy label for fans that can help you make good choices. It is therefore better to try the device in the store so that you can get an idea of ​​what the airflow feels like and how much noise the fan is making. Information about the power consumption - in watts - can be found on the packaging box or sometimes the information is written directly on the device (the declaration is mandatory). The power consumption of a fan is usually related to the moving air (i.e. to the air flow that it produces). Therefore, before buying, you should consider whether it should cool one person alone (for example at the workplace in the office) or several people. And for the choice of a suitable device it is of course also important to know whether the air flow should flow over the whole body or only blow on the upper body (e.g. if the legs are hidden under the office desk where the air flow does not get to)

Brushless motors (called "brushless DC motors") use approximately 40% less power than traditional electric motors, and they are also much quieter. The heat that a fan emits is directly related to its electricity consumption. This example may serve as a comparison: A fan with 100 watts of power emits as much heat as an adult.

The fans available on the market differ in their design and technology. On some, the propellers are hidden in the base of the device and allow the draft to flow through a ring opening. Such fans have various control options: variable speed, oscillating air flow, automatic shutdown device after a user-defined runtime, remote control, handling via smartphone, etc.

Power consumption and tips for use: Most domestic fans use between 20 and 80 watts. Always turn off the fan when no one is directly benefiting from its airflow, because its electric motor generates heat and warms up the room a bit.

The most energy-efficient fans at www.topten.ch


Ceiling fans

With a diameter that is much larger than that of ordinary fans, the rotor blades of ceiling fans naturally rotate much more slowly, which reduces the risk of accidents. The prerequisite for such fans are high rooms: The distance from the floor to the rotor blades must be at least 2.30 m. Most models can be attached to the ceiling light installation, and some are even equipped with lamps, thus combining ventilation with lighting. According to the ordinance on electrical low-voltage installations (NIV), a ceiling fan should be installed by an electrician.

Ceiling fans with a brushless motor (so-called "brushless DC motors") only consume around half the electricity of a comparable model with a normal electric motor. If you choose a fan with lighting, the power consumption of the lamps should also be taken into account. There are ceiling fans with a pull cord with which the speed levels can be changed (manually) and the device can be switched on or off, other models work with a remote control (with batteries).

Use of the ceiling fan in winter

There are also ceiling fans that can run in either direction, which can be useful during especially the heating season. In very high rooms, the warm air tends to accumulate on the ceiling. If the ceiling fan runs in the opposite direction (i.e. in the opposite direction of rotation), it can draw the cold air from the floor to the ceiling and direct the warm air that has accumulated there towards the floor. Depending on how the room is built, a ceiling fan can help reduce the heat requirement for this room and thus save heating costs.

Power consumption and usage tips: Between 20 and 120 watts (without lighting). Before buying a ceiling fan, find out about the installation options (ceiling height and thickness, location of the electrical connection). When used in summer, the fan should always be switched off when no one is in the room, because its electric motor generates heat and thus contributes to the warming of the room.


Air cooler or air freshener fans

An air cooler fan (or an air freshener fan) works on the same principle as our own body perspiration. The fan fans air onto porous and humidified material, which causes the water to evaporate: When the water changes from the liquid to the gaseous state, it extracts heat from the ambient air, which cools down by a few degrees (see also latent heat of evaporation *). The principle works very well in a very warm and dry room climate, and you get cool air with a power consumption that is far below that of a mobile air conditioner. However, the temperature cannot be precisely regulated. The following applies: the more humid the ambient air, the less efficient these devices are.

With a small, mobile air cooler device, the feeling of freshness is particularly noticeable when you are in the middle of the cool airflow from the fan. If the humidity of the room is already around 60%, the evaporation will be very weak and, of course, the resulting cooling as well. For such a device to work effectively, the room should not be closed, because the humidity accumulates. Ideally, an air cooler fan should have its back to a fresh air source (e.g. open door or ventilation inlet) and the moist air it expels to the front should be diverted from the room (e.g. through another door or the ventilation outlet). If you have to open a window to let the humidity escape, it is advisable to ensure that the warm outside air cannot re-enter the room to be cooled in large quantities!

Power consumption and usage tips: Between 70 and 150 watts. Do not run the air cooler or air freshener fan when nobody is in the room. If the ambient air in the room is already very warm and humid, it is better to use a conventional fan instead of introducing additional steam into the air - this makes it more difficult for the people present to transpire. Read the instructions carefully and make sure that no molds and germs can develop.


Nebulizer fans

These devices use a fan to dust a fine mist of tiny water droplets into the air. The smaller the water droplets, the greater the cooling effect, because the small droplets evaporate very quickly (see also latent heat of evaporation *). Since it cannot be ruled out that microorganisms can develop in the water tank, the water is disinfected in some devices before it is atomized.

Power consumption and usage tips: Between 80 and 150 watts. Read the instructions for use regarding the maintenance of the device (microorganisms and limescale). Be careful not to damage walls and furniture from the damp mist.


Fans with additional functions for air treatment

There are numerous different fans available on the market that are equipped with additional functions for air treatment and that can be used all year round (!): Fans, air purifiers (from pollen, dust, volatile organic compounds, etc.), mist nebulizers, air humidifiers, heating fans , Perfume nebulizer ...

Air cleaner: They use different technologies, sometimes even combined: Air filtration (with one or more air filters), Ionizer technology (Emission of negatively charged ions) and Photocatalysis (Ultraviolet light hits a metal catalyst and triggers a chemical reaction). In a study published in January 2017, the Agence nationale de sécurité sanitaire (ANSES, a food safety, environmental and occupational safety agency in France) found that the effectiveness of small air purifiers has not been proven under normal operating conditions at home or in the office. These devices filter the air, but the correct use of the devices requires regular maintenance of the filters, which is usually not done. As far as ionization and photocatalysis are concerned, these technologies are only partially effective in removing dirt particles from the air, often creating more "waste" particles that are harmful to health.

Les purificateurs d'air, study carried out by ANSES (in French)

Ventilate regularly

The best way to get fresh room air is regular ventilation: by opening the windows for a few minutes several times a day, the stale air is replaced by fresh air. However, if you have automatic ventilation (as in Minergie houses), manual ventilation is not necessary. If possible, you should make sure that the air in the interior is not excessively polluted: it is best not to smoke, avoid the formation of strong grease vapors when cooking and do not use strongly perfumed cleaning agents when cleaning (floors, furniture and windows are better with warm water Clean microcloths). It is also important to regularly remove any dust that collects on the floor, carpets, curtains and furniture. The room air stays cleaner with regular vacuuming, if possible with a vacuum cleaner with a HEPA filter (High Efficiency Particulate Air) so that the dust that is sucked in does not get back into the rooms with the exiting air. Ventilate well immediately after vacuuming so that the blown fine dust is removed.

Perfume atomizer:We strongly advise against the atomization of fragrances in the room air - even if they are natural substances. Small children, sensitive people and those who suffer from asthma can breathe easier without these fragrances.

Essential oils and room fragrances on the website of the Federal Office of Public Health (FOPH)

Power consumption and usage tips: The power consumption of these combination devices depends on the various options that are switched on. In heating mode, it can rise to more than 1000 watts. Before buying such a device, it is worth thinking about whether the indoor air can not be improved by simpler means without consuming electricity.


Mobile air conditioners

In most of the cantons of Switzerland, the installation of permanently installed air conditioning systems - i.e. stationary systems - is subject to a permit. Mobile air conditioning systems, on the other hand, are freely available in stores. These small air conditioning units contain fans, a compressor and a refrigerant gas circuit that is connected to a heat exchanger. In order to produce a bit of cool air, these devices use a lot more electricity than the fans described above, as they have an output between 1000 and 2000 watts. Of course, they bring cool air into the room, but they produce even more warm air and direct it outside. In this way, like all the other air conditioning units - together with the car traffic and the accumulation of solar heat in the tar pavement of the streets and the concrete walls - they help to heat the inner cities by several degrees in relation to the land that surrounds the cities.


A mobile air conditioner with an exhaust pipe that leads through a half-open shop door: it blows air at 25 ° C inwards, but blows air at 42 ° C out onto the street ...

There are two types of portable air conditioner:

  • Mobile monoblock air conditioners (left) direct the warm air out of the room with a large air hose about 12 cm in diameter (rarely shown in advertising). Since this hose has to be laid through an open window or door, the warm outside air penetrates into the room to be cooled (!), Which of course significantly reduces the performance of this air conditioner.
  • Mobile split air conditioners (right): These devices are connected to an outdoor device via a thinner hose. Their energy efficiency is a little better than that of monoblock air conditioners.

Mobile air conditioners produce cooler, but drier air. Your container for the condensation that forms during air cooling must be emptied daily. Some models can also be used "the other way around", i.e. they can also produce heat.

Power consumption and usage tips:Mobile air conditioning units are not in continuous operation, but when they are switched on they consume between 800 and 1500 watts, around 20 to 50 times more than a fan. Before deciding to buy, one should study the mandatory energy label. Do not forget that an air conditioner, even if it is classified in a good energy class, consumes a lot of electricity and produces additional heat, which it gives off to the environment when the air temperature is already very high.

Attention: Sometimes there is talk of "mobile air conditioning units without hot air discharge". These are just simple "air freshener or air cooler fans" that work with water evaporation (see above).


Comparison of the power consumption (in kilowatt hours) for one operating hour. Left: a fan, middle: an air freshener fan, right: a mobile air conditioner.

 

The most energy-efficient fans at www.topten.ch

Mobile air conditioners

Energy label for mobile air conditioners

Protection on hot days

 


* Latent heat of vaporization

When water changes from a liquid to a gaseous state, its temperature does not change. But it absorbs a lot of energy in this transformation. For one liter of boiling water (100 ° C) to evaporate completely, it takes 5.4 times more energy than heating a liter of water from 0 ° C to 100 ° C.
However, water can evaporate at all temperatures. In order to evaporate at 37 ° C - i.e. at our body temperature - water requires around 10% more energy than when evaporating at 100 ° C. This so-called latent heat of vaporization is withdrawn from our body.That is why the evaporation of sweat on our skin - perspiration - is a very efficient method to cool our body down. And for this reason it is very important to really drink enough water on hot days and to replace the salt that has been lost with the sweat.

 

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