Cold draft and draught: how air walls help reduce unwanted air movement
Drafts can occur almost anywhere, and people perceive drafts very differently. Some people are highly sensitive to unwanted air movement, while others hardly notice it. In many customer projects, however, we see that drafts are more than just a minor comfort issue.In this article, we explain how drafts develop, what effects they can have on health and comfort, and how air walls can help reduce unwanted air movement.
In US English, this is usually called a draft. In UK English, it is often spelled draught. A cold draft or cold draught is especially noticeable because moving cold air can make a room feel colder than the measured temperature.
How drafts develop
Outside, moving air is called wind. Inside buildings, moving air is often called a draft, draught, air movement or cross-draft.
There are several common causes.
Open windows, doors, gates or leaks
The most common cause of drafts is wind entering a building. Even at low wind speeds, temperature differences between incoming air and the air inside a room can be felt by people.
Drafts near the floor can create a pool of cold air. Cold air sinks because it is heavier than warm air. This can be particularly uncomfortable when people sit or work for longer periods in areas where cold air collects.
Temperature and pressure differences
Air movement can also occur even when windows and doors are closed. From a physical point of view, differences in air pressure are balanced by air flowing from areas of higher pressure to areas of lower pressure.
Temperature differences between two areas often also mean differences in air pressure. This is one of the reasons why air starts to move.
Heating and air conditioning
When indoor air is heated or cooled, this air has to be distributed throughout the room. In many cases, people do not see or feel a fan, but the air still moves.
This happens through convection. In heated or cooled rooms, air movement is created by natural convection. Even when there is no wind, air can circulate inside a building.
In most cases, this air speed is much lower than wind speed. Wind is usually the stronger influence.
Poor insulation or thermal bridges
If the inside of a building is warmer than the outside, cold surfaces on walls, doors or windows can create temperature differences. The same effect can occur in reverse.
These temperature differences can lead to air movement, just like heating or cooling systems.
Health and comfort effects of drafts
Drafts can contribute to discomfort and may be associated with a number of health-related complaints. In workplaces, this matters because people may be exposed to drafts for many hours per day.
The following effects are often mentioned in connection with drafts and cold air movement.
Colds, respiratory irritation and sore throat
When cold air reaches the throat or respiratory tract, it can feel irritating and uncomfortable. In offices, industrial buildings, logistics areas, retail stores or public buildings, this can become a real problem if employees or visitors are regularly exposed to cold drafts.
A person working all day near an industrial door, a loading area, a checkout zone or an open entrance is in a different situation from someone who only passes through briefly.
Back pain, stiff neck and muscle tension
Cold air movement can contribute to muscle tension, muscle tightness and discomfort, especially when it affects the same area of the body for a longer time.
The neck, shoulders and back are particularly sensitive areas. A stiff neck, shoulder pain or lower back discomfort may be associated with cold drafts or prolonged exposure to cold air movement.
Eye irritation
Drafts can also affect the eyes. Moving air can dry out the tear film that helps keep the eye moist and protected. This may lead to irritation, itching or dry eyes.
People who wear contact lenses may be especially sensitive to dry or moving air.
Ear discomfort
Direct air movement can also affect the ears. Some people experience discomfort, pressure or pain when they are exposed to strong drafts for longer periods.
Nerve irritation and pain sensitivity
Cold exposure can lead to muscle tension. In some cases, tense muscles may irritate nearby nerves and contribute to pain or numbness.
For people with existing nerve sensitivity or chronic facial pain, even light air movement may feel uncomfortable. This is one reason why drafts are often perceived very differently from person to person.
Perceived temperature, wind chill and drafts
People do not perceive temperature only through a thermometer. The perceived temperature can differ significantly from the actual air temperature.
There are several reasons for this.
Thermoregulation
The human body has natural mechanisms for regulating temperature. For example, we sweat to cool down when it is hot.
This is based on a physical effect: when water evaporates from the skin, it takes energy from the body. This cools us down.
Air movement can increase this effect because it removes the warm and humid layer of air around the body. As a result, we can lose heat faster.
Perceived temperature and wind chill
Drafts and wind can make cold temperatures feel even colder.
A thin layer of warm, humid air normally surrounds the body. Wind and drafts can remove this layer. When that happens, evaporation and heat loss increase, and the body cools down more quickly.
This is why the perceived temperature can be lower than the measured air temperature. At low temperatures and higher wind speeds, this is known as the wind chill effect.
Perceived temperature is subjective. People feel temperature differently. Clothing, activity level, age, muscle mass and personal sensitivity all play a role.
Relative humidity
Perceived temperature is not only influenced by air temperature and air speed. Relative humidity is also important.
If the air is humid, evaporation from the skin becomes less effective. The closer the air is to saturation, the less moisture it can absorb. That is why humid air can feel oppressive, and air movement may not provide the same cooling effect.
The relationship between temperature, humidity, pressure and air enthalpy is described in psychrometrics. In German-speaking engineering, the Mollier diagram is often used to visualize these relationships.
Air walls help reduce wind and drafts
Why do we deal with drafts?
Drafts occur wherever air flows uncontrollably through doors, gates or entrances. This can happen in industrial halls, logistics areas, stores, museums, public buildings and many other environments.
Drafts can make indoor areas uncomfortable, affect workplaces, increase energy losses and disturb room climate or processes.
An air wall can separate air zones without mechanically blocking the passage of people, customers, forklifts or materials.
SAW air walls can help block wind and drafts and reduce the associated comfort and health risks. Depending on the application, they can hold back wind and air movement of up to 5 m/s or 18 km/h.
Air walls reliably reduce wind and drafts while keeping entrances and passages open.
FAQ
Drafts are often caused by wind entering a building. The simplest solution is to close the window, door or gate and keep it closed.
In many buildings, however, this is not practical. Entrances, doors, gates and loading areas often need to remain open for people, customers, forklifts or material flow.
Air walls provide an air barrier even when doors, gates or entrances are open. They help separate air zones without creating a mechanical obstacle.
A cold draft, or cold draught in UK English, is unwanted cold air movement inside a building. It can occur near open doors, gates, entrances, loading areas, windows or leaks in the building envelope. Even when the measured room temperature is acceptable, a cold draft can make people feel uncomfortable because moving air increases heat loss from the body.
Yes and no.
A fan can lower the perceived temperature by creating air movement. This air movement removes warm and humid air from around the body and increases evaporation from the skin.
However, a fan does not lower the actual physical air temperature. It only moves air. It may transport cooler air from another area, but it does not create cooling by itself.
Cold air is heavier than warm air because it contains more molecules per unit of volume. It has a higher density.
Warm air molecules have more energy. They move faster, collide more often and occupy more space. This makes warm air less dense than cold air.
Convection is one of the three main forms of heat transfer, alongside radiation and conduction.
In convection, a gas or liquid moves past a surface with a different temperature. When they come into contact, heat is transferred.
Air walls can influence convection because they control how air moves between different areas.
Thermoregulation describes the mechanisms the body uses to maintain its normal core temperature.
The normal human body temperature is around 36.5 °C. Sweating, blood circulation and changes in heat loss all help the body regulate temperature.
The wind chill effect describes the fact that cold temperatures feel colder when there is wind or strong air movement.
A layer of warm, humid air normally surrounds the body. Wind and drafts remove this layer. As a result, the body loses heat faster and the perceived temperature drops.
Wind chill temperature is an estimate based on air temperature and wind speed. It provides an indication of how cold the air may feel.
However, perceived temperature is always subjective. It depends on the individual person, clothing, activity level and exposure time.
The heat index is an estimate of perceived temperature based on air temperature and relative humidity, usually in shaded conditions.
A similar concept is the humidex. Both values indicate how hot the air may feel when humidity is high.
