More about the elements of indoor climate

While the main elements of indoor climate — temperature, indoor air quality, light and sound — remain core, the importance of additional parameters and their interactions must be recognised and implemented. Just as importantly, these elements and additional parameters are considered in relation to each other, and their interactions are vital and interchangeable. To create a balanced and optimal indoor climate, all factors must be considered together rather than separately.

Below is short information about these important advanced parameters, with interlinking to more information (#).

Temperature

Temperature is one of the main parameters of how we experience the indoor climate. We often talk about the range of different temperatures when indoors; it can be too hot, too cold, or just right.

Dry buld temperature is what we usually talk about as temperature, which is measured with a standard thermometer. We can also describe the temperature as 'hot and muggy' or a hot heat — these descriptions have a lot to do with the humidity as much as the temperature.

• In most climates, a comfortable indoor air temperature is acceptable between 20°C and 26°C, with the lower end preferred in winter and the higher end in summer.
• Radiant temperature differences between walls, windows, and air can also cause discomfort even if the air temperature is within this range.

Temperature is one of the main parameters for ventilation in buildings.

Humidity

Humidity is one of the most important indoor parameters that affects our air quality as well as the well-being and health of people in indoor environments. Moisture, particularly in cold climates, is most often related to problems such as moisture damage, mould and bad smells. This is caused by poor ventilation that creates too high humidity.

• Science says that an optimal indoor climate should have a relative humidity (RH) between 30% and 60%.
• Within this range, microbial growth is minimised, respiratory tract defences work effectively, and static electricity issues are reduced.

Low humidity also creates problems, especially for people, such as dry eyes, dry skin, dry mucous membranes and some seasonal infections, such as influenza. For example, in Nordic climates, the indoor humidity is often as low as 5-20%, which is considered extremely dry and harms our well-being and health.

Advanced building systems use humidity as a key parameter and utilise humidity recovery and humidification techniques in buildings.

Carbon dioxide (CO₂) levels

CO₂ is an air quality parameter and a key indicator nowadays for ventilation effectivness, mostly used for occupants and density. 

Outdoor CO₂ levels are typically around 400 ppm (parts per million), depending on the location and proximity to pollution source, it can be also higher.

• Typical level ranges of 400 - 1,000 ppm are found in occupied spaces with good air exchange.
• Level of 1,000 - 2,000 ppm are associated with complaints of drowsiness and poor air, often resulting in low performance.
• The maximum exposure limit of 5,000 ppm is permissible for daily workplace exposures.
• Above 30,000 ppm are very harmful, hazard and lethal levels.

Monitoring and controlling CO₂ is crucial for advanced ventilation systems, ensuring fresh air supply matches occupancy in real time — improving both air quality and energy efficiency.

To measure is to know

Air quality encompasses a wide range of elements, which can make it challenging to understand.

Apart from temperature and humidity, another common metric is the CO₂ content, which has the advantage that it is easy to measure, quantify and set limit values ​​around. However, measuring CO₂ allows you to capture certain key aspects that significantly impact performance, but it may overlook other health aspects. Instead, measuring and ventilating based on VOCs/TVOC concentration captures a wider spectrum of potential problems.

And there is a need for interaction of other elements, including sound and light qualities, in buildings.