What is temperature?

Cold or warm

Temperature is a physical dimension quantifying how warm or cold it is. Heat is a measure of the amount of energy inside an object. In the context of air temperature, air molecules basically move faster and have more energy when it is hotter. The energy is transferred from molecules with high energy to those with low energy when the molecules bump into each other. This is how energy goes from warm to cold.

When we express that a room is being chilled, what we are actually doing is removing heat.  

Kelvin, Celsius and Fahrenheit

Temperature may be measured in different units. Scientific contexts normally use the Kelvin scale which is based on a theoretical state known as ‘absolute zero’. At absolute zero, 0 K, all vibrations in atoms and molecules have ceased and all particles are in their lowest energy states. 

In everyday context at Swegon, we refer to temperature using the Celsius scale, otherwise known as the centigrade scale. Anders Celsius was a Swedish scientist who constructed his temperature scale in the 1700s. Celsius based his scale on the freezing point of water, setting this at 0 degrees. By setting the boiling point of water at 100 degrees, he had designed a temperature scale clearly linked to phenomenon in people’s everyday lives. He had also created a scale that was precisely defined. The Celsius and Kelvin scales have the same magnitude, meaning that a temperature difference will have the same value whether expressed in °C or K. Expressed in the Celsius scale, the temperature at absolute zero is -273.15 °C; no temperature being lower than this.

However, many other temperature scales exist. Fahrenheit is commonly used in addition to Kelvin and Celsius, also called centigrade, and is the official scale in the USA as an example. On the Fahrenheit scale, water freezes at 32 °F and boils at 212 °F.

Temperature and indoor climate

In the context of indoor climate, different kinds of temperatures may be mentioned.

  • Dry bulb temperature (DBT) is what we usually refer to as ambient temperature and it is measured using a standard thermometer.

  • Wet bulb temperature (WBT) is the ambient temperature measured when the bulb of a thermometer is wrapped in a wet cloth. When the water in the cloth evaporates, heat is drawn from the thermometer, which then displays a lower temperature. WBT is dependent on the DBT and on humidity.

  • Operative temperature is a measure of the perceived temperature, taking into account the temperature of ambient air and of surrounding surfaces.