August 2021

1. Description

The dry air temperature is the usual parameter for determining the thermal comfort inside a room. The air temperature indicates its heat energy level with reference to an absolute minimum level - 0 (0°C = 273.15 K).
Thermal comfort in the body is maintained by homeothermy, which balances heat gains and losses to keep body temperature between 36 and 38°C.

2. Recommended levels

The range of temperatures considered comfortable is from 21 to 25ºC, being, according to the RITE (Thermal Installations Regulation), 21-23ºC in winter and 23-25ºC in summer, although these parameters can be increased and/or decreased depending on the rest of the variables that condition comfort.

3. My inBiot Ranks

MICA only establishes a range of risk values for indoor temperature in the case of indoor air quality assessment projects, as they must be evaluated together with other parameters such as relative humidity, mainly due to the variability of the factors that determine comfort. These comfort values are in the range of 20 - 25ºC.

4. Unit of measurement

ºC - degree Celsius belongs to the international system of units for expressing everyday temperature units, understanding temperature as the physical unit that represents the level of heat. The Celsius scale uses as a reference the melting point of ice for its value 0, and the boiling point of water for its value 100, always at normal atmospheric pressure, according to the initial 19th century definition. Since 1948, the triple point of water (0.01ºC) has been chosen as the only point of reference and its value is defined from the absolute temperature unit, the Kelvin:
Tª (ºC) = T (K) - 273.15

5. Sources

Thermal comfort is determined by indoor air temperature, surface temperature, type of heat source, relative humidity and air movement, so the source of low, high or comfortable indoor temperature depends on several factors.

The main sources conditioning the indoor temperature are direct or indirect solar radiation, internal sources such as occupancy or equipment, as well as heating and air-conditioning systems, the type of ventilation used and the construction system of the building envelope.

6. Benefits of optimal levels  

An adequate temperature has direct benefits on thermal comfort and well-being, involves proper breathing, ensures the required oxygen supply, maintains a comfortable indoor environment and facilitates the ability to concentrate.

7. Risks of inadequate levels

At excessively low temperatures, cold affects the deeper muscles, reducing their capacity and favouring joint stiffness, and the capacity for mental activities may be reduced.
On the other hand, high indoor temperatures favour the growth and spread of bacteria and fungi. Concentration and performance are reduced, heart rate increases, drowsiness and discomfort are promoted.

8. Recommendations for improvement

An assessment of the effect of indoor temperature requires a comprehensive analysis of temperature, humidity, air movement, metabolic activity and clothing to establish optimal recommendations. In this way, and in combination with other factors such as humidity or air renewal rate, both the indoor air temperature and the temperature of the surfaces surrounding a space will determine the thermal sensation.
The recommended indoor temperature ranges will vary depending on the type of activity to be carried out, although the following ranges are generally recommended:

  • 18ºC < Tª < 21ºC - Optimal temperature range for nighttime rest. Moderately low temperatures favor nocturnal respiration, partly due to the increase in oxygen when the temperature drops slightly.
  • 21ºC < Tª < 26ºC - Optimal temperature range for comfort for normal daytime activity.
  • Encourage radiant heating systems, which allow for optimal drying of building materials and allow for lower air temperature, with a higher surface temperature, ensuring comfort.

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