What is Thermal Comfort?
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LumaSense offers quality thermal comfort solutons. Creating a thermally comfortable environment is one of the most important parameters to be considered when designing buildings. Thermal Comfort is defined in the ISO 7730 standard as: "That condition of mind which expresses satisfaction with the thermal environment". A definition most people can agree on, but also a definition that is not easily converted into physical parameters.
Thermal environments are considered together with other factors such as air quality, light and noise level, when we evaluate our working environment. If we do not feel the everyday working environment satisfactory, our working performance will inevitably suffer, as thermal comfort has an impact on our work efficiency.
Parameters influencing Thermal Comfort
The Thermal Comfort Equation derived by P.O. Fanger combines the effect of 6 parameters:
- Metabolism (MET)
- Clothing level (Clo)
- Air Temperature
- Mean Radiant Temperature
- Air Velocity
Humidity
Of the four physical parameters, the Air Temperature and Mean Radiant Temperature can be combined into the Operative Temperature or the Air Temperature, the Mean Radiant Temperature and the Air Velocity can be combined into the Equivalent Temperature.
Metabolic rate estimation
The metabolism is the energy released in by oxidation processes in the human body that depends on the muscular activity. Normally, all muscle activity is converted to heat in the body, but during hard physical work this ration may drop to 75%. For instance when walking up-hill, where the energy is stored in the body at potential energy.
Traditionally, metabolism is measured in Met (1MET=58 W/m^(2) of body surface). A normal adult has a surface of 1.7 m^(2), and a person in thermal comfort with an activity level of 1 Met will thus have a heat loss of approximately 100W.
When evaluating the metabolic rate, it is important it is important to use an average of the activity the person has performed within the last hour.Met values for various activity levels can be found in our Thermal Comfort booklet or in ISO 7730.
Clothing level estimation
Clothing reduces the body's heat loss. Therefore, clothing is classified according to its insulation value. The unit normally used for measuring clothing's insulation is the Clo unit. The more technical unit is m^(2)°C/W is also used frequently (1 Clo = 0.155 m^(2)°C/W).
The Clo value can be calculated by adding the Clo value of each individual garment. The insulation value for individual garments can be found in our Thermal Comfort booklet or in ISO 7730.
Values to be measured
When measuring the thermal indoor climate, it is important to remember that man does not feel the room temperature; he feels the heat loss from the body. The parameters that must be measured are those that affect the energy loss, namely: Air Temperature, Mean Radiant Temperature, Air Velocity and Humidity. The influence of these parameters on energy loss is not equal and it is not sufficient to measure only one of them.
One of these parameters, the Mean Radiant Temperature, requires a more detailed explanation. The Mean Radiant Temperature of an environment is defined as that uniform temperature of an imaginary black enclosure that would result in the same heat loss by radiation from the person as the actual non-uniform enclosure.
Measuring the temperature of all surfaces in the room is very time consuming, and even more time consuming is the calculation of the corresponding angle factors. That is why the use of the Mean Radiant Temperature is avoided and the Operative Temperature or Equivalent Temperature is used instead.
