Thermal Comfort – All you need to know

Thermal comfort is crucial for ensuring the well-being of individuals in a wide range of environments. Our solutions at PT Teknik ApS help you evaluate thermal comfort for various applications, from indoor climate control to wearable technology.

What is Thermal Comfort?

Thermal comfort is the condition of mind that expresses subjective satisfaction with the thermal environment. It is a complex concept, which can vary greatly from one individual to another. Thermal comfort is maintained when the heat generated by human metabolism is allowed to dissipate, thus maintaining thermal equilibrium with the surroundings. The main factors that influence thermal neutrality are those that determine heat gain and heat loss from the body, namely:

• Ambient temperature – It plays an essential role in the perception of thermal comfort as there is convective heat exchange between body surface and the environment. In cold environments, the body loses more heat to the environment and in hot environments the body does not release enough heat or eventually gains heat from the environment.
• Surface temperature (radiation) – The temperature of surfaces around us also affects thermal perception as there are heat exchanges though radiation and conduction (when in contact). Heat balance of the body could be affected, for example while sitting close to a cold window in the winter or using heating/ventilated seats in the car.

• Air humidity – The relative humidity of the indoor air is another determining factor in thermal comfort. The ideal humidity level is between 40% and 60%. Any change could trigger perception of cold or hot temperature. In more extreme environments, high humidity can significantly lower the heat dissipation from the body through sweat evaporation.
• Airflow – Draughts in an indoor environment could hugely affect the perception of comfort as the local convective heat exchange between body surface and the environment is higher with higher airflows, resulting in higher heat loss from the body.
• Clothing (insulation) – Each person’s clothing has a substantial impact on thermal comfort, because it influences the heat loss from the body. Layers of insulating clothing prevent heat loss and can either help keep a person warm or lead to overheating.
• Activity level – Each person’s metabolic rate influence the perception of the environment. With higher activity levels, people produce more heat, thus more heat needs to be released to the environment.

Our thermal manikins and sweating manikins are working on the same principle. To maintain thermal comfort, the manikin’s energy balance must be reached – the heat produced by the manikin should be equal to the amount of heat lost to the environment.

How is Thermal Comfort Measured and Evaluated?

Thermal comfort is measured and evaluated using various methods that consider both subjective perceptions and objective physical parameters. The most common approaches include:

1. PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) Indexes – Developed by Fanger, these models predict the thermal sensation of a large group of people based on environmental factors such as air temperature, mean radiant temperature, air velocity, and humidity, along with personal factors like clothing insulation and metabolic rate.

• PMV scale ranges from -3 (cold) to +3 (hot), with 0 being neutral.
• PPD estimates the percentage of people likely to feel dissatisfied with the thermal environment.

2. Thermal Comfort Surveys – Subjective evaluations are collected through questionnaires where individuals rate their thermal sensation, satisfaction, and preference, helping assess comfort levels in real-world settings.