Comfort is subjective
Comfort is influenced by personal preferences, experiences, and individual perceptions, and especially by the surrounding environments. What one person finds comfortable, another person may find uncomfortable.
However, there are also certain factors contributing to a sense of comfort for many people. These factors are often rooted in basic human needs and physiological responses.
- Physical comfort & environment — based on physical factors like temperature, humidity, lighting and indoor environment quality, as mentioned above.
- Safety & security — a sense of feeling safe and secure in a person's surrounding environment.
- Familiarity & routine — as they provide a sense of predictability and control.
- Social connection & community — creating a sense of belonging and having support.
- Emotional well-being — such as emotional stability, reduced stress and a sense of fullfillment and purpose.
The overall sense of comfort is subjective and can vary significantly. However, it is
Thermal comfort in buildings
Can you measure thermal comfort in the building? Or can you feel it? And can you see it?
Thermal comfort is very difficult to define because it is based on a range of environmental, work-related and personal factors when deciding what makes a comfortable indoor temperature.
The thermal comfort is basically describing a thermal environment that satisfies the majority of people in the environment. Thermal comfort is not measured by room temperature, but by the number of people complaining of thermal discomfort.
When people feel unconfortable in their environments, they may behave and feel not safe. Also people's ability to concentrate may start to drop off, which increases the risk of errors.
There are six factors indicating thermal comfort in buidings. However, thermal comfort should always be considered in relation with the following factors.
- Personal (physiologicial) factors — based on the occupant's characteristics.
- Environmental (physical) factors — based on conditions of the thermal environment.
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Thermal comfort is subjective and can vary from person to person.
Perceived, predicted & satisfied
The predicted percentage dissatisfied model was developed by Fanger (1967). He hypothesized that human thermal comfort was based on one's skin temperature and sweat secretion and that one could only be considered 'comfortable' if these two factors were balanced within a narrow range of acceptability.
The predictive mean vote (PMV) is an index that aims to predict the mean value of votes of a group of occupants on a seven-point thermal sensation scale.
Within the PMV index, -3 translates as too cold, while +3 translates as too hot, as showned below.
The predicted percentage of dissatisfied (PPD) is an index that predicts the proportion of thermally dissatisfied people who feel too cold or too hot. It is calculated based on the PMV.
The PMV and PPD forms are closely related, and both indexes take the form of a U-shaped ratio, where percent dissatisfaction increases for PMV values above and below zero (thermally neutral).
At the neutral temperature defined by the PMV index, PPD indicates that 5% of users are always dissatisfied with the thermal environment. At least 80% satisfied, this value is considered by science to be an index to strive for in an acceptable indoor climate.
The thermal model stands among the most recognized thermal comfort models. It was developed using principles of heat balance and experimental data collected in a controlled climate chamber under steady state conditions.
Thermal comfort calculations in accordance with the ANSI/ASHRAE Standard 55, the ISO 7730 Standard and the EN 16798-1 Standards.
Watch: Visualising the Invisible — Comfort
Lecturers: Mikael Börjesson & Åsa Norén-Lundh
Webinar recording from Swegon Air Academy, 2022.
In this video, you will learn about comfort indoors what are thermal comfort and indoor thermal quality, what factors impact the comfort of a room, other influencing factors, and more:
- How comfort refers to how we feel in the indoor environments by encompassing temperature, humidity and air speed?
- Why it is also referred to as thermal comfort or indoor thermal quality?
- What factors impact the comfort of a room, including temperature and the relative humidity in a building?
- What external factors need to be considered with comfort?
Thermal comfort as a 'condition of mind'. So, can we 'adapt our minds'?
Adapted versus not-adapted?
Occupants versus visitors
Adapted people are considered those who entered a room and are already acclimatized to the situation in the room, i.e. approximately 15 minutes after entering a room. Visitors are people who just entered a room and are assessing the situation in the room at that moment of entering.
Should adaptative comfort criteria be adopted?
In determining the acceptable range of operative temperature, a clothing insulation value that corresponds to the local clothing habits and climate shall be used.
In warm or cold environments, there can often be an influence due to adaptation. Apart form clothing, other forms of adaptation, such as body posture and decreased activity, which are difficult to quantify, can result in the acceptance of higher indoor temperatures.
People used to working and living in warm climates can more easily accept and maintain a higher work performance in hot environments than those living in colder climates.
Occupant-controlled or ventilation-controlled?
Extended acceptable environments may be applied for occupant-controlled, naturally conditioned, spaces in warm climate regions or during warm periods, where the thermal conditions of the space are regulated primarily by the occupants through the opening and closing of windows.
But what about the buildings controlled by means of mechanical ventilation? Could variable ventilation modes bring a more comfortable indoor thermal environment than the fixed one? Adaptive thermal comfort could also reduce the energy consumption of heating, cooling, and ventilation systems in buildings.
Who should we ventilate for?
For people just entering the room (un-adapted) or for people already occupying a room (adapted)? But should it really be one or the other? In a conference room, auditorium or lecture room most people enter at the same time. It then takes some time before the odour level has reached an unacceptable level and meanwhile people adapt.
It may be appropriate to require a ventilation rate based on adapted persons. There may be other spaces where you would design for un-adapted people, e.g. in a first-class restaurant, offices, and department stores. It seems logical that more differentiated criteria could be used.