Thermal comfort in buildings

Thermal comfort in buildings

The human body’s comfort is essentially determined by three environmental factors: temperature, relative humidity, and air motion. The single most significant metric of comfort is the temperature of the surroundings. An extensive study on human subjects is carried out to discover the “thermal comfort zone” and the circumstances under which the body feels comfortable in an environment. Most regularly dressed persons relaxing or performing light labor feel comfortable in the operating temperature range of 23 to 27C (approximately, the average temperature of air and surrounding surfaces). This range is 29 to 31 degrees Celsius for naked persons. Relative humidity has a significant impact on comfort because it measures the ability of air to absorb moisture and consequently impacts the amount of heat a person can escape through evaporation. High relative humidity delays heat rejection through evaporation, particularly at high temperatures, whereas low relative humidity accelerates it. The ideal relative humidity level is between 30 and 70 percent, with 50 percent being the most suitable. Most people do not feel hot or cold in these settings, and the body does not need to engage any of its defensive systems to maintain normal body temperature.

Excessive air motion or draft, which produces unwanted local cooling of the human body, is another issue that has a significant impact on thermal comfort. Many people consider drafting to be the most unpleasant aspect of workplaces, vehicles, and airplanes. Persons wearing indoor attire and doing light sedentary work are more likely to feel draft discomfort, whereas people with high activity levels are less likely to feel draft pain. Air velocity should be kept below 9 m/min in the winter and 15 m/min in the summer to avoid draft discomfort, especially when the air is chilly. Low air motion is preferable since it eliminates the warm, damp air that accumulates around the body and replaces it with fresh air. As a result, air motion should be forceful enough to remove heat and moisture from the body’s proximity, yet delicate enough to go undetected. High-speed air movement is also unpleasant outside. Because of the chilling impact of air motion, an environment at 10°C with 48 km/h winds feels as cold as an environment at 7°C with 3 km/h winds (the wind-chill factor).

To eliminate discomfort induced by nonuniformities such as drafts, asymmetric thermal radiation, hot or cold flooring, and vertical temperature stratification, a comfort system should deliver uniform conditions throughout the living space. The cold surfaces of wide windows, uninsulated walls, or cold products create asymmetric thermal radiation, as do the warm surfaces of gas or electric radiant heating panels on the walls or ceiling, solar-heated masonry walls or ceilings, and warm machines. Asymmetric radiation produces pain because it exposes various sides of the body to surfaces at varying temperatures, resulting in unequal heat loss or gain from radiation. Though a person’s left side is exposed to a chilly window, for example, he or she will feel as if heat is being drained from that side of the body. Radiant temperature asymmetry should not exceed 5 degrees Celsius in the vertical direction and 10 degrees Celsius in the horizontal direction for thermal comfort. Radiation asymmetry can be reduced by correctly sizing and installing heating panels, utilizing double-pane windows, and providing enough insulation on the walls and roof.

Direct contact with cold or hot floor surfaces produces localized foot pain. The temperature of the floor is determined by its construction (whether it is directly on the ground or on top of a heated room, if it is built of wood or concrete, whether insulation is used, and so on) as well as the floor covering used, such as pads, carpets, rugs, and linoleum. Most individuals find a floor temperature of 23 to 25 degrees Celsius to be pleasant. For persons who wear shoes, floor asymmetry is irrelevant. Using radiant heating panels instead of cranking up the thermostat is an efficient and cost-effective approach to raising the floor temperature. Temperature stratification in a room, which exposes the head and feet to differing temperatures, is another nonuniform situation that causes pain. The temperature differential between the head and foot levels should not exceed 3 degrees Celsius for thermal comfort. Destratification fans can help to reduce this impact.

It should be mentioned that no temperature climate is suitable for everyone. Some individuals will be upset regardless of what we do. The thermal comfort zone is calculated using a 90% acceptance rate. That example, a place is considered comfortable if just 10% of the inhabitants are unhappy with it. Metabolism slows with aging, although this has no influence on the comfort zone. According to research, there is no discernible difference in the locations favored by elderly and young people. Experiments have also shown that men and women enjoy nearly identical environments. Women’s metabolism rates are significantly lower, although this is offset by their slightly lower skin temperature and evaporative loss. Furthermore, there is no major difference in the comfort zone from one region of the planet to another or from winter to summer. As a result, the same thermal comfort conditions may be used in every season across the world. Furthermore, people cannot acclimate to favor various levels of comfort.

This is actually part-2 of the HUMAN BODY AND THERMAL COMFORT series. part-1 is given in the link below.


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