MANILA, Philippines -- We are constantly evaluating our surroundings and finding ways to achieve thermal comfort.

When we get up in the morning, we check the weather and dress appropriately before going to work. We make sure our car air conditioner is in good shape before we drive out. And when we reach our offices we turn on the air conditioner or electric fan to ensure good working conditions.

We never travel abroad without checking if we should bring heavy or light clothes. Thermal comfort is everybody?s concern, whether you are in a temperate country or in a hot humid country like the Philippines.

What is thermal comfort? Thermal comfort is the sensation of physical well-being in relation to body heat loss to the surroundings.

Our internal body temperature is comfortable at 36.5?-37?C. We have to release body heat from involuntary factors like metabolism and blood circulation, and voluntary factors like muscular activity, clothing, and location in order to maintain a stable internal temperature. There is continuous exchange of heat between the human body and its surroundings.

When summer comes we will say goodbye to the very pleasant 30?C average temperature. We will become dependent on the electric fan and air conditioning to regulate sweating caused by the heat exchange between the human body and the thermal environment. We will be addressing the issue of thermal comfort. Comfort depends on age, gender, culture, and who foots the bill.

4 physical ways

To improve the thermal comfort levels in a room we must understand how the body relates to its surroundings.

The heat exchange between the body and its surroundings takes place in four physical ways: conduction, convection, long-wave radiation, and evaporation.

? Conduction. This is the transmission of heat from materials in contact with the skin. For example, it is not advisable to wear wool and heavy clothing in hot weather. It is also important to select the proper materials, coverings, and finishes in warm climate.

? Convection. This is the exchange of body heat with ambient air, depending on the difference in temperature between the body and the air and also air movement.

Ambient temperature is comfortable at 26?C. Window openings allow air exchange and are recommended to be not less than one-tenth of floor area, and one-third of wall area. Operable windows are preferable to fixed glass windows. Buildings and homes are comfortable when planned and designed according to topography and wind direction.

When there are two openings at different levels of a house or building, and there is a temperature difference between these two levels, the stack effect occurs. That is the tendency of warm air to rise and go out through the opening in the higher level. The hot air will be replaced by cool air entering through the lower openings.

Natural night ventilation should be allowed indoors to reduce air temperature during hot weather.

? Long-wave radiation. This is the heat transfer between the human body and the surrounding internal surfaces like the walls, ceiling, and floors. The difference in temperature between the skin and the surfaces enclosing the body highly affect thermal comfort. Heat from the ceiling is reported to affect us more than heat from walls. Ceiling height and thermal property of ceiling and wall materials are therefore important considerations in designing homes and buildings.

Poorly insulated buildings have hot internal surfaces. Light-colored paint on external walls is recommended in hot climate because it will reflect solar radiation.

Green roofs, climbing plants, and koi ponds reduce temperature of roofs and walls and internal surfaces. Sun shades and shutters reduce sunlight penetration.

? Evaporation. This occurs when the temperature of surrounding air and surfaces is above 25?C. The body loses heat through evaporation or perspiration depending on clothing worn, temperature, relative humidity, and air movement. Humans normally lose one liter of water per day due to perspiration and respiration, and it takes heat from the body and its surroundings to evaporate it. Relative humidity, or the amount of moisture in the air as percentage of the maximum moisture the air can contain at a certain temperature and pressure, affects heat loss by evaporation. If the surrounding air has higher temperature than the skin, the cooling effect of evaporation is not possible even if relative humidity is below 100 percent. Air speed does not decrease the temperature but causes a cooling sensation through heat loss by convection and increased evaporation.

Steps to cool the air will help maintain a sense of well-being in this time of crisis.

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