Post 382 – by Gautam Shah
Understanding the human body temperature management is very important for Interior Designers. It tells how space and human body interact and in the immediate term regulate the comfort and productivity. The persistent equation between the space and human body also decides the well being of a person.
Climate affects our body system very profoundly. The climatic effects are primarily sensed by the skin. Five types of sensations are involved with the skin: The Touch-Pressure (mechanic-o receptors), Cold-Warmth feeling (thermo receptors), Pain and Itch. Cold is a consequence of contraction of blood vessels and warmth is felt due to dilation of blood vessels; both are felt by the same receptors.
Our body functions as a thermo equilibrium system. It continues to strive a state of balance, by many different body mechanisms and spatial-environmental interventions. In the shorter period human body may endure or adopt to certain abnormal conditions. Frequent such shocks cause side effects which may be realized in a different form and at a different time. The Optimum or Comfort level temperature depends on the level of acclimatization.
The thermal bearing capacity has upper and lower limits. The pain occurs at the upper limit of 52° C /126° F, and has a lower limit of 3° C / 37° F. In certain acute work conditions like mines, metal smelting plants, cotton spinning-weaving plants, cold storage, the efficiency or productivity depends on the endurance level, adaptability and duration of exposure of the body.
Human body generates heat through basic three processes.
- Conversion of food matter into useful energy is a continuous heat generating process.
- Muscular activities like even sedentary work or sleeping, are heat generating processes.
- Certain infections and dysfunctions within the body, elevate or lower the body temperature by extra ordinary rate of heat generation, or weakened heat- dissipation, mechanism.
Human body utilizes only 20 % of all energy being generated by the nominal body processes, and the rest 80 % is surplus heat. The body however gains or loses heat with environmental interactions. All the surplus heat generated within the body and the excess heat gained from the environment must be adequately managed.
Human body gains heat from the atmosphere, and also dissipate excess heat to it, to maintain thermo equilibrium. Heat loss is accelerated by several body functions like perspiration, high transfer of heat to the skin by increased blood circulation (vaso-dilatation). When these prove to be insufficient, sweating occurs. In hot climates the heat loss rate is lower due to unfavourable atmospheric conditions.
Body can manage to lower the heat by lowering the metabolic and by reducing the muscular activity. But both of these require some time to take effect. On immediate basis when the heat loss is not balanced with heat gain, the `heat stroke‘ occurs. In cold climates the heat loss is higher, so heat balance is achieved by conservation of heat and by appropriate heat gain. Heat production is raised by certain reflex secretions (adrenaline, thyroxine), higher intakes of food (increased metabolic activity). Reflex shivering (muscular exercise) and with sufficient insulative protection the heat loss can be controlled. The body may control the heat loss by vaso-constriction (lower blood supply) and depressed sweating. A person exposed to a constant high rate of sweating and permanent vaso-dilation can have lots of physical strain with loss of work efficiency.
The human body maintains an average temperature of 98.4° F / 37° C (ranges between 31° and 34°C). There are many minor variations in body temperature, which are considered normal. Body temperature is lowest in the morning, and highest in the evening, within a range of 1.5° F / 1° C. Infants have a very imperfect mechanism for regulation of body temperature. A fit of crying may elevate and a cold wash may lower the body temperature. Aged persons have a low metabolism and so maintain a lower body temperature. It takes much longer for an aged person to gain or dissipate body heat. Female body temperature is slightly lower than Male.
The type food one takes affect the body temperature. High protein foods increase the body temperature. The act of ingestion and food digestion, both raise the body temperature. Exercise increases the body temperature, because only 25 % of muscular energy is converted into mechanical work, rest comes out as body heat. Many physical, chemical and bacterial agents disturb the heat regulation mechanism and cause fever. These may be due to increased heat production or reduced heat loss, or both.
In reptiles and amphibians a heat regulation mechanism is absent. Their body temperature rises or falls with the atmospheric temperature. Hence they are called cold-blooded animals. In abnormal temperature conditions they regulate the body temperature by suitable habitat. In winter they go deep into burrows or in hibernation (minimize the metabolic heat generation). Mammals and birds are known as hot blooded creatures, because the heat regulation mechanism is well developed, and they are able to maintain a level of body temperature.
Our life styles reflect culture of the place, which in turn is our response to the environment. The heat management of our body is effected by the type of food, frequency of intake, volume, proportion of liquids, the rest (siesta) periods, the daily work-rest cycles, clothing, form of our habitat, types of furniture and furnishings.
Heat management occurs through Four routes:
1 Radiation: Radiation mainly occurs when there is a difference in temperature on opposing surfaces. As long as temperature of the opposite surface or object (sun, fire, radiators) is below skin temperature, the body can lose heat by radiation. But once it reaches equilibrium occurs, body will rather gain heat by radiation.
2 Evaporation is controlled by the level of humidity in the air. Level of humidity is in turn affected by temperature of the air and air movement. It is also depends on the existing proportion of humidity. Body dissipates heat through evaporation by perspiration, sweat and exhalation of air. Dryer air encourages faster evaporation. Evaporation can occur if air has velocity and appropriate humidity (low). Even in case of very high humidity conditions a high velocity air can remove the humidity.
3 Convection occurs when the air in the vicinity of skin becomes hot, expands, decreases in density, and elevates to allow cooler air in its place. The rate of heat convection from body depends on the difference in temperatures (skin & surrounding air) and rate of air movement. When the convective process is inoperative and radiation heat gain is positive, the body can maintain the thermal balance by evaporation.
4 Conduction depends on the difference between the body temperature, duration and extent of the contact.
Average heat exchange between Human body and Environment are of following order.
- Radiation (60 %),
- Evaporation (25 %),
- Convection and Conduction (15 %).