chapter  1
47 Pages

Human comfort and ventilation

The primary function of thermoregulation is tomaintain the body core, which contains the vital organs, within the rather narrow range of temperature which is vital for their proper functioning. The temperature control centre is the hypothalamus, a part of the

“chap01” #2

brain that is linked to thermoreceptors in the brain, the skin and other parts of the body such as the muscles. The hypothalamus receives nerve pulses from the temperature sensors and coordinates information to different body organs to maintain a constant body core temperature. The thermoreceptors are particularly sensitive to changes in temperature and temperature change rates as small as +0.001 and −0.004Ks−1 can be detected. Temperature regulation is carried out by controlling metabolic heat production rate, control of blood flow, sweating, muscle contraction and shivering in extreme cold situations. Under normal conditions the body core temperature, tc, is approximately 37 ◦C and this is maintained at a constant value despite changes in the ambient temperature, as shown in Figure 1.1 for three levels of activity [2]. The figure shows the ability of the temperature-regulating mechanisms to maintain a constant core temperature up to a certain ambient temperature beyond which core temperature cannot be maintained because evaporative cooling of sweat becomes ineffective. It is also shown in Figure 1.1 that the core temperature is not always constant but depends on activity, i.e. increases with increase in metabolism, and may be as high as 39.5 ◦C in extreme activities. While the body core temperature remains almost constant over a wide range of

ambient temperatures, the skin temperature changes in response to changes in the environment and is usually different for different parts of the body. However, the variation in skin temperature over the body is reduced when the body is in a state of thermal equilibrium and comfort. The variation of mean skin temperature, ts, for a nude person with ambient temperature is shown in Figure 1.2, which also shows the rectal temperature for the purpose of comparison [3].