Thermal sensation

The temperatures monitored in Fig. 5.2 are used by the brain to regulate shivering, blood flow to the skin, and sweating. The sensed temperatures also contribute to our overall feelings of warmth and other thermal sensations. 7 hermal sensation (TS) can be predicted over a wide range of activities (0.8 to 4 met) from simple deviations in the mean body temperature (T j,) from the mean bodv temperature when the person feels neither warm or cool but neutral (Fig. 5.2). 

During transients the rate of change of mean body temperature can have a strong effect on thermal sensation. 

FIGURE 5.2 Temperature sensors for ternperature regulation and thermal sensation. 

FIGURE S.3 Schematic of skin and core temperatures for a neutral thermal sensation. 

The consequence of the relationships of Table 5.3 and Fig. 5.2 is that for a neutral thermal sensation, at steady state, the core temperature increases while the skin temperature decreases with increased metabolic activity (Fig. 5.3). The increase in metabolism causes sweating which decreases skin tem-perature. 

The clothing insulation necessary for comfort or a neutral thermal sensation (TS = 0) in a thermally uniform 50% RH still-air environment is graphed in Fig. 5.5. The slope of the graph is such that comfort temperature is decreased about 0.6 °C for each 0.1 do increase in clothing insulation. The... 

FIGURE 5.S Clothing imulation necessary for neutral thermal sensation of sedentary persons (I met) In a thermally unifonri still-air envrronment with 50% relative hurnidity. For higher activity levels the temperature at a do level can be reduced about 1.4 °C per met increase. ... 

In general, when a person is thermally comfortable, the person s thermal sensation for the whole body is at or near neutral as depicted in Fig. 5.7a. As we have seen, the thermal conditions necessary for comfort are affected by clothing insulation. Figure 5.7b shows the range of temperatures and humidities... 

Optimum comfort would be in the center of each zone. Moving away from the center, some people would be expected to have thermal sensations approaching - 0.5 and -i-0.5 at the cooler and warmer ET borders. The zones of Fig. 5.7b are for sedentary or slightly active ( M 1.2 met) people. If the activity level is higher than that, then the ET" line borders can be shifted about 1.4 K lower per met of increased activity. Similarly, if the clothing is different than the 0.9 and 0.5 do vales of Fig. 5.7a, the temperature boundaries can be decreased about 0.6 K for each 0.1 do increase in clothing insulation. Another, similar way to adjust the comfort zone for both different activity levels and do values is to shift the zone centered on the optimum temperature at... 

Conditions that are warmer than the applicable still-air comfort zone of Fig. 5.7b can often be made comfortable by increasing the air speed. If the conditions are 1 to 6 °C warmer than the still-air comfort zone of Fig. 5.7b, the necessary air speed v) to restore thermal balance and comfort can be estimated from Fig. 5.8, where Tis the temperature difference between the environment and the still-air comfort temperature. Though the increased air speed will bring the whole-body thermal sensation to the comfort level, air motions above 0.8 m/s or so may cause other kinds of discomfort frojn... 

Xia, Y, and Zhao, R. (1999). Effects of air turbulence on human thermal sensation in warm rsotliermal environment. The Third International Symposium on Hearing, Ventilation and Air Conditioning, 1 147-152. 

Nevins, R., Gonzalez, R. R., Nishi, Y, and Ciagge, A. P. (1975). Effect of changes in ambient temperature and level of humidiry on comfort and thermal sensations. ASHRAE Trans., 81(2). 

ISO EN 7730 standardizes the PMV-PPD index as the method for evaluation of moderate thermal environments. To quantify the degree of comfort, the PMV (predicted mean vote) index gives a value on a 7-point thermal sensation scale -t-3 hot, +2 warm, +1 slightly warm, 0 neutral, -I slightly cool, -2 cool, -3 cold. An equation in the standard calculates the PMV index based on the six factors (clothing, activity, air and mean radiant temperatures, air speed, and humidity). 

The PMV index predicts the mean value of the thermal preferences of a large group of people exposed to the same environment. But individual votes are scattered around this mean value, and it is useful to predict the number of people likely to feel uncomfortably warm or cool. The PPD (predicted percentage of dissatisfied) index establishes a quantitative prediction of the number of thermally dissatisfied people. The PPD predicts the percentage of a large group of people likely to feel too warm or cool, i.e., voting hot (-t-. , warm (4-2), cool (-2), or cold (-3) on the 7-point thermal sensation scale. 

For < 0.05 m s, use t, - 0.05 m s b For DR > 100%, use DR = 100%, The model applies to people at light, mainly sedentary activity with a thermal sensation for the whole body close to neutral. The sensation of draft is lower at activities higher than sedentary and for people feeling warmer than neutral. 

Figure 6.1 applies for a relative humidity of 50% however, in moderate environments the air humidity has only a modest impact on the thermal sensation. Typically, a 10% increase in relative humidity is experienced as equally warm as a 0.3 °C increase in operative temperature. 

Body thermal sensation The response of the body to changes in the thermal environment, relating to moisture, air movement, or temperature. 

Predicted mean vote index (PMV) An index used to predict the mean value of thermal sensation votes of a large group of persons, expressed on a 7-point scale. 

Ciguatera is the most famous seafood poisoning prevalent in circumtropical areas (Scheuer 1994). Its effects to human health and economic impacts are serious problems in those areas. The clinical symptoms are diverse. Neurological disturbances are prominent reversal of thermal sensation, called dry ice sensation, is one of the most characteristic symptoms of ciguatera. Other illnesses include joint pain, miosis, erethism, cyanosis, and prostration. 

Distal symmetric sensorimotor polyneuropathy is the most common form of diabetic neuropathy. Small fibre neuropathies involving unmyelinated C and A5 fibres are involved in symptoms like pain, which is burning and superficial and associated with allodynia, hypoalgesia and defective warm thermal sensation. Patients can experience dys-, para, hypo- or hyperaesthesia, tingling, pins and needles or electric-shock-like sensations. 

Figure 7.4 Thermal sensation (top) and thermal comfort (bottom) for a normal firefighting suit, a suit with cool pads inside and a water-perfused top (a perfused significantly different from control b cool pad significantly different from control c cool pad significantly different from perfused).

Human laboratory tests have the advantage that aspects like thermal comfort and thermal sensation in the sport garments can be evaluated luider realistic circumstances, for instance, in climatic chambers. 

That thermal comfort is different than thermal sensation... 

Subjective Ratings on a Seven-Point Thermal Sensation Scale ... 

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