Yoshihito Kurazumi

Convective Heat Transfer Coefficients of the Human Body under Forced Convection from Ceiling

The average convective heat transfer coefficient for a seated human body exposed to downward flow from above was determined. Thermal manikin with complex body shape and size of an average Scandinavian female was used. The surface temperature distribution of the manikin’s body was as the skin temperature distribution of an average person. The measurements were performed in a room with controlled thermal environment. Air temperature was set at 26oC for cooling and at 20oC for heating. The radiant temperature asymmetry in horizontal and vertical direction was close to zero, i.e. mean radiant temperature was equal to the air temperature. The air velocity of the isothermal downward flow from the ceiling at height of 1.5 m above the floor (above the top of the head) was set in a range between still air and 0.73 m/s. Based on the analyses of the results relationships for determination of the convective heat transfer coefficient of the whole body (hc [W/(m2•K)]) was proposed: hc=4.088+6.592V1.715 for a seated naked body at 20oC and hc=2.874+7.427V1.345 for a seated naked body at 26oC. Differences in the convective heat transfer coefficient of the whole body in low air velocity range, V<0.3 m/s, due to the natural convection were found. The results may be useful during design of air distribution in rooms, e.g. low impulse ventilation, diffuse ventilation, etc.

Effect of the Environmental Stimuli upon the Human Body in Winter Outdoor Thermal Environment

In order to manage the outdoor thermal environment with regard to human health and the environmental impact of waste heat, quantitative evaluations are indispensable. It is necessary to use a thermal environment evaluation index. The purpose of this paper is to clarify the relationship between the psychological thermal responses of the human body and winter outdoor thermal environment variables. Subjective experiments were conducted in the winter outdoor environment. Environmental factors and human psychological responses were measured. The relationship between the psychological thermal responses of the human body and the outdoor thermal environment index ETFe (enhanced conduction-corrected modified effective temperature) in winter was shown. The variables which influence the thermal sensation vote of the human body are air temperature, long-wave thermal radiation and short-wave solar radiation. The variables that influence the thermal comfort vote of the human body are air temperature, humidity, short-wave solar radiation, long-wave thermal radiation, and heat conduction. Short-wave solar radiation, and heat conduction are among the winter outdoor thermal environment variables that affect psychological responses to heat. The use of thermal environment evaluation indices that comprise short-wave solar radiation and heat conduction in winter outdoor spaces is a valid approach.

Behavioral Thermoregulation Model for Evaluation of Outdoor Thermal Environment

In the outdoor environment, the effect of the physical environmental factors that compose the sensational and physiological temperature is remarkably large in comparison to the indoor environment. The purpose of this paper is to propose and develop a behavioral thermoregulation model in the outdoor environment, in order to predict the mean skin temperature for the evaluation of outdoor environment. This model is based on a Two-Node Model, and has three components: direct solar radiation, indirect solar radiation, and heat conduction. Each body part consists of core and skin layers. The model formula, by ratio of body weight of skin layer of heat conductance between skin and core layer, was included in this model. To verify this model, experiments were conducted. It was shown from the relation between ETFe (Enhanced conduction-corrected modified effective temperature) and mean skin temperature that it is possible to quantity explicitly the effects owing to outdoor environmental factors, short-wave solar radiation, heat conduction etc. It was made clear that the current model is valid for simulated mean skin temperature in the outdoor environment.

Effects of Visual Stimuli upon Thermal Sense under Air Conditioning in Summer

Human thermal sense is not expressed only by simple heat equilibrium. The influence of visual and auditory stimuli causes differences in overall thermal sense arrived at by sophisticated sensory processing by the cerebrum. If it can be clearly shown that a thermal environment considered slightly uncomfortable could be ameliorated using visual stimuli, the cost effectiveness of such an initiative would be highly significant, particularly in terms of air conditioning system running costs. Focusing on the visual stimuli provided by greenery, experiments were conducted in a thermal environment deemed slightly uncomfortable, where the temperature was set at a base point of 28oC. Experiments were conducted in a temperature-controlled room. Thermal environmental conditions were set at three different temperatures: 25oC, 28oC and 31oC. Wall surface temperatures were set to equal these temperatures. Air velocity (calm air currents of 0.2 m/s or less) and relative humidity (60% RH) were set the same throughout. Subjects were asked to sit quietly for the test. The visual stimuli consisted of ten different types of scenery, including that of leafy vegetation. The influence of overall stimuli of the cerebrum on the indoor thermal environmental index ETF was determined to prove the significance of actively placing visual stimuli in spaces. Thermal stimuli influence the human body on mean skin temperatures, while visual stimuli do not affect mean skin temperatures. In ETF deemed fairly uncomfortable, that is at a range of hotter than 28-29oC, clear improvements were observed in thermal sense due to the influence of visual stimuli such as natural elements including vegetation like greenery. Visual stimuli were appropriate at a level of up to 69% greenery, where a dynamic effect on warmer environmental conditions can be felt and where the depth of fuller vegetation cover can be perceived.

Expansion of effective wet bulb globe temperature for vapor impermeable protective clothing

The wet bulb globe temperature (WBGT) is an effective measure for risk screening to prevent heat dISOrders. However, a heat risk evaluation by WBGT requires adjustments depending on the clothing. In this study, we proposed a new effective WBGT (WBGTeff*) for general vapor permeable clothing ensembles and vapor impermeable protective clothing that is applicable to occupants engaged in moderate intensity work with a metabolic heat production value of around 174W/m2. WBGTeff* enables the conversion of heat stress into the scale experienced by the occupant dressed in the basic clothing ensemble (work clothes) based on the heat balances for a human body. We confirmed that WBGTeff* was effective for expressing the critical thermal environments for the prescriptive zones for occupants wearing vapor impermeable protective clothing. Based on WBGTeff*, we succeeded in clarifying how the weights for natural wet bulb, globe, and air temperatures and the intercept changed depending on clothing properties and the surrounding environmental factors when heat stress is expressed by the weighted sum of natural wet bulb, globe, and air temperatures and the intercept. The weight of environmental temperatures (globe and air temperatures) for WBGTeff* for vapor impermeable protective clothing increased compared with that for general vapor permeable clothing, whereas that of the natural wet bulb temperature decreased. For WBGTeff* in outdoor conditions with a solar load, the weighting ratio of globe temperature increased and that of air temperature decreased with air velocity. Approximation equations of WBGTeff* were proposed for both general vapor permeable clothing ensembles and for vapor impermeable protective clothing.

Heat balance model for a human body in the form of wet bulb globe temperature indices

The purpose of this study is to expand the empirically derived wet bulb globe temperature (WBGT) index to a rational thermal index based on the heat balance for a human body. We derive the heat balance model in the same form as the WBGT for a human engaged in moderate intensity work with a metabolic heat production of 174W/m2 while wearing typical vapor-permeable clothing under shady and sunny conditions. Two important relationships are revealed based on this derivation: (1) the natural wet bulb and black globe temperature coefficients in the WBGT coincide with the heat balance equation for a human body with a fixed skin wettedness of approximately 0.45 at a fixed skin temperature; and (2) the WBGT can be interpreted as the environmental potential to increase skin temperature rather than the heat storage rate of a human body. We propose an adjustment factor calculation method that supports the application of WBGT for humans dressed in various clothing types and working under various air velocity conditions. Concurrently, we note difficulties in adjusting the WBGT by using a single factor for humans wearing vapor-impermeable protective clothing. The WBGT for shady conditions does not need adjustment depending on the positive radiant field (i.e., when a radiant heat source exists), whereas that for the sunny condition requires adjustments because it underestimates heat stress, which may result in insufficient human protection measures.

Refuge behaviour from outdoor thermal environmental stress and seasonal differences of thermal sense in tropical urban climate

Thermal sensation affects body temperature regulation. As a starting point for behavioral body temperature regulation taken to improve from a poor thermal environment to a more pleasant environment, thermal sense of thermal environment stimulus is important. The poupose of this sutudy is to use the outdoor thermal environment evaluation index ETFe to quantify effects on thermal sensations of the human body of a tropical region climate with small annual temperature differences, and to examine seasonal differences in thermal sensation. It was found temperature preferences were lower in the winter season than in the dry season, and that a tolerance for higher temperatures in the dry season than in the winter season. It was found effects of seasonal differences of the thermal environment appear in quantitative changes in thermal sensations. It was found that effects of seasonal differences of the thermal environment do not greatly affect quantitative changes in thermal comfort.