Tomonori Sakoi

Human response to local convective and radiant cooling in a warm environment.

The response of 24 human subjects to local convective cooling, radiant cooling, and combined radiant and convective cooling was studied at 28°C and 50% relative humidity. The local cooling devices used were (1) a tabletop cooling fan, (2) personalized ventilation providing a stream of clean air, (3) radiant panels below and above the desk in front of the desk occupant, and (4) the same two radiant panels but with small fans blowing room air toward the upper panel to be cooled and redirected toward the person. A reference condition without cooling was also tested. The cooling devices significantly (p < 0.05) improved subjects’ thermal comfort compared to the condition without cooling. The acceptability of the thermal environment was similar for all cooling devices. The acceptability of air movement and perceived air quality increased when local cooling methods were used. The best results were achieved with personalized ventilation or the tabletop fan. Only minimal improvement in perceived air quality was reported when the radiant panel was used alone, indicating that in a warm environment, local convective cooling is superior to local radiant cooling as a means of improving perceived air quality. The intensity of the reported sick building syndrome symptoms increased during the exposure time, with or without cooling devices in operation. Air movement had very little effect on sick building syndrome symptoms, but they increased when the pollution level was high. The lowest prevalence of symptoms was reported with personalized ventilation and with the radiant panel with attached fans, which also caused subjects to report less fatigue. Sick building syndrome symptoms increased most when the tabletop fan, generating movement of polluted room air, was in operation. The temperature of the inhaled air rather than any local cooling of the head was associated with sick building syndrome symptoms, although this needs further study. The most preferred cooling method was personalized ventilation for six subjects, fan for eight subjects, and radiant panel (or radiant panel + fans) for nine subjects.

Development of a Computational Thermal Manikin Applicable in a Nonuniform Thermal Environment—Part 1: Coupled Simulation of Convection, Radiation, and Smith's Human Thermal Physiological Model for Sensible Heat Transfer from a Seated Human Body in Radiant Environment

To predict the thermal sensation of people located in a nonuniform environment, it is very important to clarify the local heat transfer in detail. In this context, the coupled simulation of convection, radiation, and the multi-element thermal physiological model established by Smith is investigated. The sensible heat transfer from the surface of a human body placed in uniform and front-back asymmetric radiant environments, with ambient air temperature of 28°C, was calculated using the coupled simulation method. According to the results, the microclimate around the human body and its thermal characteristics changed in response to the radiant conditions. However, compared with the results of the human subject experiments, which were measured under the same thermal conditions, in terms of skin temperatures, it is indicated that the simulation cannot accurately predict the skin temperature at the limbs, even in a uniform environment. Finally, measures for improving the prediction accuracy of the present coupled simulation method are suggested based on examination of the cause of the discrepancy.

Development of a Computational Thermal Manikin Applicable in a Non-Uniform Thermal Environment—Part 2: Coupled Simulation Using Sakoi's Human Thermal Physiological Model

In order to develop a computational thermal manikin to enable the prediction of the thermal sensation of an occupant in a non-uniform environment, in a previous paper (Zhu et al. 2007) we proposed and examined a simulation method combining Smiths human thermal physiological model with convective and radiant simulation by applying the proposed method to calculate the sensible heat transfer over the body surface of an occupant located in several radiant environments with an air temperature of 28°C. However, the simulation results greatly underestimated the skin temperatures at the limbs, even in uniform conditions, due to the improper modeling of the Arteriovenous Anastomose phenomenon in Smiths model. Accordingly, a new human thermal physiological model, Sakois model (Sakoi et al. 2005a, 2006a), was developed with a three-dimensional body configuration similar to Smiths model and a thermo-regulatory mechanism by Yokoyama (1993). In this paper, Sakois model is coupled in the simulation of convection, radiation, and moisture transport to calculate the total (sensible and latent) heat transfer from a seated human body in uniform and front-back asymmetric radiant environments, which were introduced in the previous paper (Zhu et al. 2007). The comparison to the corresponding results of the subject experiments and the coupled simulation using Smiths model in terms of skin temperatures indicates that the prediction accuracy of the numerical simulation is greatly improved as a whole, especially at the limbs; however, it deteriorates around the face and body parts facing cold panels when using Sakois model.

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.

Effect of compressibility on heat transport phenomena in aerogel-treated nonwoven fabrics

The heat transport properties observed in nanostructured materials such as aerogel-treated nonwoven fabrics are promoting revolutionary breakthroughs as thermal insulators. This article is focused on the thermal transport characteristics of nonwoven fabrics treated with aerogel for potential uses in thermal protective applications. Highly efficient aerogel thermal blankets are now considered a viable option in applications such as clothing, building, and pipelines. A variety of fiber and fabric structures or finishing parameters influence the functional properties of nonwoven materials. In order to assess the thermal properties of aerogel-treated nonwoven fabrics, the KES Thermolabo II and NT-H1 (plate/fabric/plate method for thermal conductivity, qmax cool/warm feeling, and thermal insulation) was used. Fabrics of higher thicknesses show lower heat conductance and therefore higher thermal insulation properties. It has been found that thermal insulation is also related to the weight and compressional properties of the fabric. To make an insulating material effective, it should have low compression set and high resiliency to make the still air to be entrapped into the fibrous material.

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.