BPH5: Human perception and new indicators
Thermal comfort comparison and evaluation in different climates
1Centro Federal de Educação Tecnológica de Minas Gerais - CEFET-MG, Brazil; 2BTU Cottbus; 3UFMG; 4UKASS
The response to heat stress in cities in moderate and tropical climates can be quite different. According to the thermal adaptation and to a certain expectation regarding the thermal conditions, thermal comfort ranges change, once psychological and sociocultural processes play an important role in thermal comfort evaluation. The aim of this study was to validate the results of investigations in different climates (Brazil and Germany) using the same method to compare the limits of heat stress and to study the response from the subjective evaluation of thermal sensation to measured data. This can be seen as a realistic way of determining heat stress and can therefore be an instrument for planners to identify heat sensitive areas in the open space and develop strategies to mitigate those.
The presented methods and results were derived during measurement campaigns with microclimatic data and interviews of adult persons in Belo Horizonte /Brazil and Kassel / Freiburg in Germany. The subjective variables were data concerning perception and preferences of thermal sensation, using a seven-point scale. As thermal index derived from measurements the physical equivalent temperature PET was used and combined with the seven-point scale very hot, hot, warm, neutral, cool, cold and very cold.
In this study the index PET was chosen due to different reasons. The first reason is that – compared to other indices – it was adapted to outdoor settings. The second reason is that it is internationally used which provides comparability. In addition to its wide distribution it is furthermore continuously developed by several work groups.
Urban design need strategies and concepts for urban planning in order to mitigate the impacts of urban heat load. These strategies have to consider urban climate conditions of hot and cold seasons, but also have to take into account that in colder climates people want to have warm periods for short time, while in hotter climate people long for cool. The thermal index PET showed lower values for the scale very hot in Brazil than in Germany. For city design of open spaces in colder climates some warm places should be kept as long they do not lead to heat storage, for hot climates, as expected, shadow is important at any case. The PET neutral comfort value range in Belo Horizonte is from 15 to 30 oC PET and the hot range starts at 31 oC, while in Kassel neural range is from 18 to 28 oC PET and hot range starts with 35 oC PET.
How to transform the standing man from a box to a cylinder – a modified methodology to calculate mean radiant temperature in models and field studies
University of Gothenburg, Sweden, Sweden
Mean radiant temperature (Tmrt) has shown to be an important meteorological variable in studies of human comfort and health. The Tmrt is calculated as the surface temperature of a standing man approximated as a cylinder emitting the same amount of longwave radiation as all short- and longwave radiation fluxes received from the surrounding four cardinal points and down- and upwards. The calculation was introduced by Höppe in 1992 and has then been used both in models (e.g. SOLWEIG) and field studies. However, the formula by Höppe describes in fact a man shaped like a box and not a cylinder, which has resulted in some peculiar features noticed in studies of Tmrt such as a secondary daytime minimum and an influence of the orientation of the field equipment.
A methodology to change the box man to a cylindrical man is proposed. It will remove the peculiarities that have been observed in earlier studies. The methodology is based on the partition of the observed shortwave fluxes in direct and diffuse radiation. The minimum shortwave radiation of the four cardinal points is used as diffuse radiation since it is monitored by a sensor that is not sunlit. By subtraction of this quantity the horizontal direct fluxes are obtained. Calculation of the resultant flux of the sunlit sensors and adjustment for solar angle gives the direct shortwave radiation. The surface of the standing man (as a cylinder) perpendicular to the direct radiation must be determined and the direct shortwave radiation received by the standing man can be calculated. Then the sum of the shortwave fluxes can be calculated. The diffuse and longwave fluxes can be calculated according to the Höppe formula since they differ little with direction. In the SOLWEIG model the direct shortwave radiation is used as an input. Thus the calculation according to the new methodology is easy to apply, only the solar position needs to be added.
The new methodology is tested by model calculations with SOLWEIG and field studies in both high-latitude Gothenburg, Sweden and low-latitude Ouagadougou, Burkina Faso. The secondary minimum disappears. In Gothenburg at a site with SVF=0.95 the noon depression of Tmrt by the Höppe formula was about 2 °C and there was an overestimation of 1.5-1.7 °C two-three hours before and after noon.differences in summer. In Ouagadougou data from an open site (SVF=0.83) in the dry season the differences were slightly smaller. Sites with lower SVF and much reflected direct shortwave radiation differed less from the Tmrt obtained with the Höppe formula.
Watts in a comfort index: Evaluating pedestrian energy exchange and thermal stress in urban environments
Ben-Gurion University of the Negev, Israel
The thermal environment in cities is commonly, and habitually, described in terms of temperature. In some cases it is near-surface air temperature, and in others it is a mean radiant temperature, often embedded within a physiologically equivalent temperature or similar comfort index which is used to quantify, in degrees, the thermal effects of the environment on a person. While temperature is indeed our most familiar and intuitive measure of thermal states, it is important to remember that the human body’s thermal endings are not in fact sensors of temperature – but rather of heat flow, monitoring the rate of heat gain or loss from our body due to radiation, convection and evaporation.
This paper describes the validation and implementation of an alternative approach for assessing the thermal environment in urban spaces, using the Index of Thermal Stress (ITS). Rather than attempting to portray the effects of sun, wind, temperature and humidity as a single point on an imaginary thermometer, the ITS is based on an accounting of the individual energy exchanges between a pedestrian's body and the surroundings – expressed in watts – and the physiological response that is required for the body to maintain thermal equilibrium. Calculated values of this index, based on measurements in a hot-arid urban setting, were found to correlate closely with subjective thermal sensation as expressed in questionnaire responses by pedestrians in the same set of locations. While a number of personal and experiential factors were found to impact thermal perception, the "neutral point" was found to correspond in a variety of different circumstances to a physical situation in which the dissipation of heat from a person's body was precisely in balance with that person's internal metabolic heat production (ITS=0).
A series of experimental studies has made use of this ITS model to analyze the thermal effects of variations in street canyon geometry, of shade trees, and of vegetative ground cover, and to evaluate the "cooling efficiency" of irrigated landscaping by comparing its potential to reduce bodily heat gain with the latent heat value of water loss through evapotranspiration. Finally, a case study of a Mediterranean coastal urban park examined the ways in which thermal discomfort is perceived by local residents, and results indicated that the expressed thermal preferences of the park's users align robustly with predictions based on ITS.
SHORT-TERM ACCLIMATIZATION EFFECTS IN AN OUTDOOR COMFORT STUDY
1UTFPR, Brazil, Germany; 2KIT, Germany; 3IfADo, Germany
The ‘Alliesthesia’ concept suggests that stepping from thermal homogeneity to more dynamic and uncontrolled states (as in outdoor settings) should create immediate responses that would diminish with time of exposure. Also according to this concept, once the subject remains for a given time within a thermally static environment, with no “opportunity for the body to interpret the ‘usefulness’ of a stimulus for thermoregulation”, there is a greater chance that he will more effectively experience thermal perception under sudden dynamic conditions. Thus, if there is a means of ensuring thermal homogeneity for a given time period, short-time acclimatization could be tested over different time steps of exposure to the outdoor environment. The present research investigates short-term acclimatization effects on a subject’s thermal sensation and perception. For ensuring thermal homogeneity and almost steady-state conditions prior to the subject’s exposure to the outdoors, a climate chamber is employed, where subjects (N=16) remain for five consecutive hours under nearly thermal comfort conditions (PMV= approx. 0) in two office-like rooms. Standardized clothing is adopted on each subject and a metabolic rate of approximately 2.3 Met is assumed after subjects walk around the external precincts of the chamber within a short period of time, so that a direct comparison to estimated thermal votes can be made. Two different configurations are adopted for the indoor environment as regard visual clues on weather changes throughout the 5-h period inside the chamber, which might influence subjects’ thermal expectations: open, unobstructed view to the outside and closed shutters. In addition, three different time steps are tested: immediately after leaving the air-conditioned space, after 15 minutes and after 30 minutes outside the chamber. The pilot study took place during several days with varying outdoor conditions. The climate chamber (Laboratory for Occupants’ Behaviour, Satisfaction, Thermal Comfort and Environmental Research, LOBSTER) is located in Karlsruhe, Germany (49°00'N), at the Karlsruhe Institute of Technology (KIT). The tests performed evaluate the effects of the time spent outdoors and the subject’s expectations of outdoor meteorological conditions against predictions of the outdoor thermal comfort index UTCI (Universal Thermal Climate Index).
Physiological Response of Human Body and Thermal Sensation for Irradiation and Exercise Load Changes
1Osaka Prefecture University, Japan; 2Okayama Prefectural University, Japan; 3Kansai University, Japan; 4Technology Research Institute of Osaka Prefecture
In outdoor environment, radiation and exercise state is not always steady, and it is necessary to take into account the unsteady environment in order to predict human thermal sensation. In this study, we firstly conduct subject experiments to understand the influence of periodic change of irradiation to thermo-physiological response of the human body. Experiments were conducted in climate chamber set to 28 degree Celsius and 50% RH. The artificial light source displayed 67 metal halide lamps into a plane of 1.0 m x 2.0 m form. We performed two conditions in the same subjects on separate days for irradiation period of 18 and 6 minutes. The total experiment time was 36 minutes with both conditions. The change of skin temperature was expressed in primary delay system. High correlation was seen in the change of skin temperature and the change of thermal sensation. It was found out that the change of skin temperature was an important factor to estimate the thermal sensation under the unsteady irradiation. In this study, we secondary conduct subject experiments to understand the influence of unsteady excise to thermo-physiological response of the human body. Experiments were conducted in climate chamber set to 28 degree Celsius, 50% RH or 30% RH. Subjects were given excise load of 90 W by ergometer for 9 minutes and subsequently keep rest state for 3 minutes. The subjects performed 3 cycles in the experiment. Mean skin temperature of subjects decreased just after an exercise start and gradually rise to rest period. Eardrum temperature rose during exercise. Heart rate rose after exercise started and decreased during a rest period. The rate of change of the heart rate and the thermal sensation showed high correlation. Regression equation of thermal sensation and physiological value obtained from the experiment showed high correlation. In this study, subject experiments were carried out finally in the outdoor space where roadside trees affected. A walk and standstill were repeated. Based on the results obtained from the above-mentioned subject experiments, the evaluation of the measured results was carried out, and the possibility of the unsteady thermal seansation prediction in the everyday life was suggested.
The prediction of outdoor human thermal states in non-uniform thermal loads
1Okayama Prefectural University, Japan; 2Osaka Prefecture University; 3Technology Research Institute of Osaka Prefecture
Considering thermal states or thermal sensation is the good idea for assessing the thermal environment around humans. Human thermal states can be obtained by using thermal load of human in general and many thermal indices were developed based on steady-state human energy-balance model. However, there are so many no steady states and complex situations exist in reality. For example, our environment is surrounded by various materials with various properties and they play an important role for creating non-uniform outdoor thermal environment. Thus, the present study addresses the effect of non-uniform thermal load on human thermal state.
The authors first performed measurements for understanding of physical environment. Then, measurements were performed with human participants to grasp the relationship between human thermal states, human thermal perception, and thermal environment conditions in the proximity of a human body. In order to simulate the outdoor non-uniform thermal load, regional thermal load was applied on human surface directly by using own making thermal module. The surrounding weather factors (air temperature, humidity, air speed, solar and infrared radiations) and the physiological response of the human body (temperatures on skin and core, heart rate, inhale and exhale gas, sweat) were measured at the same time. Thermal perceptions were also asked. The results show that regional thermal load by warming or cooling had strong relationship with regional thermal sensation, and this led whole body thermal sensation. Each body parts had different thermal sensitivity. The authors established totally well-described thermal load model.
For an application, human thermal state assessment was experimentally and numerically performed in typical street environment. The authors tried to establish the new way of evaluating non-uniformity of environment and human by using non-uniform human thermal load method as an energy balance evaluation was successfully proposed. The results showed that our method could be a good thermal states prediction for non-uniform complex outdoor environment conditions.