George Havenith

UTCI—Why another thermal index?

Existing procedures for the assessment of the thermal environment in the fields of public weather services, public health systems, precautionary planning, urban design, tourism and recreation and climate impact research exhibit significant shortcomings. This is most evident for simple (mostly two-parameter) indices, when comparing them to complete heat budget models developed since the 1960s. ISB Commission 6 took up the idea of developing a Universal Thermal Climate Index (UTCI) based on the most advanced multi-node model of thermoregulation representing progress in science within the last three to four decades, both in thermo-physiological and heat exchange theory. Creating the essential research synergies for the development of UTCI required pooling the resources of multidisciplinary experts in the fields of thermal physiology, mathematical modelling, occupational medicine, meteorological data handling (in particular radiation modelling) and application development in a network. It was possible to extend the expertise of ISB Commission 6 substantially by COST (a European programme promoting Cooperation in Science and Technology) Action 730 so that finally over 45 scientists from 23 countries (Australia, Canada, Israel, several Europe countries, New Zealand, and the United States) worked together. The work was performed under the umbrella of the WMO Commission on Climatology (CCl). After extensive evaluations, Fiala’s multi-node human physiology and thermal comfort model (FPC) was adopted for this study. The model was validated extensively, applying as yet unused data from other research groups, and extended for the purposes of the project. This model was coupled with a state-of-the-art clothing model taking into consideration behavioural adaptation of clothing insulation by the general urban population in response to actual environmental temperature. UTCI was then derived conceptually as an equivalent temperature (ET). Thus, for any combination of air temperature, wind, radiation, and humidity (stress), UTCI is defined as the isothermal air temperature of the reference condition that would elicit the same dynamic response (strain) of the physiological model. As UTCI is based on contemporary science its use will standardise applications in the major fields of human biometeorology, thus making research results comparable and physiologically relevant.

UTCI-Fiala multi-node model of human heat transfer and temperature regulation.

The UTCI-Fiala mathematical model of human temperature regulation forms the basis of the new Universal Thermal Climate Index (UTC). Following extensive validation tests, adaptations and extensions, such as the inclusion of an adaptive clothing model, the model was used to predict human temperature and regulatory responses for combinations of the prevailing outdoor climate conditions. This paper provides an overview of the underlying algorithms and methods that constitute the multi-node dynamic UTCI-Fiala model of human thermal physiology and comfort. Treated topics include modelling heat and mass transfer within the body, numerical techniques, modelling environmental heat exchanges, thermoregulatory reactions of the central nervous system, and perceptual responses. Other contributions of this special issue describe the validation of the UTCI-Fiala model against measured data and the development of the adaptive clothing model for outdoor climates.

Personal factors in thermal comfort assessment: clothing properties and metabolic heat production

In the assessment of thermal comfort in buildings, the use of the Predicted Mean Vote (PMV) model is very popular. For this model, data on the climate, on clothing and on metabolic heat production are required. This paper discusses the representation and measurement of clothing parameters and metabolic rate in the PMV context. Several problems are identified and for some of these solutions are provided. For clothing insulation it was shown that effects of body motion and air movement are so big that they must be accounted for in comfort prediction models to be physically accurate. However, effects on dry heat exchange are small for stationary, light work at low air movement. Also algorithms for convective heat exchange in prediction models should be reconsidered. For evaporative heat resistance of the clothing worn, which is currently not an input factor in the PMV model, it was shown that in cases where special clothing with high vapour resistance is worn (e.g. clean-room clothing), comfort may be limited by the clothing as it will induce a high skin wettedness. Thus, for such cases clothing vapour resistance should not be neglected in the calculation of comfort using the PMV model, or the induced skin wettedness should be calculated separately. The effects on thermal comfort of reductions in vapour resistance due to air and body movements are also shown to have a substantial impact on the comfort limits in terms of skin wettedness and cannot be neglected either. For metabolic heat production it was concluded that for precise comfort assessment a precise measure of metabolic rate is needed. In order to improve metabolic rate estimation based on ISO 8996, more data and detail is needed for activities with a metabolic rate below 2 MET. Finally, it was shown that the methods for determining metabolic rate provided in ISO 8996 (typically used in comfort assessment and evaluations) do not provide sufficient accuracy to allow determination of comfort (expressed as PMV) in sufficient precision to classify buildings to within 0.3 PMV units as proposed in the upcoming revision of ISO 7730.

Heat Balance When Wearing Protective Clothing

This issue of the Annals of Occupational Hygiene is dedicated to the topic of heat stress evaluation. For this evaluation, several evaluation programs and international standards are available. In order to understand the reasoning and underlying theory behind these programs and standards, a basic knowledge of heat exchange processes between workers and their environment is needed. This paper provides an overview of the relevant heat exchange processes, and defines the relevant parameters (air and radiant temperature, humidity, wind speed, metabolic heat production and clothing insulation). Further it presents in more detail the relation between clothing material properties and properties of clothing ensembles made from those materials. The effects of clothing design, clothing fit, and clothing air permeability are discussed, and finally an overview of methods for the determination of clothing heat and vapour resistance is given.

Resultant clothing insulation: a function of body movement, posture, wind, clothing fit and ensemble thickness

Voor de modelvorming van de effecten van houding, beweging en wind is het belang van de kledinglagen veruit ondergeschikt aan dat van de ingesloten en aanhangende luchtlagen.

The relative influence of physical fitness, acclimatization state, anthropometric measures and gender on individual reactions to heat stress

SummaryAn experiment was set up to quantify the relative influence of fitness, acclimatization, gender and anthropometric measures on physiological responses to heat stress. For this purpose, 12 male and 12 female subjects were exposed to a neutral [ambient temperature (Ta) 21°C, relative humidity (r.h. 50%)], a warm, humid (Ta 34°C, r.h. 80%) and a hot, dry (Ta 45°C, r.h. 20%) climate at rest and at two exercise intensities [25%, and 45% maximal O2 intake (VO2max)], seated seminude in a net chair behind a cycle ergometer. Their physiological responses were recorded and the data submitted to a multiple regression analysis. It was shown that for the variance in heat storage, the percentage of body fat and the surface to mass ratio had relatively the largest influence of all the individual parameters, followed by VO2max and the sweat rate versus increase in core temperature (total r2=92%). For the skin temperature variation, the relative influence of individual parameters (sweat gain, VO2max) was small. For body core temperatures, individual parameters had a large influence. The largest effect was due to the percentage of fat and the surface to mass ratio, followed by the sweating setpoint and, finally, VO2max (total r2 = 54%−70%). For the variance in heart rate the VO2max was the most relevant parameter, followed by the setpoint of the sweat rate:rectal temperature relationship (total r2=88%). Blood pressure and skin blood flow predictions were also shown to improve by the addition of individual characteristics to the model. Body surface area, VO2max and the sweating setpoint were shown to have a large influence but the proportion of the variance explained by these variables was too small (r2 < 70%) to use them as strain predictors, however. For all the predicted variables, it was shown that gender lost its influence, once VO2max or anthropometric data were introduced into the prediction equation.

Clothing ventilation, vapour resistance and permeability index: changes due to posture, movement and wind

Veranderingen in de waterdampweerstand van kleding t.g.v. beweging en wind zijn af te leiden uit de verandering in warmteweerstand en een referentie meetwaarde.

The relative influence of body characteristics on humid heat stress response

AbstractThe present study was designed to determine the relative importance of individual characteristics such as maximal oxygen uptake (

The UTCI-clothing model

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