Ken Parsons

Human Thermal Environments: The Effects of Hot, Moderate, and Cold Environments on Human Health, Comfort, and Performance

In the ten years since the publication of the second edition of Human Thermal Environments: The Effects of Hot, Moderate, and Cold Environments on Human Health, Comfort, and Performance, Third Edition, the world has embraced electronic communications, making international collaboration almost instantaneous and global. However, there is still a need for a compilation of up-to-date information and best practices. Reflecting current changes in theory and applications, this third edition of a bestseller continues to be the standard text for the design of environments for humans to live and work safely, comfortably, and effectively, and for the design of materials that help people cope with their environments. See Whats New in the Third Edition: All existing chapters significantly updated Five new chapters Testing and development of clothing Adaptive models Thermal comfort for special populations Thermal comfort for special environments Extreme environments Weather Outdoor environments and climate change Fun runs, cold snaps, and heat waves The book covers hot, moderate, and cold environments, and defines them in terms of six basic parameters: air temperature, radiant temperature, humidity, air velocity, clothing worn, and the persons activity. It focuses on the principles and practice of human response, which incorporates psychology, physiology, and environmental physics with applied ergonomics. The text then discusses water requirements, computer modeling, computer-aided design, and current standards. A systematic treatment of thermal environments and how they affect humans in real-world applications, the book links the health and engineering aspects of the built environment. It provides you with updated tools, techniques, and methods for the design of products and environments that achieve thermal comfort.

Introduction to thermal comfort standards and to the proposed new version of EN ISO 7730

Abstract This paper describes existing International Standards Organization (ISO) standards and current activity concerned with thermal comfort. It describes how an ISO standard is produced from a new work item proposal to publication as an International Standard. ISO Standards should be valid, reliable, useable, and with sufficient scope for practical application. The existing thermal comfort standard—EN ISO 7730—is considered in terms of these criteria as well as ISO 8996 (metabolic rate) and ISO 9920 (clothing). The work of ISO/TC 159 SC5, ‘ergonomics of the physical environment’, is presented in Appendix A . The proposed revision of EN ISO 7730 is presented in detail. The revised standard will be based on requirements for general thermal comfort (predicted mean vote (PMV), operative temperature) and local thermal discomfort (radiant temperature asymmetry, draught, vertical air temperature differences, floor surface temperatures). One critical issue is the effect of air velocity. Increased air velocity has a beneficial effect at warm temperatures, but it may result in draught sensation in cooler temperatures. Another issue is the extent to which requirements of humidity need to be included in a standard for thermal comfort. Several recent research projects dealing with adaptation, influence of air velocity and the effect of humidity have been responsible for keeping the standards up to date.

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.

The effects of gender, acclimation state, the opportunity to adjust clothing and physical disability on requirements for thermal comfort

A program of laboratory studies into thermal comfort requirements is presented. Two studies used groups of 16 subjects over a range of conditions (warm to cool) to investigate the effects of gender over 3 h exposures in simulated living room/office environments. It was found that for identical levels of clothing and activity, there were only small differences in the thermal comfort responses of male and female subjects for neutral and slightly warm conditions. For cool conditions, female subjects tended to be cooler than males. An experiment to investigate the effects of heat acclimation on thermal comfort requirements involved six male subjects providing thermal comfort responses in neutral and slightly warm environments over 2 days. They then carried out an acclimatization program over 4 days, for 2 h per day, exercising in a hot (45 °C, 40% relative humidity) environment. Thermal comfort responses were then recorded in two sessions over 2 days in identical conditions to the pre-acclimation session. It was found that changes in thermal comfort responses were small and likely to be of little practical significance. An investigation into the behavior of people to maintain thermal comfort by adjusting their clothing was conducted using eight male and eight female subjects. Seated subjects reduced or increased their clothing level by using a wardrobe of clothing that was familiar to them. It was found that subjects can adjust their clothing to maintain thermal comfort, but within limits. Upper limits (clothing off) will be determined by modesty and acceptability. Lower limits (clothing on) will be determined by clothing design and acceptability. A low air temperature limit of 18 °C in freely available clothing may provide a working hypothesis. A laboratory study of thermal comfort requirements for people with physical disabilities compared responses with those of people without physical disabilities. It was found that there are few group differences between thermal comfort requirements of people with and without physical disabilities. However, there is a greater necessity to consider individual requirements for people with physical disability.

Clothing convective heat exchange—proposal for improved prediction in standards and models

Convection is an important determinant for both sensible and evaporative heat exchange. Heat transfer by convection for normal boundary conditions is readily described by simple power functions. Clothing affects convection in various ways and existing characterisation of clothing by its static insulation values produces inaccurate prediction of sensible heat exchange, eventually leading to erroneous risk assessment. The present paper reviews various methods for evaluation of clothing convective (sensible) heat exchange. Based on available data, two equations are proposed for determination of the reduction of the total insulation values obtained under static, still wind conditions as a consequence of wind and walking effects. The equations apply from 0 to 1.84 clo, from 0.2 to 3 m/s and for walking speeds up to 1.2 m/s. The equations are incorporated in ISO 7933 to provide a more realistic and accurate prediction of sensible heat transfer through clothing.

Displacement ventilation environments with chilled ceilings: thermal comfort design within the context of the BS EN ISO7730 versus adaptive debate

Abstract The current design standard BS EN ISO7730 [Moderate thermal environments—determination of the PMV and PPD indices and specification of the conditions for thermal comfort, International Standards Organisation (1995)] is based upon the work of Fanger, and essentially comprises a steady-state human heat balance model that leads to a prediction of the sensation of human thermal comfort for a given set of thermal conditions. The model was derived from laboratory-based measurements conducted in the mid-1960s in relatively ‘conventional’ environments. However, a chilled ceiling operated in combination with displacement ventilation represents a more sophisticated environment as compared with the original conditions in which the Fanger model was derived. This raised a question about the applicability of the current standard when designing for thermal comfort in offices equipped with chilled ceiling/displacement ventilation systems. This paper presents findings from an EPSRC-funded study that sought to answer the above question. Human test subjects (184 in total) carried out sedentary office-type work in a well-controlled environmental test room that simulated an office fitted with the above system. Measurements of environmental variables were taken at a number of locations near the subjects, each of whom wore a typical office clothing ensemble. The reported thermal comfort sensations were compared with values predicted from BS EN ISO7730 over a range of system operating conditions. It was shown that the current standard BS EN ISO7730 may be used, without modification, when designing for the thermal comfort of sedentary workers in offices equipped with chilled ceiling/displacement ventilation systems. These findings are interpreted within the context of a proposed modification to thermal comfort design standards that includes adaptive effects, and the influence of BS EN ISO7730 on the development of other radiant surface/displacement ventilation configurations is discussed.

Thermal comfort in chilled ceiling and displacement ventilation environments: vertical radiant temperature asymmetry effects

Abstract The paper presents some of the findings from a broader investigation aimed at determining thermal comfort design conditions for combined chilled ceiling/displacement ventilation environments. A typical chilled ceiling/displacement ventilation office has been created within a laboratory test room, in which the ceiling temperature can be varied over a range of typical operating values; the thermal comfort of eight female test subjects was then measured in the test room over the range of ceiling temperatures. Vertical radiant temperature asymmetry was found to have an insignificant effect on the overall thermal comfort of the seated occupants for the typical range of ceiling temperatures that would be encountered in practice in such combination environments. There was a slight trend for the reported sensation of ‘freshness’ to increase as ceiling temperature was reduced though this requires further study. It is concluded that existing guidance regarding toleration of radiant asymmetry is valid for thermal comfort design of chilled ceiling/displacement ventilation environments

Maintaining health, comfort and productivity in heat waves

Background: The aim of this paper is to summarise what is known about human response to heat and to use this knowledge to provide guidance on how to maintain the health, comfort and performance of people in heat waves. Design: The use of power and especially water are critical in providing cooling. A practical method of cooling people in a water bath is described. A warm bath slowly cooled will provide effective cooling but not thermal trauma. Result: It is concluded that for sedentary and light activities, it is not necessary to cool offices or homes below 25°C for thermal comfort. Conclusion: To compare the costs due to loss of productivity caused by a heat wave, with the cost of taking action, more research is needed into the relationship between levels of heat stress and how much distraction and ‘time off task’ it causes.

Appropriateness of international heat stress standards for use in tropical agricultural environments

Where a danger to health from heat stress is identified, standards allow decisions for implementing measures to reduce the heat stress to be made. These standards, specifically ISO 7243 (Wet Bulb Globe Temperature Index, WBGT) and ISO 7933 (Sweat Required, SWreq) were designed with European and American subjects, primarily for use in those countries. While the scope of the standards is international, little consideration has been made about how valid and usable they are in industrially developing countries. This investigation evaluated ISO 7933 and ISO 7243 in terms of validity and usability. A tropical agricultural task was simulated; 16 subjects plucking tea leaves for 2 h, (ta = tr = 37.18 degrees C; va = 0.16 m/s; rh = 70.17%). While ISO 7243 was valid (if slightly over protective) and usable, ISO 7933 was over protective and underestimated sweat and evaporation rates in its predictions. The discrepancies between predicted and observed results were attributed primarily to the calculations related to clothing in the standard. Furthermore, ISO 7933 was unusable without a computer; in regions where access to such technology may be limited, a simpler method of presentation is required.

Designing the user interface using rapid prototyping

The aim of this study was to evaluate and improve the menu interface design of an existing expert system. The system provided expertise concerned with evaluating human response to environments and was implemented onto a computer with a simple tree menu system. Two laboratory based experiments were carried out in which alternative menu interface designs were developed rapidly and compared with the original design. User acceptance tests which incorporated objective and subjective measures were iteratively used to evaluate and improve the interface designs. The results of these experiments indicated that, for the particular system under study, a graphic based design which displayed 58 options divided into levels on a single screen was preferred by users over the original menu interface which displayed one menu at a time with seven options per screen. The final interface remains to be tested under field conditions.