Effect of physical activity and air velocity on the thermal insulation of clothing

Abstract

Intrinsic thermal clothing insulation and surface air insulation were measured on human subjects by the use of indirect calorimetry. Four male clothing ensembles (0-1-1 -8 clo) and three female clothing ensembles (0-2-1-2 clo) were investigated. Using the standing position as a reference, the influence of sitting, bicycling (40r.p.m., 20 W), walking (3-75 km hour^?1) and of light packing work on the thermal insulation was studied. The influence of an air velocity of 11ms^?1 on thermal insulation during the standing and walking conditions was investigated. The results showed that: (i) intrinsic clothing insulation was maximal in the standing position. It was reduced by 8-18% in the seated position and by 30-50% during bicycling and walking. An air velocity of 11ms^?1 did not influence the intrinsic clothing insulation during walking, but decreased it by 18% in the standing position; (ii) surface air insulation varied with activity and air velocity, but not with clothing. It was increased by up to 25% in the seated position, reduced by 7-26% during bicycling and by 30-50% during walking. An air velocity of 11 ms-1 reduced the surface air insulation by 50% in the standing position and 30% during walking.     

Assessment of cold stress in terms of required clothing insulation—IREQ

A heat exchange model has been developed, by which the thermal stress associated with work in cold environments can be evaluated. Based on measurements of air temperature, mean radiant temperature, humidity and air velocity and measurements or estimates of activity level (energy metabolism) the model calculates a clothing insulation (IREQ) required to maintain body heat balance. IREQ may be regarded as an index of cold stress, and the value for IREQ specifies the insulation to be provided by clothing under given conditions, in addition to the insulation of the boundary air layer. IREQ, hence, may serve as a guideline for selection of appropriate clothing in cold environments. Basic insulation values of clothing (I_cI) measured with thermal manikins can be used for this purpose, but need to be corrected to account for the effect of body motion, posture, wind penetration and moisture absorption before a comparison is made with IREQ.     

The effect of unevenly distributed thermal stimuli on the sensation of warmth and coolness

Combinations of clothing provide different degrees of thermal insulation for various parts of the body. The effect of this uneven thermal insulation on general comfort is examined by using experimental clothing which could provide varying degrees of thermal resistance. The relationship between skin temperature and sensation was found to be approximately linear when the exposed areas were not large, and that clothing of the same thermal resistance can yield different sensations depending on the parts of the body involved.     

Performance enhancement of hybrid personal cooling clothing in a hot environment: PCM cooling energy management with additional insulation

A novel design of personal cooling clothing incorporating additional insulation sandwiched between phase change materials (PCMs) and clothing outer layer is proposed. Performance of four personal cooling systems including clothing with only PCMs, clothing with PCMs and insulation (PCM?+?INS), clothing with PCMs and ventilation fans (HYB), and clothing with PCMs, ventilation fans and insulation (HYB?+?INS) was investigated. Effect of additional insulation on clothing cooling performance in terms of human physiological and perceptual responses was also examined. Human trials were carried out in a hot environment (i.e. 36?°C, RH = 59%). Results showed that significantly lower mean skin/torso temperatures were registered in HYB?+?INS as compared to HYB. In contrast, no significant effect of the use of insulation on both skin and body temperatures between PCM and PCM?+?INS was observed. Also, no significant difference in thermal sensations, thermal comfort, and skin wetness sensation was registered between cooling systems with and without additional insulation.

Practitioner Summary: Hybrid personal cooling clothing has shown the ability to provide a relatively cool microclimate around the wearer’ body while working in hot environments. The present work addresses the importance of cooling energy saving for PCMs in a hot environment. This work contributes to optimising cooling performance of hybrid personal cooling systems.     

The assessment of heat radiation

Approximately 900 climatic chamber experiments were performed with 16 male subjects to study the thermal strain at climates including increased heat radiation. Based on the reactions of heart rate, rectal temperature and sweat rate, a heat stress index was developed for the assessment of climates with effective heat radiation intensities up to 1400 W m⁻². The index considers different combinations of dry air temperature (5–55°C), globe temperature (25–76°C), mean radiant temperature (25–160°C), air velocity (0.5–2.0 m s⁻¹), clothing, physical work load and directions of radiation and air flow.

The index integrates combinations of the variables producing the same degree of thermal strain into a single value. This value indicates the temperature of the physiologically equivalent climate in which air and radiant temperature are equal. It can be determined from a simple formula or from correspondent graphs.

In comparison, the international recommended heat stress indices are less capable to evaluate heat radiation correctly. The incorporation of the new partial index into the used indices may improve substantially their physiological validity in the assessment of climates with radiant heat stress.

Relevance to industry

The goal of this paper is to provide an improved assessment of thermal stress in working environments in which heat radiation is an important heat stress factor.     

3D quantification of microclimate volume in layered clothing for the prediction of clothing insulation

Garment fit and resultant air volume is a crucial factor in thermal insulation, and yet, it has been difficult to quantify the air volume of clothing microclimate and relate it to the thermal insulation value just using the information on the size of clothing pattern without actual 3D volume measurement in wear condition. As earlier methods for the computation of air volume in clothing microclimate, vacuum over suit and circumference model have been used. However, these methods have inevitable disadvantages in terms of cost or accuracy due to the limitations of measurement equipment. In this paper, the phase-shifting moiré topography was introduced as one of the 3D scanning tools to measure the air volume of clothing microclimate quantitatively. The purpose of this research is to adopt a non-contact image scanning technology, phase-shifting moiré topography, to ascertain relationship between air volume and insulation value of layered clothing systems in wear situations where the 2D fabric creates new conditions in 3D spaces. The insulation of vests over shirts as a layered clothing system was measured with a thermal manikin in the environmental condition of 20 degrees C, 65% RH and air velocity of 0.79 m/s. As the pattern size increased, the insulation of the clothing system was increased. But beyond a certain limit, the insulation started to decrease due to convection and ventilation, which is more apparent when only the vest was worn over the torso of manikin. The relationship between clothing air volume and insulation was difficult to predict with a single vest due to the extreme openings which induced active ventilation. But when the vest was worn over the shirt, the effects of thickness of the fabrics on insulation were less pronounced compared with that of air volume. In conclusion, phase-shifting moiré topography was one of the efficient and accurate ways of quantifying air volume and its distribution across the clothing microclimate. It is also noted that air volume becomes more crucial factor in predicting thermal insulation when clothing is layered.     

Thermal sensation of the body as influenced by the thermal microclimate in a face mask

Subjective and physiological responses were obtained from six subjects wearing a face mask while exercising (220 W m ^?2) for 15 min on a bicycle ergometer. Different combinations of ambient air temperatures (7, 16 and 25°C) and mask air temperatures (22,27 and 33°C) were studied with two different air humidities inside the mask (61 and 86% relative humidity (RH)). Control experiments were performed without the mask at the same ambient temperatures. Skin temperatures, heart rates and skin wettedness were monitored during exercise. The subjects’ thermal sensations, sensations of sweating and skin wettedness and their thermal preferences were assessed at the end of the exercise period. Whole body thermal sensation was primarily determined by the ambient air temperature, but was also significantly influenced by the mask air temperature. This could only partly be explained by the change in respiratory heat loss. Other possible avenues of influence are discussed.     

考虑不同服装热阻的层式通风供暖运行优化研究

为满足室内人员在不同着装时的热舒适需求,以某层式通风供暖办公室为研究对象,在考虑不同服装热阻的前提下,通过改进TOPSIS法优化了送风参数(即送风角度、送风速度和送风温度)；在优化过程中,将PMV/PPD、垂直温差、空气龄和能量利用效率作为通风性能评价指标,以送风温度、送风速度、送风角度和服装热阻为设计变量,通过CFD模拟分析,采用中心复合设计响应面法得到通风性能与设计变量间的函数关系,然后用于改进TOPSIS法评估所有可能方案的通风性能以达到提高计算效率的目的；结果表明：基于改进TOPSIS法优化层式通风供暖送风参数可以显著改善通风性能,PPD、空气龄和垂直温差分别平均降低了37.08%、22.46%和48.17%,能量利用效率平均提高了20.42%。     

Pumping effects on thermal insulation of clothing worn by human subjects

This study was undertaken in order to analyse the importance of the pumping effect on clothing's thermal insulation. To enhance differences in heat exchanges due to the pumping effect, two sets of condition were fixed, minimizing either the convective or the radiative heat transfers. The results showed that: (i) the clothing insulation determined on a manikin, even if he is moving, is larger than the resultant clothing insulation for living subjects; (ii) the insulation is not the same for radiant heat or cold as for convective heat or cold;(iii) the pumping effect can increase or decrease the resultant clothing insulation; (iv) the clothing insulation is smaller in warmer conditions thanin cooler ones; (v) it becomes necessary to make a definite distinction between several kinds of clothing insulation; intrinsic or basic insulation against radiation and convection; effective insulation against radiation and convection taking into account only the heat flowing through the clothing fabric; resultant insulation taking into account the magnitude of the pumping effect when clothing is worn by living subjects     

Representation of an alpine treeline ecotone in SPOT 5 HRG data

An ecotone is a zone of vegetation transition between two communities, often resulting from a natural or anthropogenic environmental gradient. In remotely sensed imagery, an ecotone may appear as an edge, a boundary of mixed pixels or a zone of continuous variation, depending on the spatial scale of the vegetation communities and their transition zone in relation to the spatial resolution of the imagery. Often in image classification, an ecotone is either ignored if it falls within a width of one or two pixels, or part of it may be mapped as a separate vegetation community if it covers an area of several pixel widths. A soft classification method, such as probability mapping, is inherently appealing for mapping vegetation transition. Ideally, the probability of membership each pixel has to each vegetation class corresponds with the proportional composition of vegetation classes per pixel. In this paper we investigate the use of class probability mapping to produce a softened classification of an alpine treeline ecotone in Austria using a SPOT 5 HRG image. Here the transition with altitude is from dense subalpine forest to treeless alpine meadow and herbaceous vegetation. The posterior probabilities from a Maximum Likelihood algorithm are shown to reflect the land-cover composition of mixed pixels in the ecotone. The relationships between the posterior probability of class membership for the two end-member classes of ‘scrub and forest’ and ‘non-forest vegetation’ and the percentage ground cover of these vegetation classes (enumerated in 15 quadrats from 1:1500 aerial photographs) were highly significant: r² = 0.83 and r² = 0.85 respectively (p < 0.001, n = 15). We identify thresholds (alpha-cuts) in the posterior probabilities of class membership of ‘scrub and forest’ and ‘non-forest vegetation’ to map the alpine treeline ecotone as a transition zone of five intermediate vegetation classes between the end-member communities. In addition, we investigate the representation of the ecotone as a ratio between the posterior probabilities of ‘scrub and forest’ and ‘non-forest vegetation’. This displays the vegetation transition without imposing subjective boundaries, and has greater emphasis on the ecotone transition rather than on the end-member communities. We comment on the fitness for purpose of the different ways investigated for representing the alpine treeline ecotone.     

Addition and removal of information for a knowledge base with incomplete information

A knowledge base containing incomplete information in the form of disjunctions and negative information shows difficulties regarding the update operators. In this paper simple and straightforward definitions are given for an ‘adding’ operator (‘+’) and a ‘removing’ operator (‘−’) using Hebrand models.     

Evaporative resistance and sustainable work under heat stress conditions for two cloth anticontamination ensembles

When a work scenario in protective clothing is a nominal two hours of work followed by a short break, the level of heat stress must be limited to conditions of thermal equilibrium. By comparing changes in maximum sustainable work rate in a fixed environment, differences due to different protective clothing ensembles can be determined. To illustrate this principle, two protective clothing ensembles were examined. The Basic Ensemble was a cotton blend coverall over gym shorts with hard hat, gloves and full face mask respirator. The Enhanced Ensemble added a light weight, surgical scrub suit under the coveralls, plus a hood worn under the hard hat. Five young, acclimated males were the test subjects. Environmental conditions were fixed at T_db=32°C and T_pwb=26°C. After a physiological steady state was established at a low rate of work, treadmill speed was increased by 0.04 m/s every 5 min. The trial continued until thermal equilibrium was clearly lost. A critical treadmill speed was noted at the point thermal equilibrium was lost for each ensemble and subject. The drop in treadmill speed from the basic to enhanced ensemble was 11%. Based on measured values of average skin temperature and metabolic rate at the critical work rate and estimated values of clothing insulation, the average evaporative resistances for the basic and enhanced ensembles were 0.018 and 0.026 kPa m²/W, respectively.

Relevance to industry

Protective clothing decisions are based on the need to reduce the risk of skin contact with chemical or physical hazards. Sometimes over-protection of the skin results in a hazard secondary to the skin, such as heat stress. With or without over-protection, protective clothing decisions may affect the level of heat stress and result in lower rates of sustainable work. This paper illustrates the affects of a relatively small change in protective clothing requirements on the ability to work in the heat.     

A quasi-physical model for predicting the thermal insulation and moisture vapour resistance of clothing

Based on the improved understanding of the effects of wind and walking motion on the thermal insulation and moisture vapour resistance of clothing induced by air ventilation in the clothing system, a new model has been derived based on fundamental mechanisms of heat and mass transfer, which include conduction, diffusion, radiation and natural convection, wind penetration and air ventilation. The model predicts thermal insulation of clothing under body movement and windy conditions from the thermal insulation of clothing measured when the person is standing in the still air. The effects of clothing characteristics such as fabric air permeability, garment style, garment fitting and construction have been considered in the model through the key prediction parameters. With the new model, an improved prediction accuracy is achieved with a percentage of fit being as high as 0.96.     

Driving performance in cold, warm, and thermoneutral environments

Driving performance deteriorates at high ambient temperatures. Less is known about the effect of low ambient temperatures and the role of subjective aspects like thermal comfort and having control over the ambient temperature. Therefore, an experiment was constructed in which 50 subjects performed a road-tracking task in a cold (5°C), a thermoneutral (20°C) or a warm (35°C) climate. All subjects had a heater/blower (H/B) which generated a fixed amount of heat/wind that could either be controlled or not controlled.

In the cold climate, averaged leg skin temperature dropped to 18.5°C and head skin temperature to 24.9°C; the thermal comfort was rated between ‘cold’ and ‘very cold’. In the warm climate, averaged leg skin temperature rose to 36.6°C and head skin temperature to 30.8°C; the thermal comfort was rated as ‘hot’. Driving performance in the ambient temperature extremes decreased 16% in the cold environment and 13% in the warm situation.

Having control over the local head temperature by adjusting a H/B affected neither thermal comfort nor driving performance. In agreement with the literature on priming effects, subjects who started with the no-control condition performed much better in all driving tasks because they were primed to focus on the driving task as such, rather than the complex combination of temperature controls and driving task.

It can be concluded that a thermoneutral temperature in a car enhances driving performance and may thus positively affect safety. Using manual climatic controls in hot or cold cars may interfere with the driving task.     

Comparison between required clothing insulation and that actually worn by workers exposed to artificial cold

Required Clothing Insulation (IREQ) is a new thermal index submitted to the International Organisation for Standardisation (ISO) for discussion. It is designed to prevent general body cooling and is based on an analysis of heat exchanges. The thermal clothing insulation actually worn (lcl) is estimated using a new method, also submitted to ISO.

IREQ of 54 workers exposed to artificial cold (air temperature between −30° C and +10° C) was compared with lcl actually worn by these workers. The results of the present study show that, on average, the workers choose accurately lcl they need if their IREQ is below and up to 1·5 clo. Moreover, these workers prefer to wear garments which provide them with thermal comfort. If IREQ of workers is higher than 1·5–2 clo (i e, workers exposed to −20° C), it is difficult for them to increase their thermal insulation with additional garments. Although their lcl is not sufficient, there is no risk of gradual body cooling because of their continuous time exposure (CTE) which is shorter than the calculated Duration Limited Exposure (DLE). On the other hand, Wind Chill Index (WCI), which is proposed to prevent local cooling, is better adapted to prevent cold injuries than physiological thermal strain; for example, impairment of manual dexterity cannot be prevented with this index.     

The influence of heated or cooled seats on the acceptable ambient temperature range

In 11 climate chamber experiments at air temperatures ranging from 15 to 45°C, a total of 24 subjects, dressed in appropriate clothing for entering a vehicle at these temperatures, were each exposed to four different seat temperatures, ranging from cool to warm. In one simulated summer series, subjects were preconditioned to be too hot, while in other series they were preconditioned to be thermally neutral. They reported their thermal sensations, overall thermal acceptability and comfort on visual analogue scales at regular intervals. Instantaneous heat flow to the seat was measured continuously. At each ambient room temperature, the percentage dissatisfied was found to be a second-order polynomial function of local heat flow. Zero heat flow was preferred at an air temperature of 22°C and the heat flow that minimized the percentage dissatisfied was found to be a single linear function of air temperature in all conditions. The analysis indicates that providing optimal seat temperature would extend the conventional 80% acceptable range of air temperature for drivers and passengers in vehicle cabins by 9.3°C downwards and by 6.4°C upwards.     

Bioequivalence revisited: non-parametric analysis of two-period cross-over studies

Hauschke et al.'s non-parametric bioequivalence procedure for treatment effects and some aspects of computer implementation, among them Meineke and De Hey's algorithm, are explored. For studies with up to sixty subjects, a table of indices of the ranked intersubject-intergroup mean ratios or differences is given, to establish non-parametric 90% confidence intervals. It is shown that non-parametric analysis is not limited to treatment effects: it can also be applied to period and sequence effects. This extended procedure can be seen as the non-parametric analogue of analysis of variance on two-period cross-over studies. A FORTRAN program (BIOQNEW) incorporating Meineke and De Mey's algorithm is presented. This program provides non-parametric point estimates for treatment and period effects, 90% and 95% confidence intervals for test-versus-reference treatments, the 95% confidence interval for periods and a test on sequence effects, so that it can also be used for other than bioequivalence studies. BIOEQNEW can handle ratios (‘multiplicative model’) as well as differences (‘additive model’). It optionally provides the complete non-parametric posterior probability distribution for treatment ratios or differences, so that Schuirmann's ‘two one-sided tests procedure’ can also be performed in a non-parametric way.     

Physiological cost of apple-farming activities

Seventeen agricultural male workers, aged between 21 and 56 years, were investigated in the field during six different job-activities of apple-farming: pruning, weeding, hand and mechanical spraying, mowing and picking. Pulmonary ventilation and oxygen consumption were recorded for short periods by Oxylog, while heart rate was monitored for more than 24 hours by Holter's method. The farmers also rated the work intensity according to Borg's RPE scale.

Pulmonary ventilation ranged on average between 13 and 30 1/min and oxygen consumption between 500 and 1300 ml/min, with a relative aerobic cost between 15 and 40%, in the different work activities. Heart rate varied on average between 80 and 94 beats/min with a relative cardiac cost between 20 and 30%. The physiological criteria (oxygen uptake and cardiac response) and the subjective rating of fatigue gave a substantially similar evaluation of the work strain, ‘moderate-heavy’ for mowing, weeding and picking, ‘moderate’ for pruning and hand spraying, ‘light’ for mechanical spraying of pesticides. On the whole, apple-farming can be evaluated as ‘moderate’ intensity, thanks to the mechanisation implemented in reducing the work-load and the work-time of many job activities.     

Design of functional work clothing for meat-cutters

The aim of this study was to design new functional work clothing for meat-cutters, paying particular attention to the metabolic requirements of the work and the thermal and general working conditions in slaughterhouses. On the basis of the results of the pilot study (review of the literature, questionnaires and interviews, work analysis, physiological measurements) different types of work clothing were designed for prolonged used during normal work in meat cutting. Physical material tests and measurements of thermal insulation values (l(cl)), and the follow-up of clothing maintenance were carried out. Further modifications and evaluations of work clothing were based on the opinions of meat-cutters and on the physiological trials in slaughterhouses. The final assembly of work clothing consists of three pieces (cotton/polyester): an apron, trousers with extra insulation in the lower back, and a work coat with extra insulation in the neck and shoulders, and at the wrists. The sleeves are protected against moisture by special textile material. The thermal insulation of this new set of work clothing together with long sleeved and legged underwear is 1.3 clo and it proved to be sufficient for thermal comfort in moderate work in an air temperature of 10 degrees C.     

Temperature rating prediction of Tibetan robe ensemble based on different wearing ways

Each piece of Western clothing has a unique temperature rating (TR); however, based on different wearing ways, one Tibetan robe ensemble can be used in various environments of the Tibetan plateau. To explain this environmental adaptation, thermal insulations and TR values of Tibetan robe ensembles in three typical wearing ways were measured by manikin testing and wearing trials, respectively. The TR prediction models for Tibetan robe ensembles were built in this research. The results showed that the thermal insulations of Tibetan robe ensembles changed from 0.26 clo to 0.91 clo; the corresponding TRs ranged from 9.90 °C to 16.86 °C because of different wearing ways. Not only the thermal insulation, but also the ways of wearing Tibetan robes was important to determining their TR values. The three TR models and a triangle area for each piece of Tibetan clothing explained its positive adaptation into the environment; this was different from the current TR models for Western clothing.