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.     

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.     

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     

Dynamic clothing insulation. Measurements with a thermal manikin operating under the thermal comfort regulation mode

The main objective of the present work is the assessment of the thermal insulation of clothing ensembles, both in static conditions and considering the effect of body movements. The different equations used to calculate the equivalent thermal resistance of the whole body, namely the serial, the global and the parallel methods, are considered and the results are presented and discussed for the basic, the effective and the total clothing insulations. The results show that the dynamic thermal insulation values are always lower than the corresponding static ones. The highest mean relative difference [(static-dynamic)/static] was obtained with the parallel method and the lowest with the serial. For I_cl the mean relative differences varied from 0.5 to 13.4% with the serial method, from 5.6 to 14.6% with the global and from 7.2 to 17.7% with the parallel method. In addition, the dynamic tests presents the higher mean relative differences between the calculation methods. The results also show that the serial method always presents the higher values and the parallel method the lowest ones. The relative differences between the calculation methods {[(serial-global)/global] and [(parallel-global)/global]} were sometimes significant and associated to the non-uniform distribution of the clothing insulation. In fact, the ensembles with the highest thermal insulation values present the highest differences between the calculation methods.     

The accuracy of estimating the thermal insulation of clothing ensembles - the effect of appraisers

The effect of the appraisers on the estimation of the thermal insulation of clothing ensembles was investigated. Nine appraisers, four experienced and five inexperienced, estimated the total thermal insulation by summing the values for individual garments. Lists of individual garments worn by workers were given during thermal comfort measurements carried out in shops and stores during one winter and summer. The beginners estimated the thermal insulation as accurately as the experienced appraisers. There were, however, great individual differences, for which three main reasons were found. Interpolation between the insulation provided by two garments was insufficient, and the insulation of these garments should be checked in more precise tables. Classification of the garments into heavy, medium and light clothing items was not adequate, and garments not listed by the workers confused the estimation given by different appraisers. The effect of error in thermal insulation on the PMV index is negligible if more than one appraiser estimates the thermal insulation and the mean of the estimates is used.     

Automatic estimation of clothing insulation rate and metabolic rate for dynamic thermal comfort assessment

Pattern Analysis and Applications - Existing heating, ventilation, and air-conditioning systems have difficulties in considering occupants’ dynamic thermal needs, thus resulting in...     

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.     

Localised boundary air layer and clothing evaporative resistances for individual body segments

Evaporative resistance is an important parameter to characterise clothing thermal comfort. However, previous work has focused mainly on either total static or dynamic evaporative resistance. There is a lack of investigation of localised clothing evaporative resistance. The objective of this study was to study localised evaporative resistance using sweating thermal manikins. The individual and interaction effects of air and body movements on localised resultant evaporative resistance were examined in a strict protocol. The boundary air layer's localised evaporative resistance was investigated on nude sweating manikins at three different air velocity levels (0.18, 0.48 and 0.78 m/s) and three different walking speeds (0, 0.96 and 1.17 m/s). Similarly, localised clothing evaporative resistance was measured on sweating manikins at three different air velocities (0.13, 0.48 and 0.70 m/s) and three walking speeds (0, 0.96 and 1.17 m/s). Results showed that the wind speed has distinct effects on local body segments. In contrast, walking speed brought much more effect on the limbs, such as thigh and forearm, than on body torso, such as back and waist. In addition, the combined effect of body and air movement on localised evaporative resistance demonstrated that the walking effect has more influence on the extremities than on the torso. Therefore, localised evaporative resistance values should be provided when reporting test results in order to clearly describe clothing local moisture transfer characteristics. PRACTITIONER SUMMARY: Localised boundary air layer and clothing evaporative resistances are essential data for clothing design and assessment of thermal comfort. A comprehensive understanding of the effects of air and body movement on localised evaporative resistance is also necessary by both textile and apparel researchers and industry.     

Scan posture definition and hip girth measurement: the impact on clothing design and body scanning

Abstract

Ergonomic measurement is central to product design and development; especially for body worn products and clothing. However, there is a large variation in measurement definitions, complicated by new body scanning technology that captures measurements in a posture different to traditional manual methods. Investigations of hip measurement definitions in current clothing measurement practices supports analysis of the effect of scan posture and hip measurement definition on the circumferences of the hip. Here, the hip girth is a key clothing measurement that is not defined in current body scanning measurement standards. Sixty-four participants were scanned in the standard scan posture of a [TC]² body scanner, and also in a natural posture similar to that of traditional manual measurement collection. Results indicate that scan posture affects hip girth circumferences, and that some current clothing measurement practices may not define the largest lower body circumference. Recommendations are made concerning how the hip is defined in measurement practice and within body scanning for clothing product development.

Practitioner Summary: The hip girth is an important measurement in garment design, yet its measurement protocol is not currently defined. We demonstrate that body posture during body scanning affects hip circumferences, and that current clothing measurement practices may not define the largest lower body circumference. This paper also provides future measurement practice recommendations.     

Impact of the medical clothing on the thermal stress of surgeons

The aim of the presented experiments was to determine thermal stress of surgeons performing their work with a high metabolic rate, wearing clothing characterized by high insulation and impermeability protecting them against water vapour but also in thermal conditions of a warm climate protecting patients against hypothermia. The experiments were conducted with the participation of 8 volunteers. Each subject took part in the experiment four times, i.e. in each of the four tested surgical gowns. The experiments were conducted in a climatic chamber where thermal conditions characteristic of an operating theatre were simulated. The parameters to be measured included: skin temperature, temperature measured in the auditory canal, sweat rate as well as temperature and humidity between clothing and a human body. The conducted experiments provided the grounds to conclude that medical clothing can be regarded as barrier clothing and it can influence thermal load of a human body.     

Reducing heat stress under thermal insulation in protective clothing: microclimate cooling by a ‘physiological’ method

Heat stress caused by protective clothing limits work time. Performance improvement of a microclimate cooling method that enhances evaporative and to a minor extent convective heat loss was tested. Ten male volunteers in protective overalls completed a work-rest schedule (130 min; treadmill: 3 × 30 min, 3 km/h, 5% incline) with or without an additional air-diffusing garment (climatic chamber: 25°C, 50% RH, 0.2 m/s wind). Heat loss was supported by ventilating the garment with dry air (600 l/min, ?5% RH, 25°C). Ventilation leads (M ± SD, n = 10, ventilated vs. non-ventilated) to substantial strain reduction (max. HR: 123 ± 12 b/min vs. 149 ± 24 b/min) by thermal relief (max. core temperature: 37.8 ± 0.3°C vs. 38.4 ± 0.4°C, max. mean skin temperature: 34.7 ± 0.8°C vs. 37.1 ± 0.3°C) and offers essential extensions in performance and work time under thermal insulation.     

Thermal comfort and clothing insulation of resting tent occupants at high altitude

Thirty-nine males and 18 females, in six groups, participated in six high altitude treks (each lasting 3–4 weeks and climbing up to 5500 m) in the Himalaya and Karakoram. Inverse relationships between mean overnight total insulation (sleeping bag plus clothing) and air temperature in tents were recorded for all treks. Average overnight thermal sensations varied little with air temperature as the subjects modified their clothing insulation to maintain thermal sensations warmer than ‘neutral’ for all treks. For combined treks, subjects adjusted their mean overnight total insulation up to 7 clo for thermal sensations of between 0 (‘neutral’) and +1 (‘slightly warm’) on average, measured on the standard seven-point thermal sensation scale developed for everyday low-altitude conditions. Very few subjects (3% of all daily responses, on average) reported ‘cool’ or ‘cold’ sensations. General tent discomfort increased with altitude suggesting that subjects interpreted tent comfort predominantly in terms of thermal outdoor conditions.     

Benefit of heat acclimation is limited by the evaporative potential when wearing chemical protective clothing.

Heat acclimation-induced sweating responses have the potential of reducing heat strain for chemical protective garment wearers. However, this potential benefit is strongly affected by the properties of the garment. If the clothing ensemble permits sufficient evaporative heat dissipation, then heat acclimation becomes helpful in reducing heat strain. On the other hand, if the garment creates an impenetrable barrier to moisture, no benefit can be gained from heat acclimation as the additional sweating cannot be evaporated. Ten subjects were studied exercising on a treadmill while wearing two different chemical protective ensembles. Skin heat flux, skin temperature, core temperature, metabolic heat production and heart rate were measured. It was found that the benefit of heat acclimation is strongly dependent on the ability of the body to dissipate an adequate amount of heat evaporatively. The evaporative potential (EP), a measure of thermal insulation modified by moisture permeability, of the clothing ensemble offers a quantitative index useful to determine, a priori, whether heat acclimation would be helpful when wearing protective clothing system. The data show that when EP is < 15%, heat acclimation affords no benefit. An evaporative potential graph is created to aid in this determination.     

Metabolic rate and clothing insulation data of children and adolescents during various school activities

Data on metabolic rates (n = 81) and clothing insulation (n = 96) of school children and adolescents (A, primary school: age 9-10; B, primary school: age 10-11 year; C, junior vocational (technical) education: age 13-16 (lower level); D, same as C but at advanced level; and E, senior vocational (technical) education, advanced level: age 16-18) were collected (Diaferometer, Oxylog, Heart Rate derivation) during theory-, practical- and physical education- lessons. Clothing insulation was calculated from clothing weight, covered body surface area, and the number of clothing layers worn. Clothing insulation was found to be similar to that expected for adults in the same (winter) season, with minimal variation with age or school type (0.9 to 1.0 clo; 1.38 clo where coverall was worn), but more variation within groups (coefficient of variation 6-12%). Metabolic rate values (W.m(-2)) were lower than expected from adult data for similar activities, but are supported by other child data. The results of this study can be used to establish design criteria for school climate control systems or as general data on energy expenditure for children and adolescents. The results emphasize the need for specific child data and show the limited value of size-corrected adult data for use in children.     

Effect of head-mounted displays on posture

OBJECTIVE: The aim of the present study was to determine if a wearable system based on a head-mounted display (HMD) causes users to alter their head position and adopt postures that place greater stress on the musculoskeletal system. BACKGROUND: HMDs are common output devices used with wearable computers. HMDs provide the wearer with visual information by projecting computer-generated virtual images in front of the eyes. Deviations of neck posture from a neutral upright position increase the stresses on the musculoskeletal system of the head and neck. METHOD: Seven paramedics simulated the treatment of a patient under a normal condition and when using an HMD wearable computer system. During the simulations a posture analysis was performed using the Rapid Upper Limb Assessment method. RESULTS: The postures adopted when wearing an HMD, as compared with a normal condition, scored significantly higher for the neck (z = 2.463, p < .05) and for overall body posture (left side of the body: z = 2.447, p < .05; right side of the body: z = 2.895, p < .05). CONCLUSION: Wearing an HMD can force the wearers to modify their neck posture. As such, the musculoskeletal system of the head and neck may be placed under increased levels of stress. APPLICATION: Potential users should be made aware that HMDs could dictate modifications in neck posture, which may have detrimental effects and may compound the weight effect of the HMD.     

Engineering design of thermal quality clothing on a simulation-based and lifestyle-oriented CAD system

Engineering design of thermal quality clothing is a promising solution by applying multi-disciplinary knowledge to achieve the design and production of clothing with desirable thermal functions. In this paper, a special simulation-based and lifestyle-oriented CAD system is introduced to help the user in engineering design of thermal quality clothing. The engineering-oriented simulation models endowed with explicit data availability arose from the material parameters that are the key issue for engineering application. To offer an easy-to-use tool, this system is implemented with a lifestyle-oriented design procedure. It can facilitate the designers to quickly implement design and simulate on the wearing scenario, and evaluate and optimize their design. Due to the design of thermal quality clothing can be achieved without making physical prototypes, it is able to speed up the design cycle and reduce the design and development cost.