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     

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.     

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 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.     

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.     

Combined effects of fabric air permeability and moisture absorption on clothing microclimate and subjective sensation during intermittent exercise at 27 degrees C

The present paper aimed at determining the combined effects of two different levels of air permeability and moisture absorption, in terms of clothing microclimate and subjective sensation, in resting and exercising subjects at an ambient temperature of 27 °C, a relative humidity of 50% and an air velocity of 0.14 m s^-1. Three kinds of clothing ensemble were investigated: (1) polyester clothing with low moisture absorption and low air permeability (A), (2) polyester clothing with low moisture absorption and high air permeability (B), and (3) cotton clothing with high moisture absorption and high air permeability (C). The subjects exercised for 10 min on a cycle ergometer at an intensity of 30% maximal oxygen uptake and then had a 10 min rest. This sequence was repeated four times. The main findings are summarized as follows: (1) The clothing microclimate humidity in the back area was significantly higher in A than in B, and in C than in B. (2) The clothing microclimate temperature in the chest area was significantly higher in B than in A, and in B than in C. (3) The clothing microclimate temperature in the back area was significantly higher in C than in B. (4) The clothing surface temperature was significantly higher in C than in B. (5) Although the positive relationships between the microclimate humidity and forearm sweat rate was significantly confirmed in all three kinds of clothing, the microclimate humidity at chest for the same sweat rate was lower in C than in A and B. (6) Although the positive relationships between subjective sensation and forearm sweat rates were significantly confirmed in all three kinds of clothing, the subjective discomfort seemed to be reduced more effectively in C than in A and B for the same sweat rate. These results were discussed in terms of thermal physiology and combined effects of air permeability and moisture absorbency of the fabrics.     

Combined effects of fabric air permeability and moisture absorption on clothing microclimate and subjective sensation during intermittent exercise at 27 degrees C.

The present paper aimed at determining the combined effects of two different levels of air permeability and moisture absorption, in terms of clothing microclimate and subjective sensation, in resting and exercising subjects at an ambient temperature of 27 degrees C, a relative humidity of 50% and an air velocity of 0.14 m s-1. Three kinds of clothing ensemble were investigated: (1) polyester clothing with low moisture absorption and low air permeability (A), (2) polyester clothing with low moisture absorption and high air permeability (B), and (3) cotton clothing with high moisture absorption and high air permeability (C). The subjects exercised for 10 min on a cycle ergometer at an intensity of 30% maximal oxygen uptake and then had a 10 min rest. This sequence was repeated four times. The main findings are summarized as follows: (1) The clothing microclimate humidity in the back area was significantly higher in A than in B, and in C than in B. (2) The clothing microclimate temperature in the chest area was significantly higher in B than in A, and in B than in C. (3) The clothing microclimate temperature in the back area was significantly higher in C than in B. (4) The clothing surface temperature was significantly higher in C than in B. (5) Although the positive relationships between the microclimate humidity and forearm sweat rate was significantly confirmed in all three kinds of clothing, the microclimate humidity at chest for the same sweat rate was lower in C than in A and B. (6) Although the positive relationships between subjective sensation and forearm sweat rates were significantly confirmed in all three kinds of clothing, the subjective discomfort seemed to be reduced more effectively in C than in A and B for the same sweat rate. These results were discussed in terms of thermal physiology and combined effects of air permeability and moisture absorbency of the fabrics.     

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.     

Perceptions of temperature, moisture and comfort in clothing during environmental transients

A study has been carried out to investigate the psychophysical mechanisms of the perception of temperature and moisture sensations in clothing during environmental transients. A series of wear trials was conducted to measure the psychological perception of thermal and moisture sensations and the simultaneous temperature and humidity at the skin surface, fabric surface and in the clothing under simulated moderate rain conditions. Jumpers made from wool and acrylic fibres were used in the trial. Analysis has been carried out to study the relationship between psychological perceptions of temperature and moisture and the objectively measured skin and fabric temperatures and relative humidity in clothing microclimate. The perception of warmth seems to follow Fechner's law and Stevens' power law, having positive relationships with the skin temperature and fabric temperatures. The perception of dampness appears to follow Fechner's law more closely than Stevens' power law with a negative relationship with skin temperature, and is nonlinearly and positively correlated with relative humidity in clothing microclimate. The perception of comfort is positively related to the perception of warmth and negatively to the perception of dampness. This perception of comfort is positively related to the skin temperature, which appears to follow both Fechner's law and Stevens' law, also non-linearly and negatively related to relative humidity in clothing microclimate.     

Perceptions of temperature,moisture and comfort in clothing during environmental transients

A study has been carried out to investigate the psychophysical mechanisms of the perception of temperature and moisture sensations in clothing during environmental transients. A series of wear trials was conducted to measure the psychological perception of thermal and moisture sensations and the simultaneous temperature and humidity at the skin surface, fabric surface and in the clothing under simulated moderate rain conditions. Jumpers made from wool and acrylic fibres were used in the trial. Analysis has been carried out to study the relationship between psychological perceptions of temperature and moisture and the objectively measured skin and fabric temperatures and relative humidity in clothing microclimate. The perception of warmth seems to follow Fechner's law and Stevens' power law, having positive relationships with the skin temperature and fabric temperatures. The perception of dampness appears to follow Fechner's law more closely than Stevens' power law with a negative relationship with skin temperature, and is nonlinearly and positively correlated with relative humidity in clothing microclimate. The perception of comfort is positively related to the perception of warmth and negatively to the perception of dampness. This perception of comfort is positively related to the skin temperature, which appears to follow both Fechner's law and Stevens' law, also non-linearly and negatively related to relative humidity in clothing microclimate.     

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.     

Determining temperature ratings for children's cold weather clothing

This study examined the physical and physiological differences between children and adults that affect body heat generation and losses and then developed a heat loss model for determining the temperature ratings of cold weather clothing designed for use by children of various ages. The thermal insulation values of selected jackets were measured using a heated manikin dressed in two base ensembles, and the temperature ratings were calculated using the model. The results indicated that the type of garments used in the base ensemble had a major effect on jacket ensemble insulation and the predicted comfort temperature. For a given level of insulation, the temperature rating decreased as the wearer's age and activity level increased. This is probably because children have a higher surface area per unit mass ratio than adults, and they lose heat faster. However, this effect is partially offset by their higher metabolic rates.     

A CAD system for multi-style thermal functional design of clothing

Designing clothing with good thermal functional performance is very demanding and time-consuming if we follow traditional design methods. An innovative method consisting of a CAD system, allowing the designer to perform multi-style clothing thermal functional design on a customized virtual human body, is presented in this paper. The new functionalities of the virtual system provide the abilities to perform intelligent design of different clothing styles and materials for different body parts according to individual design requirements, namely design of various categories of clothing, such as hat, coat, trousers, gloves and shoes in the same design scheme. The designed clothing can be worn on a virtual human body and set in various wearing scenarios. The thermal behaviors in the human body-clothing-environment are simulated to predict the thermal performance of clothing and thermal response of the human body at multi-parts. 2D/3D visualization and animation of the simulation results are presented to help the designers to preview and determine whether the thermal performance of clothing is satisfactory and then obtain feedback to improve their designs iteratively.     

Measurement of the clothing ventilation index

In order to achieve thermal comfort while wearing protective clothing, heat loss from the body by convection and by the evaporation of sweat must be readily controlled by the wearer's thermoregulatory system. This can only be achieved if air is flowing through the clothing micro-environment in sufficient quantity to remove sensible and insensible heat as required. The volume flow of air through the clothing assembly is therefore an important determinant of thermal comfort.

This paper describes a new procedure for estimating under working conditions, the volume of air flowing through the micro-environment. The method is based on two techniques: the first gives a measure of the volume of the micro-environment; the other uses a trace gas to measure the rate of air exchange. Algebraic combination of the results enables the air exchange characteristics of a garment to be described in terms of a Ventilation Index. It is proposed that this index be used to describe the performance of protective clothing assemblies.     

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.     

A novel approach for fit analysis of thermal protective clothing using three-dimensional body scanning

The garment fit played an important role in protective performance, comfort and mobility. The purpose of this study is to quantify the air gap to quantitatively characterize a three-dimensional (3-D) garment fit using a 3-D body scanning technique. A method for processing of scanned data was developed to investigate the air gap size and distribution between the clothing and human body. The mesh model formed from nude and clothed body was aligned, superimposed and sectioned using Rapidform software. The air gap size and distribution over the body surface were analyzed. The total air volume was also calculated. The effects of fabric properties and garment size on air gap distribution were explored. The results indicated that average air gap of the fit clothing was around 25–30 mm and the overall air gap distribution was similar. The air gap was unevenly distributed over the body and it was strongly associated with the body parts, fabric properties and garment size. The research will help understand the overall clothing fit and its association with protection, thermal and movement comfort, and provide guidelines for clothing engineers to improve thermal performance and reduce physiological burden.     

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 posture positions on the evaporative resistance and thermal insulation of clothing

Evaporative resistance and thermal insulation of clothing are important parameters in the design and engineering of thermal environments and functional clothing. Past work on the measurement of evaporative resistance of clothing was, however, limited to the standing posture with or without body motion. Information on the evaporative resistance of clothing when the wearer is in a sedentary or supine posture and how it is related to that when the wearer is in a standing posture is lacking. This paper presents original data on the effect of postures on the evaporative resistance of clothing, thermal insulation and permeability index, based on the measurements under three postures, viz. standing, sedentary and supine, using the sweating fabric manikin-Walter. Regression models are also established to relate the evaporative resistance and thermal insulation of clothing under sedentary and supine postures to those under the standing posture. The study further shows that the apparent evaporated resistances of standing and sedentary postures measured in the non-isothermal condition are much lower than those in the isothermal condition. The apparent evaporative resistances measured using the mass loss method are generally lower than those measured using the heat loss method due to moisture absorption or condensation within clothing. STATEMENT OF RELEVANCE: The thermal insulation and evaporative resistance values of clothing ensembles under different postures are essential data for the ergonomics design of thermal environments (e.g. indoors or a vehicle's interior environment) and functional clothing. They are also necessary for the prediction of thermal comfort or duration of exposure in different environmental conditions.     

Numerical studies on the microclimate around a sleeping person and the related thermal neutrality issues

This article reports on two numerical studies on the microclimate around, and the thermal neutrality of, a sleeping person in a space installed with a displacement ventilation system. The development of a sleeping computational thermal manikin (SCTM) placed in a space air-conditioned by a displacement ventilation system is first described. This is followed by reporting the results of the first numerical study on the microclimate around the SCTM, including air temperature and velocity distributions and the heat transfer characteristics. Then the outcomes of the other numerical study on the thermal neutrality of a sleeping person are presented, including the thermal neutrality for a naked sleeping person and the effects of the total insulation value of a bedding system on the thermal neutrality of a sleeping person. STATEMENT OF RELEVANCE: The thermal environment would greatly affect the sleep quality of human beings. Through developing a SCTM, the microclimate around a sleeping person has been numerically studied. The thermal neutral environment may then be predicted and contributions to improved sleep quality may be made.