Thermal discomfort

Humans seek and want thermal comfort, even at work in industrial settings. Clothing, activities, posture, location, and shelter are chosen, adjusted, altered, and sought consciously and unconsciously to reduce discomforts and enable us to focus more on the other tasks of life. Discomfort can contribute to mistakes, productivity decreases, and industrial accidents. " Thermal discomfort results from the physiological strain of thermoregulation. The strain can be in the form of altered body temperatures, sweating and excessive skin moisture, muscle tension and stiffness, shivering, and loss of dexterity. A small... 

Aside from the general thermal state of the body, a person may find the thermal environment unacceptable if local influences on the body from asymmetric temperature radiation, draft, vertical air temperature differences, or contact with hot or cold surfaces (floors, machinery, tools, etc.) are experienced. The data for local thermal discomfort is mainly based on studies of people under low activity levels (1.2 met). For higher activities it can be expected that people are less sensitive to local thermal discomfort. The relations between dissatisfaction and local discomfort parameters are found in CR 1752. 

Thermal comfort is defined as the condition of mind that expresses satisfaction with the thermal environment. Dissatisfaction may be caused by thermal discomfort of the body as a whole as expressed with the PMV and PPD indices, or it may be caused by unwanted cooling (or heating) of a particular part of the body. Due to individual differences, it is impossible to specify a thermal environment that will satisfy everybody. There will always be a percentage of dissatisfied occupants, but it is possible to specify an environment predicted to be acceptable by a certain percentage of the occupants. 

FIGURE 6.4 Local thermal discomfort caused by warm or cold floors. 

FIGURE 6.5 Local thermal discomfort caused by radiant temperature asymmeti-y... 

Due to local or national priorities, technical developments, and climatic regions, in some cases a higher thermal quality (fewer dissatisfied) or a lower quality (more dissatisfied) may be sufficient. In both cases the PMV and PPD indices, the model of draft, and the relation between local thermal discomfort parameters and the expected percentage of dissatisfied people may be used to determine different ranges of parameters for the evaluation and design of the thermal environment. 

The numbers of dissatisfied persons in Table 6.3 are not additive. Some of the people experiencing general thermal comfort (PMV-PPD) may be the same as the people experiencing local thermal discomfort. In practice, a higher or lower number of dissatisfied persons may be found using subjective questionnaires in field investigations (ISO 10551). 

Figure 6.6 and Tables 6.4-6.6 give ranges for local thermal discomfort parameters for the three categories listed in Table 6.3. The acceptable mean air velocity is a function of local air temperature and turbulence intensity. 7 he turbulence intensity may vary between 30% and 60% in spaces with mixed flow air distribution. In spaces with displacement ventilation or without mechanical ventilation, the turbulence intensity may be lower. 

Air velocities that will not cause thermal discomfort or disturb papers or manufactured goods such as light powders and fibers... 

High supply air velocities or cool supply air can cause uncomfortable drafts on the worker. Nonuniform supply air velocities with high turbulence intensity may result in decreased capture efficiency, increased contaminant spread, and increased thermal discomfort. 

The flow field created within the protection zone depends mainly on the density difference between supply air and room air (Fig. 10.90). With vertical flow the supply air should be isothermal or cooler than ambient air. If it were warmer, the extension of the controlled flow would be reduced due to buoyancy effects, resulting in the supply air not reaching the operator s breathing zone. As the. supply air cannot be used for heating, the operator s thermal comfort should be maintained, preferably with radiant heaters in cold environments. If the supply air temperature is lower than the room air, the denser supply air accelerates down to the operator, and for continuity reasons the supply flow contracts. Excessive temperature differences result in a reduced controlled flow area with thermal discomfort, and should only be used in special cases. 

Downdraft A natural or mechanical downward airstream, either that may, due to its temperature and/or velocity, cause thermal discomfort. In the case of a stack discharge, the term downwash may be used for the downward air current in the lee of the chimney that takes the smoke and other emissions below the emission discharge level causing ground-level pollution. 

Draft An airstream within an occupied zone that causes thermal discomfort of the occu pants due to its temperature and/or velocity. Also, the thermal uplift caused by densit) differences required to provide adequate air both for the combustion process and the removal of the products of combustion. 

Thermal discomfort Discomfort experienced due to excessive heat loss or gain from or to the human body due to radiation, convection, conduction, evaporation, or air movement. 

C What is asymmetric iheimal radiation How does it cause thermal discomfort in the occupants of a room ... 

In case of personal protective fabrics, the bulk of ACF-based garments often results in thermal discomfort and physiological burden to the wearer. Therefore, it is necessary to create less bulky ACFs for enhanced physical comfort in chemical protective suits (Wilusz 2007). In order to achieve maximum protection and reasonable comfort, novel fabric ensembles with or without ACFs are necessary (Wilusz 2007 Gurudatt et al. 1997). An alternative approach to the use of ACFs for chemical protection is the use of functionalized selectively permeable membranes (Wilusz 2007). 

Clothing thus plays an essential role in the maintenance of the thermal and fluid balance with thermal comfort and thermal discomfort as intermediate factors. 

ABSTRACT Individuals spend most of their time in work environments and because of this reason their workplaces should be provided with optimal work conditions in order to increase performance and avoid work accidents. Thermal discomfort is one of the causes of work dissatisfaction which lead to individuals behavior changes as well as works accidents. This paper aims to study a manufacturing industry inner space affected by heat thermal environments in order to identify the most critical areas regarding two thermal indexes, EsConTer and THI, in which their interpretations valorize workers thermal sensation. From the color maps developed to facilitate indexes analysis the most critical areas of the space in study were easily identified as well as the most critical workstations near those areas. The health and safety department of the industry in study valorized the results in order to develop measures that may improve the occupational health of the occupants due to the approximation of the indexes results to workers thermal sensation. 

The result of this research goes against the results of Aguilar (2012), since the average result of the workload remained similar, under the two temperatures observed, and presented an irrelevantly higher workload with higher temperature. This can be explained by the observation of Lan et al. (2009) research, which concludes that workers have to exert greater effort to maintain performance in thermal discomfort because of heat. 

From the observation of Figure 2 it can be concluded that the regions (packaging A and B) with a higher relative humidity correspond to the same regions with the lowest air temperature, as expected. When the air temperature decreases, the relative humidity is higher. Thus, areas where it is noticed an increased thermal discomfort correspond to the upper part of the section under study, which leads to greater thermal discomfort in the workers located there. 

In THI index values of highest thermal discomfort reach 12.0°C (packaging A) and 9.4°C (packaging B), which means, according to the ranges defined in Table 1, 50% of these individuals were thermally uncomfortable. 

The PPD index was applied to discover the percentage of unsatisfied workstations in the packaging section. The observation of Figure 6 shows that in case of packaging. A thermal discomfort is less that in case of packaging B, because in first case only 44% of workers are thermally uncomfortable and in second case 70% of workers are thermally uncomfortable. This means that different situations of packaging show different thermal sensations. 

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