Temperature effective, thermal comfort

Humans and the other warm-blooded animals have developed thermoregulatory systems to carefully control body temperature to levels that enable them to function and survive effectively. In general, thermal comfort occurs when the physiological effort to control body temperature is minimized for the activity. Table. 5.1... 

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. 

This has a positive effect on thermal comfort, particularly in the summer period. I he thermal space load factor p, is used to quantitatively characterirc this effect (flout> outside air temperature 0, air temperature at working spat e level f exhaint cxhaust air temperature) ... 

The measurement range is dependent on the instrument but can cover the range -50 to +500 °C. The accuracy is not as high as the best contact thermometers. One reason for this is that the emissivity of the surface has an effect on the measurement result, and an emissivity correction is necessary for most instruments. The positive features are noncontact measurement and very fast dynamics, which enable a rapid scan of surface temperatures from a distance this is convenient when carrying out, for example, thermal comfort measurements. 

Note that the operative temperature will be the arithmetic average of the ambient and surrounding surface temperatures when the convection and radiation heat transfer coefficients are equal to each other. Another environmental index used in thermal comfort analysis is the effective temperature, which combines the effects of temperature and humidity. Two environments with the same effective temperature evokes the same thermal response in people even though they are at different temperatures and humidities. 

The idea of thermal comfort is based on subjective evaluations of thermal environments. Individuals rate conditions as cold, cool, neutral, warm, or hot. An early thermal comfort scale was the Effective Temperature Scale. More recent studies led to a standard for defining thermal comfort conditions by ASHRAE. Standard 55-2013 is the most recent edition, but updates occur every few years. 

The occupational environment can be neutral, cold or hot. A combined action between the four environmental parameters (temperature, relative humidity, velocity and radiant heat) and the two individual parameters (clothing worn by the occupants and their activity) can lead to a thermal comfort, discomfort, or to a thermal stress situation (Parsons, 2013). The integration of these parameters can be done in a thermal index in a way that will provide a single value that is related to the effects on the occupants. Three types of indices can be identified empirical, rational and derived. According to Parsons (2000), rational indices are derived from mathematical models that describe the behavior of the human body in thermal environments. The analysis of these situations can be achieved using diverse techniques and comfort models, such as Computation Fluid Dynamics (CFD) and other numerical simulations (Murakami et ah, 2000). The human thermal software (Teixeira et al., 2010) is based on differential... 

Nevins, R., Gonzalez, R. R., Nishi, Y, and Ciagge, A. P. (1975). Effect of changes in ambient temperature and level of humidiry on comfort and thermal sensations. ASHRAE Trans., 81(2). 

Alagirusamy, 2010). Clothing is considered as a system that interacts with the body and must support thermoregulation of the body by maintaining its thermal balance (constant body core temperature of 37 °C) and providing a comfortable microclimate next to the skin (Li and Wong, 2006). Prevention of heat stress could lead to improved competitive performance for the athlete, whereas unnecessary heat and moisture next to the skin could have adverse effects on both performance and health. 

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