Thermal comfort defined

Thermal comfort may be defined as "that condition of mind in which satisfaction is expressed with the thermal environment" (4). It is thus defined by a statistically vaUd sample of people under very specific and controlled conditions. No single environment is satisfactory for everybody, even if all wear identical clothing and perform the same activity. The comfort zone specified in ASHRAE Standard 55 (5) is based on 90% acceptance, or 10% dissatisfied. 

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. 

The probability density function of u is shown for four points in Fig. 11.16, two points in the wall jet and two points in the boundary layer close to the floor. For the points in the wall jet (Fig. 11.16<2) the probability (unction shows a preferred value of u showing that the flow has a well-defined mean velocity and that the velocity is fluctuating around this mean value. Close to the floor near the separation at x/H = I (Fig. 11.16f ) it is hard to find any preferred value of u, which shows that the flow is irregular and unstable with no well-defined mean velocity and large turbulent intensity. From Figs. 11.15 and 11.16 we can see that LES gives us information about the nature of the turbulent fluctuations that can be important for thermal comfort. This type of information is not available from traditional CFD using models. 

Environmental Conditions. The last area of discussion concerns those studies that emphasize environmental factors indoors and their interrelationship with clothing. Fanger s multivariate equation for predicting thermal comfort indoors, which he defines as thermal neutrality, is based on statistical analysis of 1,300 Danish and American subjects and consists of six parameters metabolic activity of occupants, clothing insulative value (clo), air temperature, mean radiant temperature, relative humidity, and air velocity ( 8, TjO An instrument based m these parameters and the statistical analysis is available (Figure 2) a reading for the parameters is integrated and the percent of occupants satisfied with the thermal environment is displayed. 

Some specific studies on the measurement of heat losses and indoor temperatures in buildings deserve attention. In his review of the relative importance of thermal comfort in buildings, McIntyre considered that the mean radiant temperature was the most important parameter, followed closely by the "radiation vector," which is defined as the net radiant flux density vector at a given point and measures the asymmetry of the thermal radiation field in a room (97). Benzinger et al. characterized the mean radiant temperature, and asymmetric radiation fields, using a scanning plane radiometer, which maps the plane radiant temperature in a given space indoors (98). 

Thermal comfort may not be attainable because 1) the heat balance is unable to be satisfied for Ts and Esw, or 2) asymmetries such as drafts, asymmetric radiation, etc., exist. Defining the thermal load, L, as... 

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. 

Thermal sensation is the human thermal perception which according to thermal environment surround, triggers a human body reaction (Parsons, 2003). The skin temperature is considered by some authors (Kataoka et al., 1998 Zingano, 2001) as a reference temperature to evaluate human thermal sensation. A thermal comfort sensation is defined as a neutral sensation or the state of satisfaction of an individual when exposed to a thermal environment (ASHRAE, 2001 Chow, Fong, Givoni, Lin, Chan, 2010). On the other hand a stress thermal sensation is the state of dissatisfaction of an individual when exposed to a thermal environment (Meles, 2012 Talaia, Meles, Teixeira, 2013) When an individual are under extreme thermal environments, either hot or cold, the risk of failures and work accidents increase (Riniolo Schmidt, 2006). Furthermore, many studies demonstrate a strong relation between comfort and productivity (Bluyssen, Aries, van Dommelen, 2011). 

A guarded hot-plate method, ASTM D1518, is used to measure the rate of heat transfer over time from a warm metal plate. The fabric is placed on the constant temperature plate and covered by a second metal plate. After the temperature of the second plate has been allowed to equiUbrate, the thermal transmittance is calculated based on the temperature difference between the two plates and the energy required to maintain the temperature of the bottom plate. The units for thermal transmittance are W/m -K. Thermal resistance is the reciprocal of thermal conductivity (or transmittance). Thermal resistance is often reported as a do value, defined as the insulation required to keep a resting person comfortable at 21°C with air movement of 0.1 m/s. Thermal resistance in m -K/W can be converted to do by multiplying by 0.1548 (121). 

Clothing affects heat and moisture loss. Increasing the thickness or number of layers of clothing increases its insulating capability and reduces body heat loss. Clothing insulation is usually described with the do unit. Originally, t do was defined as the thermal resistance necessary for comfort while sedentary in a uniform still air environment of 21 °C. In conventional SI nomenclature I do has a thermal resistance of 0.155 K m-/W. Some ensembles do values and associated comfort temperatures are shown in Fig. 5.4. 

In order to elucidate a mechanism, one must first consider the nature of the states initially formed by photoexcitation as well as the natures of other expected states eventually populated by internal conversion/intersystem crossing. Although it is by no means universally true, many transition metal complexes, when excited, undergo efficient relaxation to a bound, lowest energy excited state (LEES) or an ensemble of thermally equilibrated LEESs from which the various chemical processes lead to photoproducts. In such systems, the simplest model of which is illustrated by Figure 9, one can comfortably apply transition state theory to the rates and consider pressure effects in terms of the mechanisms of the individual decay LEES processes. In this case, the quantum yield of product formation would be defined by the ratio of rate constants by which the various chemical and photophysical paths for ES decay are partitioned. For Figure 9, in the absence of a bimolecular quencher Q, this would be... 

Currently, the top sheet of a disposable diaper is usually made from a hydrophilic nonwoven fabric. These nonwoven fabrics are broadly defined as sheet or web stractures bonded together by entangled fibres or filaments, and by perforating films mechanically, thermally, or chemically to form flat, porous sheets that are made directly from separate fibre or from molten plastic or plastic film. Therefore, the mechanical and smface properties of the hygienic nonwoven fabrics used as the top sheet of disposable diapers are important for the health and comfort of the skin (Hong, Kim, Kang, 2005). 

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