Moderate Thermal Environments

The main standards for comfortable thermal environment are ISO EN 7730 and ASHRAE 55-92. The research that forms the basis for these two standards is mainly performed under environmental conditions similar to those for commercial and residential buildings, with activity levels of 1 to 2 met, normal indoor clothing (0.5 to 1.0 do), and a limited range of environmental parameters. 

ISO EN 7730 standardizes the PMV-PPD index as the method for evaluation of moderate thermal environments. To quantify the degree of comfort, the PMV (predicted mean vote) index gives a value on a 7-point thermal sensation scale -t-3 hot, +2 warm, +1 slightly warm, 0 neutral, -I slightly cool, -2 cool, -3 cold. An equation in the standard calculates the PMV index based on the six factors (clothing, activity, air and mean radiant temperatures, air speed, and humidity). 

The PMV index can be determined when the activity (metabolic rate) and the clothing (thermal resistance) are estimated and the following environmental parameters are measured air temperature, mean radiant temperature, relative air velocity, and partial water vapor pressure (see ISO EN 7726). 

Use of the PMV index is only recommended when the six main parameters are within the following intervals  

The metabolic rate can be estimated by ISO EN 9886, and the thermal resistance of clothing can be estimated by ISO EN 9920, taking into account the type of work and the time of year. For varying metabolic rates, it is recommended to estimate a time-weighted average during the previous 1 h period. For sedentary people, the insulation of a chair must also be taken into account. 

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Table 13.4 has been created from the information and estimates contained in BS/EN/ ISO 7730 1995 (Moderate Thermal Environments—Determination of the PMV and PPD Indices and Specification of the Conditions for Thermal Comfort). It represents a subset of values most likely to be useful and relevant to environmental design in control rooms. Note that some of the air temperature values are higher than those set in BS/EN/ISO 11064-6 2005 as minimum requirements. This illustrates the importance of a more fine-grained analysis linked to the subjective experience of the thermal environment. 

ISO EN 7730 Ciomfort evaluation in moderate environ-nienrs Mode.tate thermal environments Deterrnina tion of the PMV and PPD index and specification of the conditioirs for thermal comfoi r... 

ISO EN 9886 presents the principles, methods, and interpretation of measurements of relevant human physiological responses to hot, moderate, and cold environments. The standard can be used independently or to complement other standards. Four physiological measures are considered body core temperature, skin temperature, heart rate, and body mass loss. Comments are also provided on the technical requirements, relevance, convenience, annoyance to the subject, and cost of each of the physiological measurements. The use of ISO 9886 is mainly for extreme cases, where individuals are exposed to severe environments, or in laboratory investigations into the influence of the thermal environment on humans. 

Subject scales are useful in the measurement of subjective responses of persons exposed to thermal environments. They are particularly useful in moderate environments and can be used independently or to complement the use of the objective methods (e.g., thermal indices) that were described previously. ISO EN 10551 presents the principles and methodology behind the construction and use of subjective scales and provides examples of scales that can be used to assess thermal environments. 

Conversely where less stringent thermal demands are appropriate, choices are broadened to encompass materials more commonly referred to as "commodity resins". Ultimate end product operational environments will impact the material selection process. Where in-service temperatures range from room ambient to moderate thermal extremes, lesser thermally tolerant resins may be considered. Conversely, for hostile environments such as those encountered in "under the hood" automotive, down-hole (geothermal), tropical, or corrosive climatic axtremes, enhanced material properties will be required. 

The aerobic and anaerobic heterotrophic microbes present at vents often have complex nutrient requirements (e.g. organic acids, carbohydrates, elemental sulphur) some are believed to be mixotrophic, using both autotrophic and heterotrophic metabolisms (Karl, 1995 Kelley etal., 2002). Organic matter in sulphide mineral chimneys may come from other dead and/or pyrolysed microbes and invertebrates (e.g. worm tubes and muccus) during growth of chimneys. At most hydrothermal sites, thermal environments at moderate temperatures (50-90°C) are... 

Parsons, K.H., 2002. Thermal Environments The Effects of Hot, Moderate, and Cold Environments on Human Health, Comfort and Performance, second ed. Taylor Francis, London, UK. 

Table 2. Change from a moderate to a cold thermal environment comparative analysis.

Changes in face and hands skin temperatures during exposure to moderate cold thermal environment... 

The findings of this short review indicate that moderate and severe cold thermal environment reduces skin body temperature and therefore physical working performance, lower muscle performance,... 

Finally, the main components in the thermal environment are air temperature, humidity and air movement. Considering temperature, it can, of course, cause problems when either too high or too low. Moderately high temperatures can cause effects such as irritability, loss of concentration, increased errors, loss of performance in heavy work and intense fatigue, whereas moderately too low temperatures can cause less mobiUty in the hands/feet, slowing down of manrral skills, increased clumsiness and a decreased sense of touch. 

Figure 6.1 applies for a relative humidity of 50% however, in moderate environments the air humidity has only a modest impact on the thermal sensation. Typically, a 10% increase in relative humidity is experienced as equally warm as a 0.3 °C increase in operative temperature. 

The series of standards presented in this paper provides a useful package for assessment and design of HVAC systems and protective equipment to be used in moderate, cold, and hot environments. The standards may be used to estimate the optimal combination of environmental thermal factors that will provide comfortable or tolerable healthy working conditions. The standards may also be used to establish optimal work/rest schedules for environments where the working time must be limited owdng to strain on the human body. Several of these standards are being adopted as national standards in several countries. 

Copper and copper alloys are amongst the earliest metals known to man, having been used from prehistoric times, and their present-day importance is greater than ever before. Their widespread use depends on a combination of good corrosion resistance in a variety of environments, excellent workability, high thermal and electrical conductivities, and attractive mechanical properties at low, normal and moderately elevated temperatures. 

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