Book - School of Science and Technology

18 FundamentalsInletventilationThermocouples fortemperature gradientWarmradiationColdradiationSmokejetAnemometerHumidifierKata thermometerWet & dry bulbthermometerFigure 1.4 Determination of a state of comfortSummaryThe following are practical guidelines to good practice in providing a comfortableenvironment for normally clothed people in a sedentary occupation:. air temperature within range 21 C in winter to 23 C in summer. in summer mean radiant temperature below air temperature. in winter mean radiant temperature above air temperature. relative humidity normally within 45±60%. air movement not greater than 0.15 m/s. carbon dioxide concentration below 0.1%. temperature gradient between feet and head not greater than 1.5%. floor surface temperature between 17 and 26 C. radiant asymmetry not greater than 10 C horizontal and 5 C vertical.These conditions may be exceeded for short periods, say up to a maximum of 5% andpreferably for not more than 2% of time on average, for example in naturally ventilatedor passively cooled environments, to enable energy saving measures or other economies.As will be appreciated, the manner in which air temperature, radiation, humidity andair movement interrelate with one another is very complex and nothing short of anexhaustive investigation of each, as illustrated in Figure 1.4, will suffice to establish theprecise situation existing within an enclosure. Even so, when the investigation is completeand all results have been demonstrated to be within a hair's breadth of best practice, theindividualities of human sensation are such that it is unlikely that many more than 90% ofthe occupants of a building will be entirely satisfied with their environment!