Book - School of Science and Technology

10 FundamentalsIt has been suggested that low concentrations of negative ions (or high concentrationsof positive ions) lead to malaise and lethergy, and high concentrations of negative ionsproduce sensations of freshness. The Guide Section A1 states that present evidence insupport of this theory is inconclusive but the advice of the Health and Safety Commission,that adoption of `an agnostic attitude would be appropriate', praises with even fainterdamns!Thermal indicesNumerous attempts have been made to devise a scale against which comfort may bemeasured and the following deserve attention.Equivalent temperatureThis scale combines the effects of air temperature, radiation and air movement, all as measuredby a laboratory instrument named the Eupatheoscope. The late Mr A. F. Dufton,who developed this instrument and the scale at the Building Research Establishment,defined equivalent temperature as `that temperature of a uniform enclosure in which,in still air, a sizeable black body would lose heat as in the environment, the surface of thebody being one-third of the way between the temperature of the enclosure and 100 F' (i.e.approximately body temperature). The scale may be represented mathematically but, as ittakes no account of variations in humidity, it fell out of use some 20 years ago and ismentioned here only to record the work on hand at Garston during the 1920s.Effective temperatureDevised and developed in the USA for particular application to air-conditioning design,this scale combines the effects of air temperature, humidity and air movement but has nopoint of reference to radiation. It was produced following a long series of subjective testscarried out on a number of people in a wide variety of differing environmental situationsand has been revised from time to time. The results are presented in an envelope of curvessuperimposed on a nomogram, each curve relating to an air velocity. The EffectiveTemperature Lines may be adapted to provide a basis for a chart, in the form shown inFigure 1.1, where comfort zones appropriate to the British Isles are outlined for winterand summer. This scale has limited application for circumstances where no more than asimple heating system is envisaged since, within the temperature range 15±20 C, variationsin relative humidity between 40 and 70% have small effect upon comfort.Corrected effective temperatureThis is a later version of the scale noted above, modified to include the effect of radiation.It is, as before, presented in the form of a nomogram but its reliability is restricted to thecentral part of the scale between about 15 and 19 C corrected effective temperature.Fanger's comfort criteriaWork in Denmark has produced a series of comfort charts and tables based again onanalysis of the results of subjective tests which, in this case, took account of two furthervariables, namely the metabolic rate for various activities and the clothing worn. Thevolume of data provided is extremely large and enables predictions to be made with a highlevel of accuracy:for everyday use, however, the calculations which are required seemdisproportionate, having regard to the application of the end result, and in any case may