Book - School of Science and Technology

Chapter 1FundamentalsFulfilment of the need for satisfactory environmental conditions within a building,whether these be required for human comfort, material storage or in support of someprocess, is a task which has faced mankind throughout history. With the passage of time,a variety of forms of protection against the elements has been provided by structuressuited to individual circumstances, the techniques being related to the severity of the localclimatic conditions, to the materials which were available and to the skills of the builders.In this sense, the characteristics of those structures provided a form of inherent yet coarsecontrol over the internal environment:finer control had to wait upon the progressivedevelopment, over the last two centuries, of systems able to moderate the impact of theexternal climate still further.The human body produces heat, the quantity depending upon the level of physicalactivity, and for survival this must be in balance with a corresponding heat loss. When therate of heat generation is greater than the rate of loss, then the body temperature will rise.Similarly, when the rate of heat loss exceeds that of production, then the body temperaturewill fall. If the level of imbalance is severe, heat stress at one extreme and hypothermiaat the other will result and either may prove fatal.The processes of heat loss from the body are:. conduction to contact surfaces and to clothing. convection from exposed skin and clothing surfaces. radiation from exposed surfaces to the surroundings. exhalation of breath. evaporation by sweating.Involuntary control of these processes is by constriction or dilation of blood vessels,variation in the rate of breathing and variation in the level of sweating, voluntary andinvoluntary. The individual may assist by removing or adding insulating layers in theform of clothing.Keeping warm or keeping cool are primitive instincts which have been progressivelyrefined as more sophisticated means have become available to satisfy them. For example,once facilities for the exclusion of the extremes of climate became commonplace forbuildings in temperate zones, fashion introduced lighter clothing; this led to greaterthermal sensitivity and, in consequence, to less tolerance of temperature variation. Bycoincidence, however, in the same time span, architectural styles changed also and thesubstantial buildings of the past, which could moderate the effects of solar heat andwinter chill, were succeeded by lightweight structures with substantial areas of glazinghaving little or no such thermal capacity.