Book - School of Science and Technology

Chapter 4Survey of heating methodsHaving arrived at the quantity of heat energy required for each space and thus for thebuilding as a whole, as described in Chapter 2, it is now necessary to consider how thisheat is to be supplied. It is thus appropriate to take a quick look at the whole range ofavailable methods prior to examining these in more detail.The number of heating methods and systems is almost unlimited if every combinationof energy supply, method of conversion of that energy into heat, transmission mediumand type of emitting element were to be considered. It is therefore quite useless to attemptto describe them at all clearly or systematically unless they are classified under theheadings of the two main groups into which they all fall. These are:. Direct systems, in which the energy purchased is consumed as required within the spaceto be heated.. Indirect systems, in which the energy purchased is consumed at some more or lesscentral point outside the space to be heated and then transferred to equipment in thatspace for liberation.The direct systems may be divided into four primary categories, according to the type offuel or energy source: solid; liquid; gaseous or electrical, as illustrated in Figure 4.1.Secondary sub-divisions relate to the characteristics of the terminal heat emitting elementsi.e. whether these are primarily radiant or primarily convective.In the case of indirect systems, the nature of the medium selected to distribute the thermalenergy, from the point of generation or storage to the space to be heated, is of the greatestsignificance. This medium may be either a liquid (water), or a vapour (steam) or a gas (air)and each may be utilised over a wide range of temperatures and pressures. In most instances,the choice of fuel or energy source is quite independent of the distribution medium althoughthere are rare circumstances where certain combinations would be inappropriate.Consequent upon the scope thus presented for design development, the variety ofsystem arrangements and terminal heat emitting equipment associated with each is considerable.The principal criteria by which indirect systems may be categorised are thus noteasy to define since there are so many secondary, but not unimportant, sub-divisionswithin each that a diagram on the lines of Figure 4.1 would be confusing rather thanhelpful. It is more useful, therefore, to catalogue some of the options as shown in Table 4.1.The text which follows concentrates upon particulars of the various types of equipmentused with direct systems followed by no more than very brief notes covering the leadingcharacteristics of indirect systems. The latter are dealt with in greater detail under specificheadings in later chapters.