Book - School of Science and Technology

Chapter 9Piping design for indirect heating systemsHaving selected the distribution medium, the general arrangement of the system and thetype, position and size of the heat emitters, the next logical stage in the design process is toselect, from the range of commercial pipes sizes available, those which will provide themost economical and effective pattern of connection. The principal factors which mayinfluence this choice may be considered, simply as a matter of convenience, as fallingunder two headings:. External constraintsappearance;noise due to water turbulence or equipment;space occupied (i.e. pipe shaft size);force imposed on building components by mass;physical strength of pipe between supports.. Technical constraintsvelocity re erosion, turbulence, air entrainment;dynamic pressure and pump availability;total pressure re cavitation;profile of hydraulic gradient for water flow.Superimposed upon these aspects is the matter of achieving a long term balancebetween capital and recurrent costs in that a large pipe will be expensive to install initiallyand will emit heat (probably unwanted) in quantity. The energy required to induce fluidto flow through it, however, will be relatively low. A small pipe will require a greaterenergy to induce flow but will emit less heat and be cheaper to install.Water systems - principlesCirculation of water in a piping system may be maintained either by a thermo-syphoneffect or by means of a pump. A thermo-syphon or gravity circulation is produced by atemperature variation, the water in the hot flow pipe being less dense than that in thecooler return pipe. The consequent difference in mass between a rising hot water columnand a falling cold water column stimulates movement throughout the pipework system.As to circulating pumps, the centrifugal types which are most used were discussed inChapter 8 (p. 204).