Book - School of Science and Technology

582 Hot water supply systemsSteam-to-water calorifiersThe configuration generally adopted when the heating medium is steam is similar in mostrespects to that shown in Figure 20.19, with hairpin tubes. The domed cover, here knownas a steam chest, is provided with an upper connection for the steam supply and, usually, apressure gauge. Condensate, when formed, leaves by a lower connection and passes to asteam trap set.Bubble-top calorifiersUnits so described pre-dated by half a century the equipment which has produced such afurore followingthe introduction of the 1986±9 Model Water Byelaws. A calorifier of thistype consists of a vertical cylinder, not unlike the pattern shown in Figure 20.20, buthavingthe shell extended above the hot water outlet to form a sealed air space at the top,equivalent to about 15% of the water volume. The cold water feed derives directly from apressure main and, when the cylinder is first filled, air is trapped and compressed in theshell extension or `bubble-top'.When the water content is heated, it expands, and the volume of expansion is accommodatedby further compression of the air within the `bubble top'. Numerous safetyfeatures are incorporated, as shown in Figure 20.22, those on the primary side beingvaried to suit the heatingmedium which may be either hot water or steam.This principle of usingan air pocket at the top of the cylinder is adopted for domesticsystems by proprietary unit as shown in Figure 20.10, the expansion pocket beingcomplimented with safety feature valves and thermal cut-out to meet the requirementsof BuildingRegulation G3 document.Angelery hot water generatorsThis equipment is suitable for use with either steam or hot water as the primary mediumand deals with the process of supplyinghot water in a manner which differs from theconventional. As may be seen from Figure 20.23, the heat exchange surface consists of aseries of interlacingcoils which provide a high capacity in a small space and an ability toshed scale as they flex in expansion and contraction. While the generator is not strictly anSecondaryconnectionsBubble topRelief valveCold watersupply frommainsPrimaryconnectionsPressure reducingvalveFigure 20.22 `Bubble top' calorifierNon returnvalveControlvalve