Book - School of Science and Technology

140 Electrical storage heatingUtilization circuits to hotwater heating, HWS andair heater batteries etc.Expansion cisternPumpMixingvalvePumpMixingvalveBoiler pumpFlow sparge pipeStoragepumpHot water(Stratification line)Cool waterVesselElectrode boilerReturn sparge pipeExpansion pipeFigure 5.11 Diagram of a large water storage systemTable 5.13 Properties of water for thermal storageHeightofcistern(m)Operatingpressure(bar, gauge)Temperature( C)Properties of stored water (17 K anti-flash margin)Density(kg/m 3 )Specific heatcapacity(kJ/kg K)Vapour pressure(kPa)5 0.490 95 961.9 4.213 84.5310 0.981 103 956.2 4.223 112.7315 1.471 110 951.0 4.233 143.2620 1.961 117 945.5 4.243 180.4625 2.452 121 942.3 4.250 204.9830 2.942 126 938.3 4.261 239.3235 3.433 131 934.0 4.272 278.4040 3.923 134 931.4 4.278 304.0545 4.413 138 927.9 4.286 341.3650 4.904 141 925.2 4.292 371.8255 5.394 144 922.5 4.298 404.1860 5.884 147 919.7 4.307 439.0365 6.375 150 916.9 4.320 475.9770 6.865 153 914.2 4.329 515.6675 7.355 155 912.2 4.335 543.4580 7.846 157 910.3 4.341 572.44Storage cylinders are almost always mounted horizontally, the size and shape beingdetermined by site conditions. Diameters up to 4 m are common, with lengths of up to10 m. Loss of heat is reduced as far as possible by insulation, up to 100 mm of glass fibreagainst the vessel being covered in some instances by 50 mm of dense material prior to afinal casing with polished sheet metal. The cradles upon which vessels are mounted, fixed