Book - School of Science and Technology

Water systems ± characteristics 145Table 6.1 Selected properties of waterRe massRe volumeTemperature( C)Absolute vapourpressure(kPa)Specificmass(kg/m 3 )Heatcapacity(kJ/litre K)Specificvolume(litre/kg)Heatcapacity(kJ/litre K)10 1.23 999.7 4.193 1.000 4.19120 2.34 998.2 4.183 1.002 4.17525 3.17 997.0 4.180 1.003 4.16830 4.24 995.6 4.179 1.004 4.16035 5.62 994.0 4.178 1.006 4.15340 7.38 992.2 4.179 1.008 4.14645 9.58 990.2 4.180 1.010 4.13950 12.33 988.0 4.181 1.012 4.13155 15.74 985.7 4.183 1.015 4.12360 19.92 983.2 4.185 1.017 4.11565 25.01 980.5 4.188 1.020 4.10670 31.16 977.7 4.191 1.023 4.09875 38.55 974.9 4.194 1.026 4.08880 47.36 971.8 4.198 1.029 4.08085 57.80 968.6 4.203 1.032 4.07190 70.11 965.3 4.208 1.036 4.06295 84.53 961.9 4.213 1.040 4.052100 101.33 958.3 4.219 1.044 4.043110 143.26 951.0 4.233 1.052 4.026120 198.53 943.1 4.248 1.060 4.006130 270.12 934.8 4.271 1.070 3.992140 361.36 926.1 4.291 1.080 3.973150 475.97 916.9 4.322 1.091 3.961160 618.05 907.4 4.349 1.102 3.947170 792.03 897.3 4.387 1.111 3.930180 1002.68 886.9 4.422 1.128 3.920Table 6.2 Design temperatures for water heating systemsDesign temperatureSystemFlow atwater heater( C)Differential atwater heater(K)Low temperature warm water 40±70 5±10Low temperature hot water 70±95 10±15Medium temperature hot water 95±120 25±35High temperature hot water > 120 45±65situation and condensing boilers or heat pumps fall within the latter. While each of thesepresents a practical and significant source, the problem of utilisation remains.Obviously, not all new buildings are suited to the application of embedded panelheating and it is not a method which may be applied easily in refurbishment of theexisting stock. While it is possible to design systems which are able to use warm waterwith conventional equipment and yet meet a mid-winter demand, these have yet to gainacceptance. There are two practical difficulties in this respect, the first being the significant