Book - School of Science and Technology

592 Hot water supply systemsadequate supply to an elevated cistern. It is then necessary to provide suitable cold waterstorage at a low level and to use this as a supply to some form of mechanical pressurisationequipment. The more suitable types are not unlike those described for heatingsystems in Chapter 8 (p. 213) and, for simplicity, pump pressurisation as illustrated inFigure 20.26 has much to commend it.The new Model Water Byelaws require that all cisterns be provided with rigid, closefittingcovers which exclude light and that they should have properly made insect screensat all openings: where pipe connections penetrate the cover, the holes should be drilledrather than, as is often the case with present covers or insulation, apparently torn out bywolves.Unvented hot water systemsPast editions of Water Byelaws have included requirements which have inhibited designdevelopment of unventilated storage type hot water systems in the British Isles. Directconnection to a mains pressure service pipe has not been permitted and provision of anopen vent to atmosphere has been mandatory. The use of the bubble-top calorifiers whichhave been described earlier was generally confined to sites protected by Crown immunity.The 1986±9 edition of the Byelaws no longer proposes that there should be a prohibitionof connection to mains pressure service pipes and, as a result, water companies haverelaxed their previous attitudes and the use of unventilated hot water storage systemsbecame acceptable. The requirement and guidance on the unventilated units and theirinstallation are defined in the BuildingRegulations G3.These regulations cover unventilated systems with a capacity of:. A system up to 500 litres and a power input not exceeding45 kW.. A system over 500 litres or havinga heat input of over 45 kW.It defines that the unventilated storage units of 500 litres capacity and not exceeding45 kW are to be in the form of proprietary units approved by a suitable certifyingbody.A system of over 500 litres and 45 kW are to be individually designed for specificapplications and incorporate all the necessary design and safety features cited in theBuilding Regulations G3. The design of the units is to be undertaken by an appropriatelyqualified engineer. It is also a requirement of these Regulations and also of the WaterByelaws that these unventilated systems can only be fitted by a suitably trained andcertified installer.With an unventilated systems with a capacity of 15 litres or less the BuildingRegulationsare not applicable.Control packagesThe safety devices defined in the Regulations are shown in Figure 20.27 and are listedbelow:Protective. A thermostat to control the energy source. This should not be set at above 75 C andpreferably at 5 K lower.. A temperature operated cut-out actingon the energy source. This must be factory set at85 C and be of the manual reset type.