Book - School of Science and Technology

Local systems 571For applications where larger storage or heating capacities are necessary, or where acombination unit cannot be fitted high enough above the draw-off point, vented pressuretype equipment is used, as shown in Figure 20.9. All vented pressure type units require acold water supply from a remote storage cistern and an open vent. Storage volumes coverthe range 70±300 litre with heater element capacities to suit.3 121 Air gap for water expansion1211172 Float baffle for maintaining air gap3 Hot water outlet4 Stainless steel cylinder5 Cold feed inlet6 Support plinth7 Primary flow48 Primary return9 Indirect primary heating coil14810 Cold feed inlet baffle11 Plastic coated outer casing1312 Moulded top91813 Sealing grommets to pipework14 Thermal insulation151615 Capacity label16 Immersion heater17 Temperature and pressurerelief valve18 Thermal controls1710756(a)Figure 20.10 (a) Unventilated storage heater with internal air gap (Heatrae Sadia)