Ideal Boilers Concord CXD 40-100 Installation & Servicing Manual

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Ideal Boilers Concord CXD 40-100 Installation & Servicing Manual Manual pdf 7 page image

7Concord CXD - InstallationParticular reference should be made to BS. 6644: Section 2;Subsection 10 and Guidance note PM5 "Automatically controlledsteam and hot water boilers" published by the Health and SafetyExecutive.The information and guidance given below is not intended tooverride any requirements of either of the above publications orthe requirements of the local authority, gas or water undertakings.Other British Standards applicable are BS.5422 & BS.6700.The information provided is based on the following assumptions:1. An independent open vent/safety pipe connection is made tothe redundant boiler flow tapping or is positioned immediatelyafter the system flow pipe connection to the header, as shown.2. An independent cold feed/expansion pipe connection is madeto the redundant boiler return tapping. Cold feed/expansionpipe connections made to the pumped system return will resultin an increase in the static head requirement, caused by theadditional resistance of the distributor tube. Surging may alsoincrease.3. The maximum flow rate through the boiler is based on atemperature difference or 11°C at full boiler output and thecirculating pump is positioned in the flow to the system.4. The boiler is at the highest point of circulation in the system.Systems designed to rise above the boiler flow tappings willautomatically require a minimum static head higher than thatshown.5. The position of the open vent/safety pipe above the expansioncistern water level is given as a guide only. The final positionwill depend upon the particular characteristics of the system.Pumping over of water into the expansion cistern must beavoided.GENERALNote A.This minimum height must be increased, ifnecessary, to comply with the minimum headrequired by the pump manufacturer in order toavoid cavitation.Note B.This diagram does not show safety valves, waterflow switches, etc., necessary for the safe operationof the system.PUMP POSITIONSWhenever practically possible the circulating pump(s) should bepositioned so that it pressurises the system being served. Thevertical distance between the pump(s) and any cold feed andexpansion cistern MUST comply with the pump manufacturersrequirements in order to avoid cavitation. These requirementsoverride the information given in Frame 3 if the static headrequired for the pump(s) exceeds that required for the boiler.The wiring diagrams in Frames 16,17 &18 illustrate the controlmethods for achieving the above.3. Pump selection should take account of the hydraulic resistancegiven in Graph 2.MINIMUM FLOW OF WATER - Refer to Table 5The system design must provide for an adequate flow ratethrough the boiler at all times when the boiler is firing. Theminimum flow rate should correspond to a temperaturedifference across the boiler flow and return of 35 oC (63 oF),assessed at catalogue rating.WATER TREATMENT FOR HOT WATER ANDHEATING BOILERSThere is a basic need to treat the water contained in all heatingand indirect water systems, particularly open vented systems. It isassumed, incorrectly, that because boilers are operating inconjunction with what is apparently a closed circuit an open ventedsystem will not, under normal circumstances, allow damage orloss of efficiency due to hardness salts and corrosion once theinitial charge of water has been heated up a few times.1mm of lime reduces the heat transfer from metal to water by10%.In practice the deposition of these salts is liable to cause noisesfrom the boiler body or even premature boiler failure. Corrosionand the formation of black iron oxide sludge will ultimately resultin premature radiator failure.Open vented systems are not completely sealed from theTable 5 - Flow rates for fully pumped systemsBoiler Minimum flow rates for atemperature difference of 35 oC (63 o F)l/s g.p.m.CXD 40 0.28 3.7CXD 50 0.34 4.5CXD 60 0.41 5.4CXD 70 0.48 6.3CXD 80 0.55 7.3CXD 90 0.62 8.2CXD100 0.68 93 OPEN VENTED SYSTEMS - Minimum static head requirements