HAMWORTHY HEATING LTD
49
Wessex ModuMax
mk3
Boilers
500001308/C
E1.13 Unvented Systems
Refer to Figure E1.1.1 on opposite page for typical layout of an unvented (Pressurised) Hot Water System. For
system design refer to BS 7074 Part 2. In order to correctly size a pressurisation unit for any heating system the
following parameters are required.
1)
Static height of highest component in system (metres)
2)
System volume. If this is not known, a general rule of thumb of 10litres/kW of installed boiler power
can be used.
3)
Maximum flow temperature (°C)
4)
Maximum system hot working pressure, generally given in bar gauge.
From the parameters given, Hamworthy Heating can size the pressurisation unit and also the expansion vessel
required.
Care must be taken in sizing expansion vessels to ensure maximum acceptance factors are not exceeded.
Normally manufacturers of vessels impose a limit of 0.5. This value must not be exceeded at any time during the
operation of the boiler, this includes the over pressure condition should a safety valve lift.
Consideration should also be given to sizing of the safety valve(s) in the system. Refer to BS 6759: Part 1 for
further information and to BS 6880: Part 1 for design considerations.