Figure E1.6 Pump Selection Chart; Kw (Gross); Kw (Nett) - Hamworthy MILBORNE381 Series Design Installation, Commissioning And Operating Instructions

Figure E1.6 - Pump selection
One or more circulating pumps will be required to circulate water around the boilers and heating system. The
pump should be sited to facilitate servicing. It is important that when Milborne boilers are used to replace boilers
on an existing system, the pumps should be checked for performance against the new boiler waterside pressure
loss to ensure that the minimum flow rate can be obtained. It is also important that the existing system be flushed
through twice to remove any loose matter which may have accumulated. If in any doubt regarding the cleanliness
of the system, a coarse filter should be fitted in the return pipework to the boilers
E1.7 Minimum Water Flow Rates
Minimum water flow rates are shown in table at beginning of Appendix E. These flow rates should be maintained
through the boiler at all times whilst the boiler is firing. If the water flow rate is allowed to fall below the minimum
the boiler heat exchanger could fail due to the resultant scale formation. Particular attention should be paid to the
restriction of external flow circuits during periods of low heat demand.
E1.8 Waterside Pressure Drop
The waterside hydraulic resistance (Pressure drop) is given in table at beginning of Appendix E.
E1.9 Water Flow Controls
The Milborne boiler is fitted with an electrical isolating valve, which will shut off circulation through the heat
exchanger 5 minutes after the boiler has ceased firing.
Any external mixing valve / shunt pump or similar controls MUST always ensure that the minimum water flow rate
as given in table at beginning of Appendix E is maintained. As a precaution, the Milborne boiler is fitted with a flow
switch. The flow switch is designed to operate such that the boiler will shut down if insufficient flow occurs.
E1.10 Frost Protection
Consideration should be given to fitting an optional outside air sensor, to provide the necessary frost protection.
E1.11 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.
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.
HAMWORTHY HEATING LTD
No. of Boilers System Load
1 37.5
1
2 112.5
2 150
3 187.5
3 225
4 262.5
4 300
65
MILBORNE
Pump Model
kW
Biral MX13-1
75 Biral LX403
Biral LX403
Biral LX403
Biral LX503
Biral LX503
Biral LX504
Biral LX504
System Load Pump Model
kW
50 Biral M15-1
100 Biral HX501-1
150 Biral HX501-1
200 Biral HX501-1
250 Biral HX501-1
300 Biral HX501-1
350 Biral HX502-1
400 Biral HX502-1
500001130/J