Page 403 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 6 Hot water systems

l Lockshield gate valves (components 7 and 8 on the drawing) are provided
to balance the system to ensure even circulation throughout the secondary
water system.
● The secondary circulation system, shunt pumps and thermostats are
controlled through a control box (component 1 on the drawing).

1

2
6

4
5 8
3

7

p Figure 6.38 Secondary circulation on a large domestic open vented hot water storage installation

Here are some points to remember regarding large centralised hot water systems:
● The pipework should be carefully designed to prevent dead legs as this is a
major concern with regard to Legionella pneumophila.
● The hot water storage vessel should be capable of being heated to 70°C,
again to kill any Legionella that may be present.
l There should be easy access for draining, cleaning, inspection and
maintenance.
● If a shunt pump is installed, the storage vessel should be insulated on its
underside to prevent excessive heat loss.

The use of trace heating instead of secondary
circulation

Electric trace heating uses an electric cable that forms a heating element. It
is positioned directly in contact with the pipe along the whole length of the
pipe. The pipe is then covered in thermal insulation. The heat generated by the
element keeps the pipe at a specific temperature.

The operation of the trace heating element should be timed to a period when
the hot water system is in most use, i.e. early in the morning and in the evening.
If the pipe is well insulated and installed with a timer, the amount of energy
usage will be minimal.
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