Page 421 - 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 With group shower installations, it is not unusual to see pipe runs in excess
of 10 m. Pipework runs of this length carry an unacceptable Legionella risk.
These situations can be dealt with by:
● careful monitoring of the water at the showerheads and appropriate
treatment should Legionella be detected
● regular very hot water disinfection when the system is not in use.

Typical group installations are those listed below.
● Group showers: with the correct-sized TMV, a number of shower outlets
may be served at a temperature of between 38°C and 40°C. For safety
reasons, the temperature must not exceed 43°C.
● Washbasins: rows of washbasins may be served from a single TMV.
Temperatures of between 38°C and 40°C are typical, but should not
exceed 43°C for safety reasons.

Wash basins

Isolation valve
Thermostatic mixing valve

Isolation valve

p Figure 6.53 A group thermostatic mixing valve installation

Centralised mixing

Centralised mixing is very similar to group mixing but occurs when there are
groups of different hot water appliances to be served from a single TMV. The
recommendations listed below should be followed.
● If the mixed water is recirculated within the Legionella growth temperature
range, then anti-Legionella precautions similar to those recommended for
group mixing will need to be implemented.
● If the mixed water is recirculated at about Legionella growth temperature
regimes, then the recommendations for single TMV installations are appropriate.
● The operation of any one outlet should not affect other outlets.

The types of thermostatic mixing valve

Thermostatic mixing valves are certificated under a third-party certification
scheme set up and administrated by BuildCert. Under the BuildCert scheme,
thermostatic mixing valves are certificated and approved for use depending on
their application. They are divided into two groups: TMV2 and TMV3. 409

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