Page 452 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

the same temperature and this negates the need to increase heat emitter size
due to temperature loss. The temperature difference across each flow and
return is usually 12°C to 15°C with a flow temperature of around 80°C.

 Table 7.1 Advantages and disadvantages of the one-pipe system
Advantages Disadvantages
Cheap to install because The water in the system cools as it travels from one heat
there is less pipework emitter to the next, which has the effect of increasing the
KEY TERM involved in the installation heat emitter sizes the further from the boiler they are
when compared to other The system tends to circulate within the main pipework ring;
Boiler cycling: the constant heating systems circulation within the heat emitters can be induced only by
firing up and shutting a difference in the density of the water entering and leaving
down as the system water the system (gravity circulation)
cools slightly. When a Uncontrolled heating of the primary circuit leading to
heating system has reached overheating of the domestic secondary hot water
temperature, the boiler Constant boiler cycling even when the hot water and heating
shuts down on the boiler are up to temperature leads to wastage of fuel energy
thermostat. A few minutes
later the boiler will fire The system is not Building Regulations Document L
up again to top up the compliant and must be updated
temperature as the system The boilers fitted to this type of system are only about 78%
loses heat and, after a few efficient or less
seconds, shuts down again. Condensing-type boilers cannot be fitted to this type of
This wastes a lot of fuel installation because of the gravity circulation needed by the
energy. hot water storage cylinder

An obsolete system of which there are many still in existence. The system
uses a ring circuit of pipework to which both radiator connections are
made. It was usual with this system to fit a circulating pump on the return
Feed and expansion cistern to the boiler. Unlike modern systems, hot water temperature control and
heating temperature control relied upon the boiler thermostat.

22 mm vent pipe

Time clock
15 mm cold
feed pipe

Boiler
28 mm primary
flow
28 mm primary
return

Central heating circulating pump

p Figure 7.3 One-pipe system

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