Page 484 - 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 heat output, at 450 watts per metre, is quite low, which means that, to be
effective, the skirting heating would need to be at floor level on all walls of the
room to off-set the room heat losses, although the heat coverage is very similar
to that experienced with specialist underfloor heating.
One disadvantage is that efficiency is reduced by dust collecting in the fins.

Mechanical central heating components

Mechanical central heating components are those that do not use electricity
KEY POINT but still play a vital role in helping to ensure the correct and efficient operation
What is balancing a of the system.
central heating system In this section, we will look at the most common of the mechanical components
and what does it and controls used on domestic central heating systems.
involve?
Balancing a system Radiator valves: thermostatic and manual valves
is ensuring an even There is a wide selection of radiator valves available from many different
heat distribution to manufacturers. There are three basic types of radiator valve (thermostatic,
all of the radiators in wheel head and lockshield), as described below.
the system. Water will
always take the line of Thermostatic radiator valves (TRVs)
least resistance and
this means that the These control the temperature of the room by controlling the flow of water
radiators nearer to the through the radiator. They react to air temperature. TRVs have a heat-sensitive
circulating pump will head that contains a cartridge, which is filled with either a liquid, gas or wax,
always get more than and this expands and contracts with heat. As the room heats up, the wax/gas/
their fair share of heat. liquid cartridge expands and pushes down on a pin on the valve body. The pin
This is detrimental to closes and opens the valve as the room heats up or cools down. The valve head
the furthest radiators on
the system and has the has a number of temperature settings to allow a range of room temperatures to
effect of slowing down be selected.
the heating effect. Document L1 of the Building Regulations requires that TRVs are installed on
Balancing is simply new installations to control individual room temperatures, and on all radiators
evening out the heat
distribution by restricting except the radiator where the room thermostat is fitted.
the flow of water to the Most TRVs are bi-directional. This means that they can be fitted on either the
quickest radiators by flow or the return.
simply adjusting the
flow rate through the Wheel head valves
lockshield valves. This
has the effect of slowing These allow manual control of the radiator by being turned on or off. The
the heat circulation valve is turned on by rotating the wheel head anti-clockwise and turned off by
through the quick rotating clockwise.
radiators and increasing
the flow rate to the Lockshield valves
slower, furthest-away These are designed to be operated only by a plumber and not by the
radiators, thus balancing householder. They are adjusted during system balancing to regulate the flow of
the heat distribution
throughout the system. water through the radiator. The lockshield head covers the valve mechanism.
They can be turned off for radiator removal.

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