Page 376 - 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

heat pumps. The cylinder contains two heat exchanger coils. The first coil is
used with a conventional fuel source such as gas or oil and this accounts for
70 per cent of the cylinder’s hot water volume. The second coil has 30 per cent
volume dedicated to the renewable energy heat source and is usually situated
in the top third of the cylinder. They are suitable for:
● modern fully pumped heating systems (see Chapter 7)
● both vented and sealed heating systems up to 3.5 bar pressure.
They are supplied with a double thickness of CFC-free polyurethane insulation
and capacities from 130 litres to 300 litres.

p Figure 6.7 Double coil cylinder Open vented indirect (single feed, self-venting type) hot water
storage systems
This system uses a single feed, self-venting indirect cylinder, often referred to
by its trade name: the ‘Primatic’ cylinder. It contains a special heat exchanger,
KEY TERM which uses air entrapment to separate the primary water from the secondary

Single feed, self-venting water.
indirect cylinder: often
referred to as the ‘Primatic’ Hot water draw-off connection
cylinder, which is a trade 1" male thread
name of IMI Ltd. Another
version of this type of Immersion heater connection
cylinder was also available
and may be found in some
existing installations. It was
known as the ‘Aeromatic’. It Primary flow connection
is slightly different from the 1" male thread
Primatic because it has an
air release valve on the side
of the cylinder near the heat
exchanger to bleed air from Primary return connection
the heat exchanger. 1" male thread
Cold feed connection 1" male thread

p Figure 6.8 Single feed, self-venting indirect cylinder

It is fitted in the same way as a direct system, with only one cold feed cistern
in the roof space but, unlike the direct system, it allows a boiler and central
heating to be installed. It does not require a separate feed and expansion
cistern. The heat exchanger works in such a way that the primary and
secondary water are separated by a bubble of air that collects in the heat
exchanger, preventing the waters from mixing. According to the Domestic
Building Services Compliance Guide, these cylinders are no longer allowed for
new or replacement cylinders. A ‘double feed’-type cylinder must be used on
all replacement installations.
A typical open vented indirect (single feed, self-venting type) hot water storage
system utilising gravity circulation is shown in Figure 6.9.

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