Page 396 - 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

Inside the unit are two heat exchangers, which the mains cold water passes
through, and a small expansion chamber. The expansion chamber allows for
the small amount of expansion of the secondary water. The primary water can
reach temperatures of up to 82°C, which can, potentially, be transferred into
the secondary water. Because of this, an adjustable thermostatic mixing valve
blends the secondary hot water with mains cold water so that the water does
not exceed 60°C.

Gas- or oil-fired combined primary storage units

These are very similar in design to thermal stores and work in exactly the
same way, in that cold water from the mains supply is passed through a heat
exchanger. The difference here is that the unit has its own heat source, in the
form of a gas burner, to heat the primary water, eliminating the need for a
separate boiler.

Adjustable
thermostatic
mixing valve
Central
heating flow Hot water oulet

Heat exchanger coiled
around the flue pipe

Central
heating return
Mains cold
water supply
Gas burner
p Figure 6.30 Combined primary storage unit

Solar thermal systems

A solar water heating system uses roof-mounted solar collectors aligned to
face south to capture the heat generated by the Sun. The solar collector can
be either a series of vacuum tubes or a flat panel, both of which are filled with
a heating fluid (usually a mixture of water and anti-freeze). On average during
2
the summer months, 1 m of solar panel will deliver around 1 kW of energy,
therefore 1 m is needed for every occupant of the dwelling, with a minimum
2
recommended area of 2.5 m . This will supply about 80 per cent of the hot
2
water demand during the summer and around 20 per cent over the winter
season, an average of 60 per cent over the whole year. A conventional gas or
oil boiler, or an electric immersion heater, will be required for the remaining
40 per cent heating requirement or in case the solar system should fail.

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