Page 397 - 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

The components of a solar thermal hot water system

Solar hot water systems require certain components, some of them specialised,
to enable the system to work effectively. These are as follows.
● Collector: these can either be:
● Flat-plate collectors: these are the simplest form of collector. They
are tubes that run through shallow metal boxes with a front of thick
black glass to trap the heat in a greenhouse effect. As the heating fluid
is pumped through the tubes, it collects the Sun’s heat, which is then
pumped through the heat exchanger where the heat is transferred to
the water inside the storage cylinder.
● Evacuated tubes: these are a little more complicated but, in essence,
are tubes that have a vacuum inside. These collect the heat from the
Sun, passing it to a manifold through which the heating fluid runs. The
heated fluid is then pumped to the coil in a similar way to the flat plate
collector.
● Hot water storage cylinder to store the hot water. The cylinder should
contain two coils: one to transfer the heat from the solar collector and the
other to transfer the heat from a conventional boiler/water heater.
● Heat exchanger, usually in the form of a coil that transfers the heat from
the solar collector to the water stored in the hot water storage cylinder.
● Circulating pump to circulate the hot fluid from the solar collector to the
heat exchanger and back.
● Control system: the control system is used to prevent freezing fluid being
circulated through the coil during the winter or at night when the Sun goes
down. A typical control system will incorporate a pump, flow meter, pressure
gauge, a thermometer and a thermostat.

How solar thermal panels work

1 The Sun heats the fluid in the solar collector.
2 When the thermostat senses that the panel is 6°C above the temperature
inside the hot water storage cylinder, the circulation pump will start to run.
3 The heated fluid is then pumped from the solar collector to the heat
exchanger coil in the hot water storage cylinder.
4 Here, the heated fluid gives off its heat into the cylinder of stored water
before returning to the collector to be reheated. This process continues until
the hot water storage cylinder is at the required temperature.

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