A typical Domestic Hot water system (with the exception of combination boilers) consists of a boiler, which heats water that in turn, is pumped around a coil in the hot water cylinder and if needed, through the radiators for heating. The water stored within the cylinder then becomes hot for use at the hot taps within the house. See the diagram below.
A solar system works in a very similar way to this. A twin coil cylinder is generally used in place of a traditional single-coil cylinder. The bottom coil is for the solar circuit (the fluid heated in the solar panels), and the upper coil is used for the traditional boiler-heated circuit.
As you can see from the diagram above, the whole cylinder volume can be heated through solar. However the boiler is only able to heat the upper part of the cylinder.
The reason for this is very simple....heat rises. The hottest
part of a hot water cylinder is always the top. Cylinders are affected
by a process called 'thermal stratification.' In layman's terms, the
heat within the water 'stratifies' or 'layers' with the hottest layer at
the top of the cylinder. This is why the hot water draw-off points on
hot water cylinders are always at the top.
The challenge that this twin-coil system presents is that you
have to bear in mind that in Winter, when the amount of solar gain to be
had is very low, you will be relying on the boiler for your hot water,
so as a general rule of thumb your new twin coil cylinder will need to
be between 1 and a half and 2 times as big as your hot water needs.
There are generally 2 types of system to consider when installing solar panels -
drainback or pressurised.
All solar thermal systems are controlled by a differential temperature controller
The simplest way of integrating a solar system into your existing system
is by removing your single coil hot water cylinder, and replacing it
twin coil solar cylinder
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