Solar water heating
Practical Action
These systems are often designed with a storage tank and/or alternative, complementary heat
source. With the latter, a system of pre-heating the liquid is employed to ensure the water
reaches a temperature safe for domestic use, particularly with regard to the risk of legionella
(See Section “Health and Safety – Things to be aware of” for further details). Pre-heating the
liquid is achieved either by an instantaneous water heater or the collector itself.
(CIBSE Solar Heating Design and Installation Guide, 2007)
Connecting to an existing domestic hot water system
Connecting a solar hot water heating system to a conventional hot water storage vessel raises
its own problems, such as a reduced dedicated solar storage capacity or a loss of the ability to
operate the legionella control method of incorporating back-up heating appliances into the
system design. (See Section “Health and Safety – Things to be aware of” for more information
on Legionella).
Selecting and sizing a solar thermal installation
Solar collectors
Although the configuration of the system, i.e. whether it would be classified as direct or
indirect, has an effect on the efficiency of a system, the collector itself generally has a greater
influence.
The two main types of solar collector are flat plate and evacuated tube.
Flat plate These tend to be cheaper but less efficient.
In their simplest form, these collectors are a rectangular frame with a row of pipes
connected at the top and bottom. Cold water enters the system of pipework at the
bottom and travels up and down and across, whilst sandwiched between an
absorber and a plate of glass/plastic to then leave the system at the top of the
frame on the opposite side to the inlet.
Hot water leaves network
of pipes
Glass/Plastic
Network of pipes through which
water passes to heat up
Absorber
Insulation
Cold water enters
network of pipes
Figure 3: Section through a flat plate solar collector (Illustration by Author with reference
made to CIBSE Solar Heating Design and Installation Guide, 2007 & Capturing Solar Energy,
2009)
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