CPD Programme
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Members of the Chartered Institution of be used by any reader. It is organised jointly
Building Services Engineers (CIBSE) and other by CIBSE Journal and London South Bank
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Development (CPD) means the systematic record CPD activities in accordance with
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Council (UK). the information they contain remains current.
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Solar thermal – solar hot water heating
Regulatory and advisory requirements for the application of LZC (low
and zero carbon) technologies in buildings, and increased public demand
for higher environmental performance, have contributed to a signifi cant
increase in the adoption of solar thermal water heating for the commercial
sector as one of the technologies applied to reduce carbon dioxide
emissions – particularly where hot water demand is the dominant load
This CPD article will cover some of the issues can maximise the capture of this power and Sponsored by:
surrounding the design and selection of translate 60 per cent of it into useful energy
commercial solar thermal solutions. for hot water systems.
Roof-mounted solar collectors with high
U
sing solar energy to heat water has transmission and absorption efficiencies
been commercially available in typically capture energy from incident solar
the UK in a variety of forms since irradiation, passing the heat into a transfer
the mid 1970s. The UK can offer fluid – usually a pre-prepared mixture of
a good climate for solar thermal solutions, 60 per cent water and 40 per cent glycol to
benefiting from around 60 per cent of the prevent freezing during periods of low outdoor
solar energy received at the equator, and the air temperatures. Different specifi cations of
UK is comparable with the European countries heat transfer fl uid are available for different
better known for their solar applications (see types of solar collectors. The heat transfer fl uid
Figure 1). is usually pumped through a coil located in the
In the UK the average annual available lower section of an unvented indirect cylinder
solar irradiation varies between around 1,200 and, in so doing, heats the stored water that
kWh/m
2
on the south coast of England and would normally be used for domestic hot
up to 900 kWh/m
2
in Scotland – only 55 per water.
cent of the sun’s light is visible, the balance A well-designed commercial solar thermal
being ultraviolet and infra-red, and only system may be able to satisfy around 30 to 40 per
© Compiled by Yan Evans,
around 25 per cent of the sunlight is direct, cent of the annual hot water load, known as the
technical director at Baxi
Commercial Division, and
with the remainder being diffuse. A properly solar fraction (SF). To try and achieve a higher
Professor Tim Dwyer, London
designed and installed solar thermal system solar fraction may lead to solar thermal system >
South Bank University
www.cibsejournal.com February 2009 CIBSE Journal 73
CIBSEfeb09pp73-76 CPD pages•.indd 73 5/2/09 14:40:29
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