Home > Services > solar Hot Water Heating
Solar Water Heating
By John Herbert | DIRECTOR
Capturing solar radiation from the sun is on of the most cost
effective methods to reduce your energy bills - solar energy from the
sun is free!
Sun powered your water heating needs, providing trouble free operation
for many years, whilst dramatically reduce your energy bills.
Solar water heaters are not suitable for every location,
before considering a solar thermal system consult the experts. Remember
too that lower utility bills provides indirect benefits - reducing
pollution and your environmental footprint.
Operation
The radiant energy from the sun harnessed can provide free hot
water for your home or business, significantly reducing your energy
bills and helping the environment too.
During the sunshine hours, cold water is
circulated and heated within a
solar collector panel, typically installed on the roof.
Solar energy strikes the earth at a constant
rate, approximately 1Kw
per square metre, this energy can be absorbed, captured, and
transferred to heat your hot water.
The
graph (above) indicates the monthly average solar energy
and accumulated hours of sunshine recorded by the Hong Kong Observatory
at Kings Park during 2003.
The graph indicates that the monthly average incident solar
radiation exceeds 10 MJ / square metre, providing a year around energy
source. As expected the summer months show the annual peak.
Solar Collection
If the value solar energy is to be captured, effect collectors are required. There are two basic types of solar collectors
Most collectors have a standard warrantee from the manufacturer, for up to 15 years - providing free hot water for years and years.
Flat Plat Solar Collectors
The flat plate collectors comprise water channels or piping,
bonded to a large flat absorption plate, thermal insulation beneath and
covered with glass or polycarbonate.
The absorption plate and water channels exposed
to the sun are finished
with a selective coating or paint to enhance solar radiation absorption
properties.
Flat plate collectors are less expensive than
evacuated tube and the
design being very robust. However, the absorbed energy is
easily released, re-transmitted due to high emissivity coefficient -
significantly lower efficiency than evacuated tube collectors.
Evacuated Tube
To overcome the deficiency of flat plate collectors, namely
the energy losses, alternate solutions were sought to prevent
re-transmission of the captured energy.
The evacuated tube collector evolved, using the
same principal as a
flask, incorporating a vacuum to minimise energy losses.
Therefore, radiant energy from the sun still
can be readily absorbed
with a vacuum preventing convective and conductive losses.
The
tube is constructed from two glass concentric glass tubes,
with a vacuum space. Typically, borosilicate glass is used for
toughness and mitigating potential weather damage. Most collector
designs allow individual tube removal on site for maintenance
inspection or replacement of damaged tube.
With conduction and convection losses
minimised, a selective coating is
applied internally to restrict radiation losses. Over the years,
evacuated tubes have been continuously developed increasing
efficiencies and have been manufactured for the mass market. Different
manufacturer's offer variants citing different selective surfaces,
connection details. etc.
There are two basic types of evacuated tube -
Wet and Dry.
Wet Type Evacuated Tube
The wet type evacuate tube type, as one might expect, water is
circulated inside the core. Where properly mounted, at an angle,
thermo-syphon effect circulates water. This tube type is most often
used in conjunction with a high level storage tank.
Preventative measures and maintenance are
required to deal with, and
prevent accumulation of debris at the base of the tubes.
Modern wet type evacuated tubes are very
efficient, with absorption
coefficient between 0.94-0.96 and low emissivity typically between
0.04-0.06.
Dry Type Evacuated Tube
A variant of the classic evacuated tube, uses basically same
principle, except an internal heat pipe is fitted to transfer the heat
energy from the tube area to a common water filled header. Some
manufacturers offer models with heat pipes fitted with extended heat
transfer surfaces, others offer U shaped heat pipe tubing.
Without water circulating inside the tube, the
risk of water pressure
damage and debris accumulation at the base is averted.
About the Author
Mr John Herbert is the Managing Director at Kelcroft. He was educated and trained in the United Kingdom, he has managed and engineered solutions for more than twenty years, the last twelve years here in Asia. An international designer, designed solutions across three continents, whilst retaining a litigation free record.
Further information
Call Kelcroft today - (852) 2335 9830 and start saving money
tomorrow.