Solar Water Heating

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SOLAR HEATING
Solar energy can be used for
• Solar water heating
• Solar space heating
• Solar pool heating
Solar Water Heating
Active solar water heaters
Active solar water heaters rely on electric
pumps, and controllers to circulate water.
Active solar water-heating systems:
• Direct-circulation systems
• Indirect-circulation systems
Passive solar water heaters
The two most popular types of passive
systems are:
– Thermosyphon systems
– Integrated solar collectors
Solar Water Heating Applications
• Swimming pools
• Hot tubs and spas
• Domestic hot water
– Offices, malls, hotels, motels
– Large laundries and kitchens
– Facilities in remote areas
– Jails, hospitals and dormitories
Solar Water Heating Applications
• Process hot water
– Food processing, hot water cleanup
– Hot water rinses
– Pre-heat boiler makeup water
Value of Solar Water Heating
• Solar water heating systems
– Directly substitute renewable energy for
conventional energy
– Reduce the amount of heat that must be
provided by conventional water heating
– Reduce the use of electricity or fossil fuels
by as much as 80%.
Status of Solar Water Heating
• Today’s solar water heating systems are well
proven and reliable when correctly matched
to climate and load.
• Solar water heating systems are most likely to
be cost effective for facilities with expensive
energy, or facilities with large hot water
requirements.
Types of Collectors
• Low temperature – to 32ºC
– Unglazed absorbers
• Mid temperature – to 70ºC
– Glazed flat plate collectors
– Integrated collector systems (ICS),
thermosyphon, antifreeze, drainback
• High temperature
– Evacuated tube – to 175ºC
– Parabolic trough – to 300ºC
Absorber plates
There are various designs
• Bonded sheet design
• Tubes soldered or brazed to the plate
• Tubes fastened by clips, clamps or twisted
wires.
Flat-plate Collector
Exploded view of flat plate collector
Passive, Indirect Thermosyphon System
Evacuated Tube Collector
Evacuated-tube collector
http://www1.eere.energy.gov/solar/printable_versions/sh_basics_collectors.html
Two Main Types of Passive Systems
• Integrated Collector Systems (ICS)
– store the water in the collector itself
• Thermosyphon Systems
– have a separate storage tank directly above
the collector
Two Main Types of Passive Systems
(cont.)
• Good insulation of the collector and/or tank
helps prevent heat loss at night, and helps
prevent freezing.
• Connection pipes are the most critical parts for
concern over freezing. Good insulation is
necessary, but still does not totally solve the
problem.
• The most frequently used systems for large
facilities – antifreeze systems – are active,
indirect systems.
• System configurations may utilize one storage
tank or two tanks.
– Single tank – conventional h/w heater
– Single tank – wrap-around heat exchanger
– Two tank – convection flow
• The most cost-effective size for a solar water
heating system is typically to meet the full
summer demand, but to meet only 2/3 of the
year-round demand.
• Meeting the full winter demand with the reduced
solar resource is very costly.
• Experience with commercial buildings seems to
show that maximum cost-effectiveness occurs at
a solar supply of about 50% of the year-round
demand.
Efficiency Aspects of Solar Water Heating
• Colder water supply temperatures increase
system efficiency, since the fluid being heated
loses less heat to the surrounding air until it
reaches higher temperatures.
• Colder air temperatures reduce system
efficiency by increasing the loss of heat from
the collectors to the air.
• Potential for system freezing is a serious
problem, and many solutions result in
reducing system efficiency.
Solar water heating in Cyprus
• A few islands are using solar water
heaters on a very large scale (Barbados
and Cyprus).
• Cyprus is a leading country in installed
solar collectors per capita - 0.86 m² of
solar collector per capita.
• Solar water heaters were first fabricated
and installed in 1960.
Solar water heating in Cyprus
• The majority of solar domestic hot water
heaters, put up on individual houses are of
the thermosyphon type.
• Two solar collectors, with a total glazed
area of 3 square meters, are connected in
series to a hot water tank, placed at a
height, just above the top of collectors.
• The hot water tank is also fitted with an
auxiliary electric 3 kW heater.
Economics of Solar water heating
in Cyprus
• The average daily solar radiation falling on a
collector installed at an angle of 35° to the
horizontal in Cyprus is 5.4 kWh per m2.
• the annual savings per square meter of installed
collector area in Cyprus are 550 kWh.
• The total cost required to install a solar water
heating system on a house is around US$ 1000.
• The payback period is estimated to be 4 years
Conservation
• Conservation is usually the most cost-effective
way to reduce water-heating bills.
- For example, a low-flow showerhead saves
200 kWh of electrical energy (=USD 40).
Solar space heating and cooling
Solar energy can heat and cool the air
Solar space heating systems:
• Passive
• Active
• Combination
Air Heating
• Air or other gases can be heated with FPC
• The principal requirement is a large
contact area between plate and air
• Extended surfaces are used to counteract
the low heat transfer coefficients between
metal and air.
• Metal or fabric matrices or corrugated
metal sheets improve performance
Solar air collector
Air flat-plate collectors are used for space heating.
http://www1.eere.energy.gov/solar/printable_versions/sh_basics_collectors.html
Transpired air collectors
• A transpired air collector preheats air for building
ventilation by using a fan to draw fresh air
through the system.
• They are very efficient
• No glazing
• Transpired air collectors are recommended for
industrial or commercial buildings with large
ventilation requirements.
Air heating
Transpired air collectors
http://www.eere.energy.gov/de/transpired_air.html
Winter operation
Summer operation
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