Overview of Low Temperature Solar Thermal Energy Conversion Applications

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Overview of Low Temperature Solar Thermal Energy
Conversion Applications
Prepared by
Prof. Dr. A. R. El-Ghalban
Department of Mechanical Engineering
University of Engineering and Technology
Taxila, Pakistan
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Low Temperature Solar Thermal Energy Conversion
Applications

• Low temperature solar thermal systems collect
  solar radiation to heat air and water for
  industrial applications including

• Water heating.

• Domestic Hot Water.
• Industrial and Process Heat.
• Swimming Pool Heating.

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Low Temperature Solar Thermal Energy Conversion
Applications

• Space heating, ventilation and cooling.
• Solar cooking.
• Water desalination.
• Crop drying.
• Power generation.

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Water heating

• Solar water heater systems are a well-tried and
  tested technology.
• They are suitable for both new-build and
  retrofit.
• A system will typically provide 60-70 of
  domestic hot water needs over a year.
• There are many possible designs for a solar water
  heater.

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Components of Solar Water Heaters

• In general, it consists of three main components
• Solar collector, which converts solar radiation
  into useable heat.
• Heat exchanger, pump, controller module, which
  transfers the heat from the solar collector into
  the potable water.
• Storage tank to store the solar heated water.

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Solar Collectors

• There are two types of solar collectors
• Flat plate solar collector.

• Unglazed flat plate solar collector.
• Glazed flat plate solar collector.

• Evacuated tube solar collector.

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Types of water circulating

• Water circulating might be passive and active
  systems.

• Passive systems rely on gravity and the tendency
  for water to naturally circulate as it is heated,
  allowing water or heat-transfer fluid to move
  through the system without pumps.
• Because they contain no electric components,
  passive systems are generally more reliable,
  easier to maintain, and possibly longer-lasting
  than active systems.

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• Advantages of passive solar water heaters
• Passive circuits are that they dont rely on
  electrically powered pumps to circulate the
  heat-transfer fluid and they are relatively cheap.

• Disadvantages of passive solar water heaters
• They require careful planning to optimize
  performance, they are prone to sluggish
  performance and there is a poor control of
  over-heating.
• The hot water storage tank needs locating above
  the collector level

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Active circulation Pumped circulation

• The pump circulates the heat-transfer fluid from
  the collector panels through the heat exchanger
  in the hot water cylinder and back to the solar
  collectors for re-heating.
• The temperature sensors ensure that fluid is only
  circulated when the fluid in the collectors is
  hotter than in the cylinder.

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• Advantages of active circulation

• Integral protection against freezing
• Overheat control
• Heat is delivered from the collector at optimal
  rate
• Greater choice of collector and pipe layout
• Reduces heat loss through pipes

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• Disadvantages of active circulation

• Increased complexity
• Pump requires electricity (though this can be
  alleviated by PV supply)
• More expensive

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Active solar heating circuits

• Primary circuits transfer may be Direct (Open)
  or, the more usual Indirect (closed)

Direct (Open) circuits

• Direct circuits are those that directly heat the
  water that flows from the household taps. They
  are rarely used.
• Advantages of direct circuits
• Simplicity and increased efficiency over indirect
  circuits. through reduction of heat transfer loss.

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• Disadvantages of direct circuits
• They are subject to freezing unless the water is
  drained-back when the pump switches off, which
  puts constraints on the positioning of the
  collectors in relation to the feed tank.
• As new water continually flows through the
  collectors, they can be prone to furring in the
  collector waterways resulting in loss of
  efficiency.
• Pump requires electricity (though this can be
  alleviated by PV supply)
• More expensive

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• Indirect (closed) circuits
• Most circulation systems are indirect. Indirect
  circuits use a separate heat-transfer fluid
  circuit to transfer heat from the collectors to
  the pre-heat cylinder. Their main advantage is
  that they can employ a wide range of materials
  and fluids as part of the circulation. There are
  different types of circulation that can be used

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• Space heating, ventilation and cooling.

• Active space heating.
• Passive space heating and cooling.
• Passive space ventilation.
• Space air conditioning.

• Solar cooking.
• Water desalination.
• Crop drying.
• Power generation.

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Thank you
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Active solar space heating

• Water Space Heating
• Air Space Heating

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Passive Solar Space Heating

• passive solar heating allows the sun to do all
  the work.

• That is, there is no additional mechanical
  assistance.

• In cold climates, south-facing windows designed
  to let the sun's heat in while insulating against
  the cold are ideal.

• In hot and moderate climates, the strategy is to
  admit light while rejecting heat.

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Passive Solar Space Heating

• Passive solar heating system may be direct or
  indirect gain.

• Direct solar gain system

• The sun's heat is stored by the building's
  inherent thermal mass in materials such as
  concrete, stone floor slabs, or masonry
  partitions that hold and slowly release heat.

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Passive Solar Space Heating

• Direct solar gain system

• In this direct gain design - A direct gain design
  with an interior water wall for heat storage. 
  Heat stored in the water wall is radiated into
  the living space at night.

• Diffusing glazing materials. Translucent glazing
  scatters sunlight to all storage surfaces

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Passive Solar Space Heating
Indirect Solar Gain System

• Indirect gain water wall collects and stores heat
  during the day. Heat stored in indirect gain
  water wall is radiated into the living space at
  night.

• Indirect gain Trombe wall stores heat during the
  day. Excess heat is vented to the interior space.
  At night Trombe wall vents are closed and the
  storage wall radiates heat into the interior
  space.

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Passive Solar Space Heating
Indirect isolated Solar Gain System

• Attached greenhouse with vented storage wall.
  Heat is stored in the wall during the day -
  excess heat is vented to the interior space. At
  night the wall vents are closed and stored heat
  is radiated to both the greenhouse and the
  interior space.

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Passive Solar Space Heating
Indirect isolated Solar Gain System

• Heating cycle - Roof pond collects and stores
  heat during the day. At night roof ponds are
  covered and stored heat is radiated into the
  space below.

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Passive Solar Space Cooling

• An indirect gain mass wall can be used to
  significantly increase ventilation rates in
  adjoining spaces.

• An overhang above a south window will shade the
  window completely from early May to mid-August,
  yet allow for winter sun access. Shading devices
  should be sized using the given graphic method.

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Passive Solar Space Cooling

• Roof bonds utilizing cool, clear night-skies can
  provide total cooling. Panels are kept closed
  during the day and opened after dusk to radiate
  out the absorbed day time interior heat.

• An overhang above a south window will shade the
  window completely from early May to mid-August,
  yet allow for winter sun access. Shading devices
  should be sized using the given graphic method

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Passive Solar Space Cooling

• Open pond with water wall - combined systems can
  be devised to provide direct cooling for all
  interior spaces.

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Passive Solar Ventilation

• Thermal chimneys can be constructed in a narrow
  configuration (like a chimney) with an easily
  heated black metal absorber on the inside behind
  a glazed front that can reach high temperatures
  and be insulated from the house.

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Solar Cooking

• Solar cooking and baking are easy passive solar
  energy application. Solar cookers are safe around
  children and provide a great way to learn about
  and use solar energy. Solar cookers are clean,
  convenient, non-polluting and easy on the
  environment.

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Unglazed Flat Plate Solar Collectors

• Low cost
• Low temperature
• Rugged
• Lightweight
• Seasonal pool heating

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Glazed Flat Plate Solar Collectors

• Moderate cost
• Higher temperature operation
• Can operate at mains water pressure
• Heavier and more fragile

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Evacuated Tube Collectors

• Higher cost
• No convection losses
• High temperature
• Cold climates
• Fragile
• Snow is less of a problem
• Installation can be more complicated

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Evacuated Tube Collectors
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Passive solar water heating system

• Easy to install and maintain no moving parts

• Storage tank must be installed above or close to
  collector

• Uses no electricity

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Passive solar water heating system
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Passive solar water heating system
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Active indirect solar heating system
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Active closed solar heating system
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Active closed solar heating system
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Active open solar heating system
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Active solar heating system

• The main components on an active solar water
  heating system are
• Solar collector
• A circulating system
• Storage tank
• Back up heating system
• Control system

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Active space heating system
The system components in an active space heating
application are the same for water heating
with the addition of radiators for space heating
or under floor heating coils or even forced air
systems.
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Active air space heating system
A transpired air collector preheats air for
building ventilation by using a fan to draw fresh
air through the system. Outside (ambient) air
passes through holes in the collector (absorber)
and is heated as it is drawn up the air space
(plenum) between the collector and the south wall
of the building.
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Solar Cocking
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Solar Cocking
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Solar Cocking
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Solar Cocking
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Solar Assisted Air Conditioning
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Solar Assisted Air Conditioning
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Solar Assisted Air Conditioning
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Solar Water Desalination
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Solar Water Desalination
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Solar Water Desalination
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Solar Crop dryer
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Solar Power Generation
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Solar Power Generation
Prototype tower Manzanares, Spain
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Solar Power Generation
The Idea of downdraft tower
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Solar Power Generation
The Idea of Solar Driven ORC