Docstoc

Introduction to Solar Water Heating

Document Sample
Introduction to Solar Water Heating Powered By Docstoc
					Introduction to Solar Water
          Heating
         Solar Water Heating
• South Africa’s solar radiation is comparatively
  high – 6500 to 8000 MJ/m2
• Roof-mounted solar collector absorbs incident
  radiation energy and heats a fluid/water
• Fluid/water circulates to geyser to heat geyser
  water
• Typical hot water temperature is 50oC to 75oC
Factors Affecting Solar Performance
•   Orientation of collectors
•   Environmental temperature
•   Clouds, rain, wind
•   Shadows
•   Size of collectors
•   System thermal conversion efficiency
•   Circulation
•   Freezing
                   Geyser Energy Management
                                  Rate of Geyser Heat Loss




•   Heat Loss Control
     –   Decrease geyser heat loss with a geyser blanket
     –   Insulate the first 0.5 m of hot water pipe extending from the geyser with insulation material

•   Geyser control
     –   Reduce geyser temperature to 50oC because heat loss is lower when geyser is cooler
     –   Turn geyser off when away for long periods

•   Timers
     –   Use a timer to automatically turn geyser off during certain hours, such as during the night, in order to save
         more energy
Natural Convection vs Forced
         Circulation
 • Natural convection
    – Geyser must be located above collectors
    – Hot water will rise, displacing cooler
      water and creating circulation
    – Prone to circulation problems
 • Forced circulation
    – Geyser can be below collector level
    – Circulation provided by means of a
      pump
    – Pump control can be by electronic
      differential controller or photovoltaic
      panel
    – Pump displaces air locks for better
      circulation
                      Indirect System
– Glycol antifreeze fluid circulates
  through collectors and geyser
– Geyser is a special “solar geyser” with
                                                            Glycol
  integrated heat exchanger                                 solution
                                                                       Inlet from
– Glycol transfers heat to geyser water                                collector




                                            Heat transfer


                             Geyser water




                                                                        Outlet to
                                                                        collector


                   Figure : Geyser incorporating jacket-type heat exchanger
                            Direct System
                              Hot water supply
                              to house

                                                 – Geyser water is circulated
                                                   through collectors and heated
Cold water
                                                   directly
supply to geyser                                 – Freeze protection using anti-
                   geyser                          freeze valve



                                                   Anti-freeze valve


                                                 – Anti-freeze valve opens when
                                                   temperature reaches 3oC and
                                                   circulates warm water through
                                                   collectors
                                                 – Anti-freeze valve requires
                                                   water pressure to operate
 Close-Coupled vs In-Roof
        Installation



• Close-coupled            • In-roof
   – Easier installation      – Geyser installation position
   – Geyser visible             high in roof cavity
   – Roof may need            – Collector position low on roof
     reinforcement            – Geyser invisible
                              – More prone to circulation
                                problems
            Direct System: Retrofit
– Uses existing geyser – cost and installation time advantage
– Forced (pumped) circulation

             Cold supply inlet                              Hot inlet from
                                                            collector



                                 2-port
                                 valves

                                                                             Hot water
                                                                             supply to house


Cold to
collector                                 Existing geyser
        Direct System: Low Pressure
                                  Cold water supply
– Low pressure hot water supply   to tank
  only
– Suitable for farms and rural                        Ball valve level   Hot water supply
  areas not connected to                              controlled hot     to house
  municipal water supply                              water tank

– Prone to freeze damage
– Low cost – from R4000
               Vacuum Tube                                           Water header tube


                Collectors


– Heat can not transfer by                   Glass outer tube wall

  convection through vacuum
  gap                                        Glass inner tube wall

– Less absorption efficiency per
                                             Space with vacuum
  unit area than flat plate
  collectors
                                             Copper water tubes
– Low heat loss
– Appropriate for cold climates
  where heat loss is high
– Higher cost
                                   Figure : Vacuum tube cross-section (direct type)
  Comparison: Indirect vs Direct
            System
Indirect System                       Direct System
• Advantages                          • Advantages
   – Freeze proof due to                 – High efficiency
     circulation fluid                   – Self-flushing – maintenance
                                            free
• Disadvantages                          – Self-bleeding – no circulation
   – Lower efficiency – uses more           problems
      collector area to compensate
                                      • Disadvantages
   – Requires periodic flushing and
      fluid replacement                  – Prone to freezing – can
   – Requires solar geyser                  burst collector pipes
   – Prone to circulation problems       – Complex electronic pump
      such as caused by air bubbles         control
   – Expensive
              SunScience System
Description
• Pumped System
   – Forced flow direct system
   – Photovoltaic panel – operates
     pump when sun shines
• Slimline Collector
   – Patented design                 X-Connector
                                     (pump &
• X-Connector                        connector unit)
   – Fits to any existing geyser
     (including industrial tanks)
   – No draining of geyser for
     installation
   – Patented design
                 SunScience System
Advantages

• Installation
    – Light and safe to install
    – Three part installation
      1 Fit X-Connector on geyser
      2 Install collector and PV panel on roof
      3 Connect two collector pipes and cable to X-Connector
    – No interference with existing geyser

• Reliability
    – Expected lifetime 20+ years
    – Maintenance free
    – Retains geyser guarantee and insurance
• Environmental effects
   – Developed and manufactured in South Africa
   – Uses locally produced glass, aluminium sheets and extrusions
   – Minimal importation, overseas shipping and associated carbon
     generation

• Use of local labour
   – South African labour and conditions of employment adhered to
   – Minimal use of internationally sourced components
   – SABS approved components
            Conclusion
– A wide range of different types of solar
  systems are available
– Careful consideration should be taken of
  entire system costs, installation time,
  maintenance and environmental effects

– The patented SunScience system
  incorporates innovations to ensure a
  dependable and cost effective system

				
DOCUMENT INFO