Heat gain and loss calculation for a Solar Cooker

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Heat gain and loss calculation for a Solar
Cooker

• Presented by
• Abdulaziz Barkat
• Shaheen Alshaheen

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Objectives

• Advantage of solar cooker
• Purpose
• Heat Principles
• Box cooker calculation
• Heat gain
• Heat reflection calculation
• Heat loss
• Some design Factors
• Conclusion

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Advantage of solar cooker

• Solar cooking can save you time, work and fuel,
  it is also environmentally friendly.
• Smoke free cooking and stirring of food is not
  required.
• Each solar cooker in sunny climates can save one
  ton of wood per year.
• Solar Cookers help two of the worlds most
  pressing problems
• A growing shortage of cooking fuels
• the scourge of water-borne diseases.

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Purpose Project

• Helps to calculate design parameters for solar
  cooker/oven
• Also, summarize the basic principles that are
  used in the design of solar box cookers
• heat gain,
• heat loss
• heat storage

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Heat Principles

• The purpose is to heat things up
• (cook food and purify water)
• Both direct and indirect reflected turns to heat
• This heat input causes the temperature inside of
  the solar box cooker to rise until the heat loss
  of the cooker is equal to the solar heat gain

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Box cooker calculation

• Box window area 2 feet x 2 feet 4 square feet
• Solar flux 700 watts/square meter (variable)
• Heat gain solar flux x area x transmittance x
  hours of operation Heat gain 700 x 4 x 0.75 x 4
  8.4 KW/Hr
• Effective heat gain heat gain x efficiency
  (Since heat losses are there by side walls,
  bottom area /plastic glazing or window
• take efficiency 55
• Net heat gain 8.4 x 0.55 4.62 KW/Hr

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Heat gain

• Once light is absorbed by materials within the
  enclosure, it is transformed into longer
  wavelength heat energy
• The more directly the glass faces the sun, the
  greater the solar heat gain

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Heat reflection calculation

• Most solar ovens have one or more reflectors
• Find total area of reflectors
• For 2 reflectors of each 2 Sq feet.
• Total area 4 square
• Take reflectance 75 0.75
• Effective reflector area 4 x 0.75 3 square
  feet.

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Heat loss

• The loss of heat from a solar oven is described
  by the Second Law of Thermodynamics
• Heat within a solar box cooker is lost in three
  fundamental ways Conduction, Radiation, and
  Convection

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Heat loss calculation

• Taking efficiency as 55, heat loss 45
• Heat loss 0.45 x 8.4 3.78 KW/Hr
• The Heat loss occurs through side walls, bottom
  area and also through the glazing
• Insulation reduces loss through walls, nearly 40
  0.4 x 3.78 1.512 KW/Hr
• Loss thru glass/plastic window0.6x3.782.268
  KW/Hr Loss thru glass/plastic
• Note that much loss, nearly 2.268/ 8.4 27
  occurs thru glazing
• To reduce loss through window, designers use
  double glazing
• Solar ovens reach higher temperatures with more
  layers of glazing

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Heat Storage

• The capacity of a solar box cooker to hold heat
  increases when more mass is placed inside the
  cooker
• The cooker takes longer to heat with heavy
  materials inside, but will hold heat longer
  through periods

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Conclusion

• A large, flat box, depth not greater than 9
  inches is preferredthis reduces the volume of
  air inside and also side wall area
• If you have bright sunlight most of the days, do
  without reflectors or just one back reflector
  only
• Double glazing may be required for higher
  temperatures(for baking, roasting, deep fry)

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References

• http//www.builditsolar.com/Projects/Cooking/cooki
  ng.htm
• http//solarcooking.wikia.com/wiki/Solar_Cookers_W
  orld_Network_(Home)
• http//www.solarcooker-at-cantinawest.com/solar_ov
  en_comparisons.html
• http//www.freywine.com/recipes.html