Heat gain and
loss calculation
for a
Solar Cooker
Presented by:
Abdulaziz Barkat
Shaheen Alshaheen
Objectives:
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Advantage of solar cooker
Purpose
Heat Principles
Box cooker calculation
Heat gain
Heat reflection calculation
Heat loss
Some design Factors
Conclusion
Advantage of solar cooker
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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 world’s most
pressing problems:
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A growing shortage of cooking fuels
the scourge of water-borne diseases.
Purpose Project
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Helps to calculate design parameters for
solar cooker/oven
Also, summarize the basic principles that
are used in the design of solar box
cookers
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heat gain,
heat loss
heat storage
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
Box cooker calculation
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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
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
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
Heat loss calculation
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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 window=0.6x3.78=2.268 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
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
Some design Factors
A
large, flat box, depth not greater than 9
inches is preferred…this reduces the
volume of air inside and also side wall
area
 If you have bright sunlight most of the
days, do it without reflectors or just one
back reflector only.
 plastics with UV rays---use UV stabilized
plastic for longer usage
Conclusion
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A large, flat box, depth not greater than 9
inches is preferred…this 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)