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Homework Help: Flat plate solar collector

  1. Sep 16, 2010 #1
    1. The problem statement, all variables and given/known data
    We wish to size a flat plate collector to provide water for one hot shower per hour. We have determined that a shower uses 80 liters of 40°C water that has been heated from a 15°C supply line. The receiver temperature must be greater than the desired water temperature of 40°C and below 90°C to prevent the risk of pressure build up in the collector due to boiling. Determine the required area (Aa in m2) needed for the collector for the following receiver temperatures Tr=50°C, Tr=60°C, Tr=70°C and Tr=80°C. What conclusions can you draw from your calculations?

    Assume the following values:

    Gtn=400 W/m2 Total solar radiation on a surface normal to the sun’s beam
    =30° Average angle of incidence between the normal to the collector and the beam
    of the sun
    =0.97 Receiver absorptivity
    =0.87 Glass transmissivity
    UL=5 W/m2-K Overall loss coefficient including conduction, radiation and convection losses
    Ta=20°C Temperature of the air


    2. Relevant equations
    I have too many equations and don't know what to do with them.
    Qdotu=Qdotin-Qdotloss

    Q=ArUL(Tr-Ta)

    eta = Qdotu/(AaGt)
    but I don't think Gt is anything.

    and many more, but these seemed the most relevant

    3. The attempt at a solution

    mdot = 80kg/3600s

    Qdotu=mdotcp(Tout-Tin)

    =2330 W

    Qdotu is in just about every equation, but in order to find the area of the plate, we need to know eta, I believe.
     
  2. jcsd
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