Page 350 - Handbook of Energy Engineering Calculations
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3. Compute the area of unshaded collector required
               Determine  the  area  of  unshaded  collector  needed  to  heat  this  space  on  an
               average clear day in January. An average clear day is chosen because sizing
               the collector for extreme or cloudy conditions would cause space overheating
               on clear days. January is used because it generally has the highest heating

               load of all the months.
                  To compute the collector area, use the relation A  = H /(E)(i ), where E =
                                                                                    D
                                                                                            T
                                                                              c
               a rule of thumb for energy absorptance efficiency of the passive solar-heating
               system used, expressed as a decimal. Enter Table 10 for a direct gain system
                                                                                        2
                                                                                                  2
               to find E = 0.91. Therefore, A  = 53,904/(0.91)(1423) = 42 ft  (3.9 m ).
                                                   c
                          TABLE 10 Energy Absorptance Efficiency of Passive Solar-Heating
                     Systems













                  If the area of unshaded collector computed in this step varies by more than
               10 percent from the area of the collector estimated for heat-loss calculations

               in step 1, the heat loss should be recomputed with the new areas of collector
               and opaque wall. In this example, the computed and estimated collector areas
               are  within  10  percent  of  each  other,  making  a  second  computation  of  the
               collector area unnecessary.



               4. Compute the insolation stored for nighttime heating
               To compute the insolation to be stored for nighttime heating, the total daily
               insolation must be determined. Use the relation i  = (A )(i )(E), where i  =
                                                                           D
                                                                                   C
                                                                                        T
                                                                                                         D
               total daily insolation collected, Btu (J). Therefore, i   =  (42)(1423)(0.91)  =
                                                                                D
               54,387 Btu (57.4 kJ).
                  Typically 35 percent of the total space heat gain is used to offset daytime
               heat  losses,  requiring  65  percent  to  be  stored  for  nighttime  heating.
               Therefore,  i   =  (0.65)  i ,  where i   =  insolation  stored,  Btu  (J).  Thus,  i   =
                                                                                                         S
                                                         S
                                            D
                              S
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