# Seeing Through the Thermal Darkness

 Please Register and login to reply and use other advanced options Posted by Nick Pine on September 16, 2008, 4:44 pm  Laren wrote: .... the slow-moving indoor airfilm resistance is R2/3, and the solar gain is (80-70)1ft^2/(R2/3) = 15 Btu/h-ft^2? That could happen with an outdoor temp of 30 F and net solar insolation I = 150 Btu/h-ft^2 and a single-pane window with R2/3 and R1/3 indoor and outdoor air films, like this, viewed in a fixed font like courier:                         R1/3  (=1-2/3) Tb = 80 = 30+I/3 --------www---- 30 F                     |                     |    ---                      ---|<--|---|                          ---                           I = 3(80-30) = 150 Btu/h-ft^2 The rest of the window would look like this:                   R1 Ti = 70 F -------www---- 30 F              |              |    ---               ---|<--|---|                   ---                    I = 150 Btu/h-ft^2 with a net solar gain of 150-((70-30)1ft^2/R1 = 110 vs 15 Btu/h-ft^2, ie 7.3X more solar gain. Alternatively, using your calc below vs your words above, the net gain would be (80-70F)1ft^2/R1 = 10BTU/hr-ft^2... That's an enormous (11X) difference. What gives? An R2 window with an R2/3 slow-moving indoor airfilm and an 80 F box temp on a 30 F day would transmit 38 Btu/h-F of sun:                           R1.33 Tb = 80 = 30+1.33I --------www---- 30 F                       |                       |    ---                        ---|<--|---|                            ---                             I = (80-30)/1.33 = 38 Btu/h-ft^2 with a net solar gain of 38-((70-30)1ft^2/R2 = 18 Btu/h-ft^2                  R2 Ti = 70 F -------www---- 30 F              |              |    ---               ---|<--|---|                   ---                    I = 38 Btu/h-ft^2 vs the 5 you would predict? And with 150 vs 38 Btu/h-F of net sun,                          R1.33 Tb = 80 = T+1.33I --------www---- T = 80-1.33xI = -120 F :-)                       |                       |    ---                        ---|<--|---|                            ---                             I = 150 Btu/h-ft^2, with a net solar gain of 150-((70-(-120))/R2 = 55 Btu/h-ft^2                  R2 Ti = 70 F -------www---- -120 F              |              |    ---               ---|<--|---|                   ---                    I = 150 Btu/h-ft^2 vs the 5 you would predict, leaving a large thermal darkness... Nick This Thread Bookmark this thread:               Subject Author Date   Seeing Through the Thermal Darkness Nick Pine 09-16-2008 please rate this thread Please Register and login to reply and use other advanced options Related Posts Latest Posts