# Workaround for Airpak cases involving solar load and DO radiation

 In Airpak, if we have solar radiation turned on, a transparent surface defined and the DO radiation model turned on for radiation calculations, unrealistic results are obtained. Temperature values much lower than the lowest temperature definition in the space (even though no energy sinks are defined in the model) have been observed. The problem lies in the limitation that 'irradiation' information (corresponding to outside temperature for the transparent surfaces) cannot be specified in the current Airpak version. The workaround is to modify the case file to include the following lines (to define irradiation) for each semi-transparent surface. (band-q-irrad ((constant . 511.25) (profile "" ""))) (parallel-collimated-beam? . #f) Here 511.25 is the Irradiation in W/m2 corresponding to an outside temperature of 95 F (308.15 K) ****************************************** Calculation for Irradiation: Irradiation = Stefan Boltzmann constant x (Outside Temperature)^4 Units: W/m2 = W/m2/K4 x K4 For the example above, the outside temperature is 95 F which is 308.15 K. Stefan Boltzmann constant = 5.67 x 10^-8 W/m2/K4 Hence, Irradiation = 5.67 x 10^-8 x (308.15)^4 = 511.25 W/m2 ****************************************** The section of the case file that corresponds to the semi-transparent surface has been pasted below as an example: From case file as written out by Airpak: ;;; zone for wall room_default_side_minx side 1, pids 0 and -1, facing x (39 (5 wall room_default_side_minx-side1) ( (d . 0) (h (constant . 1.4192500376243)) (tinf (constant . 308.15)) (thermal-bc . 2) (int-rad? . #f) (int-rad? . #f) (roughness-height . 0.0) (material . Paint-non-metallic) (uds-bc 0) (uds ((constant . 0) (profile "" ""))) (v-transmissivity (constant . 0.8) (profile "" "")) (ir-transmissivity (constant . 0.8)(profile "" "")) (d-transmissivity (constant . 0.8)(profile "" "")) (d-st-absorbtivity (constant . 0.1) (profile "" "")) (v-st-absorbtivity (constant . 0.1) (profile "" "")) (ir-st-absorbtivity (constant . 0.1)(profile "" "")) (v-opq-absorbtivity (constant . 0.1)(profile "" "")) (ir-opq-absorbtivity (constant . 0.1)(profile "" "")) (solar-direction? . #f) (solar-irradiation? . #f) (radiation-bc . 2) (solar-flux? . #t) )) Under the Solve/Run Solution, use the "Edit Case file after writing" option in the Advanced tab, and in the section of the case file that corresponds to the semi-transparent surface, insert the command for irradiation specification as below, ;;; zone for wall room_default_side_minx side 1, pids 0 and -1, facing x (39 (5 wall room_default_side_minx-side1) ( (d . 0) (h (constant . 1.4192500376243)) (tinf (constant . 308.15)) (thermal-bc . 2) (int-rad? . #f) (int-rad? . #f) (roughness-height . 0.0) (material . Paint-non-metallic) (uds-bc 0) (uds ((constant . 0) (profile "" ""))) (v-transmissivity (constant . 0.8) (profile "" "")) (ir-transmissivity (constant . 0.8)(profile "" "")) (d-transmissivity (constant . 0.8)(profile "" "")) (d-st-absorbtivity (constant . 0.1) (profile "" "")) (v-st-absorbtivity (constant . 0.1) (profile "" "")) (ir-st-absorbtivity (constant . 0.1)(profile "" "")) (v-opq-absorbtivity (constant . 0.1)(profile "" "")) (ir-opq-absorbtivity (constant . 0.1)(profile "" "")) (band-q-irrad ((constant . 511.25) (profile "" ""))) (parallel-collimated-beam? . #f) (solar-direction? . #f) (solar-irradiation? . #f) (radiation-bc . 2) (solar-flux? . #t) ))

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