Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
NOT a definitive answer - suggestions if you wanted to take a deeper dive.
Assuming the model is in the Northern Hemisphere, a south-facing surface will see the sun rise on its left (~SE) and set on its right (~SW) in early January. Depending on the Perez Sky Model calculations, a south-facing vertical surface may receive more diffuse irradiance than a horizontal surface ("Site Diffuse Solar Radiation Rate"), when the sun is fairly low (morning & afternoon), mainly due to circumsolar and horizon brightening. The south-facing surface would also receive diffuse radiation reflected off the ground (more so when the sun is low). Your results seems to reflect that.
A deeper dive would involve reproducing the calculations in the link above, e.g. isolate the contributions from sky dome vs horizon vs circumsolar. In the meantime, here a few simple tests (may help):
BTW, the introductory paragraph stills refers to Site Direct Solar Radiation Rate per Area ...
| | 2 | No.2 Revision |
NOT a definitive answer - suggestions if you wanted to take a deeper dive.
Assuming the model is in the Northern Hemisphere, a south-facing surface will see the sun rise on its left (~SE) and set on its right (~SW) in early January. Depending on the Perez Sky Model calculations, a south-facing vertical surface may receive more diffuse irradiance than a horizontal surface ("Site Diffuse Solar Radiation Rate"), when the sun is fairly low (morning & afternoon), mainly due to circumsolar and horizon brightening. The south-facing surface would also receive diffuse radiation reflected off the ground (more so when the sun is low). Your results seems to reflect that.
A deeper dive would involve reproducing the calculations in the link above, e.g. isolate the contributions from sky dome vs horizon vs circumsolar. In the meantime, here a few simple tests (may help):
BTW, the introductory paragraph stills refers to Site Direct Solar Radiation Rate per Area ...
