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It is unlikely that I will get further answers, so I just updated my summary tables at this time. They may be updated further in the future.

The Answers at this time are as follows:

1. View Factors to ground, sky and air are roughly auto-calculated based on the tilt angle of the building exterior surface. If we want to consider longwave radiation from surrounding building surfaces, we need to input View Factors related to the surrounding surfaces manually, but the View Factors are not "from the building exterior surface to the surrounding surface" but "from the surrounding surface to the building exterior surface". It's weird. It only seems to me that EngineeringReference is incorrect.
2. Longwave radiation from exterior surfaces of the building itself is probably Not considered. It's just because I couldn't find any mention about that in EngineeringReference. I'm not 100% sure about that.
3. We can't change the emissivity of ground and surrounding building surfaces, but I think we don't need to do so because EnergyPlus doesn't seem to consider it. The equation of q"LWR (Exterior surface longwave radiation fux[W/m2]) used in EnergyPlus only have the emissivitiy of the building exterior surface. (Note that in general, radiation exchange between two surfaces is affected by the temperature and emissivity of both surfaces.)
4. Two things were corrected. Firstly, longwage radiation from surrounding buildings is hardly considered by default because the surrounding surface temperature is the same as air temperature, which means that the surrounding surfaces are almost ignored. Secondly, Sky Temperature is automatically calculated based on air temperature in weather file.
5. I mentioned in Answer 1.
6. Surrounding Surface 1 View Factor in SurfaceProperty:SurroundingSurfaces seems to be the same value for all exterior surfaces of the building including roofs and walls that are completely hidden from the surrounding surface. This is another very weird thing.

It is unlikely that I will get further answers, so I just updated my summary tables at this time. They may be updated further in the future.

The Answers at this time are as follows:

1. View Factors to ground, sky and air are roughly auto-calculated based on the tilt angle of the building exterior surface. If we want to consider longwave radiation from surrounding building surfaces, we need to input View Factors related to the surrounding surfaces manually, but the View Factors are not "from the building exterior surface to the surrounding surface" but "from the surrounding surface to the building exterior surface". It's weird. It only seems to me that EngineeringReference is incorrect.
2. Longwave radiation from exterior surfaces of the building itself is probably Not considered. It's just because I couldn't find any mention about that in EngineeringReference. I'm not 100% sure about that.
3. We can't change the emissivity of ground and surrounding building surfaces, but I think we don't need to do so because EnergyPlus doesn't seem to consider it. The equation of q"LWR (Exterior surface longwave radiation fux[W/m2]) used in EnergyPlus only have the emissivitiy of the building exterior surface. (Note that in general, radiation exchange between two surfaces is affected by the temperature and emissivity of both surfaces.)
4. Two things were corrected. Firstly, longwage radiation from surrounding buildings is hardly considered by default because the surrounding surface temperature is the same as air temperature, which means that the surrounding surfaces are almost ignored. Secondly, Sky Temperature is automatically calculated based on air temperature in weather file.
5. I mentioned in Answer 1.
6. Surrounding Surface 1 View Factor in SurfaceProperty:SurroundingSurfaces seems to be the same value for all exterior surfaces of the building including roofs and walls that are completely hidden from the surrounding surface. This is another very weird thing.

It is unlikely that I will get further answers, so I just updated my summary tables at this time. They may be updated further in the future.

The Answers at this time are as follows:

1. View Factors to ground, sky and air are roughly auto-calculated based on the tilt angle of the building exterior surface. If we want to consider longwave radiation from surrounding building surfaces, we need to input View Factors related to the surrounding surfaces manually, but the View Factors are not "from the building exterior surface to the surrounding surface" but "from the surrounding surface to the building exterior surface". It's weird. It only seems to me that EngineeringReference is incorrect.
2. Longwave radiation from exterior surfaces of the building itself is probably Not considered. It's just because I couldn't find any mention about that in EngineeringReference. I'm not 100% sure about that.
3. We can't change the emissivity of ground and surrounding building surfaces, but I think we don't need to do so because EnergyPlus doesn't seem to consider it. The equation of q"LWR (Exterior surface longwave radiation fux[W/m2]) used in EnergyPlus only have the emissivitiy of the building exterior surface. (Note that in general, radiation exchange between two surfaces is affected by the temperature and emissivity of both surfaces.)
4. Two things were corrected. Firstly, longwage Longwage radiation from surrounding buildings is hardly considered by default because the surrounding surface temperature is the same as air temperature, which means that the surrounding surfaces are almost ignored. Secondly, Sky Temperature is automatically calculated based on air temperature in weather file. ignored.
5. I mentioned in Answer 1.
6. Surrounding Surface 1 View Factor in SurfaceProperty:SurroundingSurfaces seems to be the same value for all exterior surfaces of the building including roofs and walls that are completely hidden from the surrounding surface. This is another very weird thing.

Some questions about longwave radiation remain. They may not have much impact on energy simulations, but I just wanted to know how EnergyPlus takes them into account.