How does EnergyPlus weigh incoming solar radiation?

asked 2017-10-11 17:17:36 -0500

carlobianchi89
159 ●1 ●7

updated 2017-10-12 17:59:17 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

How does EnergyPlus weight incoming solar radiation?

I thought the sun angle projection was automatically applied in the EPW file, meaning that the radiation data are already zeroed out during night and vary during the day, according to the corresponding latitude and day of the year. However, I am making some tests and this is not what happens. I am running 2 simulations with the same building model and the same EPW file, except I am using 2 different latitudes in the header of the EPW files. The output heating loads in the 2 cases are different.

Does EnergyPlus apply any other weight depending on the sun angle?

answered 2017-10-17 12:44:41 -0500

carlobianchi89
159 ●1 ●7

EnergyPlus has some sort of function to calculate, given the day of the year and the latitude, wether it is night or day. If it is night time, no incoming radiation is considered. Even if a Weather File with constant incoming radiation throughout the whole year is input, the output radiation (in Output:Variable) is 0 at night and the constant value during the day.

The time for sunrise and sunset depend on the latitude, so it makes sense that they are different in the 2 simulated cases. Since lower latitudes have longer days (for instance) during winter, the heating gain from the sun is different and the building heating load is different for 2 different latitudes.

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Plus the solar angle of incidence will be different at a different latitude. This will also impact the incident solar radiation on the surfaces. Add output variables for the various environment and surface solar quantities to compare.