Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The difference in solar gains between Trace 700 and EnergyPlus is typically due to the sizing run specifications and not the thermal engines.
The zone thermal loads in EnergyPlus for the sizing runs are based on the design days that you have provide in the IDF. Trace 700 uses monthly design days, whereas the default provided in the EnergyPlus weather files are annual (summer and winter) design days. Most people think that Trace 700 is using summer and winter design days, but it actually has an algorithm to generate monthly design day sequences. The results between each software will be significantly different unless you specify the same design day information for autosizing.
Annual design days are inadequate for sizing most thermal zones, so I would only using the monthly values. This is especially true in the case of solar-driven loads which often occur in the fall and winter.
I have not found the monthly design days packaged with the software, but you can find them in ddy format here: ASHRAE Design Day Data
You may also find differences between the software based on the load calculation methodologies. My understanding is that the Radiant Time Series method found in Trace can have issues in cases that are highly glazed due to the use of the sol-air temperature in calculating heat gains.
