I’ve been trying to get my head around how the solar loads are calculated and referenced for the total energy loads.
I have been taught to always model perimeter zones to reflect the effects of the façade design (and the solar gain) to the HVAC system.
As far as I can see the solar loads get grouped as one zone (see Air wall, Open air connection between zones: Tips and Tricks for Using EnergyPlus — EnergyPlus 9.4) but these loads don’t reflect the different perimeter zones solar loads that would be experienced. In turn this wouldn’t accurately reflect the peak heating and cooling loads experienced in these area’s. I did a test and found that with airwalls the perimeter solar zones did not reflect reality (e.g. the results for a simple box in the southern hemisphere had the highest loads in the south?)
From what I can tell to get the perimeter room details more accurate you need to model the zone with a internal window or lightweight structure? Is this correct? When I tried this I still found issue with the model as this wall was providing significant insulation (even with a simple plasterboard construction and 95% single glazing)
It all comes down to the reality of the building you are trying to model.
If there actually is a real physical barrier between the perimeter rooms and core rooms in your real building, then, yes, you should not use an AirBoundary and you should instead use an opaque construction (or a window/aperture if there’s a glass barrier). Even when they’re really thin or transparent, these real physical barriers greatly change the radiant heat exchange because they are opaque to infrared heat. So they are going to trap more of the gains in those perimeter zones (including solar gain), causing the cooling load to be higher than if they were not there.
If, however, the boundary between perimeter and core zones in your real building isn’t physical and you’re just splitting the core from the perimeter because there’s different HVAC equipment serving these areas and you want the equipment to be sized differently, then you should use an AirBoundary. Doing so will ensure that radiant heat can move across the boundary, which is what will happen in the real world.
I’m not sure what you mean by this: “I did a test and found that with airwalls the perimeter solar zones did not reflect reality”. Maybe you could give some details about your test?
In any event, the best reflection of reality is to model things as exist in reality. If there’s no physical boundary in the real building, then you should use an AirBoundary instead of an opaque or window one.
Hi @chris adding to Shanices post, Energyplus documentation says there is an option to keep two spaces having an air boundary as an adjacent scenario to be combined as a solar enclosure. Is there a way we can get two separate solar gain values for a perimeter zone and internal zone?
