I recently did something similar with an attic space for an unconditioned building. I made the attic a zone and used airflownetwork to ventilate it through
existing openings. I could then look at the effectiveness of insulation placement and amounts. Once I had an effective attic design, I scheduled the attic ventilation based on the last airflownetwork analysis and then worked on my occupied zones.
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Tuesday, July 08, 2014 10:06 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Ventilated and opened space between roof and cooled closed spaces (ExteriorNaturalVentedCavity?) [2 Attachments]
Hi all,
I’m trying to model the effect of a separated roof in a hot humid climate.
I join 2 pictures, hoping it will help you to understand the idea. In a simple way, I have various closed (occupied and cooled) volumes, with a large separated roof that protects
these volumes from direct solar radiation.
I’d like to see the radiative and convective effect of such a roof (for example depending on its construction) on the roof of the volumes, in order to decrease the cooling loads.
The matter is that I’m wondering how to model that. I’m thinking about using the GapConvectionRadiation and SurfaceProperty:ExteriorNaturalVentedCavity, but I’m not sure it will
match perfectly, because the cavity is mainly opened to exterior conditions, such as wind (although it’s not very high: 2 a 3 m/s averagely).
I see 3 options:
- Assuming the roof as a solar protection. But this way, i can’t give it thermal properties (as I’d do with an “attached” roof), or maybe the ShadingProperty:Reflectance object
(i just want to get a correct radiation from the "interior" roof's surface)? In this case, may I give the “Area Fractions of Openings” the opened surface? Would that be OK according to you?
- Should I assume the cavity as a thermal zone, with mainly AirWall as vertical surfaces�? In this casse, I think I would get to a complex place, having to model natural ventilation
in a tough way, don’t you think? Not even sure it would work�
- maybe the simplest way would be to give to my roof’s volume (not the big one that protects from solar radiation, but the one of the closed volumes) an Outside Boundary Condition
and Outside Boundary Condition Object with a GapConvectionRadiation?
I would be really grateful if some of you could tell me which of these options looks correct, or if you could give me other suggestions according to that kind of simulations!
Thanks for your attention. I hope I’ve been clear.
Regards,
Mathieu
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Posted by: "Edward G. Lyon" <EGLyon@xxxxxxx>
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