So the roof is just a shade�You could still mmake it an enclosed space but specify a very open airflownetwork. I did this for a transformer yard enclosed on
three sides and the roof by louvers. You will have to consider low angle solar that can penetrate under the roof to conditioned space surfaces.
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 11:03 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Ventilated and opened space between roof and cooled closed spaces (ExteriorNaturalVentedCavity?)
Thanks Edward.
But in your case, the attic was an unconditionned closed
space, wasn't it?
In mine, i think it's quite different, since the "air volume" between the roof that have a solar protection function and the roof of my closed (and cooled) volumes is opened (it's an "exterior space").
What do you think?
Thanks again.
Regards,
Mat
2014-07-08 9:54 GMT-05:00 'Edward G. Lyon'
eglyon@xxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:
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 case, I think I wwould 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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