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Re: [EnergyPlus_Support] Window Heat Gain of South oriented window
Thank you both for your answers.
I was aware of the general concept of apparent solar angle, but had no idea the solar gains could be so affected by it.
In the meantime, I had already noticed the variants in window gains and I confirmed that there is indeed a varying effect of conduction (and convection?) component as well, but it shows that the dominant effect responsible for the behaviour I mentioned is still the radiation component.
Yet another question:
- If the architect designs a system similar to that described by the Blind shadowing devices (fixed metallic slats), but covering a concrete wall, simply for aestethical purposes,
- Does EnergyPlus support that feature applied to an opaque wall?
- And more important, do you have some experience-based notion if it is "very" relevant to model that feature, in terms of the solar gains and thermal analysis of the building?
Regards,
Ana Rui.
----- Original Message ----
From: Michael J. Witte <mjwitte@xxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Friday, December 28, 2007 9:46:03 PM
Subject: RE: [EnergyPlus_Support] Window Heat Gain of South oriented window
Craig has explained the solar aspect.
Another factor is that you said the zone is free-floating with no heating or
cooling. If you are reporting window heat gains, these report the net impact
of both the transmitted solar gains and conduction gains/losses through the
glass. Floating zone temperatures may cloud the comparison between summer and
winter. A better comparison would be to report transmitted solar rather than
window heat gain, or to add Purchased Air (COMPACT HVAC:ZONE:PURCHASED AIR) to
control the zone to a constant indoor temperature.
Mike
On 27 Dec 2007 at 22:07, Christensen, Craig wrote:
> If I understand correctly what you describe in your email then ... yes,
> these results are normal and explainable.
>
>
>
> In the summer (for a northern latitude), the sun passes high overhead
> and solar radiation strikes a south-facing window at a very oblique
> angle. Therefore, the intensity of the incident radiation is
> significantly reduced (the direct beam radiation is multiplied by the
> cosine of the incidence angle). Window heat gains also depend on the
> sky diffuse and ground-reflected radiation and the reflection,
> absorption, and transmission of the radiation as it passes through the
> window glass, but the effect of sun angle on the incident radiation is
> the dominant effect in the month-to-month variation (see the figure).
> The fact that south-facing windows have higher gains in winter and lower
> gains in summer is a key principle for passive solar heating of
> buildings. Shading devices above south windows (overhangs) also take
> advantage of high sun angles to provide summer shading and further
> reduction of window heat gains.
>
>
>
> Craig
>
>
>
>
>
>
>
>
>
>
>
> ____________ _________ _________ __
>
> From: EnergyPlus_Support@ yahoogroups. com
> [mailto:EnergyPlus_Support@ yahoogroups. com] On Behalf Of anarui.oliveira
> Sent: Wednesday, December 26, 2007 11:31 AM
> To: EnergyPlus_Support@ yahoogroups. com
> Subject: [EnergyPlus_ Support] Window Heat Gain of South oriented window
>
>
>
> Greetings!
> I'm just starting now with E+ and I tried out some basic configurations
> (basicaly a box with a window) in "free" simulation mode (no heating or
> cooling) which returned some awkward results:
> - A south oriented window, with no shading of any type, returned lower
> Window Heat Gains in a Summer Week than in a Winter Week (I checked the
> Direct and Difuse Solar and they are lower in Winter, as would be
> expected);
> - And also the same window returns larger Window Heat Gains as I a
> rotate the exact same building (rotation relative to the North) as to
> rotate the window to East or West (as I rotate the building, the
> strange Summer-Winter behaviour also diminishes and eventually
> vanishes);
> Are these results in any way normal or explainable? Any idea what I
> might be doing wrong?
> I appreciate all help I can get. Thanks!
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> The primary EnergyPlus web site is found at:
> http://www.energypl us.gov
>
> The group web site is:
> http://groups. yahoo.com/ group/EnergyPlus _Support/
>
> Attachments are not allowed -- please post any files to the appropriate folder
> in the Files area of the Support Web Site.
>
> EnergyPlus Documentation is searchable. Open EPlusMainMenu. pdf under the
> Documentation link and press the "search" button.
>
> Yahoo! Groups Links
>
>
>
>
>
============ ========= ========= ========= ========= ========
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@ gard.com
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