RE: [EnergyPlus_Support] Window Heat Gain of South oriented window

["Michael J. Witte" <mjwitte@xxxxxxxx>]

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@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of anarui.oliveira
> Sent: Wednesday, December 26, 2007 11:31 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> 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.energyplus.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@xxxxxxxx





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