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Re: [EnergyPlus_Support] Interior windows, opaque surfaces
Rob.
Also, would really like to clear up how to look at conduction through an interior window. The conductive component is definitely not "Window Heat Gain/Loss" minus transmitted solar for an interior window, as that creates a negative flow in a cooling condition (I derived interior window transmitted solar from Zone Diffuse Solar...). That also makes me question whether the definition of Window Heat Gain/Loss is correct for exterior windows as well.
The best I can figure, conduction can be roughly determined by "Surface Int Convection Heat Rate per Area," which should seemingly account for energy entering the air heat balance from the window (and frame?). Am I close? With this I would think one could roughly derive Uvalue for the window?
While I'm on this, is Window Heat Gain/Loss used at all by the E+ engine? It carries none of the values described as useful for determining air heat balance, which is all about convection. Is this value presented only as a convenience for analysis?
Thanks again,
r3
----- Original Message -----
From: Rob Hitchcock
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Wednesday, May 21, 2008 5:16 PM
Subject: Re: [EnergyPlus_Support] Interior windows, opaque surfaces
Regarding Interior Window Solar:
"Initial Transmitted Diffuse Solar Transmitted Out through Inside of
Window Surface" is only the diffuse solar initially transmitted through
exterior windows that is then incident on and transmitted out through
another window in the zone (either to the outdoors for an exterior
window or to an adjacent zone for an interior window). You will need to
sum this value for all interior windows into the zone of interest.
For the adjacent zone on the other side of an interior window, you
should then add "Zone Beam Solar from Interior Windows" to account for
the beam solar that entered a zone through an exterior window and was
then incident on and transmitted through interior windows into the
adjacent zone. This radiation is considered diffuse once it has been
transmitted through an interior window.
And, you should also add "Zone Diff Solar from Interior Windows", which
is the combination of beam and diffuse solar that first entered a zone
through an exterior window, was subsequently reflected from interior
surfaces in that zone (becoming diffuse through that reflection), and
then transmitted through interior windows into the adjacent zone. In
answering this question I have realized that this output variable is
incorrectly defined in the EnergyPlus Input/Output Reference as of
Version 2.1 when the treatment of diffuse solar distribution was modified.
Rob
=======
coolshadow10a wrote:
> Why does Opaque Surface Inside Face Conduction not balance out over
> the course of a few days? Am I understanding correctly that this
> variable represents basically the energy transferred into a mass each
> time step? If all my opaque surfaces are adiabatic, shouldn't the
> energy balance of those surfaces remain within a reasonable margin?
>
> Interior windows:
>
> Solar through interior windows
> - From previous commentary, it was suggested to use Initial
> Transmitted Diffuse Solar Transmitted Out through Inside of Window
> Surface to get a measure of solar that has entered through exterior
> windows and is falling on/passing out through an interior window.
> This value is associated with an interior window. But it is much less
> than would be expected. It appears to be only the diffuse portion of
> solar through the exterior windows that passes out through the
> interior window. How can I get a measure of the full solar load on
> the interior zone (and thus a measure of the performance of the
> interior window)
> - Zone Diff Solar From Interior Windows gives a value much closer to
> what is expected, but I was cautioned about this variable previously.
> What are the caveats to using this value to analyze solar gains
> through interior windows?
>
> Window Heat Gain
> - This is defined in the docs as solar plus conductive for an Exterior
> window, but there are values for interior windows as well. For
> interior windows, this value is mostly less than the expected value
> for solar that should be coming through that window even when Tout is
> much higher then Tin. The solar component seems to be NOT part of
> interior Window Heat Gain values. Can this then be taken as
> conductive loads through interior windows? If not, any suggestions
> for calculating conductive loads through an interior window?
> - Window heat gain and window heat loss values do not balance out
> across adjacent window surfaces. Not even close. Is solar discounted
> at some point in the generation of these variables?
> - Zone Window Heat Gain is always Zero for interior zones, even though
> interior window Window Heat Gain is non-zero.
>
> Thanks,
> r3
>
>
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