FYI. I haven't done the parametrics to see if
this situation applies to shading of windows by shading devices, but I have
found a notable problem with direct beam reaching an interior window when the
exterior window is much larger than the interior window. While working on
a double-skin building, we found that no direct beam reached interior windows
when the outer skin window was one big surface covering 12 stories high by 8
zones/rooms of equal size wide.
The windows that did receive a direct beam
component (reported in the variable "Beam Solar Transmitted through
Interior Window" or "Zone Beam Solar from Interior Windows") were distributed in
a checkerboard approximately. To correct this, we divided the exterior
window until all interior windows reported direct beam component as
expected. The exterior window had to be no more than 4x the size of the
interior windows to have consistent results all year as expected from hand
calcs.
I don't know if this is a problem with the shading
algorithm in general or with the way it is applied to interior windows, or if
this problem was resolved between v2.2 and the latest release. Generally I
just try to keep all surfaces around the same size just to make sure. The
shading algorithm has been noted by some E+ developers as not optimal. The
Ecotect shading method is said to be the best (randomly distributed spray of
rays toward the sun to create a database of full annual conditions). I
haven't looked into the E+ algorithm enough to understand the limitations in
detail, if someone else wants to weigh in.
Daivd
----- Original Message -----From: albertoSent: Friday, March 05, 2010 2:00 AMSubject: Re: [EnergyPlus_Support] Use shadowing control
Dear Pedro,Thanks for your help .I tried to check these variables and for the windows surface I am controlling they reach 50,5 W/m2 which is lower than the 100 W/m2(setpoint). I will be still looking the variable dictionary.Regards,Alberto Hernandez Neto----- Original Message -----From: Pedro PeixeiroSent: Wednesday, March 03, 2010 3:57 PMSubject: RE: [EnergyPlus_Support] Use shadowing control Alberto,I was going through an RDD file just now and I came across these output variables:Zone,Average,Surface Ext Solar Beam Incident [W/m2] Zone,Average,Surface Ext Solar Sky Diffuse Incident [W/m2] I havent checked the Input/Output reference to be sure of their meaning, but by their names, they sounded like exactly what you need.Pedro.
To: EnergyPlus_Support@yahoogroups. com
From: ahneto@xxxxxx
Date: Wed, 3 Mar 2010 15:51:06 -0300
Subject: Re: [EnergyPlus_Support] Use shadowing control
Dear Pedro,Thanks for the help.I try those variables but I have to calculate the beam direction in order to correct the radiation that reaches the surface of the window. I was wondering if there is a variable that can give me density of "net" solar radiation that reaches the window directly withou further corrections.Regards,Alberto Hernandez Neto----- Original Message -----From: Pedro PeixeiroSent: Wednesday, March 03, 2010 3:08 PMSubject: RE: [EnergyPlus_Support] Use shadowing control Hello Alberto.I believe you're viewing the wrong outputs to verify your control. Zone Diff Solar from Exterior Windows and Beam Solar will give you the amounts of radiation that enter the zone and not the radiation that will arrive at the window for each timestep. Try using the "Difuse Solar" and "Direct Solar" outputs.I hope someone with more experience and knowledge steps forward to confirm if this is the problem or not, I'm still very "green" in E+. Anyway, untill someone does, you might want to try that.Regards,Pedro.
To: energyplus-support@gard.com; EnergyPlus_Support@ yahoogroups. com
From: ahneto@xxxxxx
Date: Wed, 3 Mar 2010 14:26:01 -0300
Subject: [EnergyPlus_Support] Use shadowing control
Dear E+ users,I am using shading control introduced into the Windowproperty:Shadingcontrol where I set the folowing parameters: 1) Shading control type: OnIfHighSolarOnWindow 2) Setpoint: 100 W/m2Looking at the E+ Input/Output reference I check that, for such control type, the shading is on if beam plus diffuse solar radiation incident on the window exceeds SetPoint (W/m2).After the simulations, I was trying to check if the control was operating properly but I don´t know which variable I can use to check that. First, I use "Zone Diff Solar from Exterior Windows" and "Zone Beam Solar from Exterior Windows" and I compared the values of these variables with and without the shading. I noticed, between 8 and 9 A.M. for a specific external window, that there is a difference on the values of such variables but when I added the values of the beam and diffuse radiation and divdided by thw window I reached a value of 13,5 W/m2 but I was expecting something close to 100 W/m2 when the shading should start operating. Any ideas which variable I should check in order to evaluate the proper operation of such shading?Thanks for any help.Alberto Hernandez Neto
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