[Equest-users] Unexpected Custom SHGC Results

[Joe Huang]

I've found this comment to be mildly offensive as well as showing a lack 
of understanding about how heat gains ultimately get translated to 
cooling energy consumption.  It's extremely hard for me to believe that 
eQUEST or DOE-2 has been flawed for 25 years in modeling something as 
fundamental as solar heat gain through windows.  In all the decades I've 
used DOE-2 to analyze window performance for DOE's EnergyStar Program as 
well as numerous other projects, whenever the results did not match or 
ran counter to first-principle expectations, it was always because there 
was some other factor that have been overlooked or ignored, chief among 
them being the size of the HVAC system, its configuration, and control 
strategy.  Locations with mild cooling loads, such as San Jose,  are 
particularly sensitive to such system interactions.  Were both runs done 
using "autosizing"?  What
kind of a system was modeled - VAV or CAV ?   Did the model have an 
economizer?   What were the HEAT-CONTROL and COOL-CONTROL strategies ?  
etc.   It's far too early to lay blame on the DOE-2 algorithms.

Joe

On 7/14/2012 1:41 PM, CleanTech Analytics wrote:
> Just admit it- eQuest is flawed, you don't have to make up things to 
> protect it-
>
> If it is a mistake to use the percent points rather then percent 
> reduced from the abrataty eQuest assumption from 1999 window specs 
> than the it should have reduced solar heat gain by more then his 
> product even provided- Using the 33 percentage points but used the 33% 
> should have provided him over stated cooling reduction, (and extra 
> added heating consumption tradeoff)
>
> O- and FYI LBLwindow does glass U-value not shading, ware-as LBLoptics 
> can be used for film coefficients and used to create a custom glass 
> type in window, but do not do any calculations for "shading"
>
> I say you try the same model in Energy Plus or TRNSYS and see if the 
> results differ.
>
>
> /Jeremiah D. Crossett/
> /CleanTech Analytics/
> /503-688-8951 <tel:503-688-8951>/
> /www.cleantechanalytics.com/ <http://www.cleantechanalytics.com>
>
>
> *
>
> This document may contain valuable information proprietary to 
> CleanTech Analytics which is private and confidential. It may not be 
> shared, copied, stored or transmitted in any form without the prior 
> written consent of CleanTech Analytics
>
> *
>
>
>
> On Sat, Jul 14, 2012 at 12:42 PM, Liam O'Brien 
> <obrien_liam at hotmail.com <mailto:obrien_liam at hotmail.com>> wrote:
>
>     Hi Pete,
>
>     I don't have a ton of experience with detailed modelling of shades
>     in eQUEST, specifically, but two things that could be at play:
>
>     - The claim from the manufacturer sounds like it's not intended to
>     universal in absolute terms. Also, it would be more conservative
>     to reduce the SHGC by 33 percent than 33_percentage points_(as you
>     did) if you're going to take this simplified approach. Therefore,
>     it would be closer to SHGC=0.44. Subtle but significant. You could
>     try using software that specializes in window/shade performance
>     like LBNL Window or Parasol to try to characterize the performance
>     of your specific shade-glazing combination
>     - Depending on the operating conditions and construction of the
>     building, there's a chance your results aren't ridiculous. If
>     shades intercept transmitted solar radiation, then a lot of that
>     energy will almost immediately transfer to the air via convection.
>     If you have thermally massive interior surfaces, there's a chance
>     your building could actually perform better without those shades
>     because the air conditioning won't kick in till later.
>
>     Liam
>
>     ------------------------------------------------------------------------
>     Date: Sat, 14 Jul 2012 11:51:02 -0700
>     From: pbaumstark at sbcglobal.net <mailto:pbaumstark at sbcglobal.net>
>     To: equest-users at lists.onebuilding.org
>     <mailto:equest-users at lists.onebuilding.org>
>     Subject: [Equest-users] Unexpected Custom SHGC Results
>
>
>     Hello,
>
>     I have an "L" shaped building with the point of the "L" facing
>     North.  The inside of the "L" has both NE and NW surfaces, that
>     include a high amount of glass, which heats up the perimeter
>     building spaces considerably during the summer.  Glazing is single
>     pane tinted.
>
>     The customer wants to install some Verisol SilverScreen shades in
>     these windows.  According to the manufacturer, the SHGC will
>     reduce by about 33%.  I modeled in eQUEST, window properties in
>     these windows to have an SHGC of 0.67 and ran an EEM reducing SHGC
>     to 0.34, and got an increase in cooling load and fan load year
>     round, even in the summer months.
>
>     Am I seeing this wrong?  I can't figure out how I could possible
>     get results like this?
>
>     Thank you,
>     Pete
>     San Jose, CA
>
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-- 
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 108D 
Moraga, CA 94556 (o) (925)388-0265 (c) (510)928-2683 
www.whiteboxtechnologies.com "Building energy simulations at your 
fingertips"
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