[Equest-users] Unexpected Custom SHGC Results

Joe Huang yjhuang at whiteboxtechnologies.com
Sun Jul 22 04:31:30 PDT 2012


Jeremiah,

I'm not quite sure what you're driving at, but performance curves are 
used throughout DOE-2 and EnergyPlus to model the performance of HVAC 
equipment.  In fact, if my memory is correct, the chiller model in 
EnergyPlus is taken directly from DOE-2.
The performance curves are not a "theory", but empirically derived 
equations that map performance as functions of the ambient air 
conditions and the part-load-ratio at that time step based typically on 
manufacturers' test data. so yes, these curves do reflect
real world  conditions. Take out these curves, i.e., assume that all 
equipment perform the same under all conditions, and there wouldn't be 
much point to simulating the system at all.

But getting back to Peter's hypothesis, I don't think the increase in 
cooling energy is due only to the shape of the equipment curves. I think 
it's a combination of that plus the zone air flows,  and the 
COOL-CONTROL. This last item is particularly tricky in a moderate 
cooling climate.  We have to remember that air-handling systems are not 
ideal - if you reduce the cooling load in a zone that's not the warmest 
without changing the relative zone air flows, you may just overcool that 
zone and in the worse case increase reheat energy.  The federal 
government learned that back in the early 70's when in response to the 
Arab Oil Embargo
they asked that all government offices raise their cooling setpoint 
temperatures as an energy saving measure.

Joe

On 7/15/2012 6:51 PM, CleanTech Analytics wrote:
> So if the curve theory is correct I wonder if this would happen in 
> other modeling software  or more importantly in the real world>? 
>  --reduce internal gain and increase cooling consumption--  or if this 
> phenomena is only possible in the virtual world of eQuest..,,
>
> Joe-Liam-Paul what do you think >?<
>
>
> /Jeremiah D. Crossett/
> /CleanTech Analytics/
> /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 Sun, Jul 15, 2012 at 5:47 PM, Peter Baumstark 
> <pbaumstark at sbcglobal.net <mailto:pbaumstark at sbcglobal.net>> wrote:
>
>     It's an interesting problem.  With this model, no matter what I
>     do, if I manually change the SHGC or SC (if I use the U-Value
>     method), or if I select different glazing types from the library
>     (with different SHGC values), no matter what face of the building
>     I change it, I get an increase in overall monthly energy use with
>     a lower SHGC.
>
>     I built the model through a zone by activity area method that
>     pretty closely matches the various zones of the building.  It's a
>     VAV with terminal reheat system (1995 Trane Intellipaks), and I
>     entered actual economizer, static pressure and SAT settings. 
>     Airflow matches as-built design drawings.
>
>     I tried using other eQUEST models I've built for other customers
>     using similar methods, changed the location to San Jose, and ran
>     window cases and results were as expected.
>
>     I'm coming to believe that one issue with the building in question
>     is the RTUs seem over sized relative to the use patterns and
>     internal heat gains.  This building previously had various lab
>     areas, then was purchased by another customer with lower internal
>     heat load rates, but they kept the same RTUs.
>
>     Could it be possible that the lower heat gains from better
>     fenestration products could place the RTUs at a more inefficient
>     spot on its performance curve?  I've ran into similar issues with
>     chilled water systems, but never looked at DOE-2 performance
>     curves for DX units.
>
>     Pete
>
>
>     ------------------------------------------------------------------------
>     *From:* Paul Diglio <paul.diglio at sbcglobal.net
>     <mailto:paul.diglio at sbcglobal.net>>
>     *To:* Joe Huang <yjhuang at whiteboxtechnologies.com
>     <mailto:yjhuang at whiteboxtechnologies.com>>; CleanTech Analytics
>     <jeremiah at cleantechanalytics.com
>     <mailto:jeremiah at cleantechanalytics.com>>
>     *Cc:* equest-users at lists.onebuilding.org
>     <mailto:equest-users at lists.onebuilding.org>
>     *Sent:* Sun, July 15, 2012 5:03:54 PM
>
>     *Subject:* Re: [Equest-users] Unexpected Custom SHGC Results
>
>     Joe:
>
>     I agree.  I find the comment to be more than mildly offensive.
>
>     I have the same experience that funky modeling results usually are
>     the result of flawed inputs or depending on too many eQuest defaults.
>     Paul Diglio, CEM, CBCP
>
>     87 Fairmont Avenue
>     New Haven, CT 06513
>     203-415-0082 <tel:203-415-0082>
>
>
>     www.pdigliollc.com <http://www.pdigliollc.com>
>
>
>     ------------------------------------------------------------------------
>     *From:* Joe Huang <yjhuang at whiteboxtechnologies.com
>     <mailto:yjhuang at whiteboxtechnologies.com>>
>     *To:* CleanTech Analytics <jeremiah at cleantechanalytics.com
>     <mailto:jeremiah at cleantechanalytics.com>>
>     *Cc:* equest-users at lists.onebuilding.org
>     <mailto:equest-users at lists.onebuilding.org>
>     *Sent:* Sun, July 15, 2012 7:21:54 PM
>     *Subject:* Re: [Equest-users] Unexpected Custom SHGC Results
>
>     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/
>>     /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 <tel:%28925%29388-0265> (c)
>     (510)928-2683 <tel:%28510%29928-2683> www.whiteboxtechnologies.com
>     <http://www.whiteboxtechnologies.com> "Building energy simulations
>     at your fingertips"
>
>


-- 
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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