[Equest-users] Unexpected Custom SHGC Results
Busman, Michael R
MBusman at chevron.com
Mon Jul 16 08:20:11 PDT 2012
Pete,
The performance curves are one item to check out if the RTUs are greatly oversized.
A couple other things come to mind:
* If they originally had lab areas with high make up air requirements, the RTUs could be greatly oversized and operating at a low enough load with the reduced SHGC to bring on hot gas by-pass (within the simulation).
* Check the minimum % cfm of the VAV boxes. If it's a high % like 60%-70% which I've seen in the past, you could be bringing on reheat, which will increase cooling load in addition to reheat energy.
Mike Busman
Chevron Energy Solutions
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bruce Easterbrook
Sent: Monday, July 16, 2012 7:04 AM
To: Peter Baumstark
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Unexpected Custom SHGC Results
If you are manipulating the envelope you should be looking at the envelope reports. Specifically LS-B, then LS-C. This is the only way you will see the actual effect of the windows before the data is lumped with everything else. You will also notice the elephants in the room, lights and occupants. Occupants are indirect and equal outside air. Have the lights been upgraded? RTU are notorious for being poorly set-up and are the first thing a building manager plays with when the bills get too high, they turn down or off the outside air. You haven't mentioned energy bills, you really need them when you are doing this kind of work. They are a check on the accuracy of your assumptions in eQuest and what is actually going on in the building. You won't likely get that close to actual costs but they are a good order of magnitude indicator. Check SV-A which will give you people counts and outside air. If your lights or your people are out, or both you won't see the window changes in the gross numbers.
After that it is trouble shooting. Most problems in eQuest are input errors or incorrect assumptions. It is quite accurate when you get everything right in your input. But it is a model and you are using canned weather so everything is relative not exact.
As for the naysayers, some people like Ford and some like GM, but in the end they are just 4 wheels to get you down the road. If you can't keep your wheels out of the ditch it is not their fault.
Bruce Easterbrook P.Eng.
Abode Engineering
On 15/07/2012 08:47 PM, Peter Baumstark 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
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 LBL window does glass U-value not shading, ware-as LBL optics 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>
[http://cleantechanalytics.com/images/stories/cleantech%20analytics%20120.PNG]
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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