[Equest-users] Modeling Light Shelves for Reduction inCooling/Heating Load?

[Nick Caton]

It's not my intent to "take sides" or anything, but a curious reader
(me) might ask "What do you use, Chris?"  

 

As I'm pointing out - a saving grace of eQuest/DOE2.2 is that you can
spoon-feed whatever scheduling you may have generated in an outside
program if you don't like what you're seeing.  I understand some
distrust eQuest's results enough to regularly use DAYsim to generate
custom scheduling.  In my practice, I've found it more time-efficient to
work within and around the known limitations of eQuest, for the sort of
energy modeling I'm regularly tasked with.  I also prefer to use other
software packages to model instantaneous daylighting behavior - anyone
interested, see archives.

 

I do think it's a bit of a stretch however to claim the hourly modeled
daylighting behavior of eQuest is comparably dumbed-down as a blanket
percentage reduction, as we do with LPD's for occupancy sensors under
90.1 (I think that's what you're referencing) - eQuest's current
capabilities do allow an end-user to effectively compare multiple custom
daylighting control strategies and their resultant effects on the rest
of a building's systems (i.e. heating/cooling) in a time-efficient
fashion.

 

I'm not disagreeing the DOE2.1e algorithms aren't the best for figuring
how many fc are incident in a given space for a given hour, but
statements that boil down to "eQuest sucks for daylighting" (for LEED
modeling or otherwise) can certainly be misleading.  If you can take
what's known to be inaccurate into account, you can realize eQuest as a
pretty useful tool for designing with daylighting.

 

~Nick

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: Chris Jones [mailto:cj at enersave.ca] 
Sent: Monday, August 23, 2010 4:03 PM
To: Nick Caton; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Modeling Light Shelves for Reduction
inCooling/Heating Load?

 

Equest, like DOE2.1e before it provides very generous estimates of the
lighting energy saved using daylighting controls.  I believe that taking
equest predictions at face value for LEED models would be inaccurately
providing more benefit than warranted.  The Appendix G power factor
ratings are likely not conservative in some cases.  I wouldn't expect to
see any more benefit using equest's daylighting than I would using the
Appendix G power factor adjustments.

A paper that attempted to explore various daylighting energy reduction
savings modelling strategies.  DOE2.1e and Daysim are the two programs
used for the analysis.
http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc46761/nrcc46761.pdf


At 03:49 PM 23/08/2010, you wrote:



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Perhaps these are the answers you're seeking:
1.       Building shades and their respective reflectance properties do
affect the modeled behavior of space daylighting systems in eQuest
models.  Be sure to pay close attention to all three values (and their
associated help files) on the right of the following image - they may
all play a part depending on what exactly you're trying to model.
 
2.       Based on your query, a caution:  eQuest's results do not have
any inherent degree of accuracy/in-accuracy with regard to the modeled
energy consumption resulting from daylighting controls - that depends
pretty much entirely on how closely you define the daylighting systems'
behavior to reality.  If you have a program which you perceive to be
producing more accurate hourly percentage consumptions for your spaces,
then by all means - there's nothing stopping you from defining a
schedule in eQuest to match the other program's results.  
 
I expect you mean to say you're utilizing another program to accurately
determine the behavior of daylight in response to adding/modifying light
shelves, but if you are indeed using another program to determine annual
hourly behavior with a weather file, I'd be very interested to hear more
about it!
 
Best of luck,
 
~Nick
 

 
NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com 
 
From: equest-users-bounces at lists.onebuilding.org [ 
mailto:equest-users-bounces at lists.onebuilding.org
<mailto:equest-users-bounces at lists.onebuilding.org> ] On Behalf Of Nilay
R. Desai
Sent: Monday, August 23, 2010 11:35 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Modeling Light Shelves for Reduction
inCooling/Heating Load?
 
E.G. Would it be accurate to model an external light shelve as a
horizontal building shade with a high reflectance value on the skyward
facing surface? I understand the day lighting benefit in Equest would be
inaccurate, but we are using separate software to obtain accurate day
lighting results. Thanks!
 
 
Nilay Desai
P  626.351.8881 Ext. 237
ndesai at ttgcorp.com <mailto:klowe at tmadtg.com> 
 


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Chris Jones
14 Oneida Avenue
Toronto, ON M5J 2E3.
Tel.  416-203-7465
Fax. 416-946-1005

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