[Equest-users] EEM vs. new model

[David Eldridge]

eQUEST’s defaults will be important here for pressure drop in the two
systems, ability to modulate airflow or chilled water flow, ability to
economize (although Google shows your company near the Gulf, so if this is
a local auto dealer then maybe economizer won’t be important).



The use of the chiller system’s cooling efficiency and pump power will be
important since these are known, and may vary from the wizard’s suggestion.
You’ll also need to make sure the DX system efficiency and fan power is
realistic.



The part-load performance of the system could also be important if the
hours for the shop and show room are different – this could be a case where
two or more right-sized DX systems may be a better match than one chiller,
depending on the magnitude for the loads and if the zones have wildly
different hours of operation.



My suggestion would be to set eQUEST aside for a half hour, and just run
through a table for the fan power, pump power, and cooling efficiency for
each of the two cases and see if the answer jumps out at you. If you get
pointed strongly in one direction, then review the eQuest files more
closely to be sure you are capturing all of the part-load effects.



Regarding your ASHRAE 90.1 baseline suggestions, that might be your best
“baseline” and then compare the proposed CHW and an enhanced DX system
against that, but shouldn’t be necessary other than as Nick suggests for a
QA reference.



David

*
*



David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

*Grumman/Butkus Associates*

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*





*From:* equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Matt Clough
*Sent:* Tuesday, April 24, 2012 7:37 AM
*To:* Nick Caton; equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] EEM vs. new model



I suppose I should have been more specific in my description:



By baseline I mean the proposed design.  So the program outputs 2 sim files
– the base(proposed, CHW) case and the iterated (DX) case





We want to use eQuest to validate the system choice on this particular
project.  This is work that was started before I joined, but I have been
selected to try and use eQuest to compare the performance of a chilled
water system and a DX system.   I’m not the most experienced energy
modeler, but it seems like a task that would be a good application for
eQuest.



My approach was to simulate the energy consumption of a building that is
similar to the actual design in orientation, shape, and square footage.  I
initially built the model in the SD wizard, using most of the default
values (building envelope, activity usage, etc.), autosize the equipment,
and use the EEM to compare the two systems.  The idea was that when the
building construction and geometry are equal, we can look at the relative
energy consumption of the two systems.  This initial simulation reported
that the DX system would be more efficient, which is not what I had
expected based on the design that had been selected.

So I figured that maybe my model was too generic, too simple.  I created
zones based on the plans, and made the geometry more representative of the
actual building.  These changes produced reports that suggest the chilled
water system is more efficient than the DX.  I realized that the EEM was
incorrectly modeling the change – it was treating the chilled water system
as having all 8 air handlers, but was modeling the DX system as one AHU.
So I created a duplicate model that has a DX system (autosized and using
equest defaults).

The comparison of these two models suggests the DX system is slightly more
efficient.  Unfortunately, my lack of experience makes me doubt the
validity of this comparison – especially considering that the engineers
selected a chilled water system for this project.



So I suppose my questions are: Does my approach seem valid? Is this an
appropriate use of the software?



After taking some time to write this note, and with a little rest, I wonder
if comparing the proposed design to an ASHRAE 90.1 baseline would have been
a better approach.



Regards,

Matt Clough


------------------------------

*From:* Nick Caton [mailto:ncaton at smithboucher.com]
*Sent:* Monday, April 23, 2012 3:40 PM
*To:* Matt Clough; equest-users at lists.onebuilding.org
*Subject:* RE: EEM vs. new model



By context, I gather by ‘baseline’ you mean something other than your
proposed design, such as an 90.1 Appendix G baseline or similar.



If that’s the case, my general advice is that you should *much* more
heavily weight the comparative results using your “actual/proposed” model.
A baseline per above inherently diverges from the actual building
materials, lighting power densities, solar load shading, and so forth.
It’s not the same building.



Best to choose systems that most efficiently handle your actual project.
Don’t get too hung up what works best for an imaginary building ;).



~Nick



[image: cid:489575314 at 22072009-0ABB]**

* *

*NICK CATON, P.E.*

SENIOR ENGINEER



Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com* *



*From:* equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Matt Clough
*Sent:* Monday, April 23, 2012 1:59 PM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] EEM vs. new model



Salutations eQuesters,



I’m doing a simple comparison between a chilled water and DX system.  It
would seem that this is a great opportunity to use the EEM, and the
simulation predicted that the CHW configuration would be more energy
efficient than the DX system.  To be conservative, I also made a copy of
the baseline model and changed the system from chilled water to DX.  Using
this method, the simulation predicts that the DX system would be more
efficient (although not by much).  Which result is most accurate?  The
building is a car dealership with a large showroom and an air-conditioned
parts storage area.



The geometry and building envelope are not exact, but I made this decision
because we are doing this for comparison purposes, so the geometry and
construction will be the same.

I have let eQuest autosize both systems.



Sincerely,

Matt Clough
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