[Equest-users] DD Wizard: Discrepancies between Proposed andBaseline

[Nick Caton]

Hi Kristy!

 

A majority of the variables affecting fan power (scheduling, kW/CFM...)
aren't explicitly specifiable until you are in detailed mode.

 

That said, a CV heatpump system may well consume less fan power than a
VAV system as you (1) don't have as many fans in quantity and (2) your
CV fan may be running intermittently whereas a VAV system has a main fan
running constantly / on a schedule.  

 

Note that by limiting yourself to the wizards you are only able to
specify inexact "standard/high/premium" efficiencies, whereas if you
moved into detailed you could specify these to your liking to get a more
accurate reading on total fan energy consumption.

 

If you are unhappy that the cooling consumptions reported aren't equal,
adjusting the corresponding cooling efficiencies is probably about all
you can do to affect that if you're stuck in the wizards.  

 

Fundamentally, all things being equal however, a VAV system with reheat
(?) is probably going to consume more energy cooling supply air, as
you're now providing cooling to supply air that needs to be reheated in
some zones during certain seasons.  What you gain in occupant comfort
you might lose in cooling consumption!

 

Kristy, the following is less for you and more for the group at large,
as I understand you're a veteran here ;):

 

Whenever your "wizards only" model is not behaving properly and time
permits, I'd encourage you to temporarily pop into detailed mode to
explore everything the wizards are really specifying as a means of
learning the why's and wherefore's of your modeled behavior.  As newer
modelers learn eQuest/DOE2, the wizards can be viewed as something like
a set of training wheels that eventually you need to remove before you
can really compete in a race.  For all they do to simplify and
streamline creating a model, the wizards are frankly limiting.  Until
you can swim in the deep end of the pool, you can't dive to the deepest
depths.

 

Experienced modelers will intentionally decide to use "wizard-bound"
models to explore things in a time-efficient manner, but that decision
hinges on knowing and accepting in what fashion the variables are
limited and determining those limitations are acceptable for the study
at-hand.  Do not avoid detailed mode based solely on any level of
discomfort you have with the level of control you are granted - dive in!
In the worst case, you can always pop back to the wizards.

 

~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] On Behalf Of Walson,
Kristy
Sent: Tuesday, November 02, 2010 2:51 PM
To: eQUEST Users List
Subject: [Equest-users] DD Wizard: Discrepancies between Proposed
andBaseline

 

Hello Equest friends,

 

I am working in the DD Wizard (and trying to not move into Detailed
Mode), building the Proposed and Baseline models for a project that is
in the middle of design.  I took the Proposed model file and did a "Save
As" to create the Baseline model, so I know that the two models are
starting out the same.  My Proposed HVAC system is a Packaged VAV with
Electric Heat and my Baseline system is a Packaged Heat Pump Constant
Volume.  When I only change the system type in the Baseline model from
the Proposed Pkgd VAV to the Constant Vol. HP, my annual energy
consumption for cooling reduces in the Baseline model (I would expect no
change), the heating consumption reduces (this is to be expected), and
the fan power goes down in the baseline.  I can't figure out, when I
change from a VAV to a Constant Volume system why the fan power would
ever go down.  I was hoping to make up for the HP's better heating
efficiency through reduced fan power.  

 

This just doesn't make sense to me.  Remember, I'm still in the DD
Wizard and only have limited access to changes.  Can anyone explain this
to me and offer advice on how to achieve more predictable results?
Thanks in advance for the help.

 

Kristy M. Walson, PE, LEED AP

Mechanical Engineer / Sustainable Design

 

TLC Engineering for Architecture
Your 2030 Challenge Partner

 

255 South Orange Avenue, Suite 1600

Orlando, FL 32801-3463

 

phone: 

407-841-9050

fax: 

407-425-7367

direct: 

407-487-1118

website: 

www.tlc-engineers.com

 

http://www.tlc-engineers.com/images/TLC_Sig_Loc_Block.gif
<http://www.tlc-engineers.com/> 

Please consider the environment before printing this email.

 

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