[Equest-users] Modeling inefficiencies of existing buildings

[Nick Caton]

Those are some good questions!  I'll be interested to hear others'
suggestions/thoughts...

 

I think I can help directly with question #2: 

-          All heat from lights can ultimately go 3 ways in eQuest,
corresponding to 3 fractional variables you can define/modify for
lighting internal loads:

o   LIGHT-TO-SPACE - what fraction of heat goes straight into the
conditioned space

o   LIGHT-TO-RETURN - directly into the return air path  (think:
recessed fixtures in a return air plenum)

o   LIGHT-TO-OTHER - allows you to specify a space for heat to go that
isn't part of a return path.

-          If you wish to model the effects of troffer diffusers, I
think the most direct way to do so would be to differentiate from normal
troffers by modifying the above fractions between the two runs, found
under the internal loads tab (not at the system level).

-          Carefully review your options (i.e. the DOE2 help entry) for
"RETURN-AIR-PATH" at the system level to be sure you aren't skewing the
meaning of what you want to input.

-          While you might take a variety of other approaches... on a
fundamental level, if you try to account for lighting system behavior at
the system level (modifying supply temps and the like), you're likely
going to run into the problem of needing to differentiate the lighting
and HVAC systems' scheduling at some point... 

 

I may be missing some fundamentals, but I suspect that light troffer
diffusers aren't that inefficient on a wholistic system level (in the
grand scheme of things) - ultimately the heat generated by the lights
doesn't just disappear if kept out of the supply/return paths... that
heat eventually needs to be dealt with by the HVAC, directly or
indirectly.  I suppose local thermostats might trip less frequently

 

Someone with more experience may be able to suggest a path to #1... I'm
stuck for ideas there.

 

To #3, I think you need to be more explicit regarding which variables
you changed, and what the new/old values were.  It might help to start
with understanding what eQuest is modeling before you 'enable' these
values... the following may help:  

 

Volume 5: Compliance Analysis > Performing Compliance Analysis >
Building Modeling Topics > Duct Efficiency Calculations > Detailed
Interface

 

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] On Behalf Of John
Bixler
Sent: Monday, November 08, 2010 7:37 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Modeling inefficiencies of existing buildings

 

Hello all,

 

I've been using eQuest recently to support studies of existing
buildings, and to evaluate the energy savings of different options.

 

I've struggled with trying to model some of the problems we've
discovered in the older buildings.  Any thoughts on the following would
be greatly appreciated.

 

1.       Failed reheat valves:  Reheat valves that are stuck in the open
position.  Not only does this increase the heating hot water use, but it
should affect fan energy and chilled water use as well.

2.       Light troffer diffusers:  All the vogue in the 60s and 70s,
these combination lights and diffusers result in a large thermal gain as
the air enters the zone.  eQuest has "duct delta T", however that
assumes a heat loss under cooling.  This condition is always a gain of
heat (and technically this will vary based on the temperature of the air
entering the zone).

3.       Duct Leakage:  A massive problem until recently, measured
leakage values can often be 30% or more.  eQuest has an apparent entry
for this, however, each time I've enabled it, I've seen large REDUCTIONS
in energy use.  Again, this is a condition that results in increased
usage of all utilities as the zones struggle to meet their setpoints.  

 

Also, duct leakage is assigned at the system level.  It appears eQuest
then wants you to assign what plenum the duct is leaking "to".
Depending on how I specified my systems in the wizard, I have ended up
with a plenum zone for each zone on a floor (which might mean 30 zones
per floor) or one big plenum per floor.  If I have a system that serves
zones on several floors, it dosent seem like eQuest will let me assign
the leakage to go all the plenums the system is assigned to, evenly.  I
have to pick a SINGLE zone that all the leakage goes to.

 

Thanks,

 

John Bixler, LEED AP BD+C

Mechanical Designer

Sebesta Blomberg 
sebesta.com | P  319.364.1005 | M  319.558.9299 

 

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