[Bldg-sim] 90.1 Baseline Model for Proposed VRV Design Model

Christian Kaltreider ckaltreider at sudassociates.com
Wed Aug 31 05:25:02 PDT 2011

Reba and Nick,


Thanks for the responses.  I believe I have resolved the issue.  Although it
is disconcerting to have such an unreasonable number of RTUs in the
baseline, this was actually not the major cause of my modeling issues.
However, it was causing part of the problem:  In TRACE, each new RTU comes
with a default amount of power associated with 'miscellaneous accessories'
(control panel and interlocks).  It's not a whole lot, but in the baseline
model this power allotment was added on over and over again (many RTUs),
while in the proposed model it is only added a couple of times.  I was able
to adjust this to more reasonable values.  This helped a good bit, but it
does not affect heating energy.  


As Nick suggests, the heating energy was not caused by the over-abundance of
RTUs at all.  I believe I actually identified the cause of this issue at
some point early on, but I'd forgotten what had caused what in my numerous
experimental iterations (another reminder to carefully document each change
and its result on the model!).  Sorry for any confusion there.  I hate
jumping the gun when posting a question.


To address the TRACE-specific plants/systems relationship:  In TRACE a
system refers to the distribution side of things and a plant is primarily
concerned with the generation of heating/cooling.  You have to specify a
plant to go with a system, even for a DX PSZ-HP.It is a little bit strange
to think of a packaged DX unit in this way, but TRACE has a well-defined
method of creating such configurations (the names for the systems and plants
are pretty clear).  In the case of a packaged unit, there should technically
be one plant for each system since the generation and distribution are tied
together in one unit and are independent of any other systems.    


I hope this makes sense.  I'm pretty new to TRACE, but I think my
explanation above is correct.  If anyone with more experience would like to
elaborate, feel free!


Thanks for your help,



From: Nick Caton [mailto:ncaton at smithboucher.com] 
Sent: Tuesday, August 30, 2011 7:13 PM
To: Reba Schaber; Christian Kaltreider; bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] 90.1 Baseline Model for Proposed VRV Design Model


The queries posed are of two sorts:  TRACE/HAP specific and 90.1/LEED
specific.  I can address the latter variety as I'm primarily an eQuest user:

-          Combining similar zones/blocks may save some time in setting up
the model (for any software package), but you may find it causes more work
in the long run as you may be required to document/justify why your modeled
systems are of a larger capacity than the proposed/actual units - food for

-          Many tiny RTU's may seem unreasonable from an equipment-selection
perspective (and often is), but the goal 90.1 is trying to establish is to
set an efficiency standard for such equipment, as Reba is alluding to.  Note
that G.3.1.1 has provisions to define additional (per floor) baseline system
types where that may be appropriate.  That said.

-          If your baseline model is outputting a significantly different
energy distribution (suggested by your concern about heating becoming the
primary consumption), that's a likely sign something else is off in one or
both models.  Make some QC checks to ensure the loads/schedules/ventilation
rates and other items that are supposed to be identical between the
baseline/proposed are as such.  A check of unmet hours may lead you down the
same path.

-          As to the PLANT/SYSTEM relationships - that sounds TRACE-specific
to me.  You might hold out for responses from others on this list more
familiar with TRACE, or perhaps post a specific question to the TRACE-users
list as well.  FYI: it's not entirely clear how/why the results are
unreasonable or whether you're talking about your proposed or baseline
results from the context ;).

-          It may be helpful to remember that terms like "zone" "space"
"plant" and "system" can have software-specific meanings/nuances, so what
may seem perfectly reasonable for HAP may not jive with TRACE and vice


Hope this helps somewhat =),



cid:489575314 at 22072009-0ABB





Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617



From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Reba Schaber
Sent: Tuesday, August 30, 2011 5:34 PM
To: Christian Kaltreider; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] 90.1 Baseline Model for Proposed VRV Design Model



I have not seen this with a VRV system, but I've had a similar experience
with a VAV system.  The LEED reviewer insisted thermal blocks be modeled
identically in Baseline and Proposed.  That meant a Proposed bldg with 2
AHU's each with about 35 VAV terminal units became about 70 package units in
the Baseline bldg.  Crazy, there is not enough roof space for 70 units.


Even though the Baseline systems do not always make sense, Appendix G
attempts to make the energy models similar between everyone. It tries to
standardize things for equal comparison.  That's my understanding.


I do have a question.  I'm not familiar with Trace.  In HAP only systems
with heating or cooling coils can be added to a plant.  How is it that Trace
allows DX units be added to a plant?  Seems you have a choice of multiple
plants, one per system OR one plant for all systems.  I think you should
choose the model that most accurately represents a PSZ-HP.  


         Reba Schaber      Mechanical Engineer, P.E.
                                     LEED Accredited Professional
1660 N. Alvernon Way                Voice: (520) 731-2060
Tucson, Arizona 85712                Fax: (520) 731-2061
                        rschaber at phmech.com


From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Christian
Sent: Tuesday, August 30, 2011 9:24 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] 90.1 Baseline Model for Proposed VRV Design Model


Hi All,


I am doing an Appendix G model for LEED.  The proposed building uses a VRV
system where each room has individual control over its own VRV unit.  All of
the VRV units share 2 heat pumps.  My problem is this:  Since each room has
individual control, each room is a 'thermal block'.  I have combined as many
as I can according to the Appendix G rules.  However, I still have many
thermal blocks.  For the baseline, I am required to model a PSZ-HP (packaged
roof top unit heat pump) for each thermal block.  This is giving a bunch of
tiny rooms their own individual RTUs, which seems ridiculous and it is
driving my baseline energy use higher than reasonable (primarily in heating
energy.not sure why). 


I am modeling in TRACE, giving one SYSTEM per thermal block, and one PLANT
per SYSTEM.  If I am allowed to connect all of my systems to just one plant,
my energy use becomes more reasonable.but this seems to go against Appendix


Has anyone come across this issue when modeling a baseline for a proposed
VRV system? 






Christian Kaltreider, LEED AP

Energy Engineer

Sud Associates, PA

20 Battery Park Ave

Flat Iron Building, Suite 706

Asheville, NC  28801

(828) 255-4691

ckaltreider at sudassociates.com




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