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

Reba Schaber Rschaber at PHMECH.com
Tue Aug 30 15:33:50 PDT 2011

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<mailto:rschaber at phmech.com>

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Christian Kaltreider
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 G.

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<mailto:ckaltreider at sudassociates.com>


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