[Trace-users] Load Calcs vs Energy Model for LEED

Tue Oct 7 12:34:17 PDT 2014

The difference of airflow is around 80% of the original cfm. Is there a threshold that they consider reasonable? Is there a document mentioning this threshold as well to reference in response?

Catalina Caballero.  AIA. Assoc., LEED GA.
Sustainability Coordinator

Johnson, Avedano, Lopez, Rodriguez & Walewski Engineering Group, Inc.
Engineering for High Performance Buildings.
MEPF - BIM - LEED - Cx

2510 NW 97 Ave, Ste 220, Miami, FL 33172.
P: 305.594.0660  Ext: 217 Ӏ F: 305.594.0907
www.jalrw.com<http://www.jalrw.com> | ccaballero at jalrw.com<ccaballero at jalrw.com%20>

[cid:image002.png at 01CFE244.273C7200]<http://www.facebook.com/jalrw> [cid:image003.png at 01CFE244.273C7200] <http://www.linkedin.com/company/johnson-avedano-lopez-rodriguez-&-walewski-engineering-group-inc./>  [cid:image004.png at 01CFE244.273C7200] <https://www.twitter.com/JALRW/>  [cid:image005.png at 01CFE244.273C7200] <https://plus.google.com/u/0/b/112470263254966771834/112470263254966771834/posts>

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From: Hintz, Scott F. (KSC-ISC-2530)[URS Federal Technical Services, Inc.] [mailto:scott.f.hintz at nasa.gov]
Sent: Tuesday, October 07, 2014 3:30 PM
To: Richard Ellison; Craig Gann; Scott Parker; Steve Jacobs; Caballero, Catalina; trace-users at lists.onebuilding.org
Subject: RE: [Trace-users] Load Calcs vs Energy Model for LEED

All design models should include all rooms. That’s just good load design.

To quote the 90.1 User’s Manual, “Grouping HVAC zones into thermal blocks requires engineering judgment to avoid modeling errors, but when it is done with reasonable care, there is no significant loss of accuracy.” Can’t say I disagree.

From: Richard Ellison [mailto:REllison at southlandind.com]
Sent: Tuesday, October 07, 2014 3:07 PM
To: Hintz, Scott F. (KSC-ISC-2530)[URS Federal Technical Services, Inc.]; Craig Gann; Scott Parker; Steve Jacobs; 'Caballero, Catalina'; trace-users at lists.onebuilding.org<mailto:trace-users at lists.onebuilding.org>
Subject: RE: [Trace-users] Load Calcs vs Energy Model for LEED

On some buildings like hospitals our design model is REQUIRED to include all rooms.  We then transform out design models into energy models to they too have all rooms.

The block models always provide different energy results when compared to the detailed room by room models from my experience.

From: Trace-users [mailto:trace-users-bounces at lists.onebuilding.org] On Behalf Of Hintz, Scott F. (KSC-ISC-2530)[URS Federal Technical Services, Inc.]
Sent: Tuesday, October 07, 2014 3:01 PM
To: Craig Gann; Scott Parker; Steve Jacobs; 'Caballero, Catalina'; trace-users at lists.onebuilding.org<mailto:trace-users at lists.onebuilding.org>
Subject: Re: [Trace-users] Load Calcs vs Energy Model for LEED

There is absolutely no reason to model every single room in TRACE for an Appendix G model. That could be a huge waste of time. Now if the team used TRACE for load and design calcs then a lot of work is already done using that same load file as the starting point for the energy model. In Appendix G, Table G3.1, #7 allows this and CDS has at least two excellent write-ups in their knowledge center giving examples on how to do this. Multi-zone systems should have the design block airflow entered under the Advanced system options and the block coil capacities under the coils tab. Proper tuning of a Proposed model must be done and not taken lightly so as to assure the proper load inputs have been made such that the entered loads align with the design coils and airflows. TRACE isn’t magic. If you enter 20,000 cfm as the block airflow for a VAV system and nowhere near or way too much load has been input, that will lead to big problems such as unmet hours and improper equipment unloading.

It’s all a tradeoff. You’re either going to spend a lot of time entering hundreds or thousands of rooms or you’re going to spend your time creating intelligent thermal blocks and tuning you’re Proposed model. I’ve found there’s significant time savings going the thermal block route but it does require more pre-planning. Proper use of templates goes a long ways too.

Scott Hintz
CEM, LEED-AP BD+C, BEMP

HVAC & Compressed Air
Systems Engineering (SE)
[cid:image006.png at 01CFE244.273C7200]Federal Technical Services
Kennedy Space Center, FL 32899

From: Craig Gann [mailto:cjg04austin at swbell.net]
Sent: Tuesday, October 07, 2014 12:55 PM
To: Scott Parker; Steve Jacobs; 'Caballero, Catalina'; trace-users at lists.onebuilding.org<mailto:trace-users at lists.onebuilding.org>
Subject: Re: [Trace-users] Load Calcs vs Energy Model for LEED

I communicated with CDS about this a couple of months ago. It's a royal pain in the @#$ to do this! What you have to do is go to the rooms and manually enter the CFM for each room such that it totals up to the desired CFM at the system level. This means you have to first figure out which rooms are assigned to each system then figure out how much to change each room CFM such that it totals to what you want then print out the calculated room CFM values. Not easy if you have hundreds of rooms. I wound up putting it all in Excel so I could figure out a room CFM multiplier that changed each room CFM by the percentage needed. It took me a half day to mess with this and is a major deficiency in the Trace software IMHO.

Regards,

Craig J. Gann, P.E.; LEED AP
On 10/7/2014 11:18 AM, Scott Parker wrote:
I agree that the proposed system model should have the same capacity as the actual equipment.  However, the challenge is that when you fix the leaving air temperature of the air handler (which matches typical design) then Trace does not allow any method for fixing the air handler CFM capacity.

For example, below I have just listed some numbers for reference to illustrate the point:

Sum of Peaks = 19,458 CFM
Block load = 18,902 CFM (actual maximum hourly airflow in Trace will typically be even less than this value)
AHU size = 20,000 CFM (scheduled on plans)

AHU size in trace = block load (18,902 CFM) – no way to force it to be 20,000 CFM.

Therefore, when the air handler (in Trace) is at 18,902 CFM it is at peak fan power (i.e. top of fan curve).  However, it actually is already part way down the true fan curve since the unit is scheduled for 20,000 CFM.  If you use the theoretical fan laws, then the fan power at 18,902 CFM is 84% of the scheduled break horsepower - (18,902/20,000)^3 = 0.84  -- even though the fan is operating at 94.5% of peak fan power.

If anyone has a work around for this I would like to hear it.  For me I have had to manually change the kW/CFM value to match the actual scheduled fan at the block airflow calculated in Trace.

Scott Parker  PE
LEED AP BD+C
Mechanical

AEI | AFFILIATED ENGINEERS, INC.
1414 Raleigh Road, Suite 305 | Chapel Hill, NC  27517

P: 919.419.9802 | F: 919.419.9803
sparker at aeieng.com<mailto:sparker at aeieng.com>  |  www.aeieng.com<http://www.aeieng.com/>

From: Trace-users [mailto:trace-users-bounces at lists.onebuilding.org] On Behalf Of Steve Jacobs
Sent: Tuesday, October 07, 2014 11:13 AM
To: 'Caballero, Catalina'; trace-users at lists.onebuilding.org<mailto:trace-users at lists.onebuilding.org>
Subject: Re: [Trace-users] Load Calcs vs Energy Model for LEED

Your proposed inputs need to match what is actually being installed in the building. If they are installing oversized equipment, you need to model oversized equipment. The model will account for part load efficiencies.

-          Steve

From: Trace-users [mailto:trace-users-bounces at lists.onebuilding.org] On Behalf Of Caballero, Catalina
Sent: Tuesday, October 7, 2014 9:04 AM
To: trace-users at lists.onebuilding.org<mailto:trace-users at lists.onebuilding.org>
Subject: [Trace-users] Load Calcs vs Energy Model for LEED

Hello experts,

We recently received comments back from LEED  and one of the comments says the following:

It appears the equipment capacities (fan volume, fan power, cooling capacity, etc.) for the HVAC systems in the Proposed model
are inconsistent with the equipment capacities in the actual design when comparing the LEED Energy Performance Summary Report
to the mechanical schedules provided for PIf4: Schedule and Overview Documents
G3.1.10 in the Proposed building column requires that the Proposed model reflect all HVAC systems at actual equipment capacities
and efficiencies. The HVAC equipment capacities cannot be autosized in the Proposed model. Revise the Proposed model to reflect
all HVAC systems at actual equipment capacities. In addition, update Table 1.4.7B, and provide a revised LEED Energy Performance
Summary Report and the System Enterd Values reports for the Proposed model reflecting the changes. Further, if the equipment
capacities and efficiencies are based on updated mechanical schedules and/or HVAC submittal sheets, provide the updated
mechanical schedules and/or HVAC submittal sheets.

The only question that I have is why would they require for the airflows, to be exactly the same, to the original load calculations when the load calculations looks for the worst case scenario (using ashrae basic envelope, lighting, values), while the energy model looks for the most energy efficient model (actual installed envelope, occupancy, etc). It make sense that they are looking for something similar but it’s definitely not going to match the capacities and or airflows, (load calcs tend to be oversized).

I would greatly appreciate your opinion.

Thanks.

Catalina Caballero.  AIA. Assoc., LEED GA.
Sustainability Coordinator

Johnson, Avedano, Lopez, Rodriguez & Walewski Engineering Group, Inc.
Engineering for High Performance Buildings.
MEPF - BIM - LEED - Cx

2510 NW 97 Ave, Ste 220, Miami, FL 33172.
P: 305.594.0660  Ext: 217 Ӏ F: 305.594.0907
www.jalrw.com<http://www.jalrw.com> | ccaballero at jalrw.com<ccaballero at jalrw.com%20>

[cid:image002.png at 01CFE244.273C7200]<http://www.facebook.com/jalrw> [cid:image003.png at 01CFE244.273C7200] <http://www.linkedin.com/company/johnson-avedano-lopez-rodriguez-&-walewski-engineering-group-inc./>  [cid:image004.png at 01CFE244.273C7200] <https://www.twitter.com/JALRW/>  [cid:image005.png at 01CFE244.273C7200] <https://plus.google.com/u/0/b/112470263254966771834/112470263254966771834/posts>

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