# Load Calcs vs Energy Model for LEED

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Joined: 2012-07-19
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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
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Joined: 2012-11-12
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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 | www.aeieng.com
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Joined: 2010-10-13
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Joined: 2011-10-01
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Greg, did your project pass? It?s been a headache so far to solve this item. Thanks for all the input so far everyone!, It you have additional suggestions let me know. 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 ? F: 305.594.0907 www.jalrw.com | ccaballero at jalrw.com [cid:image001.png at 01CFE22E.5C0DB950] [cid:image002.png at 01CFE22E.5C0DB950] [cid:image003.png at 01CFE22E.5C0DB950] [cid:image004.png at 01CFE22E.5C0DB950] This email and any files transmitted with it are confidential and intended solely for the addressee. If you are not the named addressee you should not disseminate, distribute, copy, or alter this email. Please consider the environment before printing this email.
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Joined: 2012-07-19
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It is not so hard? Just export the proposed airflows at each room to excel. Do a filter and sort to make sure the room order in your file match the Trane Trace model. Then paste the proposed airflows into the Trane Trace model using the component view. Once you learn the component view you can input 50-75% of you inputs from pastes from Excel. Rick R I C H A R D E L L I S O N BEAP, BEP, BEMP, BESA, CBEP, CDSM, CEA, CEM, CMVP, CTAB, DGCP, HBDP, LEED AP, PE Manager of Energy and Simulation Southland Industries 22340 Dresden Street, Suite 177 Dulles, VA 20166 Office: 703.834.5570 Direct: 703.834.2438 Fax: 703.834.5572
R I C H A R D E L L I S O N BEAP, BEP, BEMP, BESA, CBEP, CDSM, CEA, CEM, CMVP, CTAB, DGCP, HBDP, LEED AP, PE Manager of Energy and Simulation Southland Industries 22340 Dresden Street, Suite 177 Dulles, VA 20166 Office: 703.834.5570 Direct: 703.
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Joined: 2011-09-30
Reputation: 1
Scott/Craig ? I have two ideas that might help get a workaround ? it may not work on every system type, but it did on a FPVAV system I just experimented with: 1. To address Scott?s issue re: a the difference between block load and sum of peak zone CFMs, Trace offers an option to size the fan (and/or the main cooling coil) based on the sum of the peak airflows, rather than the block airflow. On the ?Create Systems? dialog, ?Advanced?? button there are fields that allow you to modify the parameter used to determine the fan size and the coil size (as below). Changing these from ?block? to ?peak? changed the flow of the ?Tutorialtrc.trc? file from 16160 cfm sum of peaks / 13778 block cfm to 16160 sum of peaks / 16160 block CFM. [cid:image009.jpg at 01CFE234.C0F03C20] 2. On the Create Systems ? Heating and Cooling Over-rides tab, the main cooling coil can be oversized by a specific percentage ?by adjusting airflow.? I believe this would allow you to maintain the same discharge air temp and modify the system airflow as desired. It may not offer unconstrained combinations of leaving air temp, coil capacity, and system airflow, since Trace is auto calculating entering air conditions, but it may offer you an additional degree of freedom to get close at the system level: [cid:image010.jpg at 01CFE234.C0F03C20] There may be unexpected consequences that make these ideas less than the best for your specific situations ? but it seems like I?m able (at least in this case) to get the fan CFM to match the scheduled CFM, even if the load calc block load would show a different total CFM. Hope this helps, Aaron Dahlstrom, PE, LEED? AP In Posse ? A subsidiary of AKF| 1500 Walnut Street, Suite 1414, Philadelphia, PA 19102 d: 215-282-6753| m: 267-507-5470| In Posse: 215-282-6800| AKF: 212-354-5656 e: ADahlstrom at in-posse.com | in posse web: www.in-posse.com | akf web: www.AKFGroup.com
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Joined: 2011-09-30
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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.
R I C H A R D E L L I S O N BEAP, BEP, BEMP, BESA, CBEP, CDSM, CEA, CEM, CMVP, CTAB, DGCP, HBDP, LEED AP, PE Manager of Energy and Simulation Southland Industries 22340 Dresden Street, Suite 177 Dulles, VA 20166 Office: 703.834.5570 Direct: 703.
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Joined: 2011-09-30
Reputation: 1
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 ? F: 305.594.0907 www.jalrw.com | ccaballero at jalrw.com [cid:image002.png at 01CFE244.273C7200] [cid:image003.png at 01CFE244.273C7200] [cid:image004.png at 01CFE244.273C7200] [cid:image005.png at 01CFE244.273C7200] This email and any files transmitted with it are confidential and intended solely for the addressee. If you are not the named addressee you should not disseminate, distribute, copy, or alter this email. Please consider the environment before printing this email.
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Joined: 2012-07-19
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