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NC-2009 EAp2:Minimum Energy Performance

Table 1.4.7B Entering Outdoor Airflow in Baseline

Greetings, There is a clarification issue while entering these values in the Baseline about which I'd appreciate some advice. The OA flow should be identical in both models. When calculating the HVAC systems in Baseline (system 5 or 7), and since these are multiple-zone systems, the OA is corrected at the end by Ev and with exception of Ev=1 the OA which is calculated (corrected Vot) is bigger. In Propose case however almost always the Ev is different, in most of the cases bigger than the Baseline one. The question is: should I enter the uncorrected OA flow in both cases, in order in the table these values to appear equal, besides this way it will reflect exactly the project design. Thanks.

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Tue, 12/09/2014 - 19:49

The Proposed should be based on the design value and the Baseline should be the same in all areas without DCV.

Tue, 12/09/2014 - 20:02

Thanks for the reply. However it's kind of unclear to me the comment about DCV. As I've tried to say, the only way the OA to appear identical in both Proposed and in the Baseline is to enter the uncorrected OA value in accordance to ASHRAE 62.1 terminology. The question was am I right in such suggesting. Thanks.
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Wed, 12/10/2014 - 15:02

No DCV - model OA identical based on the actual equipment designed/installed. If the equipment is designed with 1,000 cfm of OA then that is what gets modeled. With DCV - again model the proposed based on the actual equipment designed/installed. The baseline OA is modeled using the ASHARE 62 calculation for the proposed and this should be the same as the Vot calculated for IEQp1.

Thu, 12/25/2014 - 12:56

Hi Markus, thanks a lot for your replies. However there are some final clarifications on this issue I'd like to ask about. So, the number of people and the ventilation rates (as per ASHRAE 62.1) are entered absolutely identical in Proposed and Baseline model. The OA when it is 100% is also identical. The Voz (ventilation outdoor air per zone) are identical too. When it comes to compare the Vot values, the quantities are not identical with the exception of 100%OA. For the Proposed I can enter the Vot from the IEQp1 form, but for the baseline I'm taking it from the calculation reports of the energy simulation software. I assume that this difference in Vot values is due to the systems with DCV. The Baseline systems are one per every floor, whereas the Proposed ones are arranged differently and probably because of this the totals are different. The Question is: It in Table 1.4.7 in the row of Outdoor Airflow, if the Vot values are entered and the totals appeared not identical, should this be a problem or be questioned for explanation by the reviewer. Thanks.
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Fri, 12/26/2014 - 20:15

The difference between Vot and Voz is usually due to systems with DCV in the proposed case. If there is a difference reported in the 1.4.7 tables and there is DCV in the proposed the reviewer will expect to see that the baseline OA is slightly less than the proposed OA. Also keep in mind that the OA being identical is in cfm quantity not based on percentage. A 100% OA system in the proposed may not be 100% OA in the baseline depending on the auto-sized supply cfm in the baseline system. In systems without DCV the proposed OA is modeled as designed (not using the Vot). The baseline systems are identical. In systems with DCV the proposed OA is also modeled as designed but the baseline uses the Vot value.

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