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NC-2009 EAp2:Minimum Energy Performance

How to prove compliance with Mechanical Ventilation

The project is a medium sized workshop shed and will be mechanically ventilated with fans with a particular air change per hour as per the local standards. The client wants this to be LEED certified building and we wanted to check what should be the right approach towards energy modeling to meet the EA Prerequisite 2 and EA Credit 1. Normally for a naturally ventilated building we would follow the approach mentioned in the Advanced Energy Modeling Guide, Appendix D. However this is not a naturally ventilated space, though there are windows opened to allow the air changes, with mechanical fans to meet the ventilation requirement. Shall we then model the base case with the same ventilation fans as the design case and prove compliance. Please let us know which CIR/ guide could tell us more about this. Please advise.

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Wed, 12/17/2014 - 11:09

G3.1.2.5 Ventilation: "Minimum outdoor air ventilation rate shall be the same for the proposed and baseline building designs". Actually I model exactly the same ventilation flows and the same schedules in the two models, for every hour. What does "minimum" mean in this case? I know that an exception could be when in the proposed building there is Demand Control Ventilation. The fans are modeled as designed for the proposed model, according to G3.1.2.9 for the baseline model. I hope this is useful to you.
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Marcus Sheffer
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Wed, 12/17/2014 - 15:18

If the space is heated then the baseline should be modeled as a system 9 or 10 under addendum dn to 90.1. The fan power in the baseline 0.3 watts/cfm. If the space in unconditioned then the ventilation fans are considered a process load and modeled identically.
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Jean Marais
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Wed, 12/17/2014 - 15:22

The standard requires the same infiltration and window ventilations be employed on both models. I would not recommend trying to take credit for window, "natural", or infiltration ventilation unless you are an expert and have a lot of time to prove your case.

Thu, 12/18/2014 - 08:56

Thanks for your prompt response. For your information, we have considered an air-change of 15 ach for effective ventilation for the shed. There is no demand control ventilation and no heating. The windows shall be kept open to facilitate this 15 ach ventilation. This is may be comparable to mechanically assisted natural ventilation. Shall we model the baseline with the fans as process load but without any baseline air-conditioning system and likewise for the design case. Or do we have to model the baseline with the baseline HVAC system types with the 15ach ventilation rate and similarly for the design case. This approach due to the very large ventilation rate will give us absurd figures. We would like to meet only the prerequisite and not try for any points. Request your advise and are there any references to ratify this approach ? Praveen
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Marcus Sheffer
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Thu, 12/18/2014 - 15:14

This is an unconditioned space so any energy use associated with ventilation should be identical in both models. The fan power and ventilation rate would therefore also be identical. No HVAC required in the baseline for an unconditioned space.

Sat, 12/20/2014 - 12:04

Many thanks. May I request any reference document mentioning this.
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Marcus Sheffer
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Mon, 12/22/2014 - 15:48

I am not sure if there are any interpretations that address this but I would have to search them just like you. Quite often these kinds of issues are not directly addressed but must be determined based on definitions and a connect-the-dots interpretation of 90.1. In this case these fans are not regulated so it is kind of hard to point you to something that is not addressed by the standard in question.

Tue, 12/23/2014 - 06:26

Thanks for your prompt response Mr. Marcus Sheffer Regards, Praveen

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