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Forum discussion

CS-2009 EAp2:Minimum Energy Performance

Heat Recovery in the Baseline Systems

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Ciaran McCabe
Director
Passive Dynamics Sustainability Consultants
LEEDuser Basic Member
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For HVAC systems that consist of Fan Coil Units with Air Handling Units providing 100% Outside air - constant volume (based on the min ASHRAE 62.1 requirements) - Will the baseline systems require heat recovery as per ASHRAE 90.1 G3.1.2.10. All our AHU's specified have a design air capcity of greater than 2400 l/s. Not sure if this requirement applies to constant volume systems supplying min outdoor air ? can anyone provide guidance on this ?

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
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Fri, 09/09/2016 - 15:36

The Proposed systems do not matter. Model the baseline systems according to Appendix G. See G3.1.1 which tells you how to zone the baseline HVAC system depending on the type of system. If any of the baseline systems require heat recovery according to G3.1.2.10 then include it in the baseline model.
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Ciaran McCabe
Director
Passive Dynamics Sustainability Consultants
LEEDuser Basic Member
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Tue, 09/13/2016 - 22:32

Hi Marcus, Thanks for your comment. I am also wondering if the outdoor air modelled in both the baseline and proposed models should be the same OR is it the Minimum outdoor air quantity. I have a baseline auto sized model that has a much higher outdoor air quantity in CFM compared to the proposed model but the min. levels of the same. For info its not a VAV system. Can you please provide some guidnace ?
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
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Wed, 09/14/2016 - 15:14

The quantity of OA should be identical in both models. Only exception is if the Proposed has demand controlled ventilation.

Thu, 09/15/2016 - 10:12

Another exception could be if in a model there is an economizer that increase the OA flow rate in order to minimize the cooling demand, correct?
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Thu, 09/15/2016 - 13:10

Not really an exception per se, more like a different situation. The outside ventilation air should be identical in both models. The situation you describe would be bringing more OA into the building than is necessary for ventilation. If there is an economizer in one model and not the other the OA flow will vary when the economizer is operating but that is not to meet the ventilation requirements, it is to provide free cooling. So to be clear it is the minimum OA for ventilation that must be identical.

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