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NC-v4 EAc2:Optimize energy performance

Modeling a 100% fresh air Makeup AHU (MAHU) in Baseline

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Hanin Hamdan
Mechanical Engineer-Sustainability Consultant
LEEDuser Basic Member
1 thumbs up

Hi,

I am working on a Hotel Project with several Kitchen Spaces. 100% Fresh air Makeup Air Handling Units (MAHUs) are designed to supply makeup air at the hood and Ecology Units are designed to exhaust air from these spaces.

The Question is how to Model the 100% Fresh Air MAHU in the Baseline. The project is Located in Climate Zone 1B.

Thank you,

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

Fri, 08/02/2024 - 22:00

I think kitchen hood exhaust is considered a process load so it is modeled identical to the proposed design. How you model it depends on the software you are using.
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Hanin Hamdan
Mechanical Engineer-Sustainability Consultant
LEEDuser Basic Member
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Mon, 08/05/2024 - 08:41

Thank you, Marcus for the Reply, The Ecology Units (Exhaust Fans) will be modeled as process Load identically in the Proposed and Baseline. The Kitchen Spaces are served by Air Handling Units (AHUs) and FCUs to provide cooling to the spaces in the proposed Model. In the Baseline Model, these Spaces will be served by System 4. In addition to the AHUs/FCUs, The Kitchen Spaces are equipped with the MAHU 100% fresh air Units. These units are specifically designed to compensate for the air exhausted by the kitchen hoods, ensuring a balanced and well-ventilated environment. The MAHUs are equipped with a Cooling Coil to cool the Fresh air (coming at 45°C at Peak summer day) to 20°C to avoid high internal gains due to the harsh outdoor environment. The Cooling Source as per the design is Air-Cooled Chiller. The question is how to model the MAHUs in the Baseline.
  1. Will it be modeled identically in the Baseline as 100% FA  with identical flow, cooling source and Fan power?
  2. Will it be modeled identically in the Baseline (100% FA Unit with identical flow) however with a DX-coil as a cooling Source and the Fans will be sized as per ASHRAE 90.1 Baseline?
  3. Will it be modeled as System 4 with Supply air equal to the fresh air in the proposed model?
Thanks
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A Adeeb
LEEDuser Basic Member
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Mon, 09/02/2024 - 06:41

Hi,  I have a similar scenario with Makeup Air Handling Units serving kitchen spaces, serving 100% conditioned fresh air. How would this be modeled in the baseline? Would it be as System 4 with DX cooling source and flows as per design case?  

Thu, 09/05/2024 - 12:19

Since the kitchen MAHUs are serving the exhaust hoods rather than space comfort conditioning they must be modeled identically unless an Exceptional Calculation methodology is used. Therefore, you should intially model the Baseline using option 1 (100% FA with identical flow, cooling source and fan power). If you wanted to demonstrate savings for cooling source and/or fan power, these parameters would require an Exceptional Calculation using additional simulation run. 

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