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How to Model Range Hood with Make-up Air

asked 2023-05-23 08:46:56 -0500

Keigo's avatar

updated 2023-05-23 13:50:59 -0500

I want to model a range hood with make-up air as shown below.

  • The make-up air supply duct has a preheat coil. The make-up air is preheated to the indoor temperature in winter. The preheating energy varies as the outdoor air temperature varies, so the annual simulation is required. In summer, the make-up air is directly supplied without cooling.
  • The make-up air is immidiately exhausted from the range hood and not diffused into the room. Therefore, the meka-up air is Not considered a load handled by FCU. That's the point.

image description

How can I ignore the fresh air load into the room but consider the preheating energy?


Current workaround:

  1. Add a dummy zone outside the project building and model an AirLoop with preheat coil, make-up fan and exhaust fan. The kitchen has only FCU. The floor area of the dummy zone can be excluded from the total floor area in the summary report (html file), but I think the wall and roof area of the dummy zone cannot be excluded in the summary report.

  2. Pick up one unconditioned zone such as lift shaft or pipe/duct riser space in the project building, and model an AirLoop with preheat coil, make-up fan and exhaust fan. The kitchen has only FCU. Better to change the boundary condition of the unconditioned zone surfaces to Adiabatic.

image description

Is there a better solution?

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answered 2023-05-23 20:55:02 -0500

Greg Estep's avatar

Hey Keigo, I usually create a "kitchen exhaust fan" zone, with virtual partitions, inside the kitchen zone. I include all of the kitchen equipment that is to be located under the hood in this zone and would apply the appropriate "fraction lost" for this equipment. For this application, I think the default 0.7 is ok (maybe more). I also include a zone level exhaust fan with setting to match the anticipated operation. Then I apply a MAU unit for this zone and give the supply air the same schedule as the zone exhaust fan.

The rest of the kitchen will still have loads and have air conditioning. I simply let the virtual partitions leak extra heat into the kitchen zone and let that unit pick up the load.

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Comments

Thank you for your answer. A nice idea.

  1. About the "fraction lost", for example, if the kitchen equipment under the hood has 10kW, does it mean you simply input the equipment load of 3kW in the virtual partitions and input 7kW to the rest of the kitchen?
  2. The kitchen exhaust fan zone is regarded unconditioned, and the zone does not have thermostat, right?
Keigo's avatar Keigo  ( 2023-05-23 21:19:19 -0500 )edit

Hi Keigo, 1. If the kitchen equipment under the hood is 10kW, then I enter 10kW (with a schedule) for the kitchen exhaust fan zone and enter the fraction lost to be 0.7. This means 7kW will "leave the zone out the exhaust" and 3kW will add heat to the zone. 2. yes. I use design builder, so I usually just set the thermostat really high. I supposed I could just check the zone as unconditioned.

Greg Estep's avatar Greg Estep  ( 2023-05-24 10:35:16 -0500 )edit
1

Oh I see. Fraction Lost in ElectricEquipment, GasEquipment, HotWaterEquipment, SteamEquipment or OherEquipment.

Keigo's avatar Keigo  ( 2023-05-24 11:18:09 -0500 )edit

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Asked: 2023-05-23 08:46:56 -0500

Seen: 100 times

Last updated: May 23 '23