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Modeling a Split HVAC System with Separate Mechanical Ventilation in DesignBuilder

asked 2024-07-02 05:53:20 -0500

FxMad's avatar

updated 2024-07-02 08:38:36 -0500

Hello everyone,

I'm currently doing an internship in the field of energy modeling and I'm using DesignBuilder. I'm not very familiar with it, so please forgive me if this question seems basic.

I need to model a room where the HVAC system is a split system with separate mechanical ventilation. The mechanical ventilation only introduces outdoor air without any extraction. However, there is a VMC (Ventilation Mécanique Contrôlée) in the bathroom. Does anyone know how I can model this?

I used the detailed HVAC system and the pre-defined HVAC: VRF with HR and DOAS. The problem is that the Air Handling Unit includes a mechanical exhaust. If I remove the pump for the mechanical exhaust in the detailed HVAC, will this be sufficient to model an HVAC system with no extraction? Additionally, I need to model the VMC, and I thought I could use the mechanical exhaust for this, but I can't find a way to specify the extracted airflow.

Thanks for your time.

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answered 2024-07-02 14:51:20 -0500

Greg Estep's avatar

updated 2024-07-02 14:56:20 -0500

Greetings, I'm a designbuilder user and I model split systems by using the PTHP object. I'm assuming that the ventilation in the building or room is balanced (outdoor air supply = bathroom exhaust).
To model this, add a generic air loop and connect the supply and extract to the zone. add a zone exhaust fan to the zone. Set the appropriate inputs in the air loop and the zone exhaust fan so that they balance and all supplied ventilation air is exhausted through the bathroom (zone exhaust fan). the zone exhaust will ensure that no air flows through the extract. You can control the ventilation supply air by setting the ventilation outside air definition method 2-per person, then set the outdoor air ADU control per person ventilation rate mode to 1-current occupancy. then set the zone exhaust fan flow fraction schedule to the same occupancy schedule as the zone.

In summary:

  • add zone group
  • add PTHP
  • add outdoor air ADU, set to current occupancy
  • add extract
  • add zone exhaust fan,
  • apply flow fraction and occupancy schedule
  • add generic air loop with AHU
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The problem is that from the HVAC plan that I have for example for a room in a Hotel, I introduce an airflow of 60 m^3 per hour but the mechanical exhaust which is in the bathroom only activates when someone is in the bathroom with an extracted airflow of 90 m^3 per hour which doesn't meet this criteria outdoor air supply = bathroom exhaust.

Thanks for your answer, as you seem experimented, is it possible to exchange more about designbuilder, I find it very difficult to earn experience in designbuilder without any help.

FxMad's avatar FxMad  ( 2024-07-02 16:09:28 -0500 )edit

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Asked: 2024-07-02 05:53:20 -0500

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Last updated: Jul 03