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EnergyPlus: how ventilation affects heating and cooling needs

asked 2018-01-20 03:35:42 -0500

Jenny's avatar

updated 2018-01-20 08:08:07 -0500

I want to include the effect of ventilation in my simulation. A real mechanical ventilation system does not exist yet in the building I am considering. However I want to take into consideration this effect without sizing a real system. What I only know is that I should change something here C:\fakepath\Ventilation.PNG, but I do not know what type of ventilation to choose between natural, intake etc (I do not have any information concerning fan pressure rise etc..). My purpose is to consider in what extent "ventilation" affects the cooling and heating needs of my building and so the electrical consumption without the presence of a real mechanical ventilation system.

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Are you trying to analyze the impact of natural ventilation (brining outdoor air into a zone for free heating / cooling), or the impact of ventilation requirements (minimum outdoor air needs prescribed by a standard like ASHRAE 62.1)?

Are you using the Ideal Loads Air System if you're not modeling a real HVAC system?

Aaron Boranian's avatar Aaron Boranian  ( 2018-01-20 08:39:34 -0500 )edit

Yes, I am using the Ideal Loads Air System. Since there is no real mechanical ventilation system, I am considering a "fictitious" ventilation , based on flow rate regulations of my country (0,1 m3/s per person). But I do not know wether inserting natural ventilation or not.

Jenny's avatar Jenny  ( 2018-01-20 09:59:54 -0500 )edit

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answered 2018-01-20 12:53:50 -0500

The ZoneVentilation:DesignFlowRate object that you point out in your linked image can represent two cases: outdoor air entering a zone directly, or zone air exhausted outdoors directly. In your image, it looks like you have correctly set the Design Flow Rate Calculation Method input field to "Flow/Person", but the related Flow Rate per Person input field is set to 0,01 $m3/s/person$ instead of the 0,1 $m3/s/person$ value you mentioned in your comment above.

You also set the Ventilation Type input field to "Natural" meaning that outdoor air enters the zone without fans. The other three options will add fan electricity consumption and heat addition. Check this post for more info on ventilation types.

It's important to note that this ZoneVentilation:DesignFlowRate object will be treated as another zone load -- along with solar, envelope, equipment, lights, etc. -- that must then be met by the HVAC system. The incoming ventilation air flow DOES NOT impact the mass balance of the HVAC system and zone connection.

If you are applying an Ideal Loads Air System, then an alternative that might make more sense to determine impact of ventilation rates is creating a DesignSpecification:OutdoorAir object that is referenced by the Design Specification Outdoor Air Object Name input field of the Ideal Loads Air System. This way, return air from the zone is mixed with outdoor air and the resulting mixed air corresponds to each inlet stream's air state and air flow. This mixed air is then conditioned by the Ideal Loads Air System. I recommend this approach, because this is the process that a real mechanical system would likely use to provide 0,1 $m3/s/person$ of outdoor air.

Check this post for more information on the difference between zone ventilation vs outdoor air needs in HVAC systems.

The DesignSpecification:OutdoorAir object is also applied to design days when sizing HVAC equipment. This post provides some information on entering outdoor air needs for sizing zone heating and cooling needs.

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Thank you Aaron and sorry for my delay. I found your answer very useful and I succeded to perform a simulation taking into account a fictitious system ventilation. Sorry for my mistake, I meant 0,01 m3/s per person, as it was set in the field, showed in the screen uploaded above.

Jenny's avatar Jenny  ( 2018-02-02 05:38:50 -0500 )edit

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Asked: 2018-01-20 03:35:42 -0500

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Last updated: Jan 20 '18