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Offices fresh air from buffer space - HVAC Nodes Problem

asked 2018-10-26 09:07:31 -0600

rafael.alonso gravatar image

updated 2018-10-27 12:40:32 -0600

Hi all,

I´m running into some complications to model a passive space that pre-heats the fresh air coming into several offices - hopefully someone can through some light on this.

I´m modelling an office building with a central unconditioned space (like a wintergarden). The office fresh air is taken from this wintergarden (so that the sun will pre-heat it in winter). A quick sketch of the scheme:

image description

The natural ventilation of the wintergarden is modelled using the Air flow network (there is an HVAC defined for this zone, with no fresh air intake and heating/cooling setpoints set at -100/100ºC), and the Offices HVAC is set as ZoneHVAC:IdealLoadsAirSystem. Each HVAC system is defined with a supply and exhaust air node.

At first I set the Outdoor Air Inlet Node Name of one Office zones as the exhaust node of the wintergarden, and that actually worked. The problem comes when the two Office zones need to draw air from the wintergarden, as EnergyPlus complains that one Node (The wintergarden exhaust air node) cannot be defined twice.

So far, I´ve tried creating a AirLoopHVAC:ZoneSplitter, to divide the wintergarden exhaust node into several nodes, that I can define in the Outdoor Air Inlet Node Name of each ZoneHVAC:IdealLoadsAirSystem. Unfortunately, my experience modelling HVAC connections is rather limited, and I ran into all sort of errors regarding air supply paths, duplicate node names, etc.

Does anyone have experience on something similar? Many thanks in advance!


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answered 2018-10-26 13:01:44 -0600

You can do this with the AirflowNetwork.

Another simple approach would be to define a ZoneMixing object for each zone and setting the ventilation to zero in your ZoneHVAC:IdealLoadsAirSystem objects. You would then add ZoneExhaust fans (possibly with zero static pressure) to handle the exhaust air flow and make sure your system is air balanced as intended.

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Thanks for your quick reply.

How would you precisely model it with the RoomAirflowNetwork Model? It's hard to find material on how the HVAC outdoor air node could interact with the Airflow Network.

The second option is a smart workaround, but in this case I need to maintain the AFN for the natural ventilation. If Im not mistaken, ZoneMixing is disabled when the AFN is present.

rafael.alonso gravatar imagerafael.alonso ( 2018-10-27 17:43:53 -0600 )edit

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Asked: 2018-10-26 09:07:31 -0600

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Last updated: Oct 26 '18