DCV by System Node CO2 Concentration

asked 2022-04-13 03:28:48 -0500

Keigo's avatar

updated 2022-04-18 10:50:07 -0500

Is there any way to model Demand Controlled Ventilation controlled not by Zone CO2 concentration but by System Node CO2 concentration?

I want to model AHU with DCV. The AHU is connected to multiple zones as shown below.

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I know this is not a good design for DCV. This is not Dedicated Outdoor Air System. The outdoor air is fully mixed with the return air. The outdoor air flow rate supplied to each zone cannot be guaranteed as supply air flow rate of each zone varies based on each cooling/heating load. I wouldn't design like this, but unfortunately I often see this kind of design in Asian countries.

This kind of HVAC system has CO2 sensor in the main return air duct, which means the outdoor air flow rate is controlled by the average CO2 concentration of all zones. I want to model it in EnergyPlus, but zones need to be specified in ZoneControl:ContamimantController. I cannot set the contaminant controller at any Nodes.

If I list out all zones in Controller:MechanicalVentilation, can EnergyPlus calculate the average CO2 concentration? I refered to EngineeringReference, but couldn't find an answer. It seems it does not explain the logic of DCV for AHU with multiple zones.

One idea to get the average CO2 concentration is to create a dummy zone as a return plenum. If I set only one ZoneControl:Contamimant Controller to the dummy zone and use AirLoopHVAC:ReturnPlenum, the AHU may be controlled by the average CO2 concentration, but I'm not sure if the return plunum needs to be adjacent to all zones or not. If the location of the return plenum does not matter, I will assign a plant room where the AHU is actually located to the return plenum.

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Or we might able to model with EMS. Output:Variable System Node CO2 Concentration is available, but there is no actuator of ZoneControl:Contamimant Controller. I don't know how to overwrite CO2 Consenctation and trick EnergyPlus.

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Any advice would be appreciated.


I tried the Dummy Zone method, but DCV didn't work well maybe due to the following Warning. CO2 concentration in the Dummy Zone became much higer than the CO2 setpoint (1000ppm), which means the outdoor air flow rate was reduced more than necessary.

   ** Warning ** Zone name = 1F_Dummy Zone in Controller:MechanicalVentilation object name = DCV is not on the same air loop as Controller:OutdoorAir = AHU OA CONTROLLER
   **   ~~~   ** This zone will not be used and the simulation will continue...
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