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I want to model a hybrid HVAC system of VAV and Active Chilled Beam (ACB). ACB has cooling capacity of 30W per outdoor air flow rate, wchich is insufficient to handle all the cooling load, and VAV handles the remaining cooling load.

I reproduced the "problems" in simple models for posting on this site. The base model is 5ZoneWarmest.idf (but I revised parameters such as schedule and internal loads a lot).

Then, I added ACB as follows. One AirLoop has two Airterminals in each zone. I have the following issues when I autosize.

• Minimum Outdoor Air Flow Rate of Controller:OutdoorAir is double counted.

• Design Size Maximum Flow Rate of Fan:Variable is oversized.

• PlantLoop (Design Maximum Flow Rate of Pump:VariableSpeed, Reference Capacity of Chiller:Electric:EIR, Design Air Flow Rate of CoolingTower:SingleSpeed, etc.) is oversized.

Is there any way to autosize them correctly? Or is this a bug and we have to wait for it to be fixed in the future?

On the other hand, I also modelled the following AirLoops i.e., the AirLoop for ACB and the AirLoop for VAV are separated. In this model, AirLoops and PlantLoops have smaller flow rates compared to the previous model (5ZoneWarmest_rev+ACB_Integrated.idf), but still larger than 5ZoneWarmest_rev.idf.

As the above models are not autosized well, I hardsized some parameters and finally managed to get what I wanted (5ZoneWarmest_rev+ACB_Integrated_Hardsized.idf).

All the files (V23-2-0) are here.

I want to model a hybrid HVAC system of VAV and Active Chilled Beam (ACB). ACB has cooling capacity of 30W per outdoor air flow rate, wchich is insufficient to handle all the cooling load, and VAV handles the remaining cooling load.

I reproduced the "problems" in simple models for posting on this site. The base model is 5ZoneWarmest.idf (but I revised parameters such as schedule and internal loads a lot).

Then, I added ACB as follows. One AirLoop has two Airterminals in each zone. I have the following issues when I autosize.

• Minimum Outdoor Air Flow Rate of Controller:OutdoorAir is double counted.

• Design Size Maximum Flow Rate of Fan:Variable is oversized.

• PlantLoop (Design Maximum Flow Rate of Pump:VariableSpeed, Reference Capacity of Chiller:Electric:EIR, Design Air Flow Rate of CoolingTower:SingleSpeed, etc.) is oversized.

Is there any way to autosize them correctly? Or is this a bug and we have to wait for it to be fixed in the future?

On the other hand, I also modelled the following AirLoops i.e., the AirLoop for ACB and the AirLoop for VAV are separated. In this model, AirLoops and PlantLoops have smaller flow rates compared to the previous model (5ZoneWarmest_rev+ACB_Integrated.idf), but still larger than 5ZoneWarmest_rev.idf.

As the above models are not autosized well, I hardsized some parameters and finally managed to get what I wanted (5ZoneWarmest_rev+ACB_Integrated_Hardsized.idf).(5ZoneWarmest_rev+ACB_Integrated_Hardsized.idf), but this workflow takes many steps to get correct parameters. Hopefully there is a better way to model an AirLoop with two Airterminals in one zone.

All the files (V23-2-0) are here.

I want to model a hybrid HVAC system of VAV and Active Chilled Beam (ACB). ACB has cooling capacity of 30W per outdoor air flow rate, wchich is insufficient to handle all the cooling load, and VAV handles the remaining cooling load.

I reproduced the "problems" in simple models for posting on this site. The base model is 5ZoneWarmest.idf (but I revised parameters such as schedule and internal loads a lot).

Then, I added ACB as follows. One AirLoop has two Airterminals in each zone. I have the following issues when I autosize.

• Minimum Outdoor Air Flow Rate of Controller:OutdoorAir is double counted.

• Design Size Maximum Flow Rate of Fan:Variable is oversized.

• PlantLoop (Design Maximum Flow Rate of Pump:VariableSpeed, Reference Capacity of Chiller:Electric:EIR, Design Air Flow Rate of CoolingTower:SingleSpeed, etc.) is oversized.

Is there any way to autosize them correctly? Or is this a bug and we have to wait for it to be fixed in the future?

On the other hand, I also modelled the following AirLoops i.e., the AirLoop for ACB and the AirLoop for VAV are separated. In this model, AirLoops and PlantLoops have smaller flow rates compared to the previous model (5ZoneWarmest_rev+ACB_Integrated.idf), but still larger than 5ZoneWarmest_rev.idf.

As the above models are not autosized well, I hardsized some parameters and finally managed to get what I wanted (5ZoneWarmest_rev+ACB_Integrated_Hardsized.idf), but this workflow takes many steps to get correct parameters. Hopefully there is a better way to model an AirLoop with two Airterminals in one zone.

All the files (V23-2-0) are here.