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# How to model two VRF systems connected in Parallel in Openstudio?

Hello My Friends, I want to use Openstudio to model the cooling/heating energy consumption of a commercial building that is served by two parallel connected VRF system, but i have some issues with the VRF model. I expect my VRF systems have the following configuration and control logic (but now i cannot figure out how to do that) : 1. The two VRF systems are connected in parallel to serve the same zone, with the capacity of which are sized to 28000W and 16000W respectively. 2. When the cooling/heating load is in the low range, for example 8000W, the smaller VRF will be used while the larger VRF be turned off. 3. When the cooling/heating load is in median range, for example 20000W, the larger VRF will be used while the smaller VRF be turned off. 4. When the cooling/heating load is in high range, for example 40000W, both of the VRFs will be operated. PS: I have investigated the VRF model in Openstudio, and it seems that the the built-in model can only simulate a standalone VFR system and is not able to simulate the control logic i stated above for the parallel connected. Is anyone know the methods that can be used to do this kind of control? Thank you in advance!!!

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If you have multiple HVAC equipment connected to a thermal zone, you can use the ZoneHVAC:EquipmentList to specify how the equipment behaves. For example, if you use the SequentialLoad distribution scheme, you can then specify Sequential Heating/Cooling Fractions as 0.64 for the first equipment (28000 / (28000 + 16000)) and 1.0 for the second equipment such that the first equipment serves 64% of the load and the second equipment serves 100% of the remaining load.

If you want to get fancier than that to turn on/off equipment for certain load conditions, note that the fractions above are schedules and can be adjusted on a timestep basis via EMS. So you can set up an EMS program where you create an EMS sensor on one of the "Zone Predicted Sensible Load to Setpoint" output variables for the ZoneControl:Thermostat object and then create an EMS actuator to adjust the schedule value.

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Thank you Shorowit for your reply. It is a good idea to use the ZoneHVAC:EquipmentList to specify how the equipment behaves. I have searched the Openstudio Library, but i did not find this function from the Openstudio Library. I know EnergyPlus can make this setting, but i am trying to do this by Openstudio. Can this be set somewhere else in Openstudio? Many Thanks!

( 2020-07-13 20:54:11 -0600 )edit

You can use the setCoolingPriority and setHeatingPriority methods. Take a look at the other methods available for the ThermalZone object in the SDK.

( 2020-07-14 02:36:58 -0600 )edit

Interesting. This seems to apply to VRF indoor units only? Daikin, for example, builds their VRF outdoor units in a modular fashion. For example, a Daikin REYQ216 may be a combination of a Daikin REYQ96 and a Daikin REYQ120. They probably count as just one unit, and Daikin indeed provides performance data for REYQ216, but this post made me curious as to whether there is a “mechanism“ Similar to zoneHVAC:EquipmentList, but for outdoor rather than indoor units?

( 2020-09-13 08:09:35 -0600 )edit

Condensing units in OpenStudio count as a single piece of equipment even if they have multiple modules in real life.

( 2020-09-16 09:24:54 -0600 )edit

Please see this figure for reference.

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@Dr. Fan it doesn't look like your figure attached correctly. Also, this should only be used if you are posting a solution to your post. If you want to attach a figure related to your question, then please edit your question to include the link or add a comment to your question with the link.

( 2020-09-16 12:47:28 -0600 )edit