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# Why only 5 total surfaces for a room model in the Modelica building library? It should be 6.

Below is a piece of example code coming from the instruction documents of ThermalZones.Detailed.MixedAir in Modelica building library.

Buildings.ThermalZones.Detailed.MixedAir roo( redeclare package Medium = MediumA, AFlo=64, hRoo=2.7, nConExt=2, datConExt(layers={matLayRoo, matLayExt}, A={64, 63}, til={Buildings.Types.Tilt.Ceiling, Buildings.Types.Tilt.Wall}, azi={Buildings.Types.Azimuth.S, Buildings.Types.Azimuth.W}), nConExtWin=nConExtWin, datConExtWin(layers={matLayExt}, A={43}, glaSys={glaSys}, hWin={2}, wWin={2}, fFra={0.1}, til={Buildings.Types.Tilt.Wall}, azi={Buildings.Types.Azimuth.S}), nConPar=1, datConPar(layers={matLayPar}, each A=10, each til=Buildings.Types.Tilt.Wall), nConBou=1, datConBou(layers={matLayFlo}, each A=64, each til=Buildings.Types.Tilt.Floor), nSurBou=1, surBou(each A=63, each absIR=0.9, each absSol=0.9, each til=Buildings.Types.Tilt.Wall), linearizeRadiation = true , energyDynamics=Modelica.Fluid.Types.Dynamics.FixedInitial, lat=0.73268921998722) "Room model" annotation (Placement(transformation(extent={{46,20},{86,60}})));

In this example code, two Exterior construction(ConExt), one Exterior construction with window(ConExtWin), one interior construction(Conpar), one ConBou and one SurBou is defined. Based on my understanding, the ConBou and SurBou is used for one wall for two adjacent room, because two adjacent room share one wall. The ConPar stands for an interior wall or partitions in a room.

So the question is: 2 ConExt (two Exterior wall without window) + 1 ConExtWin (one Exterior wall with window) + 1 ConBou (one ConBou connected to the SurBou in adjacent room, meaning one wall shared by this room and the adjacent room) + 1 SurBou (One SurBou connected to the ConBou in adjacent room, also meaning one another wall shared by this room and the adjacent room)

So the total surfaces is 5, but for every room, there should be 6 surfaces, no matter connected to adjacent room or outside air or ground soil. I find this problem in all examples, the total surfaces are 5 for all the other examples. Unless considering the ConPar as the sixth surface, but for the ConPar, the explanation in the instruction documents is very clear: “Interior constructions such as partitions within a room. Both surfaces of this construction are inside the room model and participate in the infrared and solar radiation balance. Since the view factor between these surfaces is zero, there is no infrared radiation from one surface to the other of the same construction.”

In addition, even considering the ConPar as the sixth surface, the Are in above code is A=10, that does’t match any wall’s size of this room. In this code, we can see the length, width and high for this room is 643.

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Hello Wenyi,

probaply you already solved your problem. Sometimes the floor can also be hidden in the datConPar as in Buildings.ThermalZones.Detailed.Examples.MixedAirFreeResponse.

If you check all datCon... strings, you'll probaply could figure out the different surface areas.

I also started with the room models in Buildings recently. I figuered out a lot of the structure of the model, but I'm not able to connect the model Buildings.ThermalZones.Detailed.MixedAir with a second room model MixedAir, like in Buildings.ThermalZones.Detailed.FLEXLAB.Rooms.Examples.X3BWithRadiantFloor.

My approach till now: I opened Buildings.ThermalZones.Detailed.Examples.MixedAirFreeResponse and duplicated the Mixed Air model. I concted the 2. room with the obligatory parameters weaBus and qGain, I adjusted the romms to the meassurements of my building and exchanged the conecting wall between the rooms with an indoor wall. Till now simulation is working fine. Now I activated the ports conBou in room1 and conSur in room2 and shifted the connecting wall to SurBou in room2 and to datConBou, wich seemed to be locical. But this is causing an Error

Do you have experience in connecting mutiple rooms amongst each other?

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Last updated: May 07 '20