# Re: [EnergyPlus_Support] Why Inside and Outside face temperaures for a floor surface are same ?

For a detailed building surface, the outside surface temperature can be many things.  However, if you set it to adiabatic, the inside and outside temperatures will be the same.  Yes, of course it can store heat, but it occurs within the material.  By setting the surface temperatures equal, it is approximating a zero transmission condition through the entire set of layers.

You can set the boundary condition to many things, including fixed conditions using the OtherSideCoefficients approach.  If you want it to be the ground temperature then set it to be ground-coupled.  I can't recall the keyword now, but it's in there.

For the internal mass object, one side of the surface is exposed to the zone, while the other side of the surface uses an adiabatic boundary condition much like you specified for your surface.  But note that internal mass objects in the space don't really have location-geometry.  They interact with the zone air heat balance calculations, but not with direct solar (beam solar) calculations.

Edwin

On Fri, Aug 9, 2013 at 9:37 AM, Faran Qureshi wrote:

In our case, we do not have an adiabatic partition inside a zone, we have a floor which is adiabatic, i.e. no heat can escape the zone through the floor.

The Engineering reference document of energy plus provide the following description for the outside face temperature of a surface having adiabatic boundary condition:
"it is assumed that the outside face is not within the zone".
Based on this, I was assuming that the outside face was designating the outermost layer of the floor, which should be in contact with nothing, whereas the inside face touches the zone. As the floor can store energy, there can be a temperature difference between these two faces.

For the case of an  adiabatic partition (your example), I agree that both faces  will always be at the same temperature, but then if I got it right, you have to use internalMass object to describe such a thing.

So to rephrase the question, in case of a BuildingSurface:detailed, what is the surface outside face temperature output ?
Identically, what is it in the case InternalMass object ?

Thanks,

From: Edward G. Lyon <eglyon@xxxxxxx>
To: "EnergyPlus_Support@xxxxxxxxxxxxxxx" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Sent: Friday, August 9, 2013 4:31 PM
Subject: RE: [EnergyPlus_Support] Why Inside and Outside face temperaures for a floor surface are same ?

Fine, but the code probably does not use an outside surface temperature as the driving mechanism for heat storage.  Consider an ordinary concrete partition between two rooms held to the same temperature.  If you vary the room temperature, the wall gains and gives up heat but does not transfer heat from room to room.  There is a temperature difference between the wall and the room only that drives the exchange.

Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Faran Qureshi
Sent: Friday, August 09, 2013 10:15 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Why Inside and Outside face temperaures for a floor surface are same ?

According to the following definition of Adiabatic surfaces (given in the input/output reference of energy plus documentation (buildingsurface: detailed)), there can be heat flow through this surface but not out of the outside face of the surface. If the surface stores energy then it should have a temperature difference throughout the surface.

Adiabatic ? an internal surface in the same Zone. This surface will not transfer heat out of the zone, but will still store heat in thermal mass. Only the inside face of the surface will exchange heat with the zone (i.e. two adiabatic surfaces are required to model internal partitions where both sides of the surface are exchanging heat with the zone). The Outside Boundary Condition Object can be left blank.

From: Edward G. Lyon <eglyon@xxxxxxx>
To: "EnergyPlus_Support@xxxxxxxxxxxxxxx" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Sent: Friday, August 9, 2013 3:43 PM
Subject: RE: [EnergyPlus_Support] Why Inside and Outside face temperaures for a floor surface are same ?

The outside boundary is adiabatic, no heat flow, so both sides have to be the same temperature?

Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of qureshi.faran
Sent: Friday, August 09, 2013 9:35 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Why Inside and Outside face temperaures for a floor surface are same ?

I have a building model with its floor having one insulation layer. The details are given below. My question is that the energy plus simulation shows me exactly the same temperatures for the Inside and the Outside face of this floor. I am expecting a difference due to insulation layer. How can this be explained ?

BuildingSurface:Detailed,
Zn001:Flr001, !- Name
Floor, !- Surface Type
Slab Floor with Radiant, !- Construction Name
ZONE ONE, !- Zone Name
, !- Outside Boundary Condition Object
NoSun, !- Sun Exposure
NoWind, !- Wind Exposure
1.000000, !- View Factor to Ground
4, !- Number of Vertices
15.24000,0.000000,0.0, !- X,Y,Z ==> Vertex 1 {m}
0.000000,0.000000,0.0, !- X,Y,Z ==> Vertex 2 {m}
0.000000,15.24000,0.0, !- X,Y,Z ==> Vertex 3 {m}
15.24000,15.24000,0.0; !- X,Y,Z ==> Vertex 4 {m}

Material,
INS - EXPANDED EXT POLYSTYRENE R12 2 IN, !- Name
Rough, !- Roughness
5.0000001E-02, !- Thickness {m}
2.0000000E-02, !- Conductivity {W/m-K}
56.06000, !- Density {kg/m3}
1210.000, !- Specific Heat {J/kg-K}
0.9000000, !- Thermal Absorptance
0.5000000, !- Solar Absorptance
0.5000000; !- Visible Absorptance

Construction:InternalSource,
Slab Floor with Radiant, !- Name
4, !- Source Present After Layer Number
4, !- Temperature Calculation Requested After Layer Number
1, !- Dimensions for the CTF Calculation
0.1524, !- Tube Spacing {m}
CONCRETE - DRIED SAND AND GRAVEL 4 IN, !- Outside Layer
INS - EXPANDED EXT POLYSTYRENE R12 2 IN, !- Layer 2
GYP1, !- Layer 3
GYP2, !- Layer 4
FINISH FLOORING - TILE 1 / 16 IN; !- Layer 5

--
Edwin Lee, PhD
Engineer, Commercial Buildings Research Staff
National Renewable Energy Laboratory

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