# 4.16 SURFACE

Surface constructs a ZONE subobject of class SURFACE that represents a surrounding or interior surface of the zone. Internally, SURFACE generates a QUICK surface (U-value only), a DELAYED (massive) surface (using the finite-difference mass model), interzone QUICK surface, or interzone DELAYED surface, as appropriate for the specified construction and exterior conditions.

**sfName**

Name of surface; give after the word SURFACE.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

63 characters | none | No | constant |

**sfType= choice**

Type of surface:

FLOOR | Surface defines part or all of the ‘bottom’ of the zone; it is horizontal with inside facing up. The outside of the surface is not adjacent to the current zone. |

WALL | Surface defines a ‘side’ of the zone; its outside is not adjacent to the current zone. |

CEILING | Surface defines part or all of the ‘top’ of the zone with the inside facing down. The outside of the surface is not adjacent to the current zone. |

sfType is used extensively for default determination and input checking, but does not have any further internal effect. The Floor, Wall, and Ceiling choices identify surfaces that form boundaries between the zone and some other condition.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

FLOOR WALL CEILING | none | Yes | constant |

**sfArea= float**

Gross area of surface. (CSE computes the net area for simulation by subtracting the areas of any windows and doors in the surface.).

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

ft^{2} | x \(>\) 0 | none | Yes | constant |

**sfTilt= float**

Surface tilt from horizontal. Values outside the range 0 to 360 are first normalized to that range. The default and allowed range depend on sfType, as follows:

sfType = FLOOR | sfTilt=180, default = 180 (fixed value) |

sfType = WALL | 60 \(<\) sfTilt \(<\) 180, default = 90 |

sfType = CEILING | 0 \(\leq\) sfTilt \(\leq\) 60, default = 0 |

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

degrees | Dependent upon sfType See above | Dependent upon sfType See above | No | constant |

**sfAzm= float**

Azimuth of surface with respect to znAzm. The azimuth used in simulating a surface is bldgAzm + znAzm + sfAzm; the surface is rotated if any of those are changed. Values outside the range 0 to 360 are normalized to that range. Required for non-horizontal surfaces.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

degrees | unrestricted | none | Required if sfTilt \(\neq\) 0 and sfTilt \(\neq\) 180 | constant |

**sfModel= choice**

Provides user control over how CSE models conduction for this surface.

QUICK | Surface is modeled using a simple conductance. Heat capacity effects are ignored. Either sfCon or sfU (next) can be specified. |

DELAYED, DELAYED_HOUR, DELAYED_SUBHOUR | Surface is modeled using a multi-layer finite difference technique that represents heat capacity effects. If the time constant of the surface is too short to accurately simulate, a warning message is issued and the Quick model is used. The program cannot use the finite difference model if sfU rather than sfCon is specified. |

AUTO | Program selects Quick or the appropriate Delayed automatically according to the time constant of the surface (if sfU is specified, Quick is selected). |

FD (or FORWARD_DIFFERENCE) | Selects the forward difference model (used with short time steps and the CZM/UZM zone model). |

KIVA | Uses a two-dimensional finite difference model to simulate heat flow through foundation surfaces. |

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

– | QUICK, DELAYED, DELAYED_HOUR, DELAYED_SUBOUR , AUTO, 2D_FND | AUTO | No | constant |

Either sfU or sfCon must be specified, but not both.

**sfU= float**

Surface U-value (NOT including surface (air film) conductances). For surfaces for which no heat capacity is to be modeled, allows direct entry of U-value without defining a CONSTRUCTION.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

Btuh/ft^{2}-^{o}F | x \(>\) 0 | Determined from sfCon | if sfCon not given | constant |

**sfCon= conName**

Name of CONSTRUCTION of the surface.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

Name of a CONSTRUCTION | none | unless sfU given | constant |

**sfLThkF= float**

Sublayer thickness adjustment factor for FORWARD_DIFFERENCE conduction model used with sfCon surfaces. Material layers in the construction are divided into sublayers as needed for numerical stability. sfLThkF allows adjustment of the thickness criterion used for subdivision. A value of 0 prevents subdivision; the default value (0.5) uses layers with conservative thickness equal to half of an estimated safe value. Fewer (thicker) sublayers improves runtime at the expense of accurate representation of rapid changes.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

x \(\ge\) 0 | 0.5 | No | constant |

**sfExCnd= choice**

Specifies the thermal conditions assumed at surface exterior, and at exterior of any subobjects (windows or doors) belonging to current surface. The conditions accounted for are dry bulb temperature and incident solar radiation.

AMBIENT | Exterior surface is exposed to the ‘weather’ as read from the weather file. Solar gain is calculated using solar geometry, sfAzm, sfTilt, and sfExAbs. |

SPECIFIEDT | Exterior surface is exposed to solar radiation as in AMBIENT, but the dry bulb temperature is calculated with a user specified function (sfExT). sfExAbs can be set to 0 to eliminate solar effects. |

ADJZN | Exterior surface is exposed to another zone, whose name is specified by sfAdjZn. Solar gain is 0 unless gain is targeted to the surface with SGDIST below. |

GROUND | The surface is in contact with the ground. Details of the two-dimensional foundation design are defined by sfFnd. Only floor and wall surfaces may use this option. |

ADIABATIC | Exterior surface heat flow is 0. Thermal storage effects of delayed surfaces are modeled. |

**sfExAbs= float**

Surface exterior absorptivity.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

0 \(\le\) x \(\le\) 1 | 0.5 | Required if sfExCnd = AMBIENT or sfExCnd = SPECIFIEDT | monthly-hourly |

**sfInAbs= float**

Surface interior solar absorptivity.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

0 \(\le\) x \(le\) 1 | sfType = CEILING, 0.2; sfType = WALL, 0.6; sfType = FLOOR, 0.8 | No | monthly-hourly |

**sfExEpsLW= float**

Surface exterior long wave (thermal) emittance.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

0 \(\le\) x \(\le\) 1 | 0.9 | No | constant |

**sfInEpsLW= float**

Surface interior long wave (thermal) emittance.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

0 \(\le\) x \(\le\) 1 | 0.9 | No | constant |

**sfExT= float**

Exterior air temperature.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

^{o}F | unrestricted | none | Required if sfExCnd = SPECIFIEDT | hourly |

**sfAdjZn= znName**

Name of adjacent zone; used only when sfExCnd is ADJZN. Can be the same as the current zone.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

name of a ZONE | none | Required whensfExCnd = ADJZN | constant |

**sfGrndRefl= float**

Ground reflectivity for this surface.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

fraction | 0 \(\leq\) x \(\leq\) 1 | grndRefl | No | Monthly - Hourly |

**sfInH= float**

Inside surface (air film) conductance. Ignored for sfModel = Forward_Difference. Default depends on the surface type.

sfType = FLOOR or CEILING | 1.32 |

other | 1.5 |

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

Btuh/ft^{2}-^{o}F | x \(>\) 0 | See above | No | constant |

**sfExH= float**

Outside combined surface (air film) conductance. Ignored for sfModel = Forward_Difference. The default value is dependent upon the exterior conditions:

sfExCnd = AMBIENT | dflExH (Top-level member, described above) |

sfExCnd = SPECIFIEDT | dflExH (described above) |

sfExCnd = ADJZN | 1.5 |

sfExCnd = ADIABATIC | not applicable |

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

Btuh/ft^{2}-^{o}F | x \(>\) 0 | see above | No | constant |

When sfModel = Forward_Difference, several models are available for calculating inside and outside surface convective coefficients. Inside surface faces can be exposed only to zone conditions. Outside faces may be exposed either to ambient conditions or zone conditions, based on sfExCnd. Only UNIFIED and INPUT are typically used. The other models were used during CSE development for comparison. For details, see CSE Engineering Documentation.

Model | Exposed to ambient | Exposed to zone |
---|---|---|

UNIFIED | default CSE model | default CSE model |

INPUT | hc = sfExHcMult | hc = sfxxHcMult |

AKBARI | Akbari model | n/a |

WALTON | Walton model | n/a |

WINKELMANN | Winkelmann model | n/a |

DOE2 | DOE2 model | n/a |

MILLS | n/a | Mills model |

ASHRAE | n/a | ASHRAE handbook values |

TARP | n/a | TARP model |

**sfExHcModel= choice**

Selects the model used for exterior surface convection when sfModel = Forward_Difference.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

choices above | UNIFIED | No | constant |

**sfExHcLChar= float**

Characteristic length of surface, used in derivation of forced exterior convection coefficients in some models when outside surface is exposed to ambient. See sfExHcModel.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

ft | x \(>\) 0 | 10 | No | constant |

**sfExHcMult= float**

Exterior convection coefficient adjustment factor. When sfExHcModel=INPUT, hc=sfExHcMult. For other sfExHcModel choices, the model-derived hc is multiplied by sfExHcMult.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

x \(\ge\) 0 | 1 | No | subhourly |

**sfExRf= float**

Exterior surface roughness factor. Used only when surface is exposed to ambient (i.e. with wind exposure). Typical values:

Roughness Index | sfExRf | Example |
---|---|---|

1 (very rough) | 2.17 | Stucco |

2 (rough) | 1.67 | Brick |

3 (medium rough) | 1.52 | Concrete |

4 (Medium smooth) | 1.13 | Clear pine |

5 (Smooth) | 1.11 | Smooth plaster |

6 (Very Smooth) | 1 | Glass |

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

sfExHcModel = WINKELMANN: 1.66 else 2.17 | No | constant |

**sfInHcModel= choice**

Selects the model used for the inside (zone) surface convection when sfModel = Forward_Difference.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

choices above (see sfExHcModel) | UNIFIED | No | constant |

**sfInHcMult= float**

Interior convection coefficient adjustment factor. When sfInHcModel=INPUT, hc=sfInHcMult. For other sfInHcModel choices, the model-derived hc is multiplied by sfInHcMult.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

x \(\ge\) 0 | 1 | No | subhourly |

The items below give values associated with CSE’s model for below grade surfaces (sfExCnd=GROUND). See CSE Engineering Documentation for technical details.

**sfFnd= fdName**

Name of FOUNDATION applied to ground-contact Floor SURFACEs; used only for Floor SURFACEs when sfExCnd is GROUND.

Units | Legal Range | Default | Required | **Variability |
---|---|---|---|---|

– | Name of a Foundation | none | whensfExCnd = GROUND and sfType = Floor | constant |

**sfFndFloor= sfName**

Name of adjacent ground-contact Floor SURFACE; used only for Wall SURFACEs when sfExCnd is GROUND.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

– | Name of a Surface | none | whensfExCnd = GROUND and sfType = Wall | constant |

**sfHeight= float**

Needed for foundation wall height, otherwise ignored. Maybe combine with sfDepthBG?

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

ft | x \(>\) 0 | none | when sfType is WALL and sfExtCnd is GROUND | constant |

**sfExpPerim= float**

Exposed perimeter of foundation floors.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

ft | x \(\geq\) 0 | none | when sfType is FLOOR, sfFnd is set, and sfExtCnd is GROUND | constant |

**sfDepthBG= float**

*Note: sfDepthBG is used as part of the simple ground model, which is no longer supported. Use sfHeight with sfFnd instead.*

Depth below grade of surface. For walls, sfDepthBG is measured to the lower edge. For floors, sfDepthBG is measured to the bottom face.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

ft | x \(\ge\) 0 | none | No | constant |

*Note: The following data members are part of the simple ground model, which is no longer supported. Use sfFnd instead.*

**sfExCTGrnd= float**

**sfExCTaDbAvg07= float**

**sfExCTaDbAvg14= float**

**sfExCTaDbAvg31= float**

**sfExCTaDbAvgYr= float**

Conductances from outside face of surface to the weather file ground temperature and the moving average outdoor dry-bulb temperatures for 7, 14, 31, and 365 days.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

Btuh/ft^{2}-^{o}F | x \(\ge\) 0 | see above | No | constant |

**sfExRConGrnd= float**

Resistance overall construction resistance. TODO: full documentation.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

x \(\ge\) 0 | none | No | constant |

**endSURFACE**

Optional to indicates the end of the surface definition. Alternatively, the end of the surface definition can be indicated by END, or by beginning another SURFACE or other object definition. If used, should follow the definitions of the SURFACE’s subobjects – DOORs, WINDOWs, SHADEs, SGDISTs, etc.

Units | Legal Range | Default | Required | Variability |
---|---|---|---|---|

none | No | constant |

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