Envelope Presets

Status: Current as of S6 (part B); infiltration added in D-124 · Date: 2026-10-02 · Decisions: D-023, D-031, D-069, D-112, D-124; ADR-010, ADR-017

Read this first: the envelope that ships with BEMGen (ExampleEnvelopePresets.Example) holds illustrative round numbers chosen for development and tests. Its layers and glazing are NOT taken from ASHRAE 90.1, the DOE prototype buildings, a national code, or any other standard, and no result based on it may be presented as if they were. Sourced envelopes are an open research input (§4), like sourced program presets (program presets §3).

An envelope preset describes the constructions of a building: one layered construction per envelope role, one simple glazing for every window (ADR-010, D-112), and since D-124 the building's infiltration. It is separate from the program presets on purpose: the envelope is the same at every level of detail, whatever zones are merged, so geometry effects are not confounded with envelope changes (GLOBAL.md scientific rule 4). Convert2BEM and Convert2IDF take the same preset, so both outputs describe one envelope.

1. What an envelope preset is

In code an envelope preset is an EnvelopePreset (src/Lod.Core/Envelope/EnvelopePreset.cs), built from its plain values EnvelopeValues with ToPreset(), which reports every invalid value at once.

Type	Values	Rejected with diagnostic
Layer (massive)	Name, Thickness (m), Conductivity (W/(m·K)), Density (kg/m³), SpecificHeat (J/(kg·K)), and an optional Finish	EmptyName; EnvelopeValue when a property is not positive and finite, the specific heat below 100 (the EnergyPlus minimum), or a finish value is out of range
NoMassLayer	Name, Resistance (m²·K/W), and an optional Finish; no heat capacity	EmptyName; EnvelopeValue when the resistance is below 0.001 (the EnergyPlus minimum) or not finite
AirGapLayer	Name, Resistance (m²·K/W); no capacity and no surface	EmptyName; EnvelopeValue when the resistance is not positive and finite
SurfaceFinish	Optional Roughness (SurfaceRoughness), ThermalAbsorptance, SolarAbsorptance, VisibleAbsorptance, the same on both faces; unset is the converter's default (medium rough, and EnergyPlus's 0.9, 0.7, 0.7)	EnvelopeValue when thermal is not in (0, 0.99999] or solar or visible not in [0, 1]
Construction	Name and 1 to 10 layers of any kind, listed from the outside to the inside as the zone whose surface it is sees them	EmptyName; ConstructionLayers for no layers, more than 10 (the EnergyPlus limit), or an air gap as the outside or inside layer (EnergyPlus rejects it)
GlazingSpec	A simple glazing system: Name, UFactor (W/(m²·K)), SolarHeatGainCoefficient, and VisibleTransmittance of the whole window, or no visible transmittance, which EnergyPlus then calculates	EmptyName; EnvelopeValue when the U-factor is not in (0, 7] or SHGC or a given VT is not in (0, 1)
LayeredGlazing	A window of GlassLayer (spectral averages at normal incidence: thickness, solar and visible transmittance and front and back reflectances, infrared transmittance, front and back emissivity, conductivity) and GasLayer (GasType air, argon, krypton, or xenon, and thickness), glass and gas alternating with glass on both sides, 1 to 4 glass layers	EmptyName; ConstructionLayers for layers out of order or more than 4 glass layers; EnvelopeValue for a value out of range, a transmittance and reflectance summing to more than 1, or an infrared transmittance and emissivity summing to 1 or more
Infiltration	DesignRate (finite, not negative), Basis (InfiltrationBasis), and a fraction Schedule, the same for every zone (§2.5)	InfiltrationValue when the rate is negative or not finite or the basis is not defined; ScheduleKindMismatch when the schedule is not a fraction schedule
EnvelopeValues	Name, one construction per role (below), Window, and Infiltration	EmptyName for the preset name

Names identify materials and constructions in the converters' output, so ToPreset also checks that they are unambiguous, ignoring case as EnergyPlus does (DuplicateEnvelopeName): one material name per layer, whatever its kind and finish, the window's glass and gas layers included; one construction name per layer sequence, the window construction included; and a simple glazing's name, which names both the window construction and its glazing material, used by no other material or construction. Names are written as they are, so they must also be valid IDF names (EnvelopeName): at most 100 characters, the generated "{Name} Reversed" included, and none of , ; !. The same Construction may serve several roles, and a layer used by several constructions is checked once.

1.1 Roles

ConstructionRole	Surfaces	Layers listed from
ExteriorWall	walls facing outdoors	outdoors to the zone
Roof	ceilings facing outdoors: roofs and terraces (ADR-015)	outdoors to the zone
GroundFloor	floors on the ground	the ground to the zone
ExposedFloor	floors facing outdoors: overhangs and storeys the storey below does not carry (D-074)	outdoors to the zone
InteriorWall	walls between zones, written interzone or adiabatic (D-069): the wall whose zone ID sorts first uses the construction, its partner the reverse	the adjacent zone to the owning zone, as the wall whose zone ID sorts first sees them
InteriorFloor	slabs between storeys: the floor above uses the construction, the ceiling below its reverse	the zone below to the zone above
InternalMass	slabs inside one zone that became internal mass (D-031)	— (both faces exposed; Convert2IDF writes each face as a half slice, D-143)

ConstructionRoles.Of(surface, exportedBoundary) (src/Lod.Core/Conversion/ConstructionRoles.cs) gives a surface its role from its kind and the boundary a converter writes for it (HeatTransferOptions.Exported), as a Result<ConstructionAssignment> holding the role and Reversed; an unresolved boundary or a wall or ceiling on the ground, which no floor aggregator produces but which an overridden validation can let through, is the error NoConstructionRole. The heat-transfer options only turn interzone surfaces adiabatic, so they never change a role. A ceiling between storeys has Reversed = true, and so has a wall between zones whose zone ID sorts after the adjacent zone's (ordinal comparison, read from the building's adjacency, so the same wall is reversed whatever the options); this is the one rule both converters use to pick the reversed side: EnvelopePreset.For(assignment) then returns Construction.Reversed(), the same layers in reverse order named "{Name} Reversed" (a symmetric construction is its own reverse). The two sides of a surface between zones thereby list the same layers in opposite order, as EnergyPlus expects of paired interzone surfaces. EnvelopePreset.Constructions lists every construction a converter may write, each once (the roles' constructions in role order, then the reverses of the interior wall and floor where they differ), and EnvelopePreset.Materials every layer, each material once.

2. The example envelope

ExampleEnvelopePresets.Values and ExampleEnvelopePresets.Example (src/Lod.Core/Envelope/ExampleEnvelopePresets.cs), named Example Envelope. Every name starts with Example, so no output can be mistaken for a sourced envelope.

2.1 Materials

Round numbers of the order found in general material property tables; not taken from any particular table or standard.

Material	Thickness (m)	Conductivity (W/(m·K))	Density (kg/m³)	Specific heat (J/(kg·K))	Resistance (m²·K/W)
Example Brick	0.1	0.8	1800	840	0.125
Example Wall Insulation	0.12	0.04	30	1400	3.0
Example Roof Insulation	0.16	0.04	30	1400	4.0
Example Floor Insulation	0.08	0.04	30	1400	2.0
Example Partition Insulation	0.1	0.05	20	1000	2.0
Example Concrete	0.2	2.0	2300	900	0.1
Example Screed	0.05	1.25	2000	840	0.04
Example Gypsum Board	0.0125	0.25	900	1000	0.05

2.2 Constructions

Layers from the outside to the inside; the resistance is that of the layers alone, without surface films (Construction.ThermalResistance).

Role	Construction	Layers	Resistance (m²·K/W)
Exterior wall	Example Exterior Wall	Brick, Wall Insulation, Concrete, Gypsum Board	3.275
Roof	Example Roof	Roof Insulation, Concrete, Gypsum Board	4.15
Ground floor	Example Ground Floor	Floor Insulation, Concrete, Screed	2.14
Exposed floor	Example Exposed Floor	Wall Insulation, Concrete, Screed	3.14
Interior wall	Example Interior Wall	Gypsum Board, Partition Insulation, Gypsum Board (symmetric)	2.1
Interior floor	Example Interior Floor	Gypsum Board (ceiling below), Concrete, Screed (floor above); its reverse is Example Interior Floor Reversed	0.19
Internal mass	Example Interior Floor	the interior floor slab, which internal mass keeps (D-031)	0.19

2.3 Window

Example Double Glazing: U-factor 1.8 W/(m²·K), SHGC 0.4, visible transmittance 0.7, for the whole window (frame and glass together, as a simple glazing system). The glazed area itself comes from the program presets' WWR and the generators' window rule (D-026, D-079); the envelope only gives its properties.

2.4 Why these values

• The example only has to be physically plausible and valid, so that converters, tests, and example definitions have an envelope to write; its numbers carry no research meaning.
• The interior wall is symmetric and the interior floor is not, so both cases of interzone pairing (a construction that is its own reverse and one that is not) are exercised.
• Internal mass uses the interior floor construction, because a slab that becomes internal mass keeps its construction (D-031). (Refined by D-143, 2026-10-16: Convert2IDF writes it as "{name} Half", the construction with massive layers at half thickness and massless layers and air gaps at half resistance, on twice the slab area, so that the IDF holds the slab's heat capacity once. The slab construction is unchanged here and in Convert2BEM.)

2.5 Infiltration (D-124)

Infiltration is the building's, not a space type's: its magnitude follows each zone's exterior surfaces or volume, which a program preset does not know, so it left the program presets and is a field of the envelope preset (ADR-017; program presets §1.1). One design rate with a basis and a fraction schedule applies to every zone, at every level of detail, so zoning does not change the infiltration the model assumes (GLOBAL.md scientific rule 4).

InfiltrationBasis	The rate is per	EnergyPlus method of Convert2IDF
PerExteriorSurfaceArea	m² of the zone's exterior surface: the gross area, windows included, of its outdoor walls, roofs, and exposed floors, not its ground floor (m³/h per m²)	Flow/ExteriorArea
PerExteriorWallArea	m² of the zone's gross outdoor wall area (m³/h per m²)	Flow/ExteriorWallArea
AirChangesPerHour	the zone's volume per hour (1/h)	AirChanges/Hour

ExampleEnvelopePresets has 0.3 air changes per hour, always on (the schedule Example Always On, constant 1). Like the rest of the example envelope it is illustrative: 0.3 was the value most of the example program presets carried before infiltration moved here, and it is NOT taken from ASHRAE 90.1, the DOE prototypes, or any other standard. The per-type rates those presets had (mall 0.8, lobby 0.6, retail 0.5, operating theatre 0.1) are dropped, not moved (program presets §2.2). A sourced envelope would state its infiltration with the source, for example a rate per exterior surface area as the prototype models give it (§4).

3. Using an envelope preset

• In C#: ExampleEnvelopePresets.Example, or (ExampleEnvelopePresets.Values with { Window = new GlazingSpec("My Glazing", 1.4, 0.35, 0.6) }).ToPreset(), or a new EnvelopeValues with your own constructions.
• In Grasshopper: Envelope Preset (panel 1 Program Presets) outputs the example envelope; its inputs Name, Glazing, U-Factor, SHGC, VT, Infiltration Rate (default 0.3), Infiltration Basis (an enum input; default AirChangesPerHour, right-click lists PerExteriorSurfaceArea, PerExteriorWallArea, and AirChangesPerHour), and the optional Infiltration Schedule (unset: always on) default to the example values and replace the name, the glazing, and the infiltration. The layered constructions are the example's. Convert2BEM takes the preset on its Envelope input (the example when unconnected) and outputs each surface's and window's construction and the infiltration with each zone's design flow (convert2bem.md); Convert2IDF writes one ZoneInfiltration:DesignFlowRate per zone (convert2idf.md).

4. Sourced envelopes: an open research input

Sourcing envelope constructions, for example from a code or a prototype building for a chosen climate, is an open research input, decided together with climates and weather when simulations are run (D-112). When sourced envelopes are added, they must cite every value (document, version, table), state every conversion (for example from a U-value requirement to layers), be added alongside ExampleEnvelopePresets without changing it, and be recorded in the decision log and in this document.