Opaque Constructions - Tabs & Layers

 

This tab is only displayed if you have a licence for a relevant compliance application such as VE Compliance Part L2, Title 24 California or ASHRAE 90.1 PRM. The parameters set here are only required for special purposes (e.g. categorisation of the Construction element) in the relevant regulation.

 

Thermal bridging coefficient: Part L2 (2006) requires an allowance to be made for non-repeating thermal bridging. In the <VE> implementation this is handled via a coefficient expressing this component of heat loss as a multiple of element area. This can be thought of as an addition to element U-value. The default value of 0.035 W/m²K represents a typical value for office spaces built to the standards of the Robust construction details defined in IP 17/01. In the notional building, thermal bridging coefficients are set to standard values laid down in the NCM methodology document.

Metal cladding: Constructions can be identified as metal clad. This is used for thermal bridging in SBEM compliance testing.

Curtain wall: If the construction belongs to the Wall category it can be identified as a curtain wall. This is used for UK Building Regulations compliance testing.

Standard: Generic, UK NCM, etc.

Retain in notional/reference building:  If the construction belongs to the Partition or Floor/ceiling categories this additional parameter must be set for UK Building Regulations compliance testing.

Door Type:  If the construction belongs to the Door category an additional parameter must be set for UK Building Regulations compliance testing (U-value checks).

 

Select from the following options

·     Personnel door: standard door.

·     Vehicle access or similar large door: a category of door to which special rules, including more stringent U-value requirements, are applied in the Building Regulations.

·     Wall or roof element: select this option if you have used a door to represent elements of a wall or roof. This will place these elements in the correct category for Building Regulations purposes.

·     Smoke vent: select this option for a roof ventilator.

·     High usage entrance door: select this option to represent the entrance to a building with a high throughput of people (e.g. shopping centre, airport).

·     Curtain Wall: Select this option if the door if representing a curtain wall (opaque) panel in the model.

 

This tab is only displayed if the construction belongs to the Door category.

 

LCA frame materials: The assigned list of special LCA frame materials is displayed. The Edit button displays a dialog allowing you to edit this list of special LCA frame materials to your construction. This is only relevant to users of the cost planning and life cycle software where the datasets include some special materials with quantity method set to length instead of area. These are used in LCA to account for the environmental impact or costs of frame materials.

 

The construction may consist of up to 10 homogeneous layers, which are listed in order from outside to inside. With the exception of air gaps, each layer has a thickness and a material. The material has a set of properties which are stored in the Project Materials database, but which may be edited within the layer. Any new materials created by edits of this kind will be added to the list of Project Materials. Air gaps (which can include cavities filled with other gases such as argon) are assigned a thermal resistance in place of a material.

Material: the id and description of the material composing the layer, or alternatively ‘Cavity’.

Thickness: the thickness of the layer.

Conductivity: the thermal conductivity of the material. Values for commonly used building materials are listed in Table 6 in the Apache Tables document and in CIBSE Guide A.

Density: the density of the material. Values for commonly used building materials are listed in Table 6 in the Apache Tables document and in CIBSE Guide A.

Specific heat capacity: the specific heat capacity of the material. Values for commonly used building materials are listed in Table 6 in the Apache Tables document and in CIBSE Guide A.

Resistance: (cavity only) the thermal resistance of the cavity or air gap, taking account of both convection and radiation across the gap.

Vapour Resistivity: the vapour resistivity of the material or air gap. This field is blank for many materials, but a value must be supplied before condensation analysis is carried out. Values for commonly used building materials are listed in Table 16 in the Apache Tables document.

Category: the material category from the materials database.

 

The following buttons, which are mostly also available as context menu (right-click) options, are provided for tasks related to layer editing:

Copy: copies the properties of the selected layer to the clipboard. This is the same as Copy Layer on the context menu.

Paste: copies the material properties (but not the layer thickness) from the clipboard to the selected layer. The contents of the clipboard may have been copied from another layer, from a layer of a system construction or from a project or system material. This is the same as Paste Layer on the context menu.

Cavity: creates an air gap adjacent to and on the outer side of the selected layer. This is the same as Insert Cavity on the context menu.

Insert: inserts a layer adjacent to the selected layer on its outer side and assigns it the material properties stored in the clipboard. If the clipboard contains a construction layer, the new layer is also assigned the copied thickness. This is the same as Insert Layer on the context menu.

Add: adds a layer to the inside surface of the construction and assigns it the material properties stored in the clipboard. If the clipboard contains a construction layer, the new layer is also assigned the copied thickness. This is the same as Add Layer on the context menu.

Delete: deletes the selected layer. This is the same as Delete Layer on the context menu.

Flip: reverses the order of the layers. There is no equivalent option on the context menu.

Composite: converts a non-composite layer to a composite layer with two sub-layers, or a composite layer with two sub-layers to a composite layer with three sub-layers. Sub-layers initially use “in-line” data instead of real materials, but they can be “promoted” to using real materials. There is no equivalent option on the context menu.

Composite layers are generated in certain ASHRAE wizard-generated constructions. However these do not normally require subsequent editing. See Composite layers for details.

Composite layers are also used in the cost planning and life cycle software where sub-layers using real materials can be used to increase the accuracy of material usage. This software imposes certain rules on allowed combinations of BRE materials in a composite layer; after any such edit any rule violations will be checked and if necessary a validation window will display showing the rule violations and inviting you to fix them or enter a justification for the edit. See BRE materials for details.

NB A composite layer cannot be turned back into a non-composite layer – you would have to delete the layer and re-add it.

 

U-Value adjustment: Sets the selected layer as the layer to be adjusted in the U-value adjustment calculation, and displays a dialog allowing you to select whether to adjust conductivity or thickness to achieve the desired U-value.

Make real material (only available when you right-click on a composite layer sub-layer): displays a sub-menu where you can select from project, system or library materials, to “promote” the “in-line” data for the selected sub-layer into a reference to a real material. See Composite layers for details.

NB A sub-layer using a real material cannot be turned back into a sub-layer using “in-line” data.

 

System Materials…: display the materials used in the system database, with the option of copying them into the construction. See System Materials for details.

Project Materials…: display the materials in the project database, with the option of copying them into the construction. See Project Materials for details.

NB Library materials cannot be viewed from a button on this dialog.

 

Two further buttons perform analysis functions on the selected construction:

Condensation analysis: carries out an analysis of condensation risk for the construction under given temperature and humidity conditions. See Condensation Analysis for details.

Derived parameters: displays, in a separate window, a set of derived parameters for the selected construction. These include U-values and parameters relating to the CIBSE admittance procedure. The derived parameters will be dynamically updated as the construction is edited. See Derived Parameters for details.

 

The construction editing session is completed by clicking on either the OK or the Cancel button:

OK: Exits the opaque construction dialog and keeps any changes.

Cancel: Exits the opaque construction dialog and discards any changes.