By clicking on the Derived Parameters button on a Construction dialog or using the Derived Parameters option on the Calculations menu, you can bring up a window displaying parameters derived from the current construction’s data. These include U-values, CIBSE admittance parameters and optical properties of glazed constructions. The derived parameters are dynamically updated in response to edits made to the construction.
Derived parameters (opaque construction)
The derived parameters for an opaque construction are as follows:
Outside surface resistance : the thermal resistance between the outside surface and its environment, as set in the construction data.
Inside surface resistance: the thermal resistance between the inside surface and its environment, as set in the construction data.
Outside convective heat transfer coefficient: the convective heat transfer coefficient for the outside surface, calculated from the surface resistance and emissivity.
Inside convective heat transfer coefficient : the convective heat transfer coefficient for the inside surface, calculated from the surface resistance and emissivity.
Outside radiative heat transfer coefficient : the radiative heat transfer coefficient for the outside surface, calculated from the emissivity.
Inside radiative heat transfer coefficient : the radiative heat transfer coefficient for the inside surface, calculated from the emissivity.
CIBSE U-Value : the U-value of the construction as calculated by the CIBSE method.
EN-ISO U-Value : the U-value of the construction as calculated by the EN-ISO method.
Admittance : the CIBSE admittance of the construction, which relates inside surface heat transfer to inside environmental temperature.
Admittance time lead : the time lead associated with the admittance
Internal admittance : (for partitions and ceilings only) the combined admittance of both surfaces of the construction, which features in CIBSE calculations for partitions contained entirely within a room.
Decrement factor : the CIBSE decrement factor, which, taken together with the admittance, relates inside surface heat transfer to outside environmental temperature.
Decrement factor time lag : the time lag associated with the decrement factor.
Surface factor : the CIBSE surface factor for the inside surface of the construction.
Internal surface factor: (for partitions and ceilings only) the combined surface factor of both surfaces of the construction, which features in CIBSE calculations for partitions contained entirely within a room.
Checkbox
Include construction properties in printed output ?: adds the construction to the list of those to be printed from the main Print facility.
Buttons
Copy : copies the derived parameters to the clipboard for pasting into other applications.
Print : prints the derived parameters.
Close : closes the dialog.
Derived parameters (glazed construction)
The derived parameters for a glazed construction are as follows:
Calculate values based on Electrochromic Clear State/Dark State: this option is only displayed if the construction includes an Electrochromic Glazing layer – it allows you to choose whether to display the optical properties based on the clear or the dark state of the glazing (the radio controls default to “Clear State”).
Outside surface resistance : the thermal resistance between the outside surface and its environment, as set in the construction data.
Inside surface resistance: the thermal resistance between the inside surface and its environment, as set in the construction data.
Outside convective heat transfer coefficient: the convective heat transfer coefficient for the outside surface, calculated from the surface resistance and emissivity.
Inside convective heat transfer coefficient : the convective heat transfer coefficient for the inside surface, calculated from the surface resistance and emissivity.
Outside radiative heat transfer coefficient : the radiative heat transfer coefficient for the outside surface, calculated from the emissivity.
Inside radiative heat transfer coefficient : the radiative heat transfer coefficient for the inside surface, calculated from the emissivity.
CIBSE U-value (glass only) : the centre-pane U-value of the construction as calculated by the CIBSE method.
CIBSE net U-value (including frame) : the U-value as calculated by the CIBSE method with a correction applied for the effect of the frame.
EN-ISO U-value : the U-value centre-pane as calculated by the EN-ISO method.
EN-ISO net U-value (including frame) : the U-value as calculated by the EN-ISO method with a correction applied for the effect of the frame.
g-value (BS EN 410) : the g-value of the glazing construction as calculated by BS EN 410. This is the total solar transmittance at normal incidence under specified conditions.
g-value (BFRC): the g-value of the glazing construction as defined under the conventions of the British Fenestration Rating Council:
g-value (BFRC) = 0.9 * (1 – frame fraction) * g-value (BS EN 410)
Frame occupies... : the percentage of the glazing element taken up by the frame
T(D) : the short wave solar transmittance at 10 angles of incidence
T(R) : the solar transmittance at 10 angles of incidence arising from absorption in the glazing construction and subsequent conduction, convection and long-wave radiation into the room.
Short-wave shading coefficient : the shading coefficient for directly transmitted short-wave solar radiation, defined as T(D)/0.87, where T(D) is the value at 0 ° (normal) incidence.
Long-wave shading coefficient : the shading coefficient for absorbed solar that enters the room by conduction, convection and radiation, defined as T(R)/0.87, where T(R) is the value at 0 ° (normal) incidence.
Total shading coefficient : the sum of the short-wave and the long-wave shading coefficients.
Checkbox
Include construction properties in printed output ?: adds the construction to the list of those to be printed from the main Print facility.
Buttons
Copy : copies the derived parameters to the clipboard for pasting into other applications.
Print : prints the derived parameters.
Close : closes the dialog.
