National Calculation Methodology (NCM) - Scottish Government

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30. Special considerations apply to ground floors in the notional building, where the Uvalue is a function of the ‘perimeter/area’ ratio. The following adjustments 9 must be made: a. If the calculated U-value is greater than 0.25 W/m 2 K, the value of 0.25 W/m 2 K must be used in the notional building. b. If the calculated U-value is less than 0.25 W/m 2 K with no added insulation, this lower value must be used in the notional building. 31. When modelling an extension, the boundary between the existing building and the extension must be disregarded (i.e. assume no heat transfer across it). 32. The effective thermal capacity of the construction elements, κm (kappa-m) value, in the notional building must be as shown in Table 2 (the thermal mass of windows should be ignored). DSMs must use the construction elements whose reference IDs are given in Table 1. The information in the NCM Construction Database includes the necessary technical parameters to evaluate the impact of thermal capacity. Table 2: Thermal capacity of construction elements in the notional building Element κm, Effective thermal capacity* (kJ/m 2 K) Roofs 12 Walls 11.7 Floors 36 Internal wall 11.9 Internal floor (and ceiling) 8.6 * Effective thermal capacity, κm, is defined in EN ISO 13790 33. The air permeability of the notional building must be defined as 10m 3 /(h.m 2 envelope area) at 50 Pa. The calculation method used to predict the infiltration rate must use the air permeability as the parameter defining the envelope leakage. For compliance and certification purposes, the same method must be used in the actual and notional buildings. Acceptable methods include: a. The method specified in EN 15242 10 . b. Other methods that use a relationship between the infiltration rate and air permeability and are set out in national or international standards, or recognised in UK professional guidance documents, which relate the average infiltration rate to envelope permeability. An example of the latter would be tables 4.13 to 4.20 of CIBSE Guide A (2006). 9 This follows the guidance given in CIBSE Guide A (2007). 10 Ventilation for buildings – Calculation methods for the determination of air flow rates in buildings including infiltration, EN 15242, CEN/TC 156, 2006. 12
Methods that use flow networks are not acceptable for compliance or certification of energy performance of buildings purposes as there is no simple way to check that the permeability of the notional building delivers the required permeability standard. Solar and Daylight Transmittance 34. The total solar energy transmittance (BS EN 410 g-value) and the daylight transmittance of glazing in the notional building must be as given in Table 3. These data apply to all windows, roof windows, and rooflights (for display windows, solar transmittance is 0.72 and daylight transmittance 11 is 0). The data in the tables are based on a normal incidence value of 0.72 for solar transmittance and 0.76 for daylight transmittance, which are further adjusted for certain orientations in order to limit overheating in the notional building. Appropriate values for intermediate orientations can be based on linear interpolation. DSMs must use the glazing element as identified by the reference IDs in the NCM Glazing Database for Scotland. Table 3: Solar and daylight transmittances in the notional building Orientation of glazing Solar transmittance (BS EN 410 g-value) Daylight transmittance N 0.72 0.76 274 NE 0.72 0.76 276 E 0.58 0.61 277 SE 0.58 0.61 278 S 0.72 0.76 279 SW 0.58 0.61 280 W 0.58 0.61 281 NW 0.72 0.76 282 Horizontal 0.43 0.46 275 Areas of Windows, Doors and Rooflights Database reference IDs 35. The areas of windows, doors and rooflights in the notional building must be determined as set out in the following sub-paragraphs and must also conform to the measurement conventions set out in the guidance beginning at paragraph 87. a. Subject to the following criteria, all external walls must have windows and, for industrial and storage buildings, roofs must have rooflights. b. Copy into the notional building the areas of pedestrian doors (high-usage entrance doors in the actual building should be copied as personnel doors in the notional building), vehicle access doors and display windows that exist in the corresponding element of the actual building. 11 The daylight transmittance of display windows in the actual building is also set to 0. 13
Page 1 and 2: Directorate for the Built Environme
Page 3 and 4: Contents. Contents 3 List of Tables
Page 5 and 6: BER Building Emission Rate BSD Buil
Page 7 and 8: 2 Approved Software Tools. 5. Non-d
Page 9 and 10: of building or building features. T
Page 11: Building Fabric 26. The U-values in
Page 15 and 16: egarded as being mechanically venti
Page 17 and 18: d. The electricity used by fossil-f
Page 19 and 20: . For other spaces, divide the illu
Page 21 and 22: Table 6: Carbon dioxide emission fa
Page 23 and 24: 4 Energy Performance Certificates (
Page 25 and 26: 5 Input Data to Approved Tools. 74.
Page 27 and 28: d. Any fuel used in generating the
Page 29 and 30: Table 8: Measurement and other conv
Page 31 and 32: pressure filtration is also defined
Page 33 and 34: Building Type Description 16 Non-re
Page 35 and 36: Activity Type Description 33 Generi
Page 37 and 38: Construction and Glazing Databases
Page 39 and 40: ID Category Construction Name 518 P
Page 41 and 42: ID Category Construction Name 565 P
Page 43 and 44: 101. It may also be that more compl

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