National Calculation Methodology (NCM) - Scottish Government

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Constructions 78. The thermal performance of construction elements must take account of thermal bridges as follows: a. Repeating thermal bridges must be included in the calculated plane element Uvalue as explained in BR 443 24 and set out in BS EN ISO 6946: 2007. Simulation tools that use layer by layer definitions will need to adjust the thicknesses of insulation layers to achieve the U-value that accounts for the repeating thermal bridges. b. Non-repeating thermal bridges, such as at junctions and around openings, as described in IP 1/06 25 . 79. Available on the NCM website is the NCM Construction Database containing the calculated U-values, κm values, etc, and for consistency, all implementations of the NCM should preferably use this database. It is accepted that a required construction may not always exist in the NCM database. In such cases, alternative sources of data may be used, but the person submitting for building regulations approval must declare this and demonstrate how the values were derived. 80. When using the software tool to generate an EPC for an existing building, the performance parameters for some constructions may not be known. In such situations, the parameters must be inferred, for example, using the inference procedure in SBEM which is defined in paragraph 95 of this document. This is an important aspect of ensuring consistency in energy rating calculations, and so all software tools must adopt these procedures. This will be checked as part of the approvals process. Low and zero carbon systems 81. The approach described below must be followed when calculating the impact of on-site electrical generation for both Section 6 compliance and EPC calculations, as applied to non-domestic buildings: a. Calculate the annual electrical energy used by the building irrespective of the source of supply. Multiply that demand by the CO2 emission factor of gridsupplied electricity (Table 6). b. Calculate the electricity generated by the on-site system and multiply that by the CO2 emission factor of grid-displaced electricity (Table 6), irrespective of the proportion of electricity that is used on-site and how much is exported. c. The electricity-related CO2 emissions used to establish the building’s emission rate is the net figure, i.e. the result of paragraph 81.a minus the result of paragraph 81.b. 24 Conventions for U value calculations, BRE, 2006. 25 BRE IP 1/06: Assessing the Effects of Thermal Bridging at Junctions and around Openings. 26
d. Any fuel used in generating the electricity (e.g., in a CHP 26 generator) is added (at its appropriate CO2 emission factor) to arrive at the total building’s CO2 emissions. Weather Location 82. In order to calculate the reaction of the building fabric and systems to the variable loads imposed by the external environment, the NCM needs an input of weather data. A standard weather set 27 has been adopted for Scotland, which must be used. Zoning Rules 83. The way a building is subdivided into zones will impact on the energy performance calculations. Therefore, this guide defines zoning rules that must be applied when assessing a building for the purposes of Section 6 compliance or producing the Energy Performance Certificate. 84. The end result of the zoning process should be a set of zones where each zone is distinguished from all others in contact with it by differences in one or more of the following: a. The activity attached to it. b. The HVAC system which serves it. c. The lighting system within it. d. The access to daylight (through windows or rooflights). 85. To this end, the zoning process within a given floor plate is as follows: a. Divide the floor into separate physical areas, enclosed by physical boundaries, such as structural walls or other permanent elements. b. If any part of an area is served by a different HVAC or lighting system, create a separate area bounded by the extent of those services. c. If any part of an area has a different activity taking place in it, create a separate area for each activity. d. Attribute just one “activity” (selected from the options available for each building type in the NCM Activity Database) to each resulting area. If the building is speculative, and the activity is not fully defined, select the appropriate ‘speculative activity’ for the relevant building type. 26 Combined heat and power. 27 This is the 2006 CIBSE Test Reference Year for Glasgow. See http://www.cibse.org/index.cfm?go=publications.view&item=332. Monthly average files have been created for use within SBEM. 27
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 and 12: Building Fabric 26. The U-values in
Page 13 and 14: Methods that use flow networks are
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: 5 Input Data to Approved Tools. 74.
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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