National Calculation Methodology (NCM) - Scottish Government
National Calculation Methodology (NCM) - Scottish Government National Calculation Methodology (NCM) - Scottish Government
7 Suitability of Calculation Method. 96. Selection of the software tool to be used for a particular project will depend on a number of issues. These issues may apply to any software used for these purposes, not only to the use of iSBEM 31 /SBEM. Availability of Tools and Competence of Users 97. First, the choice of software tool will depend on whether the tools that are available are within the competence of the users – ideally the users have successfully undertaken training on use of the chosen tool and have further practical experience of its use. Formal accreditation in the use of the tool, whilst not essential, is beneficial. It may be that the user has already used one of the DSM tools or a CAD 32 package that interfaces with one of the software tools for design work, so that the bulk of the input has already been undertaken; this will mean that it is preferable to continue to use the tool that the project has already been started on. 98. Where the project requires that the software should be used outside the standard scenarios, for instance inputting a system that is not on the standard drop-down menus, it is important that the user should understand and be competent to extend the software in such ways. The user should also be prepared to document and justify any extraordinary uses of the software to an auditor or verifier in relation to compliance issues. 99. It is important that there should be consistency in the rating of similar buildings, otherwise the credibility of the rating procedure is undermined. When software tools are used and assessors follow a standard set of conventions to minimise differences that may arise from interpretation, it should be possible to ensure that consistent results are obtained. On the other hand, using software that does not have such conventions governing its use may allow inconsistencies between assessors. Consistency may diminish if the simulation depends on user interpretation to set appropriate inputs. The Complexity of the Building and its Services 100. The more complex a building and its building services, the greater the possibility that it may not be simulated accurately by a user. This is because data entry may depend on the vigilance and competence of the user to enter all necessary parameters reliably, and whether any checks on this can be made using the chosen software (e.g. if it produces a graphical representation to compare with the actual building). 31 Interface to SBEM. 32 Computer-Aided Design. 42
101. It may also be that more complex building configurations and HVAC systems cannot be mapped onto the features and system descriptions listed directly in the software. In this case, either the software may be unsuitable to model this building or systems, or alternatively, it may be possible to develop a workaround that allows novel configurations to be entered in terms of features that are available in the software (see paragraph 104 below). Whether Workarounds are Available 102. Where features that are not listed amongst the options in the software are to be simulated, the choice of software will depend on whether “official” workarounds that define those features in terms of parameters that the user can access have been developed. Software providers should inform users of any limitations of their software to model any aspects of the energy performance of buildings. They should also inform of acceptable workarounds to overcome these limitations. This information, consistently provided by all software vendors and frequently updated, should facilitate the appropriate choice of software tool to be made. 103. If no recognised and verifiable workaround exists, the choice of software will be limited to those tools which can model the proposed building and its features directly. 104. It is not feasible to prescribe a definitive, exhaustive list of workarounds in iSBEM. Practical workarounds are developed and added to the FAQ 33 page of the NCM website as and when the need for them arises due to common requests from users. Limitations of all Software Tools 105. Ultimately, there might be a point at which it would have to be decided that the calculation provided by a given software tool cannot give credit for a particular unlisted feature, either directly or via a workaround. This decision will itself depend on whether the evaluation of the unlisted features depends on the software’s ability to simulate dynamic thermal interaction between the people, equipment and air inside the building, the building elements and building services, and the external environment, or whether this dynamic interaction can be simulated on a representative building or system and the results used to adjust a steady state simulation. 106. Also, there will be features which cannot be simulated by any of the tools directly or via recognised and verifiable workarounds. Users should report such circumstances to BSD, who may consider if it is worth commissioning software providers to develop workarounds or new software capabilities to simulate such features. 33 Frequently Asked Questions. http://www.ncm.bre.co.uk/faqs.jsp 43
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101. It may also be that more complex building configurations and HVAC systems<br />
cannot be mapped onto the features and system descriptions listed directly in the<br />
software. In this case, either the software may be unsuitable to model this building<br />
or systems, or alternatively, it may be possible to develop a workaround that<br />
allows novel configurations to be entered in terms of features that are available in<br />
the software (see paragraph 104 below).<br />
Whether Workarounds are Available<br />
102. Where features that are not listed amongst the options in the software are to be<br />
simulated, the choice of software will depend on whether “official” workarounds<br />
that define those features in terms of parameters that the user can access have<br />
been developed. Software providers should inform users of any limitations of their<br />
software to model any aspects of the energy performance of buildings. They<br />
should also inform of acceptable workarounds to overcome these limitations. This<br />
information, consistently provided by all software vendors and frequently updated,<br />
should facilitate the appropriate choice of software tool to be made.<br />
103. If no recognised and verifiable workaround exists, the choice of software will be<br />
limited to those tools which can model the proposed building and its features<br />
directly.<br />
104. It is not feasible to prescribe a definitive, exhaustive list of workarounds in iSBEM.<br />
Practical workarounds are developed and added to the FAQ 33 page of the <strong>NCM</strong><br />
website as and when the need for them arises due to common requests from<br />
users.<br />
Limitations of all Software Tools<br />
105. Ultimately, there might be a point at which it would have to be decided that the<br />
calculation provided by a given software tool cannot give credit for a particular<br />
unlisted feature, either directly or via a workaround. This decision will itself depend<br />
on whether the evaluation of the unlisted features depends on the software’s<br />
ability to simulate dynamic thermal interaction between the people, equipment and<br />
air inside the building, the building elements and building services, and the<br />
external environment, or whether this dynamic interaction can be simulated on a<br />
representative building or system and the results used to adjust a steady state<br />
simulation.<br />
106. Also, there will be features which cannot be simulated by any of the tools directly<br />
or via recognised and verifiable workarounds. Users should report such<br />
circumstances to BSD, who may consider if it is worth commissioning software<br />
providers to develop workarounds or new software capabilities to simulate such<br />
features.<br />
33 Frequently Asked Questions. http://www.ncm.bre.co.uk/faqs.jsp<br />
43
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