A Practical Guide To Building Thermal Modelling

Transcription

1 BG (Building Thermal Modelling)_D Legislation cover.qxd 13/08/ :08 Page 1 A BSRIA Guide A Practical Guide To Building Thermal Modelling By Richard Tudor BG 48/2013

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3 Acknowledgements PLANNING 1 This guide was authored by Richard Tudor of WSP, with input from industry representatives. Particular thanks are due to: Claire Das Bhaumik Catherine Simpson Chunli Cao Mike Whalley Sushil Pathak Piotr Liwen Hoare Lea Building Simulation BRE Building Performance Cudd Bentley Grontmij Every opportunity was taken to incorporate the views of the contributors, but final editorial control of this document rested with BSRIA. This publication was designed and produced by Joanna Smith of BSRIA. The guidance given in this publication is correct to the best of BSRIA s knowledge. However BSRIA cannot guarantee that it is free of errors. Material in this publication does not constitute any warranty, endorsement or guarantee by BSRIA. Risk associated with the use of material from this publication is assumed entirely by the user. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic or mechanical including photocopying, recording or otherwise without prior written permission of the publisher. BSRIA July 2013

4 1 PLANNING CONTENTS 1 PLANNING Brief and purpose Contractual requirements Software selection Execution plan Modelling approach Data collection Assumptions Risks and uncertainties Managing change 9 2 MODEL CONSTRUCTION Data logging Data checking Identifying high risk data Entry of data into software Checking Simulation Validation Outputs Iterations 14 3 MODEL OUTPUT REPORTING Reporting objectives Approach to reporting Report content Presenting data 16 4 FILING AND ARCHIVING File and folder naming Backup and archive Backup and archive procedures How long to keep backups and archives Archive and backup medium Storing backups and archives What information to archive ` Archive review 20

5 APPENDICES PLANNING 1 Appendix A Thermal model scope 22 Appendix B Assumption register 24 Appendix C Approach to infiltration 25 Appendix D EPC audit requirements 26 GLOSSARY OF TERMS 28 REFERENCES 29

6 1 PLANNING PREFACE The development and preparation of thermal models for projects is now an integral part of the design process, in particular to demonstrate compliance with carbon emissions targets as required by Building Regulations. The requirement for design, construction and maintenance teams to commit to future energy use is increasing and the benchmarks against which comparisons are made are often the result of thermal modelling. In addition, designers and contractors are being asked to underwrite contract commitments with respect to energy targets. Dynamic modelling can provide very accurate energy consumption data for a set of defined input criteria but can require assumptions to be made which may generate risks for a project. It is important that thermal models are subject to rigorous quality control procedures to mitigate risk, reduce design errors and provide a design audit in the event of future disputes or claims. Thermal models should therefore be reviewed as part of a technical quality review process prior to the reporting of findings by the originator. The aim of this publication is to provide practical guidance in the delivery of thermal models and is based on feedback from practising engineers experienced in thermal modelling. The guidance focuses on dynamic and compliance thermal modelling and not CFD simulation. It has no alignment to any particular software. The publication provides an overview of the thermal modelling process with a high level strategic approach to the quality requirements including guidance on procedures and principles to be followed in order to achieve a common standard. Primarily aimed at thermal modellers, this publication also provides guidance for organisations undertaking thermal modelling so as to improve working practices and help mitigate risks. Richard Tudor, July 2013

7 1 PLANNING Simulation planning Simulations should be planned to achieve the deliverables, ideally minimising the number of simulations / iterations to give overall clarity, save time and reduce costs. It is not always possible to have just a few simulations. Changing one thing at a time will more clearly identify the causal effect or benefit. The use of a matrix or some other visual planning aid can be helpful if several simulations are required, and in addition can provide an audit trail. In order to minimise the number of modelling runs, changes made from one case to another should ideally follow a logical sequence, for example base case, base case plus improved ventilation, base case plus improved ventilation plus solar control glazing and so on. Each simulation should be simply referenced with the detail of each reference recorded in a log book and / or a matrix of simulations. An example of a simulation planner is given in table 1. Table 1: Example of simulation planner Reference Improved Ventilation Solar Control Glazing Brise Soleil Case 1 (Base Case) Case 2 Yes Case 3 Yes Yes Case 4 Yes Yes Case 5 Yes Yes Case 6 Yes Yes Mechanical Cooling Information and decision planning In addition, the actual input parameters used in each case should be recorded, for example the g-value used for solar control glazing. Information flow and the decision making process should be carefully planned and managed. Considerations in planning information include: timescales including lead times for information such as wind tunnel data sources for information such as construction details and glazing properties, internal gains, services, infiltration and zoning key decisions and the process for establishing information on building information such as operating hours, occupancy patterns, mechanical / automated control issues and human issues such as how blinds will be used or at what temperature people would open windows establishing provenance of data. 4

8 PLANNING 1 Programme The amount of time required to undertake modelling should not be underestimated. Timescales should be determined by scheduling out the various different stages and allowing for a given number of iterations. Ideally the number of iterations should be agreed as part of the appointment and as required to achieve the objectives. EPC quality planning Energy Performance Certificates (EPCs) are produced using standard methods and assumptions about energy use to enable the energy efficiency of buildings of the same type to be compared. The EPC is an official instrument and a lack of quality can destroy credibility of the document and give false facts regarding compliance with legal requirements. An EPC must be accurate and include high quality evidence with no obvious errors or omissions, with any impact on the EPC being within set limits. Energy assessors, who have responsibility for EPCs, are subject to QA audits and could be suspended or removed from the scheme at any time for failing a quality assurance audit. Assessors may find an increased number of audits being requested to comply with the sampling rates required under the scheme operating requirements. Employing a quality framework and procedures will provide a safety mechanism and ensure consistency and accuracy of the certificates. It is important that the information used to prepare the EPC, which will also form evidence for an external audit if called upon, is carefully planned and collated as part of the modelling process. Appendix D provides tips on meeting audit requirements and outlines the evidence that may be required. 1.5 Modelling approach It is important to have a clear understanding of the approach to the modelling process, particularly with respect to the collation of data and the quality assurance procedures. The purpose for undertaking a model may vary (for example design calculations, CO 2 emissions check, Energy Performance Certificate or Building Regulations compliance) but the approach can be very similar. Figure 1 provides a typical approach to modelling. The flow chart also provides references to sections in this document that detail further information. The availability of data may vary, particularly between a new and an existing building, and it is important to manage the collation process. It is important to understand the level of information required, when to use assumptions in the absence of information and when to employ other activities to establish data (for example undertaking surveys of an existing building to establish information). Where assumptions are being made it is important to understand the impact these may have on the accuracy or quality of the output, and to make sure that the client is aware of this too. 5

9 1 PLANNING Figure 1: Typical approach to modelling Execution plan See section 1.4 Data collation See section 1.6 Assumptions Register See section 1.7 and Appendix B Assumptions Identify Agree with necessary parties See section 1.7 Input data log See section 2.1 Data logging See section 2.1 Identify high risk data See section 2.3 Data checking See section 2.2 Data entry into software See section 2.4 and figure 2 Check data entry is correct See section 2.5 Simulation See section 2.6 Archive See section 4 Output data Quality check and validation See section 2.7 Not Acceptable Change to input data Acceptable Model completion Reporting See section 3 6

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