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Library of System Control Strategies A BSRIA Guide www.bsria.co.uk Library of System Control Strategies By A J Martin and A P Banyard AG 7/98 Application Guide AG 7/98 LIBRARY OF SYSTEM CONTROL STRATEGIES A J Martin C P Banyard The Building Services Research and Information Association Old Bracknell Lane West, Bracknell, Berkshire RG12 7AH Tel: + 44 (0)1344 426511 Fax: + 44 (0)1344 487575 e-mail: [email protected] www.bsria.co.uk 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, mechanical, photocopying, recording or otherwise without prior written permission of the publishers. ISBN 0 86022 497 X ©BSRIA 78040 April 1998 EXECUTIVE SUMMARY EXECUTIVE SUMMARY The Library of System Control Strategies provides a reference document for use when specifying, developing and configuring control strategies. The Library is published in five chapters, each containing control strategies relating to the following main types of plant: · Chapter 1: BMS plant start /stop signals · Chapter 2: Heating systems · Chapter 3: Air handling plant · Chapter 4: Pumping · Chapter 5: Cooling systems In each chapter the control of the principal plant items in current use are described. Where there are many plant items which carry out the same function but using different techniques, for example, water heating, the modular format of the Library allows a ‘pick and mix’ selection of plant modules to be made to provide the required configuration of a complete system. Each plant module is shown in the form of a schematic and is described in terms of its general function and how it is controlled. Specification clauses are included which the system designer can copy into a particular specification document. Italics are used in the specification clauses to indicate where options are available from which the user can select the one required. Underlined text is used to indicate default values of setpoints and other parameters which the user should change for the particular specification. Total digital and analogue input and output points are given in a BMS points list for each plant item and a further table summarises the modes of plant operation for each of the controlled devices. Finally, each strategy has a flow chart which presents the control strategy information in an easy to follow format as an aid to understanding the sequence of control events. The ‘standardisation’ initiated by the Library of System Control Strategies will lead to easier system specification, configuration, commissioning and witnessing due to the better understanding of and familiarity with the control software provided. Subsequent operational problems will also be easier to identify. This will provide more effective system design, installation, operation and maintenance and consequent productivity gains that such performance improvements bring about. Note: This document is also contained on the accompanying diskette. ©BSRIA AG 7/98 Library of System Control Strategies i ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS BSRIA would like to thank the following for their financial contribution to the development of the Library of System Control Strategies: Department of the Environment, Transport and the Regions Andover Controls Europe Ltd Caradon Trend Ltd Sauter Automation Ltd TAC [UK] Ltd Acknowledgement is also given to Mrs Sheila Mills who drew all the schematics and flow charts, and to the following individuals who provided technical comment: Dr D Arnold (Troup Bywaters+Anders) Mr C Banyard (Hoare Lea and Partners) Mr R Brailsford (Oscar Faber Plc) Mr C Flitcroft (Bovis Lelliott Ltd) Mr L Ford (Sauter Automation Ltd) Mr T Godding (Symonds Group Ltd) Ms D Hobbs (MEPC UK Ltd) Mr A Langford (Andover Controls Ltd) Mr B Martin (TAC [UK] Ltd) Mr C Monson (Caradon Trend Ltd) Mr A Norén (TAC [UK] Ltd) Mr N Pennell (Land Securities Properties Ltd) Mr N Skemp (Building Design Partnership) Mr K Shenstone (Meica Services) Mr B Stevens (Max Fordham and Partners) Mr A Wallenborg (TAC AB) Mr C Wood (Glaxo Welcome). Every opportunity has been taken to incorporate the views of the sponsors and technical panel but final editorial control of this document rests with BSRIA. ii Library of System Control Strategies ©BSRIA AG 7/98 CONTENTS CONTENTS 1 GENERAL CONTROL STRATEGIES .........................................................................................13 1.1 BMS start/stop control.........................................................................................................13 1.1.1 Time control..............................................................................................................13 1.1.2 Low temperature interlock signals (plant protection)........................................................ 3 1.1.3 Low inside air temperature interlock (building fabric and contents protection) .................... 5 1.1.4 Optimum start heating.................................................................................................. 6 1.1.5 Optimum stop heating .................................................................................................. 8 1.1.6 Boost - fixed time ........................................................................................................ 9 1.1.7 Domestic hot water (DHW) demand.............................................................................10 1.1.8 Optimum start cooling.................................................................................................11 1.1.9 Optimum stop cooling.................................................................................................13 1.1.10 Night cooling..............................................................................................................14 1.1.11 Fan overrun ...............................................................................................................19 1.1.12 Pump overrun ............................................................................................................19 1.2 Other control signals............................................................................................................20 1.2.1 Hand/off/auto selection switch.....................................................................................20 2 HEATING SYSTEMS ................................................................................................................21 2.1 Water heating plant..............................................................................................................22 2.1.1 General boiler control strategy based on a single conventional boiler ..................................22 2.1.2 Single boiler installation - condensing boiler with split heat exchanger ................................33 2.1.3 Sequencing boiler installation with 2 or more parallel low water content boilers...................39 2.1.4 Sequencing boiler installation with 2 or more boilers with isolating valves...........................48 2.1.5 Sequencing boiler installation with 2 or more boilers, each with individual pump and bypass circuit ...............................................................................................58 2.1.6 Sequencing of non-identical groups of boilers .................................................................67 2.1.7 Modular boiler installation .............................................................................................77 2.1.8 Combined heat & power (CHP).....................................................................................84 2.1.9 District heating............................................................................................................93 2.2 Pressurisation .....................................................................................................................97 2.2.1 Static head pressurisation .............................................................................................97 2.2.2 Sealed expansion vessel pressurisation ...........................................................................99 2.2.3 Gas pressurisation .....................................................................................................101 2.2.4 Pump pressurisation...................................................................................................103 2.3 Hot water distribution (Secondary circuits) ..........................................................................105 2.3.1 Constant volume / variable temperature........................................................................105 2.3.2 Constant temperature / variable volume ........................................................................112 2.3.3 Non-storage calorifier ................................................................................................117 2.3.4 Storage calorifier .......................................................................................................122 2.3.5 Water heated underfloor system ..................................................................................126 2.4 Self contained heating systems............................................................................................130 2.4.1 Gas fired heater .........................................................................................................130 2.4.2 Radiant heating systems .............................................................................................134 2.4.3 Electrical underfloor heating........................................................................................137
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