CIBSE Guide H: Building Control Systems

Cibse

• Publisher: Routledge
• Year: 2007
• Print ISBN: 9780367398187
• eBook ISBN: 9781136421730
• Topic: Technology & Engineering
• Subtopic: Construction & Architectural Engineering
• Index: Technology & Engineering

'Building Control Systems' provides the building services engineer with a comprehensive understanding of modern control systems and relevant information technology. This will ensure that the best form of control systems for the building is specified and that proper provision is made for its installation, commissioning, operation and maintenance. Beginning with an overview of the benefits of the modern building control system, the authors describe the different controls and their applications, and include advice on their set-up and tuning for stable operation. There are chapters on the practical design of control systems, how to work from the hardware components and their inclusion in networks, through to control strategies in Heating, Ventilation and Air Conditioning (HVAC) systems and whole buildings. The relationship between Building, Management Systems (BMS) and information technology systems is discussed, and the building procurement process and the importance of considering control requirements at an early stage in the design process

1 Introduction: the need for controls

1.1 Overview of the Guide

1.2 The modern control system

1.3 The global environment

1.4 The indoor environment

1.5 Energy conservation

1.6 Information technology and systems integration

1.7 Building operation

1.8 The benefits of a BMS

1.9 Summary

This introductory section provides an overview of the Guide and will be of value when preparing the general case for a control system. It demonstrates the importance of controls in ensuring effective and efficient control of a building in order to:

— provide comfortable and productive working conditions

— provide the proper environment for industrial processes

— operate in an energy efficient manner

— be environment friendly.

1.1 Overview of the Guide

The first edition of this Guide was published in 1985 as an Applications Manual, under the title Automatic Building Controls and Their Implications for Systems Design. The many developments since then, particularly in the fields of microprocessor control and communications networks, have necessitated the production of an entirely new edition. The aim of the Guide has been restated since the first edition to reflect the growing importance of IT, and now reads: to provide the building services engineer with a sufficient understanding of modern control systems and relevant information technology to ensure that the best form of control system for the building is specified and that proper provision is made for its installation, commissioning, operation and maintenance.

Table 1.1 Organisation of the Guide

1	Introduction	The contribution that a modern building management system can make to the efficient and economical operation of a building
2	Control fundamentals	The basic types of control operation that are found in practice, ranging from the simple thermostat to microprocessor controlled self-learning algorithms. Guidance on the application of different control types and their tuning for optimum operation
3	Components and devices	The whole range of hardware components that constitute a control system, including sensors, valves, dampers, actuators, motors and basic controllers
4	Systems, networks and integration	The means by which components are brought together to form an operating control system. The various BMS architectures and the major standard protocols for bus systems. Characteristics of networks and the extension to full systems integration
5	Control strategies for subsystems	Control strategies for the fundamental parts of HVAC systems: safety interlocks, boilers, chillers, water and air systems, lighting
6	Control strategies for buildings	Control strategies for whole buildings. Avoiding conflict between subsystems. Illustrations of successful control installations
7	Information technology	The relation between BMS and IT. Energy monitoring and targeting, maintenance scheduling, facilities management
8	Management issues	The importance of the procurement method on the BMS design process. Commissioning, CDM requirements and cost issues

The structure of the Guide is indicated in Table 1.1. This introductory section sets out the benefits to be gained from a modern building control system and will be of value in making the case that adequate provision be made at an early stage for a proper control system. The following section deals with the different types of control mode and their application in different situations; advice is given on the setting up and tuning of controllers to ensure stable operation.

Sections 3–6 deal with the practical design of control systems, starting with the hardware components, then their incorporation into control systems by linking them into networks, and then two sections on control strategies for HVAC systems and whole buildings. The Guide thus starts with the constituent components and moves up to complete systems. The user may prefer to consult the control strategies for systems of interest and then refer back in the Guide to obtain a fuller understanding of the component parts.

Section 7 deals with the relation between building management systems and information technology. The BMS and IT systems may share a communications network and the information gathered by the BMS can be used by the IT system for further purposes, enhancing the value of both systems. The final section shows the importance of the building procurement process in determining whether adequate resources are devoted to the design and installation of a suitable BMS and emphasises the necessity of taking control requirements into consideration at an early stage in the design process.

1.2 The modern control system

Good controls are essential for the safe and efficient operation of a modern building. The control system does more than keep the inside of a building comfortable for the occupants. It is required to keep the HVAC plant operating efficiently, to ensure that all plant operates safely in the event of any unforeseen circumstances, and it must be capable of two-way communication with the personnel charged with its operation. While it may be self-evident that modern highly serviced buildings require a sophisticated control system, it should be realised that simpler buildings relying on a boiler system and natural ventilation can still benefit from a modern BMS. The increasing emphasis on energy conservation and reduction of greenhouse gas emissions serves to increase the importance of efficient controls.

The late 1970s saw the introduction of digital data technology, in which information is transmitted not as an analogue electrical value, but as a number. Digital data transmission is less susceptible to error than analogue transmission and it is standard practice to construct the signal protocol in such a way that it is possible to detect whether an error has occurred during transmission. This was the beginning of direct digital control (DDC). It required the codification of rules by which values are converted to numerical messages for sending; such messages have to contain not only the value of the variable under consideration, but additional information such as the origin and destination of the message and error-checking information. Such conventions on the structure of the messages are the basis of data communication protocols. At the early stage of DDC, data handling was centralised and multiplexing circuits were used so that the central unit could contact each remote unit as required. As computing power rapidly increased, the functionality of the central control unit became more and more sophisticated, with the ability to handle increasing amounts of data and to perform additional functions such as the monitoring of energy consumption and the printing or reports.

The advent of the microprocessor allowed considerable computing power to be incorporated in a small device and meant that it was now no longer necessary for all control and monitoring functions to be carried out by a large centralised computer. Intelligent outstations placed round the building became capable of carrying out local control functions, while communicating with a central supervisor which could oversee their actions, receive any alarm signals and alter set points or operating times as required. There has been enormous progress in the field of data communication and the application of local area networks (LANs), which allow microprocessors and computers to communicate with each other over standardised networks. Communication may be extended to link together the operation of several buildings, which may be located miles apart, or even in different countries.

All these have contributed to the modern building management system. In this Guide the term ‘control system’ or ‘building control system’ is used to cover all control elements, including hardware, controllers, any linking network and central controllers. The term BMS refers to a system where components may communicate with each other and generally implies some form of central supervisor, which permits monitoring and control of the building from a single point. The period that saw the development of the BMS has also seen the rise in information technology (IT). A modern operation, whether it is office or factory, is likely to distribute and process large amounts of information dealing with the operation of the business. There may be advantages in linking IT and BMS, either for the economy of using shared networks or for the more efficient integration of management control over the many activities taking place in a building.

1.3 The global environment

The building industry is implicated in two major concerns about the possibility of global environmental change: global warming and damage to the ozone layer. Buildings are a major source of carbon dioxide emissions, whether directly by the consumption of fuel for space and water heating, or indirectly by the consumption of electricity for lighting, air conditioning and other uses. It is estimated that energy use in buildings in t...

Table of contents

• Front Cover
• Title Page
• Copyright
• Contents
• Foreword
• Preface
• Acknowledgements
• 1 Introduction: the need for controls
• 2 Control fundamentals
• 3 Components and devices
• 4 Systems, networks and integration
• 5 Control strategies for subsystems
• 6 Control strategies for buildings
• 7 Information technology
• 8 Management issues
• Appendix A1: Bibliography
• Appendix A2: Tuning rules
• Appendix A3: Glossary
• Index