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Control systems are an essential part of building services design and this statement has never been more accurate. With increasing fuel costs and pressure to reduce CO2 emissions, control systems are integral parts of ensuring building service systems operate efficiently and effectively to reduce waste whilst maintaining safety, comfort and flexibility. 'Studies have shown that even well-managed buildings waste up to 15% of their energy they purchase and, typically, businesses could cut their energy consumption by a quarter.' (CIBSE Knowledge Series KS4, 2005).
Role of the Specification
During the design of building service systems the building services engineer will produce design drawings and a specification for the project in order to clearly identify the works to be carried out. The specification accompanies the design drawings and should provide a clear definition of what has to be done and how. The control specification like any other specification will form the basis of the installation and the contract between the client and the contractor. The role of the control specification is to ensure that the installation specialist is aware of the key criteria; the performance objectives, design parameters, standards and specific control requirements for each system which has to be controlled as well as testing, commissioning and training requirements for the entire system. The control specification is also an important part of the procurement contract between client and installation specialist and will allocate responsibility to each party to ensure that no disputes or disagreements arise.
In terms of the control specification the following key criteria should be considered;
Performance objective - This is the final outcome which should be delivered.
Design parameters - What are the working conditions to be controlled to and from.
Standards - Are there any British Standards, Building Regulations, benchmarks, guidelines which must be followed?
Specific control requirements (functional specification only) - How does the system operate and is their any supplementary information required?
In order for a control specification to be effective it must outline the operational requirements rather than detailing equipment and technological requirements. This is to ensure that the specification is future proof as only objectives and deliverables have been identified and will also ensure that when tendering costs are competitive.
There are two main types of control specification, performance and functional. The performance specification outlines the strategic operation of systems and the standards to be met, it does not detail how each system will operate. Whereas a functional specification does detail the exact requirements to be delivered, and generally considers the following key information;
Operation - Who will operate and supervise the control systems?
Application - Complexity of the building services to be controlled?
User - What operator interface is required?
Occupant Control - Do non technical users have control over systems?
Integration - What communication protocol is required?
Flexibility - How flexible does the system need to be?
Security - Who can operate the control systems?
Cost - Capital cost and payback should be considered.
BMS - Is a Building Management System required?
Expansion - Additional capacity or future proofing to built in?
The building services engineer should agree with the client which type of specification should be produced. A performance specification should be used where the proposed control systems are relatively simple or as part of a scope design in a design and build contract. If an advanced building management system is required or the building services engineer is part of a traditional contract it may be more appropriate to produce a functional specification.
Elements of Specification
The control specification should be written to ensure that the BMS operates to a high standard throughout the lifetime of the system. The control specification should aim to comply with all relevant British Standards and follow CIBSE and BSRIA guides where appropriate. Testing schedules, commissioning plans and training programmes should all form part of the specification document. By meeting these standards this will help to preserve the life and maximise the efficiency of the system.
The control specification should detail the control systems testing requirements, and ensure all components are tested and calibrated in accordance with the relevant British Standards and codes of conduct. The client's representative can also insert into the specification a performance-testing schedule, ensuring each component is tested at regular intervals. Performance testing schedules should be devised and carried out by fully trained operators.
It is vital that the control system is commissioned correctly to ensure the buildings control strategy is implemented and ensures all services work together. Failure to commission the system correctly will lead to system inefficiencies, energy waste, additional operating costs and uncomfortable internal environments.
Commissioning of a control system involves two major activities;
Checking that the control system works
Setting all parameters and switches to appropriate values
(REFERENCE CIBSE Guide H - 18.104.22.168)
The specification should state that a record is kept of the values of the variable parameters that have been set during the commissioning process. Once commissioning has taken place the installation specialist as well as the contractor and building services engineer will witness a percentage of the systems and sign off the control installation guaranteeing its performance.
The commissioning plan and strategy should be devised at the initial design stage and included within the specification. A thorough specification will ensure that each component is set up correctly and to the required values as part of the design.
Pre-commissioning should be undertaken during the installation and the system should then be re-commissioned after the handover once the building is in operation. This is referred to as seasonal commissioning. This will allow for the buildings performance to be evaluated and finely tuned achieving maximum efficiency and the correct internal environment.
Commissioning is usually the last major task in a construction project, and as a result of this, generally carried out under time constraints. In large buildings up to 1,000 control points can be installed so careful planning is required in order to configure the system as close to the handover as possible.
To ensure the system is used to its full potential, skilled operators are required with in-depth knowledge of the control functions and how the building should operate. This is achieved through specialist training.
CIBSE recommend that;
At least two control system operators attend an in-house training course delivered by control specialists prior to completion of the BMS
The operators are invited to attend the commissioning of the control system
The operators are present during handover period to learn about the system
All new operators receive proper training
CIBSE Guide H - 22.214.171.124 Training
All training requirements will be detailed in the specification. With sufficient training operators will gain technical knowledge enabling them to interpret data, identify faults and resolve potential issues proactively.
As previously stated the control specification's role is to communicate the projects requirements and it forms part of the contract between the client (purchaser) and the contractor (supplier). The method of procurement will ultimately affect the role played by the controls specialist. Different procurement contracts will give the building services engineer varying levels of control and thus have bearing on the final product. The two main procurement routes that currently dominate the construction industry are the traditional and design and build methods. In order to deliver a successful control system the above procurement methods must be considered.
If a project is delivered as part of a traditional contract, design and construction are independent. Detailed design work is fully complete prior to the construction phase. In the traditional method of procurement after the detailed design work has been completed it is sent to tender with the specification and drawings. At this point the contractor will cost the scheme based on the design.
Traditional procurement allows the building services engineer a greater level of control for design and specification. It will ensure that all the requirements for the project are delivered and will allow monitoring and supervision of the installation to ensure no mistakes are made. The only disadvantage to procuring the contract in the traditional manner will be that a control specialist will not review the design prior to costing, if designed incorrectly this could cause expensive additions later within the project.
Fig 1.1 Traditional Procurement Structure (Source: CIBSE, 2000)
Design and Build Procurement
If a project is delivered as part of a design and build contract, the contractor will take full responsibility for delivering the project once appointed. Design and build contracts usually allow projects to be built at a quicker and cheaper rate which can cause quality and specification issues.
The main contractor will normally appoint specialists to deliver the clients brief, however if this brief is not clear and ambiguous the contractor may not deliver the clients aspirations but may only deliver the minimum requirements. Amendments to the contract can be made to allow specialists to work on behalf of the client at brief stage and this is usually known as scope design.
Fig 1.2 Design and Build Procurement Structure (Source: CIBSE, 2000)
The quality and content of the specification will ultimately represent the standard of installation and functionality of a control system. Although good HVAC, lighting and other building systems can be designed correctly, the design and operation of the control system will ultimately drive these systems efficiencies and capabilities. Control systems play an important part in building design and will continue to do so, by ensuring control systems are considered carefully during all stages of development energy consumption, costs and CO2 emissions can be reduced.