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The role of a controls specification is to communicate the client's requirements and provide a complete and unambiguous definition of the building control system (1). In other words it describes the features and performance requirements that the client has requested within the client brief. Further to this it also contains information on the standards that need to be attained; the testing and commissioning that is to be carried out to ensure the system is working correctly, and training of the end user to ensure that they will operate the system efficiently and to achieve the desired comfort conditions. It also plays a part in defining responsibilities at different stages of the control system installation and the procurement process.
The specification needs to be clear, precise and direct so that it provides all of the necessary information but without being too complex.
There are 2 general types of control specification, either performance or functional. In practice most controls specifications are hybrid specifications of the above containing elements of both.
Generally speaking a performance specification is used to describe what tasks the controls system should be able to carry out and also what equipment each system is to control.
A functional specification contains more detailed information on how the system should function including monitoring and control of information for specific items of equipment (e.g. boilers) and descriptions of parts of the controls system such as the sensors, outstations & actuators.
Generally a performance specification is a looser specification than a functional specification, this means that there is more scope for error; however a performance specification is acceptable if the required system is fairly simple or there is an element of trust between the controls contractor and the author of the controls specification. The big disadvantage of a functional specification is that the author requires detailed knowledge of controls technology which many M&E consultants may not have, also as with IT in general the field of controls is developing very fast and as such information becomes redundant quickly.
Some of the issues that may need to be considered when preparing a specification are as described below:
The controls specification would normally include information on the required internal comfort conditions, and environmental tolerances (what variance from the specified set point is acceptable). These are the most important aspect of the controls system and need to be taken into account within the specification. Specific comfort criteria can be taken from CIBSE Guide A: Environmental Design.
Some areas of a building may need to be controlled independently to the rest of the building due to various reasons, including; different hours of occupancy, different use of the building, such as computer rooms, and also different requirements of the occupants.
It is important to ensure that these criteria are realistic and achievable since if they are not than poor system performance and decreased plant performance may result which in turn can lead to increased energy usage and running costs.
The controls system needs to be flexible in terms of being able to accommodate the future plans for the building. Over the lifetime of a building it can be altered significantly. The layouts of the buildings can change, the use of the building can change and also the system requirements can change therefore this needs to be clearly identified within the specification as future proofing the controls system at the time of installation can save a lot of time and money later on.
The specification would also contain information on alarm output criteria such as alarm set points, actions, texts, and handling. These are used to report plant fault conditions or out of set tolerance warnings, how outputs are presented to the user (on screen, printouts etc), and what should be done to rectify the alarm.
The specification should also cover integration of the controls systems for various building services systems such as the heating, cooling and ventilation plant with other systems such as fire, security, access control and lighting.
Without a good quality specification a lot of potential issues can occur such as, poor environmental comfort due to inadequate control systems being in place, excessive energy usage and therefore unnecessary costs and also occupant dissatisfaction due to uncomfortable working conditions. Any changes to the control system during the construction process may significantly increase the cost of a control system.
3. Task B
Describe the standards to be met, including testing, commissioning and training to be carried out and the guarantees to be given:
The controls specification will include details of standards to be met by the controls system, these can include relevant British Standards (such as EN 13646:1999 - Building Control Systems and EN ISO 16484-2 - Building Control Systems Part 2) current Building Regulations (such as Part L), local by-laws, CIBSE Guides (such as guide A and H), and BSRIA publications. (2) Refer to bibliography for list of further relevant British Standards.
Commissioning is the process of setting up the controls system to ensure that it works as it is required to by both the client brief and the controls specification. It is a 2 stage process comprising Pre-Commissioning and Commissioning.
Pre-Commissioning is the process of checking that all the components of a control system work correctly by bench testing and site testing. Bench testing is done pre installation and is done to ensure that equipment such as sensors and valves function as they are supposed to and are not faulty (manufacturer faults), site testing is mainly to ensure that the components have been installed correctly (e.g. check a sensor is wired up properly, no installation faults).
Commissioning involves setting up the control system as a whole to ensure that all the components work together, including the BMS supervisor (the computer that acts as the brains of the BMS) and the head end (the input/output device for the BMS such as a GUI - Graphical User Interface). The operational control parameters for various pieces of equipment must also be set (such as temperature set points) to ensure all the components of the system work together as they are supposed to. As a note all plant equipment must have been commissioned before the control system can be commissioned, also it is important at this stage to input the correct operational parameters as very often the settings are not altered by the user after commissioning.
Once a system is commissioned to the satisfaction of the installer, witness testing is carried out. Witness testing can be overseen by the project supervisor or his nominated representative and is to prove to the satisfaction of the nominated representative that the system is operating correctly. This can include ensuring plant and equipment is installed as per the controls specification and testing operator / user controls and interfaces. Generally the nominated representative should witness test the control of all major plant items and depending on the size of the control system they should also witness test a percentage of other control points. They should also witness a percentage of system outputs such as plant alarms and safety alarm responses (plant shutdown).
A BMS system will only perform correctly and be cost effective if its operator knows how to control it. For this reason operator training is required. The client must decide if they wish to directly employ the operator or if they want to employ a contracted management company. The cost of training to be provided will directly relate to the required skill and knowledge of the operator.
The control system should be provided with a guarantee by the system installer which is to ensure that the system will perform as detailed in the controls specification. The guarantee will also cover control equipment manufacturer warranties.
Once all the above has been done then building handover can be completed and a practical completion certificate issued.
4. Task C
Describe its role as a part of the procurement contract between the purchaser and the supplier / installer:
There are 4 main types of procurement process within the building industry:
Design & Build
Design & Manage
The traditional and Design & Build type procurement contracts the most common within the UK.
With design and build, the client places a contract with a single contractor who has responsibility for both design and construction. The client may appoint an adviser to act as employer's agent, to advise on the preparation of the client's brief, evaluation of tenders and to provide independent advice throughout the project. Design and build has advantages:
The client has single point responsibility from one organisation
As the contractor has responsibility for both design and construction, economies should be possible
A well-written client's brief is essential to the achievement of a satisfactory controls solution in the final building; an inadequately detailed initial brief may lead to the contractor providing an absolute minimum specification. A variation is known as develop and construct, where the client uses a design consultant to produce a scope design, before obtaining tenders from contractors who develop and complete the design and then construct the building.
The traditional procurement method separates design from construction. The client appoints design consultants who prepare a detailed design of the building. The design is put out to tender, following which a main contractor, responsible to the client, is appointed. The main contractor may appoint subcontractors. During construction, the design consultants exercise a supervisory role. This method is well understood in the UK and has the advantages of:
Providing clear contractual responsibility for each aspect of the work
A well-understood procedure
From the controls point of view, it has disadvantages:
There is no involvement of a specialist subcontractor at the design stage
Modifications to the design during construction are expensive
The controls specification forms the basis of a contractual agreement between the client and the contractor which forms part of the procurement contract. This role does not alter between different types of procurement contracts, what does alter is the design responsibility. So if using the traditional contract then the responsibility is with the clients design consultant within the design team. If a D&B contract is used the responsibility is with the contractor.
Responsibility diagram for the traditional procurement method. (3)
Responsibility diagram for the design & build procurement method. (4)