Delivering an effective control system
Doug Robins offers advice on how to realise a control system that will result in a well run and energy efficient building.Control and building-management systems (BMSs) represent the highest technological aspects of the building construction process, which, in view of the ever increasing use of integrated systems, will become even more relevant in the future. Commissioning is probably the most important physical aspect of a project. Unfortunately it is rarely given the priority and attention that it deserves, and without its proper implementation the host building will never perform to anyone’s satisfaction. Ironically, since commissioning is also the last activity in any programme of works, it is also the least likely to have its full implementation time. The time requirements stated in BMS suppliers’ programmes are invariably shortened when incorporated into the services sub-contractor’s programmes. As contracts proceed and delays occur, the actual time for commissioning becomes condensed to fit the time available within the overall contract programme. Inevitably, commissioning remains incomplete at handover and causes poor post-occupancy satisfaction and high energy usage. The commissioning phase can sometimes be perceived as a hindrance to achieving the main aims of a building project — completion on time and on budget. A question that has exercised industry thinking for a considerable time is how can we improve the commissioning of systems and give the building occupier a system that not only operates correctly but is energy efficient and easy to manage. The commissioning process should start at the design stage and remain a major focus throughout the construction phase of the building. A detailed commissioning plan should be implemented to cover all the phases of the project — including design, system engineering, off-site testing and simulation, site testing, post-occupancy, and handover phases.
Typical approach Most control systems are engineered when they become required in the construction process and are usually left until the last minute, which can lead to inadequate testing of the control strategies. Each element is normally done in an isolated way. Software engineering, graphic engineering and descriptions of operation, along with the operating and maintenance information, can often be prepared by different people. Inevitably communication between these people can be problematic — leading to additional management time for the systems installer and frustration for the customer waiting for information. This is further compounded when changes are made to the original design and not passed on to the relevant people. Most software tools allow for free programming. While this can be advantageous when looking to produce some innovative way of controlling the plant, control strategies that do not have a demonstrable efficient case history must be thoroughly thought through and adequate provision made to ensure they are fully tested in the off-site commissioning phase. However, the mainstream requirement is for standard control modules to control standard items of equipment — i.e. AHU, boiler plant etc. Another issue with most control software tools is that they can be freely programmed with no enforced standards, the quality of the software produced being dependent on the skills and knowledge of the individual engineer. A constant problem for system installers is that when different engineers work on the same project there is a tendency to alter the software because one engineer thinks their way is better. Incorrect selection of control strategies and a lack of commissioning are often found to be the major reason for poor building energy performance. This can become a very difficult situation to manage, and the costs that follow are often overlooked when the systems are being selected in the initial design. Another problem with the non integrated approach is that operating and maintenance manuals are often difficult to produce and can be inaccurate — leading to frustration for the eventual occupier.
New approach We need to adopt an integrated approach to designing a control system from estimating, engineering, simulation, user access, graphics and monitoring, and have a complete software family for intelligent building control in which applications work closely with one another and with their controllers. With an integrated system, a building can be efficiently maintained and controlled, and the time to produce engineering strategies and graphics can be reduced substantially. Much of the cost of installation, maintenance and expansion of building-control systems is the labour cost, so software must work quickly and efficiently. Operating from one source, data is imported into the project database only once, and this information is then used in all of the applications such as software engineering, graphic engineering and descriptions of operation. A wide variety of tried-and-tested control modules for almost all equipment and installations that occur in a building should be available — such as, heating, cooling, ventilation, heat and cold storage, heat pumps, indication of legionella, load shredding and many more. Control modules should be individually equipped with typical control strategies and detailed definitions that automatically adjust themselves to the selected configuration, also including initial and default parameters such PID control loop settings, time delays and set points. Further, standard control modules should be created to provide the most energy- efficient solution applicable to the configuration. Graphic representation should be available for each of these modules which are then made available to the ‘front-end’ packages. Each module would also have full documentation aligned with the specific configuration, which could then be produced for the operating manuals. The ability to freely programme further modules should also be possible when new innovative ideas are created, so that complete building control systems can be created without the knowledge of specific programming languages. The resulting systems are easily maintained and installed or expanded, ensuring a guarantee of low costs during the entire lifespan. The system should also be open and future oriented based on the most up-to-date automatic control ideas, including Internet technology and standards such as XML, BACnet, Echelon/LonMark, KNX/EIB, Modbus, M-bus, ODBC, SQL and OPC, to allow easy integration into third-party equipment. One such system is Priva Top control provided by Priva Building Intelligence.
Off-site commissioning It can take significantly less time to commission equipment off-site rather than on a construction site. Doing as much off-site as possible will mean less effort and fewer resources are needed for the completion of the project. This becomes particularly important when interfacing to third-party equipment and, significantly, when data communications are involved. The ability to at least simulate and test software off-site should be possible, and, when used with tried and tested standard software modules, some predictability can be assured. This allows for functional tests to be carried out when working with the associated panel manufacturer and gives some assurance to the commissioning engineer going to site that what has been supplied will operate correctly.
On-site commissioning: Provided off-site commissioning has occurred, the on-site time should be reduced — especially if full point-to-point testing has been carried out so that only leaves functional and validation tests and calibration of sensors is still needed. The fine tuning of control loops could then be carried out with the full confidence that the system will operate according to its configuration.
Job handover and post occupancy The important aim of commissioning is to set up the building so that it can be operated and maintained throughout its lifetime. This includes the provision and transfer of design and commissioning information and even to adequate labelling of system components and the inclusion of appropriate information in the controls head end/graphics. When using the integrated approach, most of these elements are taken care of during the engineering process — giving all those concerned a degree of satisfaction and confidence that they will be getting a fully commissioned building. The building energy performance is assured, with the outcome of a satisfied occupier and easy to operate control system. Post-occupancy testing should form an integral part of the first year’s preventative maintenance programme. Benchmarks for energy should be established during this period to provide a basis for comparison in future years.
Doug Robins is business development manager with Priva Building Intelligence.
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