Design for Business Needs Reliability
Start Date: Sep 2004
End Date: Mar 2006
Project Status: Complete
Optimum reliability
Building services typically have a lifetime of 15-25 years and wear out comparatively quickly compared to the building's structure. It is important to have regular maintenance so that the systems continually perform to their optimum efficiency at full and part load conditions. All of this is made much easier if at the original design concept stage the components and the system configuration for the building services systems are selected in a way that ensures optimum reliability with flexibility to cater for future requirements (change of tenants and usage).
An integrated approach
An integrated approach to the optimisation of whole life cycle costs and resources results in better quality buildings and healthier working environments at optimum economic costs. Maintenance is usually referred to nowadays as facilities management but is much more extensive and includes taking into account the needs of the building occupants. Well-maintained buildings that have good reliability are also good for sustainability because energy consumption remains low, and they have a better quality environment. Since environment affects health this leads to higher productivity and there is greater value for money.
Services systems are difficult to pattern because they are composed of many different kinds of components. The choice of components, systems layout and the inter-connections are all important so that design, selection and workmanship all contribute towards reliability. Clearly in a system each component will have its particular failure rate pattern. However, strong interactions occur between system elements and the ultimate system performance depends very much on how these various components are combined within the system. Hence the initial design and selection are key stages that ultimately have a large part to play in determining the success of the building services system performance.
System reliability
The reliability of a large installation is not usually quoted as a single figure. Ideally the minimum mean time before failure or maximum failure rate is quoted. The pattern of use, duty cycle, maintenance requirements and how long the system can remain out of use determine their target reliability. System reliability is improved if each element is as reliable as possible and if simple layouts using few different parts are planned.
Redundancy
In practice components are combined in series and parallel pathways with means of systems operation defined by active redundancy or stand-by redundancy. In critical situations, such as in aircraft, all alternative means are energised and work simultaneously constituting an active redundancy system. Most buildings incorporate standby redundancy services systems where if one component of the plant fails then another is switched on. The part-load operation of systems is highly important because for most of the year environmental systems will not be operating at the maximum load. It is important to take into account the part-load operation of components to ensure that the systems are operating efficiently over most of the year and with varying occupancy patterns. Matching the load characteristic with the equipment performance is important. In line with this the offshore industry has got profound knowledge of predicting the serviceability of building services and extensive work had been carried out by the Institute of Electrical and Electronic Engineers in the USA on the reliability of electrical distribution.