Achieving the benefits of condition-based maintenance
The attractions of condition-based maintenance – Andy Thorn.
Condition-based maintenance is much less costly than taking action only when plant fails. Building-management systems are a vital tool in exploiting its benefits, as Andy Thorn explains.Condition-based maintenance (CBM) of building-services plant has obvious attractions, not least of which are the cost savings it can make. The gains are greatest if the collection, reporting and analysis of data are automated. The most logical and cost-effective way of achieving this is through the building management system. Lower bills
Unlike planned maintenance, which is done at set time intervals or after a piece of equipment has run for a specified number of hours, condition-based servicing is carried out only when the plant actually needs attention. This can mean lower repair and energy bills and improved plant performance. Minimising the risk of services failing also reduces the possibility of costly disruption to the business of the building user. To be truly effective, CBM requires a regular flow of monitored data. Building-management systems are well placed to provide this. Sometimes they will already be measuring the appropriate variables for control purposes, particularly temperature data. When this is not the case, adding a few extra sensors will often be all that is needed. The most common example of the use of a BMS in condition based maintenance is for indicating when the filters in air-handling units need to be replaced, which the system determines from differential-pressure readings. Condition monitoring of other types of plant may require it to measure a number of variables and then calculate operational efficiency. This is particularly worthwhile on items with high capital and operating costs, such as chillers and large boilers — for which it is especially important to maintain optimum performance. Vibration monitoring
An increasingly popular CBM technique, and one highly relevant to building services, is vibration monitoring of rotating machinery. Normally based on piezo-electric technology, it can warn of various potentially serious problems on equipment such as fan and pump motors. Importantly, vibration sensors are low cost, easy to install and able to produce signals that can be output directly to a BMS. Depending on the amount of information available from a sensor, the BMS may be able to diagnose the cause of a problem, warning say that a bearing needs lubricating or a fan is out of balance. Because vibration monitoring enables a more effective maintenance strategy, it should appeal to a wide range of users. It is of particular value where there is a high price to be paid if the services go down — for example, in data centres, clean rooms or operating theatres. For a building-management system to be an effective CBM tool, it must be able to quickly send alarms to whoever needs to see them, on-site or off. Many BMSs meet this requirement by offering a variety of alarm-handling options. Bureau services, such as that operated by Trend can also offer a remote condition-monitoring service, to automatically compare actual and expected profiles for particular variables (e.g. boiler efficiency) and report any deviations. If sufficient data is available, it can even specify what remedial action is necessary. Valuable asset
The practice of only carrying out building-services maintenance when plant actually fails is sadly far too common, presumably because it is thought to save money. Condition-based maintenance is, in fact, the lower-cost option. What is more, it enables building users and owners to make the most of a very valuable asset — their building management system. Andy Thorn is commercial sales manager with Trend Control Systems Ltd, PO Box 34, Horsham, West Sussex RH12 2YF.