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Focus on Consequences

01 January 2007

Maintenance can keep equipment in the same condition or improve it. Bill McLaughlin explains how air conditioning systems can benefit from applying reliability centre maintenance techniques to improve performance and energy efficiency

Delrac engineers install a packaged chiller

LAST SUMMER'S BAKING TEMPERATURES placed a greater burden than usual on the country's air conditioning systems. Indeed, many systems were unable to cope with the extra loads caused by the sweltering conditions and broke down. With the prospect of more hot weather in the coming years, it makes sense to review your air conditioning maintenance policy to prevent future failures and preserve the integrity of the system.

There are, essentially, three types ofmaintenance:
..Corrective - carried out to restore a defective item to a working condition as quickly as possible.
..Preventive - to ensure the best possible operation of equipment and avoid costly unplanned equipment failure or shutdown.
..Predictive - examining the 'vital signs' of the system through testing, inspection and 'condition monitoring'.

All these are designed to preserve existing operating conditions, but there is one maintenance regime that can actually improve a system's performance. Reliability-centred maintenance (RCM) focuses on the function rather than the equipment - what the system does rather than what it is. In his book, Reliability-centred Maintenance, John Moubray lists seven questions you should ask about the 'asset' - the air conditioning system:

1. What are the functions and associated performance standards of the asset in its present
operating context?
2. In what ways does it fail to fulfil its functions?
3. What causes each functional failure?
4. What happens when each failure occurs?
5. In what way does each failure matter?
6. What can be done to predict or prevent each failure?
7. What should be done if a suitable proactive task cannot be found?

The development of RCM has re-defined maintenance. It emphasises that the objective should be to prevent or mitigate the consequences of failures rather than to prevent the failures themselves. The consequences of failure differ depending on where and how air conditioning is installed and operated. A formal review of failure consequences will focus attention on maintenance tasks that have most effect, and diverts energy away from those that have little or no effect.

However, RCM does not preclude the need for good housekeeping practice. The Carbon Trust also recommends the following general advice for air conditioning systems:
..Ideally, set timers so that there is no cooling when the building is unoccupied
..Time-control each unit in localised cooling systems to avoid out-of-hours operation
..Check temperature settings. Find out the temperature at which your air conditioning switches on and your heating system switches off. The greater the temperature gap the better. Check and compare temperature settings for each unit in localised air conditioning systems. The Carbon Trust says it is common to see one unit heating and another cooling in the same space.
..Clean ductwork, fans and grilles regularly, and ensure furniture doesn't obstruct air pathways - any blockage can increase energy consumption and maintenance costs.

By taking these measures, you will be reducing the chance of an air conditioning system failure. But, equally importantly, you will be helping to cut carbon dioxide emissions from your buildings. This is a critical consideration. The April 2006 revision to Part L of the Building Regulations means that, for the first time, all new buildings will have to meet a target rate of carbon dioxide emissions. The EPBD, which has far-reaching implications for FMs, demands more energy efficient new and refurbished buildings, energy benchmarking of existing buildings against a national standard, and certificates for buildings for purchasers or potential tenants of property.

According to the UK Government, the principal objectives of the Directive are to promote improvement of the energy performance of buildings within the EU through cost effective meaures, and the convergence of building standards towards those of EU Member States.

The EPBD has four main components:
..Article 3 - Establish a framework for a common methodology for calculating the energy performance of all buildings. For buildings other than dwellings, a new calculation process is required to assess both the target emissions and the proposed building emissions. The default method for carrying out these calculations is the Simplified Building Energy Model developed for Department for Communities and Local Government (DCLG) by the Building Research Establishment.
..Article 4 - Minimum energy performance standards (came into force under Building Regulations Part L on April 6, 2006).
..Article 7 - Energy performance certificates (currently under review with the DCLG)
..Articles 8 and 9 - Boiler and air conditioning inspections (under review with the DCLG).

According to the Building Services Research and Information Association (BSRIA), the EPBD places far more emphasis on the performance of mechanical and electrical services in buildings, forcing more attention to be paid to management and maintenance practices.

BSRIA's view is that FMs faced with poorly performing M&E services have to ask themselves is it worth maintaining? This, says the Association, usually happens around the time of the annual budget process.

It adds: "Faced with a lack of information on the true maintenance needs of building services, a financial director is forced to set aside a sum of money every year based on little more than the opinion of the facilities engineer, plus some hazy idea of what nasty things might happen to the business if the lights went out.

"As a result, maintenance is usually based on preserving the physical assets using failure prevention and asset care. However, such a strategy must add value to the business process. What's needed is a reliable way of assessing the maintenance needs of the services against the business risk of plant failing in service."

BSRIA has produced a risk assessment toolkit designed to do just that. The Business Focussed Maintenance Toolkit enables facilities managers to focus their maintenance activities based on a logical assessment of risk to the business, says BSRIA.

It concludes: "The Toolkit also provides a costeffective way to assess, manage and maintain services, and reduces the risks of system failure. The result is maintenance that will protect your business without wasting money. The toolkit contains everything you need to prepare a complete maintenance programme based on the risk to your business."

It includes automated risk assessment forms; maintenance schedules, technical preambles and a supporting guide to help you through the process."

Five principles
RCM defines failure as 'any unsatisfactory condition'. It may be either a loss of function (in other words, the air conditioning stops working) or a loss of acceptable quality (for example, the air conditioning continues, but fails to improve air quality).RCM can be used to gather data from the results achieved and feed this back to improve future maintenance. In other words, it can improve systems and procedures and not simply keep them the same.

The US-based 'Whole Building Design Guide' defines RCM's primary principles as:
..Function oriented - RCM seeks to preserve system or equipment function, not just operability for operability's sake.
..System focused - RCM is more concerned with maintaining system function than with individual component function.
..Reliability centred - RCM is not overly concerned with simple failure rate; it seeks to know the probability of failure at specific ages.
..Design limitations - RCM's objective is to maintain the reliability of the equipment design recognising that changes in inherent reliability are the province of design rather than of maintenance. Maintenance can, at best, only achieve and maintain the level of reliability for equipment that was provided for by design However, RCM recognises that maintenance feedback can improve on the original design.
..Safety, security, and economics - Safety and security must be ensured at any cost; thereafter, cost-effectiveness becomes the criterion.

..Bill McLaughlin is managing director of Delrac ACS


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