The rate of development of information and communications technology (ICT), sensor technology and data processing systems is creating major opportunities for the development of new services and solutions in a wide range of industrial sectors. In particular it provides the opportunity to significantly improve our understanding of the condition of built environment, and in particular the different assets in buildings. These could improve the efficiency & effectiveness of asset management procedures, facilitating the move from planned, preventative to condition-based maintenance and create a wider performance database to inform component and structural design, building information modelling (BIM) etc.
The use of interactive components incorporating embedded sensors in mechanical and electrical (M&E) equipment will also create opportunities for the aggregation and exploitation of data from a large number of buildings, component types in a wide range of applications and environments.
The purpose of this Information Paper is to provide a simple overview on the basis of condition-based maintenance in the built environment, with a specific focus on mechanical and electrical (M&E) equipment, reviewing its current state-of-the-art practice, possible knowledge transfer from other industry, as well as potential future developments.
- 1 Background
- 2 Asset Management
- 3 Asset Performance Degradation
- 4 Existing standards for condition-based maintenance
- 5 Current practice for condition-based maintenance, gap analysis and future development
The development of Information and Communications Technology (ICT) was very rapid in the recent years. The technology itself has become very mature, and the cost for the production of the associated hardware (for example sensors, wireless connection devices, computer) has gone down significantly as a result of the maturity as well as mass production.
Since sensors are available at an economical rate, and the technology for different wireless connections (e.g. Wi-Fi, Zigbee, Bluetooth, etc.) is very mature and readily available, vast amount of data can be generated and collected at ease through these interactive components. With the appropriate analysis and exploitation of these data, there is huge potential to make use of these data in different applications.
One of the possible applications is asset management in the built environment. Appropriate sensors can be deployed on various assets (e.g. pumps, air handling units, chillers, boilers, etc.) and monitor their health and performance throughout their service life. The data gathered can provide information when the asset starts to malfunction, and provide alert when maintenance is required. This could improve the efficiency & effectiveness of asset management procedures, facilitating the move from planned, preventative maintenance (PPM) to condition-based maintenance (CBM) and create a wider performance database to inform component and structural design.
The research underpinning this Information Paper was funded by the BRE Trust and the Technology Strategy Board (now Innovate UK) to identify opportunities and priorities for ICT-enabled solutions that can improve asset and building information management across a range of settings in the built environment. It assessed solutions arising from recent developments in ICT with data capture and mapped these against data processing needs in the built environment.
Traditionally assets in the built environment are being looked after using the planned preventive maintenance (PPM) approach. Maintenance is done at regular intervals which are usually shorter than the expected time between failures, and irrespective of what actual status or condition the asset is in. The advantage of this method is that most maintenance can be planned well in advance and that catastrophic failure is greatly reduced. However, a small number of unforeseen failures can still occur, and there is a possibility that too much maintenance is carried out. It is possible that an excessive number of replacement components are being consumed unnecessarily. PPM is best applied to assets which the time to failure can be reasonably accurately predicted.
Condition-based maintenance (CBM), on the other hand, works on a different principle. The asset is being regularly monitored and any malfunction and potential breakdown is being identified and predicted by the health and performance data gathered. Maintenance is carried out when it is required, and it is possible that the monitoring data can indicate the type and severity of the defect detected. With more advanced system, it is possible to predict the remaining life of the asset based on its current health or performance status.
The advantage of CBM over PPM is that the on-going maintenance fee could possibly be lower overall, and that the service life of the asset could be extended as it is always kept in a good working condition. The value of the asset can also be improved, as there is a track record of the health of the asset, and it is possible to tell the actual condition of the asset when it is being sold off.
To facilitate condition-based maintenance, it is essential to understand how the performance of various assets degrades over time and the internal and peripheral changes that may occur. This section provides a simple description on these aspects.
3.1 Asset components performance degradation
Either under ideal conditions or in an environment where condition is not optimal, the performance of continuously running assets and their components will deteriorate. This could be due to a number of factors such as normal wear and tear between moving parts, and accidents/human errors (e.g. inappropriate operation of machines). With the components degrading over time, a failure will eventually occur. Simple descriptions of the common failure that could occur in some of the typical components of the assets are provided in the sections below[i][ii]. This Information Paper focuses on assets with moving parts.
Shafts in various assets support the rotating components or transmit torque from one part of the train to the other. There can be a combination of different loads acting on the shaft. The useful life of shafts generally is indefinite, so it should be considered an abnormality should a shaft fail.
Most shaft failures are fatigue fractures. Fatigue is a progressive and localised process that causes permanent structural modifications in the material. Fatigue only occurs when the stress is alternative or fluctuating, and will not occur when it is constant and steady in terms of its direction and magnitude.
Shaft wear is usually observed in the bearings and seals area. Very often shaft wear is a result of another failure, probably of the bearing or seals.
Shaft distortion usually is the result of accidental overload. Since there are only small clearances inside a typical rotating machine, a very small distortions may lead to internal rubbing. High-speed machinery may experience high vibration levels with shaft deformation as small as a few hundredths of a millimetre.
Bearings failure occurs through metal fatigue. With careful selection and correct maintenance, it is achievable to obtain reliable service. There are many different types of errors that can lead to premature failure in bearings. In most cases, the bearing becomes noisy and probably warmer than usual. If they are allowed to continue working, for example for unattended installations, the bearing seizes and the machine stops. Further damage could happen if the driving power of the asset is very strong, and that automatic stopping mechanism is not provided in case of failure.
Failure in bearings could initially be caused by various reasons, for example:
- Lack of lubrication
- Wrong or defective lubrication
- Inadequate or excess lubricate
- Contamination of lubricate
- Inadequate or excessive interference between inner race and shaft
- Errors in axial position.
The bearings will subsequently suffer from chipping, flaking from the active surfaces (becoming noisy), growth in the area and depth of the surface defects (there may be vibration and heating at this stage) and ultimately seizures of the bearing.
The function of gears is to adjust the speed of rotating shafts. The life of gear service is determined by the teeth wear and smoothness of the operation. Severity of service is directly related to the factors that reduce gear life, for example the conditions of lubrication, unexpected transients, and environmental factors such as temperature, corrosion and abrasives.
Contact load is the main load acting on a gear tooth. This load generates a certain stress distribution and the largest one is the contact stress at the contact point between two teeth and the flexion stress at the tooth root. Most gear failures begin in one of these two regions.
The ultimate failure for gears is tooth wear. The points of contact suffer plastic deformation. The relative movement causes deformation in the direction of the movement, resulting in cracks and material removal. The heat generated from the process may result in fast oxidation on the exposed active metal surface.
Most gear failures are related to operation or maintenance factors, like assembly, installation, lubrication, and overload.
Gear surface fatigue can also happen, and is similar to other surface fatigue on other components. Light pitting at the pitch may be a sign of the natural accommodation to surface irregularities. The other possibility is the appearance of surface fatigue on the dedundum of the driver gear. This situation often indicates that the gears are overloaded. The third possible situation is surface scaling due to the load concentration, caused by gear misalignment. This can be easily identified by the uneven distribution of the damage on the tooth surface.
Plastic deformation of gear teeth occurs when the contact stresses combine with the sliding stresses and overcome the yield strength of the material.
Brittle fracture of gear tooth from a local overload provided by a foreign body, which causes huge stress concentration and may originate a fracture. This local overload could also originate from shaft misalignment.
3.1.4 Belt drives
Belt transmissions are simple devices used to transmit torque and movement between rotating shafts. These occur through the friction or engagement between a belt and a sheave.
It is important that the correct belt is chosen for the operation. Apart from this, sheave diameter and operating temperature are also important factors affecting the operation life. Sheave diameter is directly related to the flexion stress on the belt. A sheave having a diameter that is smaller than required results in higher bending stresses, thus reducing belt life. Higher operating temperature causes oxidation and softening of the rubber on the belt. The top five causes of elevated temperature in “V” belts are, in order of their importance:
- Slippage (due to inadequate belt tension);
- High ambient operating temperatures;
- High operating loads;
- Misalignment (causing friction on the pulley flanges);
- Belt bending stresses (due to the use of small sheaves).
Couplings are used to connect rotating shafts. The main purposes include the following:
- Torque and rotation transmission within the prescribed design limits;
- Vibration dampening;
- Allowing for some shaft misalignment
- Influence the resonance frequencies of the machines connected.
Fatigue failure of the flexible element is common. When a shaft rotates, elastic deformation forms to absorb any misalignment. Should the cyclic stresses be high enough, fatigue failure may result. Large oscillations in the transmitted torque may also result in fatigue failure.
A fault in the coupling could also result in a heavily unbalanced coupling that causes high machine vibration.
3.2 Parameters to monitor for condition-based maintenance
Based on the above review, it is known that when the performance of an asset with moving components starts to degrade, various symptoms will surface based on the faults it is developing. These symptoms can be effectively monitored by appropriate methods and technologies. The table below summarises the symptoms of some of the common faults that could be found from assets with moving components, and the appropriate condition-based monitoring methods that can be deployed. The table is based on the study carried out by BRE, as well as from the Application Guide published by BSRIA[iii].
|Asset||Measurements||Methods||Possible component faults causing the symptom|
|Pumps||Vibration||3-axis vibration monitoring||Bearing degradation|
|Problem with lubrication|
|Misalignment and imbalance|
Surface-mount temperature sensor
Infra-red temperature sensor / thermography
|Problem with lubrication|
|Noise||Noise signature / Frequency analysis||Bearing degradation|
|Problem with lubrication|
|Oil||Composition analysis, particles count||Bearing degradation|
|Problem with lubrication|
|Shafts||Vibration||3-axis vibration monitoring||Misalignment and imbalance|
|Noise||Noise signature / Frequency analysis||Misalignment and imbalance|
|Belt drives||Vibration||3-axis vibration monitoring||Misalignment and imbalance|
|Temperature||Infra-red temperature sensor / thermography||Misalignment and imbalance|
|Slippage of belt|
|Compressors||Vibration||3-axis vibration monitoring||Misalignment and imbalance|
|Oil||Composition analysis, particles count||Bearing degradation|
|Problem with lubrication|
|Motors||Noise||Noise signature / Frequency analysis||Bearing degradation|
|Vibration||3-axis vibration monitoring||Bearing degradation|
Surface-mount temperature sensor
Infra-red temperature sensor / thermography
|Power||Current, voltage||Harmonic voltage|
There are existing international standards, either directly or indirectly, relate to condition-based maintenance and the aggregation of data from condition-based maintenance. This section provides a brief summary of the existing relevant standards, but it is by no means exhaustive, especially the relevant knowledge and technology are rapidly expanding.
BACnet is “a data communication protocol for building automation and control networks.” A data communication protocol is a set of rules governing the exchange of data over a computer network. The rules take the form of a written specification (in BACnet’s case they are also on compact disk) that spells out what is required to conform to the protocol.
What makes BACnet special is that the rules relate specifically to the needs of building automation and control equipment, i.e., they cover things like how to ask for the value of a temperature, define a fan operating schedule, or send a pump status alarm[i].
The BACnet protocol provides mechanisms for computerized building automation devices to exchange information, regardless of the particular building service they perform. BACnet became ASHRAE/ANSI Standard 135 in 1995, and ISO 16484-5 in 2003.
International Electrotechnical Commission (IEC) standards
IEC 60706: Maintainability of equipment
This standard has six parts and is intended to make recommendations for maintainability practices, and to simulate ideas in the maintainability field. Organisations acquiring items will find the standard useful in assisting them in defining maintainability requirements and associated programmes. Item suppliers will benefit from use of the standard, gaining an understanding of the requirements for achieving and verifying maintainability objectives.
IEC 60812: Analysis techniques for system reliability – Procedure for failure mode and effects analysis (FMEA)
This standard describes Failure Mode and Effects Analysis (FEMA) and Failure Mode, Effects and Criticality Analysis (FMECA), and gives guidance as to how they may be applied to achieve various objectives by:
- providing the procedural steps necessary to perform analysis,
- identifying appropriate terms,
- defining basic principles,
- providing examples of the necessary worksheets or other tabular forms.
IEC 61025: Fault tree analysis (FTA)
Fault tree analysis (FTA) is concerned with the identification and analysis of conditions and factors that cause or may potentially cause or contribute to the occurrence of a defined top event. With FTA this event is usually seizure or degradation of system performance, safety or other important operational attributes.
This standard addresses two approaches to FTA. One is a qualitative approach, where the probability of events and their contributing factors, – input events – or their frequency of occurrence is not addressed. This approach is a detailed analysis of events/faults and is known as a qualitative or traditional FTA. The second approach, adopted by many industries, is largely quantitative, where a detailed FTA models an entire product, process or system, and the vast majority of the basic events, whether faults or events, has a probability of occurrence determined by analysis or test.
IEC 61164: Reliability growth – statistical test and estimation methods
This standard gives models and numerical methods for reliability growth assessments based on failure data, which were generated in a reliability improvement programme. These procedures deal with growth, estimation, confidence intervals for product reliability and goodness-of-fit tests.
International Organization for Standardization (ISO) standards
ISO 10816: Mechanical vibration – Evaluation of machine vibration by measurements on non-rotating parts
This set of Standards contains seven parts, which establishes the general conditions and procedures for measurement and evaluation of vibrations from the non-rotating parts of machines.
The Standards provide guidance for machines operating in the 10 to 200 Hz (600 to 12,000 RPM) frequency range. Examples of these types of machines are small, direct-coupled, electric motors and pumps, production motors, medium motors, generators, steam and gas turbines, turbo-compressors, turbo-pumps and fans. Some of these machines can be coupled rigidly or flexibly, or connected through gears. The axis of the rotating shaft may be horizontal, vertical or inclined at any angle.
Figure 1 below shows the vibration severity chart as produced by ISO 10816.
ISO 13374: Condition monitoring and diagnostics of machines – Data processing, communication and presentation
The intent of ISO 13374 is to provide the basic requirements for open software specifications which will allow machine condition monitoring data and information to be processed, communicated and displayed by various software packages without platform-specific or hardware-specific protocols.
ISO 13379: Condition monitoring and diagnostics of machines — Data interpretation and diagnostics techniques
This Standard contains general procedures that can be used to determine the condition of a machine relative to a set of baseline parameters. Changes from the baseline values and comparison to alarm criteria are used to indicate anomalous behaviour and to generate alarms: this is usually designated as condition monitoring. Additionally, procedures that identify the cause(s) of the anomalous behaviour are given in order to assist in the determination of the proper corrective action: this is usually designated as diagnostics.
ISO 13381: Condition monitoring and diagnostics of machines – Prognostics
This International Standard provides guidance for the development of prognosis processes. It is intended
- to allow the users and manufacturers of condition monitoring and diagnostics systems to share common concepts in the fields of machinery fault prognosis,
- to enable users to determine the necessary data, characteristics and behaviour necessary for accurate prognosis,
- to outline an appropriate approach to prognosis development, and
- to introduce prognoses concepts in order to facilitate the development of future systems and training.
ISO 17359: Condition monitoring and diagnostics of machines – General guidelines
This International Standard provides guidelines for condition monitoring and diagnostics of machines using parameters such as vibration, temperature, flow rates, contamination, power, and speed typically associated with performance, condition, and quality criteria. The evaluation of machine function and condition may be based on performance, condition or product quality.
It is the parent document of a group of standards which cover the field of condition monitoring and diagnostics. It sets out general procedures to be considered when setting up a condition monitoring programme for all machines, and includes references to other International Standards and other documents required or useful in this process.
This International Standard presents an overview of a generic procedure recommended to be used when implementing a condition monitoring programme, and provides further detail on the key steps to be followed. It introduces the concept of directing condition monitoring activities towards root cause failure modes and describes the generic approach to setting alarm criteria, carrying out diagnosis and prognosis, and improving the confidence in diagnosis and prognosis, which are developed further in other International Standards.
ISO 18436: Condition monitoring and diagnostics of machines — Requirements for qualification and assessment of personnel
This Standard contains nine parts. Part 1 of the Standard defines the requirements for persons and organizations operating assessment systems in the non-intrusive machine condition monitoring and diagnostic technologies that use the technology parts of ISO 18436. General requirements for assessment body personnel are contained in this part of ISO 18436.
Specific requirements for the assessment of personnel in condition monitoring and diagnostics are contained in ISO 18436-2 and ISO 18436-4 to ISO 18436-9.
5.1 Condition-based maintenance in the aviation industry
Health Usage and Monitoring System (HUMS) approach was first introduced into the aviation industry, with the purpose of automatically monitor the health of mechanical components in a helicopter, as well as usage of the airframe and its dynamic components. HUMS enable aircraft to record transmission usage, transmission vibrations, rotor track and balance information, and engine power assurance data. HUMS do not only monitor the health of rotating components such as gearboxes, bearings, shafts, engines and rotors through vibration, they can also record parametric data from the aircraft’s bus for usage and event analysis.
All HUMS systems consist of a basic vibration health monitoring system, focusing on external vibration readings only, along with rotor track and balance capabilities. A more complete HUMS will additionally connect the VHM to the engine data collection units for a more comprehensive look at the aircraft’s and engine’s internal health. Some even more advanced systems will include airframe flight data recorders and cockpit voice recorder[i].
HUMS deploy both proactive and reactive methods to anticipate failure:
- Proactive methods include usage spectrum analysis, allowing remaining component safe life to be estimated based on the actual stress a component has been under for the duration of its service.
- The reactive approach is based on detecting propagating component failure at an early stage, before seizure occurs. This method relies on a sensor network covering key components like engines and transmission systems. For the current generation of HUMS, this sensor network is mainly limited to vibration sensors and angular shaft speed sensors.
The basic components in all HUMS systems are largely similar, which are made up of a combination of accelerometers, velocimeters, magnetic pickups, photocells, some type of acquisition unit, and a ground station for analysis. The differences could be in the location, quantity and types of sensors, and the complexity of the system required.
5.2 Condition-based maintenance in the construction industry and the gaps
Comparing with the aviation industry, the construction sector has far less uptake on condition-based maintenance. There are products to facilitate facilities managers or building managers to carry out condition-based maintenance, with a focus on the overall building performance, e.g. energy use, comfort level, carbon emissions. However, planned-preventive maintenance is currently still the mainstream, and even if condition-based maintenance is carried out, there is little focus on the performance and life prediction of individual assets in a building’s plant room.
The possible reasons for the lack of uptake on condition-based maintenance in the construction industry are that there is limited demand for it in the market, and there is a lack of relevant information to support this approach.
Inevitably there is an upfront cost at the start for condition-based maintenance, for example the installation of the appropriate monitoring. The cost may appear to be large at the beginning which can be deterrent for facility management to adopt condition-based maintenance. However, it should be realised that in the long run, it is possible that cost saving can be made.
One key piece of information that is missing or not well-established for condition-based maintenance is the expected life remaining of an asset or its components when a fault is detected. To establish this information, there is a need to collect performance data from running equipment over a long period of time, preferably from an asset when it is brand new until its end of life. However, this will take a lot of time if only a small number of assets are being monitored by a limited number of organisations.
It must be noted that, if CBM is widely adopted, the potential benefit provided would be huge. Take the example of a hospital; if all its M&E equipment is monitored by vibration and temperatures sensors continuously, the amount of performance data generated will be enormous. The information derived from these data will be extremely useful on various aspects, including:
- Prevention of premature failure;
- Characteristics and time element of performance degradation;
- True whole life costing based on actual monitored data;
- Comparison of the effect of usage pattern on the life of equipment;
- Compare the performance of equipment from different makes and models.
5.3 Future development of condition-based maintenance in the construction industry
Despite the fact that condition-based maintenance is not currently the mainstream practice in the construction industry, it is anticipated that its benefits will soon be better realised and there will be a lot more uptake. The reason for this is that the price for the equipment required, e.g. sensors, wireless communication hardware, computer, will go down in the future, making the upfront capital cost less and much more attractive. The ICT-enabled data capture solution will also become more mature and affordable, enabling the approach to be more reliable and trustworthy.
The data and information to support condition-based maintenance is crucial to the value of such approach, as explained in the above section.
Client can also create a demand or a pull, driving the supplier to respond to this demand and generate a momentum in the market and create competition for better service.
With the advancement on ICT-enabled data capture technologies, it is obvious that there are opportunities to significantly improve our understanding of the condition of built environment, as well as to improve the efficiency & effectiveness of asset management procedures. The benefits of condition-based maintenance should be better realised and the approach should be rolled out more widely into the construction industry in the future.
- Hattangadi, A.A. (2004). Failure Prevention of Plant and Machinery. Tata McGraw-Hill. ISBN 0-07-048309-4
- Sachs, N.W. (2007) Practical Plant Failure Analysis – A Guide to Understanding Machinery Deterioration and Improving Equipment Reliability. CRC Press, Taylor & Francis Group. ISBN 0-8493-3376-8
- BSRIA (2001) Application Guide AG 5/2001. Condition based maintenance – An evaluation guide for building services. Author: A Seaman. ISBN: 0-86022-575-5
- BACnet: Answers to Frequently Asked Questions. URL: http://www.bacnet.org/FAQ/HPAC-3-97.html. Last accessed: 31 July 2013.
- International Helicopter Safety Team. Health and Usage Monitoring Systems Toolkit (2013).