By Keith Sanders
In the first article in our series on successful pump project management, Keith Sanders looked at the upcoming opportunities for the industry, manufacturing in Australia in the past and present, what you need to know about sourcing equipment from overseas, and the roadmap for energy efficiency regulation in the EU. Here, he continues the discussion, taking a deep dive into the first of three pillars that will help upcoming projects not only be successful, but also help to contribute to better outcomes for other important objectives such as climate change, water resources and energy conservations.
Pillar 1: System design and equipment selection
What do we mean by efficient pumping systems? What most pump users are looking for is “functionality” through the operating life of the plant. The whole system needs to be “fit for purpose”, to get the job done at reasonable cost and with minimum interruption to normal services.
This is generally assessed by evaluating three important factors.
a. Optimise power consumption
b. Maximise reliability
c. Minimise downtime
Pumping systems come in all shapes and sizes, but the one thing they all have in common is that the user has a particular purpose in mind and seeks to achieve the operational outcome as effectively as possible at reasonable cost. This requires a detailed knowledge of the conditions of service that the pumping equipment must tolerate and the system parameters that exist within the plant.
• Project flow rates – Constant, variable, intermittent? Demand profile over time?
• Drive speed – Fixed or variable?
• Circuit type – Open loop, closed loop?
• Fluid properties – SG, viscosity, solids content?
• Operating temperatures, humidity, altitude?
Much of this information can be provided by the end user based on historical data from similar installations. Past experience is often helpful in avoiding some hidden pitfalls or traps in the application. The trick is to find the right people to talk to.
The following information is a summary of the key initiatives outlined in the Ecopump documentation and developed by cooperation between the pump industry and legislators.
Optimising power consumption
There has been much study of pump performance aimed at determining the relative efficiency of similar products. In Europe, the EU has legislated for minimum efficiency criteria for various categories. Commission Regulation (EU) 547/2012 prompted a response from the European Association of Pump Manufacturers (Europump) to classify centrifugal pumps and pumping systems from an efficiency perspective based on the ECOPUMP approach, as outlined in the European Pump Industry- Energy Commitment brochure.
The product approach – The House of Efficiency
Originating from a preparatory study for the Energy Using Products (EuP) Directive (2005/32/EC), the ‘House of Efficiency’ is a pass or fail scheme that takes into account design and application requirements as well as pump minimum efficiency, dependent on flow capacity and other design parameters.
It sets out formulae to calculate energy efficiency of water pumps, based on three flow rates (BEP flow, 75 per cent BEP flow and 110 per cent BEP flow). From this, the concept of Minimum Efficiency Index (MEI) was developed and many products now carry an MEI rating on their nameplate. Special procedures are required for manufacturers to nominate an MEI for a particular product to ensure that the data can be trusted.
For a given set of operating conditions, this allows the most efficient pump product to be selected. This approach gave rise to the development of MEI ratings for pumps, which enables manufacturers to rate their products in the marketplace. Similar legislation is being introduced in the US.
The product approach can also be applied to electric motors used to drive the pump, thereby improving the overall efficiency of the pumping unit. MEPS standards for electric motors have existed in Australia for many years, but these are now being formalised by GEMS legislation introduced in 2019.
The extended products approach
This approach employs a methodology to focus on the different operating points that may exist within an installation. It has a major advantage for installations with a high variability in load e.g. HVAC systems. In this approach, an Energy Efficiency Index (EEI) is calculated which incorporates flow v time profiles and envisages an appropriate control system to match pump output to the needs of the system at any point in time.
The systems approach
This approach involves selection of individual components which in themselves can be efficient, but which are interacting within a system that does not allow the pump to operate in its preferred zone.
By investigating the total system need (demand) and then looking at the actual operating conditions, a comparison of how efficient the actual system might be, can be assessed.
Pumping systems are often oversized for a variety of reasons. This results in a mismatch between anticipated (design) pump performance and the actual performance experienced in service. Once the total system demand is realised, individual components can be investigated to see if they are operating efficiently or can be improved.
The system approach potentially offers the most energy savings within motor driven systems, but also can result in significant improvements in equipment reliability and reduced maintenance. Acceptance of a systems approach requires the user (operator) to be made aware of the potential energy savings within motor driven systems.
If energy audits are conducted after a period in service, this can provide a basis for considering changes to the pump or other system components to achieve optimal power consumption for the operating life of the equipment.
For many pumping applications, reliability is equally as important as efficiency. In fact, some pump design features may sacrifice efficiency for greater reliability, so a compromise has to be considered. For example, pumps required to handle solids in suspension may require special non-clog impeller designs that are lower in efficiency but have a greater solids-handling tolerance. Again, there are some principal issues to consider
a. Product design
b. Production quality control
c. Careful determination of the operating point
If we consider each of these issues, it should be possible to select equipment with optional features that make it fit for purpose, even though the operating conditions may be too severe for pumps in standard execution.
Pump manufacturers around the world often have decades of experience in designing products to suit particular pump applications. Many products are suitable for pumping water at ambient temperatures and the main focus is on hydraulic design to achieve high efficiency.
However, many pump applications are more severe in terms of service conditions, having to deal with different fluids, different temperature ranges, higher pressures etc. The conditions of service are influential in the selection of pump construction and materials used for key components to provide corrosion resistance or erosion resistance etc.
In the ISO system, there are three pump design standards that deal with the severity of operating conditions:
- ISO 9908 – Technical specifications for centrifugal pumps – Class III (Low severity)
- ISO 5199 – Technical specifications for centrifugal pumps – Class II (Medium severity)
- ISO 9905 – Technical specifications for centrifugal pumps – Class I (High severity)
These specifications do not appear to be in regular use in Australia, as many consultants and end users prefer to use their own pump specifications based on experience. API 610 has been regarded as a global standard for the oil and gas sector. More recently, ISO 13709 – Centrifugal pumps for petroleum, petrochemical and natural gas industries was developed to mirror the requirements of API 610 in the
It is recommended that pump users make themselves aware of standards that may be appropriate to their industry, since there is a wealth of knowledge that underpins the development of such standards.
Production quality control
Pumps, like most industrial products, are manufactured in a workshop environment with a mix of materials and labour brought together in a controlled environment, often with specialist machine tools used to complete critical operations.
Production control systems need to be monitored to ensure consistent quality and reliability for the end product, both by in-process control systems and final product testing, prior to dispatch. ISO 9000 is a set of international standards on quality management and quality assurance developed to help companies effectively document the quality system elements needed to maintain an efficient quality system and many suppliers use ISO 9001 to manage their product quality.
It should be recognised that many “standard pumps” are not subjected to an individual performance test and selection is based on a published curve or a computerised selection program. Users should be aware that the hydraulic performance is based on type testing and the information included is subject to tolerances that should be made clear on the data provided.
Most published data is based on ISO 9906 Grade 3 test tolerances and reference should be made to Table 8 in that document. Individual factory testing is recommended for pumps that are used in critical applications or with a high annual usage factor, but this usually involves an extra cost.
Careful determination of the operating point
It is well-known that a pump will operate at the point where the pump curve and system curve intersect. The intersection should ideally occur close to the Best Efficiency Point (BEP) of the pump, under which conditions the pump is operating with minimum losses in vibration, heat and internal leakage. However, it is not unusual for system resistance to be overestimated, with a consequent overspecification of the head requirements of the pump at the design flow rate.
Operating away from BEP can result in adverse conditions for the pump. However, this often results in premature failure of seals, bearings, overheating and can even result in shaft breakage under extreme conditions.
If pumping equipment is unavailable for operation when required, it represents a cost to the pump user that is measured by the loss of service provision or production depending on the purpose of the plant. Once reliability issues have been explored, it is also helpful to consider matters that might influence the speed with which it might be put back into service.
• Access – Ease of access to the product is important. All too often pumping equipment doesn’t have the necessary space for service personnel to both routinely service the plant or conduct speedy repair in the event of a failure of a key component
• Sealing method – Perhaps the most common component failure in a pump would be at the stuffing box. While packed glands are less common these days, as they do require periodic replacement of the packing material, they are simpler to work with by unskilled operators. They can be serviced in situ, assuming adequate access is provided. Mechanical seals may have a longer service life if correctly matched to the application, but replacement is usually a workshop job and pumps will be out of service for the period of that replacement. Cartridge seals are now becoming more common even on standard pumps to speed up the replacement process and minimise the risk of incorrect installation by operators
• Bearing arrangements – Another common item for routine service and maintenance, the bearing arrangement will need periodic attention. Many pumps have “sealed for life” bearings and in this regard the lubrication system needs to be verified as suitable for the conditions of service. Many pump manufacturers can provide re-greasable bearing arrangements or oil lubrication options and these need to be considered for pumps handling fluids at higher temperatures or other more severe conditions
• Scheduled maintenance – If high levels of availability of service are required, it may be necessary to consider standby pump capacity and development of scheduled maintenance programs to avoid an unplanned failure. These may vary from plant to plant and based on operational experience. If routine maintenance is required, then rapid change out strategies may help minimise downtime
• Condition monitoring – Pumping equipment with a high service level may demonstrate changes on their condition over time. By monitoring some key indicators, it is possible to sense any deterioration before any major failure occurs.
Typical areas for consideration are:
» Differential pressure monitoring
» Temperature monitoring
» Noise level monitoring
» Vibration monitoring
If these parameters are measured at the time of original commissioning of the pumping plant, a history of changes can be developed over time, which will assist in scheduled maintenance planning.
There is an old saying, “If you can’t measure it, you can’t manage it”. In general terms, it is usually more cost effective to install appropriate instrumentation within the original equipment package, so that routine readings of operating performance can be taken and recorded. Often, a careful study of these key performance indicators can assist in troubleshooting or premature failure analysis.
Look out for Part 3 of this article in the Winter edition of Pump Industry, looking at the second pillar for successful project management.