Total Cost of Ownership of Pumps
“Total Cost of Ownership” (or TCO) refers to the lifetime cost of owning and operating a piece of equipment such as an industrial pump set. TCO includes a number of factors, including:
- Initial investment, including the purchase price, the cost of preparing the installation site, setting up power supplies and coupling the pump(s) to the piping system.
- Availability-related costs: The cost of operating and maintaining the pump and motor, including clearing blocked or clogged pumps, replacing worn or broken parts such as wear-rings, seals and bearings or eroded impellers. Maintenance costs can also cover major overhauls undertaken to extend the useful life of long-service machines.
- Energy costs: the cost of energy consumed by the pump set.
As shown in Figure 1, the cumulative cost of installation, maintenance and operations will typically be significantly larger than the initial purchase price. This immediately suggests that it can make sense to pay a bit more at the outset to obtain a piece of equipment that will result in useful reductions in other areas.
Cost Savings Opportunities
1. Right-Sizing Equipment
Each pump/impeller combination have a “best efficiency point” (BEP) – the combination of developed head and flow volume at which the pump will operate most efficiently. Moreover, operating pumps at or near their BEP avoids cavitation or vibration problems that can cause impeller erosion or accelerated wear to bearings and seals. Clearly then, selecting a pump set with a BEP close to the system’s required duty point can help reduce long run operating and maintenance costs. Many of KSB’s industrial pump models are available in a wide range of closely-spaced sizes. This makes it possible to find a pump with head and capacity characteristics close to the required duty point of the application. For pumps that will mainly operate at constant head and capacity levels, impeller trimming – the process of slightly reducing the diameter of an impeller so that the head and volume are decreased – is a good way to fine-tune a pump’s operating characteristics to more closely match the system requirements.
Of course there are many applications where head and capacity requirements will vary drastically over the operating cycle or over the lifetime of the pump. In the past, it has been common for designers to specify pumps with ‘extra’ capacity, then to reduce flows to the desired level through limiter valves and/or bypass circuits. This approach, unfortunately, results in wasted energy and excessive operating costs. A far better way of dealing with time-varying performance requirements is to add a variable frequency drive (VFD) to the control system. Adjusting output by modifying the pump’s rotational speed can result in significant energy savings. For pumps that will operate on a continuous basis, the extra up-front cost of the VFD will be offset very quickly by reduced energy costs. (VFDs are also referred to as variable speed drives or frequency inverters.)
2. Reducing Maintenance Requirements
A good preventative maintenance program is the key to extending pump life and avoiding forced outages (which always seem to occur at the most inconvenient times!). Maintenance can involve the replacement of components such as wear rings and seals. Many KSB pumps are designed to simplify these tasks through mechanical designs that make critical components easily accessible. This saves time, and as we know, time is money!
Pumps used in wastewater treatment facilities can present a special case for maintenance requirements. These pumps can become clogged with solid waste, especially fibrous materials. This results in a messy and unpleasant maintenance operation. A variety of special impellers are available that can help reduce the incidence of pump clogging. These include vortex impellers (which provide extra free passage clearance), impellers with built in cutters to help break up solid materials and impellers with specially shaped leading edges designed to avoid catching fibrous materials. (See Figure 2) These special-purpose impellers are typically less efficient than conventional multi-vane closed impeller designs. However, for pumps in critical wastewater applications, reducing the number of times pumps have to be lifted to the surface to clear blockages may reduce labour costs enough to offset the reduction in energy efficiency.
3. Optimizing Energy Efficiency
With the possible exception of the case of wastewater pumps described above, it is almost always cost-effective to optimize the energy efficiency of the pump set. Methods of improving the hydraulic efficiency of pumps (including matching each pump’s BEP to the required duty point and employing VFDs to adjust outputs for variable requirements) have been described earlier.
A further option to improve energy efficiency is to make use of high-efficiency electric motors. These motors are designated as NEMA Premium (US) or IE3 (European). While sometimes more costly than older motor designs, these motors can easily pay for themselves over the lifetime of the pump by saving energy costs.
A piece of good news for plant operators seeking to reduce their energy bills is the introduction of a new generation of ultra-high-efficiency motors for small to mid-size pumps. KSB’s new SuPremeE® motor is a prime example. Based on the synchronous reluctance operating principle, this design provides very high efficiency when operated at full load. More important though, unlike traditional asynchronous electric motors, which show a marked reduction in energy efficiency when operated at partial loads, the new designs deliver high levels of energy efficiency across a wide range of torque outputs. This characteristic is extremely useful for the many small to mid-size pumps that may be required to operate under highly variable system conditions.
4.Taking a Systems Approach
To truly minimize the TCO of pump equipment, it is often valuable to look beyond the machines and consider the full environment in which they will operate. KSB can provide “System Efficiency Services” (SES) – a comprehensive program that examines pump performance within the machine’s operating environment. SES makes use of sophisticated measurement and data logging equipment to determine the actual load profile of the pump and to compare this to design conditions. Potential savings can thus be identified (energy efficiency analysis) and the causes of any damage detected (damage analysis). In-situ measurements with instruments connected to a data logger create an operating record of process and vibration variables that help determine the operating characteristics of the pump. (See Figure 3) Using mobile performance measurements in the control cabinet, the effective power of the pump can be determined regardless of where it is located.
5.Taking Advantage of Government Incentives
For businesses operating in Ontario, the Ontario Power Authority offers a variety of incentives to encourage plant operators to reduce energy consumption by upgrading their equipment. Click to find more information on impeller trimming and variable frequency drives.