Feb 24, 2005

Life Cycle Cost Analysis for Pumping Systems

When used as a comparison tool between possible design or overhaul alternatives, Life Cycle Cost (LCC) analysis reveals the most cost effective solution.

Just a small part of a high usage pump’s total life cycle cost (LCC) is its initial purchase price.

What’s the largest?

Ever-voracious energy, consuming budgets like there’s no tomorrow.

Pumping systems, according to the U.S. Department of Energy (DOE) account for nearly 20% of the world’s electrical energy demand.

But there are ways to minimize energy consumption while meeting the needs specific applications. Even though operating requirements sometimes take precedence over energy cost considerations, long-term balance between the optimal and the practical is possible through careful LCC analysis.

LCC analysis is a valuable tool that can help management maximize energy efficiency while minimizing waste for many types of equipment, including pumping systems.

Following are highlights from Pump Life Cycle Costs: A Guide to LCC Analysis for Pumping Systems, developed by the Hydraulic Institute and Europump to assist plant owners, management and operators in employing the LCC methodology to pumping systems.

LCC defined

The LCC of any piece of machinery is the total cost to purchase, install, operate, maintain and dispose of that equipment over its entire lifetime. To determine that total cost, management must follow a specific method of identifying and quantifying each part of the LCC equation.

Managers use the LCC process as a comparison tool weighing all possible design or overhaul alternatives. The process helps them arrive at the most cost effective solution based on the available data.

LCC analysis typically includes initial costs, installation and commissioning costs, energy costs, operation costs, maintenance and repair costs, downtime costs, environmental costs, and decommissioning/disposal costs.

Proper design is essential

The single most important factor in minimizing a pumping system’s LCC is proper pumping system design. Each element of the system — the pump, the driver, pipe installation and operating controls — is considered individually. Proper design takes into account the interaction between the pump and the rest of the system, as well as the calculation of the operating duty point(s).

The duty point of the pump is determined by the intersection of the system curve and the pump curve as shown below.

Both procurement costs and operational costs make up the total cost of an installation during its lifetime. Several installation and operational costs are directly related to the piping diameter, as well as the components within the system.

A significant amount pressure loss within the system is caused by valves — especially control valves in throttle-regulated installations. In systems with several pumps, the workload is divided among them. Together, and in conjunction with the piping system, the pumps deliver the required flow.

Pipe diameter is selected based on the following considerations:

  • Economy of the whole installation (pumps and system);
  • Required lowest flow velocity for the application (e.g., avoid sedimentation);
  • Required minimum internal diameter for the application (e.g., solids handling);
  • Maximum flow velocity to minimize erosion in piping and fittings; and
  • Plant standard pipe diameters.

Decreasing the pipeline diameter results in:

  • A decrease in piping and component procurement and installation costs;
  • An increase in pump installation procurement costs due to increased flow losses, which in turn calls for higher head pumps and larger motors;
  • An increase in procurement costs for electrical supply systems; and
  • An increase in operating costs, as a result of higher energy usage due to increased friction losses.

Some costs increase with increasing pipeline size and some decrease. An optimum pipeline size may be found, based on minimizing costs over the life of the system.

A pump application may need to cover several duty points. The largest flow and/or head will determine the rated duty for the pump. To properly select the number of pumps in the installation — and to select output control — the pump specifier must consider the duration of operation at the individual duty points.

Many software packages are available to help specifiers determine friction losses, generate system curves, and handle pump selection or piping system design. In addition, most pump manufacturers can recommend software suitable for the intended application.

Different programs may use different methods of predicting friction losses and may give slightly different results. Very often such software also is linked to pump-selection software from that particular manufacturer.

Analyzing existing pumping systems

An excellent tool for evaluating existing systems is the U.S. DOE Pump System Assessment Tool. Information is available from www.pumps.org.

The following are general guidelines to improve an existing pumping system:

  • Assemble a complete document inventory of the items in the pumping system;
  • Determine the flow rates required for each load in the system;
  • Balance the system to meet the required flow rates of each load;
  • Minimize system losses needed to balance flow rates;
  • Affect changes to the pump to minimize excessive pump head in the balanced system; and
  • Identify pumps that have high maintenance costs.

Two methods can be used to analyze existing pumping systems: 1) Observing the operation of the actual piping system — pressures, differential pressures and flow rates, and 2) Performing detailed calculations using fluid analysis techniques. After creating an accurate mathematical model of the piping system, the system analyst calculates the pressures and flow rates within the model.

Observing the operating system allows one to view how the actual system is working, but system operational requirements limit the amount of experimentation that plant management will allow. By developing a model of the piping system, one can easily consider system alternatives. However, the model must first be validated to ensure it accurately reflects the operating piping system.

With either method, the objective is to gain a clear indication of how the various parts operate and to discern where improvements can be made to optimize system performance.

In the analysis, keep in mind the following factors to reduce a pumping system’s LCC and maximize overall benefits:

  • Consider all relevant costs to determine the LCC.
  • Procure pumps/systems using LCC considerations.
  • Match the equipment type to its intended duty within the system. This includes the pump (don’t oversize it), driver and power tranmission.
  • Optimize total cost by considering operational costs along with procurement costs.
  • Consider the duration of the individual pump duty points.
  • Specify motors that are high efficiency.
  • Evaluate system effectiveness.
  • Monitor and sustain the pump and system.
  • Consider the energy wasted using control valves.
  • Utilize auxiliary services wisely.
  • Optimize preventative maintenance.
  • Maintain internal pump clearances.
  • Follow available guidelines for rewinding motors.
  • Analyze existing pump systems for possible improvement opportunities.

An important part of a plant’s overall asset management, thorough LCC analysis ensures you get what you pay for… and then some!

About the author

Technical information for this article was provided by the Hydraulic Institute, excerpted from Pump Life Cycle Costs: A Guide to LCC Analysis for Pumping Systems.