Introduction

The US Department of Energy’s (US DOE) Industrial Technologies Program has created a Save Energy Now program with the goal of reducing the country’s energy intensity by 25% in the next 10 years. Part of the program is to encourage companies to increase the energy efficiency of various types of mechanical systems found within industrial plants. To do that they have encouraged the American Society of Mechanical Engineers (ASME) to development a set of standards for conducting energy assessments for the various types of systems. I had the privilege of being involved with the development of the ASME Standard EA-2-2009, Energy Assessment for Pumping Systems. 

This article covers the big picture of why the standard is a good idea, and what is involved in setting up an assessment team within a company.

What’s the Big Deal?

Engineered Software, Inc. (ESI) has been involved with making pumped systems more efficient since the late 1980’s. We were involved with the BC Hydro’s Power Smart program in which industrial customers in the Canadian Province of British Columbia were encouraged by the electrical utility to make their systems more energy efficient. The BC Hydro project was extremely successful with many of their industrial customers taking advantage of the program. 

ESI attempted to work with the US DOE to bring a similar systems approach to evaluating pumped systems in the United States in the late 80’s. It seems we were ahead of our time because the DOE wanted to concentrate primarily on lighting improvements and motor efficiency programs which are easier to explain to industrial users.

Fast forward to 2007: the DOE looked at ways to have industry evaluate the efficiency of their facilities by focusing on compressed air, steam distribution, pumping and process heating systems. The DOE asked the American Society of Mechanical Engineers to develop system assessment standards for the four major industrial system types, and in December 2009 the ASME issued the pumping system assessment standard.

In addition to establishing these four standards, the DOE would like to get individual assessors trained and certified to perform accurate assessments for the various types of industrial process systems. We at Engineered Software are working with the DOE to help develop the body of knowledge needed by pumped system assessors, and then assist in development of the training material needed to train the assessors. 

Our goal at ESI has always been to provide the training needed so each industrial plant can have a well trained assessment team to continually look at the operation of their pumped systems.

Why You Should Implement an Assessment Program

In business when someone suggests embarking on a new initiative, I always ask the questions “What problem will it solve?” followed by “Does the benefit justify the cost?” I always frame my discussions with these two questions in mind.  So here I am suggesting that you implement an Energy Assessments for Pumping Systems program, and I need to provide you with a value position.

First let’s answer “What problem will it solve?” I will address this with a high level response. 

In my discussions with business owners, plant managers, and C-level managers I find that it is common practice that they regularly perform operational audits for a wide variety of their mission critical processes. 

It appears that one exception to this practice deals with performing operational audits on process piping systems within the plant. In process plants we have a tendency to chip away at the corners, instead of attacking the problem head on. For example we perform safety reviews, process improvement reviews, maintenance cost reduction reviews, and more recently, reviews to minimize energy consumption.  What is truly lacking is a comprehensive operational audit for the entire process piping system.

The ASME Energy Assessment for Pumping Systems is a watershed document that provides a comprehensive way of looking at the operation of the total piping system. It provides an outline of the steps that should be performed to conduct an operational audit of a process piping system. In addition it provides a variety of system related items that increase the efficiency of the total pumping system. It is flexible enough to allow the user to implement the standard to meet their company’s specific needs.  This provides operational flexibility, but it does require the user to develop a methodology they can use.

Regarding the second question “Does the benefit justify the cost?” In order to answer this question you must have an easy to use method of arriving at the costs, a straightforward presentation of the cost, along with a method for identifying the greatest costs items, followed by a way to determine realistic cost savings.

Engineered Software has developed a methodology compatible with the ASME Pumping System Assessment standard; it provides rigorous calculation methods, while providing the results in a format that can be used by everyone involved in the pumped system. The key element of our pumped system assessment methodology is to calculate an operating cost for every element found in the pumping system, and then present the information in a balance sheet format listing the pumping costs against all expenses for the system. 

To demonstrate the methodology, Figure 1 shows an example pumping system found in a paper mill. The objective of the system is to pump 4,000 gpm of water to a White Water Storage Tank and 750 gpm to a filtrate tank. There is an overflow line upstream of the White Water Storage Tank in the event of a high level in the White Water Storage Tank. The drawing shows the elevation of the various tanks, along with the levels, pressures and flow rates for a system assessment. The installed plant instrumentation is displayed on the drawing with the exception of the flow rate going to the filtrate tank T-210 and the White Water Storage overflow which are measured using portable flow meters. 

 
Figure 1- A process and instrumentation diagram showing the operation of a White Water system in a paper mill.

Looking at the process variables on Figure 1, you can see what is happening in the system but nothing looks out of the ordinary, with the possible exception of the flow going to the sewer. If one were to calculate the pumping cost for each item in the system and tabulate them in a system energy balance sheet the picture becomes much clearer. Table 1 is an example of the Energy Cost Balance Sheet for this system. 
 

Table 1 - The Energy Cost Balance Sheet shows the cost of each item in the white water system and provides a starting point for making decisions.

Each one of the costs in the Energy Cost Balance Sheet was calculated using a series of spreadsheets that were developed to take the process data from Figure 1 and arrive at a cost based on the performance of the installed equipment.

The first thing you notice on the Energy Cost Balance Sheet is it looks very similar to a financial balance sheet with all the energy input cost on the top and the energy consumptions costs on the bottom. The Table 1 shows an energy input cost for the pump based on the pump’s operating data (flow and pressures), and an energy input cost for the motor based on its operating data (current and voltage). The cost to run the electric motor and the cost to operate the pump are almost identical, which should be expected because the motor is driving the pump.  Since the motor and pump cost calculations were arrived by two different methods this shows the results for pumping cost have been cross-validated.

Now look at the Energy Consumption Cost of the energy balance sheet. Notice there is a cost for each of the three paths being fed by the system: Filtrate tank, sewer, and White Water Storage Tank. Let’s look at the information presented in the Energy Consumption Costs side of the equation and discuss the operating costs for each path. 

Filtrate Tank Path

Looking at the Filtrate Tank path there are two major items that result in head loss of the pumped fluid:  the differential pressure across the Level Control Valve LCV-210 and the differential pressure across the restriction orifice RO-231. The function of the level control valve LCV-210 is to maintain the level in the filtrate tank T-210. The cost of the energy dissipated by the level control valve is $18,661. The restriction orifice RO-231 was installed by the plant maintenance department to eliminate the cavitation occurring downstream of LCV-210 which was caused by the high differential pressure across the control valve. The cost for the energy dissipated in the restriction orifice is $5,837. Since the two loss components are required to supply fluid to the filtrate tank the total cost to supply 750 gpm to the filtrate tank is $24,498. The cost of the “minor” head loss for the pipe lines, valves, and fittings will be accounted for later.  

The Sewer Path

The purpose of the sewer path is to keep the White Water storage tank T-220 from overflowing. The sewer path was not a part of the original design of the system, but was added after an upset condition caused the elevated tank to over flow, resulting in shorting out several motors located below the tank. The maintenance costs to replace the motors and the associated down time and lost production justified the cost of adding the sewer path to prevent a repeat occurrence of the incident.

Looking at the Energy Cost Balance Sheet, the operating cost for the sewer path consists of the $14,822 for the LCV-220 and $11,674 for the restriction orifice, RO-232. Once again the restriction orifice was installed downstream of LCV-220 to eliminate cavitation in the control valve.

WW Storage Tank Path

The purpose of the White Water Storage tank is to provide 4,000 gpm of make up to various load in the plant using gravity feed. The white water storage tank is located 102 ft above the white water sump to provide sufficient gravity head to the various loads in the plant. This elevation difference results in static head for the system, which is energy that has to be added at the pump. The static head accounts for $78,209 of the total energy costs. In addition there is the cost for the pressure drop across the Level Control Valve LCV-200 ($50,836) along with the pressure drop associated with the non-recoverable pressure drop across the flow element FE-200 ($1,687). As a result the total cost to feed the White Water Storage Tank is $130,732. 

To complete the energy audit a total of $9,858 is attributed to the losses associated with the pipelines, valves and fittings throughout the system. In this example the head losses in each pipeline were calculated, and this information was used to calculate the cost for the flow rate through all the pipelines. Notice when adding all the losses for the three paths and the pipeline head loss the total energy consumption is $191,584 which is close enough to the energy input costs calculated with the pump and motor data. This further cross-validates the energy calculations.

Reviewing the System to Identify Energy Savings

Now that we know how much this system costs to operate, let’s used the Energy Cost Balance Sheet to see what can be done to minimize costs. The first thing we can say is that everyone involved in the decision making process now knows the associated costs of each flow path. Now we can look at the various flow paths to see what can be done to minimize energy consumption and costs.  We will start by looking at the highest cost item: the White Water Storage Tank.

WW Storage Tank Path

Looking at the system, the 4,000 gpm going to the White Water Storage tank is the largest single cost item. The greatest cost associated with this portion of the system is the energy needed to overcome the static head. In looking at this existing system there is little we can do to minimize this cost because the White Water Storage tank is already in place and it is doubtful that relocating the tank to a lower elevation would be cost effective. 

The next largest cost in the White Water Storage Tank path is the $50,836 cost associated with the differential pressure across the control valve LCV-200. In performing the calculations to determine the cost for the control valve a differential pressure of 28.6 psid occurs across the control valve. Reducing the differential pressure to approximately 10 psid will result in a 65% reduction of the head loss and associated energy cost of the control valve.

The flow meter FE-220 is a differential pressure type meter in which a differential pressure is measured across the meter. This type of meter is widely used because of its simple design, but they do have a non-recoverable pressure drop associated with them. For example, in this application the non-recoverable pressure drop across the orifice plate cost $1,687 per year in operating cost. Replacing the differential pressure meter with a linear flow meter with a much lower pressure drop could result in a large cost savings when looking at the life time cost of the flow element.

Sewer Valve Path

Currently the sewer valve has a continual 750 gpm flow rate. The reason for the continual dumping of fluid through the sewer valve is an indication that the system is not balanced properly. Without knowing the true cost for having an unbalanced system, no one considered it a high priority item. Now that we know that the pumping cost of operating the sewer valve is approximately $26,500 per year it may increase the visibility of the problem and prompt action to remedy the unbalanced system.

Filtrate Tank Path

The filtrate tank path provided make up water to the filtrate tank, with the filtrate tank level control valve LCV-210 modulated to maintain a constant level in the tank. In looking at Figure 1 the pressure at pressure gage PG-220 is 76 psig. Both the white water sump and the filtrate tank are located at the same elevation and both tanks are open to atmospheric pressure. As a result, the entire 76 psig of pressure in the main header where the water to the filtrate tank branches off must be dropped across the control valve and restricting orifice. This level control is needed to control the process.

Another option that could be considered is to eliminate feeding the filtrate tank from the main white water header, and adding a new smaller sized pump from the White Water Sump T-200 to feed the filtrate tank T-210 directly. A pump and control valve would need to be sized to control the flow of white water into Filtrate Tank T-210. 

The pump needs to be sized for 750 gpm and need to overcome the:

• Static head caused by the level difference levels between the White Water Sump T-200 and the Filtrate Tank T-210
• Head loss in the new piping to supply white water to the filtrate tank
• Head loss across the Filtrate Tank LCV needed for proper control (approximately 5 – 10 psid).

One final point prior to making any changes to the system, we must evaluate how the original pump is being operated in the modified system. It is always important to ensure the pump is still operating close to its best efficiency point to minimize the pump’s operating and maintenance cost.

Evaluate Options for the Overall System

With a clear understanding of where the fluid energy is being used in the system, options can be developed to reduce the energy consumption of the system. In addition to balancing the system to reduce unnecessary flow through the pump, the impeller of the White Water Pump (P-201) can be trimmed or the pump placed on a variable speed drive to reduce the amount of head the pump develops, and therefore the amount of energy the pump adds to the fluid and the cost of the energy to the pump.

The costs involved with implementing each option can also be estimated and a life cycle cost, simple payback, or return on investment can be calculated to economically justify each option. If several options are being considered, the most economical option can be selected.

Conclusion

Organizing an assessment team and performing an energy assessment of a pumping system requires the skills and knowledge of a wide variety of people at a facility. Operators, maintenance personnel, and supervisors have the in-depth knowledge about their systems that is invaluable to the assessment. Process engineers, controls engineers, electrical engineers, and equipment vendors play a key role in performing the necessary calculations and to ensure the system will meet the needs of the end user after modifications are made. Financial personnel can provide key data to calculate energy costs and savings. Lastly, the management team has the ultimate authority to approve optimization projects based on sound calculations and an understanding of what the system currently cost and how much can be saved.

As you can see by performing a Pumping System Energy Assessment as outlined in ASME Standard EA-2-2009 you can collect the necessary information to perform a system assessment. By developing a System Energy Cost Balance everyone involved in the system is able to determine the cost associated with each element in the system, group the costs together and determine the costs for each process path. Finally, by reviewing the costs the team can determine how the system can be improved to minimize operating costs.

Engineered Software’s three day Pumping System Assessment & Optimization seminar provides energy managers and members of a pumping system assessment team with the information needed to implement the ASME standard, establish a pumping system energy assessment program, and incorporate the necessary methodology to evaluate the results.