Reducing Energy Costs in Water Utilities

In the struggles associated with today?s economy and aging infrastructure, many utilities are faced with the financial challenge of meeting their operating budgets while finding capital funds to make needed improvements. To add to this financial hardship, the price of commodities such as power and chemicals continues to rise.

Energy costs can account for a large portion of a utility?s budget and often rank as one of the top expenditures, along with labor and chemicals. Although energy savings can be found in different operational areas of a water utility such as lighting and the treatment processes, the pumping of water makes up a majority of the production costs. Water must be moved multiple times between the source, treatment process and customers.

This article explores ways to create energy savings and thus reduce costs in water utilities.

Rate Structure

Many electric utilities offer different rate structures. An electric utility?s rate structure is typically determined by a combination of monthly energy use (kilowatt-hours), load factor, and KW demand, actual and connected. In some service territories the electric utility may offer special water pumping rates to municipal water supply and wastewater service providers. Therefore, one of the first steps in identifying energy cost savings is determining if individual accounts are in the correct rate structure with the energy provider. It is also possible that a utility may qualify for a different rate as electrical usage and loading changes under different pumping scenarios. Determining a utility?s proper rate structure can prove to be an ongoing issue with some electric service providers.
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Individual bills should be audited for the correct rates, billing charges or overcharges to the account. This may take some expertise in understanding energy utility billing. For example, when Veolia Water Indianapolis LLC retained a consultant (Energy Consultants Inc.) to review its bills for accuracy, it resulted in a $25,000 one-time savings primarily due to account restructuring and billing errors.

Power factor (PF) is not a part of every energy provider?s cost structure, but if present can significantly impact energy costs. PF is an indicator of the overall health and efficiency of your power distribution system. It can be defined as the ratio of working or active power (watts or kilowatts) to apparent power (volt amperes or kilovolt amperes ? KVA). Simply put, power factor is the amount of a power system?s availability to perform productive work. PF management is critical to a successful overall energy management program.
For some, PF appears as a specific line item charge based on each month?s power factor. Other utilities require that a minimum power factor be maintained or there is a penalty. Still other utilities compensate for power factor losses by charging for demand in KVA instead of KW. Particularly with larger demand services, a utility will use a power factor to make adjustments to customer bills. Smaller customers typically do not have a power factor component. However, when a power factor is applied it should be closely monitored.

For example, a booster station might have a demand usage of 1,793 KW and a PF rating of 85 percent. This results in an actual demand of 2,109 KVA (1,793/.85). With a demand charge of $8.75/KVA the resulting cost would be $18,454 ($8.75*2,109). A power factor can be improved with devices such as capacitor banks. If a capacitor bank resulted in the power factor increasing to 98 percent, a savings of $2,448 could be realized.

Another recommendation is to understand and benchmark a utility?s power consumption per flow rate. This is typically expressed as kilowatt per million gallons per day (KW/MGD). Once the utility has established this rate, it should benchmark itself against other water utilities of similar size. Tracking this unit cost will allow for evaluation of a utility?s relative efficiency performance. This KW/MGD can also be used to evaluate the effectiveness of any efficiency improvements that were implemented.

Pump Efficiency

Optimizing pump efficiency is critical to reducing power costs in water utilities. The first step in optimizing pumping efficiency is to gather data. A complete list of pumps and pumping systems of interest should be compiled. Pump curves, nameplate data, process diagrams, and process data should be collected.

Given the numerous pumping systems within any given utility and limited resources, a screening process should be developed. A weighted ranking should be assigned for each pump in a system. Centrifugal pumps with the greatest horsepower and the greatest runtime should be given highest rankings. Additional weighting should be given to systems that are known to have throttle valves or bypass lines where efficiency losses are known to exist. Any pumps with recurring maintenance issues or cavitation should also receive increased ranking. Pumps in systems that have grossly changed since installation should be noted and weighted.

Lastly, positive displacement pumps or those pumps that utilize variable speed drives should have the lowest rankings.

Once a prioritized list of pumps and systems is developed, process data must be evaluated. Often times, there is a rush to evaluate pumps or systems and generate a pump efficiency number immediately. A pump efficiency measurement is specific to the instant at which you take the measurements. You first need to establish how you typically operate your pumps. At a municipal water booster station such as those operated by Veolia Water Indianapolis, pumps may operate at multiple pressures and flows based on peak demand times and seasons. There may be four or more operating conditions for a pump in a booster station. Historical data can help identify these operating conditions and attribute runtime hours to each flow and pressure point. At a minimum, you should identify the most frequently operated flow and pressure, even if historical data is lacking.

A quick operating efficiency evaluation can be made by going to the manufacturer?s pump curve and evaluating where the pump is typically operated. Most performance curves include an efficiency curve that will allow you to approximate your pump efficiency at all potential operating conditions. The goal is to have the pump operating at its best efficiency point (BEP), which is typically the same as the design point on the pump nameplate. A typical best practice is to operate the pump within 10 percent below and 5 percent above the BEP. Operating a pump in this range should result in an efficient pump requiring minimal maintenance.

As you move farther away from the pump you lose efficiency and increase wear or damage to the pump.
A more thorough efficiency measurement can be achieved by using suction pressure, discharge pressure, flow voltage, ampere and voltage (or power) readings to determine a wire-to-water efficiency. If possible, these measurements should be taken with calibrated equipment. A wire-to-water efficiency is a measure of the electrical energy put into a pump vs. the hydraulic power produced.

A very powerful and free tool for evaluating wire-to-water efficiency, pump optimization and cost savings is the U.S. Department of Energy?s Pumping System Assessment Tool (PSAT). This software is available through the DOE?s Industrial Technologies Program, Best Practices, Software Tools web page http://www1.eere.energy.gov/industry/bestpractices/software.html. DOE also offers manuals, webinars and courses on using this tool in increasing pump system efficiency. Quantifying potential efficiency improvements and resulting cost savings can help to justify pump upgrades, pump replacements, or VFD installations.

VFD Controls

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Installing a Variable Frequency Drive (VFD) on a motor allows it to adjust to varying pumping loads and can save energy (and costs) by controlling the motor?s speed to match varying flows and pressures. VFDs also provide a soft start, controlling the motor?s speed during start-up to avoid a large rush of current. Pump affinity laws can be used to illustrate how energy is saved. These laws indicate that a change in flow is proportional to a change in speed; a change in head is proportional to the square of a change in speed; and a change in horsepower is proportional to the cube of a change in speed. Therefore, by changing the frequency, the speed of the pump is changed to develop/match the desired flow and pressure. By doing so, the horsepower required also changes. Reducing the motor speed to match the pumping needs decreases the power consumed, which results in electrical costs being saved. In addition to direct energy consumption reductions, the power factor is also typically improved, adding to the cost benefit.

Installation of VFDs resulted in an efficiency improvement at Indianapolis Water?s Riverside Pumping Station. The Riverside Station contained four 25 MGD pumps that were each driven by a 1,250- HP, high-speed or a 700-HP, low-speed motor. The pumps were operated in different combinations to meet various discharge flow and pressure requirements. Veolia Water, the day-to-day operator of the utility, recommended the installation of a VFD on the 1,250-HP pump.

The installation was completed in August 2007. The project cost approximately $250,000 and resulted in a yearly savings of $100,000, or a return on investment in just 2.5 years. Additional benefits were also realized. Running the different pump combinations caused pressure fluctuations in the system when pumps were brought on or off line. Since the VFD speed is paced off a pre-set discharge pressure, the number of required pump changes necessary to meet demand was reduced. This helped to stabilize pressure in the district the station serves. One other advantage was the reduction of energy costs related to heating the station. In the summer months, the VFD cooling air is exhausted to atmosphere. During the winter months the VFD cooling exhaust is vented to the interior of the building, leading to a reduction in heating costs. This resulted in an additional energy savings ranging from $2,000 to $4,000 per month in the winter.

Utilities are operating in a climate of crumbling infrastructure, rate increase avoidance and rising operating costs. With little control over these factors, cost reductions are critical to most utilities? survival. Energy cost savings can be found through rate structure adjustments, increased pump efficiency or VFD installations, and these savings can have significant impacts to a utility?s bottom line.

Chris Barron and Jeremy Boyer are with Veolia Water Indianapolis LLC.

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Reducing Energy Costs in Water Utilities

In the struggles associated with today?s economy and aging infrastructure, many utilities are faced with the financial challenge of meeting their operating budgets while finding capital funds to make needed improvements. To add to this financial hardship, the price of commodities such as power and chemicals continues to rise.

Energy costs can account for a large portion of a utility?s budget and often rank as one of the top expenditures, along with labor and chemicals. Although energy savings can be found in different operational areas of a water utility such as lighting and the treatment processes, the pumping of water makes up a majority of the production costs. Water must be moved multiple times between the source, treatment process and customers.

This article explores ways to create energy savings and thus reduce costs in water utilities.

Rate Structure

Many electric utilities offer different rate structures. An electric utility?s rate structure is typically determined by a combination of monthly energy use (kilowatt-hours), load factor, and kW demand, actual and connected. In some service territories the electric utility may offer special water pumping rates to municipal water supply and wastewater service providers. Therefore, one of the first steps in identifying energy cost savings is determining if individual accounts are in the correct rate structure with the energy provider. It is also possible that a utility may qualify for a different rate as electrical usage and loading changes under different pumping scenarios. Determining a utility?s proper rate structure can prove to be an ongoing issue with some electric service providers.

Individual bills should be audited for the correct rates, billing charges or overcharges to the account. This may take some expertise in understanding energy utility billing. For example, when Veolia Water Indianapolis LLC retained a consultant (Energy Consultants Inc.) to review its bills for accuracy, it resulted in a $25,000 one-time savings primarily due to account restructuring and billing errors.

Power factor (PF) is not a part of every energy provider?s cost structure, but if present can significantly impact energy costs. PF is an indicator of the overall health and efficiency of your power distribution system. It can be defined as the ratio of working or active power (watts or kilowatts) to apparent power (volt amperes or kilovolt amperes ? kVA). Simply put, power factor is the amount of a power system?s availability to perform productive work. PF management is critical to a successful overall energy management program.

For some, PF appears as a specific line item charge based on each month?s power factor. Other utilities require that a minimum power factor be maintained or there is a penalty. Still other utilities compensate for power factor losses by charging for demand in kVA instead of kW. Particularly with larger demand services, a utility will use a power factor to make adjustments to customer bills. Smaller customers typically do not have a power factor component. However, when a power factor is applied it should be closely monitored.

For example, a booster station might have a demand usage of 1,793 kW and a PF rating of 85 percent. This results in an actual demand of 2,109 kVA (1,793/.85). With a demand charge of $8.75/kVA the resulting cost would be $18,454 ($8.75*2,109). A power factor can be improved with devices such as capacitor banks. If a capacitor bank resulted in the power factor increasing to 98 percent, a savings of $2,448 could be realized.
Another recommendation is to understand and benchmark a utility?s power consumption per flow rate. This is typically expressed as kilowatt per million gallons per day (kW/mgd). Once the utility has established this rate, it should benchmark itself against other water utilities of similar size. Tracking this unit cost will allow for evaluation of a utility?s relative efficiency performance. This kW/mgd can also be used to evaluate the effectiveness of any efficiency improvements that were implemented.

Pump Efficiency

Optimizing pump efficiency is critical to reducing power costs in water utilities. The first step in optimizing pumping efficiency is to gather data. A complete list of pumps and pumping systems of interest should be compiled. Pump curves, nameplate data, process diagrams and process data should be collected.

Given the numerous pumping systems within any given utility and limited resources, a screening process should be developed. A weighted ranking should be assigned for each pump in a system. Centrifugal pumps with the greatest horsepower and the greatest runtime should be given highest rankings. Additional weighting should be given to systems that are known to have throttle valves or bypass lines where efficiency losses are known to exist. Any pumps with recurring maintenance issues or cavitation should also receive increased ranking. Pumps in systems that have grossly changed since installation should be noted and weighted. Lastly, positive displacement pumps or those pumps that utilize variable speed drives should have the lowest rankings.

Once a prioritized list of pumps and systems is developed, process data must be evaluated. Often times, there is a rush to evaluate pumps or systems and generate a pump efficiency number immediately. A pump efficiency measurement is specific to the instant at which you take the measurements. You first need to establish how you typically operate your pumps. At a municipal water booster station such as those operated by Veolia Water Indianapolis, pumps may operate at multiple pressures and flows based on peak demand times and seasons. There may be four or more operating conditions for a pump in a booster station. Historical data can help identify these operating conditions and attribute runtime hours to each flow and pressure point. At a minimum, you should identify the most frequently operated flow and pressure, even if historical data is lacking.

A quick operating efficiency evaluation can be made by going to the manufacturer?s pump curve and evaluating where the pump is typically operated. Most performance curves include an efficiency curve that will allow you to approximate your pump efficiency at all potential operating conditions. The goal is to have the pump operating at its best efficiency point (BEP), which is typically the same as the design point on the pump nameplate. A typical best practice is to operate the pump within 10 percent below and 5 percent above the BEP. Operating a pump in this range should result in an efficient pump requiring minimal maintenance.

As you move farther away from the pump you lose efficiency and increase wear or damage to the pump.
A more thorough efficiency measurement can be achieved by using suction pressure, discharge pressure, flow voltage, ampere and voltage (or power) readings to determine a wire-to-water efficiency. If possible, these measurements should be taken with calibrated equipment. A wire-to-water efficiency is a measure of the electrical energy put into a pump vs. the hydraulic power produced.

A very powerful and free tool for evaluating wire-to-water efficiency, pump optimization and cost savings is the U.S. Department of Energy?s Pumping System Assessment Tool (PSAT). This software is available through the DOE?s Industrial Technologies Program, Best Practices, Software Tools web page www1.eere.energy.gov/industry/bestpractices/software.html. DOE also offers manuals, webinars and courses on using this tool in increasing pump system efficiency. Quantifying potential efficiency improvements and resulting cost savings can help to justify pump upgrades, pump replacements, or variable frequency drive (VFD) installations.

VFD Controls

Installing a VFD on a motor allows it to adjust to varying pumping loads and can save energy (and costs) by controlling the motor?s speed to match varying flows and pressures. VFDs also provide a soft start, controlling the motor?s speed during start-up to avoid a large rush of current. Pump affinity laws can be used to illustrate how energy is saved. These laws indicate that a change in flow is proportional to a change in speed; a change in head is proportional to the square of a change in speed; and a change in horsepower is proportional to the cube of a change in speed. Therefore, by changing the frequency, the speed of the pump is changed to develop/match the desired flow and pressure. By doing so, the horsepower required also changes. Reducing the motor speed to match the pumping needs decreases the power consumed, which results in electrical costs being saved. In addition to direct energy consumption reductions, the power factor is also typically improved, adding to the cost benefit.

Installation of VFDs resulted in an efficiency improvement at Indianapolis Water?s Riverside Pumping Station. The Riverside Station contained four 25 mgd pumps that were each driven by a 1,250-hp, high-speed or a 700-hp, low-speed motor. The pumps were operated in different combinations to meet various discharge flow and pressure requirements. Veolia Water, the day-to-day operator of the utility, recommended the installation of a VFD on the 1,250-hp pump.

The installation was completed in August 2007. The project cost approximately $250,000 and resulted in a yearly savings of $100,000, or a return on investment in just 2.5 years. Additional benefits were also realized. Running the different pump combinations caused pressure fluctuations in the system when pumps were brought on or off line. Since the VFD speed is paced off a pre-set discharge pressure, the number of required pump changes necessary to meet demand was reduced. This helped to stabilize pressure in the district the station serves. One other advantage was the reduction of energy costs related to heating the station. In the summer months, the VFD cooling air is exhausted to atmosphere. During the winter months the VFD cooling exhaust is vented to the interior of the building, leading to a reduction in heating costs. This resulted in an additional energy savings ranging from $2,000 to $4,000 per month in the winter.

Utilities are operating in a climate of crumbling infrastructure, rate increase avoidance and rising operating costs. With little control over these factors, cost reductions are critical to most utilities? survival. Energy cost savings can be found through rate structure adjustments, increased pump efficiency or VFD installations, and these savings can have significant impacts to a utility?s bottom line.

Chris Barron and Jeremy Boyer are with Veolia Water Indianapolis.

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