In the hot, dry desert around Las Vegas, pumping water to a million people at high elevations requires a lot of electricity. An Energy and Water Quality Management System (EWQMS) helped the Las Vegas Valley Water District enact energy saving programs that have cut the operating budget substantially.

The district, a not-for-profit agency that began providing water to the Las Vegas Valley in 1954, is the largest agency member and managing partner of the Southern Nevada Water Authority (SNWA), a cooperative formed in 1991 to address the region’s water needs. The district receives 90 percent of its water from the SNWA.

The water is lifted from Lake Mead and treated at two conventional water treatment plants able to produce 900 mgd. The plants use ozone to control Cryptosporidium. One plant produces its own sodium hypochlorite to avoid the cost and risk of delivering chemicals through residential neighborhoods. Water is delivered to the district’s nine receiving reservoirs, where it is continually lifted to higher elevations or pressure zones through an additional 28 reservoir sites.  The reservoirs’ total storage capacity is 900 million gallons.

In summer when peak demand can reach 480 mgd, the district draws additional water from 64 production wells that can generate up to 190 mgd. The groundwater is treated with sodium hypochlorite and injected into the distribution system’s 4,500 miles of pipeline. The district employs 1,100 people and has an annual budget of $300 million for treatment and distribution operations and maintenance.

Making improvements

Realizing the potential to improve energy efficiency and water quality, the district began using an EWQMS process in 2005. The system, custom designed based on a prototype developed by the Water Research Foundation, uses a SCADA system, a computerized maintenance management system (CMMS), a hydraulic model to estimate energy requirements, historical water delivery data and a water-quality model. After two years of observing the system, the district centered its efforts around using daily hydraulic models to produce pumping schedules that lower energy costs and keep water from sitting in storage too long.

“It’s just-in-time water delivery,” says Kevin Fisher, director of operations. “We move the right amount of water to the right areas in the system and keep it flowing. We don’t store 900 million gallons in one day if we only need 200 million. Using SCADA data, we determine which pump combinations produce the lowest cost per acre-foot of water, and then prioritize the corresponding pumps to support the day’s projected demand. Between keeping water fresh and using the least energy, our electric bill is down 8 to 10 percent.” Before the EWQMS, the district budgeted $14 to $16 million a year for electricity to run 276 booster pumps at 53 pump stations. Today, the budget is $12 million.

Pump monitoring

Using real-time data from the EWQMS, the operating team maintains a spreadsheet of all 276 booster pumps that use incoming SCADA data on pressures, flows and energy. The pump data is periodically reassessed to look for changes over time. The team balances the cost to repair an underperforming pump against potential energy savings from making it more efficient. Teams have also been optimizing use of the well pumps.

“The differences in the water table and the pumping water levels can vary greatly in the valley, so the cost to deliver water from the wells varies greatly,” says Charles Scott, engineering project manager.  “We try to lower total power consumption per acre-foot, per well, by zone.” From 2007 to 2012, the district cut its energy use from 688 kWh/acre-foot to 649 kWh/acre-foot, saving some $749,000 over five years.

Reducing reservoir storage

To reduce operating costs in 2008, the district’s operating team analyzed the water storage needed in each zone, taking into account electrical costs, minimum emergency storage requests, minimum pump suction head requirements, minimum service pressure requirements and U.S. EPA water-quality requirements. As a result, two reservoirs were taken offline. Five or more basins are taken out of service during off-peak winter months. The original 900 million gallons of storage has been reduced to as low as 750 million gallons during winter.

Using daily modeling and the EWQMS, the system limits levels of reservoir storage to reduce electrical use. “We keep water at appropriate levels instead of superfluously filling up the reservoirs for no reason,” Scott says. “The net savings on energy are minimizing storage in the system, so we don’t have to hold as much water and we don’t have to exercise the reservoirs. When water gets old in a basin, it takes energy to drop the levels and raise them back up. It’s better to hold the level constant where it should be.”

The district has installed a total of 44 SolarBee mixers (Medora Corporation), spread over 14 reservoirs, which circulate the water more efficiently than propeller-type mixers. Each mixer uses a small DC motor to recirculate water across the reservoir surface at a rate of 10,000 gpm. Previous mixers drew 7.5 hp with AC motors. Since their installation in 2008, each new mixer saves $2,700 in electricity per year, or more than $89,000 in 2012 alone.

Using solar power

To further reduce reliance on grid power, the district installed 1,500 SunPower solar panels on six roof sites with a total 3.1 MW capacity. Since its 2007 installation, the $23 million array has offset $4 million in energy costs and generated $7.5 million in revenue from renewable energy credits from NV Energy.

Although payback on the array is just under 25 years, the main impetus for the solar installation was to improve sustainability. At the time of the installation, the state legislature mandated that NV Energy, the local electric utility, obtain 25 percent or more of its energy from renewable sources. “Installing the solar panels was our way of supporting the electric utility while benefiting the community and state overall,” Fisher says. “We strive to be leaders in setting an example for green technology usage in our industry. Sustainability is in our culture.”