Measuring pressure & temperature to minimize water loss
The water meter industry has manual read meters, drive-by or walk-by read meters and remote read meters. Some meters are one-way communicators and others are two-way communicators, such as automatic meter reading (AMR), advanced metering infrastructure (AMI) and advanced metering analytics (AMA); however, the only data the operator is receiving is volume readings. Of course, these systems make it possible to get volume data more easily than in the past, and that makes it easier to do the job.
In order to manage a multimillion-dollar utility, however, there also should be more information than volume readings. With the capability of passing information remotely from the meter to the utility, users can take advantage of this opportunity to glean as much information as possible, in addition to volume.
What if pressure data was readily available at each meter?
Many states require a utility to maintain minimum pressure and volume amounts per meter. For example, the Texas Administrative Code (Rules and Regulations for Public Water Systems 290.44) requires a minimum psi of 35 at all points within the distribution network at flow rates of at least 1.5 gal per minute per connection. Not abiding by these requirements can mean significant penalties from the state and subsequently in expenditures of capital that could have been used for new infrastructure for the utility.
Maintaining minimum requirements of pressure and volume has long been the standard for utility operators. Now many states are adding requirements for auditing water loss. For example, in Texas, the legislature passed a statute requiring that retail public utilities providing water within Texas file a standardized water audit once every five years with the Texas Water Development Board. In response, the Texas Water Development Board developed a water audit methodology for utilities that measures efficiency, encourages water accountability, quantifies water losses and standardizes water loss reporting across the state. Many utilities now are seeking further efficiencies by performing field auditing tasks to determine more precisely where losses are occurring. The big question is, other than searching for leaks, what can the utility do about water loss?
How could knowing pressure at the meter level help an operator reduce leaks? It is easy to understand when one considers that a pipe with 80 lb of pressure will leak more volume than the same pipe under 10 lb of pressure.
To the Test
Honeywell Building Solutions, in cooperation with Ponca City, Okla., launched a 60-day pilot program to test the IntelliH2O wireless water meter created by Capstone Metering of Carrollton, Texas. The purpose of the pilot program was to validate five product features of the IntelliH2O: two-way communications; remote on/off valve; water measurement accuracy; self power generation; and pressure reading. The pilot program began on Aug. 2, 2011, and ended on Sept. 28, 2011.
Capstone Metering used its software to track volume, pressure and temperature. The actual pressure and volume readings from the Capstone pilot in Figure 1 paint an interesting picture of what can result when water pressure rises in a sys- tem. This graph shows a single residence’s water volume over a period of 30 days. The blue line represents the water volume, which peaks every few days, when the resident watered the lawn. The red line represents the water pressure multiplied by 10 for purposes of graphing. About 10 days into the pilot, the city saw a significant rainfall. As a result of the rain, system pressure increased because of less demand, primarily from less lawn watering. In this case, the resident continued to water the lawn for the same amount of time every week, but since the water pressure was higher, the volume of water used for the same period of time almost doubled.
The ‘Aha’ Moment
What was so significant about this data is that city officials realized that having not only volume information, but also pressure information, at each meter would give them another management tool to assist in conserving water and determining how significant leaks are to their system. Also knowing the pressure and volume readings would give additional information to the management of the wastewater treatment facilities.
How can pressure readings from each meter be used to determine leaks? Obviously, there are two locations for leaks: on the customer side of the meter and on the utility side of the meter. On the customer side, leaks are relatively easy to determine by measuring constant volume over time. If the meter reading never goes to zero, this is indicative of a possible leak.
It is much harder to find the leaks on the utility side of the meter. Figure 2 shows a benchmark for water pressure readings, depicted in light blue, that were performed for a line of meters on Oak Street. This benchmark data then is stored in the management software for future comparisons. The dark blue portion is a snapshot of pressure readings at a particular point in time. The dip shown at 2217 Oak indicates that there is an issue on the utility side. This is water that the utility has paid to have purified and transported that is not being paid for by the end user; therefore, it results in both a revenue and expense loss for the utility.
Familiarity with water pressure levels is significant. Reducing just 1% of lost water in the U.S. would save 540 million gal of water per day, 626 million kW of electricity annually and 420,000 metric tons of CO2 emissions—the equivalent of electricity savings to power 31,000 homes and the equivalent savings of CO2 emissions from 30 coal-fired plants.
How could saving water from leaks save electricity? Think about it this way: Water has to be purified and pumped through all kinds of infrastructure before it gets to the end user. If it leaks before the customer gets it, there is no revenue, only loss. Not only is the utility losing water, but it also has wasted the electricity to purify and pump that water.
Although volume information is important, there could be other information that could assist the operator in managing a water utility. Pressure data at the meter level is one type of information. Water temperature at the meter level is another. Maybe someday operators also will be able to detect chem- icals in the water at the meter and more effectively protect the population. Another possibility would be to have a software program that could assist in ensuring that customers do not violate city lawn watering ordinances. There is no reason why, in the 21st century, we should not have as much information as possible to protect and conserve our most precious resource. Having this valuable information and being able to easily act upon it could revolutionize this industry.
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/CapstonePressureReadings.jpgFigure 1. Pressure & Volume Readings
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/LeakDetection.jpgFigure 2. Benchmark Data & Leak Detection