The Issue at LVVWD
It is important to monitor the temperature in water pipelines to understand potential impacts to corrosion, the interior lining of the pipeline, as well as residual degradation when water is being pumped and not pumped. LVVWD uses pressure transmitters to address this, but there is an added benefit to be able to know the temperature sensitivity leaving the pump station. In particular, LVVWD was looking at an above-ground set of piping that goes underground and feeds into areas of PVC and iron pipe of various sizes and dimensions. If LVVWD could have a good understanding of the water temperature throughout the distribution system, it could help drive some decisions on pipe material selection and/or customer concerns, as utilities can occasionally get water quality complaints related to temperature.
Understanding the temperature in reservoirs is also important because it could help determine if there is stratification in the reservoir. Some of the more progressive utilities have installed mixing units to circulate the water from top to bottom, to help keep the residual and temperature stable. Various studies have found temperature can change a few degrees from the top of the tank to the bottom, but more importantly, the residual can change. With the stratification, typically the higher residual goes lower and the lower residual goes higher (sodium and chlorine both settle naturally in water) but keeping it mixed assures the customer appropriate protection from bacteria. The other factor is, depending on how the tank is configured to receive inlet water, the technology could show that there is a severe short-circuiting issue (which mixers have become a solution to nowadays) and it can help in the design of future inlet-outlet systems to keep the water mixed throughout.
Most of LVVWD’s tanks turn over the top three feet of water. Underground reservoirs, because they’re inherently kept cooler with a dirt berm around them and are concrete (as opposed to steel or metal), tend to have a more stable temperature range across the mass of the water. But the stratification effect is something that utilities need to understand whether they have it or not, and if they have it, then they need to take steps to eliminate it.
The temperature is probably not so much a factor of the outside external temperatures as many might think it is. It’s really the residual effect and dissolved oxygen that will be affected by both the temperature and stratification in the reservoir. If a utility is turning the water over daily, they may not have as big of a problem, but if a tank sets for two or three days before it turns over, (based on size) that is important to know because the longer the water stands the lower the residual goes and the higher the temperature has the potential to go. Elevated tanks have the same challenge. Wintertime is a slightly different challenge with elevated tanks and even ground tanks. In severe cold weather, some utilities have to worry about water temperature freezing, as a sheet of ice on top causes problems. Some elevated tanks, before mixing became involved, could freeze into ice blocks and cause problems.
The Ayyeka technology was one of the first to approach LVVWD on this issue, and according to Stephen Anderson, Systems Operations Manager at Las Vegas Valley Water District, “It just seemed like a good thing to test, not only for us but for them.” Ayyeka technology is a temperature-sensing device that uses a wireless signal to a cloud service device. There are a lot of temperature probes, but the Ayyeka technology was one of the first that would measure stratification and perform in the entire depth of the tank, which is what was really intriguing for LVVWD.
LVVWD installed one device inside of a pipeline to measure water temperature and installed another on a discharge line to a pump station to monitor the temperature when they are pumping and not pumping to understand if there were any drastic changes. They also installed Ayyeka on an aboveground tank to measure the stratification of temperature at different levels, which will help influence LVVWD’s reservoir residual and understand how it’s impacted by the filling and draining of the tank on a daily basis. The pilot idea was to track a data trend, analyze it and gain an understanding of the inlet-outlet short-circuiting challenges, pumping in, gravity feeding out, and understanding the impacts.
In a relatively short period of time, LVVWD was able to confirm the data and validate that it matched what their expectations were. “Nothing unusual jumped out at us,” said Stephen Anderson. LVVWD was able to confirm the rising temperature during the gravity feeding and that flushing in the cooler freshwater tended to stir it up and let it stabilize at a lower temperature. These temperature swings for the tank were quite minimal, where they noticed changes from 0 to 3 degrees across the spectrum for the tank. For the installation on the pipeline, the above-ground exposed pipeline saw more sun impact to it, but when it went back underground through the cooler pipe and cooler ground surface, it stabilized at an acceptable temperature.
Over the years, LVVWD decided that for daily operational needs, it wasn’t beneficial for the operators to be constantly monitoring and managing the data. They saw the technology as providing more of an analysis function for others to look at, pull data from, and assess. “Just the value of knowing what’s going on to confirm some ideas or suspicions of what’s happening was valuable and validating for us,” said Anderson. The technology is still installed but has not been looked at or monitored since, as LVVWD only required its use to validate their initial suspicions about pipeline and reservoir temperature. “Once everything was validated and we believe that our mixing systems are handling everything properly, it became an on the shelf book that we could refer to if we had a situation that needed us to,” said Anderson.
Anderson believes if the technology was tied into their current SCADA system where the operators would have ready access to it without logging into a different server/website, that it would get a lot more attention and interest at various times. “Because we go through the SCADA data largely every day and every point is looked at regularly. This would just add access to it for people with inquiring minds,” said Anderson.
“It was unfortunate that we didn’t have a long-term plan to access data quarterly, weekly, monthly, annually, or anything like that.”
The device itself, installation, and getting the information to the cloud is fairly simple and straight forward according to Anderson, so LVVWD could move it elsewhere and conduct another study if they wanted to. This has not yet happened as LVVWD stated that the information validated their inlet-outlet designs and validated their residual expectations at the various levels. “We believe the pilot summarized the configuration of the tanks that we use. We did discuss trying to move it briefly but saw no value in it,” said Anderson.
There are occasionally events driven by customer complaints that LVVWD might have a great need for a lot of data, but the events aren’t consistent enough on any one particular topic or area to drive the need for additional infrastructure to monitor. Anderson mentioned, “It’s on the bookshelf. If we needed it, we could extract it at this location and get data as appropriate. But if the water quality complaint is four miles away in a different part of the system, fed by a different tank, we wouldn’t necessarily need one on that tank. We would just analyze what we have already installed as infrastructure.” So the value-added for customer complaint analysis, water quality analysis would be hit and miss, and not lead to an area-wide installation.
The technology is still in place. LVVWD is unsure if the data is still going to the cloud as nobody has looked at them for some time. LVVWD installed them in the fall of 2015, and they were just used shortly thereafter to validate their suspicions of water temperature. The operators are all generally aware that the technology is there, but they don’t have a business need to go out and actively access the data. According to LVVWD, this was a shortcoming on their part as they didn’t write an official monitoring plan.
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