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Technologies for increasing water use efficiency in cooling towers and alternatives to conventional evaporative cooling
The Issue for the Drinking Water Industry
Southern Nevada, and particularly Las Vegas, is a place with lack of access to fresh water. For a long period of time, the Southern Nevada Water Authority has been dealing with the issue of reducing the amount of water being consumed by the city. They have been working for many years on water reuse, water quality and many other issues related to water security, but something that is now of interest is saving water in other conventional uses throughout the city, and one of those uses they have identified is the use of water in cooling towers.
Cooling towers use a lot of water in the process of cooling the air temperature. Cooling towers dissipate heat from recirculating water used to cool chillers, air conditioners, or other process equipment to the ambient air. Heat is rejected to the environment from cooling towers through the process of evaporation. Therefore, by design, cooling towers use significant amounts of water. There are ways to reduce total water use by identifying opportunities for using water multiple times. However, when water is used more than once there is another issue that comes to the table, which is the water quality. As the water is being used more than once, you begin concentrating some of the salt that the water carries and build up scale.
In Las Vegas, water is very hard and it contains a lot of salts. When this water is used for the cooling tower processes, those cooling tower operators need to understand that this water will get worse and worse. The amount of salt will be increasing as more water is being evaporated.
Trying to remove the salts or trying to contain the salts in the water is a very significant issue in cooling towers. If you can keep the water quality good enough for using the water more than once, 10 times, 100 times or 1,000 times, you can save that much more water. In order to do that, chemicals are used to control the way the water is behaving, and for example, the levels of salt that will get into the cooling tower. This means that cooling tower operators need to continue paying for the chemicals to keep this water in good quality.
Cirrus Ecowater has developed an electric-based technology to attempt to reduce scale forming potential in cooling water and reducing the need for chemical treatment. This technology that Cirrus was trying to demonstrate was an approach that claimed to use much less chemicals while still keeping the water quality acceptable for being reused several times within the cooling towers. The potential of the technology is to save significant amounts of water used in cooling towers but also save operators money from reducing the amount of chemicals they need to purchase. "It is important for Las Vegas because if they can find these types of technology, then the water savings in the Las Vegas area and any other places in the world will be very significant," said Erick Bandala, Assistant Research Professor at the Desert Research Institute (DRI). “This could lead to big reductions in water waste that could otherwise be used for other applications across Las Vegas such as drinking, irrigation or anything else.”
The Cirrus technology has been identified as a potential solution to be piloted at the Las Vegas Convention Center cooling tower to achieve two very specific goals:
- Reduce water consumption
- Reduce equipment scaling
In order to follow up the performance of the proposed technology, the Environmental Engineering Lab (EEL) from the DRI carried out the evaluation of water quality and assessment of scale forming potential in the water as the standard way to estimate the capability of the technology during 60 days. The main objective of this project is to evaluate the water savings achieved by reducing scale forming potential in cooling water using a novel technology proposed and tested at pilot plant scale at the Las Vegas convention Center.
DRI works in different ways, doing research and technology development for many water and environmental related projects. DRI is able to serve as an unbiased partner to provide testing of various technologies and delivering the results without any sort of conflict of interest. DRI is not interested in supporting any technology or helping any particular industry promoting technology, they are the institution which will run the tests and determine the effectiveness of the process and technology.
DRI got involved in this project to be that third party, unbiased research team to evaluate the Cirrus technology. DRI used a standard methodology to test the technology with agreement from the technology company, Cirrus Ecowater, the location where the technology was deployed (Las Vegas Convention Center) and the Southern Nevada Water Authority (SNWA). SNWA was an interested party in monitoring the results of the study as they saw this as a potential technology that could be used with other partners throughout Southern Nevada to potentially reduce water use. If the technology works as advertised, SNWA could help by endorsing the technology and explaining the use of the technology to others throughout Southern Nevada.
The research project consisted of evaluating the performance of the Cirrus technology. They deployed the technology in one cooling tower in a specific location at the Las Vegas Convention Center and they monitored its performance against another cooling tower in the convention center that was not using the technology. DRI used a standard procedure for testing these types of technologies by monitoring and analyzing the scale potential of the systems. As the water is being used in the cooling tower, the scale in the water will pass in to the cooling tower walls. DRI is able to measure the scale of this water and then compares those levels with the cooling tower that does have any technology deployed. There are scale formation index numbers that have to be reached in order to determine how many times the water load is able to be reused before it needs to be discarded. The higher number of times that you can use the water, the more water savings and chemical cost savings you can realize.
Results of the Pilot
According to DRI there were some issues while testing the technology. The testing was done over the summer of 2018 and it lasted only seven weeks. The standard process would be to test the cooling tower technology for at least six months but Cirrus Ecowater was confident in the ability of the technology to deliver results in the short time period. The second issue to consider is that during the time of the testing, the cooling tower was not operating consistently because of the varied schedule of the Las Vegas Convention Center. At some times the facility will be extremely busy with high cooling demands and at other times it will not be as busy and the cooling demands are lower. According to DRI, there were times when the cooling towers would be down for two to three days over a weekend.
With that in mind, what DRI found with all of the data available was that there was no significant difference in water quality between the cooling towers using the Cirrus technology and the cooling tower not using the technology. According to Bandala, "This led to the conclusion that the technology, as far as we tested, was not operating in the way that it was expected.
DRI was not given information on exactly how the technology works by Cirrus. According to Bandala, "if we were able to understand how the technology works, it would have been easier to come up with a better approach in measuring the efficiency of the technology." DRI tested with the conventional process for improving the water quality in cooling towers, but because this technology doesn't use the conventional methods to controlling water quality, a different approach in measuring the efficiency of this specific technology may have provided more accurate data and results. "But sadly, because of the short period of time that we tested and the lack of knowledge on how the technology was supposed to work, we used the standard methodology for testing." According to Bandala, this possibly could have been the reason for the lack of significance in the difference between the towers using or not using the technology.
Further Development and Potential
According to Bandala, “this could be a very significant piece of technology that ought to be explored because having the capability of saving water in cooling tower systems is something that is not only useful for southern Nevada but many other places around the world.” There are many water stressed places around the world that have buildings, hotels, convention centers etc. that could really benefit from a cooling tower technology that increases the ability to reuse water several times and ultimately reduces the amount of water used.
"So yes, these types of technologies are very needed, and the problem is very complicated," according to Bandala. "I will say that there is also a need for multidisciplinary research in developing this type of technology. In this case the need is not only to have something that may work as good as the conventional way, but also in a cheaper or more efficient way so it could be economically interesting for those investing in these technologies."
Reducing and eliminating the need for chemical treatment in cooling towers leading to cost savings
Increasing number of times water can be reused in cooling towers leading to water savings
Decreasing man-hours needed for chemical management
The technology did not show any statistically significant difference in water quality when compared to cooling towers not using the technology
member managerErick Bandala – Assistant Research Professor at the Desert Research Institute
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