Can automation in an aquatic facility be counterproductive?
By: Dr. John Psaroudis
Within an aquatic facility, a UV disinfection system is traditionally installed as a stand-alone device. Its presence usually goes unnoticed as it treats countless gallons of water every day, ensuring chloramines are destroyed and water borne pathogens are inactivated. It also pays little attention to the other equipment surrounding it, that is until recently. Now, UV systems are much more commonly integrated with other pieces of equipment; chemical controllers, pumps and filters are installed to add additional layers of protection to the treatment process and these are usually all connected.
But can the connection of a UV system to another piece of equipment be counterproductive?
The chemical controller acts as the `brain’ of an aquatic facility and manages much more than just the chemicals. Chemical controllers now have I/O that enable them to connect several pieces of equipment together. For example, the controller will have an input from the filter that alerts it to the beginning of a backwash cycle. The controller will also have an output to the heater and UV system, enabling it to shut them both down when that backwash occurs. This is done to ensure that neither the heater or UV system overheat due to a lack of flow caused by the filter backwash. Once the backwash is complete, the controller sends a signal to the heater and UV system for them to start back up.
Another example is when the UV system is integrated with a pump. If the pump stops, a signal is sent to the UV system to stop and vice-versa. If the UV stops or cannot meet its intended level of performance, a signal is sent to the pump to stop. This ensures that when the pump is operating, the UV is operating and likewise when the UV system is on the pump is on. This automation ensures that both the equipment and the patrons of the aquatic facility remain safe.
However, at times, automation can be counterproductive.
A common question asked by aquatic operators is whether they should connect ppm probes on the chemical controller to the UV system? The idea being that the UV system will turn on or operate at high power when chloramines are detected and turn off or operate at low power when chloramines are below the required limit. In order to answer this question, it’s important to understand two important features related to UV systems.
Firstly, the ability of the UV system to increase and decrease power to the UV lamps. This is commonly referred to as variable power or ramping power. When flow through the UV system increases and decreases, water quality changes, lamps age or fouling of the quartz sleeves and sensor windows occur, the UV system recognizes this through built in sensors. It then varies power to the lamps, ensuring the required performance set-point is always maintained. Many UV systems have gradients of power delivered such as low, medium and high. While other UV systems ramp power up and down in 1% increments.
Variable power works very much like the cruise control on your car. As the car goes up a hill, the cruise control increases engine power to maintain the mph set-point. When the car goes down a hill, power is reduced, again so that the set-point is maintained. With a UV system, variable power enables the power to the lamps to be adjusted as changes within the process are sensed, ensuring the set-point is maintained, without ever going over or under. Regardless of how the UV system increases and decreases power, the result is a UV system that only consumes the necessary power to meet the required performance set-point.
Secondly, the aquatic industry has agreed that, because there are always chloramines in a pool, there is a requirement for a UV system to deliver a dose of 60 mJ/cm2 for chloramine destruction. A UV system delivering a dose lower than 60 mJ/cm2 may be suitable for the inactivation of harmful pathogens, but it does not reduce the chloramines in the pool. However, operating the UV system so that it delivers a dose greater than 60 mJ/cm2 does not result in a greater level of chloramine destruction. If the goal is to reduce chloramines quicker, increasing the dose above 60 mJ/cm2 does not accomplish this, it simply wastes power. Increasing the speed at which chloramines are destroyed relies on increasing the turn-over of the pool.
Returning to our operator that wants to know if there is a benefit to linking the UV system with the chemical controller ppm probes. In this scenario, the UV system would be connected to the ppm probes via a digital input. While chloramines are always present in the pool, they may not be at the harmful levels at which the probes are set to detect them. That means the UV system would operate at the minimum power level, delivering a dose less than 60 mJ/cm2 and therefore failing to destroy the chloramines. When the chloramine level is detected as being high, a signal is sent to the UV system to ramp up power to the lamps, resulting in a dose exceeding 60 mJ/cm2.
Using our cruise control example, as the car begins to go uphill (chloramines started to increase) the cruise control would push the accelerator to the floor, exceeding the mph set-point drastically. As the car moves downhill (chloramines started to reduce), the cruise control would take the foot completely off the accelerator, leaving the car to coast at a level far below the mph set-point. This back and forth motion of full power and no power leads to unnecessary wear and tear on the car, decreased gas mileage and possibly a ticket for speeding.
Having a UV system linked to the chemical controller ppm probes creates an unescapable cycle, with the UV system providing doses that either are too low to destroy the chloramines, or at levels greater than necessary, resulting in unnecessary power consumption and greater equipment wear and tear.
As you can see, within water treatment applications, some types of automation and integration can therefore be counterproductive and allowing the UV system to provide the required 60 mJ/cm2 dose by ramping power up and down continuously actually provides the optimum solution.