It is not enough to just feed the water treatment products to, cooling towers and closed loops to protect them; you also need to monitor the treatment program to make sure that no adjustments need to be made to your treatment program.
When your cooling towers are serviced, you should have a feed water sample and a cooling water sample pulled. You should be having the following tests run each service call:
|Make-Up Water||Cooling Tower||Chilled Loop|
Now that the tests are complete “mass balance” can be run on the cooling tower water. We calculate how many more times the cooling tower water is concentrated than the city water. To do this we simply divide the cooling tower test result by the city water result for each of the above parameters - this is termed cycles of concentration.
If the cycles for the total alkalinity or the total hardness is lower than the chloride or conductivity cycles – then the cooling tower is in a scaling condition. Meaning the cooling tower is losing alkalinity or hardness (in the form of a soft white/beige mineral scale).
If the cycles for the total alkalinity or the total hardness is higher than the chloride or conductivity cycles – then the cooling tower is in a cleaning condition. Meaning the cooling tower is removing alkalinity or hardness (in the form of a soft white/beige mineral scale).
If the cycles are the same as the chloride or conductivity cycles (it is rare that these are the same) then the cooling tower is neither scaling or in a cleaning condition.
In this example of a field service report you will see that for the cooling towers the cycles of concentration for both the total alkalinity and the total hardness are higher than the cycles based on chlorides or conductivity. Therefore, the cooling tower is in a cleaning condition.
There is one commonly overlooked test and that is for microbiological growth. During the summer months of May to October a total aerobic bacteria (TAB) test should be run on your cooling towers. If your TAB microbiological test results are 100 to 103 you are in control. If your TAB results are 104, you should closely monitor the system. If the TAB are 105 or higher, you need to make a change in your biocide treatment program.
In the example used the iron levels were elevated but the inhibitor was in the desired control range. Elevated iron can be due to mechanical problems, improper inhibitor levels, or from microbiologically influenced corrosion (MIC). Elevated aerobic bacteria levels, can result in MIC. An appropriate adjustment would be to increase the biocide dosage or increase the number of days the biocide is dosed or to alternate to a second biocide to reduce the total aerobic bacteria counts.
By following these basic steps, you can improve the control you have over your water treatment program and recognize when changes need to be made in a water treatment program. Monitoring a treatment program will help prevent many corrosion and scaling problems down the road.