Approximately 75% of the water that is added to the cooling tower evaporates and therefore does not enter the sewer. Still, since the sewer charges are typically based on water meter readings, most customers do not receive credit for the water that evaporates and does not enter the sewer. Our competitors rarely offer this service because it brings to light the significant savings the customer could enjoy by operating their tower at higher cycles of concentration. Less water used means fewer chemicals sold by the vendor. Chardon’s approach is benefited by saving water because we use fewer chemicals to treat the water.
In addition to monitoring water consumption by the cooling tower for sewage credit, it is essential to record the amount of water used by the tower system every month. Our sales team bases the contract price for cooling tower service on the amount of water used, and precise knowledge of changes in the usage rate gives us data on which to base contract prices.
Another important reason we record water meter readings on every service call is to confirm that the amount of inhibitor used during the period correlates with the amount that should have been used. Recall that most of our cooling tower controllers base inhibitor feed on make-up water.
Valuable troubleshooting information may be learned by comparing the amount of water used during the past month with the amount that has been pumped out of the batch tank. Ideally, the two values are equal, and the inhibitor level in the tower water at present is within the appropriate range.
Given our ability to calculate the amount of inhibitor the tower system will require over a given amount of time, it is possible to determine how much inhibitor will be required to ensure that the batch tank does not run out before your next service call.
This may be accomplished in two ways. First, by increasing the volume of the batch tanks which hold the inhibitor, we can be confident that it will hold an adequate volume to maintain a continuous supply to the tower for at least one month. Secondly, the concentration can be increased so that less batch is required for every 100 gallons of make-up water. The batch strength should be concentrated enough to allow 2-3 months of operation without preparing more inhibitor batches.
Biocide use rates are based on the total tower system volume and the severity of the microbiological problem. The dose rate of most biocides is based on ounces of biocide per 1,000 gallons of system water. It is therefore imperative to know the total system volume. Recall that the EPA sets stringent guidelines on the maximum legal concentration of each biocide. Exceeding this maximum legal concentration can be very costly.
Additionally, doses above the EPA limit are often less effective or tend to compound other problems in the system, both of which reduce the account’s profitability by using more biocide than necessary. Using less biocide than needed becomes obvious quickly as bacterial slime and algal growth accumulate on visible tower surfaces, but using too much biocide is rarely visible and often goes unnoticed until the profitability of the account is reviewed, and it is discovered that you are using twice as much biocide as projected. Spending a few minutes with a calculator can literally save thousands of dollars.
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Matt Welsh
Matt Welsh is the Vice President and Water Consultant at Chardon Labs. He helps consult a wide range of customers utilizing various methods of water treatment, from chemical to chemical-free approaches, large and small applications, and across a wide range of geographical influences. With 20 years of water treatment experience, including a wide range of troubleshooting and service in potable water and non-potable HVAC and industrial applications, he is an expert in water treatment chemistry for cooling towers, boilers, and closed-loop systems.