The following page contains articles on:

"The 10 Commandments of Cooling Systems"
"Automating Biocide Feed To Cooling Systems"
"Cleaning Cooling Towers"
"The Dilemma of Tower Overflow in 'Bleed & Feed Programs'"
"Tower Freeze Protection"
"Water Common Sense"
"Solids Accumulation in Water Systems Due to Evaporation"

1. Maintain Proper Cycles of Concentration and Saturation Indices.
2. Maintain Proper Treatment (Inhibitor & Biocide).
3. Keep Feed & Control Equipment Set Properly, Operating and Calibrated.
4. Passivate.  Keep Distribution Decks Covered.  Maintain Equal Water Distribution.
5. Know Make-Up Water Characteristics.  Make Proper Product Selections.
6. Know Operating Characteristics of Equipment (Chillers, AHU & Towers).
7. Keep Tower Basin Clean.  Maintain Proper Water Level.
8. Record Equipment operating Temperature/Pressures and Pump & Controller Settings.
9. Report Scaling/Corrosive Conditions.  Review Daily Logs - Evaluate Trends.
10. Have full knowledge of communication with, and, training of, operating, supervisory and management personnel.

Microbiological control can be frustrating at times.  One of the most important elements in a biocide program is to apply the product in the correct dosage at specific intervals.  The concept of not adding biocide until you see an indication of "algae" places you in the position of playing "catch up" on microbiological control.  The interval at which a biocide should be applied is based on your system's specific retention time.

Retention time is calculated based on system volume and bleed off rate.  When biocide is added to a system, the recommended dose is based on your system water volume.  This dose establishes a specific level of the biocide's active ingredient.  Through the normal cycling and subsequent bleed off of the system, the level of biocide is gradually lowered to a point where the biocide can become ineffective.  The time frame from one biocide addition until the next is important.  If the level of biocide is allowed to fall below its effective range, microbiocidal proliferation can occur.

Much of today's system control equipment incorporates automatic biocide features and many existing controllers can have this retrofitted.  This can also be accomplished by adding a timing device and chemical metering pump to your existing control equipment.  The timer can then be set to add the correct dose of biocide at the intervals dictated by the calculated retention time.

Automatic biocide feeding will establish a consistent, effective biocide treatment program and free up the man-hours used to manually apply the biocide.  An added benefit of automation is that it will reduce handling of the microbiocide product as well as reduce the change of waste from spills and measuring errors.

If you think you may be interested in automating your biocide treatment program, discuss the options and benefits that are available with your Water Treatment Consultant.

Cooling Towers should be cleaned periodically to remove dirt, mud, and debris from the basin.  These items can form a barrier between the metal of the basin and the water.  When the inhibitors are not in contact with the basin, under deposit corrosion can occur.  Under deposit corrosion is just as it sounds, corrosion occurring under a deposit.  It should also be noted that mud, dirt, and debris in the cooling tower basin provide an excellent breeding ground for microbiological organisms.  Some microorganisms secrete an acidic solution that can increase corrosion.

At least once a year, Cooling Tower evaporative salts need to be cleaned.  This is done differently on each tower as different fill material requires different cleaning procedures.  The distribution decks and distribution nozzles should be checked and cleaned or replaced as needed at the same time.

 If the tower can be shut down, drained, flushed, and pressure washed, this would be the preferred method of cleaning.  As the tower is being refilled, it is important that the proper Water Treatment inhibitor level is added to ensure adequate system protection upon system start up.  If the tower cannot be shut down, do not despair.  You can do a fairly good job of cleaning a cooling tower while it is on-line with a vacuum or siphon arrangement; that will allow you to remove the bulk of mud and debris that accumulate in the tower basin's low flow areas.  A disadvantage to cleaning on-line is that there will be some debris that will become dislodged and will end up being re-circulated in the bulk water and will settle out in the basin in a day or so.  However, this is the preferred method of Tower Cleaning throughout the year when debris is in the Tower Basin.  Again, after the cleaning, make sure the inhibitor level is brought back into the normal control range.

A common problem that the Water Treater encounters in "bleed and feed" cooling treatment is tower overflow.  Although this is a common problem, the harm that is does to the chemical treatment is not generally well understood by the customer and may not be corrected immediately.  

In a "bleed and feed" regimen, a system controller uses a probe in a constant flow of water to maintain a certain "safe" dissolved solid level to prevent scale formation on heat transfer surfaces.  When the probe senses the maximum solid level established by the controller setting, it electronically activates a bleed valve which begins purging concentrated water from the system.  At the same time, a chemical metering pump is also activated which begins pumping scale and corrosion inhibitor into the system.  The pump is set to add a certain amount of inhibitor necessary to control scale and corrosion based upon the amount of bleed required to maintain the desired solids level.

When a tower overflows, it is because the make-up valve is either not adjusted properly to maintain a "low-enough" water level in the tower, or it is no longer functional and needs replacement.  When overflow occurs, the properly treated water is lost from the system and the make-up valve is constantly adding fresh water to the system thereby causing a dilution.  This dilution is not called for by the controller, so no inhibitor is added.  If evaporation is great enough after the overflow has happened, the system will "cycle up" again without the necessary inhibitor level, and scale will form.  Not only does overflow undermine the "bleed and feed" cycle, it creates a state of poor water usage adding to the customer's water and sewage costs.  When tower overflow is found, the make-up valve should be properly adjusted or replaced immediately.  Once the correct tower water level is achieved, the proper inhibitor levels should be restored by manually adding treatment to the tower so that a sound bleed and feed program can continue.

Through the cooler months we have noticed different freeze protection techniques.  The most common of these is overflowing.  The following will point out some of the problems associated with this practice. 

While overflowing the tower addresses freezing of condenser and make-up water, it also creates a few problems.  Overflowing causes conductivity to drop.  If the tower has a feed/bleed controller, once the system is returned to normal, the inhibitor level will be low.  It must be brought back into range to prevent the build-up of scale and to control corrosion.  If your system has a proportional feed system, while you overflow water, you also waste chemical.  With this in mind, you may ask yourself, "How do I properly protect my system from freezing?"

Water only freezes at 32° F or less, and this can be extended much below that if the system is recirculating.  Most chiller manufacturers recommend you do not start your system if your condenser water is below 65° F.  As a result, many towers have basin water heaters and/or tower by-passes.  If the forecast indicates freezing weather, turn on the basin heaters and circulate the water or by-pass the tower.  If the make-up line needs protection,  heat stripping or insulation is recommended.  These actions will eliminate the need to readjust the make-up float as the weather changes.

Many preventative maintenance programs recommend overflowing, but, as already pointed out, this may cause more problems than you anticipate.  If you have any specific questions or concerns regarding your system, please discuss them with your Water Treatment Consultant.

Cooling Systems

Often times Water Treatment Consultants have problem situations arise that are easily avoided with a little applied common sense.  Some customers feel that instead of figuring out a problem on their own, will wait until their Consultant's service visit and let them address it.  This unfortunately only causes further problems.  Maintenance and engineering staffs have a great advantage over the Water Treatment Consultant.  They are at their facility daily and can observe changes in the system, which allows them to prevent any great problems from arising.  The Water Treatment Consultant is only in a facility once or twice a month typically.

Listed below are a few basic procedures that should always be performed on a regular basis.  For a relatively small amount of time, these actions can save time and money.

First, test the system and chemical levels.  This will greatly eliminate problems down the road because once an oddity arises you can address it immediately and prevent scale and corrosion from occurring.

In cooling towers, a common problem can be low or high conductivity level even though the controller calibrated.  Three reasons are often the cause:

1. A failed solenoid due to no signal or power to the solenoid.

2. Trash keeping the solenoid either open or closed.

3. Excessive water level in the basin.  Often in the cooler months when the demand on the tower is less, the system comes on line periodically and often the tower overflows when the recirculation pump shuts off.  Uncontrolled water loss causes the tower to refill when on line with untreated water and can cause scale and corrosion problems.

Low or high chemical levels are also a problem that occasionally occurs.  If so, check and see if one of these might be the reason:

If the level is low:

1. Has the pump lost prime?

2. Is the pump getting the signal to energize?

If the level is high:

1. Is the bleed valve bleeding when called for?

For high levels the most obvious solution is to turn down the pump (make sure to check levels regularly to ensure that the adjustment wasn't too much.  Adjusting chemical levels and dosages is not like turning on a light switch and getting immediate results, it is necessary to check later to make sure the correct changes were made.

After testing is complete and chemical additions are made, if everything is all right, pay yourself on the back.  If there are any problems, spend some time trying to solve them.