Cooling towers are large heat exchangers: they remove the heat from the water that is leaving the chiller or air conditioner’s condenser. Although different types of cooling towers (i.e., cross flow, counter flow, induced draft and forced draft) have different maintenance requirements, there are some common areas for potential problems (and solutions!):
1. Fouling
Beyond bacteria and viruses there are microbiological deposits like fungi and algae that can form a slime (known as a biofilm) on the heat transfer surfaces of your cooling tower. This slime impairs the heat transfer which leads to significant fouling and overall cooling inefficiencies. If the deposits get bad enough, they can also obstruct the free flow of water and air, weighing down the structural members of the tower and potentially causing them to deform or break.
2. Particles and Particulates
Over time, dirt and other small particles will slowly build up within the tower. These particles can clog the tower fill, and drainage nozzles reducing its ability to cool the recirculation water. The smaller the particle, the harder it is to remove. Fine particles, especially those below 5 microns in diameter, will cause significant issues due to their high surface area and the difficulty in effectively removing/filtering them out of a system.
3. Scaling
Scaling occurs within a cooling tower when the concentration of dissolved solids becomes greater than their solubility in the water. Saturation happens after high evaporation of tower water coupled with increased additions of tower water chemical treatment. Like biofilms, scale will impact the heat transfer surfaces in the tower and lower its cooling efficiencies. Scale can also be imparted on the condenser tubes of a water chiller thereby reducing its capacity and efficiency.
4. Corrosion
As with any water-handling system, wherever the water meets metal, it is susceptible to corrosion. Open, recirculating cooling water systems can lead to corrosion from the water’s higher concentrations of electrolytes caused by evaporation. This problem gets worse as the water’s pH levels become more unstable.
5. Foaming
While not as common as the other leading causes of cooling tower problems, foaming can occur from the cascading water in the tower. This can then make the cooling tower sump overflow or cause the fans to blow foam out of the top of the tower. Increased fouling can occur from foaming since there will be higher concentrations of microbiological contaminants in the foam.
Maintenance Tips
Proper maintenance of the cooling tower is critical for preventing airborne diseases, as well as for the overall efficiency and reliability of the cooling system.
1. Remove Scale Deposits
Because cooling towers work using evaporation, there is a build-up of scale deposits, which has to be removed regularly. These deposits are caused by the minerals in the water and can vary in severity according to the minerals that are present in the water you are using. Limescale, for example, can build up and decrease both the efficiency and performance of the system. Consider periodic blow down of the tower when water quality becomes saturated.
2. Keep Air Flow Running
System breakdowns are often caused by poor fan performance. Loose parts, improper fan alignment and lack of gearbox maintenance can all result in poor air flow and water that is not sufficiently cooled. It is important to check for sludge build-up on the basin floor of the cooling tower, as it could be blocking air flow. You might also add a biocide to reduce algae and bacterial growth in the cooling tower.
3. Keep the Strainers and Tubes Clean
Strainers are provided to keep the water clean; periodic cleaning empties the trapped sediment. When the sediment goes beyond the strainer’s capacity, the tubes can become contaminated with mud, slime, algae and scale. This can lead to partially or totally clogged tubes. The water quality and rate of build-up will determine how often the tubes need to be cleaned. All units will experience build-up, and cleaning strainers and tubes regularly is the most efficient way to remove debris.
4. Inspect Your Water Pump
You can save on your monthly energy bills by making the pumping process as efficient as possible. The pump is essential for moving water back and forth. Pumps should be checked for leaks, abnormal vibrations and proper pressure flows with log readings showing trends over time.
5. Treat Your Water
Water quality is an important part of maintaining the efficiency of the cooling tower. Quality problems can lead to scum and scale build-up. Test and treat the water to prevent premature system issues. Water treatment is an essential investment, as it will help keep the system running at peak performance levels.
6. Inspect the Motor, Fans and Other Equipment
If the motor fails, it can bring the whole building down along with it. Because these motors are extremely heavy, hoisting a new one to the cooling tower isn’t the easiest task. Proper fan maintenance is equally important, as broken fan blades can destroy bearings and cause other problems. Other checks include inspecting spray nozzles, baffles, sump, drains and valves.
Cooling towers maintenance is essential to the health of your building occupants. Work with an experienced HVAC maintenance company (like CM3) to ensure that the system is generating healthy, clean air, as well as operating efficiently.