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Keeping Your Cooling Towers Healthy (by Aneesh Kadyan)
Cooling towers are a large consumer of energy in a HVAC system due to not onyly the fans but alos the pumping systems associated with the unknit. With the nearly continuous usage of the CT’s, the energy use can be a large amount. While the design efficiency of the fans is in the range of 85 – 92%, the actual achievable efficiency is significantly lower due to factors such as fouling, tip clearance tec. Cooling towers also use large amounts of water and hence, contribute to the sustainability of the plant. Due to these two factors – high energy and water usage, the focus of the maintance team should be higher than other systems but in nreaity, the importance that the plant operations and maintenance personnel pay to these is not as desired in most cases, especially in the building sector installations. The chiller is usually under an Annual Maintenance Contract with the OEM, but there is no such arrangement for the cooling tower, although the AMC will include the CT maintenance as well. Basic maintenance activities, such as monitoring of water hygiene and cleaning of the tanks is usually undertaken. Leaking CT wells, broken float valves, damaged fills etc. are a common sight on building terraces. Leaking water is a major ground pollutant as the chemicals added to the water to maintain hardness levels leak into the ground and mix with the underground water sources.

The Indian cooling tower industry is in a growth stage, in line with the developments in the HVAC sector and the building sector is again seeing larger number of installations due to the booming commercial and retail developments across the country. However, the upkeep of the installations is not at the desired levels leading to inefficient operations of the overall air conditioning systems.

Optimal cooling tower operation helps in efficient operation of the chiller. A one degree increase in the condenser water temperature results in 2.7% increase in chiller compressor kW. Thus, maintain the cooling water temperature close to design values has significant savings potential for plant operations. Key focus areas during operations, that lead to higher efficiencies and lower operating costs are shown in figure 2 and elaborated below.

- Maintain Water hygiene: This is one of the most basic maintenance requirements and the one that gets neglected most often. A robust water hygiene monitoring system requires checking of not only the hardness of the water but also the conductivity. The conductivity is an indication of the concentration of chemicals in the water. Incase blow down controllers are not installed, the conductivity should be manually measured on alternate days. The concentration of dissolved solids in the blow down water to that of in the makeup water is called the CoC and is used to measure CT performance. CoC can also be approximated as the ratio of volume of makeup water to blow down water. Thus, higher CoC results in lower blow down and consequently lower make up water requirement. Cooling towers have a typical CoC of 2 -4 but effective water management can increase the CoC to 6. By increasing CoC from 3 to 6, the makeup water requirement is reduced by 20%.

- Optimize cooling tower operations: In installations with multiple cooling towers, operation of the correct number of cooling towers as per the load requirement will result in lowering energy costs as well as increase asset life. Simple modifications to the cooling tower piping system can allow even distribution of load across cooling towers.

- Install Flow meters for make up as well as blow down water lines. This will allow the operators correlate the CoC measurements and identify system losses in case of differences in readings.

- Regular maintenance of Fills and fan: Damage to Fills due to foreign objects and dust is common. This reduces the heat transfer effectiveness and lowers CT capacity. Fan blades are also suspect to fouling and require regular cleaning. Fouling leads to improper flow patterns which in turn reduce fan flow rate. Thus, regular maintenance of the fills and fans is essential for optimum performance.

- Covers for wells: Sunlight enhances algae growth which causes biological fouling of the downstream systems such as condenser tubes. Covers over wells when not in use helps in blocking out the sunlight and prevents algae growth.

- Retrofits: When possibilities of retrofitting the CT exist, evaluate options to install VFD’s and hollow FRP blades to lower energy costs. Installation of automation devices can also be evaluated.

Efficiently operating cooling towers have a positive impact on the whole air conditioning system of the building, in addition to keeping energy costs low. A well maintained cooling tower also reduces the plants impact on the environment by way of reducing the use of water and also minimizing dissolved chemicals from leaking into the ground water. Thus, the onus is on the Operations and maintenance teams to have a robust and detailed preventive maintenance plan for the cooling towers, which includes not only maintenance activities but also regular monitoring of system parameters and healthiness.

Aneesh Kadyan, Director - Operations, for a leading real estate services firm directs the operations of a large team of professionals in the building and facility management arena. He is a post graduate in Mechanical Engineering and has over 19 years’ experience in management of services in technology intensive environments. His areas of interest include Maintenance management, corporate governance, Strategic planning and technology interventions in Industry. Aneesh is a Professional Engineer (PE), a certified Energy Auditor and an IGBC Accredited Professional (AP)

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