COOLING TOWER WATER USAGE CALCULATOR
Water Make-Up Requirements of Cooling Towers
To determine how much water is consumed by a typical commercial cooling tower used in air conditioning system follow the steps below:
Enter the nominal cooling capacity of the base building or supplementary chiller or water cooled package units served by the towers, If tower capacity is known, divide it by 1.3 and enter in chiller capacity
Enter cooling tower's annual operation days (consult BMS log or building manager for existing buildings)
Enter average daily operation hours of the cooling tower (consult BMS log or building manager for existing buildings)
Enter average HOR capacity per year (0.5 for typical office building, 1 for data center with stable IT heat rejection profile)
Enter drift windage loss (assume 10% for typical application)
Input blowdown cycle of concentration (obtain from water treatment company or BMS system if available)
Note(s):
COC can range between 4-8, depending on the make-up water quality, treatment system efficiency, tower's efficiency in removing heat, etc. A typical COC of 5 can be used if this figure is unkown at this stage for an estimation
COC = Cycle of Concentration
HOR = Heat of Rejection
The calculator will provide an estimated water usage of the cooling tower system.
The main sources of water loss in a cooling tower are typically evaporation, drift, and blowdown. Here's a brief explanation of each:
Blowdown: Blowdown is the intentional removal of a portion of the cooling tower water to control the concentration of dissolved solids in the system. As water evaporates, the concentration of dissolved minerals and impurities in the remaining water increases. Blowdown helps maintain water quality by removing a portion of the concentrated water and replacing it with fresh makeup water. This process reduces the buildup of scale and corrosion in the cooling tower. However, blowdown also leads to water loss.
Evaporation: Cooling towers use the process of evaporation to remove heat from the water being circulated. As the warm water is exposed to air in the tower, a portion of it evaporates, transferring the heat to the air and cooling the remaining water. Evaporation is the primary source of water loss in a cooling tower.
Drift: Drift refers to small water droplets or mist that are carried away from the cooling tower by the exhaust air stream. These droplets can contain dissolved solids and can be lost to the environment. While drift can be minimized through the use of drift eliminators, a small amount of water loss may still occur.
It's important to note that water conservation measures, such as optimizing operating conditions, improving drift elimination, and utilizing efficient water treatment technologies, can help reduce water loss in cooling towers. Additionally, some cooling systems employ water recovery or recycling methods to minimize overall water consumption.
The Cycle of Concentration (COC) in a cooling tower refers to the ratio of the concentration of dissolved solids in the circulating water to the concentration of dissolved solids in the makeup water. The COC can vary based on several factors, including:
Water Quality: The initial quality of the makeup water, including its mineral content and dissolved solids concentration, affects the COC. Water sources with higher mineral content will typically result in lower COC values.
Cooling Tower Design: The design and operation of the cooling tower can influence the COC. Factors such as the tower's efficiency in removing heat, the effectiveness of drift eliminators in reducing water loss, and the extent of mixing between fresh makeup water and recirculated water can impact the COC.
Cooling Tower Operating Conditions: The operating conditions of the cooling tower, such as the flow rate of makeup water, the rate of evaporation, and the blowdown rate, can affect the COC. Higher evaporation rates and lower blowdown rates can result in higher COC values.
Water Treatment: The effectiveness of water treatment processes in controlling scale and corrosion within the cooling tower system can influence the COC. Adequate water treatment can help maintain higher COC values by preventing excessive buildup of dissolved solids.
It's important to note that maintaining an appropriate COC is crucial for water efficiency and preventing scaling and corrosion issues in the cooling tower. Regular monitoring and adjustment of the COC can help optimize cooling tower performance while minimizing water consumption.
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