As a developer, property manager, or plant operator, you understand how crucial it is to have cooling towers. Still, you may not realize various factors that can negatively impact a cooling tower's effectiveness. For example, oxidation-reduction potential (ORP) can lower the cooling tower's water quality, leading to inefficiency and other operational problems.
But have you stopped to think about how much water a cooling tower consumes?
How Much Water Does a Cooling Tower Consume?
Various air conditioning and industrial equipment require the use of cooling towers as a means of removing excess heat. This heat generated during the process occurs in the form of tons of hot water. So, you may wonder precisely how much water a cooling tower consumes? There's no one answer! But for industrial and commercial applications, the most significant water consumption occurs within cooling towers.
The cooling tower is a specialized heat exchanger whose purpose is to conserve water by keeping it from escaping into the atmosphere. The heated water produced is pumped to the cooling tower, where the flow is sprayed onto "fill" material, slowing down the flow of water and exposing a large surface area of water to air blown from a fan. Maximizing air-water contact facilitates the cooling effect that reduces the temperature of the hot water. The cooled water is pumped back to the cool chiller, condenser, or other parts, where it becomes heated and undergoes the cooling cycle all over again. However, the cooling process causes a small amount of the water to evaporate, which ironically is what facilities the cooling effect. The need to replenish the lost water supply makes it an environmental concern.
Cooling towers are critical pieces of equipment in the industry. Even though every cooling tower continuously cycles heated and chilled water, it can still consume 20-30 percent or more of the total water used. That's why it's vital for facility managers to monitor water consumption and take steps to keep water loss to a minimum.
Measuring Water Consumption in a Cooling Tower
The amount of water consumption during industrial, manufacturing, and air conditioning processes varies widely. It can depend on the equipment being used, how well it's maintained, and its level of operational efficiency. Regardless of efficiency, the Environmental Protection Agency (EPA) estimates water consumption to be about 1.8 gallons of water evaporation per ton-hour of cooling.
Cooling Tower Efficiency Metrics
Cooling tower efficiency can be measured by general metrics of Range and Approach using the following formula:
Efficiency = Range / (Range + Approach) x 100
The Approach is calculated by determining the degree of difference between the Cold Water Temperature (CWT) and the Wet Bulb Temperature (WBT). The CWT is the temperature of the chilled water, whereas the WBT relates to how much water vapor the air can hold. The Range is a measure of the difference in temperature between the hot water and the cooled water.
Cooling Tower Water Consumption Metrics
One critical data point to measure and control cooling tower efficiency is water consumption. You can estimate water consumption knowing that for every 10°F of water, 1% will be lost by evaporation. Because evaporation is a necessary part of the cooling process, minimizing evaporation in the cooling tower is not looked at as a way to control water consumption.
However, in addition to evaporation, water is lost in several other ways within a cooling tower. To get an accurate measure of the total cooling tower water loss, you must calculate all the different types of water loss, including evaporation, drift, and blowdown loss.
Water Consumption = E + D + B
Evaporation Loss is the amount of water lost through evaporation as the heated water is cooled, where T1 – T2 refers to the difference between the inlet water temperature (T1) and the outlet water temperature (T2), with 0.00085 being an evaporation constant.
- Evaporation Loss (E) = 0.00085 Wc (T1-T2)
Drift Loss (also called Windage) is a function of drift eliminators and represents the percentage of circulating water (C).
- Drift loss (D) for natural draft towers = 0.3-1.0% of C
- Drift loss (D) for induced draft towers = 0.1-0.2% of C
- Drift loss (D) for high efficiency towers = 0.0005-0.00 % or less of C
Blowdown Loss (also called Blowoff Loss) refers to the water that circulates and dissolves magnesium, chloride, calcium, silica, and other solids. As the water evaporates, these solids get pumped back into the system, where they can cause corrosion. The blowdown loss of water relates to the ratio of chloride in the circulating water and the replacement water added to the cooling tower.
- Blowdown (B) = [Evaporative loss – (COC – 1) x Drift loss] / (COC – 1)
The total amount of water a cooling tower uses is also the amount of water that must be replaced. This is known as Makeup Water. The key is to minimize water loss so as not to need as much fresh water to replace it.
Ways to Reduce Cooling Tower Water Consumption
Despite their ability to conserve water and reduce air pollution during industrial processes, cooling towers demand a lot of energy and water, placing a burden on the environment. The overconsumption of water in cooling towers wastes natural resources and has health implications. Cooling towers have been linked to Legionnaires' Disease, which is caused by a bacteria (Legionella) that grows and thrives under hot conditions. When a person breathes in bacteria-laden water droplets from a facility's cooling system, they can develop the disease. Symptoms are much like pneumonia; the resulting lung infection can be fatal.
You can take several approaches to reduce the amount of water consumed in your cooling tower.
- Reduce the heat load to the cooling tower
- Install an automatic meter reading system
- Use hybrid/combination towers (wet/dry cooling options)
- Leverage geothermal cooling
If you've learned that your cooling tower uses too much water, you have many reasons to be concerned. The next step is to take action to reduce consumption. If you're not sure how much your cooling tower is using, then it's vital to measure and monitor that consumption regularly — ideally, in real-time.
Is Your Cooling Tower Consuming Too Much Water?
Knowing the amount of water being consumed by your cooling tower is critical. It involves much more than water lost through evaporation, which is required to facilitate cooling. Calculating total water consumption based on various metrics related to cooling tower efficiency is a step towards conserving water. Doing these complex calculations manually can be a time-consuming task. That's where automated water consumption monitoring comes in. At Appia IoT, we provide you with the ability to measure water consumption in your cooling towers. If you'd like more information about remote monitoring of your water consumption and water quality, get in touch with us today.