The Ultimate Buyer's Guide for Purchasing how to design cooling tower

When it comes to purchasing a cooling tower, there are several important factors to consider. A cooling tower plays a crucial role in many industries, and making the right decision can impact the efficiency, performance, reliability, and long-term operational costs. In this article, we will explore the key questions that should be taken into account when purchasing a cooling tower.

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1.Efficiency and Performance:

Efficiency and performance are vital considerations when buying a cooling tower. Understanding the cooling capacity, heat exchange efficiency, water treatment requirements, and airflow resistance are essential to evaluate a cooling tower's capabilities. Ensuring that the cooling tower meets your specific cooling needs and operates efficiently under different conditions is crucial.

High heat transfer performance, counterflow closed cooling tower structure display

2.Quality and Reliability:

The quality and reliability of a cooling tower should never be overlooked. Cooling towers are long-term investments, and their durability and reliability are paramount. Assessing the material quality, manufacturing processes, and reliability of components is essential. Additionally, researching the reputation and experience of the manufacturer is advisable. Choosing a high-quality cooling tower from a reliable manufacturer reduces the risk of failures, extends equipment lifespan, and minimizes maintenance and replacement costs.

High Quality And Reliability

3.Maintenance and Upkeep:

Maintenance and upkeep are important considerations when purchasing a cooling tower. Regular cleaning, repairs, and preventive maintenance are necessary to ensure optimal performance. Understanding the maintenance requirements, workload, and associated costs is crucial. Seeking advice from the manufacturer or other users regarding maintenance plans and best practices is recommended. Opting for a cooling tower with user-friendly designs and comprehensive maintenance support can lower maintenance costs, downtime, and keep the equipment operating at its best.

Internal Access for Easy Maintenance

4.Energy Efficiency and Environmental Impact:

Energy efficiency and environmental impact are increasingly important considerations for buyers. Inquiring about energy consumption, energy-saving measures, emission standards, and sustainability aspects of the cooling tower is essential. Choosing a cooling tower that meets energy efficiency standards not only reduces operational costs but also minimizes environmental footprint. Prioritizing energy-efficient and environmentally friendly cooling towers aligns with sustainable practices and demonstrates social responsibility.

Traditional industrial waste heat treatment destroys the environment

5.Cost and Price:

Cost and price are significant factors when purchasing a cooling tower. Evaluating the price, operational costs, maintenance expenses, and making comparisons with competing products is necessary. It's important to strike a balance between performance, quality, and affordability. While high-quality and reliable cooling towers may have a higher initial investment, they may offer lower overall costs in the long run by requiring less frequent repairs and component replacements.

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When purchasing a cooling tower, a comprehensive approach that considers efficiency, performance, quality, maintenance, energy efficiency, and cost is crucial. Engaging in dialogue and seeking advice from manufacturers, suppliers, and other users is recommended. Only by thoroughly understanding and weighing all these factors, can an informed decision be made. By selecting the most suitable cooling tower that aligns with specific needs and industry requirements, one can ensure efficient and reliable operation, resulting in long-term benefits for their business.

Find Your Optimal Cooling Tower Type

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Explore Delta’s Cooling Tower Sizing Calculator

To determine the perfect cooling tower design and size for your needs, Delta makes it easy with our downloadable sizing program. To discover Delta’s cooling tower sizing & selection program, simply click here.

Narrowing Down Your Cooling Tower Selection

If you are interested in learning the methods of determining the proper size cooling tower, rest assured that Delta is here with guidance. Explore our handy information. Click here to learn about sizing & selecting.

Know Your Cooling Tower Capacity Calculation

Whether your application is for industrial process cooling or HVAC condenser cooling, the data required is the same. The following design data is required for cooling tower sizing to properly select the appropriate model:

• Flow Rate in GPM
• Range of cooling in °F (T1 – T2)
• Area Wet Bulb Temperature in °F (Twb)
  
  

Cooling Tower Heat Load Calculation

The Design Heat Load is determined by the Flow Rate, and the Range of cooling, and is calculated using the following formula:

Heat Load (BTU/Hr) = GPM X 500 X Range (T1 – T2) °F

If the range of cooling, Heat Load, and one of the other two factors are known (either the GPM or the ° Range of cooling), the other can be calculated using this formula.

• GPM = Heat Load (BTU/Hr) / 500 X ° Range of cooling
• ° Range of cooling = Heat Load (BTU/Hr) / 500 X GPM The Design GPM and the °
  
  

The range of cooling is directly proportional to the Heat Load.

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The cooling tower selection table may look confusing, but after you have made a few selections, the process is straightforward. If you need a refresher, this may help. The following design data is required to select cooling towers:

Flow Rate in GPM

Range of cooling in °F (T1 - T2)

Area Wet Bulb Temperature in °F (Twb)

The Design Heat Load is determined by the Flow Rate, and the Range of cooling, and is calculated using the following formula: Heat Load (BTU/Hr) = GPM X 500 X ° Range of cooling.

More importantly, if the Heat Load and one of the other two factors are known, either the GPM or the ° Range of cooling, the other can be calculated using this formula.

For example: GPM = Heat Load (BTU/Hr), or 500 X ° Range of cooling ° Range of cooling = Heat Load (BTU/Hr) 500 X GPM

So, as you can see, the Design GPM and the ° Range of cooling, are directly proportional to the Heat Load.

And, 500 is the “fluid factor” which is based on water as the heat transfer fluid. The fluid factor is obtained by using the weight of a gallon of water (8.33 lbs.) multiplied by the specific heat of the water (1.0) multiplied by 60 (minutes/hour).

The first step in selecting a cooling tower is to determine the Nominal cooling tower load. Since a cooling tower ton is based on 15,000 BTU/Hr, the formula is:

Nominal Load = GPM X 500 (Constant) X ° Range of cooling, 15,000 BTU/Hr/Ton or, the more simplified version of the same formula, Nominal Load = GPM X ° Range of cooling 30

More on Sizing & Selecting

Examples of Different Applications

Once the Nominal cooling load has been calculated, a Correction Factor must be determined to calculate the Actual Rated cooling tower tons required for the specific conditions of service. The correction factor adjusts for the ease or difficulty of cooling based on the Theoretical Design of all cooling towers.

The Nominal Ton Correction Factor is determined by using the COUNTERFLOW COOLING TOWER SELECTION AND PERFORMANCE CHART enclosed. Note that the curves are shown as three separate sections. The WET BULB CORRECTION SECTION, the APPROACH SECTION, and the CAPACITY MULTIPLIER FACTOR SECTION. First, find the Range line in the WET BULB CORRECTION SECTION in the upper left-hand section of the chart. Move along the Range line over to the intersection of the Wet Bulb line.

Now move down along the Wet Bulb line to the APPROACH SECTION, in the lower left-hand section of the chart, and stop at the intersection of the Approach line. Move across to the CAPACITY MULTIPLIER FACTOR SECTION to the right-hand curves and stop at the intersection of the Range line and read the CAPACITY MULTIPLIER FACTOR.

The Actual Rated cooling tower tons can now be calculated by multiplying the Nominal cooling tons, which was previously calculated, by the CAPACITY MULTIPLIER FACTOR. The Actual Rated cooling tower tons is the capacity required for the specific conditions of service, and the next largest size cooling tower should be selected for the application.

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Following are selection examples for three different applications. One example is based on conditions that are identified as "Theoretical Design," for reasons which will become apparent.

The second example, entitled "Actual Design" is a selection based on adjusting from Theoretical to Actual design.

The third example, "Modified Application", converts an actual once-through well water system to a cooling tower recirculation system.

Sizing & Selecting

Read on to Learn about the Cooling Tower Selection Procedure

Example 1. Theoretical Design

The following conditions are provided for selection purposes:

The operating water flow rate is 600 GPM.

Hot water temperature (T1) to the cooling tower is 95° F.

Cold water temperature (T2) desired from the cooling tower is 85° F.

The installation location's wet bulb temperature (Twb) is 78° F.

You can now make a cooling tower selection with this information:

The water flow is 600 GPM. The Range of cooling is 10° - (T1 - T2). The Approach to the wet bulb temperature is 7° - (T2 - Twb).

First the cooling tower NOMINAL load has to be determined:

Nominal Load = GPM x 500 x ° Range, = GPM x ° Range, therefore, 15,000 BTU/Hr 30

Nominal Load = 600 gpm x 10° Range = 200 tons of cooling required.

30 Since the Heat Load = Flow (gpm) x 500 x °Range of cooling= 600 gpm x 500 x 10° = 3,000,000 BTU/Hr and a cooling tower nominal ton = 15,000 BTU/Hr, the nominal cooling tower ton is derived from the actual heat load. Therefore, a heat load of 3,000,000 BTU/Hr = 200 nominal cooling tower tons.

Now the Nominal Ton Correction Factor has to be determined for the conditions established:

A 10° Range of cooling, and a 7° Approach to the design wet bulb temperature of 78°F, using the COUNTERFLOW COOLING TOWER SELECTION AND PERFORMANCE CHART enclosed.

Find the 10° Range line in the WET BULB CORRECTION SECTION in the upper left-hand section of the chart. Move along the 10° Range line over to the intersection of the 78° Wet Bulb line.

Move down along the 78° Wet Bulb line to the APPROACH SECTION, (the lower left-hand section), and stop at the intersection of the 7° Approach line.

Move across to the CAPACITY MULTIPLIER FACTOR SECTION to the right-hand curve and stop at the intersection of the 10°Range line, and read the CAPACITY MULTIPLIER FACTOR, which is 1.0.

To select the proper cooling tower for this application, multiply the 200 Nominal tons calculated, by the 1.0 CAPACITY FACTOR. As previously stated, the correction factor adjusts for the ease or difficulty of cooling in relation to the Theoretical Design. So in this case, since the CAPACITY CORRECTION FACTOR is 1.0, the Nominal and Actual Rated tons are the same as the Theoretical Design, and a Model DT-200I cooling tower can be quoted. 

Sizing & Selecting

Cooling Tower Selection Procedure

Example 2. Actual Design

Now we will select a cooling tower for the same 200-ton Nominal Load as Example #1 but is different from the Theoretical Design. The operating water flow rate is 300 GPM.

Hot water temperature (T1) to the cooling tower is 105° F.

Cold water temperature (T2) desired from the cooling tower is 85° F. The installation location's wet bulb temperature (Twb) is 76° F.

You can now make a cooling tower selection with this information:

The water flow is 300 GPM. The Range of cooling is 20° - (T1 - T2). The Approach to the wet bulb temperature is 9° - (T2 - Twb).

First, the cooling tower NOMINAL load must be determined:

Nominal Load = GPM x 500 x ° Range, = GPM x ° Range; therefore, 15,000 BTU/Hr 30.  Nominal Load = 300 gpm x 20° Range = 200 cooling tons required.  30 Since the Heat Load = Flow (gpm) x 500 x °Range of cooling= 300 gpm x 500 x 20° = 3,000,000 BTU/Hr and a cooling tower nominal ton = 15,000 BTU/Hr, the Nominal cooling tower ton is derived from the actual Heat Load. Again, a 3,000,000 BTU/Hr heat load = 200 Nominal cooling tower tons.

Now the Nominal Ton Correction Factor must be determined for the conditions established; a 20° Range of cooling, and a 9° Approach to the design wet bulb temperature of 76°F, using the COUNTERFLOW COOLING TOWER SELECTION AND PERFORMANCE CHART enclosed.

First, find the 20° Range line in the WET BULB CORRECTION SECTION in the upper left-hand section of the chart. Move along the 20° Range line over to the intersection of the 76° Wet Bulb line. Move down along the 76° Wet Bulb line to the APPROACH SECTION, in the lower left-hand section of the chart, and stop at the intersection of the 9° Approach line. Move across to the CAPACITY MULTIPLIER FACTOR SECTION to the right-hand curves and stop at the intersection of the 20° Range line, and read the CAPACITY MULTIPLIER FACTOR, which in this case is 0.62.

The final step to select the proper cooling tower for this application is to multiply the 200 nominal cooling tons required, which was calculated above, by the CAPACITY FACTOR, which in this case is 0.62. The cooling tower Actual Rated tons for the conditions given are therefore 124 tons, and a Model DT-125I cooling tower can be quoted. Since the correction factor adjusts for the ease or difficulty of cooling based on the Theoretical Design, in this case, the Actual Rated tower conditions are easier than Theoretical Design.

Sizing & Selecting

Cooling Tower Selection Procedure

3. Modified Application

The following is an example of modifying a "once through non-recirculating cooling application" to a recirculating cooling tower system. A cooling tower is required for heat exchanger process cooling, which is now being cooled using 55°F well water at a flow rate of (1 Million gallons/day - 300,000 sanitary = 700,000 gal per day).

Approximately 500 GPM, and discharging to a lake at 80°F. With this information we can establish the Heat Load, which is 500 GPM x 500 x 25° R (80°F - 55°F) = 6,250,000 Btu/Hr.

We can establish the cooling tower design for a 6,250,000 Btu/Hr Heat Load based on the installation location design Twb, which, for this example, we'll say is determined to be 76°F, and by establishing a reasonable cold water temperature at a 7° Approach to the Twb, at 83°F.

What we have to determine now is either the design range of cooling or the appropriate design flow rate based on the established Heat Load. Let’s select the appropriate design flow rate by using a reasonable 15° Range of cooling; 83°F cold water + 15° = 98°F hot water.

Use the Cooling Tower Heat Load Calculation to find the design flow rate as follows:

Heat Load (BTU/Hr) = GPM X 500 X ° Range of cooling, or rearranged to determine the design flow rate. GPM = Heat Load (BTU/Hr) = 6,250,000 Btu/Hr = 835 gpm 500 X ° Range of cooling 500 x 15° R Now you can make your cooling tower selection based on 835 gpm, cooling from 98°F to 83°F @ a design 76°F Twb. The cooling tower selection is = 418 Nominal Tons x .83 DCF = 347 Rated cooling tower tons, or a 350-ton cooling tower selection.

Alternate #1:

A commercial cooling tower can also be selected for this heat load based on a 25° Range of cooling. The conditions for selection would be 500 GPM, cooling from 108°F to 83°F @ 76°F Twb, which is equal to 418 Nominal tons x .62 DCF = 259 Rated cooling tower tons, for a 260 ton cooling tower requirement.

Alternate #2:

Or select for a design to cool 110°F to 83°F = 27° R of cooling, the design flow would be 6,250,000 Btu/Hr = 465 GPM. 27° R x 500

The selection for 465 GPM cooling from 110°F to 83°F @ 76°F Twb = 418 Nominal tons x .58 DCF = 242 Rated tons; so you can recommend a single Model DT-250I cooling tower.

Contact us to discuss your requirements of crossflow vs counterflow cooling towers. Our experienced sales team can help you identify the options that best suit your needs.