Guide to Reading Cooling Tower Performance Curves for Engineers

Choosing the right cooling tower is a crucial technical decision that affects the efficiency of your entire cooling system. One of the most important tools in this process is the Performance Curve, which is usually available in product catalogues.

This curve is a roadmap that shows how the cooling tower will perform under different operating conditions. Understanding how to read it will ensure you choose a unit that not only meets the specifications but also delivers optimal performance.

Let's examine the key elements of a performance curve.

Understanding the Four Key Parameters

A cooling tower performance curve shows the relationship between four key parameters:

1. Flow Rate: The amount of water cooled by the cooling tower, typically measured in GPM (Gallons Per Minute) or m³/hour. This is the horizontal (X) axis on the curve.

2. Range (Temperature Drop): The temperature difference between the hot water entering and the cold water exiting. Range is a measure of how much heat is removed by the unit.

3. Approach: The temperature difference between the cold water exiting and the wet-bulb temperature of the air entering. Approach is an indicator of how effectively the cooling tower is approaching the thermodynamic cooling limit.

4. Wet-Bulb Temperature: The air temperature measured with a thermometer whose tip is wrapped in wet cloth and through which air is passed. This is the lowest temperature that can be achieved through evaporative cooling and is the most important environmental factor affecting cooling tower performance.

How to Read a Performance Curve

Performance curves are usually presented in graph form with:

• X-axis: Water flow rate (m³/hour or GPM).

• Y-axis: Relative measure of cooling tower performance, often referred to as unit capacity.

• Curve lines: Each line represents a specific combination of range and approach at a constant wet-bulb temperature.

Simple Example:

Suppose you are looking for a cooling tower to cool water from 43∘C to 32∘C with a flow rate of 250 m³/hour. The local wet-bulb temperature in your area is 28∘C.

1. Calculate the Range and Approach:

   • Range = 43∘C−32∘C=11∘C

   • Approach = 32°C − 28°C = 4°C

2. Find the Point on the Curve:

   • Find the curve line that most closely matches the combination of Range 11°C and Approach 4°C.

   • On the X-axis, find the point that corresponds to a flow rate of 250 m³/hour.

   • Connect these two points. The intersection point will indicate the model of cooling tower that suits your needs.

If the intersection point is between two model curves, choose the larger model to ensure reliable performance, especially when operating conditions fluctuate.

Why is this important?

Understanding the performance curve allows you to:

• Validate Performance: Ensure that the cooling tower can meet your required specifications.

• Optimise Design: Select the most efficient model for your operating conditions, avoiding oversizing or undersizing.

• Prevent Operational Issues: Anticipate unit performance at extreme wet-bulb temperatures (e.g., during summer).

At BHL Cooling Tower, we are committed to providing transparent and accurate technical data. Our team of engineers is ready to assist you in reading and interpreting performance curves to ensure you get the best cooling solution.