Selecting the appropriate induced draft cooling tower is not a buying decision. It determines if your process operates at consistent temperatures or not. Many industrial facilities find this out after the tower is installed, as it may appear adequate when designing it on paper, but fails to meet the demands of actual use. A wrong cooling tower capacity is typically a result of oversizing or unrealistic design temperatures or assumptions that are not applicable to the site.
Even the slightest mistake in cooling tower sizing can cause water temperatures to be higher in the cooling tower and lower production efficiency and expensive corrections post installation. Fortunately, many of these issues can be addressed by knowing the factors that influence thermal performance. This guide takes you through the most common sizing pitfalls and how to avoid ordering the wrong size.
If an industrial cooling tower is not able to discharge the heat needed, it will return the heat to your process. That affects:
Flow alone cannot be used to convey the meaning of induced draft cooling tower capacity. The amount of heat to be rejected by a tower that processes 100 m³/h can vary widely with the temperature change, site characteristics, and thermal design.
The majority of cooling tower sizing errors can be attributed to a few parameters: heat load, flow, wet bulb temp, range, approach and future load as well as physical installation. Each of them must be correct to be the basis of a good cooling tower capacity calculation.
Cooling tower heat load is a measure of the heat to be rejected from the cooling tower based on water flow and the temperature difference across the load. One of the common mistakes is to equate the heat rejection duty of the tower with the process cooling load. Duty may increase above the process figure due to heat added by pumps, the compressor work in chiller systems and any other source. Before entering a number into an enquiry, always check what it is.
The cooling tower water flow rate should be equal to the actual water flow rate and not the nameplate of the pump. The design duty is skewed by estimated or out-of-date flow values. Actual flow changes due to throttled valves, worn pumps, piping changes. If possible measure it, since the incorrect flow rate will be directly transferred to the tower you choose.
The evaporative cooling limit is determined by the cooling tower wet bulb temperature, not by the dry-bulb temperature from the weather report. If such an approach is taken, based on dry bulb temperatures, or around a mildest average in the season, the result is under-performance in humid peak months. Because induced draft cooling tower efficiency is directly related to the site-specific design wet-bulb value, use a value that reflects realistic worst-case conditions.
These two terms can be confused:
For instance, a 5°C range can be achieved when water is cooled from a high temperature of 37°C to a low temperature of 32°C. The tighter the approach, the greater the tower or the higher the thermal capability, with the same heat load at a 28°C wet-bulb.
A tower that is only large enough for average load during peak production. Think about normal heat loads and operating times, planned expansions. It's not about arbitrary oversizing to justify a cooling tower design capacity but a justifiable capacity with a reasoned extent of allowance which has no downside in terms of capital or operating costs. Record the rationale for any margin you use.
Capacity is related to the interaction between air, water, and cooling tower fill media. The fill provides an area for heat transfer, water distribution must be uniform and the cooling tower fan airflow must be designed accordingly. Capacity is not the same as the power of the fan motor. Even if the fan is powerful, if it can only fill the compartment with a low percentage, or if it is not evenly distributed, it is not very efficient.
The design of a site can subtly affect its performance. Review:
A well-designed tower on paper may not perform as expected if these factors are not considered for the cooling tower installation.
With that knowledge of where sizing fails, it's time to allocate numbers to your own responsibility. Any enquiry or quotation can be based on a reliable starting point from a simple heat-load calculation.
The simple cooling tower heat load formula is:
Heat load = Water flow × Specific heat × Temperature range
Let's have a look at an example with common process values:
| Parameter | Value | How It Is Obtained |
|---|---|---|
| Water flow | 100 m³/h (about 100,000 kg/h) | Measured circulating flow |
| Hot water temperature | 37°C | Water entering the tower |
| Cold water temperature | 32°C | Water leaving the tower |
| Range | 5°C | 37°C - 32°C |
| Specific heat of water | 1 kcal/kg°C | Standard water property |
| Heat load | 500,000 kcal/h | 100,000 × 1 × 5 |
| Heat load in kW | About 581 kW | 500,000 ÷ 860 |
| Heat load in TR | About 165 TR | 500,000 ÷ 3,024 |
This is not the manufacturer's rated heat load, but the calculated value. The tower ratings are given for a specific flow, temperature and wet-bulb condition and will vary under different conditions. Never compare your duty with the rating only headline number quoted in a brochure.
The following cooling tower procurement checklist should be used when developing an RFQ for induced draft cooling tower selection:
When you've got complete information, the supplier can make an educated guess on a tower that meets your duty, instead of guessing.
Here are a couple of things you should do before committing to a manufacturer:
Among the induced draft cooling tower manufacturers in India, choose the ones that ask detailed questions related to your conditions. Typically indicates a thoughtful design process.
For any industrial buyer that wants the most reliable induced draft cooling tower suppliers, a list of products is not enough. From FRP induced draft cooling tower designs that have been shaped around the application, to the many choices SP Cooling Towers offers, there is no one size fits all when it comes to choosing an FRP cooling tower.
The technical enquiry process assists in matching the tower to the actual conditions. Provide SP Cooling Towers with your flow, temperatures and wet-bulb information and get a quote based on your duty.
There are a few disciplined checks to do when sizing correctly: accurate heat load, real water flow, site-specific wet-bulb temperature, and understanding the range and approach, realistic peak loads, balancing fan and fill performance and avoiding recirculation.
Verify these design parameters prior to selection of an induced draft cooling tower and communicate these parameters to the supplier. If you are looking for a comparison of the best induced draft cooling tower manufacturers in India, then SP Cooling Towers is ready to look at your needs and propose the right cooling tower.
|
Looking to size the cooling tower properly? Pass on your duty to SP Cooling Towers and their design will deliver a quotation for your duty as it is specified. |
Capacity is related to heat load, circulating water flow, desired hot and cold water temperatures and the design wet-bulb temperature. These are all to be defined simultaneously. Changing any one shifts the tower size needed.
Yes. Thermal performance is affected by operating temps, design wet bulb temp and equipment capability. A tower with the same flow closer approach or wider range requires more thermal capacity.
No. The overall performance is dependent on a matched fan, fill, water distribution and thermo design. An oversized fan on an unmatched tower typically consumes more electricity, but does not provide greater capacity.
The approaches are usually in the range of 3°C to 6°C above wet-bulb. Larger towers and higher costs are needed for tighter approaches. The value should be based on your process needs and budget.
Check performance at least on a seasonal basis, and following any change of load or water quality. Inspect cold water temperature, flow, and fan condition and cleanliness. Capacity loss is identified before impacting production through regular checks.
Allowances, when moderate and justifiable, are good, but extended to large dimensions can lead to control issues when at light loads. The margins must be based on the known peak load and future loads, not on speculation.
Share the flow rate, hot and cold water temperatures, and site wet-bulb for tower selection and a budgetary estimate.
