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Sizing and Horse Power Estimation of Counterflow Induced-Draft Cooling Tower

In this post I want to share to you how to do preliminary sizing and horse power estimation for counterflow induced-draft cooling tower. Calculation in this post parallel or cross-flow cooling tower. Also they do not apply when the approach to cold water temperature is less than 5oF (2.8oC).

Approach temperature is the temperature of the water leaving the cooling tower minus ambient wet bulb temperature.

[Read more: Assessment of Cooling Tower Performance]

To do this, we need this data:

  • Hot water temperature
  • Cold water temperature
  • Wet-bulb temperature
  • Water rate

Let’s start sizing the estimation. Let say we have cooling tower with the following process data:

  • Hot water temperature = 102oF
  • Cold water temperature = 78oF
  • Wet-bulb temperature = 70oF
  • Water rate = 1000 gallon per minute

Step 1: Find water concentration by using chart

Chart below is used to find water concentration, which is expressed in gallon per minute per square feet (gal/(min.ft2)).

When hot water temperature is 102oF and cold water temperature is 78oF, we get water concentration at around 2.8 gal/(min.ft2).

Step 2: Calculate required area of cooling tower

Required area of cooling tower is quantity of water circulated divided by water concentration = 1000/2.8 = 357.14 ft2.

Step 3: Find horsepower per area of cooling tower

Horsepower per area of cooling tower is estimated by using the following chart. Connecting the point representing 100 percent of standard tower performance with the turning point and extending this straight line to the horsepower scale show that it will give around 0.04 hp/ft2 of actual effective tower area. For a tower 357.14 ft2 (see Step 2), 14.6 hp is required to perform the necessary cooling.

Step 4: Check if commercial tower size is less than required area

Suppose the actual commercial tower size has an area of only 300 ft2. Within reasonable limit, the shortage of actual area can be compensated by increasing air velocity through the tower. This requires boosting fan horsepower to achieve 110 percent of standard tower performance. From chart in Step 3, we found the fan horse power is 0.057 hp/ft2 of actual area, or 0.057 x 300 = 17.1 hp.

Step 5: Check if commercial tower size is more than required area

On the other hand, if the actual commercial tower size is 370 ft2, the cooling equivalent to 357.14 ft2 of standard tower area can be accomplished with less air and less fan horsepower. From figure in Step 3, the fan horsepower for a tower operating at 90 percent of standard performance is 0.028 hp/ft2 of actual tower area, or 370 x 0.028 = 10.4 hp.


Perry’s Chemical Engineers’ Handbook.

Preliminary Sizing of Compressed Air Receiver

You may already read my blog about how to size air compressor and instrument air capacity. Please check this link if you have not read the article. I hope you find it useful.

As a continuation of the post, I want to share you how to size capacity of compressed air receiver.

Compressed air receiver is used as buffer and storage medium between the compressor and air consumers.

A common formula used to size compressed air receiver is as followed: Read More

Weir trough

Primary Treatment of Wastewater

Aims of primary treatment of wastewater is to separate suspended solids and greases from wastewater. What does primary treatment of wastewater remove? Sedimentation remove both organic and inorganic suspended solids. In addition, skimming, as part of sedimentation tank, remove grease, oil, scum, and floating solids.

Primary treatment of wastewater includes primary sedimentation (also called clarification), microscreen, Imhoff tanks. In most facilities, primary treatment is used as preliminary step ahead of biological treatment. Read More

Wastewater Treatment – How Wastewater is Treated

In earlier posts, we learned sources of wastewater, which are domestic wastewater, industrial wastewater, and infiltration/inflow. In this post, I want to share to you how wastewater is treated.

Wastewater is treated at wastewater treatment plants before it is permitted to be discharged to the environment/water bodies. Basic function of wastewater treatment is to speed up the natural processes of water purification. Read More

Where Does Wastewater Come From

Where does wastewater come? This basic question shall be answered if we want to design a wastewater treatment system. Source of wastewater, its characteristics, and its flow rate, will influence the type of technology to treat the wastewater.

Components that make up the wastewater depend on the type of collection systems. Urban wastewater that contribute to a wastewater treatment is originated from the following three main resources:

  • Domestic (also called sanitary) wastewater. This type of wastewater is discharged from residential districts, commercial districts, institutional facilities, or recreational facilities.
  • Industrial wastewater. Wastewater which predominantly consists of industrial waste.
  • Infiltration/inflow.
    • Infiltration is water entering a sewer system including service connections, defective pipes, pipe joints or manhole walls.
    • Inflow is the water discharged into a sewer system from roof leader, cellar, yard and area drains, foundation drains, cooling water discharges, drains from springs and swampy area, manhole covers, cross connections from storm and combined sewers.

Read More

What Is Wastewater Treatment  

After a quite long absence of updating this blog, I want to begin this March’s post with refreshing our knowledge about wastewater treatment. Let’s begin with one fundamental question: what is wastewater treatment?

In general, wastewater treatment is a process converting wastewater into effluent that can be discharged back into the environment. This terms contains at least four keywords, which are wastewater, effluent, converting process, and environment.

Sewage wastewater

Read More

Cooling Pond Sizing

In this post, I want to share to you how to size cooling pond. Cooling pond is used to remove heat from water by means of air. Example of application of cooling pond is to remove heat from brine water in geothermal power plant facilities.

To design cooling pond, you need process data and environment data. Process data are flow rate of liquid to be cooled, initial temperature, final temperature, and density of liquid. Environent data are relative humidity, wind velocity, average air temperature, and solar heat gain. Here is example of cooling pond sizing. Read More

Sedimentation basin

Visiting Drinking Water Treatment Plant in Tirtawening

On December 2017, I got an opportunity to visit drinking water treatment plant in Tirtawening, Bandung, which is near my college. It was a very amazing experience, because this is my first experience visiting water treatment plant. And also, experience like this is very rare after I entered working environment.

This site visit is actually a part of water treatment plant training. I will share you about this training in different post.

Drinking water treatment facility in Tirtawening is actually the biggest one in Indonesia. It processed 2000 liter/second water, from two trains (rate of each trains is 1000 liter/second). 1900 liter/second water is sent to customers and 100 liter/second water is own used. Read More