Why cool the water (part 3)

The ability of the air to cool water has many practical benefits.

As mentioned in the previous post, one way to transfer heat from one element to another is to put them in contact with each other (conduction). This is one of the principles used in cooling water; by putting water in contact with water as much as possible.

Water is dispersed as much as possible in order to break water drops. This action is repeated continuously so as to avoid that the reforming of the drops by the power of attraction of the water. Or, water can be conveyed in rivulets, layers that continuously break down and so on ...

In other words, the largest possible water surface is offered to the air, the greater the surface in contact with the air, the greater the flow of heat by contact or conduction.

It's not just the principle can be exploited to cool the water with air. During the air-water contact another phenomenon occurs. The air has the ability to absorb water up to its saturation. The capacity varies depending on the difference of air temperatures. If the air is cold, even if very dry, it can absorb very little water (a few grams per cubic meter).

If the air is warm, the capacity to absorb water increases dramatically. Therefore: in summer the air has a the capacity to absorb humidity and significant water. If water is transferred from water in order to be cooled by air, the heat contained in that water is also being transferred. And this is what we're looking for. This way the amount of heat that is transferred from the water to be cooled by air is very significant. In winter we cool the water by conduction, and in summer we cool water by means of a phenomenon called "mass transfer ". 

When we talk about conduction we mean only conduction, in the summer, in some air conditions, we will have reverse flow of heat; air is hotter than water and, hence, water heats up by minimum part, but greater heat transfer happens by mass of water. 

Another consideration is when we cool water in the winter. Because the output water is warmer than the air inlet, the air itself heats up and thus increases the capacity to absorb water. In spring and autumn season, it is common to cool water using the two phenomena to the benefit of the water temperature in outlet.

Where are the plant used for cooling water?

The cooling of water is the last action of a heat disposal process. Water is used as an element to transport energy (heat), and if at one point heat is absorbed (all machines discard energy), in another point this energy must be disposed always as heat.

Differentiation of plants for cooling water at low temperature required for the process of specific production processes: plastic mold cooling, air conditioning.

Heat disposal is obtained by cooling the element that is used for heat transport (energy): in our case water. The temperature of the cooled water must be chosen in the design phase because it is crucial for the overall performance of the system.

The analysis of the plant allows to know if it's sufficient to dispose only heat with temperatures from water cooled relatively high at 40 to 50 ° C, as in the case of oil-water heat exchanger where oil can be cooled up to 50 ° C, or the temperature of the water has to be the lowest and obtainable in an economical way, such as refrigerators.

Why cool the water (part 1)

Water is a precious commodity. Spoiling water is not only a waste of money, it also destroys a natural resource that is otherwise beneficial to all of us. Without saving water, irrigation and drinking water sources will be compromised. 

Machinery, labor, efficiency, and energy scrap to dispose of.

Today, machines are used to produce goods that help us to live a better life and to manufacture a whole range of products. 

Machines use energy to transform work into products. Not all of the energy used will be transformed into work; part of it will be dispersed in various forms such as friction and, in any case, heat. 

Hence, heat is energy scrap and its amount depends on the efficiency of the machine.

Water as a means of transporting energy as heat.

The heat transmitted from machines that is no longer used, must be dispersed. And, the first think that comes to mind is to use air as a cooling element. However, if you think about it, it would take an enormous quantity of air to cool industrial machines such as welders, chemical reactors, or even a machine for molding plastics. Another element available in nature and much more effective than air is water. The specific heat, the ability to "hold" the heat, make it such that water is much more convenient to use it as a mean of transporting intense heat, that is, scrap energy from operating machines.

Need to recycle the water.

Water heats up when used to cool machines. If the same water is used again to cool the same machine, at the end of the second cycle the water will be even hotter than before. After several cycles the water temperature equals to that of the machine, therefore heat transporting will be no longer beneficial. This is because after a period of time, more or less long, the water and the machine will have the same temperature. At this point, the machine can no longer expel the heat and its efficiency will decrease dramatically up to the point where it will fatally block production, for which the machine itself was intended to operate. 

Hence, the need to throw away hot water and use fresh water. But, is it better to use fresh water in a squanderly way or reuse the same hot water coming out of the machine that is cooled down and put it back into the circuit.

Examples of amounts of water needed in manufacturing plant. 

Energy performance in manufacturing machines is unfortunately very low. In some cases machine performance can be around 70%, but most machines perform below 50%. This means that the majority of energy must be disposed as heat. If the heat is disposed with water, then the water is either thrown away or put back into the circuit. Throwing it all away would be a big waste. 

Let's try to calculate how many people consume the same water in a small plastic molding plan:

a) a plastics molding plant that employs 20-30 people, needs 40 cubic meters per hour of water, or more than 40,000 liters per hour, equivalent to 40,000 x 24h = 960,000 liters per day, to cool its machines.

b) a person in a well-being environment consumes 250 liters of water per day.

The result is that an average small-medium size plant consumes as much as a country of 3,840 inhabitants.

Other examples can apply to steel plants, oil refineries, cold storage and any other manufacturing plant.

Film fill vs. TURBOsplash PAC ®™ ... after 3 years

We can design any cooling tower with our TURBOsplash PAC ®™

Induced draft counter flow data chart

Counter Flow 4 cells 14 m x 14 m

TURBOsplash PAC ®™

Evaporative Cooling Towers (part 2)

WATER-AIR TURBULENCE

Water cooling takes place according to three phenomena:

1. CONDUCTION: (disposal of sensible heat1).

The heat flows from a region with a higher temperature to a region with a lower temperature through one or more means that are in direct physical contact, in compliance with the laws of heat conduction (Fourier Transform). Energy is transmitted by direct contact between the molecules, and the potential that governs this phenomenon is the difference of temperature between the two different regions.

2. EVAPORATION: (disposal of latent heat2).

The change of state from liquid to vapor causes the absorption, from the side of the evaporated mass unit, of a quantity of heat called evaporation latent heat, which causes the cooling of the mass unit that remained in the liquid state.

The potential difference that governs this phenomenon is due to the difference of concentration levels, which for the gas phase it's expressed in terms of partial pressures assuming we're using assimilated gases to ideal gases.

    The loss of energy and, consequently, the obtained cooling, with the transfer of latent heat, is important:  to evaporate one kilogram of water there is a need to dispose of approximately 540 kcal or 2257 kJ (evaporization latent heat), i.e.,  100 liters of water gets cooled to about 6 ° C ..

3. IRRADIATION

Electromagnetic waves propagation, in absence of physical contact, make heat flow from a body that has a greater temperature to a body with a lower temperature. When the radiation emitted by a body meet another body, their energy remains absorbed near the surface.

Thermal exchange by irradiation becomes always more important as the temperature of a body increases, and in the case of temperatures close to the atmospheric ones, the irradiation can be neglected.

We can again highlight the concept that the evaporative towers are essentially based on the use of latent heat by mixing air stream with water flow, by which a small part evaporates by passing through the air current, taking away latent heat from the remaining water.

The heat removed from the water will be dispersed in the environment as water vapor that is contained in the outgoing air stream, so that it will be more humid and warmer with respect to the incoming air.

The water exiting the tower will be colder but in smaller quantities than the incoming water. This is the reason that the tower is replenished with make-up water in quantities (Wo) equal to that lost by evaporation and temperature qo.

Principles

1. Thermal balance (first principle of thermodynamics)

In the following set of equations, we are neglecting the effect of the barometric pressure; although in some cases, for example, plant installations that are 500 meters above sea level, the barometric pressure is important because it helps to vary pressures relative to air.

Cooling system thermal balance

1. Q + (Wo qo ).= L(i2 - i1)
2. Q = W( q2 - q1).+ Wo( q1 - q0).
3. W( q2 - q1).+ Wo( q1 ).= L(i2 – i1)

From the moment the amount of make-up water (Wo) is not thermally significant with respect to the total quantity of water W.

1Sensible heat is the one that transferred/subtracted to/from a body varies the temperature.

2Latent heat is the one that transferred/subtracted to/from a substance causes the physical state to vary.

Designing a cooling tower could be a risky business ... if not done correctly!

Vulnerabilities(1)	Threats(2)	Risks(3)
Evaluation error of how much thermal load to dispose of	Plant served by the tower is lacking efficiency	A decrease in production and/or possible damage to the plant
Lower cost	Objective not achieved	Ineffective or useless project

A cooling tower project, like every project, could result in vulnerabilities if not designed correctly. 

As we mentioned in our previous post, one of the causes of why cooling towers do not work properly is bad design. This issue is leading to the topic of risk management.

For this purpose, we will limit our discussion to the design of the tower and how to analyze issues that otherwise could result in risk and endanger the achievement of objectives such as performance, energy saving, …

It is important to identify potential risks.
Early detection of risk is important because it is easier, less costly, and less disruptive to make changes and correct work efforts during the earlier, rather than the later, phases of the project.

Hence, it's important to define a risk management strategy that:

• identifies and analyzes risks,
• manages the identified risks,
• implements a mitigation/contingency plan when needed.

⁽¹⁾ Weaknesses or flaws in the design process. The vulnerability can be seen as that part of a system, explicitly or implicitly, where security measures are either absent, reduced or compromised. This represents a weak point in the system, allowing an attacker to compromise the level of security of the entire system.

⁽²⁾ Anything that can exploit a vulnerability to cause damages. Alerting?

⁽³⁾ The potential for loss, damage or destruction as a result of a threat exploiting a vulnerability. Here we have uncertainty which can result in a positive or negative result, regardless of our will or capacity.

The importance of water in the cooling tower industry - Water (part 9)

HOW TO MEASURE THE EFFICIENCY OF A COOLING TOWER

 

In the design process of a cooling tower, there is a need to have at least seven data values or rather 7 variables. If only one of these values is changed, the result will be a cooling tower with different dimensions.

Some of this data or design values are questionable, such as the temperature of the air at wet-bulb temperature, that seems to shift every year for speculation reasons.

To measure the efficiency of each tower, there is a need to know the exact design data and the theory that allows designing the tower, hence, knowing the values detected by lab effective testing.

All this will be treated in another chapter with interesting considerations.

Now we shall discuss how to evaluate the efficiency of the cooling tower in a simple and practical way.

We shall use the method that will allow, at least, to compare the efficiency of the tower at the any given time with the efficiency of the tower at the time it was installed: in other words, the degradation of efficiency (if it exists).

The main element for cooling water is air. The amount of air is essential for the amount of heat to dissipate, temperature, etc.

The amount of air measurement is synonymous of tower efficiency.

The degradation over time can decrease the amount of air in the tower because there are occlusions within the filling material that block the passage of air. Occlusions may originate from collapsed material, limestone, dust, algae, etc.

The water will always circulate.

The masses of water and air inside the tower are huge. The water weight is about 15,000 to 30,000 kg/m² of the tower. Thus, the water will always fall via preferential routes: holes or by laminating on the tower walls. The amount of air passing through the tower is of vital importance.

A quick way to know the efficiency of the cooling tower is to measure the amount of air all you need to is to measure the speed of the air incoming to the tower or outgoing from the tower.

The speed in m/s and is measured with an anemometer (a very simple tool with fan). This tool is used to measure wind speed, etc. Hence, the speed through the cross-section (m² top view) of the tower MUST be between 2.5 m/s and 4 m/s.

If the speed is lower than 2.5 m/s, the amount of air through the tower is very low and the cooling is compromised. The tower will be not efficient!

This method is basically a rule of thumb, but it serves as an alarm that a more accurate review is required.

The importance of water in the cooling tower industry - Water (part 10)

WHAT ARE THE CONSEQUENCES OF A COOLING TOWER OPERATING AT LOW EFFICIENCY?

Cooling tower detailed calculations

A low efficient cooling tower brings very serious consequences.

Bruno Neri

The tower is part of a system designed to dispose residual waste heat from the production plant or other primary system. The lower efficiency of the tower affects the performance of the primary plant with considerable waste of energy and, most of all, reduction or lack of production.

CONSTRUCTION OF A COOLING TOWER: TIPS ON ITS COMPONENTS AND THEIR USE.

As we saw, the cooling tower is an essential part of the plant system and, generally, it is separated from the primary plant system to which it drives.

The cooling tower is normally ignored until it goes into failure. Hence, the choice of components is of utmost importance.

Choose a tower made of stainless steel. Towers that need to be installed in heavy environments, such as chemical industries, choose polyester reinforced with glass fiber.

We have witnessed towers that have been operating for over 30 years, in these heavy environments, in perfectly stable structure.

Other useful tips and / or necessary will be exposed our next documentation work for publishing:

"A practical guide for the design of components that impact cooling tower thermal efficiency"

The importance of water in the cooling tower industry - Water (part 9)

 HOW TO MEASURE THE EFFICIENCY OF A COOLING TOWER

 

In the design process of a cooling tower there is a need to have at least seven data values, or rather 7 variables. If only one of these values is changed, the result will be a cooling tower with different dimensions.

Some of this data or design values are questionable, such as the temperature of air at wet-bulb temperature, that seems to shift every year for speculation reasons.

To measure the efficiency of each tower, hence, there is a need to know the exact design data and the theory that allows to design the tower, knowing the values detected by lab effective testing.

All this will be treated in another chapter with interesting considerations.

Now we will discuss how to evaluate the efficiency of the cooling tower in a simple and practical way.

We shall use the method that will allow, at least, to compare the efficiency of the tower at the any given time with the efficiency of the tower at the time it was installed: in other words, the degradation of efficiency (if it exists).

The main element for cooling water is air. The amount of air is essential for the amount of heat to dissipate, temperature, etc.

The amount of air measurement is synonymous of tower efficiency.

The degradation over time can decrease the amount of air in the tower because there are occlusions within the filling material that block the passage of air. Occlusions may originate from collapsed material, limestone, dust, algae, etc.

The air will always circulate.

The masses of water and air inside the tower are huge. The water weight is about 15,000 to 30,000 kg/m2 of the tower. Thus, the water will always fall via preferential routes: holes or by laminating on the tower walls. The amount of air passing through the tower is of vital importance.

A quick way to know the efficiency of the cooling tower is to measure the amount of air all you need to is to measure the speed of the air incoming to the tower or outgoing from the tower.

The speed in m/s and is measured with an anemometer (a very simple tool with fan). This tool is used to measure the wind speed, etc. Hence, the speed through the cross section (m2 top view) of the tower MUST be between 2.5 and 4 m/s.

If the speed is lower than 2.5 m/s, the amount of air through the tower is very low and the cooling is compromised. The tower will be not efficient!

This method is basically a rule of thumb, but it serves as an alarm that a more accurate review is required.

Evaporative Cooling Towers (part 2)

Water cooling takes place according to three phenomena:

1. CONDUCTION: (disposal of sensible heat1).

The heat flows from a region with a higher temperature to a region with a lower temperature through one or more means that are in direct physical contact, in compliance with the laws of heat conduction (Fourier Transform). Energy is transmitted by direct contact between the molecules, and the potential that governs this phenomenon is the difference of temperature between the two different regions.

2. EVAPORATION: (disposal of latent heat2).

The change of state from liquid to vapor causes the absorption, from the side of the evaporated mass unit, of a quantity of heat called evaporation latent heat, which causes the cooling of the mass unit that remained in the liquid state.

The potential difference that governs this phenomenon is due to the difference of concentration levels, which for the gas phase it's expressed in terms of partial pressures assuming we're using assimilated gases to ideal gases.

    The loss of energy and, consequently, the obtained cooling, with transfer of latent heat, is important:  to evaporate one kilogram of water there ia a need to dispose of approximately 540 kcal or 2257 kJ (evaporization latent heat), i.e.,  100 liters of water get cooled to about 6 ° C ..

3. IRRADIATION

Eelectromagnetic waves propagation, in absence of physical contact, make heat flow from a body that has a greater temperature to a body with a lower temperature. When the radiation emitted by a body meet another body, their energy remains absorbed near the surface.

Thermal exchange by irradiation becomes always more important as the temperature of a body increases, and in the case of temperatures close to the atmospheric ones, the irradiation can be neglected.

We can again highlight the concept that the evaporative towers are essentially based on the use of latent heat by mixing air stream with water flow, by which a small part evaporates by passing through the air current, taking away latent heat from the remaining water.

The heat removed from the water will be dispersed in the environment as water vapor that is contained in the outgoing air stream, so that it will be more humid and warmer with respect to the incoming air.

The water exiting the tower will be colder but in smaller quantities than the incoming water. This is the reason that the tower is replenished with make-up water in quantities (Wo) equal to that lost by evaporation and temperature qo.

Principles

1. Thermal balance (first principle of thermodynamics)

In the following set of equations, we are neglecting the effect of the barometric pressure; although in some cases, for example, plant installations that are 500 meters above sea level, the barometric pressure is important because it helps to vary pressures relative to air.

Cooling system thermal balance

1. Q + (Wo qo ).= L(i2 - i1)
2. Q = W( q2 - q1).+ Wo( q1 - q0).
3. W( q2 - q1).+ Wo( q1 ).= L(i2 – i1)

From the moment the amount of make-up water (Wo) is not thermally significant with respect to the total quantity of water W.

1Sensible heat is the one that transferred/subtracted to/from a body varies the temperature.

2Latent heat is the one that transferred/subtracted to/from a substance causes the physical state to vary.

Evaporative Cooling Towers (part 1)

The system that allows used water that was heated during the cooling of a technological system to be cooled, thus making it again, and continuously, available to give continuity to the cooling cycles, is called "evaporative cooling tower”.

Liquid refrigerant cooling is obtained through part evaporation of the same because of the simultaneous presence of heat transfer and matter transport phenomena, whose effects are increased with forced ventilation.

The towers are composed of an enclosure made of various kinds of shapes and materials, even if the most prevalent geometry is that of rectangular parallelepiped. Inside there is a motor fan that activates air circulation that is counter-flow with respect to the water, that falls from the top of the tower; once cooled, it's collected in a tank and put at the base of the structure, and then put back in the refrigeration cycle.

Diagram of a counter-flow cooling tower

Another tower configuration is that of 'cross-flow'. This is where the descending falling water gets hit by a stream of air, crossing it transversely horizontally.

Diagram of a cross-flow cooling tower

All the towers, except those with natural ventilation, are equipped with one or more fans, which can be both axial (also called helical) and radial (centrifugal).

The fans can be placed either at the tower air inlet (forced fan) or at the outlet (induced fan), but the centrifugal fans are just as pressing (forced).

The efficiency of the evaporative cooling system is directly proportional to the surface and the time for which the two moving fluids come in contact with each other; to further increase this feature, different types of "fill material” are used with the specific aim to increase the contact surface and, hence, the heat exchange between the two fluids by diverting, breaking and maintain, as much as possible, in contact with each other.

Inside the cooling tower, thanks to the humidification phenomenon, heat and mass transfer take place simultaneously, i.e. the evaporation of a liquid substance into a gas.

The transport of mass consists in transferring a fluid solution component from a region that has a higher concentration to a lower one; in our case, this takes place between two different phases and, simultaneously, with heat transfer .

What are the consequences of a poorly efficient cooling tower?

The lower the efficiency of a tower the more serious the situation in terms of performance and productivity. The tower is part of an overall system designed to dispose residual heat from a production plant or at least from an aforetime primary system. A decreasing of efficiency in cooling tower affects the yield of the primary system with a considerable waste of energy and, especially, reduced production.

Counter-flow heat exchanger that removes heat from water and transfers it to air.

A cooling tower can also be defined as a cross-flow heat exchanger that removes heat from water and transfers it to air. 

Click on "Energy Loop Assessment for Water Cooling Tower" to see how to assess energy in a production plant scenario served by a water cooling tower and to see the correlation between energy, efficiency and productivity.

Designing a cooling tower could be a risky business ... if not done correctly!

Vulnerabilities(1)	Threats(2)	Risks(3)
Evaluation error of how much thermal load to dispose of	Plant served by the tower is lacking efficiency	Decrease in production and / or possible damage to the plant
Lower cost	Objective not achieved	Ineffective or useless project

A cooling tower project, like every project, could result into vulnerabilities if not designed correctly. 

As we mentioned in our previous blog, one of the causes why cooling towers do not work properly is bad design. This issue is leading to the topic of risk management. For this purpose, we will limit our discussion to the design of the tower and how to analyze issues that otherwise could result into a risk and endanger achievement of objectives such as performance, energy saving, …

Hence, it is important to identify potential risks. Early detection of risk is important because it is easier, less costly, and less disruptive to make changes and correct work efforts during the earlier, rather than the later, phases of the project.

Said that, it's important to define a risk management strategy that:

•  identifies and analyzes risks,
• manages the identified risks,
• implements a mitigation/contingency plan when needed.

⁽¹⁾ Weaknesses or flaws in the design process. Vulnerability can be seen as that part of a system, explicitly or implicitly, where security measures are either absent, reduced or compromised. This represents a weak point in the system, allowing an attacker to compromise the level security of the entire system.

⁽²⁾ Anything that can exploit a vulnerability to cause damages. Alerting?

⁽³⁾ The potential for loss, damage or destruction as a result of a threat exploiting a vulnerability. Here we have uncertainty which can result in a positive or negative result, regardless of our will or capacity.

What happens if the tower is not working properly? First thing, don't panic!

What happens if the tower is not working properly? First thing, don't panic!

Actually, many things could go wrong!  We might not even be aware of the many inconveniences that can occur to an industrial plant when the water cooling tower is not working properly.​

Some of the causes are:

• malfunctioning of one or more components that make up the tower (breakage, wear, fluid hammer, high temperature)
• encrustation, algae and clogging of the water or air side passages
• bad design

We shall focus on the last point, i.e., bad design.

Bad design is due to:

• thermal load assessment error
• water tower temperature outlet assessed with great accuracy
• wrong design assumption for the we-bulb air temperature

What will happen in the various plants?

Usually the tower, used in industry, serves:

• steelworks
• refineries
• plants for the production of chemical products
• others

For each different plant, the damage caused by a non-functioning tower can be calculated in terms of production lost.

In the next posts, we will analyze the risk and try to resolve bad accuracy in the design work with the help of our followers.

Computer Flow Design Processing

The following diagrams shows the change in static and dynamic pressure inside the TURBOsplash PAC fill material/evaporative panels, depending on the speed of the air.

CFD Processing

This temperature approach graph is essential for cooling tower design. But, is it enough for comparing/verifying projects and/or real value results?

The importance of water in the cooling tower industry - Water (part 10)

WHAT ARE THE CONSEQUENCES OF A COOLING TOWER OPERATING AT LOW EFFICIENCY?

Cooling tower detailed calculations

A low efficient cooling tower brings very serious consequences.

 

Bruno Neri

The tower is part of a system designed to dispose residual waste heat from the production plant or other primary system. The lower efficiency of the tower affects the performance of the primary plant with considerable waste of energy and, most of all, reduction or lack of production.

CONSTRUCTION OF A COOLING TOWER: TIPS ON ITS COMPONENTS AND THEIR USE.

As we saw, the cooling tower is an essential part of the plant system and, generally, it is separated from the primary plant system to which it drives.

The cooling tower is normally ignored until it goes into failure. Hence, the choice of components is of utmost importance.

Choose a tower made of stainless steel. Towers that need to be installed in heavy environments, such as chemical industries, choose polyester reinforced with glass fiber.

 

We have witnessed towers that have been operating for over 30 years, in these heavy environments, in perfectly stable structure.

 

Other useful tips and / or necessary will be exposed our next documentation work for publishing:

"A practical guide for the design of components that impact cooling tower thermal efficiency"

The importance of water in the cooling tower industry - Water (part 9)

 HOW TO MEASURE THE EFFICIENCY OF A COOLING TOWER

 

 

In the design process of a cooling tower there is a need to have at least seven data values, or rather 7 variables. If only one of these values is changed, the result will be a cooling tower with different dimensions.

Some of this data or design values are questionable, such as the temperature of air at wet-bulb temperature, that seems to shift every year for speculation reasons.

To measure the efficiency of each tower, hence, there is a need to know the exact design data and the theory that allows to design the tower, knowing the values detected by lab effective testing.

All this will be treated in another chapter with interesting considerations.

 

Now we will discuss how to evaluate the efficiency of the cooling tower in a simple and practical way.

We shall use the method that will allow, at least, to compare the efficiency of the tower at the any given time with the efficiency of the tower at the time it was installed: in other words, the degradation of efficiency (if it exists).

The main element for cooling water is air. The amount of air is essential for the amount of heat to dissipate, temperature, etc.

The amount of air measurement is synonymous of tower efficiency.

The degradation over time can decrease the amount of air in the tower because there are occlusions within the filling material that block the passage of air. Occlusions may originate from collapsed material, limestone, dust, algae, etc.

The air will always circulate.

The masses of water and air inside the tower are huge. The water weight is about 15,000 to 30,000 kg/m2 of the tower. Thus, the water will always fall via preferential routes: holes or by laminating on the tower walls. The amount of air passing through the tower is of vital importance.

A quick way to know the efficiency of the cooling tower is to measure the amount of air all you need to is to measure the speed of the air incoming to the tower or outgoing from the tower.

The speed in m/s and is measured with an anemometer (a very simple tool with fan). This tool is used to measure the wind speed, etc. Hence, the speed through the cross section (m2 top view) of the tower MUST be between 2.5 and 4 m/s.

If the speed is lower than 2.5 m/s, the amount of air through the tower is very low and the cooling is compromised. The tower will be not efficient!

 

This method is basically a rule of thumb, but it serves as an alarm that a more accurate review is required.