In this article, we will learn what is evaporative cooling, cooler its basic definition, meaning, process, how does it work, types, the difference between air conditioners and evaporative cooler, applications, advantages, disadvantages, etc. Let’s explore!
What is Evaporative Cooling & Cooler? Definition
Definition of Evaporative Cooling
Evaporative word is derived from “vapor,” which means water drops in gas, e.g., fog, moisture, steam, etc. Evaporative cooling, also known as adiabatic cooling, is a technique that helps cool a surface or surrounding air by using the water evaporation process. It can also be defined as converting water into a gas by using thermal energy, which leads to the cooling of the surface. In this process, water is used as a refrigerant.
Evaporative Cooler
The concept of evaporative cooler lies in the name itself. It is basically a device that uses evaporative cooling or evaporation.
- Dont be confused with air conditioners vs evaporative coolers, these are different, we will discuss at the end of this article.
- As it is related to evaporation, evaporative cooler is not effective near sea coast or high humid regions.
Evaporative Cooling & Cooler Basic Concept
Phenomenon
Evaporation is a scientific phenomenon in which water changes into vapors. This process needs heat as energy to get in the air. When a water molecule gets enough heat, it will escape into the air. When a molecule leaves the liquid, it will reduce the overall temperature of the liquid. A downfall in temperature will lead to a sense of cooling, also known as evaporative cooling.
Example
The most lucid example of evaporative cooling is the sweating process in the human body. Imagine yourself on a hot day of summer. You come out of your room for work. There is a high temperature outside. After some time, your body starts sweating, and tiny drops of water appear on your skin.
A gust of breeze passes by you; you will feel a sense of cooling on your skin. The drop of water which escaped into the air absorbed heat and reduced the body’s temperature. This phenomenon is called evaporative cooling.
Explanation
Water changes its forms from solid to liquid and liquid to gas; it is also known as the water cycle. All changes in the hydrologic cycle involve transferring energy from one form to another. Evaporation is an essential part of the hydrologic process.
It is estimated that 90% of humidity and moisture come from the evaporation process. It is done by the oceans, rivers, lakes, and ponds in sunlight. It helps maintain natural cycles and our environment and is also a helpful technique in separating clean water from wasteful water.
Industries use the evaporation process in the preparation of salt and other chemicals. It is also very effective in our everyday life, e.g., drying clothes, wet floors, and cooling down hot liquids. But the question is, how does evaporation take place?
How Does Evaporative Cooling and Cooler Work?
Evaporative Cooling and cooler working principle
Molecules in a liquid move freely, but they stay together. When we heat a liquid, molecules start moving towards each other. As temperature increases, motion among molecules increases gradually. Molecules start colliding with fellow molecules. When a molecule gets enough heat and moves faster, it escapes into the air. Still, there’s a question about how evaporation causes cooling?
How does evaporative cooling or cooler cause cooling?
Liquids on evaporation have cooling effects. It differs from liquid to liquid and depends on its boiling points and how quickly a liquid evaporates. For example, alcohol has a more cooling effect than water. The reason is alcohol is more volatile, and it escapes in the air quicker than water.
A water molecule absorbs heat from its surroundings as water has a high heat capacity. When a molecule escapes in the air, it takes heat in itself. The heat a water vapor takes comes from the evaporation surface. As vapors take the heat, it causes cooling effects on the surface, called evaporative cooling. To understand the whole concept, we will discuss its factors and some examples of how evaporation and evaporating cooling help maintain our body and natural environment.
Evaporative cooling is a natural process
Evaporative cooling is a natural process. Here’s how it’s natural:
Evaporative cooling in plants
Evaporation takes place in plants through transpiration. Plants need water to grow. They take water from the soil through their deep roots. This water moves from soil to stem and then towards leaves. The plant also consists of tiny pores, as in human skin.
These pores are known as stomata through which respiration takes place. Due to direct exposure to sunlight, water evaporates from these stomata. It gives plants a cooling effect which prevents them from overheating due to intense sunlight. It not only benefits plants but is also a source of human breath. When stomata open to evaporate water, it also omits oxygen needed by most living things for survival. We can feel this cooling effect by sitting beneath the trees on sunny days of Summer.
Evaporative cooling due to wind
Wind also increases the evaporation rate and also gives a sense of cooling. If a person comes out of a swimming pool and a gust of wind passes by him, he will feel a sense of cooling because the wind takes more vapors from our body with itself. It is also known as the so-called wind chill factor.
Temperature regulation and evaporative cooling in the human body
The human body uses water as a temperature stabilizer because water absorbs heat and transforms it through the evaporation process. When the body burns the calories, it produces heat. Water molecules in human muscles tend to absorb this heat.
Those molecules travel in the body’s bloodstream and carry the heat through sweat glands. The hypothalamus sends a sensory message to sweat glands when blood temperature arises due to heat-containing molecules. Sweat glands open and evaporation takes place. It is how evaporation maintains overall body temperature and gives us a sense of cooling.
This technique is also valuable for salt preparation. In this process of evaporation, salt-occupying water is placed in sunlight. Sun evaporates all the water from salt. Harvesting machines gather the remaining salt. Many heat chambers are also used to carry out this process.
Factors affecting Evaporation & Evaporative Cooling
The major factors affecting evaporation include:
- Thermal energy
- Boiling point
- Saturation of the air
- Air pressure
If there is no thermal energy, there is no evaporation. Because heat breaks the bonds between water molecules, and it evaporates quickly. Water starts evaporating at its boiling point, i.e., 100 C(Celsius) and 212 F(Fahrenheit). Other factors also affect the evaporation process.
It also depends upon the saturation of the air. If air is already occupied by other elements or the air’s humidity level is 100%, there is zero chance of evaporation of more water molecules. Another factor is air pressure. If the air pressure is very high on the surface of the liquid, there are very low chances for water to evaporate. But if the air pressure is low, there is more evaporation. Therefore, strong winds and storms push back the evaporation level.
Types of Evaporative Coolers
Evaporative cooling is an old technique used to cool hot air. We find its precursors back in ancient Egypt when Egyptian people achieved it by hanging wet blankets on the doors and windows. They also had servants for this purpose who fanned them. Although scientific development changed the whole system, the fundamental principle of cooling remained the same.
An evaporator cooler is a device that cools the air through water evaporation. It is different from air conditioning systems. It is a very eco-friendly cooling system but not effective in humid environments. Various air coolers include a direct water cooler, indirect water cooler, and mounted water cooler. Some are portable, while others are fixed to a specific part. It also depends on the size of space and other geographical conditions. We will explain each of them in detail;
Direct Evaporative Cooler
What is Direct Evaporative Cooler?
These are also known as swamp coolers. These are very simple operating devices used in the majority of houses for cooling purposes all around the world. These are more energy-efficient devices and very easy to operate. These coolers are very inexpensive and easy to install. It also uses less electrical energy as compared to other cooling systems. There is no need for a specific installation; anyone with basic knowledge can operate it.
If someone bought the device, they could operate it by putting water in its pad and plugging the switch into the power source. It can also be an economical alternative to costly air conditioners because there is no need for extra refrigerants.
Construction and Working of Direct Evaporative Cooler
It consists of filters, direct heat exchange, water pads, a recirculation pump, an exhaust fan, and water sprays. A larger fan pulls hot air inside the device and passes it through wetted membranes or water pads in this system. Then the hot air goes through water pads which provides a large surface area for evaporation.
Water is sprayed on the membrane, which causes vapor formation with external air. Water droplets from the membrane dip down in a pan and recirculate in the system. It increases the humidity level of the air. Air is pushed outside with a fan in the room or surrounding environment. It works very well in less humid environments by lessening the evaporation rate.
For example, we can clarify it better if a person wraps up a wet handkerchief around his neck and stands in front of a fan. That wet handkerchief will absorb heat from his body and convert water molecules into vapors. The direct evaporating cooling system applies the same principle for working. It takes the hot air from outside, passes it over water droplets, and pushes out cool air. It changes the warm, dry air into the cool, moist air. Proper maintenance and regular cleaning are required for optimal working.
Indirect Evaporative Cooler
What is Indirect Evaporative Cooler?
The indirect evaporative coolers are pretty different from direct or swamp coolers. They are fixed rather than portable coolers. Moreover, the indirect coolers don’t affect the humidity level of a space. It reduces the temperature of a space where it is cooling.
Sometimes it needs a duct system to transfer air in the required area. However, they are more expensive than direct evaporative coolers and cheaper than air conditioners. They are very efficient in cooling large spaces as compared to direct coolers. They are used in restaurants, commercial areas, industrial spaces, and other businesses. This cooling method is best for the places which need less humid cooling air.
Construction and Working of Indirect Evaporative Cooler
It also works on the same principle of direct evaporative coolers with some distinction. An indirect evaporative cooler consists of two extra components: metal tubes and an extra fan. The heat exchanger blows the hot air over the wet metal tubes, water evaporates, and causes cooling.
The moist air is exhausted towards the outside. It cools down the exterior surface of the heat exchanger. Hot external air is drawn through those metal tubes, which blows down the cool air without humidity. Its cooling progress increases when there is an increase in outside temperature. It gives more cooling up to 5-degree Celsius and 60% less moisture than the direct evaporating system. It also uses 15-20% less air than the direct coolers.
Mounted Air Cooler
What is Mounted Air Cooler?
Mounted air coolers use the hybrid technique of both direct and indirect evaporative cooling systems. They are larger as compared to direct evaporative coolers. As the name mentioned, it is mounted either on the ground, wall, or roof. Ground mounting requires the installation of the device on ground level.
It is very least efficient, that’s why it is not very popular Because cold air generated near the ground is not much needed. Window or wall mounting is the most favorite and popular place for hybrid air coolers. These are built to maintain room temperature through ventilation and supply of fresh air.
These are made according to the space and need of the location. They are more efficient because they have continuous, direct contact with fresh air. Roof-mounting air coolers are pretty expensive as compared to others. They need extra infrastructure, including ducts that help distribute the cool air. Their maintenance cost is also very high. That’s why these are used very little by private residents. People use such types of evaporative coolers in industrial places.
Working of Mounted Air Cooler
The air is cooled down without humidity at the first stage through the indirect evaporative cooling system. Then the pre-cooled air is passed through a water pad of a direct evaporative cooler. In this way, air gains enough moisture by passing over water.
According to climate changes, it contains relative humidity of 50-70%. This type of cooler is advanced and more effective. It has the ability of both direct and indirect coolers with more effective pads and more efficient motors. It creates a balance between required air moisture and climate conditions.
Application of Evaporative Coolers
Preservation of food in Ancient times
Evaporative cooling is an old phenomenon through which people preserved their foods and liquids in ancient times. Before the advent of refrigerators, porous earthenware pottery and Egyptian pottery Qullahs were used for cooling purposes. People were supposed to cool milk bowls by putting them into cold water.
Evaporative coolers in residential sectors
With time, science has changed the whole scenario. New devices came which are more efficient and easier to use. But they all are legit to their fundamental principles. Now evaporative coolers are very efficient and innovative devices. They have a wide range of applications in both the residential and commercial sectors. Almost most people around the world prefer evaporative coolers for cooling purposes.
- Evaporative coolers are highly recommended for places where the air is hot and humidity is low. It is a blessing, especially for deserts and dry climate areas inhabitants. They are also effective in moderate humid regions, especially where air saturation is less than 60%. But in highly moisturized climates, there is less thermal energy and a low evaporation rate. That’s why they are least efficient in highly humid areas.
- Evaporative coolers are primarily used in households and private residences.
Evaporative coolers in the commercial sector
- They are highly recommended in data centres. The primary rationale is that data centres have thousands of PC systems that produce overheat in the environment; evaporative coolers are the best options to counter this heat and maintain fresh air ventilation. It maintains the inner space of those centres and protects data and hard drives from overheating.
- They also have scope in office buildings.
- Additionally, installing such coolers in offices is essential to maintain a comfortable environment and proper humidity level. They provide fresh air, which is relatively healthy for the wellness and productivity of employees.
- Goods in warehouses are prone to damage by dry climates. This issue can also be resolved by putting evaporative cooling systems in such places.
- Laboratories and hospitals are susceptible places. They need a specific temperature and humidity level for both the patients and drugs. Patients also need fresh air and proper ventilation for their smooth respiration. Installation of evaporative cooling can assure a balanced environment for such sensitive places.
- Despite these unique applications, it is widely used in industries, commercial kitchens, laundry houses, greenhouses, workshops, athletic events, garages, and confinement framings.
Differences between evaporative coolers and air conditioners
- Air conditioners are costly, while evaporative coolers are very low in cost.
- They have a very high uplift installation cost, while some evaporative coolers don’t need any fixation. Some evaporative coolers need installation, but they are less economical than AC.
- Air conditioners use more energy and are less efficient, while air coolers use less energy and are more efficient.
- Evaporative coolers add moisture to the air while AC removes the moisture from the air to take advantage of dry air.
- Evaporative coolers are environment friendly and omit minimal Carbon Dioxide. They use water as a refrigerant. At the same time, AC has much higher emissions of gases and uses artificial refrigerants for cooling purposes.
- Air conditioners require regular checking and cleaning, while coolers are very simple and need less maintenance.
- Air conditioners are efficient in both humid and dry environments, while coolers are less efficient in humid climates.
- The air conditioner recirculates and cools only the inner air of space. That’s why we have to shut the doors and windows of that room. On the other hand, evaporative coolers ventilate the fresh air from outside, and we can keep doors and windows open.
- Air Conditioners are much more effective in small and closed spaces, while coolers are more effective in large spaces.
Advantages of Evaporative Coolers
Let’s see the advantages of evaporative coolers, or evaporative cooling:
- They are very cost-effective in the case of price and maintenance.
- They are also very cheap to install. A person with some basic knowledge can quickly run it.
- It consumes very little electric energy, almost one-fourth of energy compared to other refrigerators.
- It consists of a small electric motor while AC has more than three electric motors.
- It moisturizes the air and maintains a natural environment for products.
- It circulates the fresh air from outside, which is best for the health of residents.
- As it uses water as a refrigerant, it is very eco-friendly.
- It can be used in large spaces, including industries and factories.
- It works best in dry climates, especially in deserts and hot areas.
Disadvantages of Evaporative Coolers
Let’s see the disadvantages of evaporative coolers or evaporative cooling:
- The main disadvantage of this type of cooling is that they are significantly less efficient in highly humid areas. They produce cool air through the process of evaporation. If the moisture saturation of air is 100%, there is no chance for further evaporation.
- They have very little control over temperature as compared to air conditioning systems.
- There is also a high risk of water leakage. It is also estimated that evaporative coolers use more than 25 litres of water per hour. It also depends on temperature and humidity level.
- During ventilation of air from outside, there is no proper filtration process. It can create problems for asthma and respiratory patients.
Conclusion
An Evaporative cooling system is innovative and advanced machinery for cooling purposes. It is relatively cost-effective in the case of purchasing, maintenance, and installation. It uses less electronic energy and is more energy-efficient. It is the best option for areas with a hot, dry climate and less moisturized air. Its cooling increases in hot air, especially in deserts.
It is pretty eco-friendly and significantly less harmful to our environment. We live in a world where global warming and air pollution are rising issues and dangerous for our environment. To tackle such a big dilemma, we should prefer eco-friendly and best products for our environments to leave a better natural environment for our future generations.
