How air conditioner works?

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In the scorching heat of summer, we often seek refuge in the cool comfort of air-conditioned spaces. We owe this modern-day luxury to Willis Haviland Carrier, an innovative electrical engineer who revolutionized our lives with his invention over a century ago. Back in 1902, Carrier developed the first modern air conditioning system to address a humidity problem at a printing company in Brooklyn, New York. Little did he know that his invention would pave the way for a technology that would shape the way we live, work, and relax.

Background:

At the Sackett-Wilhelms Lithographing and Publishing Company, the warm summer air posed a challenge. The moisture in the air would cause the paper stock to absorb moisture, disrupting the delicate layered inking process. Recognizing the need for a solution, Carrier devised a groundbreaking approach. He introduced chilled pipes into the building and blew the air across them, causing it to cool down. As a result, the air’s ability to hold moisture decreased, reducing the humidity levels within the plant and stabilizing the moisture content of the paper. Interestingly, this humidity control also led to a decrease in the air temperature, giving birth to an entirely new technology.

The success of Carrier’s invention quickly became apparent, and air conditioning systems started to emerge in various public spaces like theaters and stores. Suddenly, the unbearable summer months became far more bearable, making these spaces not only comfortable but also enticing to customers. Carrier’s realization of the vast potential of his invention laid the foundation for a remarkable transformation in the way we experience indoor environments.

While the principles of air conditioning may seem complex, at its core, the process relies on a simple scientific principle. In fact, air conditioners share a striking resemblance to another common household appliance – the refrigerator. However, unlike the refrigerator, air conditioners do not have the external housing to insulate a cold box. Instead, the walls of our homes play a crucial role in maintaining cool air inside and keeping hot air at bay.

With this understanding of the background and the pivotal role played by Willis Haviland Carrier, let us delve deeper into how air conditioners work and unravel the mechanical techniques that make them such indispensable companions during sweltering summers.

Table of Contents

Air conditioning basics

Air conditioners work based on a fundamental scientific principle, employing several clever mechanical techniques to achieve their cooling effect. In fact, the concept behind air conditioning is quite similar to that of a refrigerator.

While a refrigerator relies on an insulated cold box to keep its contents cool, an air conditioner operates differently. Instead, air conditioners utilize the walls of our homes or buildings to create a controlled environment. These walls act as barriers, keeping cold air inside and preventing hot air from entering.

The primary component of an air conditioning system is the refrigerant, a chemical substance that undergoes a continuous cycle of evaporation and condensation. The refrigerant circulates through a closed-loop system, transitioning between liquid and gas states as it absorbs and releases heat.

The cooling process begins with the compressor, which compresses the gaseous refrigerant, raising its temperature and pressure. As a result, the refrigerant becomes a high-pressure, high-temperature gas. This hot gas then flows into the condenser, typically located outside the building, where it releases heat to the external environment. The condenser coils help dissipate the heat efficiently, allowing the refrigerant to transform into a high-pressure liquid.

The high-pressure liquid refrigerant then enters the expansion valve, a narrow opening that restricts its flow. As the refrigerant passes through this valve, it undergoes a rapid pressure drop, causing it to cool down significantly. The refrigerant now enters the evaporator coils, located inside the building.

Inside the evaporator coils, the low-pressure liquid refrigerant starts to evaporate, absorbing heat from the surrounding air. As the refrigerant evaporates, it transforms into a low-pressure gas, while the air in the room loses its heat and becomes cooler. A blower fan inside the air conditioner helps circulate the cooled air throughout the space.

The gaseous refrigerant, having absorbed the heat from the room, is then drawn back into the compressor to restart the cycle. This continuous circulation of the refrigerant, alternating between high-pressure gas and low-pressure liquid states, allows the air conditioner to consistently cool the air in the room.

It is worth noting that air conditioners not only reduce the temperature but also remove moisture from the air. As the warm air passes over the evaporator coils, the moisture in the air condenses on the cold surface, dehumidifying the room and providing additional comfort.

By understanding the principles and mechanisms at play, we can appreciate the complexity and ingenuity behind air conditioning systems. These innovations have made a significant impact on our daily lives, ensuring that we can enjoy comfortable, cool environments even during the hottest summer days.

Parts of air conditioner

An air conditioner consists of several components that work together to cool the indoor air, regulate temperature, remove humidity, and circulate air. Let’s explore the main parts of a standard air conditioner:

Evaporator: This component receives the liquid refrigerant and is located on the cold side of the air conditioner. It contains chilled coils that help cool the air.
Condenser: The condenser is situated on the hot side of the air conditioner and facilitates heat transfer. It contains coils and a fan that vent hot air generated during the cooling process to the outdoors.
Expansion Valve: The expansion valve regulates the flow of refrigerant into the evaporator. It controls the amount of compressed liquid refrigerant entering the evaporator, where it undergoes a pressure drop and changes back into a gas.
Compressor: The compressor is a vital part of the air conditioner. It acts as a pump, pressurizing the refrigerant gas and helping to turn it back into a liquid. The compressor is typically located on the hot side of the unit.

These components, along with the onboard filter and thermostat, form the core of an air conditioner. The filter removes airborne particles from the circulating air, improving indoor air quality. The thermostat monitors and regulates the air temperature, ensuring it stays at the desired level.

It’s important to note that there are variations in air conditioner setups. For example:

Examples of variation in air conditioner setups

Window Air Conditioners: These units incorporate all the components within a small metal box that can be installed in a window opening. The hot air is vented out from the back of the unit, while the condenser coils and a fan cool and circulate indoor air.
Central Air Conditioners: In larger homes and buildings, central air conditioners are commonly used. They share a control thermostat with the heating system and have the compressor and condenser located in a separate housing outdoors. The cool air is then distributed through ducts to various rooms.
Commercial Buildings: Very large buildings like hotels and hospitals often have exterior condensing units mounted on the roof for efficient operation and space utilization.

Window Air Conditioner Units and Split-System Air Conditioners

Window Air Conditioner Units:

A window air conditioner is a compact unit that houses a complete air conditioning system. Designed to fit into a standard window frame, these units provide a convenient cooling solution. When you remove the cover of a window unit, you will find the following components:

Compressor: The compressor plays a crucial role in the cooling process. It pressurizes the refrigerant gas, initiating the cycle of cooling and heat removal.
Expansion Valve: The expansion valve regulates the flow of refrigerant into the chilled coil, controlling the cooling capacity of the unit.
Hot Coil: The hot coil, located on the outside of the unit, facilitates the release of heat to the outdoor environment.
Chilled Coil: The chilled coil, situated on the inside of the unit, cools the air as it passes over it.
Two Fans: Window units have two fans. One fan blows air over the hot coil to dissipate heat, while the other fan blows air over the chilled coil to circulate cool air into the room.
Control Unit: The control unit contains the necessary electronics for operating and regulating the air conditioner’s functions.

Split-System Air Conditioners:

In larger air conditioning applications, split-system units are commonly used. These units separate the hot side from the cold side of the system. Here’s how they work:

Cold Side: The cold side comprises the expansion valve and the cold coil. It is typically installed within a furnace or an air handler. The air handler blows air through the coil and distributes it throughout the building via a network of ducts.
Hot Side: Known as the condensing unit, the hot side is located outside the building. It consists of a long, spiral coil, a fan for blowing air over the coil, a weather-resistant compressor, and control logic. This configuration reduces noise inside the building but may generate increased noise outside.

For larger buildings, such as warehouses, offices, and malls, the condensing unit is often placed on the roof. In some cases, multiple smaller units are installed on the roof, each connected to a small air handler that cools a specific zone within the building.

In multi-story buildings, the split-system approach may encounter limitations due to distance restrictions or impractical amounts of ductwork. In such cases, a chilled-water system becomes a viable option.

A chilled-water system utilizes a network of pipes to distribute chilled water to air handlers or fan coil units located throughout the building. This system offers more flexibility and efficiency for cooling larger structures.

Chilled-Water and Cooling Tower Air Conditioners

Chilled-Water Systems:

Chilled-Water Systems: In some large installations, such as office buildings, alternative cooling methods are employed to improve energy efficiency. Chilled-water systems and cooling tower air conditioners are two well-known examples:

Chilled-Water Systems

Chilled-Water Systems: In this system, the entire air conditioning unit is located on the roof or behind the building. The system cools water to temperatures between 40 and 45 degrees Fahrenheit (4.4 and 7.2 degrees Celsius). The chilled water is then circulated throughout the building via pipes and connected to air handlers. These water pipes function similarly to the evaporator coils in a standard air conditioner. One advantage of chilled-water systems is that, if properly insulated, there are no practical distance limitations for the length of the pipes.

Cooling Tower Air Conditioners:

Cooling Tower Technology: In some large-scale air conditioning systems, a cooling tower is used instead of relying solely on air to dissipate heat from the condenser coils. The cooling tower creates a stream of cold water that passes through a heat exchanger, cooling the hot condenser coils. The tower blows air over the water stream, causing some of it to evaporate. This evaporation cools the water, facilitating the cooling process. However, one drawback of this system is the regular addition of water to compensate for the liquid lost through evaporation. The efficiency of a cooling tower-based system depends on factors such as the relative humidity of the air and the barometric pressure.

Exploring Other Cooling Methods:

Aside from chilled-water and cooling tower systems, other cooling methods are being researched for their energy efficiency:

Off-Peak or Ice-Cooling Technology: This system utilizes ice that is frozen during off-peak hours (typically in the evening) to cool the interior air during the hottest part of the day. While the system still requires energy, it takes advantage of lower energy costs during off-peak hours and helps reduce demand on the power grid during peak times.
Geo-Thermal Heating and Cooling: Geo-thermal cooling takes advantage of the relatively constant temperature of the earth underground. Using a closed-loop system, polyethylene pipes filled with a liquid mixture are buried underground. During the winter, the fluid collects heat from the earth and transfers it into the building, while during the summer, the system reverses to cool the building by depositing heat underground. This approach reduces reliance on electricity for heating and cooling.
Solar-Powered Air Conditioners: Solar-powered air conditioners are emerging as a potential energy-efficient option. While still in development, these systems harness solar energy to power air conditioning units, offering an eco-friendly alternative to traditional electricity-dependent cooling methods.

With the increasing focus on energy efficiency and environmental concerns, alternative cooling technologies are gaining attention. Chilled-water systems, cooling tower air conditioners, off-peak cooling, geo-thermal systems, and solar-powered air conditioners represent some of the innovative approaches being explored to provide energy-friendly cooling options for a significant market demand.

BTU and EER

An air conditioner’s efficiency is a measure of how effectively it cools a room while consuming electrical power. This efficiency is quantified using a metric called the energy efficiency ratio (EER). The EER is calculated by dividing the cooling capacity of the air conditioner (measured in British thermal units per hour, or Btu/h) by its power input (measured in watts).

In simpler terms, the EER reflects how many Btu of cooling the air conditioner can provide per hour for each watt of power it consumes. A higher EER rating indicates a more efficient air conditioner because it can deliver more cooling power while using less electricity.

For example, let’s say an air conditioner has a cooling capacity of 10,000 Btu/h and a power input of 1,000 watts. The EER would be calculated as follows:

EER = Cooling capacity (Btu/h) / Power input (watts) = 10,000 Btu/h / 1,000 watts = 10 Btu/watt

In this case, the air conditioner has an EER of 10, meaning it can provide 10 Btu of cooling for each watt of power it consumes.

By comparing the EER ratings of different air conditioners, you can determine which models are more energy-efficient. Choosing an air conditioner with a higher EER rating can help you save on electricity bills and reduce your environmental impact, as it operates more efficiently and minimizes energy waste.

BTU and Air Conditioner Capacity:

Most air conditioners are rated in British thermal units (Btu), which is a measure of heat. It represents the amount of heat required to raise the temperature of 1 pound (0.45 kilograms) of water by one degree Fahrenheit (0.56 degrees Celsius).
In heating and cooling terms, one ton is equal to 12,000 Btu. So, a typical window air conditioner with a rating of 10,000 Btu is equivalent to 0.83 tons.
For residential applications, the size of an air conditioner is often determined based on the square footage of the space it needs to cool. A rough estimate suggests that you might need around 30 Btu per square foot. However, it’s best to consult an HVAC contractor for accurate sizing based on your specific needs.

EER and Energy Efficiency:

The energy efficiency rating (EER) of an air conditioner is calculated by dividing its Btu rating by its wattage. It represents the cooling capacity of the unit relative to the amount of energy it consumes.
A higher EER indicates a more energy-efficient air conditioner. However, higher EER ratings often come with a higher price tag.
EER can be used to compare different air conditioner models. For example, if one 10,000-Btu unit consumes 1,200 watts and has an EER of 8.3, while another 10,000-Btu unit consumes 1,000 watts with an EER of 10, the latter unit is more energy-efficient.

Calculating Payback Period:

When comparing air conditioner models with different EERs and prices, you can calculate the payback period to determine the cost-effectiveness over time.
To calculate the payback period, you need to estimate the number of hours per year you will be operating the air conditioner and the cost of electricity per kilowatt-hour (kWh) in your area.
The difference in energy consumption between two units can be used to estimate the additional cost incurred by the less energy-efficient unit.
By multiplying the extra energy consumption (in watts) by the number of hours of operation, dividing by 1,000 (to convert watts to kilowatts), and multiplying by the cost per kWh, you can determine the additional cost per year.

Example for calculating pay back period of air conditioner

Let’s consider an example using specific values to calculate the payback period for two air conditioner models with different EER ratings.

Model A:

Cooling capacity: 12,000 Btu
Power consumption: 1,500 watts
EER: 8.0
Price: $400

Model B:

Cooling capacity: 12,000 Btu
Power consumption: 1,200 watts
EER: 10.0
Price: $500

Assumptions:

Operating hours per year: 1,500 hours
Cost per kilowatt-hour: $0.15/kWh

To calculate the payback period, we need to determine the difference in energy consumption between the two models and calculate the additional cost incurred by the less energy-efficient unit.

Model A (Less Efficient):

Energy consumption per hour: 1.5 kWh (1,500 watts ÷ 1,000)
Additional energy consumption compared to Model B: 0.3 kWh (1.5 kWh – 1.2 kWh)
Additional cost per hour: $0.045 (0.3 kWh × $0.15/kWh)

Now, let’s calculate the annual additional cost for Model A compared to Model B:

Annual additional cost:

Additional cost per hour × Operating hours per year: $67.50 ($0.045 × 1,500 hours)

To determine the payback period, we divide the price difference between the two models by the annual additional cost:

Payback period:

Price difference: $100 ($500 – $400)
Payback period: 1.48 years ($100 ÷ $67.50)

In this example, it would take approximately 1.48 years for Model B (the more expensive, but more energy-efficient unit) to break even with Model A in terms of energy savings.

Please note that the example above is a simplified calculation, and actual payback periods may vary based on individual usage patterns, electricity costs, and other factors

Energy Efficient Cooling Systems

Introduction: As electricity costs rise and environmental concerns grow, the demand for energy-efficient cooling systems is increasing. lets explores alternative methods that not only save money but also contribute to a greener environment. Both businesses and homeowners are adopting these technologies to lower their overhead and reduce their carbon footprint. In this regard, two prominent options are ice cooling systems and geo-thermal heating and cooling systems.

Ice Cooling Systems: Ice cooling systems provide a cost-effective solution to combat high electricity costs during summer months. This method involves freezing large tanks of water into ice during off-peak hours when energy demands are lower. The following day, a system similar to a conventional air conditioner pumps cool air from the ice into the building. Ice cooling not only saves money but also reduces pollution and eases the strain on the power grid. However, it should be noted that the initial installation costs and space requirements are relatively high. Despite these factors, more than 3,000 ice cooling systems are in use worldwide, highlighting their effectiveness.
Geo-Thermal Heating and Cooling Systems: Geo-thermal units, also known as ground source heat pumps (GSHP), have been recognized by the Environmental Protection Agency as the most energy-efficient and environmentally sensitive space conditioning systems. These systems utilize the Earth’s constant underground temperature, ranging from 45 to 75 degrees Fahrenheit, to provide heating and cooling. The most common type of geo-thermal unit for homes is the closed-loop system, where polyethylene pipes are buried vertically or horizontally. Water or an anti-freeze/water mixture circulates through these pipes. During winter, the fluid collects heat from the ground and transfers it into the building, while in summer, the system reverses to cool the building by dissipating heat into the ground.

Benefits of Geo-Thermal Systems:

Energy Savings: Homeowners can save 30 to 50 percent on cooling bills by replacing traditional HVAC systems with ground source heat pumps.
Long-Term Cost Recovery: Although the initial costs are higher compared to traditional units, the investment can be recouped within three to five years.
Financial Incentives: Many states offer financial incentives to promote the adoption of geo-thermal systems, further reducing the overall cost.
Durability: Geo-thermal systems tend to have a longer lifespan compared to traditional units as they are protected from the elements and less susceptible to theft.

Conclusion: With the goal of saving money and reducing environmental impact, alternative cooling methods are gaining popularity. Ice cooling systems and geo-thermal heating and cooling systems offer energy-efficient solutions for businesses and homeowners. While ice cooling is suitable for large buildings, geo-thermal systems provide homeowners with substantial energy savings and long-term cost benefits. By embracing these technologies, individuals and organizations can contribute to a greener future while enjoying the advantages of reduced energy consumption and lower utility bills.