The Central air conditioning system is among the most prominent players in enhancing your space aesthetically and functionally. While there are several air conditioners to choose from, what makes the central air conditioning system stand out? Well, for starters, a central AC is not only easy but also convenient to operate. What’s more, it offers better efficiency than typical room air conditioners.
So, the accompanying benefits are endless, whether switching from a window air conditioning unit to a central air conditioning system or installing a new central AC for the first time. That said, while it may seem costly, the payoffs of installing a central AC system will ultimately prove worthwhile. From better air quality, quiet operation, reduced humidity, and reduced allergens, to better indoor living, you will be glad you installed a central air conditioning system!
This piece provides more information about a central AC system, its types, components, and how it works. By the end of the article, you will be a more educated buyer should you consider installing a central AC in your home or commercial space.
Read ahead.
What is a central air conditioning system?
Thanks to its quick and efficient cooling, quiet operation, and enhanced aesthetics, the central air conditioning system has grown in popularity. So, how do you describe or identify a central AC system?
A central air conditioning system is a cooling system that works by cooling air at a centralized location before distributing the cool air to several different rooms or spaces through fans and ducts. In other words, once the air is cooled sufficiently, the central AC system circulates it to the relevant rooms with the help of both supply ducts and return ducts.
The supply ducts and registers shall use as openings on floors, ceilings, or walls with grill covers. They are responsible for transporting cool air from the central cooling unit to your home or commercial space. As the cooled air circulates throughout your space, it picks up the heat within the room and gets warmer. The warm air again enters the central AC system for cooling through another set of return ducts and registers.
Through this simple cycle, your central cooling unit cools while dehumidifying your air for a comfortable, healthy, and livable space. Thus, a central air conditioning system differs from a window air conditioner. While the central AC features many parts and relies on a building’s duct system, the window AC comes as a standalone unit with no extra parts.
That means the central AC is ideal for cooling larger spaces, while the window AC performs well when used to cool single rooms or smaller areas.
What are the types of central air conditioning systems?
Having understood what a central air conditioning system is, time now to shift the gear to the types of Central AC systems available.
Usually, central air conditioning systems come as either:
- Split-system air conditioners
- Packaged air conditioners
- Chiller System
If you want to install central heating in your space, which of the two options is right for you? Take a closer look at the unique distinctions.
Split-system air conditioners
As the name states, split-system AC units come with split components. They feature a separate evaporator coil split from the compressor and condenser coils.
Usually, the evaporator is inside an indoor cabinet somewhere, while the compressor and condenser are in an outdoor cabinet. That means the AC comprises an indoor and outdoor unit linked with copper tubing.
With that in mind, split-system AC units are the most common type of central AC systems thanks to their flexibility and value-addition. They are also the most economical to install if your space has a furnace but lacks an air conditioner.
Furthermore, split-system AC systems are ideal for homes or commercial properties with additional space to accommodate large indoor cabinets.
Packaged air conditioners
From the sound of the name, packaged air conditioners house all their significant components (evaporator, compressor, and condenser) in a single metallic cabinet to save installation space. Typically, the housing cabinet sits on a designated concrete slab next to the structure’s foundation or on the roof.
The packaged unit (sitting outdoors) links to the building through supply and return ducts emerging from the exterior walls or roof. Therefore, it draws air from inside the building, cools it sufficiently, and then sends it back through the special ductwork.
You don’t need a separate indoor furnace with a packaged AC unit. Most such systems are equipped with electric heating coils to provide central heating.
Packaged air conditioners are suited for buildings with little to zero crawlspace or lack a basement.
What are the components of a central air conditioning system?
Beyond the essential operation of your central air conditioner, it is imperative to master the components of your cooling system. This knowledge comes in handy when diagnosing and possibly troubleshooting problems with the unit.
Here is a closer look at the main parts of your central AC system and how they fit together to keep your indoor temperature comfortable.
Compressor
Sitting at the heart of your central AC system, the compressor plays an integral role in keeping your space cool and comfy. The compressor sits next to the condenser in the outdoor cabinet of your cooling system. It works by compressing (adding pressure on) the refrigerant vapour. This effect increases the vapour’s pressure while converting it into a hot gas. The extra pressure (force) then pushes the denser refrigerant into the condenser coil for cooling. Thus, a compressor’s primary role is to complement a condenser’s cooling function by pressurizing the refrigerant.
Condenser
As the refrigerant absorbs warm air from your space, it passes through the compressor for pressurizing into hot vapour. Once the hot refrigerant vapour lands on the condenser from the compressor, it is relieved of all its heat. As the vapour reaches the condenser, it is also converted into a liquid as it cools. The liquid refrigerant flows through the condenser and condenser coils before being circulated indoors for another cooling cycle.
Evaporator
Safely tucked inside your central air conditioner, the evaporator serves the direct opposite function of the condenser. After cooling in the condenser, the cool liquid refrigerant flows to the evaporator. The refrigerant encounters a lower pressure in the evaporator and turns back into a gas. As a lighter gas, it absorbs the warm air around it, cooling your indoors. After absorbing the hot indoor air, the warm refrigerant heads to the compressor and the condenser. This cooling cycle continues until your indoors reach a comfortable temperature.
Expansion valve
Think of the expansion valve as an intermediary equal to but opposite in function to the compressor. That is to say, while the compressor helps the condenser by increasing the refrigerant’s pressure, the expansion valve assists the evaporator by reducing the stress. Thus, the expansion valve helps to effectively reduce the pressure of the liquid refrigerant to facilitate conversion back into a gas when passing through the evaporator.
Chiller system
From the sound of the name “chiller,” a chiller system means a cooling system responsible for removing heat through the circulation of a heat-absorbing refrigerant and chilled water.
The primary role of a chiller system is to facilitate the movement of heat from an indoor space to the outdoors using chilled water as a medium.
A chiller system essentially features a compressor, condenser, evaporator, and expansion valve that work together to circulate a refrigerant. Through this circulation, the refrigerant releases heat from a climate-controlled space, process, operation, or equipment to chilled water and the atmosphere.
The unique cooling ability allows chillers to easily sit at the heart of any central HVAC system.
Types of Chiller System
Chiller systems are classified as either water-cooled chillers or air-cooled chillers. They adopt different mechanisms of releasing heat and use water or air as a cooling medium.
For instance, while a water-cooled chiller system relies on a cooling tower to circulate water, an air-cooled chiller system relies on fans to circulate cool air.
Generally, chiller systems support a continuous coolant circulation to maintain a specific preset temperature indoors through heat reduction.
Water-cooled chiller systems
Essentially, water-cooled chillers use water as a medium to surround refrigerant pipes and absorb the heat in the refrigerant.
They come attached to a cooling tower that ensures the cooling water stays cool by channeling it to the chiller and recirculating it.
How does Water-cooled chiller systems work?
Cooling in a water-cooled chiller system starts at the evaporator. Water enters the evaporator, where the heat from the water is transferred to the refrigerant. The chilled water then flows to the water tank. Here, it is further distributed by the water pump to the different spaces requiring temperature control (heat reduction).
Upon reaching the targeted space, the cool water absorbs all the heat in the air handler. When the air is cooled, it is blown by a fan into the room through ductwork. After absorbing the heat, the warm water heads back to the chiller to be cooled again.
Meanwhile, the heat absorbed by the refrigerant needs urgent transfer for the refrigerant to take on more heat. Thus, the refrigerant flows from the evaporator to the compressor at low pressure and high temperature.
The refrigerant’s pressure and temperature rise as soon as it enters the compressor. It then flows to the condenser for cooling through surrounding chilled water. Passing through the condenser cools the refrigerant before sending it to the expansion valve.
The expansion valve then lowers the refrigerant’s temperature and pressure before releasing it into the evaporator for another cooling cycle.
Where are Water-cooled chiller systems applied?
Thanks to their consistent and efficient performance and better durability, water-cooled chiller systems are popular in industrial applications.
Therefore, facilities such as airports, shopping malls, and other commercial buildings can rely on water-cooled chillers as long as they have a reliable water supply.
- Air-cooled chiller systems
Air-cooled chiller systems work best where there are no discharge constraints. The chiller absorbs heat from the water and dispels it into the air.
In other words, instead of cooling the refrigerant with water, air-cooled chillers cool the refrigerant with air using an in-built propeller fan.
How do Air-cooled chiller systems work?
The cooling cycle begins with warm water entering the chiller through the primary return. Then, inside the evaporator, the refrigerant absorbs all the heat in the water. The chilled water then proceeds to the areas needing cooling through the primary supply.
In the meantime, the warm refrigerant flows through the compressor, which increases its temperature and pressure. This change in the refrigerant state facilitates its movement to the condenser. Then, the in-built propeller fan blows outside air through the condenser.
The cold air absorbs all the heat from the refrigerant and dispels it to the atmosphere. Next, the cool refrigerant flows to the expansion valve for pressure and temperature reduction before returning to the evaporator for another cooling cycle.
Where are Air-cooled chiller systems applied?
In terms of application, air-cooled chiller systems are more suitable for small and medium-sized facilities with limited space and water supply. Their typical applications include corporate events, sporting events, restaurants, and temporary structures.
Furthermore, air-cooled chillers are way cheaper to install and maintain than their water-cooled counterparts. However, although inexpensive, they tend to have a shorter lifespan altogether.
Other common uses of chiller systems include medical and industrial applications. Chillers are essential for high-powered equipment and facilities such as MRI machines, lasers, assembly equipment, and construction sites. Optimally working chillers make it easy to maintain workable temperatures even in an expansive facility.
What are the components of a chiller system?
In addition to the essential components of a central HVAC system, chiller systems also feature other critical parts that make the cooling process seamless.
Thus, the components of a chiller system also include a cooling tower, chiller, AHU, FCU, chilled water pipe, valves, Y-strainer, BMS, ducts, and diffusers.
Cooling Tower
A cooling tower is a tall cylindrical structure with an open top. It is paired with a water-cooled chiller to serve as a heat exchanger.
It receives warm water from a chiller (condenser water), expels the heat into the atmosphere, and then returns cold water to the chiller (usually located in a lower level like a basement).
In other words, a cooling tower cools the cooling water before recirculating it for more cooling functions. The cooling tower relies on outside air to keep this water cool and render it reusable.
Without a cooling tower, the cooling water’s temperature would steadily rise and become unusable in the chiller system.
Generally, cooling towers may vary by build, heat transfer mechanism, and airflow generation.
Chiller
The chiller is part of the more extensive chiller system that supports the refrigeration cycle. It comprises four essential components for the cooling process, including the condenser, compressor, evaporator, and expansion valve.
Inside the chiller, the refrigeration cycle involves the refrigerant absorbing all the heat from the coolant water to chill it. As the process progresses, the refrigerant releases the absorbed heat into the condenser water. The condenser water then loses the heat to the atmosphere through the cooling tower.
Thus, the chiller essentially acts as an intermediary air conditioner. On the one hand, it drives the water for cooling inside the evaporator. That allows the cold water to pass through AHUs and FCUs to cool the building as more warm air enters the evaporator.
On the other end, the chiller facilitates heat expulsion to the cooling tower through the condenser. This cycle ensures seamless air conditioning of spaces.
Air Handling Unit (AHU)
Once the chiller has produced chilled water, it pumps it around the building. Then, the water encounters Air Handling Units (AHUs) and Fan Coil Units (FCUs) for further circulation.
Thus, the AHU is a box comprising fans responsible for sucking air from the building and pumping it across cooling and heating coils. Through this action, AHUs alter the air temperature before blowing it back into the building.
AHU’s major components include a fan, filter, and cooling coil. The chiller releases chilled water into the AHU’s cooling coil. The AHU then blows air through the coil to cool the building.
Fan Coil Unit (FCU)
Although it is a close companion of the AHU, the fan coil unit (FCU) has a smaller capacity and physical dimension. It also features fewer components than the AHU. The FCU’s major components include an air intake, filter, fan, and cooling coil.
Generally, the FCU transfers heat from the air flowing over the heat exchanger to the chilled water passing through the exchanger. Using its fans, it blows cool air into the climate-controlled space.
An FCU is unique because it can regulate its cooling power by controlling the chilled water flow through its coil.
Chilled Water Piping
The chilled water pipe is responsible for linking the chiller to the AHU’s cooling coils. The pipe transports chilled water into the coils, where the cooling air recirculates the building through ducting systems.
Most of the time, these pipes come pre-insulated. They come in carbon steel, galvanized, stainless steel, and HDPE.
Valves
A chiller system features valves on inlet and outlet chilled water lines. Generally, the most popular valves used in a chiller system are the 2-way and 3-way valves.
A 2-way valve has two openings, an outlet and an inlet. These valves can function as on/off valves to regulate the flow of fluid in them by altering the size of the valve opening.
On the other hand, a 3-way valve comes with three openings. Sometimes, that may mean two inlets and a single outlet, and other times, a single inlet and two outlets. As the former, they are suitable for mixing fluids and the latter for diverting chilled water.
Y-Strainer
The Y-strainer plays a crucial role in removing solids and other particulate matter from the chiller system. It traps all the contaminants in the system and prevents them from re-entering the chiller. This way, it protects the essential components of the chiller system, such as heat exchangers and pumps which may suffer potential clogging and inefficiency.
Ducts
Ducts in a chiller system receive the cooled air and distribute it throughout the climate-controlled areas inside the building. Generally, a duct system works closely with fans and blowers that force contaminated air out of the building while bringing in cleaner, colder, and drier air.
Thus, consider a duct a channel, tube, or pipe (synthetic or metallic) used to ferry moving air between a chiller system and climate-controlled spaces.
Diffusers
Attached to the end of ducts, diffusers in a chiller system act as vents for cooled air to flow into a space. In other words, diffusers are devices that help to evenly distribute cooled air in a building.
They come with fins that are sometimes adjustable to regulate airflow. This flexibility maximizes the chiller system’s cooling effectiveness and keeps the cooling bills down.
Building Management System (BMS)
A building management system (BMS) helps to control the chiller system for maximum energy efficiency. By enhancing the energy efficiency of the building’s chiller system, a BMS essentially helps to lower operating costs.
The BMS monitors and controls the operation of essential elements of a chiller system, such as the chiller, AHU, fans, and pumps. It has sensors that monitor these operations and conveys information on key control parameters such as temperature, humidity, and system pressure, among others.
This information allows one to adjust the chiller system to the changing conditions to minimize energy consumption.
Simply put, a BMS helps optimize a chiller system’s operation.
How does the chiller system work?
As discussed earlier, a chiller system keeps water cool while facilitating heat transfer from one point to another. It packages with the essential AC components such as the compressor, condenser, evaporator, and thermal expansion valve to aid this process.
While the operation of a chiller system differs according to the system type, the underlying principle is that chiller systems rely on a refrigeration cycle to accomplish their heat transfer goal.
As a significant component, the chiller facilitates heat expulsion from the cooling water before releasing it back into the cooling cycle.
When the water absorbs heat and becomes warm, the chiller evaporator eliminates the heat from the water.
Finally, the evaporator sends the heat to the chiller condenser. Here, the condenser can either transfer heat to the condenser water, if it’s a water-cooled chiller, or to the outside air, if it’s an air-cooled chiller.
How does central air conditioning work?
As detailed above, the central air conditioner works through the collaborative function of its different components.
The whole operation revolves around the system’s refrigerant and how its changing states (temperature and pressure) support the cooling process of your ambient air.
The cooling process of a central AC system starts with the thermostat. Usually located centrally inside the building, the thermostat monitors the indoor temperature. Sensing the indoor air temperature needs some regulation alerts your central cooling system’s indoor and outdoor components.
When the different components start running, the indoor fan drives out indoor hot air through return ducts. The hot air passes over the evaporator coil after the filtering process. At this very instance, the evaporator is busy converting the liquid refrigerant from the condenser into a gas.
The gaseous refrigerant then absorbs all the heat from the hot indoor air before heading outdoors to the compressor and condenser through copper tubing for cooling. Once cooled, the indoor unit’s fan blows the cooled air back into the building through the ductwork.
The cold air then begins absorbing indoor hot air again, and the cycle repeats itself until the desired indoor temperature.
