Chiller Systems

As you grapple with the hot summer days, you are probably up and about trying to ensure your AC is in perfect working order. That’s absolutely commendable!

But have you ever wondered how a chiller system works and why it is essential? If not, here is your chance to make another discovery for your cooling needs this summer.

This elaborate article sets everything plain for you, from what a chiller system is, its main types, components, and how it works.

Read on to explore more!

 

What is a 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.

Put simply, 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 sit at the heart of any central HVAC system easily.

 

What are the types of chiller systems, and how do they work?

Broadly speaking, 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 are specially designed to support a continuous coolant circulation to maintain a certain preset temperature indoors through heat reduction.

 

1.      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 do they 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. Once the air is cooled, it is blown by a fan into the space through ductwork. Having absorbed 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 they applied?

Thanks to their consistent and efficient performance and better durability, water-cooled chiller systems are popular in large-scale applications.

As long as large facilities such as airports, shopping malls, hotels, hospitals, and other commercial buildings have adequate water supply, water-cooled chillers do a better cooling job than their counterparts.

 

2.      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 they 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, where it undergoes temperature and pressure rise.  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 they 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 handy for high-powered equipment and facilities such as MRI machines, lasers, assembly equipment, and construction sites, among others, to help them maintain workable temperatures.

 

What are the components of a chiller system?

In addition to the essential components of a central HVAC system (condenser, compressor, evaporator, and expansion valve), 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 simply cools the cooling water before recirculating it for more cooling functions. The 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 the part of the larger 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 to be cooled 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 also facilitates heat expulsion to the cooling tower through the condenser. This cycle ensures seamless air conditioning of spaces.

 

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 help 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.

 

FCU

Although a close companion of the AHU, the fan coil unit (FCU) has a smaller capacity and physical dimension. Moreover, it 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 then blows the 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 Pipe

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 air is cooled before recirculating the building through ducting systems.

Most of the time, these pipes come pre-insulated and feature different materials such as carbon steel, galvanized carbon steel, stainless steel, and HDPE.

 

Different types of 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 protects the essential components of the chiller system, such as heat exchangers and pumps which may suffer potential clogging and inefficiency.

 

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 convey information on key control parameters such as temperature, humidity, and system pressure, among others.

Based on this information, the chiller system can then be adjusted to the changing conditions to minimize energy consumption.

Simply put, a BMS helps optimize a chiller system's operation.  

 

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 where it is most needed in a building.

They come with fins that are sometimes adjustable to regulate airflow. This helps to maximize the chiller system’s cooling effectiveness and keep the cooling bills down.

 

How does the chiller system work?

As discussed earlier, a chiller system is primarily used to keep water cool while facilitating heat transfer from one point to another. It is generally packaged 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 itself 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 the heat to the condenser water in case of a water-cooled chiller or to the outside air in case of an air-cooled chiller.