In this article, we will learn what are chillers in HVAC system, along with the definition, meaning, working, types, selection, applications, advantages, disadvantages, etc.
Chillers are widely used machines to remove heat from a liquid, and they are extensively used in industries. There are several chiller options available. The application, cooling temperature requirements, and cooling characteristics need to match the needs when choosing one. Significant parameters to ponder are the operating temperatures and pressures.
They vary in size; small chillers are available for smaller applications. While commercially or industrially, large chiller units are required, but the basic principle stays intact, and they provide cooling for the entire process accordingly.
Chillers are significant to use. Machines are never 100% efficient, and they produce a lot of heat as a by-product that needs to be removed. If not removed, it can cause many issues such as reduced production times, equipment shutdowns, and premature equipment malfunctioning.
Hence, it is essential to incorporate cooling into industrial process system design to prevent such problems.
Chillers operate on some principles. They are:
The liquid coolant undergoes a phase change and transforms into a gas when heated. This gaseous coolant will condense back into liquid when supercooled.
Heat flow is an important aspect that takes place in chillers. Heat energy always flows from an area of high concentration to an area of low concentration.
The boiling point of liquid reduces when pressure on the liquid decreases, and the boiling point increases if the pressure increases.
These are the basic working principles of chillers. The essential components of chillers and working are further discussed in-depth in terms of these principles.
The basic components of chillers found in all types are:
There are numerous types of refrigerant compressors; the widely used ones include scroll, screw, centrifugal, and reciprocating types of compressors.
The condenser is located next to the compressor, right before the expansion valve.
The evaporator picks up heat from the refrigerant, and this heat needs to be removed.
There is a valve present between evaporator and condenser, which is known as an expansion valve.
The common types of expansion valves fitted in chillers include pilot-operated thermal expansion valves, electronic expansion valves, thermal expansion valves, and fixed orifice expansion valves.
Between the expansion valve and compressor, there is an evaporator. The primary purpose of the evaporator is to collect the extra heat and move it into the refrigerant, which sends it further to the cooling tower.
The power panel is mounted on chillers in industries; it may be mounted directly to chillers or fixed to the room’s wall where the plant is located.
The control unit is located on the chiller. It monitors several aspects like the chiller’s performance and has adjustments for the proper functioning of the chiller.
Water boxes are present along with condensers and evaporators in water-cooled chillers. The number of entrances in the water box depends on the number of passes in the evaporator and condenser.
The primary function of water boxes is separating the entrance and exit paths and also aids in directing the flow.
After discussing the working principle and components, let’s get into the working process of chillers.
A pumping system circulates cool water or a water/glycol solution from the chiller into the process. The cool fluid removes unwanted heat from the process when hot liquid returns—the heat transfers from the process to the chiller by water.
A chemical compound known as a refrigerant is present in process chillers. There are several types of refrigerants depending upon the required temperatures. However, the basic principle of compression and phase change of refrigerant from liquid to gas and back to liquid stays intact. This whole process of phase change, heating, and cooling is known as the refrigeration cycle.
The refrigeration cycle begins with a low-pressure liquid/gas mix that enters the evaporator. The heat from process water or water/glycol solution boils the refrigerant inside the evaporator. It results in a change from a low-pressure liquid into a low-pressure gas.
Now, the compressor compresses low-pressure gas into high-pressure gas. This high-pressure gas enters the condenser, where ambient air or condenser water removes the heat. In this way, the high-pressure gas converts to a high-pressure liquid.
The high-pressure liquid now enters the expansion valve. The valve controls the amount of refrigerant liquid entering the evaporator, allowing the refrigeration cycle to start again.
The condensers are of two types; either water-cooled or air-cooled. In the latter, water from the cooling tower is used to cool and condense refrigerants. On the contrary, the air-cooled condenser uses ambient air to cool and re-condense the heated refrigerant gas into the liquid.
There are numerous types of chillers. Chillers are both commercially and industrially used for cooling. The types are:
Water-cooled chillers are the most common type of chillers, and they utilize water from an external tower to cool the gaseous refrigerant in the chiller’s condenser.
In this way, refrigerants can undergo a phase change, and the refrigeration cycle goes on.
Instead of water, air-cooled chillers use ambient air for the refrigeration cycle to go on smoothly. Air fans are attached to them, which makes the cooling process pretty speedy.
On the contrary, they are preferred less because they produce a large amount of heat.
However, they are used in colder areas where heat discharge can keep the place warm. This way, it is beneficial.
Industrial chillers are further classified into the following types based on the transportation of refrigerant inside the system.
The types are discussed below.
Vapor compression chillers extract extra heat using a compressor to pump refrigerant.
Vapor absorption chillers transport the refrigerant around the system for cooling using a heat source heated using water or steam.
Screw chillers are vapor compression chillers, and it uses a screw compressor to move coolant through the system. They are most suitable for high-rise buildings and offer high energy efficiency.
Other benefits include low maintenance costs, quiet working, and compact installation.
Centrifugal chillers are vapor compression chillers best for medium to large-scale cooling operations.
They comprise an evaporator, compressor, condenser, and expansion valve fitted with a rotating impeller which aids in compressing the refrigerant and then transporting it through the system.
Reciprocating chillers use reciprocating compressors. They are pretty efficient as they deliver small refrigerant quantities at high pressure.
Scroll chillers constitute two spiral plates, one fixed and the other rotating to compress the refrigerant—the momentarily separating scrolls with a solenoid valve and electric modulation controls capacity.
Machines work well, but sometimes issues arise. Chillers are also machines, and there are few common issues that you may face. They include:
Metal tubes (copper or carbon steel) are used to construct chillers, and their primary function is transferring water between the chiller and climate-controlled space.
If sediment or bacteria builds up, the oxygenation level disrupts, and metal corrodes. When two metals are used at some point in the system, there is more risk for corrosion.
It is due to differences in the electrochemical properties of both metals. Corrosion is terrible since it can cause leakage and damage the chiller and surrounding area, reducing efficiency in chillers.
It is necessary to ensure that chillers are working correctly, for this maintenance is required. If not maintained adequately, it can lead to corrosion, clogging, loss of efficiency, and numerous other issues.
The electrical system inside chillers is complex and is vulnerable to malfunctioning. A high voltage surge can throw off balance and cause wear and tear in the whole electrical system.
Every environment is different, and every application requires a specific chiller for best results.
Below is a quick guide that will help you in selecting the appropriate chiller for your application.
The first step before selecting a chiller that best suits your needs is determining the heat load. It is better to understand the process first to calculate the accurate heat load in kW.
It is important to ensure that the chiller you are choosing is appropriate for the intended application.
After knowing the heat load, determine the coolant type, temperature, and flow rate. It is determined through the method of heat transfer from the process to the type of coolant used.
For instance, water-cooled and air-cooled chillers have different characteristics.
The third step involves knowing the environment. It may be outdoor or indoor. Therefore, the requirements for both environments slightly differ; hence you will need specific accessories for that.
For instance, the outdoor environment needs accessories like air filters or sump heaters since chillers are vulnerable to a number of factors.
Use the chiller performance curves available with each model. Considering the application, an appropriate frame size is selected, and the capacity of the chillers and safety margins are taken into consideration.
Consult experts for pump performance curves. It is essential to ensure that the pump will provide enough pressure at the design flow rate that is best suitable for the application.
For instance, some liquid-cooled systems have small coolant flow paths or longer distances resulting in higher than average pressure losses.
The final step involves considering power characteristics, control options, agency listing, color, footprint, size, etc.
Chillers are widely used on a small and large scale. The applications are given below:
There are numerous advantages of using chillers in businesses. Some of them are listed below.
Along with the advantages, every system or machine has disadvantages, and some of them are discussed below.
The article gives an insight into the working principles, types, categorization, application, merits, and demerits of Chillers in HVAC system. Chillers are widely used on large and small scales to remove heat from liquids, and it comes in several types like water-cooled and air-cooled chillers.
Industrial chillers are categorized into different types: vapor compression, vapor absorption, screw, scroll, centrifugal, and reciprocating chillers.
These cost-effective and budget-friendly machines are globally used, but they are vulnerable to malfunctioning due to corrosion, electrical issues, and negligence in maintenance. Therefore, it’s vital to ensure adequate care for proper working.
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