What is a chiller?
A chiller (cooling water circulation device) is a general term for a device that controls the temperature by circulating a liquid such as water or heat medium as a cooling liquid whose temperature was adjusted by the refrigerant cycle. In addition to maintaining the temperature of various industrial devices and laboratory instruments, equipment and apparatuses at a constant level, it is also used for air conditioning in buildings and factories. It is referred to as a “chiller” because it is often used for cooling.
A chiller can supply chilled water continuously while circulating water in a cooling device. It is used a lot as a suitable device to cool heat generating parts and air conditioning equipment such as laser processing devices and high frequency heating devices at a constant temperature, solves various cooling problems and can reduce running costs while improving energy efficiency.
Differences between a chiller and freezer
The role of a chiller is mainly cooling, but a freezer has a similar function. The differences between a chiller and freezer are extremely vague, and some parts may be difficult to comprehend. However, as you can tell from the different names, strictly speaking, they are different devices. So, what are the differences between a chiller and a freezer? Here we will be explaining the differences between them.
Principles of a chiller and freezer
You can think of the principles of a chiller and freezer as almost the same. Because both are used to cool their intended objects, they both possess cooling capacities. The basic principle of a chiller and freezer is to cool the intended object and lower the temperature, so there is little difference in that respect. It's hard to tell the differences between a chiller and freezer, and it’s easy to get confused because the principles are almost the same. There is no doubt that they are very similar devices.
However, even if the principles are almost the same, several differences can be seen in the cooling mechanisms. In other words, if you can understand the mechanisms, you can begin to see the differences between a chiller and a freezer. Let’s take a detailed look at the mechanisms.
Differences between the mechanisms of a chiller and freezer
First, let’s take a look at the mechanism of a chiller. The way a chiller works is that a liquid called a coolant circulating inside the chiller cools the intended object. Various liquids, including water, are used to produce the coolant, but in any case, this coolant removes heat from the object and cools it. The coolant spins around inside the chiller and removing the heat of an object also means that the temperature of the coolant rises. To reuse it, you need to lower the temperature again, so this is where water or air is used. The temperature of the coolant is reduced by using water or air taken in from the outside, and the coolant that has cooled down is used again to cool the intended object. By doing this, it allows continuous cooling of the intended object. On the other hand, with a freezer, cooling is performed by creating chilled air by exchanging heat between the refrigerant and air. Chilled air is created by the refrigerant without using any liquids such as circulating fluid. Perhaps it is easier to imagine if you think of it like an air conditioner. In this way, the mechanisms are different even though they are both devices used for cooling. If you can remember the differences between these mechanisms, it will become easier to tell the difference between a chiller and a freezer.
Both the chiller and freezer use a compressor. Gas can be compressed and emitted by the compressor.
In terms of their differences, in the case of a chiller, generally, all equipment except the capacitor, is contained in a single package, including the compressor. This is a unique feature of a chiller.
In the case of a freezer, each device is not packaged as a single package and is in a disjointed state. Although subtle, these differences are used to distinguish between a chiller and a freezer. You should understand the difference between whether the equipment including the compressor is contained in a single package or not.
Usage in the chiller industry
In the industrial field, highly efficient and highly accurate heat source machines that can supply a large amount of water at a stable water temperature are required to improve the quality and efficiency of production, and there is a demand for these heat source machines in a wide range of facilities such as factories, supermarkets, leisure facilities, hydroponics and aquaculture farms. Cooling required for the manufacturing process, such as suppressing heat generation in production and processing machines, cooling products and water temperature adjustment required for production, is referred to as “process cooling”, and this is especially used for factories that produce chilled water and low temperature heat source machines. A chiller is used to cool products, machines and factory machinery from a wide range of industries, and the contents are roughly divided into "equipment cooling" and "article cooling".
The purpose of equipment cooling is to suppress heat generation due to the operation of the processing equipment and avoid malfunctions and deterioration of processing accuracy and is used in a wide range of applications such as cooling of semiconductor manufacturing equipment, medical equipment such as CT and MRI, printers and laser processing machines and component analyzers.
On the other hand, the purpose of article cooling is to cool the heat generated by processing products and to maintain and cool the temperature required for processing and storage, and is used for cooling plastic molded products, metal processing products, plating solvents, cutting oil and brewing tank and cooked foods.
Usage in chiller air conditioning
In the field of air conditioning, it is common to use a chiller, which is a cooling device, for cooling, but currently, it is used as a device for cooling and heating.
The basic mechanism is to generate both chilled and hot water by heat exchange between the cooling water of the cooling tower and the refrigerant in the chiller, and the function of heating and cooling is realized by transporting it to the heating and cooling terminal. The chiller and cooling tower are extremely similar devices, but strictly speaking, each has a different role. The function of a cooling tower is to cool the cooling water mainly in air conditioning equipment. The cooling water with rising temperature is cooled using the power of the outside air to lower its temperature.
On the other hand, chillers are also used to cool the liquid inside the machine, but its purpose is not only cooling.
The purpose of a chiller is to utilize the power of outside air and water to maintain the target temperature at a constant level. Therefore, it can be used to cool or heat. Because it is necessary to keep the temperature constant at all times, it is not limited to cooling. Of course, it is often used for cooling, but sometimes it is used for heating, which is a major difference between a chiller and cooling tower. By knowing this difference, it can help you understand the mechanism and structure of a cooling tower.
Cooling towers are used for air conditioning equipment of a building and uses outside air to keep the cooling water cool. The cooling water can be reused by cooling it, and you can continue to use it in a way that circulates air conditioning equipment, etc. Without a cooling tower, the water cannot be cooled, and when the temperature of the cooling water rises steadily it becomes unusable.
Types of chillers
A chiller draws removes from the target device and cools it. The removed heat needs to be exhausted by the chiller itself, and as a heat exhaust method, there are those that use chlorofluorocarbons called refrigerants and those that consist of water circuits that circulate water. There are various types of cooling methods, such as the air-cooled type and water-cooled type.
This is a type of system that sends wind to the heat exchanger and cools the refrigerant with air. There is a built-in fan motor inside the chiller, and it is easy to install, but because exhaust heat is generated in the room, exhaust equipment may be required in tight spaces. The gas compressed with the freezer (compressor) is cooled by a condenser (radiator) and liquefied. It is comprised of a refrigerant gas cycle and a circulating water cycle, and refrigerant gas is used as a heat medium to cool the circulating water.
By passing liquefied gas through the expansion valve, the pressure is reduced, and it becomes a cooling gas, and a water cooler (heat exchanger) exchanges heat with the circulating water to cool the circulating water. Because there is no freezing or clogging, aquarium cleaning maintenance is easy. Also, in the case of the air-cooled chiller, the heat of vaporization due to the evaporation of rainwater lowers the temperature of the radiator when rainwater comes into contact with the cooling tower when it rains, and because the temperature drops due to the evaporation of rainwater around the air-cooled chiller, the cooling efficiency can be maintained regardless of the rise in humidity, such that the cooling efficiency improves even if the humidity is high.
This is a type of system that uses a cooling tower to cool water. Cooling water for the refrigerator is required, but it offers advantages such as excellent cooling efficiency and does not generate exhaust heat in the room.
A water-cooled chiller that uses water, which is active in the field of large-scale air conditioning, as a refrigerant, is referred to as a natural chiller (absorption chiller) and is adopted as a heat source refrigerator for central air conditioning of air conditioning equipment for medium and large-scale buildings. The system configuration is comprised of an evaporator, absorber, regenerator and condenser, and produces chilled water (hot water) with pressure control by circulating the refrigerant sealed in the equipment (cooling water circulation device).
It is a cooling cycle, but by changing the pressure of the refrigerant in the equipment, chilled water (hot water) is produced by changing its composition to gas and liquid (latent heat transfer) inside an airplane. It can be stably operated throughout the year, and a compact design is possible so that it can be installed in small spaces.
Mechanism of the absorption chiller
The absorption chiller cools the inside of the refrigerator by utilizing the property of removing heat from its surroundings when the cooling unit is enclosed with natural refrigerant ammonia aqueous solution and hydrogen and the ammonia vaporizes. With technology that does not require any driving parts, such as compressors and fans used for typical chillers, the cooling system can be operated without vibration and noise.
The aqueous ammonia solution of refrigerants used by the absorption chiller is a natural refrigerant with zero ozone depletion potential (ODP) and global warming potential (GWP).
In addition to providing excellent solutions for energy saving and environmental conservation, it also contributes to reducing corporate costs.
Advantages of a chiller
One of the main features is that it offers a high degree of freedom in designing the main unit installation location and water piping system. The chiller uses a method of producing chilled water and sending water to the chilled water coil of the air conditioner, so depending on the combination, it can be used for various purposes such as large capacities and large spaces. On the other hand, there is generally no need to consider the difference in the height of the refrigerant pipe and the limitation of the pipe length like a direct expansion type (air conditioner).
Furthermore, steam and hot water such as factory exhaust heat can also be used, and it is possible to construct a cogeneration system that uses waste heat (hot water) of a generator.
Selecting a chiller
When selecting a chiller, it is important to match the functions, performance and specifications of the chiller with the equipment usage conditions and status. If you neglect this matching work, it may not demonstrate the expected performance when it is actually operated, and it is also possible that the equipment to be cooled and the chiller itself may cause problems.
In addition to problems with the set temperature and amount of heat to be cooled, the lifting height of the piping that connects the cooled objects and chiller may change due to the thickness, length and shape of the piping, so selecting the chiller type is not as simple compared to other equipment.
In order to properly select a chiller, first determine the temperature of the circulating water and then determine the cooling method from the installation environment, whether it is air-cooled or water-cooled.
After determining the cooling capacity from the equipment to be cooled and the capacity of the pump, you can move on to the chiller selection. It is important to make a selection while confirming the usage conditions with these processes.
Chiller cooling capacity
The cooling capacity is an important value that can be used as a guide for the operating temperature range for how much the chilled water chiller can cool the intended object (the object to be cooled). The unit of the chiller’s cooling capacity is fixed and is usually expressed in W (watts). However, it is easier to calculate with kcal/h, so we will be using kcal/h to provide an explanation here (1kW＝860kcal/h).
Various conditions are fixed and calculated based on what this value is used as a heat medium and what its capacity is. However, there are other elements such as when self-heating the object to be cooled and when there is a large difference from room temperature and when the degree of endothermic is high, so strictly speaking, there are some aspects that are difficult to grasp, but the following method is used as a rough calculation method.
Q: 0.07 x Cb x γb x Lbx （Tout－Tin）
Q: Cooling capacity (impossible capacity) (kw)
Cb: Specific heat of circulating water (cal/g℃)
*Water is approx. 1.0 cal/g℃
γb: Density of circulating water (g/m³)
*Water is approx. 1.0 g/m³
Lb: Circulating water amount (ℓ/min)
Tout: Load outlet temperature (℃)
Tin: Load inlet temperature (℃)