It is quite difficult to understand everything that is in the world. And to be a professional in all areas of science and technology is completely impossible. However, on duty, for training purposes, or simply to increase our own awareness, we need to quickly get the most information about any device or process, in an easy and accessible way for non-professionals. For these purposes, there are so-called “manuals for dummies,” that is, for those who need to quickly understand what is at stake and how it works. We will analyze a similar instruction and consider the principle of operation of the chiller (for dummies).
What it is
A chiller (or a refrigeration machine in another way) is an aggregate for creating artificial cold and transferring it to the appropriate refrigerant. As a rule, ordinary water acts as such, less often brines (solutions of salts in water). The etymology of the word relates it to the English language, to the verb to chill (English) - to cool, and the noun chiller (English) formed from it - cooler . The chiller can be of two different types. There is a vapor compression and absorption chiller. The principle of operation of each of them is significantly different.
Always cool
The main task of any refrigeration unit is to obtain cold in artificial conditions, that is, where it is impossible to do this due to nature (freecooling). It is clear that to cool the water in winter, with a deep minus on the street, is not difficult. But what to do in the summer when the ambient temperature is much higher than we need? Here the chiller comes to the rescue. Its principle of operation is based on the use of special media created by certain substances (refrigerants). They have the ability to remove heat from another medium (that is, cool it) during boiling, transfer and release it to another medium during condensation. During the operation of the refrigeration cycle, such refrigerants change their phase (aggregate) state from liquid to gaseous and vice versa.
Heat exchangers
Any refrigeration machine can be divided into two zones: low and high pressure. Regardless of the type, there will always be two heat exchangers in any chiller: an evaporator in the low pressure zone and a condenser in the high pressure zone. Without these two system components, the chiller cannot work. The principle of operation of such heat exchangers is based on thermal conductivity (conduction), that is, the transfer of heat from one medium to another through the wall separating these two environments. The evaporator of the chiller returns the generated cold to the system to the consumer, and the condenser either discharges the heat removed to the environment or sends it to recovery (heating the first stage of hot water supply, warm floors, etc.).
How does it work
Consider a standard vapor compression chiller. The principle of operation of such a refrigeration machine is theoretically based on the Carnot cycle. The compressor increases the gas pressure, while simultaneously raising its temperature. Hot gas under high pressure is supplied to the condenser, where it is involved in the process of heat exchange with another medium of lower temperature. As a rule, it is either water (brine) or air. Here, the gas condenses into a liquid, in the process of which excess heat is released, which is given to the coolant and thus removed from the consumer. Then the fluid enters the throttling device, where there is a decrease in pressure in the system with a corresponding drop in temperature. After this, the liquid partially boiling in the expansion valve (thermostatic expansion valve) enters directly into the evaporator, which is also an important part of the chiller-fan coil system. The principle of operation of the evaporator is similar to a condenser. Here, heat exchange occurs between the coolant (which carries the cold to the fan coil) and the refrigerant, which begins to boil and at the same time takes the heat from another medium. After the evaporator, gas enters the compressor and the cycle repeats.
Absorption chiller
The operation of the compressor in the vapor compression cycle requires significant energy costs. However, already now there is equipment to avoid these expenses. Consider the principle of operation of the absorption chiller. Instead of a compressor, a pressure-boosting system based on an absorbing substance using an external heat source is used here. Such a source can be hot steam, hot water, or thermal energy from burning gas or other fuel. This energy goes to the rectification or evaporation of the absorbent, during which the refrigerant pressure rises and it is supplied to the condenser. Further, the cycle works similarly to vapor compression, and after the evaporator, gaseous refrigerant is fed to the heat exchanger-absorber, where it is mixed with the absorbent. Ammonia (in water-ammonia chillers) or lithium bromide (bromistolitievye ABKhM) is used as an absorbent.
Chiller fan coil system
The principle of operation is based on the preparation of air in special heat exchangers, closers, fan coils (from the words fan (English) - fan and coil - coil ), which are installed in the air ducts before its direct distribution to the serviced room. The advantages of such systems over central air conditioning is that in each room you can maintain different air parameters (temperature, humidity, mobility), depending on the purpose of the room and the calculation of the heat balance. And although the air from the air handling unit is sometimes passed through closers for its final processing, that is, in the same way as in the chiller-fan coil system, the principle of operation of the described systems is noticeably different.