A refrigerator is one of the most sought-after electrical appliances in this day and age. And it makes sense why: after all, refrigerators help store food and beverage and keep them fresh for a little while longer. In other words, refrigerators help avoid food wastage, and because of that, every building — whether it’s residential, commercial, or industrial — needs to have one.
This is where you come in as an HVAC professional: you’re going to provide your customers with their refrigerator needs. But before you can do that, you first have to know about the various components that make up a refrigerator. That way, you will understand better how refrigerators work, thus allowing you to enrich your future services to your customers.
With that said, here are the essential components that comprise a refrigerator and how each of these works.
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Essential Components of Refrigerators and How They Work
Hermetic Refrigeration Compressor
Generally speaking, a compressor is a mechanical device that increases the pressure of a gas by reducing its volume. There are actually various kinds of compressors, and in the field of refrigeration specifically, compressors are often described as being either hermetic, open, or semi- hermetic. These terms describe how the compressor and motor drive are situated in relation to the gas or vapor being compressed. The industry name for a hermetic is hermetically sealed compressor while a semi-hermetic is commonly called a semi-hermetic compressor.
In hermetic and most semi-hermetic compressors, the compressor and motor driving the compressor are integrated and operate within the pressurized gas envelope of the system. The motor is designed to operate in, and be cooled by, the refrigerant gas that is compressed.
The primary difference between the hermetic and the semi- hermetic is that the hermetic uses a one-piece welded steel casing that cannot be opened for repair. This means that if the hermetic fails, it is simply replaced with an entirely new unit. Meanwhile, a semi-hermetic uses a large cast metal shell with gasket covers with screws that can be opened to replace motor and compressor components.
With all the features of a hermetic and semi-hermetic compressor being said, the biggest advantage of this kind of compressor is that there is no route for the gas to leak out of the system. This is unlike open compressors, which rely on shaft seals to retain the internal pressure and these shaft seals require a lubricant such as oil to retain their sealing properties.
On the flip side, the main disadvantage of hermetic compressors is that the motor drive cannot be repaired or maintained, and the entire compressor has to be replaced if a motor fails. Another big disadvantage is that burnt-out windings can contaminate whole systems, thus requiring the system to be entirely pumped down and the gas replaced. This scenario can also happen in semi-hermetic compressors where the motor operates in the refrigerant.
Usually, hermetic compressors are used in low-cost factory-assembled consumer goods where the cost of repair and labor is high compared to the value of the device and it would be more economical to just purchase a new device or compressor. Meanwhile, semi-hermetic compressors are used in mid-sized to large refrigeration and air conditioning systems, where it is cheaper to repair the compressor rather than buying and installing a new one.
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As you already know, the process of condensation changes gas to a liquid form. And so, the primary purpose of a liquid refrigerant is to liquefy the refrigerant gas sucked by the compressor from the evaporator. As condensation begins, the heat will flow from the condenser into the air, only if the condensation temperature is higher than that of the atmosphere. Then, the high-pressure vapor in the condenser will be cooled to become a liquid refrigerant again, this time with a little heat. After that, the liquid refrigerant will flow from the condenser to a liquid line.
Commonly placed before the evaporator and at the end of the liquid line, the expansion valve — particularly a thermostatic expansion valve — is the one that acts as a regulator where the refrigerant is metered from the high-pressure side to the low-pressure side of the system. This is where the liquid refrigerant goes to after it has been condensed.
The expansion valve’s primary purpose is to reduce the pressure of the refrigerant so that its temperature will also decrease to a level below its atmosphere. Additionally, the expansion valve also controls the flow of refrigerant to the evaporator according to the load, and it prevents the liquid refrigerant from entering into the compressor. In other words, the expansion valve helps maintain an appropriate amount of refrigerant in the high-pressure side and low-pressure side of the system.
An evaporator is used to turn any liquid refrigerant into gas. In this process, heat is absorbed, and the evaporator transfers heat from the refrigerated space into a heat pump through a liquid refrigerant, which boils in the evaporator at a low-pressure. In achieving heat transfer, the liquid refrigerant should be lower than the goods being cooled. After the transfer, the liquid refrigerant is drawn by the compressor from the evaporator through a suction line. Upon leaving the evaporator coil, the liquid refrigerant will be in vapor form.
There is always pressure drop across the evaporator, and it’s even higher in large evaporators. Because of this, evaporators that have a pressure drop of 0.15 kg/cm2 and above should have an equalizing line attached to the evaporator outlet. Otherwise, the evaporator gets starved of refrigerant.
As the name suggests, filter drier is a device used in a refrigeration system that is a combination of a filter and a drier. This means that a filter drier removes any particle such as dirt, metal, or chips from entering the refrigerant flow control while also removing the moisture from the refrigerant at the same time. It is important that there will be little moisture inside a refrigeration system. This is because moisture may cause the failure of compressor valves as well as deteriorate the property of lubricating oil and cause the formation of metallic or other acidic sludge, which may lead to clogging or chocking of valves and other oil passages.
Because of this, a filter drier is necessary for a refrigeration system. It has to be installed in the liquid line at the condenser coil outlet so as to filter or trap minute foreign particles and absorb any moisture or water present in the system. Filter driers are usually used in bigger systems where the refrigerant circuit is designed for field service. Residential units that are charged with refrigerant at factory-level and hermetically sealed do not use these devices since the possibility of moisture and particles entering the system is minimal.
Simply put, a heat exchanger is a system used to transfer heat between two or more fluids, and it can be used in both cooling and heating processes. In refrigeration circuits, heat exchangers are actually used as an evaporator during cooling so as to absorb energy from the refrigerant. On the other hand, during heating, exchangers are used as refrigerant condensers to discharge energy. Meanwhile, in some refrigeration cycles, depending on the application, it is necessary to super-heat or super-cool the refrigerant. In these cases, heat exchangers can also be used.
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Sight glasses are used to indicate whether refrigerant vapors are present in the pipe, which should be carrying only liquid refrigerant. Because of this, the sight glass is installed closest to the thermostatic expansion valve so as to determine how much liquid is present at the expansion valve and being drawn from the filter drier.
Additionally, the sight glass can also be used to indicate the moisture content present in the refrigerant. For this kind of sight glass — appropriately named moisture-indicating sight glass — it has a color indicator that changes color when the moisture content of the refrigerant exceeds the critical value.
The solenoid valve is an electromagnetic valve that is used for the automatic opening and closing of liquid and gas lines. When the coil gets energized, the diaphragm valve plate moves up into the open position and vice versa when the coil is de-energized. The bleed hole will then allow the refrigerant to pressurize the top side of the diaphragm to provide a tight seating closure when the solenoid valve is in a closed position.
Solenoid valves are used in refrigeration and air conditioning systems to isolate the thermostatic expansion valve to avoid evaporator flooding. A burnt-out coil, a damaged diaphragm, or blockage by dirt can cause the solenoid valve to malfunction.
Back Pressure Valve
A back-pressure valve creates back pressure on the evaporator coil and ensures that most of the liquid refrigerant is made available at lower temperature zones. With this, the component may sometimes be fitted into the system to hold back a high evaporator pressure, where two to three evaporator outlet feeds into a common compressor suction line. Other times, it can be fitted at the outlet of the evaporator in a multi-temperature zone system or at warmer rooms where the temperature is set at 4°C to 5°C or higher.
If there is no back-pressure valve, it can lead to low temperatures or over-flooding of the evaporator. This could cause a problem like freezing in water coolers and spoilage of perishable items such as vegetables and fruits. Backpressure valves are spring-loaded and non-return valves.
Refrigerators are some of the most incredibly important appliances as of right now. And this is not surprising at all: after all, refrigeration systems are the ones responsible for keeping our food and beverage cool and fresh. In other words, refrigerators help avoid food spoilage.
Because of the undeniable importance of refrigeration systems, HVAC professionals like you must be ready to provide this kind of HVAC system to those who need it. But before you can do that, you must first know all about the important components that make up a refrigeration system. That way, you’ll have a better understanding of just how exactly this HVAC system works, thus allowing you to improve your service to your customers.
For that reason, that is the purpose of this post: to educate you on the basics of refrigeration systems. Hopefully, after reading this post, you’ll be able to use the knowledge you’ve just gained to enrich your own service to your customers. Additionally, with this knowledge, you’ll hopefully be able to provide the best refrigeration systems possible, and you will also be able to help your customers when they will experience refrigerator problems.
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