Cooling Device Equipment
A cooling device consists of many equipment. Cooling devices, which are divided into two as outdoor unit and indoor unit, have the following components in addition to basic components such as compressor, fan, pipes.
Solenoid and Thermostatic Expansion Valves
As with any refrigeration system, controlling refrigerant flow is vital to the proper operation of a cold room. The two most common types of refrigerant control valves are thermostatic expansion valves and solenoid valves.
Thermostatic Expansion Valves
Thermostatic expansion valves (TXVs) operate as a type of throttling device and are one of the four basic components in a refrigeration cycle, along with evaporators, compressors, and condensers. Like other throttling devices, thermostatic expansion valves reduce the pressure by causing the refrigerant to expand as it flows. This lowers the temperature of the refrigerant and allows it to absorb heat from the cold room through the evaporator. The goal of any throttling device is to keep the evaporator as full as possible of refrigerant and to allow all of the refrigerant to evaporate. This helps prevent compressor damage due to liquid refrigerant entering the suction port. However, unlike some other throttling devices, thermostatic expansion valves automatically regulate the refrigerant flow according to the needs of the evaporator.
The basic parts of a thermostatic expansion valve consist of the sensing bulb, diaphragm, balancing chamber and superheat adjustment spring which work against each other to control the operation of the valves. First, the sensing bulb, filled with a specific liquid corresponding to the specific refrigerant used, is mounted in the suction pipe on the downstream side of the evaporator; as the temperature of the refrigerant increases, the sensing chamber liquid expands and pushes the diaphragm downwards. The superheat adjustment spring then pushes back, creating a constant pressure. Finally, the evaporator pressure in the balancing chamber varies according to different operating conditions such as the refrigerant temperature, ambient temperature, bulb and spring pressures. Depending on the balance created by these three pressures, the valve will open or close, ensuring that a constant superheat is maintained even in changing ambient conditions. Although other throttling devices are available, thermostatic expansion valves work best for cold rooms due to their ability to regulate the refrigerant flow according to the needs of the system. This refrigerant regulation not only ensures that the cold room operates as efficiently as possible, but also means that the cold room will need a lower refrigerant charge, saving money during daily operation and regular maintenance.
Selenoid Valfler
Solenoid valves are a type of regulating valve that uses electromagnets to open or close. Valves come in either normally open (NO) or normally closed (NC), depending on the needs of the system. Each solenoid is equipped with a coil that contains the electromagnet that controls the internal armature assembly. For example, in an NO solenoid, when the valve is activated, it moves the armature assembly downward, closing the valve.
Solenoid valves can be used to redirect refrigerant (closing an NO valve or opening an NC valve) and are most often operated using a controller, although many can also be operated manually. Solenoids work well in a number of cold room applications, including hot gas defrosting and humidity control.
It is ideal to start the hot gas defrost immediately after loading. When the hot product is placed in the cold room, the thermostat senses that the temperature has risen and turns on the compressor to start the cooling cycle. If the cycle continues long enough, the evaporator can start to ice up. When the hot gas from the condenser passes through the evaporator a second time, it melts any ice that may have formed.
When it comes to extending the shelf life of food, humidity control is just as important as temperature control, another great application for solenoid valves. If the temperature in the cold room is low enough but the humidity is too high, one way to reduce the humidity without lowering the temperature any further is to use only half of the evaporator. If there are two evaporator coils in the cold room, installing a NO solenoid valve in front of the one that will be controlled by a humidistat will reduce the humidity in the cold room without affecting the temperature.
As we’ve seen throughout this series, each component can have a major impact on how a refrigeration cycle works, and these valves are no exception. These two small valves have the power to affect the rest of the cold room in significant ways, so it’s vital to choose the one that best suits the specific needs of the cold room. Source: Tunelgroup Cooling System
Pressure switches
While most refrigeration systems use a thermostat to regulate temperature, an alternative method is the low-pressure switch, also called low-pressure control. It works by using the relationship between the saturated refrigerant pressure in the evaporator and the evaporation temperature. In this way, the pressure switch can be set to shut off the refrigeration system when the suction pressure returning to the compressor corresponds to the correct evaporation temperature, thus controlling the temperature of the cold room.
A pressure switch has two main functions: protection and control. On the protection side, it limits the refrigeration pressure by stopping the flow of refrigerant if the pressure exceeds the safe operating limit or if the pressure drops too low (usually due to a leak in the system). On the control side, controlling the pressure also controls various aspects of the refrigeration cycle, such as the compressor cycle, fan cycle, and pumping. Basic pressure switches can be for either high or low pressure. If the refrigerant discharge pressure gets too high, the switch will switch from closed to open, reducing the pressure. Similarly, if the suction pressure drops too low, the switch will switch back to closed, bringing the pressure back to an acceptable level. As with thermostats, setting the differential correctly is vital to ensuring proper operation.
Ball valves
Ball valves are manually operated shut-off valves, usually used on liquid, suction and hot gas lines. Ball valves get their name from their internal structure: the shut-off mechanism is ball-shaped. Because of this shape, all that is required to close the valve is a simple quarter turn, cutting off the flow of refrigerant. The seal is not only tight, but also very reliable, capable of maintaining a complete seal after years of non-use. Although ball valves do not have the precise control of other types of valves, they are not designed for any purpose other than an on/off function.
While the ball valve would normally remain in the open position, it becomes invaluable during maintenance and repair. By fitting ball valves into the cold room’s refrigeration system, the refrigerant can be blocked from one section or another. This means that less refrigerant needs to be recovered, saving time and money in labor and materials. Ball valves are superior to other types of shut-off valves, such as right-angle and Z-type valves, because ball valves can operate without any drop in pressure. When these other types of shut-off valves are in the open position, the refrigerant is forced to change direction, both slowing it down and creating small vortices or whirlpools where the flow changes direction. In contrast, when ball valves are open, the internal opening in the ball is the same size as the surrounding pipe, allowing the refrigerant to flow without any impedance.
Fan speed controllers
Fan speed controls are increasingly being used in cold rooms because of their ability to reduce noise and balance condensing pressures in different climates. In addition to these benefits, fan speed controls can often increase the energy efficiency of cold rooms. By maintaining a constant low speed, fans will consume less electricity than when switching between full speed and off.
An additional factor to consider is the operation of the evaporator fan motors. Under normal operating conditions, fan motors run 24/7, adding heat to the cold room and consuming energy to constantly move air. A more personalized control option involves turning off the evaporator fans during the thermostat off cycle and running the fans at specific intervals to ensure that the cold room air temperature circulates through the thermostat sensor and maintains a constant cold room temperature. Depending on the application, another control option for special areas such as food processing preparation rooms is to use two-speed fan motors. Each of these products affects a relatively small aspect of a cold room’s cooling cycle, but when combined, they create an energy-efficient cold room that fits your needs.
Kaynak: Tunelgroup Cooling System