The 2019 World Refrigeration Day was established with the aim of educating people worldwide about the importance of HVAC-R in modern life. Humanity relied only on nature to produce cold for centuries. From the terracotta-ringed underground storage systems created by the Chinese emperor Shi Huang Ti (220 B.C.) to the Hudson River ice farms in the middle of the 19th century, the development of refrigeration technologies was constrained by the seasonal availability of natural ice (Gantt 2015).
We can claim that the "ice farms" of the Hudson River in New York, in the United States, where the ice blocks were collected through the procedure known as Ice Harvesting, was where the commercial sector we now know as the cold chain got its beginnings. The blocks were divided into smaller pieces, removed, and then shipped to various locations to be stored in Ice Houses (warehouses with thermal isolation to preserve the ice collected from the natural world). William Cullen of the University of Edinburgh is credited with the first attempts to create artificial ice. In 1755, he created ice by producing a vacuum in a container containing a volatile fluid. The earliest description of a comprehensive refrigeration system encompassing the four fundamental processes (compression, condensation, expansion, and evaporation) was only developed in 1834, thanks to the work of British engineer and inventor Jacob Perkins (British patent 6.662). Since then, we have gone a long way, developing new technologies that have facilitated the growth of industries and improved living standards all around the world. But how does a fundamental refrigeration system function?
The operation of a refrigeration system
The vast majority of freezers operate using the vapor compression theory. Compressor, condenser, expansion device, and evaporator are the four fundamental parts of a standard refrigeration system. The refrigeration system circulates a volatile fluid (refrigeration fluid), which is repeatedly transformed into liquid and vapor forms. Superheated vapor must be compressed in order to move from a low pressure (evaporating pressure) to a high pressure (condensation pressure) state. Following that, the condenser is approached by the high-pressure, high-temperature refrigeration fluid.
And what purpose does the condenser serve? A heat exchanger known as the condenser works at high pressure and temperatures that are higher than the environment in which the system is installed. The condenser can reject heat from the refrigerant fluid to the environment in this way. By rejecting heat, the refrigerant fluid is converted from a superheated vapor to a subcooled liquid at the heat exchanger exit, reducing its overall energy.
Typically, a filter drier is used to remove humidity from the system while the refrigerant fluid is still in the liquid condition.
Part of the refrigerant shifts phases (from liquid to vapor state) as it expands in the expansion device (a capillary tube or expansion valve, for example) on its way out of the filter drier after having its pressure dropped.
The fluid's temperature is reduced as a result of the refrigerant's conversion from liquid to vapor. A CT SL EX (capillary tube suction line heat exchanger), also known as an intermediate heat exchanger, is typically used in refrigeration systems. In general, this heat exchanger works by raising the refrigerant temperature in the compressor suction, which lowers issues such line sweating or liquid return into the compressor, and lowering the enthalpy in the evaporator inlet (specific cooling capacity gain).
The refrigerant fluid is in a two-phase (vapor + liquid) state at evaporating pressure when it exits the expansion mechanism. The removal of energy from the refrigerated environment (for instance, the freezer section of a residential refrigerator) is made possible by the refrigerant flow, which occurs at low temperature, through the heat exchanger (evaporator). The refrigerant stops evaporating when it absorbs energy from the refrigerated environment (lowering the freezer's temperature), and normally all the liquid that is left is converted to vapor and flows into the compressor suction, where the cycle is repeated.
Replacement of the compressor based on return pressure
Applications for compressors are often categorized based on the system's evaporation temperature level. Three categories of compressors are distinguished:
(i) Low Back Pressure (LBP),
Medium Back Pressure (MBP)
High Back Pressure, or HBP,
Low back pressure (LBP) compressors are recommended for applications with evaporation temperatures of about between -35 C and -10 C such as the horizontal and vertical freezers, as well as the refrigerated islands merchandisers frequently found in supermarkets and convenience stores.
MBP (medium back pressure) compressors are recommended for usage in applications where the evaporation temperature is roughly between -20 C and 0 C such as in supermarket freezers, bakeries, and dairy merchandisers. To maintain food freshness and prevent freezing damage, some of these products can function even at positive compartment temperatures.
Wine coolers and drinking fountains are examples of applications that benefit from HBP (high back pressure) compressors, which are recommended for evaporation temperatures between -15 C and 10 C.
Characteristics that matter when replacing a compressor
Knowing the major features of the refrigeration system is crucial for choosing the right compressor replacement. Each application requires a different type of refrigerant fluid, oil, and electric components. Before making any changes, always refer to the Tool Box app for embrace. Incorrect substitutes not only compromise system performance, but they also pose hazards.
The cooling capacity of a compressor is another important consideration when choosing it for a particular application.
It must be sufficient to meet system demands during operation, such as quick cabinet temperature reduction upon first system start-up (known as pull down), temperature recovery following door openings, or even upon the introduction of hot cargo (such as cans, bottles, or hot food), to the system. The array of embrace products is designed to provide the optimal cooling capacity at the highest levels of energy efficiency.
The system insulation is crucial when discussing the required cooling capacity, since it prevents energy from the environment from entering the refrigerated compartment. Better thermal insulation results in a system that is more cost-effective and requires less cooling capacity.
According to test conditions, the addition of doors to merchandisers like those found in supermarkets significantly reduces the infiltration of latent (humidity) and sensitive (hot and dry air) thermal loads, which can result in an energy consumption reduction of up to 40% (Lighter 2007; Humdinger 2019).
As we can see, refrigeration involves a lot of technology and has evolved into an essential aspect of our way of life. As a result, everyone working in the cold chain industry—from component makers to technicians and installers—must keep up with the industry's ongoing and rapid change.
Because of this, we can rejoice in the establishment of World Refrigeration Day and know that the world is a better place because of what we do.
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