This chapter includes all research into the current state of the art. Section 2.2 details the history of refrigeration, the refrigeration cycle, and the various types of refrigeration equipment available and most commonly used. Section 2.3 discusses the refrigeration and freezing of various products. Section 2.4 provides information on programmable logic controllers (PLC). This section includes a brief history of PLCs, how they work, different programming languages used and some commonly used instructions. Section 2.5 describes various types of signals used in control including digital, analog, serial, fieldbus, and SCADA.
2.2 Refrigeration Process
2.2.1 Background
For most of history, ice and snow, packed into cellars insulated with wood or straw, were used for refrigeration. It wasn’t until 1755 that the first artificial refrigeration system was established by William Cullen (Koelet, 1992). Throughout the 1800s, many mechanical refrigeration systems were designed and developed, and the vapour compression cycle most commonly used today dates back to this time.
Different refrigeration cycles exist including the gas cycle, the vapour-absorption cycle, and the vapour-compression cycle. The gas cycle uses a refrigerant, often air, which does not change state, but instead remains as a gas throughout the entire cycle. The vapour-absorption cycle, which preceded the vapour-compression cycle, is a heat operated cycle. It requires little electricity, but a lot of heat energy, and is usually only used where waste heat is plentiful (Ameen, 2006). The vapour-compression cycle is favoured over all others in both domestic and industrial installations as it is the most efficient system available. It works by pumping a refrigerant, which chang...
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... two devices, which were connect together using an RS-232 cable, to communicate. A fieldbus, which transfers data serially, reduces the number of cables required over long distances. The data transferred is available at all the nodes at the same time. Fieldbus is a flexible system allowing new units to be easily connected to the bus.
2.5.5 SCADA
SCADA (supervisory control and data acquisition) is a graphical application used for monitoring and controlling systems in industry from a centralized location. It receives real time data from the PLC, and can be used to input values and turn on/off outputs. It can provide alarms to allow the user to know when a process has finished or if a fault has occurred. SCADA systems often use HMI (human-machine interface) to allow the user to control valves, pumps, etc. which the HMI is connected to (Inductive Automation, 2014).
Ruth Schwartz Cowan wrote “How the Refrigerator Got Its Hum” in 1983. It was included in the section, “Failed Machines” of her book. I never thought about why most refrigerators are electric. We have owned gas stoves and dryers, but never a gas refrigerator. Gas appliances cost more upfront, but are inexpensive to run over time. Personally, I would rather have gas appliances than electric and believe many other people would too; however, there are major factors that caused the gas refrigerator to fail.
Next, the refrigerant moves on to the next side of the refrigeration cycle, which is the high pressure side. The refrigerant leaves the compressor as a high temperature, high pressure gas and then moves to the condenser. At the condenser, the hot gas is condensed back to a liquid and it’s heat is given to the outside air. The refrigerant then moves from the condenser to the expansion valve where the amount of flow is restricted and lowers the pressure as the refrigerant leaves the expansion valve.
Refrigeration is the process of cooling down a space or thing below normal environmental temperature. Food preservation is vital in today’s day and age. From the meats to the dairy, everything needs to be kept at room temperature, cold, or frozen. People even like to make themselves cold and frozen by using air conditioning. But, it does make you wonder “how” and “when”. How did refrigeration become such an important invention and how did people survive without it? When did our ancestors realize it takes the cold to keep their food preserved and looking fresh? We now have fridges that have an automated ice machine and touch screens.
A. Bar-Cohen, G. Sherwood, M. Hodes, and G. Solbreken, "Gas-assisted evaporative cooling of high density electronic modules," Components, Packaging, and Manufacturing Technology, Part A, IEEE Transactions on, vol. 18, pp. 502-509, 1995.
improving building central plant system. To do so, we are going to maximize the chiller
In this paper over natural refrigerant I will be covering the pros and cons of natural refrigerant in light commercial and residential applications. There are many natural substances in this world that can be used to help or decrease the efficiency of a heating ventilation air conditioning system. Some of these substances are water, air, ammonia, and hydrocarbons. All these substances are natural that come from the earth we live on. Over the course of this paper I will be covering the pros and cons of swamp coolers, geo thermal heating and cooling units and how these natural substances can help and or decrease how your heating and cooling unit performs.
The diagram below the text shows the components of a vapor-compression refrigeration cycle: a compressor, condenser, expansion valve, and evaporator. A low pressure, low temperature liquid is converted to vapor in the evaporator, thus absorbing heat from the refrigerated space and keeping that space cool. The fluid is driven around the cycle by the compressor, which compresses the low temperature, low pressure vapor leaving the evaporator to high pressure, high temperature vapor. That vapor is condensed to liquid in the condenser, thus giving off heat at a high temperature to the surrounding environment. Finally, the high pressure, high temperature liquid leaving the condenser is cooled and
The factors for exponential growth for air-conditioning are the HVAC Market, energy, environment, communication, societal, political, preparing for the future, looking ahead, and the conclusion. Buildings of the U.S. use approximately 35% of the nation’s precise total of energy consumption. The worth of shipments by U.S. HVAC manufacturers was over $28 billion of 1996. Since there are 52,000 CHC chillers needed to be replaced among the U.S., there’s a large opportunity for new chillers, new technology for the HVAC industry. The ozone depletion is an international issue in which is currently being resolved. The 3rd world countries are still allowed to manufacture CFC’s. Illegal imports of CFC’S to the U.S. is a consistent concern. Many illegal imports are virgin CFC’s. Those whom have a political overtones are specifically the ones whom create a protectionism of local commerce, having a negative impact on those inside and out of the country.
In order to accomplish this some input of energy is needed. The two major methods of refrigeration in use today are the vapour compression cycle and the slightly less common absorption refrigeration cycle. Vapour compression refrigerators are most common in residential and commercial refrigeration systems. This refrigeration system takes mechanical work as an input via a compressor to extract heat from a cold environment and expel it to ambient. The basis of the cycle is compression of a vapour refrigerant into a superheated state via mechanical work, condensing the vapour by expelling heat to ambient, throttling the vapour to a cold saturated mixture, and externally absorbing heat from a refrigerated space. Absorption chillers take heat as an input to accomplish the same task. In this case the refrigerant is typically ammonia or lithium bromide. The cycle is similar, but in place of a mechanical compressor there is a thermal compressor which absorbs heat as energy and requires very little mechanical work as an
Electric Thermal Storage (ETS) heat is a quiet, odorless, affordable technology utilizing electricity. ETS pertains to the development of transforming electricity to thermal energy and saving it as heat. ETS has been around for decades and is commonly used in Europe and Canada. However, this type of storage is not feasible in areas with a lack of electrical service or high-priced electricity. ETS is effective where low-priced off-peak power capacity is offered. Heat can be stored in a few types of storage materials. The most common type of storage material is high-density ceramic bricks with an electrical heating element at its core. The bricks are encased in insulat...
It is a hot, humid evening in Pittsburgh, Pennsylvania, and you find yourself dripping with sweat. The air is still, and you stick to your sheets as you toss and turn and try to sleep in your house that has retained all of the heat from the summer sun’s rays. Uncomfortable and miserable, you think to yourself, “How did people ever live without air conditioning?” yours has been on the fritz, and you cannot imagine what your life would be like if you didn’t have the luxury of an air conditioning unit in your home. If it weren’t for Willis Carrier, and his ground-breaking invention of a mechanical air conditioning unit in 1902, our lives would be drastically different.
Refrigerators are a life necessity by everyone in the world today their basic feature which is the ability to keep food and drinks cooled and fresh are essential for daily life. Artificial refrigeration began in the mid- the 1750s and developed in the early 1800s (Figure2f,2016). Throughout the year’s fridges have become a higher tech and can do so much more than just its regular functions. Many companies have made modern day top of the line refrigerators and they have amazing features.
RTDs are sensors used to measure temperature by relating the resistance of the RTD element with temperature. Most RTD elements are made up of finely coiled wire wrapped around a ceramic or glass core.The RTD element is made from a pure material which is usually platinum, nickel or copper. Platinum is often the choice made in resistance thermometers as it can measure different measures of extreme ends, is very unreactive and has a linear resistance relationship with temperature.The material has a calculable change in resistance as the temperature changes and this change is used to determine the temperature. RTDs are typically used to measure fluid or gas temperatures in pipes and tanks.
In thermodynamics Refrigeration is the major application area, in which the heat is transferred from a lower temperature region to a higher temperature region. The devices which produce refrigeration are known as Refrigerators and the cycle on which it operates are called refrigeration cycles. Vapour compression refrigeration cycle is the most regularly used refrigeration cycle in which the refrigerant is alternately vaporized and condensed and in the vapor phase it is compressed. Gas refrigeration cycle is the well-known refrigeration cycle in which cycle refrigerant remains in the gaseous phase throughout the cycle. Cascade refrigeration are the other refrigeration cycles discussed in this chapter; absorption refrigeration is the one more refrigeration cycle which is used where the refrigerant is dissolved in liquid before it is compressed. One more refrigeration in which refrigeration is produced by passing the electric current through two dissimilar materials is called as the thermoelectric refrigeration.
As compared to an ideal refrigerator(Carnot cycle), the thermoelectric junctions are 5-10% efficient, whereas, the conventional compression cycle systems(compression/ expansion used by reverse Rankine systems) have 40-60% efficiency. Therefore, thermoelectric cooling, due to it’s a ...