Air Conditioning - Basic Refrigeration Cycle
How an Air Conditioner Works | The Refrigeration Cycle The first is the relationship between pressure and temperature, known as the. Figure shows the relation between refrigeration and air conditioning in a pictorial form. At lower temperatures cryogenic systems are more economical. If you experience any problems with the site, please contact Pete Hoffman immediately For an air conditioning system to operate with economy, the refrigerant must be For this reason, all air conditioners use the same cycle of compression.
The Science Behind Refrigeration
The outside unit is normally located on the side or back of the building. Other kinds of air conditioning systems, such as ground-source and water-source, follow the refrigeration cycle, but some of the specifics, such as location and parts may differ.AC Avalanche - Auto Air Conditioning 101 Made Easy
Here are the basic parts of the refrigeration cycle the same process that your refrigerator used to keep food cold: Air flows over the indoor coils, which contain extremely cold refrigerant. When air flows over the cold coils, heat from the air gets transferred to the refrigerant inside the coils. After the air flows over the coils, it gets cold, normally dropping around 20 degrees.
This process follows the 2nd law of thermodynamics, which says that heat naturally spontaneously flows from a warmer body to a cooler body. After the refrigerant absorbs the heat, its state changes from a liquid to a vapor.
This warmer refrigerant gas then gets transferred to the compressor step 2 in the refrigeration cycle. Warmer, vaporized refrigerant gets compressed pressurized to a hot temperature. Even though the refrigerant has absorbed heat from the indoor air, it is still fairly cool. The still cool, but warmer vaporized gas enters the compressor located in the outside unit to increase its pressure and temperature.
We increase the temperature of the refrigerant because it needs to be warmer than the outdoor air. Remember the 2nd law of thermodynamics again—heat flows from warmer to cooler bodies. If the refrigerant is degrees and the outdoor air is 90 degrees, the outdoor air is cooler, which means the heat from the refrigerant will flow in the direction we want—outside. If the temperature outside is degrees, the compressor will have to work extra hard to increase the temperature of the refrigerant to a higher temperature.
Very hot refrigerant flows into condenser coils where it loses heat to the outdoor air. Since the refrigerant has been compressed pressurizedit is now hotter than the outdoor air. A condenser fan blows hot outdoor air over the even hotter outdoor condenser coils.
Then, more heat specifically the latent heat of condensation is released as the refrigerant liquefies. There are air-cooled and water-cooled condensers, named for their condensing medium. The more popular is the air-cooled condenser. The condensers consist of tubes with external fins. The refrigerant is forced through the condenser. In order to remove as much heat as possible, the tubes are arranged to maximize surface area. Fans are often used to increase air flow by forcing air over the surfaces, thus increasing the condenser capability to give off heat.
This is the part of the refrigeration system that is doing the actual cooling. Because its function is to absorb heat into the refrigeration system from where you don't want itthe evaporator is placed in the area to be cooled. The refrigerant is let into and measured by a flow control device, and eventually released to the compressor. The evaporator consists of finned tubes, which absorbs heat from the air blown through a coil by a fan.
Fins and tubes are made of metals with high thermal conductivity to maximize heat transfer.
Refrigeration - Wikipedia
Phosphonates are particularly useful as threshold inhibitors of scale formation and as iron oxide dispersants. Certain low-molecular-weight polymers also have the ability to control calcium carbonate scale formation. Suspended solids airborne dust and debris from the air passing through the cooling tower contribute to general fouling and can aggravate scale formation.
The deposits may also cause localized under-deposit corrosion.
Fouling of heat transfer surfaces has an insulating effect that reduces the energy efficiency of the process. Failure to control scale formation also reduces the rate of heat transfer. Accordingly, a properly designed treatment program must include polymeric dispersants and scale control agents to minimize general fouling and inhibit scale formation. Corrosion Water in an open recirculating cooling system is corrosive because it is saturated with oxygen. Systems in urban areas often pick up acidic gases from the air that can be beneficial in scale reduction.
However, excessive gas absorption can result in severely corrosive water. Chromate-based corrosion inhibitors are very effective, but their use is now prohibited in comfort cooling towers. The most commonly used corrosion inhibitors are phosphate, molybdate, zinc, polyphosphate, silicate, and organic-based treatments. These inhibitors can be applied in low or alkaline pH treatment ranges. At low pH, a high phosphate level is used to promote the passivation of steel.
At high pH, a combination of various corrosion inhibitors and deposit control agents is used. These programs use organic inhibitors in combination with zinc, phosphate, or molybdate.
Where these are environmentally unacceptable, silicates may be used at an alkaline pH. This type of inhibitor program also includes deposit control agents. However, silica concentration must be controlled to prevent deposition of silicate, which forms a hard and persistent scale.
Azoles, functioning as copper corrosion inhibitors, are used in most programs to improve the corrosion protection of copper and to minimize pitting of ferrous metals. Because the heat load on many cooling tower systems varies with changing weather conditions, water evaporation rates tend to be irregular. As a result, cooling system protection can be less than desired or expected under conditions of wide load fluctuation.
Automated water treatment control equipment substantially improves treatment results in systems that operate under these conditions. Slime and Algae Many types of antimicrobials are available for control of algae and biological slime in open cooling systems. Nonoxidizing organic materials such as quaternary ammonium salts, other organic nitrogen compounds, and organosulfur compounds are frequently used.
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Some antimicrobials can be detoxified before discharge into the environment. Microbiological programs often employ a combination of nonoxidizing and oxidizing chemicals. Oxidizing chemicals include chlorine, hypochlorites, organic chlorine donors, and bromine compounds. Chlorine gas requires chlorination equipment and controls, which are not practical for most air conditioning systems. Chlorine and hypochlorites must be applied carefully, because excessive chlorine will increase corrosion and may contribute to deterioration of cooling tower wood and reduction of heat transfer efficiency.
For more information on microbiological problems and antimicrobial use in cooling systems, see Chapter The chilled water is contained in an open systemor circulated from a closed system. Air washers remove dust, smoke, and odors from the air. Additionally, the return air from a manufacturing process may contain unique contaminants that must be removed.
Process contaminants include fiber and oil in textile plants, tobacco dust in tobacco plants, and sizing material in cloth weaving plants. Filters remove particulate matter from the air before it passes through the spray section.
Eliminator blades prevent mist or water droplets from leaving the unit with the air. In addition to cleaning, air washers usually perform other functions. Air temperature and humidity can be controlled through adjustment of the spray water temperature. When air must be humidified in winter, some water is evaporated.
This increases the solids concentration in the remaining liquid. Generally, scale does not form, because the temperature of the water is relatively low. If the spray water temperature is below the dew point of the entering air, the air is dehumidified. In summer, dehumidification involves condensing water vapor from the air, diluting the solids in the recirculating water, and causing water to overflow from the bottom sump or pan of the air washer.
Corrosion can develop in air washers as it does in recirculating cooling water systems.