File Name: troubleshooting and servicing modern air conditioning and refrigeration systems .zip
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For more than a century, industrial air conditioning has been used for drying, humidity control, and dust and smoke abatement. Its most familiar function is to provide a comfortable working environment, to increase the comfort and productivity of personnel in offices, commercial buildings, and industrial plants.
Air conditioning is the process of treating and distributing air to control temperature, humidity, and air quality in selected areas.
Direct water sprays also remove dust and odors. Other air cleaning systems may include mechanical separation, adhesion, screening, filtration, or static attraction, depending on the type of air contaminants encountered and the required air quality Figure Refrigeration is the process of lowering the temperature of a substance below that of its surroundings and includes production of chilled water for air conditioning or process applications. Chilled water for use in processes such as injection molding may be in the same temperature range as chilled water used for air conditioning.
Refrigeration systems are also used to provide chilled antifreeze solutions brines at temperatures below the freezing point of water. Brines are used in icemaking and cold storage, in addition to a variety of chemical process applications. Chilled water may be used in air washers, either in closed coils or as spray water. Chilled water may also be used for closed systems and for individual spray water systems.
Many methods are used to produce and distribute chilled air. In central air conditioning systems, air is passed over coils chilled by water, by brine, or by direct expansion of a volatile refrigerant. The chilled air is then distributed through ductwork. The water systems associated with air conditioning can be classified into three general categories: open recirculating cooling, air washers, and closed or open chilled water systems.
In water treatment applications, open recirculating cooling systems are similar to open chilled water systems. The basic mechanical components of an air conditioning system are the air and water distribution systems, a refrigeration machine, and a heat rejection system. Refrigeration for air conditioning is usually provided by either absorption or compression cycles.
Absorption refrigeration uses low-pressure steam or high-temperature hot water as the energy source, water as the refrigerant, and lithium bromide or lithium chloride as the absorbent.
Compression refrigeration systems generally utilize a halocarbon compound or ammonia as the refrigerant. An internal combustion engine, turbine, or electric motor supplies the power to drive a centrifugal or positive displacement compressor. Refrigeration, or cooling, occurs when the liquid refrigerant absorbs heat by evaporation, generally at low temperature and pressure.
When the refrigerant condenses, it releases heat to any available cooling medium, usually water or air. The basic refrigeration cycle used for single-stage vapor compression has four components in the system.
They are the compressor, condenser, metering device, and evaporator. Low-pressure liquid refrigerant in an evaporator extracts heat from the fluid being cooled and evaporates.
The low-pressure vapor is then compressed to a pressure at which the refrigerant vapor can be condensed by the cooling media available. The vapor then flows to the condenser, where it is cooled and condensed.
The liquid refrigerant flows from the condenser to a metering device, where its pressure is reduced to that of the evaporator. The cycle is thus completed. In industrial or commercial air conditioning systems, the heat is usually rejected to water. Once-through cooling may be used, but municipal restrictions and water costs generally dictate recirculation and evaporative cooling processes.
Evaporative condensers or cooling towers are normally used for evaporative cooling. A spray pond may be used as an alternative. Cooling capacity is measured in tons of refrigeration. Evaporation of the recirculating water occurs at a rate of approximately 3. Other than the solution and refrigerant pumps, there are no moving parts in an absorption system. Although this is an economical design advantage, the cost of producing the necessary low-pressure steam or high-temperature hot water HTHW must also be considered.
Compression systems also impose an additional heat load. This is due to the energy required to compress low-pressure, low-temperature refrigerant gas from the evaporator and deliver it to the condenser at a higher pressure.
The major energy consumer in a compression refrigeration system is the compressor, which is designed to operate at a certain head pressure for a given load. This pressure equals the refrigerant pressure in the condenser. The term "high head pressure" refers to condenser pressure that is higher than it should be at a specific load condition.
High head pressure can be costly in two ways. First, it presents the danger of a system shutdown; a safety control will stop the compressor motor when the safe maximum head pressure is exceeded in the compressor.
Second, an increase in power consumption results when a compressor operates at greater than design head pressure. Fouled condenser tubes are a common cause of high head pressures.
Fouling increases the resistance to heat transfer from the refrigerant to the cooling water. In order to maintain the same heat transfer rate, the temperature of the refrigerant must be increased.
The compressor fulfills this need by increasing the pressure at which the refrigerant is condensed. Fouling and the formation of scale in absorption systems also reduce operating efficiency.
Because the highest water temperatures exist in the condenser, deposition first occurs in this unit. Under extreme conditions, scale formation can also occur in the absorber. Deposition in the condenser imposes a higher back-pressure on the generator, so that increased steam or HTHW is required to liberate the refrigerant from the absorbent. The result is an increase in refrigerant vapor pressure and a greater temperature differential between the condensing water vapor and the cooling water.
Although this compensates for the resistance to heat flow, more energy is required to provide the increased heat input. If water conditions are severe enough to cause deposition in the absorber, less refrigerant is removed by the absorber, and cooling capacity is reduced. The reduction in refrigerant circulation diminishes the ability of the equipment to satisfy cooling requirements.
If the absorption rate in the absorber is reduced while the absorbent is heated above the normal temperature in the generator, the danger of over-concentrating the brine solution also exists. This over-concentration can cause crystallization of the brine, leading to a system shutdown. Fouling and scale formation waste energy and can ultimately cause unscheduled system shutdown. Effective water treatment can minimize the possibility of high head pressure and excessive steam consumption caused by condenser deposition.
Corrosion can cause problems in either the open recirculating or chilled water circuits. When corrosion is not properly controlled, the resulting corrosion products inhibit heat transfer, increasing energy consumption in the same manner as fouling and scale formation. Unchecked corrosion can cause heat exchanger leaks and catastrophic system failures. In any cooling application, attention to cooling tower operation is important.
Proper tower maintenance maximizes cooling efficiency, or ability to reject heat. This is critical for continuously running refrigeration machinery at full load conditions. For best performance, the cooling tower fill should be kept clean and protected from deterioration.
The water distribution system must provide uniform wetting of the fill for optimal air-water contact. Other components, such as drift eliminators, fill supports, regulating valves, distribution decks, and tower fans, should be kept clean to maintain efficient heat rejection.
Inefficient cooling or heat rejection increases the temperature of the water in the cooling tower sump and, consequently, that of the water sent to the condenser. This makes it necessary to condense the refrigerant at a higher temperature absorption or higher temperature and pressure compression to reject heat at the same rate into the warmer water.
This increases the amount of energy steam, hot water, electricity required to operate the system. As water evaporates in a cooling tower or an evaporative condenser, pure vapor is lost and dissolved solids concentrate in the remaining water.
If this concentration cycle is allowed to continue, the solubilities of various solids will eventually be exceeded. The solids will then deposit in the form of scale on hotter surfaces, such as condenser tubes. The deposit is usually calcium carbonate. Calcium sulfate, silica, and iron deposition may also occur, depending on the minerals contained in the water. Deposition inhibits heat transfer and reduces energy efficiency. Deposition is prevented by threshold inhibitors that increase the apparent solubility of the dissolved minerals.
Therefore, they do not precipitate and are removed by blowdown. Blowdown is automatically replaced by fresh water.
The ratio of dissolved solids in the circulating water to that in the makeup water is called "cycles of concentration. The cooling capacity of a tower is affected by how finely the water is atomized into droplets. Smaller droplets lose more heat to the atmosphere; however, more of the smaller droplets are carried away by the air drawn through the tower.
This "windage loss," or "drift loss," becomes part of the total blowdown from the system. Windage loss is approximately 0. Windage can have undesirable effects, such as the staining of buildings and the spotting and deterioration of car finishes.
These problems are caused by the dissolved solids in the circulating water, which evaporate to dryness as water droplets fall on surfaces. Because water treatment chemicals produce only a slight increase in the dissolved solids content of the water, they usually do not contribute significantly to spotting problems.
Continuous blowdown, or bleed-off, is adequate for scale control in some cooling systems. The importance of continuous blowdown, as opposed to periodic complete draining, cannot be overemphasized. The volume of water in most cooling systems is small compared to the amount of water evaporated.
Therefore, excess solids concentrations can develop in a short period of time. Continuous blowdown prevents excessive solids concentrations from developing in the tower water. In order to maintain solids in solution, water that is high in alkalinity and hardness may require the feed of sulfuric acid or an acid salt in addition to blowdown.
Acid feed requires careful handling and control and should only be used where the blowdown rate would otherwise be excessive. Sodium zeolite softening of the makeup water is also an effective way to control scale.
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For more than a century, industrial air conditioning has been used for drying, humidity control, and dust and smoke abatement. Its most familiar function is to provide a comfortable working environment, to increase the comfort and productivity of personnel in offices, commercial buildings, and industrial plants. Air conditioning is the process of treating and distributing air to control temperature, humidity, and air quality in selected areas. Direct water sprays also remove dust and odors. Other air cleaning systems may include mechanical separation, adhesion, screening, filtration, or static attraction, depending on the type of air contaminants encountered and the required air quality Figure
Thanks to the different technical fields involved in our trade, the variety of material we need to be familiar with fills up some pretty hefty textbooks. These textbooks contain a lot of information that we technicians can forget over time, and I found myself re-learning some basic material when I had to review a textbook to prepare for a class I taught at the local community college. It describes the Marine Refrigeration Manual we have available in pdf format, and explains how to access it on-line at your convenience. You're also welcome to download the free digital edition of our Air Conditioning and Refrigeration System Evaluation Manual, which discusses the pressures, temperatures, superheat, and subcooling readings you can expect to find when air conditioning, refrigeration, and reciprocating chiller systems are running normally.
Air conditioning is used in domestic, commercial settings, including to cool and dehumidify rooms filled with heat-producing electronics, such as computer servers and delicate items such as artworks. Systems that also provide heating as referred to as heating, ventilation and air conditioning systems. The cooling is typically achieved either using an electrically powered device using the vapor-compression refrigeration or by passive cooling. Air conditioning systems can also be made based on desiccants chemicals that remove moisture from the air.
Prior to going out into the field, the student should fully understand the theory and operational or service techniques behind each specific system. They can be found in high schools, colleges, and so on all over the world. The training units in this catalog represent a wide variety of subjects in the heating, refrigeration and air conditioning industries.
The work of energy transfer is traditionally driven by mechanical means, but can also be driven by heat, magnetism , electricity , laser , or other means.