Refrigeration Unit of HVAC System
Refrigeration Unit of HVAC System
April 10, 2023
Refrigeration schemes should be compared technically and economically based on cooling requirements (cooling consumption, cooling method, frozen water temperature, etc.), water source conditions in the project construction area (water temperature, water quality, water quantity, etc.), and power and heat source preparation parties. Not only requires good economic indicators, but also consider local possibilities.
The selection of refrigeration devices is the central link in the process of determining the refrigeration scheme. The main types of refrigeration devices are as follows.
The main equipment of the piston (reciprocating) compression refrigeration device is a piston refrigeration compressor, and the commonly used working fluids are ammonia (NH3), Freon-12, 22 (F-12, 22). This type of equipment is driven by a motor, easy to use, has many varieties, and has a complete range of products. It can meet the cooling requirements of various air conditioners and is widely used. But once the investment is large, the equipment cost is high, the power consumption is large, and the maintenance management is relatively complicated.
The main equipment of the centrifugal compression refrigeration device is a centrifugal refrigeration compressor, and the commonly used working fluid is Freon-11, 113, 114 (F-11, 113, 114). The principle of this machine is the same as that of the piston refrigeration compressor, but it only has rotary motion, which is smoother than the piston type, with less vibration and fewer parts. It is often combined with an evaporator and a condenser, and the equipment is compact and occupies a small area. Centrifugal refrigeration compressors have a large cooling capacity, so this type of equipment is only used when the cooling capacity of the air conditioner is large.
The main equipment of the screw compression refrigeration device is a screw refrigeration compressor, and the commonly used working fluids are Freon-12, 22, ammonia (F-12, 22, R717). Compared with the piston type, the screw refrigeration compressor currently produced has a slightly lower efficiency, but due to its simple structure, small size, high suction coefficient, low exhaust temperature, and large single-stage compression ratio, it is not sensitive to wet strokes. The advantages of small exhaust pulsation, less wearing parts, long column maintenance period, and stepless adjustment of cooling capacity are widely used in various refrigeration devices. Generally, it has better technical and economic indicators to use this machine in refrigeration devices within the capacity range of (120—800)x105kJ\h.
It has great adaptability to the pressure of the steam heat source. When the steam pressure is 0.02-0.1MPa, a single lithium bromide absorption refrigerator can be used, and when the steam pressure is 6.0-1.0MPa, a double-effect lithium bromide refrigerator can be used.
Secondly, the equipment is simple, basically a combination of heat exchangers, easy to manufacture, except for small power shielded pumps and vacuum pumps, there are no moving parts, so the vibration is small and the operation is stable; The equipment works under vacuum, the working medium is odorless, non-toxic, harmless to people, safe to use, and easy to operate and manage; It is easy to realize the automation of equipment operation, and the refrigeration capacity can be automatically adjusted within the range of 10% to 100%. It has strong adaptability to the temperature of cooling water, and the equipment can still operate normally even if it reaches 37-38°C. Energy saving, under the same cooling capacity of a single unit, the power consumption of lithium bromide refrigerators is only about 5% of that of compression refrigerators, which is very suitable for areas with tight power supply and sufficient heat sources. However, lithium bromide absorption refrigeration also has shortcomings and limitations in use. The main reason is that lithium bromide aqueous solution is highly corrosive to metals when exposed to air. Once corroded, it will not only affect the heat transfer effect, reduce the service life, but also cause equipment damage. Therefore, it is required that the equipment must be strictly sealed, and great attention must be paid to the operation and management.
The main disadvantage of steam injection refrigeration is its low efficiency. It is uneconomical to set up a special boiler and use a small heating boiler to supply steam. It can be used when the freezing water temperature is above 5°C, and it is more economical when it is above 100°C. Its efficiency varies with the chilled water temperature, the lower the chilled water temperature, the greater the steam consumption and the lower the efficiency. In addition, the amount of cooling water is large. Under the same cooling capacity of a single machine, the cooling water required by the steam jet refrigerator is about 1.5 times that of the compression or bromide absorption type, which is not suitable for areas with water shortages.
The selection of refrigeration devices is the central link in the process of determining the refrigeration scheme. The main types of refrigeration devices are as follows.
1. Compression refrigeration device
Compression refrigeration devices include piston (reciprocating) type, centrifugal type and screw type.The main equipment of the piston (reciprocating) compression refrigeration device is a piston refrigeration compressor, and the commonly used working fluids are ammonia (NH3), Freon-12, 22 (F-12, 22). This type of equipment is driven by a motor, easy to use, has many varieties, and has a complete range of products. It can meet the cooling requirements of various air conditioners and is widely used. But once the investment is large, the equipment cost is high, the power consumption is large, and the maintenance management is relatively complicated.
The main equipment of the centrifugal compression refrigeration device is a centrifugal refrigeration compressor, and the commonly used working fluid is Freon-11, 113, 114 (F-11, 113, 114). The principle of this machine is the same as that of the piston refrigeration compressor, but it only has rotary motion, which is smoother than the piston type, with less vibration and fewer parts. It is often combined with an evaporator and a condenser, and the equipment is compact and occupies a small area. Centrifugal refrigeration compressors have a large cooling capacity, so this type of equipment is only used when the cooling capacity of the air conditioner is large.
The main equipment of the screw compression refrigeration device is a screw refrigeration compressor, and the commonly used working fluids are Freon-12, 22, ammonia (F-12, 22, R717). Compared with the piston type, the screw refrigeration compressor currently produced has a slightly lower efficiency, but due to its simple structure, small size, high suction coefficient, low exhaust temperature, and large single-stage compression ratio, it is not sensitive to wet strokes. The advantages of small exhaust pulsation, less wearing parts, long column maintenance period, and stepless adjustment of cooling capacity are widely used in various refrigeration devices. Generally, it has better technical and economic indicators to use this machine in refrigeration devices within the capacity range of (120—800)x105kJ\h.
2. Absorption Refrigeration Device
Absorption refrigeration plants use thermal energy for cooling. The common ones are ammonia-water absorption refrigeration device and water-lithium bromide aqueous solution absorption refrigeration device. The former is suitable for low-temperature freezing; the latter is suitable for air-conditioning cooling, producing cold water for air-conditioning or processes above 4°C. In lithium bromide absorption refrigeration, water is the working medium, and lithium bromide aqueous solution is the absorbent. Its advantages are as follows.It has great adaptability to the pressure of the steam heat source. When the steam pressure is 0.02-0.1MPa, a single lithium bromide absorption refrigerator can be used, and when the steam pressure is 6.0-1.0MPa, a double-effect lithium bromide refrigerator can be used.
Secondly, the equipment is simple, basically a combination of heat exchangers, easy to manufacture, except for small power shielded pumps and vacuum pumps, there are no moving parts, so the vibration is small and the operation is stable; The equipment works under vacuum, the working medium is odorless, non-toxic, harmless to people, safe to use, and easy to operate and manage; It is easy to realize the automation of equipment operation, and the refrigeration capacity can be automatically adjusted within the range of 10% to 100%. It has strong adaptability to the temperature of cooling water, and the equipment can still operate normally even if it reaches 37-38°C. Energy saving, under the same cooling capacity of a single unit, the power consumption of lithium bromide refrigerators is only about 5% of that of compression refrigerators, which is very suitable for areas with tight power supply and sufficient heat sources. However, lithium bromide absorption refrigeration also has shortcomings and limitations in use. The main reason is that lithium bromide aqueous solution is highly corrosive to metals when exposed to air. Once corroded, it will not only affect the heat transfer effect, reduce the service life, but also cause equipment damage. Therefore, it is required that the equipment must be strictly sealed, and great attention must be paid to the operation and management.
3. Steam injection refrigeration device
The steam injection refrigeration device is also a kind of equipment that uses heat energy for refrigeration. It uses water as the refrigerant and steam as the cooling power. The steam pressure requirement is 0.2-0.8MPa. Its main advantages are: the equipment works under vacuum, and there are no rotating parts except the pump; the refrigerant is water, which is harmless to people, safe to use, and easy to operate; The equipment is simple and easy to manufacture, and can be processed and manufactured by general machinery factories or machine repair workshops; the one-time investment of the equipment is small, and it can be installed outdoors to save civil construction costs; it can use waste heat in industrial enterprises or heating boilers in industrial enterprises to provide heating in winter and steam for cooling in summer.The main disadvantage of steam injection refrigeration is its low efficiency. It is uneconomical to set up a special boiler and use a small heating boiler to supply steam. It can be used when the freezing water temperature is above 5°C, and it is more economical when it is above 100°C. Its efficiency varies with the chilled water temperature, the lower the chilled water temperature, the greater the steam consumption and the lower the efficiency. In addition, the amount of cooling water is large. Under the same cooling capacity of a single machine, the cooling water required by the steam jet refrigerator is about 1.5 times that of the compression or bromide absorption type, which is not suitable for areas with water shortages.
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