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A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. A vapor-compression water chiller comprises the 4 major components of the vapor-compression refrigeration cycle (compressor, evaporator, condenser, and some form of metering device). These machines can implement a variety of refrigerants. Absorption chillers use municipal water as the refrigerant and benign silica gel as the desiccant. Absorption chillers utilize water as the refrigerant and rely on the strong affinity between the water and a lithium bromide solution to achieve a refrigeration effect. Most often, pure water is chilled, but this water may also contain a percentage of glycol and/or corrosion inhibitors; other fluids such as thin oils can be chilled as well.
Contents
Contents
[hide]
- 1 Use in air conditioning
- 2 Use in industry
- 3 Vapor-Compression Chiller Technology
- 4 How Adsorption Technology Works
- 5 How Absorption Technology Works
- 6 Industrial chiller selection
- 7 Refrigerants
- 8 See also
- 9 References
- 10 External links
[edit] Use in air conditioning
In air conditioning systems, chilled water is typically distributed to heat exchangers, or coils, in air handling units, or other type of terminal devices which cool the air in its respective space(s), and then the chilled water is re-circulated back to the chiller to be cooled again. These cooling coils transfer sensible heat and latent heat from the air to the chilled water, thus cooling and usually dehumidifying the air stream. A typical chiller for air conditioning applications is rated between 15 to 1500 tons (180,000 to 18,000,000 BTU/h or 53 to 5,300 kW) in cooling capacity. Chilled water temperatures can range from 35 to 45 degrees Fahrenheit or 1.5 to 7 degrees Celsius, depending upon application requirements.[1][2]
[edit] Use in industry
In industrial application, chilled water or other liquid from the chiller is pumped through process or laboratory equipment. Industrial chillers are used for controlled cooling of products, mechanisms and factory machinery in a wide range of industries. They are often used in the plastic industry in injection and blow molding, metal working cutting oils, welding equipment, die-casting and machine tooling, chemical processing, pharmaceutical formulation, food and beverage processing, paper and cement processing, vacuum systems, X-ray diffraction, power supplies and power generation stations, analytical equipment, semiconductors, compressed air and gas cooling. They are also used to cool high-heat specialized items such as MRI machines and lasers, and in hospitals, hotels and campuses.
The chillers for industrial applications can be centralized, where each chiller serves multiple cooling needs, or decentralized where each application or machine has its own chiller. Each approach has its advantages. It is also possible to have a combination of both central and decentral chillers, especially if the cooling requirements are the same for some applications or points of use, but not all.
Decentral chillers are usually small in size (cooling capacity), usually from 0.2 tons to 10 tons. Central chillers generally have capacities ranging from ten tons to hundreds or thousands of tons.
Chilled water is used to cool and dehumidify air in mid- to large-size commercial, industrial, and institutional (CII) facilities. Water chillers can be either water cooled, air-cooled, or evaporatively cooled. Water-cooled chillers incorporate the use of cooling towers which improve the chillers' thermodynamic effectiveness as compared to air-cooled chillers. This is due to heat rejection at or near the air's wet-bulb temperature rather than the higher, sometimes much higher, dry-bulb temperature. Evaporatively cooled chillers offer efficiencies better than air cooled, but lower than water cooled.
Water cooled chillers are typically intended for indoor installation and operation, and are cooled by a separate condenser water loop and connected to outdoor cooling towers to expel heat to the atmosphere.
Air Cooled and Evaporatively Cooled chillers are intended for outdoor installation and operation. Air cooled machines are directly cooled by ambient air being mechanically circulated directly through the machine's condenser coil to expel heat to the atmosphere. Evaporatively cooled machines are similar, except they implement a mist of water over the condenser coil to aid in condenser cooling, making the machine more efficient than a traditional air cooled machine. No remote cooling tower is typically required with either of these types of packaged air cooled or evaporatively cooled chillers.
Where available, cold water readily available in nearby water bodies might be used directly for cooling, or to replace or supplement cooling towers. The Deep Lake Water Cooling System in Toronto, Canada, is an example. It dispensed with the need for cooling towers, with a significant cut in carbon emissions and energy consumption. It uses cold lake water to cool the chillers, which in turn are used to cool city buildings via a district cooling system. The return water is used to warm the city's drinking water supply which is desirable in this cold climate. Whenever a chiller's heat rejection can be used for a productive purpose, in addition to the cooling function, very high thermal effectiveness is possible.
[edit] Vapor-Compression Chiller Technology
There are basically four different types of compressors used in vapor compression chillers: Reciprocating compression, scroll compression, screw-driven compression, and centrifugal compression are all mechanical machines that can be powered by electric motors, steam, or gas turbines. They produce their cooling effect via the "reverse-Rankine" cycle, also known as 'vapor-compression'. With evaporative cooling heat rejection, their coefficients-of-performance (COPs) are very high and typically 4.0 or more.
In recent years, application of Variable Speed Drive (VSD) technology has increased efficiencies of vapor compression chillers. The first VSD was applied to centrifugal compressor chillers in the late 1970s and has become the norm as the cost of energy has increased. Now, VSDs are being applied to rotary screw and scroll technology compressors.
.
In air conditioning systems, chilled water is typically distributed to heat exchangers, or coils, in air handling units, or other type of terminal devices which cool the air in its respective space(s), and then the chilled water is re-circulated back to the chiller to be cooled again. These cooling coils transfer sensible heat and latent heat from the air to the chilled water, thus cooling and usually dehumidifying the air stream. A typical chiller for air conditioning applications is rated between 15 to 1500 tons (180,000 to 18,000,000 BTU/h or 53 to 5,300 kW) in cooling capacity. Chilled water temperatures can range from 35 to 45 degrees Fahrenheit or 1.5 to 7 degrees Celsius, depending upon application requirements.[1][2]
[edit] Use in industry
In industrial application, chilled water or other liquid from the chiller is pumped through process or laboratory equipment. Industrial chillers are used for controlled cooling of products, mechanisms and factory machinery in a wide range of industries. They are often used in the plastic industry in injection and blow molding, metal working cutting oils, welding equipment, die-casting and machine tooling, chemical processing, pharmaceutical formulation, food and beverage processing, paper and cement processing, vacuum systems, X-ray diffraction, power supplies and power generation stations, analytical equipment, semiconductors, compressed air and gas cooling. They are also used to cool high-heat specialized items such as MRI machines and lasers, and in hospitals, hotels and campuses.
The chillers for industrial applications can be centralized, where each chiller serves multiple cooling needs, or decentralized where each application or machine has its own chiller. Each approach has its advantages. It is also possible to have a combination of both central and decentral chillers, especially if the cooling requirements are the same for some applications or points of use, but not all.
Decentral chillers are usually small in size (cooling capacity), usually from 0.2 tons to 10 tons. Central chillers generally have capacities ranging from ten tons to hundreds or thousands of tons.
Chilled water is used to cool and dehumidify air in mid- to large-size commercial, industrial, and institutional (CII) facilities. Water chillers can be either water cooled, air-cooled, or evaporatively cooled. Water-cooled chillers incorporate the use of cooling towers which improve the chillers' thermodynamic effectiveness as compared to air-cooled chillers. This is due to heat rejection at or near the air's wet-bulb temperature rather than the higher, sometimes much higher, dry-bulb temperature. Evaporatively cooled chillers offer efficiencies better than air cooled, but lower than water cooled.
Water cooled chillers are typically intended for indoor installation and operation, and are cooled by a separate condenser water loop and connected to outdoor cooling towers to expel heat to the atmosphere.
Air Cooled and Evaporatively Cooled chillers are intended for outdoor installation and operation. Air cooled machines are directly cooled by ambient air being mechanically circulated directly through the machine's condenser coil to expel heat to the atmosphere. Evaporatively cooled machines are similar, except they implement a mist of water over the condenser coil to aid in condenser cooling, making the machine more efficient than a traditional air cooled machine. No remote cooling tower is typically required with either of these types of packaged air cooled or evaporatively cooled chillers.
Where available, cold water readily available in nearby water bodies might be used directly for cooling, or to replace or supplement cooling towers. The Deep Lake Water Cooling System in Toronto, Canada, is an example. It dispensed with the need for cooling towers, with a significant cut in carbon emissions and energy consumption. It uses cold lake water to cool the chillers, which in turn are used to cool city buildings via a district cooling system. The return water is used to warm the city's drinking water supply which is desirable in this cold climate. Whenever a chiller's heat rejection can be used for a productive purpose, in addition to the cooling function, very high thermal effectiveness is possible.
[edit] Vapor-Compression Chiller Technology
There are basically four different types of compressors used in vapor compression chillers: Reciprocating compression, scroll compression, screw-driven compression, and centrifugal compression are all mechanical machines that can be powered by electric motors, steam, or gas turbines. They produce their cooling effect via the "reverse-Rankine" cycle, also known as 'vapor-compression'. With evaporative cooling heat rejection, their coefficients-of-performance (COPs) are very high and typically 4.0 or more.
In recent years, application of Variable Speed Drive (VSD) technology has increased efficiencies of vapor compression chillers. The first VSD was applied to centrifugal compressor chillers in the late 1970s and has become the norm as the cost of energy has increased. Now, VSDs are being applied to rotary screw and scroll technology compressors.
.
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قسمت دوم
[edit] How Adsorption Technology Works
Adsorption chillers are driven by hot water. This hot water may come from any number of industrial sources including waste heat from industrial processes, prime heat from solar thermal installations or from the exhaust or water jacket heat of a piston engine or turbine.
The principle of adsorption is based on the interaction of gases and solids. With adsorption chilling, the molecular interaction between the solid and the gas allow the gas to be adsorbed into the solid. The adsorption chamber of the chiller is filled with solid material, silica gel, eliminating the need for moving parts and eliminating the noise associated with those moving parts. The silica gel creates an extremely low humidity condition that causes the water refrigerant to evaporate at a low temperature. As the water evaporates in the evaporator, it cools the chilled water.
The use of a benign silica gel desiccant keeps the maintenance costs and operating costs of adsorption chillers low.
[edit] How Absorption Technology Works
Absorption chillers' thermodynamic cycle are driven by heat source; this heat is usually delivered to the chiller via steam, hot water, or combustion. Compared to electrically powered chillers, they have very low electrical power requirements - very rarely above 15 kW combined consumption for both the solution pump and the refrigerant pump. However, their heat input requirements are large, and their COPs are often 0.5 (single-effect) to 1.0 (double-effect). For the same tonnage capacity, they require much larger cooling towers than vapor-compression chillers. However, absorption chillers, from an energy-efficiency point-of-view, excel where cheap, high grade heat or waste heat is readily available. In extremely sunny climates, solar energy has been used to operate absorption chillers.
The single effect absorption cycle uses water as the refrigerant and lithium bromide as the absorbent. It is the strong affinity that these two substances have for one another that makes the cycle work. The entire process occurs in almost a complete vacuum.
1. Solution Pump – A dilute lithium bromide solution is collected in the bottom of the absorber shell. From here, a hermetic solution pump moves the solution through a shell and tube heat exchanger for preheating.
2. Generator – After exiting the heat exchanger, the dilute solution moves into the upper shell. The solution surrounds a bundle of tubes which carries either steam or hot water. The steam or hot water transfers heat into the pool of dilute lithium bromide solution. The solution boils, sending refrigerant vapor upward into the condenser and leaving behind concentrated lithium bromide. The concentrated lithium bromide solution moves down to the heat exchanger, where it is cooled by the weak solution being pumped up to the generator.
3. Condenser – The refrigerant vapor migrates through mist eliminators to the condenser tube bundle. The refrigerant vapor condenses on the tubes. The heat is removed by the cooling water which moves through the inside of the tubes. As the refrigerant condenses, it collects in a trough at the bottom of the condenser.
4. Evaporator – The refrigerant liquid moves from the condenser in the upper shell down to the evaporator in the lower shell and is sprayed over the evaporator tube bundle. Due to the extreme vacuum of the lower shell [6 mm Hg (0.8 kPa) absolute pressure], the refrigerant liquid boils at approximately 39°F (3.9°C), creating the refrigerant effect. (This vacuum is created by hygroscopic action - the strong affinity lithium bromide has for water - in the Absorber directly below.)
5. Absorber – As the refrigerant vapor migrates to the absorber from the evaporator, the strong lithium bromide solution from the generator is sprayed over the top of the absorber tube bundle. The strong lithium bromide solution actually pulls the refrigerant vapor into solution, creating the extreme vacuum in the evaporator. The absorption of the refrigerant vapor into the lithium bromide solution also generates heat which is removed by the cooling water. The now dilute lithium bromide solution collects in the bottom of the lower shell, where it flows down to the solution pump. The chilling cycle is now completed and the process begins once again.
[edit] Industrial chiller technology
Industrial chillers typically come as complete packaged closed-loop systems, including the chiller unit, condenser, and pump station with recirculating pump, expansion valve, no-flow shutdown, internal cold water tank, and temperature control. The internal tank helps maintain cold water temperature and prevents temperature spikes from occurring. Closed loop industrial chillers recirculate a clean coolant or clean water with condition addititives at a constant temperature and pressure to increase the stability and reproducibility of water-cooled machines and instruments. The water flows from the chiller to the application's point of use and back.
If the water temperature differentials between inlet and outlet are high, then a large external water tank would be used to store the cold water. In this case the chilled water is not going directly from the chiller to the application, but goes to the external water tank which acts as a sort of "temperature buffer." The cold water tank is much larger than the internal water tank. The cold water goes from the external tank to the application and the return hot water from the application goes back to the external tank, not to the chiller.
The less common open loop industrial chillers control the temperature of a liquid in an open tank or sump by constantly recirculating it. The liquid is drawn from the tank, pumped through the chiller and back to the tank. An adjustable thermostat senses the makeup liquid temperature, cycling the chiller to maintain a constant temperature in the tank.
One of the newer developments in industrial water chillers is the use of water cooling instead of air cooling. In this case the condenser does not cool the hot refrigerant with ambient air, but uses water cooled by a cooling tower. This development allows a reduction in energy requirements by more than 15% and also allows a significant reduction in the size of the chiller due to the small surface area of the water based condenser and the absence of fans. Additionally, the absence of fans allows for significantly reduced noise levels.
Most industrial chillers use refrigeration as the media for cooling, but some rely on simpler techniques such as air or water flowing over coils containing the coolant to regulate temperature. Water is the most commonly used coolant within process chillers, although coolant mixtures (mostly water with a coolant additive to enhance heat dissipation) are frequently employed.
[edit] Industrial chiller selection
Important specifications to consider when searching for industrial chillers include the total life cycle cost, the power source, chiller IP rating, chiller cooling capacity, evaporator capacity, evaporator material, evaporator type, condenser material, condenser capacity, ambient temperature, motor fan type, noise level, internal piping materials, number of compressors, type of compressor, number of fridge circuits, coolant requirements, fluid discharge temperature, and COP (the ratio between the cooling capacity in RT to the energy consumed by the whole chiller in KW). For medium to large chillers this should range from 3.5-7.0 with higher values meaning higher efficiency. Chiller efficiency is often specified in kilowatts per refrigeration ton (kW/RT).
Process pump specifications that are important to consider include the process flow, process pressure, pump material, elastomer and mechanical shaft seal material, motor voltage, motor electrical class, motor IP rating and pump rating. If the cold water temperature is lower than -5°C, then a special pump needs to be used to be able to pump the high concentrations of ethylene glycol. Other important specifications include the internal water tank size and materials and full load amperage.
Control panel features that should be considered when selecting between industrial chillers include the local control panel, remote control panel, fault indicators, temperature indicators, and pressure indicators.
Additional features include emergency alarms, hot gas bypass, city water switchover, and casters.
[edit] Refrigerants
A vapor-compression chiller uses a refrigerant internally as its working fluid. Many refrigerants options are available; when selecting a chiller, the application cooling temperature requirements and refrigerant's cooling characteristics need to be matched. Important parameters to consider are the operating temperatures and pressures.
There are several environmental factors that concern refrigerants, and also affect the future availability for chiller applications. This is a key consideration in intermittent applications where a large chiller may last for 25 years or more. Ozone depletion potential (ODP) and global warming potential (GWP) of the refrigerant need to be considered. ODP and GWP data for some of the more common vapor-compression refrigerants:
R-134a
0
1300
R-123
0.012
120
R-22
0.05
1700
R401a
0.027
970
R404a
0
3260
R407a
0
???
R407c
0
1525
R408a
0.016
3020
R409a
0.039
1290
R410a
0
1725
R500
0.7
???
R502
0.18
5600
[edit] How Adsorption Technology Works
Adsorption chillers are driven by hot water. This hot water may come from any number of industrial sources including waste heat from industrial processes, prime heat from solar thermal installations or from the exhaust or water jacket heat of a piston engine or turbine.
The principle of adsorption is based on the interaction of gases and solids. With adsorption chilling, the molecular interaction between the solid and the gas allow the gas to be adsorbed into the solid. The adsorption chamber of the chiller is filled with solid material, silica gel, eliminating the need for moving parts and eliminating the noise associated with those moving parts. The silica gel creates an extremely low humidity condition that causes the water refrigerant to evaporate at a low temperature. As the water evaporates in the evaporator, it cools the chilled water.
The use of a benign silica gel desiccant keeps the maintenance costs and operating costs of adsorption chillers low.
[edit] How Absorption Technology Works
Absorption chillers' thermodynamic cycle are driven by heat source; this heat is usually delivered to the chiller via steam, hot water, or combustion. Compared to electrically powered chillers, they have very low electrical power requirements - very rarely above 15 kW combined consumption for both the solution pump and the refrigerant pump. However, their heat input requirements are large, and their COPs are often 0.5 (single-effect) to 1.0 (double-effect). For the same tonnage capacity, they require much larger cooling towers than vapor-compression chillers. However, absorption chillers, from an energy-efficiency point-of-view, excel where cheap, high grade heat or waste heat is readily available. In extremely sunny climates, solar energy has been used to operate absorption chillers.
The single effect absorption cycle uses water as the refrigerant and lithium bromide as the absorbent. It is the strong affinity that these two substances have for one another that makes the cycle work. The entire process occurs in almost a complete vacuum.
1. Solution Pump – A dilute lithium bromide solution is collected in the bottom of the absorber shell. From here, a hermetic solution pump moves the solution through a shell and tube heat exchanger for preheating.
2. Generator – After exiting the heat exchanger, the dilute solution moves into the upper shell. The solution surrounds a bundle of tubes which carries either steam or hot water. The steam or hot water transfers heat into the pool of dilute lithium bromide solution. The solution boils, sending refrigerant vapor upward into the condenser and leaving behind concentrated lithium bromide. The concentrated lithium bromide solution moves down to the heat exchanger, where it is cooled by the weak solution being pumped up to the generator.
3. Condenser – The refrigerant vapor migrates through mist eliminators to the condenser tube bundle. The refrigerant vapor condenses on the tubes. The heat is removed by the cooling water which moves through the inside of the tubes. As the refrigerant condenses, it collects in a trough at the bottom of the condenser.
4. Evaporator – The refrigerant liquid moves from the condenser in the upper shell down to the evaporator in the lower shell and is sprayed over the evaporator tube bundle. Due to the extreme vacuum of the lower shell [6 mm Hg (0.8 kPa) absolute pressure], the refrigerant liquid boils at approximately 39°F (3.9°C), creating the refrigerant effect. (This vacuum is created by hygroscopic action - the strong affinity lithium bromide has for water - in the Absorber directly below.)
5. Absorber – As the refrigerant vapor migrates to the absorber from the evaporator, the strong lithium bromide solution from the generator is sprayed over the top of the absorber tube bundle. The strong lithium bromide solution actually pulls the refrigerant vapor into solution, creating the extreme vacuum in the evaporator. The absorption of the refrigerant vapor into the lithium bromide solution also generates heat which is removed by the cooling water. The now dilute lithium bromide solution collects in the bottom of the lower shell, where it flows down to the solution pump. The chilling cycle is now completed and the process begins once again.
[edit] Industrial chiller technology
Industrial chillers typically come as complete packaged closed-loop systems, including the chiller unit, condenser, and pump station with recirculating pump, expansion valve, no-flow shutdown, internal cold water tank, and temperature control. The internal tank helps maintain cold water temperature and prevents temperature spikes from occurring. Closed loop industrial chillers recirculate a clean coolant or clean water with condition addititives at a constant temperature and pressure to increase the stability and reproducibility of water-cooled machines and instruments. The water flows from the chiller to the application's point of use and back.
If the water temperature differentials between inlet and outlet are high, then a large external water tank would be used to store the cold water. In this case the chilled water is not going directly from the chiller to the application, but goes to the external water tank which acts as a sort of "temperature buffer." The cold water tank is much larger than the internal water tank. The cold water goes from the external tank to the application and the return hot water from the application goes back to the external tank, not to the chiller.
The less common open loop industrial chillers control the temperature of a liquid in an open tank or sump by constantly recirculating it. The liquid is drawn from the tank, pumped through the chiller and back to the tank. An adjustable thermostat senses the makeup liquid temperature, cycling the chiller to maintain a constant temperature in the tank.
One of the newer developments in industrial water chillers is the use of water cooling instead of air cooling. In this case the condenser does not cool the hot refrigerant with ambient air, but uses water cooled by a cooling tower. This development allows a reduction in energy requirements by more than 15% and also allows a significant reduction in the size of the chiller due to the small surface area of the water based condenser and the absence of fans. Additionally, the absence of fans allows for significantly reduced noise levels.
Most industrial chillers use refrigeration as the media for cooling, but some rely on simpler techniques such as air or water flowing over coils containing the coolant to regulate temperature. Water is the most commonly used coolant within process chillers, although coolant mixtures (mostly water with a coolant additive to enhance heat dissipation) are frequently employed.
[edit] Industrial chiller selection
Important specifications to consider when searching for industrial chillers include the total life cycle cost, the power source, chiller IP rating, chiller cooling capacity, evaporator capacity, evaporator material, evaporator type, condenser material, condenser capacity, ambient temperature, motor fan type, noise level, internal piping materials, number of compressors, type of compressor, number of fridge circuits, coolant requirements, fluid discharge temperature, and COP (the ratio between the cooling capacity in RT to the energy consumed by the whole chiller in KW). For medium to large chillers this should range from 3.5-7.0 with higher values meaning higher efficiency. Chiller efficiency is often specified in kilowatts per refrigeration ton (kW/RT).
Process pump specifications that are important to consider include the process flow, process pressure, pump material, elastomer and mechanical shaft seal material, motor voltage, motor electrical class, motor IP rating and pump rating. If the cold water temperature is lower than -5°C, then a special pump needs to be used to be able to pump the high concentrations of ethylene glycol. Other important specifications include the internal water tank size and materials and full load amperage.
Control panel features that should be considered when selecting between industrial chillers include the local control panel, remote control panel, fault indicators, temperature indicators, and pressure indicators.
Additional features include emergency alarms, hot gas bypass, city water switchover, and casters.
[edit] Refrigerants
A vapor-compression chiller uses a refrigerant internally as its working fluid. Many refrigerants options are available; when selecting a chiller, the application cooling temperature requirements and refrigerant's cooling characteristics need to be matched. Important parameters to consider are the operating temperatures and pressures.
There are several environmental factors that concern refrigerants, and also affect the future availability for chiller applications. This is a key consideration in intermittent applications where a large chiller may last for 25 years or more. Ozone depletion potential (ODP) and global warming potential (GWP) of the refrigerant need to be considered. ODP and GWP data for some of the more common vapor-compression refrigerants:
Refrigerant
ODP
GWP
0
1300
R-123
0.012
120
R-22
0.05
1700
R401a
0.027
970
R404a
0
3260
R407a
0
???
R407c
0
1525
R408a
0.016
3020
R409a
0.039
1290
R410a
0
1725
R500
0.7
???
R502
0.18
5600
آمونياك چيست؟
مولكول آمونياك NH3 است. كه يك ماده عالي و يكي از فرايندهاي ابتدايي در پتروشيمي است، كه در حالت عادي بصورت گاز مي باشد.
چرا آمونياك بهترين مبرد در دنيا شناخته شده است؟
زيرا :
1- ارزانترين مبرد در دنياست و از اين نظر هيچ مبردي توان رقابت با آن را ندارد.
2- از تبخير هر كيلوگرم آمونياك در اواپراتور يك چيلر 300 كيلوكالري سرما توليد مي شود و اين در حالي است كه بهترين مبردهاي فريوني مانند R22 در اين شرايط 50 كيلوكالري سرما ايجاد مي كنند. يعني يك ششم!. به همين دليل است كه سرماي توليد شده توسط آمونياك نياز به صرف انرژي كمتري دارد.
3- تمامي مبردهاي فريوني اثر مخرب بر محيط زيست دارند، يا بر لايه ازون اثر تخريبي دارند و يا باعث گرم شدن كره زمين (بر اثر تأثير گلخانه اي اين گازها بر اتمسفر و جو زمين) خواهند شد. در واقع اين گازها با احاطه كردن كره زمين در بالاترين لايه هاي اتمسفر مانند پتويي كره زمين را احاطه كرده و از خروج گرما از كره زمين ممانعت مي نمايند و لذا دماي كره زمين به تدريج افزايش مي يابد كه اين پديده تأثيرات بسيار مخربي بر آب و هواي كره زمين، ذوب شدن يخ هاي قطب جنوب و شمال و تغييرات غيرمتعارف آب و هوايي و طوفان و سيل هاي بسيار مهلك و مخرب خواهد شد.
4- دفع آمونياك در اتمسفر اثر تخريبي به جا نگذاشته و در صورت جذب شدن توسط خاك، اثر تقويتي بر خواص آن خواهد داشت.
فشار كار آمونياك و ساير مبردها در يك ماشين توليد سرما
هنگامي كه در يك چيلر هوا خنك فريون R22 شارژ مي شود، فشار رانش و مكش آن در يك هواي گرم تابستاني معادل (20bar) 300 psig در فشار رانش و (3.5bar) 50 psig در فشار مكش خواهد بود. در يك چيلر جذبي آمونياكي نيز تقريباً همين فشارها حاكم است و لذا از اين حيث تفاوت چشمگيري ما بين اين دو سيستم وجود ندارد و چيلرهاي جذبي گازسوز آمونياكي در خلاء كار نمي كنند و مشكلات چيلرهاي جذبي ليتيوم برومايدي در مورد شرايط كاركرد در خلاء را ندارد.
اما
آمونياك در تمام حالات تمايل شديدي به انحلال در آب دارد. تمايل انحلال آمونياك در آب با هيچ ماده ديگري قابل مقايسه نيست. اگر در يك بطري آب به ظرفيت يك ليتر (معادل يك كيلوگرم) در دماي متعارف، گاز آمونياك وارد كنيد. تمامي مولكول هاي آمونياك جذب آب خواهند شد و تقريباً هيچ گاز آمونياكي در محيط پخش نخواهد شد. به عبارت ديگر تمايل آمونياك به انحلال در آب به مراتب بيشتر از تمايل آمونياك به پراكنده شدن در هوا است. به همين دليل در برخي از محلول هاي ضد عفوني يا سفيد كننده معمولي كه در اغلب منازل يافت مي شود، محلول آمونياك و آب بدون ايجاد هيچ مزاحمتي مورد استفاده و نگهداري قرار مي گيرد.
خطر آمونياك
آمونياك گازي سمي است و تنفس آن به مدت چند دقيقه موجب مسموميت و در صورت تمديد اين شرايط موجب مرگ انسان مي گردد. به همين جهت كار با اين ماده نيازمند مهارت و استفاده از لوازم ايمني مناسب مي باشد.
اما
هنگامي كه در يك دستگاه چيلر جذبي مقدار 8 kg آمونياك در مقدار 11 kg آب حل شود، در صورت نشت آمونياك حداكثر 1 kg دفعتاً از دستگاه چيلر گاز آمونياك خارج مي شود و اين در حالي است كه :
1- دستگاه چيلر گازسوز در فضاي باز مثلاً بام ساختمان نصب شده است و اين مقدار آمونياك خارج شده از دستگاه به راحتي در هوا حل شده و از بام ساختمان دور مي شود و به دليل رقيق شدن در هوا هيچ خطري براي هيچ موجود زنده اي ندارد.
2- مدار بسته چيلرگازسوز در فشار 70 bar مورد تست فشار واقع مي شود و اين در حالي است كه حداكثر فشار كاري دستگاه در گرم ترين هواي محيط (50 ºC) معادل 25 bar يعني يك سوم فشار تست است و احتمال بروز نشتي در حد صفر كاهش يافته است.
3-تاكنون هيچ موردي از نشت آمونياك منجر به مسموميت يا فوت در اين دستگاه ها طي 50 سال توليد و نصب در سرتاسر جهان ثبت يا گزارش نشده است.
4-عمده ترين مراكز فروش و نصب اين دستگاه ها، كشورهاي ايالات متحده، استراليا و اروپاي غربي است و لذا در صورت وجود خطر نشت آمونياك با توجه به قوانين بسيار سخت گيرانه در اين كشورها، اين دستگاه ها قابل نصب و بهره برداري نبودند. در حالي كه طي مدت 50 سال قريب به 1.000.000 دستگاه در حال كار در اين كشورها وجود دارد.
آيا اين شايعه كه كاربرد آمونياك در ساخت دستگاه ها و لوازم خانگي غير مجاز است صحت دارد؟
متأسفانه برخي از رقباي تجاري اين محصول يعني چيلر جذبي گازسوز، با نشر اين مطالب كه كاربرد آمونياك در لوزم خانگي ممنوع شده، ذهن متقاضيان اين دستگاه ها را از رسيدن به حقيقت منحرف مي نمايند.
آمونياك از حدود 60 سال پيش تاكنون در يخچال هاي نفتي كه داراي سيكل جذبي اوليه مشابه چيلرهاي جذبي است كاربرد داشته است. هزاران دستگاه از اين نسل يخچال ها در منازل پدران ما طي ساليان متمادي بدون هبچ گونه مشكل آفريني در خدمت رفاه و آسايش نسل دهه هاي 1330 تا 1350 خورشيدي بوده و علي رغم نصب اين يخچال ها در قلب خانه يعني آشپزخانه تاكنون هيچ حادثه منجر به خسارت جاني و يا مالي در مورد اين لوازم ثبت نشده است.
در حال حاضر بسياري از شركت هاي پيشرو در توليد لوازم برودتي در پي استفاده از سيستم هاي جذبي آمونياكي در توليد برودت براي مصارف تجاري و خانگي هستند. در زير به نام و آدرس اينترنتي تعدادي از آنها اشاره شده است.
Mayakawa Mfg . Co . Ltd – httP://www.mycomj . Co.JP
Coolmax Co . httP://www. Coolmaxbar.com
Gas Refrigerator . httP://gasrefrigerator.net
در حال حاضر در تمامي هتل هاي چهار و پنج ستاره قاره اروپا و آمريكا، فقط استفاده از يخچال هاي جذبي آمونياكي به دليل كاركرد بي صداي آنها مجاز بوده و از اين يخچال استفاده مي گردد.
يكي از معتبرترين اين شركت ها، شركت Indel است كه محصولات آن در حال حاضر در تمام كشورهاي توسعه يافته مورد استفاده قرار مي گيرد.اين شركت انواع يخچال هاي و minibar هاي هتل هاي بسيار معتبر در جهان را از نوع يخچال هاي جذبي آمونياكي تأمين مي نمايد.
هيچ يك از قوانين و سازمان هاي بين المللي در نفي استفاده از گاز آمونياك در لوازم خانگي ادعايي نداشته و آمونياك به عنوان "مبرد سبز" يكي از بهترين مبردها براي حفظ محيط زيست و صرفه جويي در مصرف انرژي است.
- درحال حاضر محصولات توليد شده توسط شركت Robur ايتاليا در پيشرفته ترين كشورهاي دنيا و در كاربردهاي مسكوني، تجاري و صنعتي مورد استفاده قرار مي گيرد. مثال هاي زير كاربرد و نصب اين چيلرها در 5 قاره جهان را نشان مي دهد. مراجعه به سايت رسمي شركت Robur ايتاليا به آدرس www.robur.it نيز آخرين نصب اين دستگاه ها را با ذكر آدرس و عكس هاي محل نصب در اختيار علاقه مندان قرار مي دهد.
پس
1- آمونياك سمي است، اما استفاده از آن در يك دستگاه ايمن هيچ خطري را متوجه بهره بردار آن نمي كند. همانطور كه گاز طبيعي نيز بسيار خطرناك و استفاده نادرست از آن مرگ بار و كشنده است. اما در تمامي منازل به درستي از آن استفاده مي شود.
2- استفاده از آن در لوازم خانگي كاملاً مجاز بوده و در حال حاضر به دليل جلوگيري از تخريب محيط زيست استفاده از آن در صنايع تهويه مطبوع خانگي، تجاري و صنعتي رو به توسعه و فزوني است.
3- كاركرد دستگاه هاي جذبي آمونياكي به هيج وجه تحت شرايط فشار خلاء نيست و مشكلات چيلرهاي جذبي ليتيوم برومايدي در اين زمينه را ندارد.
4- دستگاه چيلر جذبي در محيط باز (بام ساختمان) نصب شده و نشت آمونياك (كه در دستگاه تقريباً غيرممكن است) حداكثر به مقدار 1 kg رخ خواهد داد كه به راحتي در اتمسفر رقيق سازي و دفع خواهد شد.
5- بر اساس هيچ يك از قوانين و قواعد بازدارنده ايمني، استفاده از گاز آمونياك در دستگاه ها و لوازم خانگي منع نشده بلكه استفاده از آن توصيه نيز شده است.
6- در حال حاضر بيش از 1.000.000 دستگاه چيلر جذبي گازسوز در سرتاسر جهان و خصوصاً در قاره آمريكا و اروپا در حال كار است و تاكنون هيچ مورد حادثه اي در مورد نشت آمونياك خارج از دستگاه گزارش نشده است.
7- دستگاه چيلر جذبي گازسوز در كشورهاي آمريكا و ايتاليا و در قلب اروپا توليد شده و اين محصول داراي مهرCE ( گواهينامه توزيع در اروپا ) است و بيش از 85% اين محصولات در كشورهاي اروپايي نصب و بهره برداري مي گردد.
8- شركت Robur در سال 2003 موفق به كسب جايزه تعالي سازماني EFQM به عنوان برترین شركت سرآمد اروپايي گرديده است.
9- نصب و راه اندازي بيش از 1000 دستگاه از اين چيلرها در ايران توسط شركت صنایع یکتا تهویه اروند تاكنون بدون كوچكترين خطري در زمينه نشت آمونياك صورت گرفته و رزومه اين شركت در تحقيق در اين زمينه در اختيار علاقه مندان قرار خواهد گرفت.
1-سازمان بهينه سازي مصرف سوخت كشور پس از سال ها تحقيق و بررسي نمونه هاي مختلف سيستم هاي جذبي موجود در بازارهاي جهاني اين چيلرها را با توجه به راندمان عملكرد بالا، عمر مفيد بسيار طولاني، عملكرد ايمن و تكنولوژي بسيار بالاي ساخت اين محصول، انتخاب و شركت صنايع يكتا تهويه اروند افتخار مونتاژ و نصب اين محصولات را با حمايت اين سازمان كسب نموده است.
استفاده از چيلرهاي جذبي آمونياكي يعني، صرفه جويي در مصرف انرژي، كاهش هزينه هاي بهره برداري، خذف عمليات خسته كننده نگهداري، بهره برداري مطمئن، حفظ محيط زيست و آسايش و آرامش خيال
براي انتقال حرارت از داخل يك محفظه يا اتاق به خارج , احتياج به يك واسطه است. در يك سيستم سرد كننده مكانيكي استاندارد , عمل گرفتن حرارت با تبخير مايعي در دستگاه تبخير (Evaporator), و پس دادن آن در دستگاه تقطير (Condenser) صورت مي گيرد و اين امر باعث تغيير حالت ماده سرمازا از بخار به مايع مي گردد .مايعاتي كه بتوانند به سهولت از مايع به بخار و بالعكس تبديل شوند به عنوان واسطه انتقال حرارت به كار برده مي شوند, زيرا اين تغيير حالت باعث تغيير حرارت نيز مي گردد .برخي از اين مواد سرمازا از مواد ديگر مناسب تر هستند .
خصوصيات مواد سرمازا :
سيالي كه به عنوان ماده سرمازا مورد استفاده قرار مي گيرد بايد داراي كيفيات زير باشد:
1- سمي نباشد.
2- قابل انفجار نباشد .
3-اكسيد كننده نباشد .
4- قابل اشتعال نباشد .
5- در صورت نشت به سهولت قابل تشخيص باشد
6- محل نشت آن قابل تعيين باشد .
7- قادر به عمل كردن در فشار كم باشد (نقطه جوش پايين) .
8- از نوع گازهاي پايدار باشد .
9- قسمت هايي كه در داخل مايع حركت مي كند به سهولت قابل روغنكاري باشند.
10- تنفس كردن آن مضر نباشد .
11- داراي گرماي نهان متعادلي براي مقدار تبخير در واحد زمان باشد .
12- جابجايي نسبي آن براي ايجاد مقدار معيني برودت كم باشد .
13- داراي كمترين اختلاف, بين فشار تبخير و تقطير باشد .
ماده سرمازا نبايد خورنده باشد (ايجاد زنگ زدگي كند) تا ساختن تمام قطعات سيستم از فلزات معمولي با عمر خدمتي طولاني تر عملي گردد.
مبناي مقايسه مواد سرمازاي به كار رفته در صنعت سرد كنندگي , بر اساس حرارت تبخير 5 درجه فارنهايت و حرارت تقطير 68 درجه فارنهايت است .
شناسايي مواد سرمازا بوسيله شماره گذاري :
روش جديد مشخص كردن مواد سرما زا در صنايع تبريد , شماره گذاري اين مواد است . پيش حرف R كه مخفف كلمه REFRIGERANT به معناي سرمازا است نوشته مي شود. روش مشخص نمودن شماره اي توسط انجمن مهندسين تهويه ,تبريد و حرارت مركزي آمريكا متداول شده است .
طبقه بندي مواد سرما زا :
اين مواد بوسيله دو سازمان ملي آمريكايي به نام هاي :
The national refrigeration safety code
The national board of fire underwriters طبقه بندي شده اند.
سازمان اول تمام مايعات سرمازا به سه گروه زير تقسيم بندي مي كند:
گروه اول – بي خطر ترين مواد كه شامل R-500,R-14,R-13,R-502,R-744 R-13BL,R-22,R-30,R-12,R-114,R-21,R-11,R-113 مي باشد.
گروه دوم _ مواد سمي و تا حدي قابل اشتعال كه شاملR-717,R-40,R-764, R-1130,R-160,R-611 مي باشد.
گروه سوم _ مواد قابل اشتعال كه شامل R-50,R-1150,R-170,R-290-
مي باشد.
موسسه NBFU نيز مواد سرمازا را نسبت به درجه سمي بودن آن ها طبقه بندي كرده است كه شامل شش گروه است كه بي خطر ترين آن ها گروه يك است.
GROUP 1 CLASS
R-744 Carbon Dioxide 5
R-12 6
R-13B1 Kulene-131 6
R-21 6
R-114 6
R-30 Carrene No. 1 4
R-11 6
R-22 5
R-113 4
R-500 6
R-502 6
R-503 6
R-504 6
R-40 Methylene Chloride 4
GROUP 2
R-717 Ammonia 2
R-1130 Dichloroethylene 4
R-160 Ethyl Chloride 4
R-40 Methyl Chloride 4
R-611 Methyl Formate 3
R-764 Sulphur Dioxide 1
GROUP 3
R-600 Butane 5
R-170 Ethane 5
R-601 Iso Butane 5
R-290 Propane 5
در اينجا به بررسي بعضي از مبردهاي متداول مي پردازيم
22-R (دي كلرودي فلورو متان ) (CCl2F2) :
ماده اي است بيرنگ تقريبا بي بو و در فشار اتمسفر داراي نقطه جوشي معادل 7/21 درجه فارنهايت است . ماده اي غير سمي و غير قابل اشتعال است و خورنده نيست , از نظر شيميايي در حرارت هاي عملياتي بي اثر است و از نظر حرارتي تا 1022 درجه پايدار باقي مي ماند .
12- R داراي گرماي نهان نسبتا پايين است و براي مصرف در دستگاه هاي كوچك تر مناسب مي باشد , زيرا گردش مقدار زيادي ماده سرما زا امكان استفاده از مكانيزم هاي عملياتي و تنظيم دقيق تر و در عين حال با حساسيت كمتر را ميسر مي كند . از اين مبرد در كمپرسور هاي پيستوني و دوراني و انواع بزرگ گريز از مركزي استفاده مي شود .
اين ماده در فشار هاي سر , و معكوس (پس فشار) كم , ولي مثبت با يك بازدهي حجمي خوب كار مي كند , 12- R , در 5 درجه فارنهايت , فشاري معادل 5/26 پوند بر اينچ مربع مطلق , و در 86 درجه فارنهايت داراي فشاري مطلق معادل 8/108 پوند بر اينچ مربع است .
گرماي نهان آن در 5 درجه فارنهايت 2/68 بي-تي- يو است و نشت آن به سهولت و با استفاده از نشت ياب الكترونيكي يا مشعل هالايد مشخص مي گردد.
در حرارت صفر درجه مقدار كمي آب در 12-R حل مي شود كه نسبت آن بر حسب وزن 6 در مليون است . مايعي كه توليد مي شود تا حدودي بر روي اكثر فلزات معمولي كه در ساختمان دستگاه هاي سرد كننده استفاده مي شود , ايجاد زنگ مي كند . اضافه كردن روغن هاي معدني هيچگونه اثري در ايجاد رنگ بوسيله مايع ندارد ولي احتمالا كم رنگ شدن مايع به وسيله آب را كاهش مي دهد . حساسيت ماده 12-R نسبت به آب در مقايسه با 22-R و 502-R بيشتر است . تا 90 درجه قابل حل شدن در روغن است . در اين حرارت روغن شروع به جدا شدن مي كند و به علت سبك تر بودن وزن در سطح آن جمع مي شود .
به كار بردن 30 پوند از اين ماده به ازاي هر 1000 فوت مكعب فضاي تهويه شده كاملا بي خطر است .
اين ماده در سيلندر هاي به اندازه مختلف عرضه مي شود و احتمالا در قوطي هاي سر بسته و محكم نيز يافت مي شود . كد رنگي مخصوص 12- R سفيد است .
22-R منوكلرودي فلورو متان (CHCLF2)
22-R يك ماده سرمازاي مصنوعي است كه انحصارا براي دستگاه هاي تبريدي كه درجه تبخير پاييني دارند ساخته شده است . يكي از موارد استفاده آن در دستگاه هاي انجماد سريع است كه حرارت آن ها بين 20 تا 40 درجه فارنهايت حفظ مي گردد . همچنين در دستگاه هاي تهويه مطبوع و يخچال هاي خانگي نيز به طور موفقيت آميزي مورد استفاده قرار گرفته است . 22-R فقط در كمپرسورهاي پيستوني به كار گرفته مي شوند و فشار عملياتي آن به نحوي است كه براي نيل به درجات پايين , نيازي به كار كردن در فشار هاي كمتر از جو نيست . گرماي نهان آن به ازاي هر پوند در 5 درجه فارنهايت 21/93 بي-تي-يو است . فشار عادي سر كمپرسور در 86 درجه 82/172 پوند بر اينچ مربع مطلق است .
22-R ماده اي پايدار ,غير سمي ,بدون اثر اكسيد كنندگي , بي آزار و غير قابل اشتعال است . فشار اواپراتور در 5 درجه فارنهايت 43 پوند بر اينچ مربع است . حلاليت آن در آب 3 برابر 12-R است . بنابراين رطوبت در اين ماده بايد حداقل باشد .به همين دليل استفاده از رطوبت گير و خشك كن در اين مورد بيشتر است .
به علت تمايل شديد تر 22-R به آب تعداد بيشتري رطوبت گير براي خشك كردن آن لازم است. 22-R تا حرارت16درجه فارنهايت در روغن حل مي شود وپس از ان روغن شروع به جدا شدن نموده و چون از مايع سبك تر است در سطح آن جمع مي شود. وجود نشت را مي توان به وسيله ي نشت ياب الكترونيكي و يا مشعل هالايد تيين كرد.
مواد سرما زا ي مخلوط:
همانطور كه از نامشان پيداست , اين مواد مخلوطي از دو يا چند ماده ي سرما زا هستند, ولي مانند يك ماده سرما زاي واحد عمل مي كنند. و چهار نوع متداولتر آنها عبارتند از:
1)R-500 كه مخلوطي است از 8/73 درصد R-12 و 2/26 درصد R-152a
2)R-502 كه مخلوطي است از8/ 48 درصد R-22 و 2/ 51درصد R-115
3) كه مخلوطي است از 1/ 41 درصد R-23 و 9/ 59 درصد R-13
4) كه مخلوطي است از 2/ 48 درصد R-32 و 8/ 51 درصد R-115
اين مواد سرما زا موادي ثبت شده هستند كه مراحل تركيب آنها پيچيده است و متصدي سرويس نبايد با اختلاط مواد مبرد اقدام به ساختن ماده اي مخصوص بنمايد.
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