Steam jet cooling uses a high-pressure jet of steam to cool water or other fluid media. Typical uses include industrial sites, where a suitable steam supply already exists for other purposes or, historically, for air conditioning on passenger trains which use steam for heating.
Contents[hide]
1 Principle
2 Usage
3 See also
4 References
5 External links
//
[edit] Principle
Steam is passed through a vacuum ejector of high efficiency to exhaust a separate, closed vessel which forms part of a cooling water circuit. The partial vacuum in the vessel causes some of the water to evaporate, thus giving up heat through evaporative cooling. The chilled water is pumped through the circuit to air coolers, while the evaporated water from the ejector is recovered in separate condensers and returned to the cooling circuit.
[edit] Usage
The AT&SF railroad (Santa Fe) used this method, which they called "Steam Ejector Air Conditioning", on both heavyweight and lightweight passenger cars, built until the mid 1950s.
[edit] See also
Steam generator (railroad)
Steam jet ejector
Injector or Ejector
Monday, June 16, 2008
AIR CONDITIONER
An air conditioner is an appliance, system, or mechanism designed to extract heat from an area using a refrigeration cycle. In construction, a complete system of heating, ventilation, and air conditioning is referred to as HVAC. Its purpose, in the home or in the car, is to provide comfort during either hot or cold weather.
Contents[hide]
1 History
2 Air conditioning applications
3 Air conditioning system basics and theories
3.1 Refrigeration cycle
3.1.1 Humidity
3.1.2 Refrigerants
4 Types of air conditioner equipment
4.1 Window and through-wall units
4.2 Evaporative coolers
4.3 Absorptive chillers
4.4 Central air conditioning
5 Thermostats
6 Equipment capacity
6.1 Seasonal Energy Efficiency Rating (SEER)
7 Insulation
8 Home air conditioning systems around the world
9 Health implications
10 References
11 See also
12 External links
12.1 Energy efficiency
//
[edit] History
Main article: Air conditioning#History
[edit] Air conditioning applications
Main article: Air conditioning#Air conditioning applications
[edit] Air conditioning system basics and theories
[edit] Refrigeration cycle
A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor.
In the refrigeration cycle, a heat pump transfers heat from a lower temperature heat source into a higher temperature heat sink. Heat would naturally flow in the opposite direction. This is the most common type of air conditioning. A refrigerator works in much the same way, as it pumps the heat out of the interior into the room in which it stands.
This cycle takes advantage of the universal gas law PV = nRT, where P is pressure, V is volume, R is the universal gas constant, T is temperature, and n is the number of moles of gas (1 mole = 6.022×1023 molecules).
The most common refrigeration cycle uses an electric motor to drive a compressor. In an automobile, the compressor is driven by a belt over a pulley, the belt being driven by the engine's crankshaft (similar to the driving of the pulleys for the alternator, power steering, etc.). Whether in a car or the house, both use electric fan motors for air circulation. Since evaporation occurs when heat is absorbed, and condensation occurs when heat is released, air conditioners are designed to use a compressor to cause pressure changes between two compartments, and actively condense and pump a refrigerant around. A refrigerant is pumped into the cooled compartment (the evaporator coil), where the low pressure and low temperature cause the refrigerant to evaporate into a vapor, taking heat with it. In the other compartment (the condenser), the refrigerant vapor is compressed and forced through another heat exchange coil, condensing into a liquid, rejecting the heat previously absorbed from the cooled space.
[edit] Humidity
Refrigeration air conditioning equipment usually reduces the humidity of the air processed by the system. The relatively cold (below the dewpoint) evaporator coil condenses water vapor from the processed air, (much like an ice cold drink will condense water on the outside of a glass), sending the water to a drain and removing water vapor from the cooled space and lowering the relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In food retailing establishments large open chiller cabinets act as highly effective air dehumidifying units.
Some air conditioning units dry the air without cooling it. They work like a normal air conditioner, except that a heat exchanger is placed between the intake and exhaust. In combination with convection fans they achieve a similar level of comfort as an air cooler in humid tropical climates, but only consume about 1/3 of the electricity. They are also preferred by those who find the draft created by air coolers uncomfortable.
[edit] Refrigerants
Main article: Refrigerants
"Freon" is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties. Unfortunately, evidence has accumulated that these chlorine bearing refrigerants reach the upper atmosphere when they escape. The chemistry is poorly understood but general consensus seems to be that CFCs break up in the stratosphere due to UV-radiation, releasing their chlorine atoms. These chlorine atoms act as catalysts in the breakdown of ozone, which does severe damage to the ozone layer that shields the Earth's surface from the strong UV radiation. The chlorine will remain active as a catalyst until and unless it binds with another particle forming a stable molecule. CFC refrigerants in common but receding usage include R-11 and R-12. Newer and more environmentally-safe refrigerants include HCFCs (R-22, used in most homes today) and HFCs (R-134a, used in most cars) have replaced most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hydrofluorocarbons (HFCs), such as R-410A, which lack chlorine.
The external section of a typical single-room air conditioning unit. For ease of installation, these are frequently placed in a window. This one was installed through a hole cut in the wall.
The internal section of the same unit. The front panel swings down to reveal the controls.
A modern Americool window air-conditioner internal section
[edit] Types of air conditioner equipment
[edit] Window and through-wall units
Many traditional air conditioners in homes or other buildings are single rectangular units used to cool an apartment, a house or part of it, or part of a building. For an example, see the photos to the right. Hotels frequently use PTAC systems, which combine heating into the same unit. Air conditioner units need to have access to the space they are cooling (the inside) and a heat sink; normally outside air is used to cool the condenser section. For this reason, single unit air conditioners are placed in windows or through openings in a wall made for the air conditioner; the latter type includes portable air conditioners.[1]
Window and through-wall units have vents on both the inside and outside, so inside air to be cooled can be blown in and out by a fan in the unit, and outside air can also be blown in and out by another fan to act as the heat sink. The controls are on the inside.
A large house or building may have several such units. Should virtually every room be cooled with its own air conditioning unit, most of the day, it would be less expensive to use central air conditioning, though that may not be physically possible.
[edit] Evaporative coolers
Main article: Evaporative cooler
In very dry climates, evaporative coolers (or "swamp coolers") are popular for improving comfort during hot weather. This type of cooler is the dominant cooler used in Iran which has the largest number of units of any country in the world, hence some referring to them as Persian coolers[2]. An evaporative cooler is a device that draws outside air through a wet pad, such as a large sponge soaked with water. The sensible heat of the incoming air, as measured by a dry bulb thermometer, is reduced. The total heat (sensible heat plus latent heat) of the entering air is unchanged. Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite comfortable. These coolers cost less and are mechanically simple to understand and maintain.
An early type of cooler, using ice for a further effect, was patented by John Gorrie of Apalachicola, Florida in 1842. He used the device to cool the patients in his malaria hospital.
There is a related, more complex process called absorptive refrigeration which uses heat to produce cooling. In one instance, a three-stage absorptive cooler first dehumidifies the air with a spray of salt-water or brine. The brine osmotically absorbs water vapor from the air. The second stage sprays water in the air, cooling the air by evaporation. Finally, to control the humidity, the air passes through another brine spray. The brine is reconcentrated by distillation. The system is used in some hospitals because, with filtering, a sufficiently hot regenerative distillation removes airborne organisms.
[edit] Absorptive chillers
Main article: Absorptive chiller
Some buildings use gas turbines to generate electricity. The exhausts of these are hot enough to drive an absorptive chiller that produces cold water. The cold water is then run through radiators in air ducts for hydronic cooling. The dual use of the energy, both to generate electricity and cooling, makes this technology attractive when regional utility and fuel prices are right. Producing heat, power, and cooling in one system is known as trigeneration.
[edit] Central air conditioning
Central air conditioning, commonly referred to as central air (US) or air-con (UK), is an air conditioning system which uses ducts to distribute cooled and/or dehumidified air to more than one room, or uses pipes to distribute chilled water to heat exchangers in more than one room, and which is not plugged into a standard electrical outlet.
With a typical split system, the condenser and compressor are located in an outdoor unit; the evaporator is mounted in the air handling unit (which is often a forced air furnace). With a package system, all components are located in a single outdoor unit that may be located on the ground or roof.
Central air conditioning performs like a regular air conditioner but has several added benefits:
When the air handling unit turns on, room air is drawn in from various parts of the building through return-air ducts. This air is pulled through a filter where airborne particles such as dust and lint are removed. Sophisticated filters may remove microscopic pollutants as well. The filtered air is routed to air supply ductwork that carries it back to rooms. Whenever the air conditioner is running, this cycle repeats continually.
Because the central air conditioning unit is located outside the home, it offers a lower level of noise indoors than a free-standing air conditioning unit.
[edit] Thermostats
Main article: Thermostat
Thermostats control the operation of HVAC systems, turning on the heating or cooling systems to bring the building to the set temperature. Typically the heating and cooling systems have separate control systems (even though they may share a thermostat) so that the temperature is only controlled "one-way". That is, in winter, a building that is too hot will not be cooled by the thermostat. Thermostats may also be incorporated into facility energy management systems in which the power utility customer may control the overall energy expenditure. In addition, a growing number of power utilities have made available a device which, when professionally installed, will control or limit the power to an HVAC system during peak use times in order to avoid necessitating the use of rolling blackouts. The customer is given a credit of some sort in exchange, so it is often to the advantage of the consumer to buy the most efficient thermostat possible.
[edit] Equipment capacity
Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration". A "ton of refrigeration" is defined as the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. This is equal to 12,000 BTU per hour, or 3517 watts (http://physics.nist.gov/Pubs/SP811/appenB9.html). Residential "central air" systems are usually from 1 to 5 tons (3 to 20 kW) in capacity.
The use of electric/compressive air conditioning puts a major demand on the nation's electrical power grid in warm weather, when most units are operating under heavy load. In the aftermath of the 2003 North America blackout locals were asked to keep their air conditioning off. During peak demand, additional power plants must often be brought online, usually natural gas fired plants because of their rapid startup. A 1995 study of various utility studies of residential air conditioning concluded that the average air conditioner wasted 40% of the input energy. This energy is lost in the form of heat, which must be pumped out. There is a huge opportunity to reduce the need for new power plants and to conserve energy.
In an automobile the A/C system will use around 5 hp (4 kW) of the engine's power.
[edit] Seasonal Energy Efficiency Rating (SEER)
Main article: Seasonal Energy Efficiency Rating
For residential homes, some countries set minimum requirements for energy efficiency. In the United States, the efficiency of air conditioners is often (but not always) rated by the Seasonal Energy Efficiency Ratio (SEER). The higher the SEER rating, the more energy efficient is the air conditioner. The SEER rating is the BTU of cooling output during its normal annual usage divided by the total electric energy input in watt-hours (W·h) during the same period. [3]
SEER = BTU ÷ W·h
For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, operating for a total of 1000 hours during an annual cooling season (i.e., 8 hours per day for 125 days) would provide an annual total cooling output of:
5000 BTU/h × 1000 h = 5,000,000 BTU
which, for a SEER of 10, would be an annual electrical energy usage of:
5,000,000 BTU ÷ 10 = 500,000 W·h
and that is equivalent to an average power usage during the cooling season of:
500,000 W·h ÷ 1000 h = 500 W
SEER is related to the coefficient of performance (COP) commonly used in thermodynamics and also to the Energy Efficiency Ratio (EER). The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures, while SEER is calculated over a whole range of external temperatures (i.e., the temperature distribution for the geographical location of the SEER test). SEER is unusual in that it is composed of an Imperial unit divided by a metric unit. The COP is a ratio with the same metric units of energy (joules) in both the numerator and denominator. They cancel out leaving a dimensionless quantity. Formulas for the approximate conversion between SEER and EER or COP are available from the Pacific Gas and Electric company in California:[4]
(1) SEER = EER ÷ 0.9
(2) SEER = COP x 3.792
(3) EER = COP x 3.413
From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43 units of heat energy are pumped per unit of work energy.
Today, it is rare to see systems rated below SEER 9 in the United States, since older units are being replaced with higher efficiency units. The United States now requires that residential systems manufactured in 2006 have a minimum SEER rating of 13 (although window-box systems are exempt from this law, so their SEER is still around 10).[5] Substantial energy savings can be obtained from more efficient systems. For example by upgrading from SEER 9 to SEER 13, the power consumption is reduced by 30% (equal to 1 - 9/13). It is claimed that this can result in an energy savings valued at up to $US 300 per year (depending on the usage rate and the cost of electricity). In many cases, the lifetime energy savings are likely to surpass the higher initial cost of a high-efficiency unit.
As an example, the annual cost of electric power consumed by a 72,000 BTU/h air conditioning unit operating for 1000 hours per year with a SEER rating of 10 and a power cost of $0.08 per kilowatt-hour (kW·h) may be calculated as follows:
unit size, BTU/h × hours per year, h × power cost, $/kW·h ÷ (SEER, BTU/W·h × 1000 W/kW)
(72,000 BTU/h) × (1000 h) × ($0.08/kW·h) ÷ [(10 BTU/W·h) × (1000 W/kW)] = $576.00 annual cost
Air conditioner sizes are often given as "tons" of cooling. Multiplying the tons of cooling by 12,000 converts it to BTU/h.
A common misconception is that the SEER rating system also applies to heating systems. However, SEER ratings only apply to air conditioning.
Air conditioners (for cooling) and heat pumps (for heating) both work similarly in that heat is transferred or "pumped" from a cooler "heat-source" to a warmer "heat-sink". Air conditioners and heat pumps usually operate most effectively at temperatures around 50 to 55 °F (10−13 °C). A 'balance point' is reached when the heat source temperature falls below about 40 °F (4 °C), and the system is not able to pull any more heat from the heat-source. (This point varies from heat pump to heat pump). Similarly, when the heat-sink temperature rises to about 120 °F (49 °C), the system will operate less effectively, and will not be able to 'push' out any more heat. Ground-source (geothermal) heat pumps do not have this problem of reaching a balance point because they use the ground as a heat source/heat sink and the ground's thermal inertia prevents it from becoming too cold or too warm when moving heat from or to it. The ground's temperature does not vary nearly as much over a year as the air above it does.
[edit] Insulation
Insulation reduces the required power of the air conditioning system. Thick walls, reflective roofing material, curtains, and trees next to buildings also cut down on system and energy requirements.
[edit] Home air conditioning systems around the world
This article does not cite any references or sources. (April 2008)Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Domestic air conditioning is most prevalent and ubiquitous in developed Asian nations such as Japan, Taiwan, South Korea, Singapore and Hong Kong, especially in the latter two due to most of the population living in small high-rise flats. In this area, with soaring summer temperatures and a high standard of living, air conditioning is considered a necessity and not a luxury. Japanese-made domestic air conditioners are usually window or split types, the latter being more modern and expensive. It is also increasing in popularity with the rising standard of living in tropical Asian nations such as Thailand, India, Malaysia and the Philippines. In Indonesia, an air-conditioning set is a must in every home due to the high temperature.[citation needed]
In the United States, home air conditioning is more prevalent in the South and on the East Coast, in most parts of which it has reached the ubiquity it enjoys in East Asia. Central air systems are most common in the United States, and are virtually standard in all new dwellings in most states.
In Europe, home air conditioning is generally less common in part due to higher energy costs and more moderate summer temperatures. Some European countries like Switzerland even forbid installation without permission, motivating that these devices use lots of energy and are environmentally unfriendly. Southern European countries, such as Greece, on the other hand, have seen a wide proliferation of home air-conditioning units in the past few years[1]. The lack of air conditioning in homes, in residential care homes and in medical facilities was identified as a contributing factor to the estimated 35,000 deaths left in the wake of the 2003 heat wave.
[edit] Health implications
This article or section is in need of attention from an expert on the subject.
WikiProject Medicine or the Medicine Portal may be able to help recruit one.If a more appropriate WikiProject or portal exists, please adjust this template accordingly.
Air conditioning has no greater influence on health than heating—that is to say, very little—although poorly maintained air-conditioning systems (especially large, centralized systems) can occasionally promote the growth and spread of microorganisms, such as Legionella pneumophila, the infectious agent responsible for Legionnaire's disease, or thermophilic actinomycetes.[6] Conversely, air conditioning (including filtration, humidification, cooling, disinfection, etc.) can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where an appropriate atmosphere is critical to patient safety and well-being. Air conditioning can have a positive effect on sufferers of allergies and asthma.[7]
In serious heat waves, air conditioning can save the lives of the elderly. Some local authorities even set up public cooling centers for the benefit of those without air conditioning at home.
Properly maintained air-conditioning systems do not directly cause or promote illness, despite superstitions that air-conditioning is unconditionally dangerous to one's health. However, they may indirectly lead to air pollution if the electricity required to power them is produced from fossil fuels.
Contents[hide]
1 History
2 Air conditioning applications
3 Air conditioning system basics and theories
3.1 Refrigeration cycle
3.1.1 Humidity
3.1.2 Refrigerants
4 Types of air conditioner equipment
4.1 Window and through-wall units
4.2 Evaporative coolers
4.3 Absorptive chillers
4.4 Central air conditioning
5 Thermostats
6 Equipment capacity
6.1 Seasonal Energy Efficiency Rating (SEER)
7 Insulation
8 Home air conditioning systems around the world
9 Health implications
10 References
11 See also
12 External links
12.1 Energy efficiency
//
[edit] History
Main article: Air conditioning#History
[edit] Air conditioning applications
Main article: Air conditioning#Air conditioning applications
[edit] Air conditioning system basics and theories
[edit] Refrigeration cycle
A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor.
In the refrigeration cycle, a heat pump transfers heat from a lower temperature heat source into a higher temperature heat sink. Heat would naturally flow in the opposite direction. This is the most common type of air conditioning. A refrigerator works in much the same way, as it pumps the heat out of the interior into the room in which it stands.
This cycle takes advantage of the universal gas law PV = nRT, where P is pressure, V is volume, R is the universal gas constant, T is temperature, and n is the number of moles of gas (1 mole = 6.022×1023 molecules).
The most common refrigeration cycle uses an electric motor to drive a compressor. In an automobile, the compressor is driven by a belt over a pulley, the belt being driven by the engine's crankshaft (similar to the driving of the pulleys for the alternator, power steering, etc.). Whether in a car or the house, both use electric fan motors for air circulation. Since evaporation occurs when heat is absorbed, and condensation occurs when heat is released, air conditioners are designed to use a compressor to cause pressure changes between two compartments, and actively condense and pump a refrigerant around. A refrigerant is pumped into the cooled compartment (the evaporator coil), where the low pressure and low temperature cause the refrigerant to evaporate into a vapor, taking heat with it. In the other compartment (the condenser), the refrigerant vapor is compressed and forced through another heat exchange coil, condensing into a liquid, rejecting the heat previously absorbed from the cooled space.
[edit] Humidity
Refrigeration air conditioning equipment usually reduces the humidity of the air processed by the system. The relatively cold (below the dewpoint) evaporator coil condenses water vapor from the processed air, (much like an ice cold drink will condense water on the outside of a glass), sending the water to a drain and removing water vapor from the cooled space and lowering the relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In food retailing establishments large open chiller cabinets act as highly effective air dehumidifying units.
Some air conditioning units dry the air without cooling it. They work like a normal air conditioner, except that a heat exchanger is placed between the intake and exhaust. In combination with convection fans they achieve a similar level of comfort as an air cooler in humid tropical climates, but only consume about 1/3 of the electricity. They are also preferred by those who find the draft created by air coolers uncomfortable.
[edit] Refrigerants
Main article: Refrigerants
"Freon" is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties. Unfortunately, evidence has accumulated that these chlorine bearing refrigerants reach the upper atmosphere when they escape. The chemistry is poorly understood but general consensus seems to be that CFCs break up in the stratosphere due to UV-radiation, releasing their chlorine atoms. These chlorine atoms act as catalysts in the breakdown of ozone, which does severe damage to the ozone layer that shields the Earth's surface from the strong UV radiation. The chlorine will remain active as a catalyst until and unless it binds with another particle forming a stable molecule. CFC refrigerants in common but receding usage include R-11 and R-12. Newer and more environmentally-safe refrigerants include HCFCs (R-22, used in most homes today) and HFCs (R-134a, used in most cars) have replaced most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hydrofluorocarbons (HFCs), such as R-410A, which lack chlorine.
The external section of a typical single-room air conditioning unit. For ease of installation, these are frequently placed in a window. This one was installed through a hole cut in the wall.
The internal section of the same unit. The front panel swings down to reveal the controls.
A modern Americool window air-conditioner internal section
[edit] Types of air conditioner equipment
[edit] Window and through-wall units
Many traditional air conditioners in homes or other buildings are single rectangular units used to cool an apartment, a house or part of it, or part of a building. For an example, see the photos to the right. Hotels frequently use PTAC systems, which combine heating into the same unit. Air conditioner units need to have access to the space they are cooling (the inside) and a heat sink; normally outside air is used to cool the condenser section. For this reason, single unit air conditioners are placed in windows or through openings in a wall made for the air conditioner; the latter type includes portable air conditioners.[1]
Window and through-wall units have vents on both the inside and outside, so inside air to be cooled can be blown in and out by a fan in the unit, and outside air can also be blown in and out by another fan to act as the heat sink. The controls are on the inside.
A large house or building may have several such units. Should virtually every room be cooled with its own air conditioning unit, most of the day, it would be less expensive to use central air conditioning, though that may not be physically possible.
[edit] Evaporative coolers
Main article: Evaporative cooler
In very dry climates, evaporative coolers (or "swamp coolers") are popular for improving comfort during hot weather. This type of cooler is the dominant cooler used in Iran which has the largest number of units of any country in the world, hence some referring to them as Persian coolers[2]. An evaporative cooler is a device that draws outside air through a wet pad, such as a large sponge soaked with water. The sensible heat of the incoming air, as measured by a dry bulb thermometer, is reduced. The total heat (sensible heat plus latent heat) of the entering air is unchanged. Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite comfortable. These coolers cost less and are mechanically simple to understand and maintain.
An early type of cooler, using ice for a further effect, was patented by John Gorrie of Apalachicola, Florida in 1842. He used the device to cool the patients in his malaria hospital.
There is a related, more complex process called absorptive refrigeration which uses heat to produce cooling. In one instance, a three-stage absorptive cooler first dehumidifies the air with a spray of salt-water or brine. The brine osmotically absorbs water vapor from the air. The second stage sprays water in the air, cooling the air by evaporation. Finally, to control the humidity, the air passes through another brine spray. The brine is reconcentrated by distillation. The system is used in some hospitals because, with filtering, a sufficiently hot regenerative distillation removes airborne organisms.
[edit] Absorptive chillers
Main article: Absorptive chiller
Some buildings use gas turbines to generate electricity. The exhausts of these are hot enough to drive an absorptive chiller that produces cold water. The cold water is then run through radiators in air ducts for hydronic cooling. The dual use of the energy, both to generate electricity and cooling, makes this technology attractive when regional utility and fuel prices are right. Producing heat, power, and cooling in one system is known as trigeneration.
[edit] Central air conditioning
Central air conditioning, commonly referred to as central air (US) or air-con (UK), is an air conditioning system which uses ducts to distribute cooled and/or dehumidified air to more than one room, or uses pipes to distribute chilled water to heat exchangers in more than one room, and which is not plugged into a standard electrical outlet.
With a typical split system, the condenser and compressor are located in an outdoor unit; the evaporator is mounted in the air handling unit (which is often a forced air furnace). With a package system, all components are located in a single outdoor unit that may be located on the ground or roof.
Central air conditioning performs like a regular air conditioner but has several added benefits:
When the air handling unit turns on, room air is drawn in from various parts of the building through return-air ducts. This air is pulled through a filter where airborne particles such as dust and lint are removed. Sophisticated filters may remove microscopic pollutants as well. The filtered air is routed to air supply ductwork that carries it back to rooms. Whenever the air conditioner is running, this cycle repeats continually.
Because the central air conditioning unit is located outside the home, it offers a lower level of noise indoors than a free-standing air conditioning unit.
[edit] Thermostats
Main article: Thermostat
Thermostats control the operation of HVAC systems, turning on the heating or cooling systems to bring the building to the set temperature. Typically the heating and cooling systems have separate control systems (even though they may share a thermostat) so that the temperature is only controlled "one-way". That is, in winter, a building that is too hot will not be cooled by the thermostat. Thermostats may also be incorporated into facility energy management systems in which the power utility customer may control the overall energy expenditure. In addition, a growing number of power utilities have made available a device which, when professionally installed, will control or limit the power to an HVAC system during peak use times in order to avoid necessitating the use of rolling blackouts. The customer is given a credit of some sort in exchange, so it is often to the advantage of the consumer to buy the most efficient thermostat possible.
[edit] Equipment capacity
Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration". A "ton of refrigeration" is defined as the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. This is equal to 12,000 BTU per hour, or 3517 watts (http://physics.nist.gov/Pubs/SP811/appenB9.html). Residential "central air" systems are usually from 1 to 5 tons (3 to 20 kW) in capacity.
The use of electric/compressive air conditioning puts a major demand on the nation's electrical power grid in warm weather, when most units are operating under heavy load. In the aftermath of the 2003 North America blackout locals were asked to keep their air conditioning off. During peak demand, additional power plants must often be brought online, usually natural gas fired plants because of their rapid startup. A 1995 study of various utility studies of residential air conditioning concluded that the average air conditioner wasted 40% of the input energy. This energy is lost in the form of heat, which must be pumped out. There is a huge opportunity to reduce the need for new power plants and to conserve energy.
In an automobile the A/C system will use around 5 hp (4 kW) of the engine's power.
[edit] Seasonal Energy Efficiency Rating (SEER)
Main article: Seasonal Energy Efficiency Rating
For residential homes, some countries set minimum requirements for energy efficiency. In the United States, the efficiency of air conditioners is often (but not always) rated by the Seasonal Energy Efficiency Ratio (SEER). The higher the SEER rating, the more energy efficient is the air conditioner. The SEER rating is the BTU of cooling output during its normal annual usage divided by the total electric energy input in watt-hours (W·h) during the same period. [3]
SEER = BTU ÷ W·h
For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, operating for a total of 1000 hours during an annual cooling season (i.e., 8 hours per day for 125 days) would provide an annual total cooling output of:
5000 BTU/h × 1000 h = 5,000,000 BTU
which, for a SEER of 10, would be an annual electrical energy usage of:
5,000,000 BTU ÷ 10 = 500,000 W·h
and that is equivalent to an average power usage during the cooling season of:
500,000 W·h ÷ 1000 h = 500 W
SEER is related to the coefficient of performance (COP) commonly used in thermodynamics and also to the Energy Efficiency Ratio (EER). The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures, while SEER is calculated over a whole range of external temperatures (i.e., the temperature distribution for the geographical location of the SEER test). SEER is unusual in that it is composed of an Imperial unit divided by a metric unit. The COP is a ratio with the same metric units of energy (joules) in both the numerator and denominator. They cancel out leaving a dimensionless quantity. Formulas for the approximate conversion between SEER and EER or COP are available from the Pacific Gas and Electric company in California:[4]
(1) SEER = EER ÷ 0.9
(2) SEER = COP x 3.792
(3) EER = COP x 3.413
From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43 units of heat energy are pumped per unit of work energy.
Today, it is rare to see systems rated below SEER 9 in the United States, since older units are being replaced with higher efficiency units. The United States now requires that residential systems manufactured in 2006 have a minimum SEER rating of 13 (although window-box systems are exempt from this law, so their SEER is still around 10).[5] Substantial energy savings can be obtained from more efficient systems. For example by upgrading from SEER 9 to SEER 13, the power consumption is reduced by 30% (equal to 1 - 9/13). It is claimed that this can result in an energy savings valued at up to $US 300 per year (depending on the usage rate and the cost of electricity). In many cases, the lifetime energy savings are likely to surpass the higher initial cost of a high-efficiency unit.
As an example, the annual cost of electric power consumed by a 72,000 BTU/h air conditioning unit operating for 1000 hours per year with a SEER rating of 10 and a power cost of $0.08 per kilowatt-hour (kW·h) may be calculated as follows:
unit size, BTU/h × hours per year, h × power cost, $/kW·h ÷ (SEER, BTU/W·h × 1000 W/kW)
(72,000 BTU/h) × (1000 h) × ($0.08/kW·h) ÷ [(10 BTU/W·h) × (1000 W/kW)] = $576.00 annual cost
Air conditioner sizes are often given as "tons" of cooling. Multiplying the tons of cooling by 12,000 converts it to BTU/h.
A common misconception is that the SEER rating system also applies to heating systems. However, SEER ratings only apply to air conditioning.
Air conditioners (for cooling) and heat pumps (for heating) both work similarly in that heat is transferred or "pumped" from a cooler "heat-source" to a warmer "heat-sink". Air conditioners and heat pumps usually operate most effectively at temperatures around 50 to 55 °F (10−13 °C). A 'balance point' is reached when the heat source temperature falls below about 40 °F (4 °C), and the system is not able to pull any more heat from the heat-source. (This point varies from heat pump to heat pump). Similarly, when the heat-sink temperature rises to about 120 °F (49 °C), the system will operate less effectively, and will not be able to 'push' out any more heat. Ground-source (geothermal) heat pumps do not have this problem of reaching a balance point because they use the ground as a heat source/heat sink and the ground's thermal inertia prevents it from becoming too cold or too warm when moving heat from or to it. The ground's temperature does not vary nearly as much over a year as the air above it does.
[edit] Insulation
Insulation reduces the required power of the air conditioning system. Thick walls, reflective roofing material, curtains, and trees next to buildings also cut down on system and energy requirements.
[edit] Home air conditioning systems around the world
This article does not cite any references or sources. (April 2008)Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Domestic air conditioning is most prevalent and ubiquitous in developed Asian nations such as Japan, Taiwan, South Korea, Singapore and Hong Kong, especially in the latter two due to most of the population living in small high-rise flats. In this area, with soaring summer temperatures and a high standard of living, air conditioning is considered a necessity and not a luxury. Japanese-made domestic air conditioners are usually window or split types, the latter being more modern and expensive. It is also increasing in popularity with the rising standard of living in tropical Asian nations such as Thailand, India, Malaysia and the Philippines. In Indonesia, an air-conditioning set is a must in every home due to the high temperature.[citation needed]
In the United States, home air conditioning is more prevalent in the South and on the East Coast, in most parts of which it has reached the ubiquity it enjoys in East Asia. Central air systems are most common in the United States, and are virtually standard in all new dwellings in most states.
In Europe, home air conditioning is generally less common in part due to higher energy costs and more moderate summer temperatures. Some European countries like Switzerland even forbid installation without permission, motivating that these devices use lots of energy and are environmentally unfriendly. Southern European countries, such as Greece, on the other hand, have seen a wide proliferation of home air-conditioning units in the past few years[1]. The lack of air conditioning in homes, in residential care homes and in medical facilities was identified as a contributing factor to the estimated 35,000 deaths left in the wake of the 2003 heat wave.
[edit] Health implications
This article or section is in need of attention from an expert on the subject.
WikiProject Medicine or the Medicine Portal may be able to help recruit one.If a more appropriate WikiProject or portal exists, please adjust this template accordingly.
Air conditioning has no greater influence on health than heating—that is to say, very little—although poorly maintained air-conditioning systems (especially large, centralized systems) can occasionally promote the growth and spread of microorganisms, such as Legionella pneumophila, the infectious agent responsible for Legionnaire's disease, or thermophilic actinomycetes.[6] Conversely, air conditioning (including filtration, humidification, cooling, disinfection, etc.) can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where an appropriate atmosphere is critical to patient safety and well-being. Air conditioning can have a positive effect on sufferers of allergies and asthma.[7]
In serious heat waves, air conditioning can save the lives of the elderly. Some local authorities even set up public cooling centers for the benefit of those without air conditioning at home.
Properly maintained air-conditioning systems do not directly cause or promote illness, despite superstitions that air-conditioning is unconditionally dangerous to one's health. However, they may indirectly lead to air pollution if the electricity required to power them is produced from fossil fuels.
Wednesday, May 28, 2008
1.
Introduction to How Refrigerators Work
2.
The Purpose of Refrigeration
3.
Parts of a Refrigerator
4.
Understanding Refrigeration
5.
The Refrigeration Cycle
6.
Gas and Propane Refrigerators
7.
Electric Coolers
8.
Cold Packs
9.
Lots More Information
10.
See all Kitchen Appliances articles
Parts of a RefrigeratorAs we learned in the introduction, the basic idea behind a refrigerator is to use the evaporation of a liquid to absorb heat. You probably know that when you put water on your skin it makes you feel cool. As the water evaporates, it absorbs heat, creating that cool feeling. Rubbing alcohol feels even cooler because it evaporates at a lower temperature. The liquid, or refrigerant, used in a refrigerator evaporates at an extremely low temperature, so it can create freezing temperatures inside the refrigerator. If you place your refrigerator's refrigerant on your skin (definitely NOT a good idea), it will freeze your skin as it evaporates.
There are five basic parts to any refrigerator (or air-conditioning system):
Compressor
Heat-exchanging pipes - serpentine or coiled set of pipes outside the unit
Expansion valve
Heat-exchanging pipes - serpentine or coiled set of pipes inside the unit
Refrigerant - liquid that evaporates inside the refrigerator to create the cold temperatures
Many industrial installations use pure ammonia as the refrigerant. Pure ammonia evaporates at -27 degrees Fahrenheit (-32 degrees Celsius). The basic mechanism of a refrigerator works like this:
The compressor compresses the refrigerant gas. This raises the refrigerant's pressure and temperature (orange), so the heat-exchanging coils outside the refrigerator allow the refrigerant to dissipate the heat of pressurization.
As it cools, the refrigerant condenses into liquid form (purple) and flows through the expansion valve.
When it flows through the expansion valve, the liquid refrigerant is allowed to move from a high-pressure zone to a low-pressure zone, so it expands and evaporates (light blue). In evaporating, it absorbs heat, making it cold.
The coils inside the refrigerator allow the refrigerant to absorb heat, making the inside of the refrigerator cold. The cycle then repeats.
This is a fairly standard -- and somewhat unsatisfying -- explanation of how a refrigerator works. So let's look at refrigeration using several real-world examples to understand what is truly happening.
PREVIOUS
NEXT
Inside This Article
1.
Introduction to How Refrigerators Work
2.
The Purpose of Refrigeration
3.
Parts of a Refrigerator
4.
Understanding Refrigeration
5.
The Refrigeration Cycle
6.
Gas and Propane Refrigerators
7.
Electric Coolers
8.
Cold Packs
9.
Lots More Information
10.
See all Kitchen Appliances articles
Introduction to How Refrigerators Work
2.
The Purpose of Refrigeration
3.
Parts of a Refrigerator
4.
Understanding Refrigeration
5.
The Refrigeration Cycle
6.
Gas and Propane Refrigerators
7.
Electric Coolers
8.
Cold Packs
9.
Lots More Information
10.
See all Kitchen Appliances articles
Parts of a RefrigeratorAs we learned in the introduction, the basic idea behind a refrigerator is to use the evaporation of a liquid to absorb heat. You probably know that when you put water on your skin it makes you feel cool. As the water evaporates, it absorbs heat, creating that cool feeling. Rubbing alcohol feels even cooler because it evaporates at a lower temperature. The liquid, or refrigerant, used in a refrigerator evaporates at an extremely low temperature, so it can create freezing temperatures inside the refrigerator. If you place your refrigerator's refrigerant on your skin (definitely NOT a good idea), it will freeze your skin as it evaporates.
There are five basic parts to any refrigerator (or air-conditioning system):
Compressor
Heat-exchanging pipes - serpentine or coiled set of pipes outside the unit
Expansion valve
Heat-exchanging pipes - serpentine or coiled set of pipes inside the unit
Refrigerant - liquid that evaporates inside the refrigerator to create the cold temperatures
Many industrial installations use pure ammonia as the refrigerant. Pure ammonia evaporates at -27 degrees Fahrenheit (-32 degrees Celsius). The basic mechanism of a refrigerator works like this:
The compressor compresses the refrigerant gas. This raises the refrigerant's pressure and temperature (orange), so the heat-exchanging coils outside the refrigerator allow the refrigerant to dissipate the heat of pressurization.
As it cools, the refrigerant condenses into liquid form (purple) and flows through the expansion valve.
When it flows through the expansion valve, the liquid refrigerant is allowed to move from a high-pressure zone to a low-pressure zone, so it expands and evaporates (light blue). In evaporating, it absorbs heat, making it cold.
The coils inside the refrigerator allow the refrigerant to absorb heat, making the inside of the refrigerator cold. The cycle then repeats.
This is a fairly standard -- and somewhat unsatisfying -- explanation of how a refrigerator works. So let's look at refrigeration using several real-world examples to understand what is truly happening.
PREVIOUS
NEXT
Inside This Article
1.
Introduction to How Refrigerators Work
2.
The Purpose of Refrigeration
3.
Parts of a Refrigerator
4.
Understanding Refrigeration
5.
The Refrigeration Cycle
6.
Gas and Propane Refrigerators
7.
Electric Coolers
8.
Cold Packs
9.
Lots More Information
10.
See all Kitchen Appliances articles
Wednesday, May 14, 2008
MAGNETIC REFRIGERATION
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures (well below 1 kelvin), as well as the ranges used in common refrigerators, depending on the design of the system.
The fundamental principle was suggested by Debye (1926) and Giauque (1927),[1] and the first working magnetic refrigerators were constructed by several groups beginning in 1933. Magnetic refrigeration was the first method developed for cooling below about 0.3 kelvin (a temperature attainable by 3He/4He dilution refrigeration).
Contents[hide]
1 The magnetocaloric effect
1.1 Thermodynamic cycle
1.2 Applied technique
2 Working materials
2.1 Paramagnetic salts
2.2 Nuclear demagnetization
3 Commercial development
3.1 Current and future uses
4 History
4.1 Room temperature devices
5 References
5.1 Notes
6 See also
7 External links
//
[edit] The magnetocaloric effect
The Magnetocaloric effect (MCE, from magnet and calorie) is a magneto-thermodynamic phenomenon in which a reversible change in temperature of a suitable material is caused by exposing the material to a changing magnetic field. This is also known as adiabatic demagnetization by low temperature physicists, due to the application of the process specifically to effect a temperature drop. In that part of the overall refrigeration process, a decrease in the strength of an externally applied magnetic field allows the magnetic domains of a chosen (magnetocaloric) material to become disoriented from the magnetic field by the agitating action of the thermal energy (phonons) present in the material. If the material is isolated so that no energy is allowed to (re)migrate into the material during this time (i.e. an adiabatic process), the temperature drops as the domains absorb the thermal energy to perform their reorientation. The randomization of the domains occurs in a similar fashion to the randomization at the curie temperature, except that magnetic dipoles overcome a decreasing external magnetic field while energy remains constant, instead of magnetic domains being disrupted from internal ferromagnetism as energy is added.
One of the most notable examples of the magnetocaloric effect is in the chemical element gadolinium and some of its alloys. Gadolinium's temperature is observed to increase when it enters certain magnetic fields. When it leaves the magnetic field, the temperature returns to normal.The effect is considerably stronger for the gadolinium alloy Gd5(Si2Ge2).[2] Praseodymium alloyed with nickel (PrNi5) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero.[3]
[edit] Thermodynamic cycle
Analogy between magnetic refrigeration and vapor cycle or conventional refrigeration. H = externally applied magnetic field; Q = heat quantity; P = pressure; ΔTad = adiabatic temperature variation
The cycle is performed as a refrigeration cycle, analogous to the Carnot cycle, and can be described at a starting point whereby the chosen working substance is introduced into a magnetic field (i.e. the magnetic flux density is increased). The working material is the refrigerant, and starts in thermal equilibrium with the refrigerated environment.
Adiabatic magnetization: The substance is placed in an insulated environment. The increasing external magnetic field (+H) causes the magnetic dipoles of the atoms to align, thereby decreasing the material's magnetic entropy and heat capacity. Since overall energy is not lost (yet) and therefore total entropy is not reduced (according to thermodynamic laws), the net result is that the item heats up (T + ΔTad).
Isomagnetic enthalpic transfer: This added heat can then be removed by a fluid like water or helium for example (-Q). The magnetic field is held constant to prevent the dipoles from reabsorbing the heat. Once sufficiently cooled, the magnetocaloric material and the coolant are separated (H=0).
Adiabatic demagnetization: The substance is returned to another adiabatic (insulated) condition so the total entropy remains constant. However, this time the magnetic field is decreased, the thermal energy causes the domains to overcome the field, and thus the sample cools (i.e. an adiabatic temperature change). Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).
Isomagnetic entropic transfer: The magnetic field is held constant to prevent the material from heating back up. The material is placed in thermal contact with the environment being refrigerated. Because the working material is cooler than the refrigerated environment (by design), heat energy migrates into the working material (+Q).
Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle begins anew.
[edit] Applied technique
The basic operating principle of an Adiabatic Demagnetization Refrigerator (ADR) is the use of a strong magnetic field to control the entropy of a sample of material, often called the "refrigerant". Magnetic field constrains the orientation of magnetic dipoles in the refrigerant. The stronger the magnetic field, the more aligned the dipoles are, and this corresponds to lower entropy and heat capacity because the material has (effectively) lost some of its internal degrees of freedom. If the refrigerant is kept at a constant temperature through thermal contact with a heat sink (usually liquid helium) while the magnetic field is switched on, the refrigerant must lose some energy because it is equilibrated with the heat sink. When the magnetic field is subsequently switched off, the heat capacity of the refrigerant rises again because the degrees of freedom associated with orientation of the dipoles are once again liberated, pulling their share of equipartitioned energy from the motion of the molecules, thereby lowering the overall temperature of a system with decreased energy. Since the system is now insulated when the magnetic field is switched off, the process is adiabatic, i.e. the system can no longer exchange energy with its surroundings (the heat sink), and its temperature decreases below its initial value, that of the heat sink.
The operation of a standard ADR proceeds roughly as follows. First, a strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. The heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off, increasing the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the He heat sink. In practice, the magnetic field is decreased slowly in order to provide continuous cooling and keep the sample at an approximately constant low temperature. Once the field falls to zero (or to some low limiting value determined by the properties of the refrigerant), the cooling power of the ADR vanishes, and heat leaks will cause the refrigerant to warm up.
[edit] Working materials
The magnetocaloric effect is an intrinsic property of a magnetic solid. This thermal response of a solid to the application or removal of magnetic fields is maximized when the solid is near its magnetic ordering temperature.
The magnitudes of the magnetic entropy and the adiabatic temperature changes are strongly dependent upon the magnetic order process: the magnitude is generally small in antiferromagnets, ferrimagnets and spin glass systems; it can be substantial for normal ferromagnets which undergo a second order magnetic transition; and it is generally the largest for a ferromagnet which undergoes a first order magnetic transition.
Also, crystalline electric fields and pressure can have a substantial influence on magnetic entropy and adiabatic temperature changes.
Currently, alloys of gadolinium producing 3 to 4 K per tesla of change in a magnetic field can be used for magnetic refrigeration or power generation purposes.
Recent research on materials that exhibit a giant entropy change showed that Gd5(SixGe1 − x)4, La(FexSi1 − x)13Hx and MnFeP1 − xAsx alloys, for example, are some of the most promising substitutes for Gadolinium and its alloys (GdDy, GdTy, etc...). These materials are called giant magnetocaloric effect materials (GMCE).
Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature since they undergo second-order phase transitions which have no magnetic or thermal hysteresis involved.
[edit] Paramagnetic salts
The originally suggested refrigerant was a paramagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms.
In a paramagnetic salt ADR, the heat sink is usually provided by a pumped 4He (about 1.2 K) or 3He (about 0.3 K) cryostat. An easily attainable 1 tesla magnetic field is generally required for the initial magnetization. The minimum temperature attainable is determined by the self-magnetization tendencies of the chosen refrigerant salt, but temperatures from 1 to 100 mK are accessible. Dilution refrigerators had for many years supplanted paramagnetic salt ADRs, but interest in space-based and simple to use lab-ADRs has recently revived the field (for example see http://www.cmr.uk.com/abcmrhis.html).
Eventually paramagnetic salts become either diamagnetic or ferromagnetic, limiting the lowest temperature which can be reached using this method.
[edit] Nuclear demagnetization
One variant of adiabatic demagnetization that continues to find substantial research application is nuclear demagnetization refrigeration (NDR). NDR follows the same principle described above, but in this case the cooling power arises from the magnetic dipoles of the nuclei of the refrigerant atoms, rather than their electron configurations. Since these dipoles are of much smaller magnitude, they are less prone to self-alignment and have lower intrinsic minimum fields. This allows NDR to cool the nuclear spin system to very low temperatures, often 1 µK or below. Unfortunately, the small magnitudes of nuclear magnetic dipoles also makes them less inclined to align to external fields. Magnetic fields of 3 teslas or greater are often needed for the initial magnetization step of NDR.
In NDR systems, the initial heat sink must sit at very low temperatures (10–100 mK). This precooling is often provided by the mixing chamber of a dilution refrigerator or a paramagnetic salt ADR stage.
[edit] Commercial development
This refrigeration, once proven viable, could be used in any possible application where cooling, heating or power generation is used today. Since it is only at an early stage of development, there are several technical and efficiency issues that should be analyzed. The magnetocaloric refrigeration system is composed of pumps, electric motors, secondary fluids, heat exchangers of different types, magnets and magnetic materials. These processes are greatly affected by irreversibilities and should be adequately considered. Appliances using this method could have a smaller environmental impact if the method is perfected and replaces hydrofluorocarbon (HFCs) refrigerators (some refrigerators still use HFCs which have considerable greenhouse effect). At present, however, the superconducting magnets that are used in the process have to themselves be cooled down to the temperature of liquid nitrogen, or with even colder, and relatively expensive, liquid helium. Considering these fluids have boiling points of 77.36 K and 4.22 K respectively, the technology is clearly not cost-efficient and efficient for home appliances, but for experimental, laboratorial, and industrial use only.
Recent research on materials that exhibit a large entropy change showed that alloys are some of the most promising substitutes of Gadolinium and its alloys (GdDy, GdTb, etc...). Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature. There are still some thermal and magnetic hysteresis problems to be solved for them to become really useful and scientists are working hard to achieve this goal. Thermal hysteresis problems is solved therefore in adding ferrite (5:4) A good review on magnetocaloric materials is entitled "Recent developments in magnetocaloric materials" and written by Dr. Gschneidner et al.[6]
Recent discovery has succeeded using commercial grade materials and permanent magnets on room temperatures to construct a magnetocaloric refrigerator which promises wide use.
This technique has been used for many years in cryogenic systems for producing further cooling in systems already cooled to temperatures of 4 kelvins and lower. In England, a company called Cambridge Magnetic Refrigeration produces cryogenic systems based on the magnetocaloric effect.
On 20 August 2007, the Risø National Laboratory at the Technical University of Denmark, claimed to have reached a milestone in their magnetic cooling research when they reported a temperature span of 8.7 C[4]. They hope to introduce the first commercial applications of the technology by 2010.
[edit] Current and future uses
There are still some thermal and magnetic hysteresis problems to be solved for these first-order phase transition materials that exhibit the GMCE to become really useful; this is a subject of current research. A useful review on magnetocaloric materials is entitled "Recent developments in magnetocaloric materials" and written by Dr. Gschneidner et al.[7]
This effect is currently being explored to produce better refrigeration techniques, especially for use in spacecraft. This technique is already used to achieve cryogenic temperatures in the laboratory setting (below 10K). As an object displaying MCE is moved into a magnetic field, the magnetic spins align, lowering the entropy. Moving that object out of the field allows the object to increase its entropy by absorbing heat from the environment and disordering the spins. In this way, heat can be taken from one area to another. Should materials be found to display this effect near room temperature, refrigeration without the need for compression may be possible, increasing energy efficiency.
[edit] History
The effect was discovered in pure iron in 1881 by Emil Warburg. Originally, the cooling effect varied between 0.5 to 2 K/T.
Major advances first appeared in the late 1920s when cooling via adiabatic demagnetization was independently proposed by two scientists: Debye (1926) and Giauque (1927).
This cooling technology was first demonstrated experimentally by chemist Nobel Laureate William F. Giauque and his colleague Dr. D.P. MacDougall in 1933 for cryogenic purposes when they reached 0.25 K. [8]. Between 1933 and 1997, a number of advances in utilization of the MCE for cooling occurred. See Reviews:[5][6][7][8]
In 1997, the first near room temperature proof of concept magnetic refrigerator was demonstrated by Prof. Karl A. Gschneidner, Jr. by the Iowa State University at Ames Laboratory. This event attracted interest from scientists and companies worldwide who started developing new kinds of room temperature materials and magnetic refrigerator designs.[2]
Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using magnetic fields starting at 0.6 T up to 10 teslas. Magnetic fields above 2 T are difficult to produce with permanent magnets and are produced by a superconducting magnet (1 tesla is about 20,000 times the Earth's magnetic field).
[edit] Room temperature devices
Some recent research has focused on the use of the process to perform refrigeration near "room temperature". Constructed examples of room temperature magnetic refrigerators are listed in the table below:
Room temperature magnetic refrigerators
Institute/Company
Location
Announcement date
Type
Max. cooling power (W)[1]
Max ΔT (K)[2]
Magnetic field (T)
Solid refrigerant
Quantity (kg)
Ames Laboratory/Astronautics[9]
Ames, IA/Madison, Wisconsin, USA
20 February 1997
Reciprocating
600
10
5 (S)
Gd spheres
Mater. Science Institute Barcelona[10]
Barcelona, Spain
May 2000
Rotary
?
5
0.95 (P)
Gd foil
Chubu Electric/Toshiba[11]
Yokohama, Japan
Summer 2000
Reciprocating
100
21
4 (S)
Gd spheres
University of Victoria[12][13][14]
Victoria, British Columbia Canada
July 2001
Reciprocating
2
14
2 (S)
Gd & Gd1−xTbx L.B.
Astronautics[15]
Madison, Wisconsin, USA
18 September 2001
Rotary
95
25
1.5 (P)
Gd spheres
Sichuan Inst. Tech./Nanjing University[16]
Nanjing, China
23 April 2002
Reciprocating
?
23
1.4 (P)
Gd spheres and Gd5Si1.985Ge1.985Ga0.03 powder
Chubu Electric/Toshiba[17]
Yokohama, Japan
5 October 2002
Reciprocating
40
27
0.6 (P)
Gd1−xDyx L.B.
Chubu Electric/Toshiba[18]
Yokohama, Japan
4 March 2003
Rotary
60
10
0.76 (P)
Gd 1−xDyx L.B.
1
Lab. d’Electrotechnique Grenoble[19]
Grenoble, France
April 2003
Reciprocating
8.8
4
0.8 (P)
Gd foil
George Washington University
USA
July 2004
Reciprocating
?
?
? (P)
Gd foil
Astronautics[20]
Madison, Wisconsin, USA
2004
Rotary
95
25
1.5 (P)
Gd and GdEr spheres / La(Fe0.88Si0.12)13H1.0
University of Victoria[21]
Victoria, British Columbia Canada
2006
Reciprocating
15
50
2 (S)
Gd, Gd0.74Tb0.26 and Gd0.85Er0.15 pucks
0.12
1maximum cooling power at zero temperature difference (ΔT=0); 2maximum temperature span at zero cooling capacity (W=0); L.B. = layered bed; P = permanent magnet; S = superconducting magnet
In one example, Prof. Karl A. Gschneidner, Jr. unveiled a proof of concept magnetic refrigerator near room temperature in February 20, 1997. He also announced the discovery of the giant MCE (GMCE) in Gd5Si2Ge2 on June 9, 1997 [9] (see below). Since then, hundreds of peer-reviewed articles have been written describing materials exhibiting magnetocaloric effects
The fundamental principle was suggested by Debye (1926) and Giauque (1927),[1] and the first working magnetic refrigerators were constructed by several groups beginning in 1933. Magnetic refrigeration was the first method developed for cooling below about 0.3 kelvin (a temperature attainable by 3He/4He dilution refrigeration).
Contents[hide]
1 The magnetocaloric effect
1.1 Thermodynamic cycle
1.2 Applied technique
2 Working materials
2.1 Paramagnetic salts
2.2 Nuclear demagnetization
3 Commercial development
3.1 Current and future uses
4 History
4.1 Room temperature devices
5 References
5.1 Notes
6 See also
7 External links
//
[edit] The magnetocaloric effect
The Magnetocaloric effect (MCE, from magnet and calorie) is a magneto-thermodynamic phenomenon in which a reversible change in temperature of a suitable material is caused by exposing the material to a changing magnetic field. This is also known as adiabatic demagnetization by low temperature physicists, due to the application of the process specifically to effect a temperature drop. In that part of the overall refrigeration process, a decrease in the strength of an externally applied magnetic field allows the magnetic domains of a chosen (magnetocaloric) material to become disoriented from the magnetic field by the agitating action of the thermal energy (phonons) present in the material. If the material is isolated so that no energy is allowed to (re)migrate into the material during this time (i.e. an adiabatic process), the temperature drops as the domains absorb the thermal energy to perform their reorientation. The randomization of the domains occurs in a similar fashion to the randomization at the curie temperature, except that magnetic dipoles overcome a decreasing external magnetic field while energy remains constant, instead of magnetic domains being disrupted from internal ferromagnetism as energy is added.
One of the most notable examples of the magnetocaloric effect is in the chemical element gadolinium and some of its alloys. Gadolinium's temperature is observed to increase when it enters certain magnetic fields. When it leaves the magnetic field, the temperature returns to normal.The effect is considerably stronger for the gadolinium alloy Gd5(Si2Ge2).[2] Praseodymium alloyed with nickel (PrNi5) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero.[3]
[edit] Thermodynamic cycle
Analogy between magnetic refrigeration and vapor cycle or conventional refrigeration. H = externally applied magnetic field; Q = heat quantity; P = pressure; ΔTad = adiabatic temperature variation
The cycle is performed as a refrigeration cycle, analogous to the Carnot cycle, and can be described at a starting point whereby the chosen working substance is introduced into a magnetic field (i.e. the magnetic flux density is increased). The working material is the refrigerant, and starts in thermal equilibrium with the refrigerated environment.
Adiabatic magnetization: The substance is placed in an insulated environment. The increasing external magnetic field (+H) causes the magnetic dipoles of the atoms to align, thereby decreasing the material's magnetic entropy and heat capacity. Since overall energy is not lost (yet) and therefore total entropy is not reduced (according to thermodynamic laws), the net result is that the item heats up (T + ΔTad).
Isomagnetic enthalpic transfer: This added heat can then be removed by a fluid like water or helium for example (-Q). The magnetic field is held constant to prevent the dipoles from reabsorbing the heat. Once sufficiently cooled, the magnetocaloric material and the coolant are separated (H=0).
Adiabatic demagnetization: The substance is returned to another adiabatic (insulated) condition so the total entropy remains constant. However, this time the magnetic field is decreased, the thermal energy causes the domains to overcome the field, and thus the sample cools (i.e. an adiabatic temperature change). Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).
Isomagnetic entropic transfer: The magnetic field is held constant to prevent the material from heating back up. The material is placed in thermal contact with the environment being refrigerated. Because the working material is cooler than the refrigerated environment (by design), heat energy migrates into the working material (+Q).
Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle begins anew.
[edit] Applied technique
The basic operating principle of an Adiabatic Demagnetization Refrigerator (ADR) is the use of a strong magnetic field to control the entropy of a sample of material, often called the "refrigerant". Magnetic field constrains the orientation of magnetic dipoles in the refrigerant. The stronger the magnetic field, the more aligned the dipoles are, and this corresponds to lower entropy and heat capacity because the material has (effectively) lost some of its internal degrees of freedom. If the refrigerant is kept at a constant temperature through thermal contact with a heat sink (usually liquid helium) while the magnetic field is switched on, the refrigerant must lose some energy because it is equilibrated with the heat sink. When the magnetic field is subsequently switched off, the heat capacity of the refrigerant rises again because the degrees of freedom associated with orientation of the dipoles are once again liberated, pulling their share of equipartitioned energy from the motion of the molecules, thereby lowering the overall temperature of a system with decreased energy. Since the system is now insulated when the magnetic field is switched off, the process is adiabatic, i.e. the system can no longer exchange energy with its surroundings (the heat sink), and its temperature decreases below its initial value, that of the heat sink.
The operation of a standard ADR proceeds roughly as follows. First, a strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. The heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off, increasing the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the He heat sink. In practice, the magnetic field is decreased slowly in order to provide continuous cooling and keep the sample at an approximately constant low temperature. Once the field falls to zero (or to some low limiting value determined by the properties of the refrigerant), the cooling power of the ADR vanishes, and heat leaks will cause the refrigerant to warm up.
[edit] Working materials
The magnetocaloric effect is an intrinsic property of a magnetic solid. This thermal response of a solid to the application or removal of magnetic fields is maximized when the solid is near its magnetic ordering temperature.
The magnitudes of the magnetic entropy and the adiabatic temperature changes are strongly dependent upon the magnetic order process: the magnitude is generally small in antiferromagnets, ferrimagnets and spin glass systems; it can be substantial for normal ferromagnets which undergo a second order magnetic transition; and it is generally the largest for a ferromagnet which undergoes a first order magnetic transition.
Also, crystalline electric fields and pressure can have a substantial influence on magnetic entropy and adiabatic temperature changes.
Currently, alloys of gadolinium producing 3 to 4 K per tesla of change in a magnetic field can be used for magnetic refrigeration or power generation purposes.
Recent research on materials that exhibit a giant entropy change showed that Gd5(SixGe1 − x)4, La(FexSi1 − x)13Hx and MnFeP1 − xAsx alloys, for example, are some of the most promising substitutes for Gadolinium and its alloys (GdDy, GdTy, etc...). These materials are called giant magnetocaloric effect materials (GMCE).
Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature since they undergo second-order phase transitions which have no magnetic or thermal hysteresis involved.
[edit] Paramagnetic salts
The originally suggested refrigerant was a paramagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms.
In a paramagnetic salt ADR, the heat sink is usually provided by a pumped 4He (about 1.2 K) or 3He (about 0.3 K) cryostat. An easily attainable 1 tesla magnetic field is generally required for the initial magnetization. The minimum temperature attainable is determined by the self-magnetization tendencies of the chosen refrigerant salt, but temperatures from 1 to 100 mK are accessible. Dilution refrigerators had for many years supplanted paramagnetic salt ADRs, but interest in space-based and simple to use lab-ADRs has recently revived the field (for example see http://www.cmr.uk.com/abcmrhis.html).
Eventually paramagnetic salts become either diamagnetic or ferromagnetic, limiting the lowest temperature which can be reached using this method.
[edit] Nuclear demagnetization
One variant of adiabatic demagnetization that continues to find substantial research application is nuclear demagnetization refrigeration (NDR). NDR follows the same principle described above, but in this case the cooling power arises from the magnetic dipoles of the nuclei of the refrigerant atoms, rather than their electron configurations. Since these dipoles are of much smaller magnitude, they are less prone to self-alignment and have lower intrinsic minimum fields. This allows NDR to cool the nuclear spin system to very low temperatures, often 1 µK or below. Unfortunately, the small magnitudes of nuclear magnetic dipoles also makes them less inclined to align to external fields. Magnetic fields of 3 teslas or greater are often needed for the initial magnetization step of NDR.
In NDR systems, the initial heat sink must sit at very low temperatures (10–100 mK). This precooling is often provided by the mixing chamber of a dilution refrigerator or a paramagnetic salt ADR stage.
[edit] Commercial development
This refrigeration, once proven viable, could be used in any possible application where cooling, heating or power generation is used today. Since it is only at an early stage of development, there are several technical and efficiency issues that should be analyzed. The magnetocaloric refrigeration system is composed of pumps, electric motors, secondary fluids, heat exchangers of different types, magnets and magnetic materials. These processes are greatly affected by irreversibilities and should be adequately considered. Appliances using this method could have a smaller environmental impact if the method is perfected and replaces hydrofluorocarbon (HFCs) refrigerators (some refrigerators still use HFCs which have considerable greenhouse effect). At present, however, the superconducting magnets that are used in the process have to themselves be cooled down to the temperature of liquid nitrogen, or with even colder, and relatively expensive, liquid helium. Considering these fluids have boiling points of 77.36 K and 4.22 K respectively, the technology is clearly not cost-efficient and efficient for home appliances, but for experimental, laboratorial, and industrial use only.
Recent research on materials that exhibit a large entropy change showed that alloys are some of the most promising substitutes of Gadolinium and its alloys (GdDy, GdTb, etc...). Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature. There are still some thermal and magnetic hysteresis problems to be solved for them to become really useful and scientists are working hard to achieve this goal. Thermal hysteresis problems is solved therefore in adding ferrite (5:4) A good review on magnetocaloric materials is entitled "Recent developments in magnetocaloric materials" and written by Dr. Gschneidner et al.[6]
Recent discovery has succeeded using commercial grade materials and permanent magnets on room temperatures to construct a magnetocaloric refrigerator which promises wide use.
This technique has been used for many years in cryogenic systems for producing further cooling in systems already cooled to temperatures of 4 kelvins and lower. In England, a company called Cambridge Magnetic Refrigeration produces cryogenic systems based on the magnetocaloric effect.
On 20 August 2007, the Risø National Laboratory at the Technical University of Denmark, claimed to have reached a milestone in their magnetic cooling research when they reported a temperature span of 8.7 C[4]. They hope to introduce the first commercial applications of the technology by 2010.
[edit] Current and future uses
There are still some thermal and magnetic hysteresis problems to be solved for these first-order phase transition materials that exhibit the GMCE to become really useful; this is a subject of current research. A useful review on magnetocaloric materials is entitled "Recent developments in magnetocaloric materials" and written by Dr. Gschneidner et al.[7]
This effect is currently being explored to produce better refrigeration techniques, especially for use in spacecraft. This technique is already used to achieve cryogenic temperatures in the laboratory setting (below 10K). As an object displaying MCE is moved into a magnetic field, the magnetic spins align, lowering the entropy. Moving that object out of the field allows the object to increase its entropy by absorbing heat from the environment and disordering the spins. In this way, heat can be taken from one area to another. Should materials be found to display this effect near room temperature, refrigeration without the need for compression may be possible, increasing energy efficiency.
[edit] History
The effect was discovered in pure iron in 1881 by Emil Warburg. Originally, the cooling effect varied between 0.5 to 2 K/T.
Major advances first appeared in the late 1920s when cooling via adiabatic demagnetization was independently proposed by two scientists: Debye (1926) and Giauque (1927).
This cooling technology was first demonstrated experimentally by chemist Nobel Laureate William F. Giauque and his colleague Dr. D.P. MacDougall in 1933 for cryogenic purposes when they reached 0.25 K. [8]. Between 1933 and 1997, a number of advances in utilization of the MCE for cooling occurred. See Reviews:[5][6][7][8]
In 1997, the first near room temperature proof of concept magnetic refrigerator was demonstrated by Prof. Karl A. Gschneidner, Jr. by the Iowa State University at Ames Laboratory. This event attracted interest from scientists and companies worldwide who started developing new kinds of room temperature materials and magnetic refrigerator designs.[2]
Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using magnetic fields starting at 0.6 T up to 10 teslas. Magnetic fields above 2 T are difficult to produce with permanent magnets and are produced by a superconducting magnet (1 tesla is about 20,000 times the Earth's magnetic field).
[edit] Room temperature devices
Some recent research has focused on the use of the process to perform refrigeration near "room temperature". Constructed examples of room temperature magnetic refrigerators are listed in the table below:
Room temperature magnetic refrigerators
Institute/Company
Location
Announcement date
Type
Max. cooling power (W)[1]
Max ΔT (K)[2]
Magnetic field (T)
Solid refrigerant
Quantity (kg)
Ames Laboratory/Astronautics[9]
Ames, IA/Madison, Wisconsin, USA
20 February 1997
Reciprocating
600
10
5 (S)
Gd spheres
Mater. Science Institute Barcelona[10]
Barcelona, Spain
May 2000
Rotary
?
5
0.95 (P)
Gd foil
Chubu Electric/Toshiba[11]
Yokohama, Japan
Summer 2000
Reciprocating
100
21
4 (S)
Gd spheres
University of Victoria[12][13][14]
Victoria, British Columbia Canada
July 2001
Reciprocating
2
14
2 (S)
Gd & Gd1−xTbx L.B.
Astronautics[15]
Madison, Wisconsin, USA
18 September 2001
Rotary
95
25
1.5 (P)
Gd spheres
Sichuan Inst. Tech./Nanjing University[16]
Nanjing, China
23 April 2002
Reciprocating
?
23
1.4 (P)
Gd spheres and Gd5Si1.985Ge1.985Ga0.03 powder
Chubu Electric/Toshiba[17]
Yokohama, Japan
5 October 2002
Reciprocating
40
27
0.6 (P)
Gd1−xDyx L.B.
Chubu Electric/Toshiba[18]
Yokohama, Japan
4 March 2003
Rotary
60
10
0.76 (P)
Gd 1−xDyx L.B.
1
Lab. d’Electrotechnique Grenoble[19]
Grenoble, France
April 2003
Reciprocating
8.8
4
0.8 (P)
Gd foil
George Washington University
USA
July 2004
Reciprocating
?
?
? (P)
Gd foil
Astronautics[20]
Madison, Wisconsin, USA
2004
Rotary
95
25
1.5 (P)
Gd and GdEr spheres / La(Fe0.88Si0.12)13H1.0
University of Victoria[21]
Victoria, British Columbia Canada
2006
Reciprocating
15
50
2 (S)
Gd, Gd0.74Tb0.26 and Gd0.85Er0.15 pucks
0.12
1maximum cooling power at zero temperature difference (ΔT=0); 2maximum temperature span at zero cooling capacity (W=0); L.B. = layered bed; P = permanent magnet; S = superconducting magnet
In one example, Prof. Karl A. Gschneidner, Jr. unveiled a proof of concept magnetic refrigerator near room temperature in February 20, 1997. He also announced the discovery of the giant MCE (GMCE) in Gd5Si2Ge2 on June 9, 1997 [9] (see below). Since then, hundreds of peer-reviewed articles have been written describing materials exhibiting magnetocaloric effects
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types of compressors used in refrigeration
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LATEST AT SEA-BIRD
Diversified into
Engineering Products
Empowered by Makino Japan make of CNC machines, we are capable of producing wide range of engineering and industrial products.
Send Query
TURNKEY PROJECTS
We supply all equipments controls and accessories as well as undertake turnkey plant projects for Cold Storages. 1. Ice Making Plant 2. Ice Cream Plant3. Chilling Plants4. Marine Refrigeration................
more
OPEN TYPE COMPRESSORS
Open type compressors and variable speed compressors by a continuous development and the use of high-quality materials.
more
High Speed Compressors
This model series has been further developed from the proven two,four and six cylinder series after extensive research.
more
SEMI HERMETIC COMPRESSORS
The technical highlights of "Sea Bird" Semi-hermetic compressors series the leading technology with displacement from 4 to 151.6m3/h(50Hz)
more
COMPRESSOR SPARE PARTS & ACCE.
We manufacture Replacement Parts & Spare Parts of Refrigeration & Air-Conditioning Compressors for OEMs
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AMMONIA VALVE FITTINGS
All kind of ammonia valves and fittings including Globe Valves, Angle Valves, Check Valves, Strainer Valve & others.
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We manufacture Replacement Parts & Spare Parts of Refrigeration & Air-Conditioning Compressors for OEMS
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Monday, March 17, 2008
End Uses
Chillers typically cool water, which is then circulated to provide comfort cooling throughout a building or other location. Chillers can be classified by compressor type, including centrifugal, reciprocating, scroll, screw, and rotary. SNAP has identified substitutes for CFC-11, CFC-12, CFC-113, CFC-114, R-13B1, HCFC-22, R-500 and other ODSs. Chillers used to cool industrial processes are discussed under Industrial process refrigeration systems.
Industrial process refrigeration systems cool process streams in industrial applications. The choice of substitute for specific applications depends on ambient and required operating temperatures and pressures. SNAP has identified substitutes for CFC-11, CFC-12, HCFC-22 and other ODSs.
Ice skating rinks frequently use secondary refrigeration loops. They are used by the general public for recreational purposes. SNAP has identified substitutes for CFC-12, HCFC-22, R-502 and other ODSs.
Industrial process air conditioning is distinct from commercial and residential air conditioning. It is often used when ambient temperatures near 200 degrees Fahrenheit (93 degrees Celsius) and corrosive conditions exist. Units in this end-use provide comfort cooling for operators and protect process equipment. SNAP has identified substitutes for CFC-12, CFC-114 and other ODSs.
Cold storage warehouses are used to store meat, produce, dairy products and other perishable goods. The majority of cold storage warehouses in the United States use ammonia as the refrigerant in a vapor compression cycle, although some rely on other refrigerants. SNAP has identified substitutes for CFC-12, HCFC-22, R-502, and other ODSs.
Refrigerated transport moves products from one place to another while maintaining necessary temperatures, and include refrigerated ship holds, truck trailers, railway freight cars, and other shipping containers. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Retail Food Refrigeration includes all cold storage cases designed to chill food for commercial sale. In addition to grocery cases, the end-use includes convenience store reach-in cases and restaurant walk-in refrigerators. Icemakers in these locations are discussed under commercial ice machines. SNAP has identified substitutes for CFC-12, HCFC-22, R-502 and other ODSs.
Vending machines are self-contained units which dispense goods that must be kept cold or frozen. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Water coolers are self-contained units providing chilled water for drinking. They may or may not feature detachable containers of water. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Commercial ice machines are used in commercial establishments to produce ice for consumer use, e.g., in hotels, restaurants, and convenience stores. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Household refrigerators and freezers are intended primarily for residential use, although they may be used outside the home. Household freezers only offer storage space at freezing temperatures, unlike household refrigerators. Products with both a refrigerator and freezer in a single unit are most common. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Residential dehumidifiers are primarily used to remove water vapor from ambient air for comfort or material preservation purposes. While air conditioning systems often combine cooling and dehumidification, this application serves only the latter purpose. SNAP has identified substitutes for CFC-12, HCFC-22 and other ODSs.
Motor vehicle air conditioning systems, or MVACS, provide comfort cooling for passengers in cars, buses, planes, trains, and other forms of transportation. MVACS pose risks related to widely varying ambient conditions, accidents, and the location of the evaporator inside the passenger compartment. Given the large number of cars in the nation's fleet, and the variety of designs, new substitutes must be used in accordance with established retrofit procedures. Flammability is a concern in all applications, but the conditions of use and the potential for accidents in this end-use increase the likelihood of a fire. In addition, the number of car owners who perform their own routine maintenance means that more people will be exposed to potential hazards. SNAP has identified substitutes for CFC-12 and HCFC-22.
Residential and light commercial air conditioning and heat pumps includes central air conditioners (unitary equipment), window air conditioners, and other products. HCFC-22, a class II substance, is the most common refrigerant for this application. SNAP has identified substitutes for HCFC-22 and other ODSs.
Heat transfer includes all cooling systems that rely on convection to remove heat from an area, rather than relying on mechanical refrigeration. There are, generally speaking, two types of systems: Systems with fluid pumps, referred to as recirculating coolers, and those that rely on natural convection currents, referred to as thermosiphons. SNAP has identified substitutes for CFC-11, CFC-12, CFC-113, CFC-114, CFC-115 and other ODSs.
Very Low Temperature Refrigeration systems require maintaining temperatures in the vicinity of -80 degrees F (-62 degrees C) or lower. Examples include medical freezers and freeze-dryers, which generally require extremely reliable refrigeration cycles to maintain low temperatures and must meet stringent technical standards that do not normally apply to refrigeration systems. SNAP has identified substitutes for CFC-13, R-13B1 (Halon 1301), R-503 and other ODSs.
Chillers typically cool water, which is then circulated to provide comfort cooling throughout a building or other location. Chillers can be classified by compressor type, including centrifugal, reciprocating, scroll, screw, and rotary. SNAP has identified substitutes for CFC-11, CFC-12, CFC-113, CFC-114, R-13B1, HCFC-22, R-500 and other ODSs. Chillers used to cool industrial processes are discussed under Industrial process refrigeration systems.
Industrial process refrigeration systems cool process streams in industrial applications. The choice of substitute for specific applications depends on ambient and required operating temperatures and pressures. SNAP has identified substitutes for CFC-11, CFC-12, HCFC-22 and other ODSs.
Ice skating rinks frequently use secondary refrigeration loops. They are used by the general public for recreational purposes. SNAP has identified substitutes for CFC-12, HCFC-22, R-502 and other ODSs.
Industrial process air conditioning is distinct from commercial and residential air conditioning. It is often used when ambient temperatures near 200 degrees Fahrenheit (93 degrees Celsius) and corrosive conditions exist. Units in this end-use provide comfort cooling for operators and protect process equipment. SNAP has identified substitutes for CFC-12, CFC-114 and other ODSs.
Cold storage warehouses are used to store meat, produce, dairy products and other perishable goods. The majority of cold storage warehouses in the United States use ammonia as the refrigerant in a vapor compression cycle, although some rely on other refrigerants. SNAP has identified substitutes for CFC-12, HCFC-22, R-502, and other ODSs.
Refrigerated transport moves products from one place to another while maintaining necessary temperatures, and include refrigerated ship holds, truck trailers, railway freight cars, and other shipping containers. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Retail Food Refrigeration includes all cold storage cases designed to chill food for commercial sale. In addition to grocery cases, the end-use includes convenience store reach-in cases and restaurant walk-in refrigerators. Icemakers in these locations are discussed under commercial ice machines. SNAP has identified substitutes for CFC-12, HCFC-22, R-502 and other ODSs.
Vending machines are self-contained units which dispense goods that must be kept cold or frozen. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Water coolers are self-contained units providing chilled water for drinking. They may or may not feature detachable containers of water. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Commercial ice machines are used in commercial establishments to produce ice for consumer use, e.g., in hotels, restaurants, and convenience stores. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Household refrigerators and freezers are intended primarily for residential use, although they may be used outside the home. Household freezers only offer storage space at freezing temperatures, unlike household refrigerators. Products with both a refrigerator and freezer in a single unit are most common. SNAP has identified substitutes for CFC-12, R-502 and other ODSs.
Residential dehumidifiers are primarily used to remove water vapor from ambient air for comfort or material preservation purposes. While air conditioning systems often combine cooling and dehumidification, this application serves only the latter purpose. SNAP has identified substitutes for CFC-12, HCFC-22 and other ODSs.
Motor vehicle air conditioning systems, or MVACS, provide comfort cooling for passengers in cars, buses, planes, trains, and other forms of transportation. MVACS pose risks related to widely varying ambient conditions, accidents, and the location of the evaporator inside the passenger compartment. Given the large number of cars in the nation's fleet, and the variety of designs, new substitutes must be used in accordance with established retrofit procedures. Flammability is a concern in all applications, but the conditions of use and the potential for accidents in this end-use increase the likelihood of a fire. In addition, the number of car owners who perform their own routine maintenance means that more people will be exposed to potential hazards. SNAP has identified substitutes for CFC-12 and HCFC-22.
Residential and light commercial air conditioning and heat pumps includes central air conditioners (unitary equipment), window air conditioners, and other products. HCFC-22, a class II substance, is the most common refrigerant for this application. SNAP has identified substitutes for HCFC-22 and other ODSs.
Heat transfer includes all cooling systems that rely on convection to remove heat from an area, rather than relying on mechanical refrigeration. There are, generally speaking, two types of systems: Systems with fluid pumps, referred to as recirculating coolers, and those that rely on natural convection currents, referred to as thermosiphons. SNAP has identified substitutes for CFC-11, CFC-12, CFC-113, CFC-114, CFC-115 and other ODSs.
Very Low Temperature Refrigeration systems require maintaining temperatures in the vicinity of -80 degrees F (-62 degrees C) or lower. Examples include medical freezers and freeze-dryers, which generally require extremely reliable refrigeration cycles to maintain low temperatures and must meet stringent technical standards that do not normally apply to refrigeration systems. SNAP has identified substitutes for CFC-13, R-13B1 (Halon 1301), R-503 and other ODSs.
Wednesday, March 5, 2008
Process applications aim to provide a suitable environment for a process being carried out, regardless of internal heat and humidity loads and external weather conditions. Although often in the comfort range, it is the needs of the process that determine conditions, not human preference. Process applications include these:
Hospital operating theatres, in which air is filtered to high levels to reduce infection risk and the humidity controlled to limit patient dehydration. Although temperatures are often in the comfort range, some specialist procedures such as open heart surgery require low temperatures (about 18 °C, 64 °F) and others such as neonatal relatively high temperatures (about 28 °C, 82 °F).
Cleanrooms for the production of integrated circuits, pharmaceuticals, and the like, in which very high levels of air cleanliness and control of temperature and humidity are required for the success of the process.
Facilities for breeding laboratory animals. Since many animals normally only reproduce in spring, holding them in rooms at which conditions mirror spring all year can cause them to reproduce year round.
Aircraft air conditioning. Although nominally aimed at providing comfort for passengers and cooling of equipment, aircraft air conditioning presents a special process because of the low air pressure outside the aircraft.
Data processing centers
Textile factories
Physical testing facilities
Plants and farm growing areas
Nuclear facilities
Chemical and biological laboratories
Mines
Industrial environments
Food cooking and processing areas
In both comfort and process applications the objective may be to not only control temperature, but also humidity, air quality, air motion, and air movement from space to space
Hospital operating theatres, in which air is filtered to high levels to reduce infection risk and the humidity controlled to limit patient dehydration. Although temperatures are often in the comfort range, some specialist procedures such as open heart surgery require low temperatures (about 18 °C, 64 °F) and others such as neonatal relatively high temperatures (about 28 °C, 82 °F).
Cleanrooms for the production of integrated circuits, pharmaceuticals, and the like, in which very high levels of air cleanliness and control of temperature and humidity are required for the success of the process.
Facilities for breeding laboratory animals. Since many animals normally only reproduce in spring, holding them in rooms at which conditions mirror spring all year can cause them to reproduce year round.
Aircraft air conditioning. Although nominally aimed at providing comfort for passengers and cooling of equipment, aircraft air conditioning presents a special process because of the low air pressure outside the aircraft.
Data processing centers
Textile factories
Physical testing facilities
Plants and farm growing areas
Nuclear facilities
Chemical and biological laboratories
Mines
Industrial environments
Food cooking and processing areas
In both comfort and process applications the objective may be to not only control temperature, but also humidity, air quality, air motion, and air movement from space to space
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