A chiller is a machine that removes heat from a liquid through a vapor compression cycle or absorption. This liquid can then be circulated through a heat exchanger to cool the equipment, or other process streams (such as air or process water). As a necessary product, cooling creates waste heat that must be discharged into the atmosphere, or for greater efficiency, restored for heating purposes.
Cold water is used to cool and remove air humidity in medium to large commercial, industrial and institutional facilities. The water cooler can be cooled with water, air-cooled, or cooled evaporatively. Water-cooled systems can provide the efficiency and benefits of environmental impacts through air-cooled systems.
Video Chiller
Use in the air conditioner
In air conditioning systems, cold water is usually distributed to heat exchangers, or coils , in air handlers or other types of terminal devices that cool air in their respective spaces. The water is then circulated back to the chiller for cooling again. This cooling coil transfers the sensible heat and latent heat from air to cold water, thereby cooling and usually moisturizing airflow. A typical chiller for air conditioning applications is rated between 15 and 2000 tons, and at least one producer can produce a coolant capable of reaching 5,200 tons of cooling. Cold water temperatures can range from 35 to 45 Â ° F (2 to 7 Â ° C), depending on the application requirements.
When refrigerators for air conditioning systems can not be operated or they require repair or replacement, emergency cooling can be used to supply cold water. Hired coolers are installed in trailers so they can be quickly placed to the site. A large cold water hose is used to connect between rental cooling systems and air conditioning systems.
Maps Chiller
Use in industry
In industrial applications, cold water or other liquids from the chiller are pumped through laboratory processes or equipment. Industrial refrigerants are used for product cooling, mechanisms and factory machineries that are controlled in various industries. They are often used in plastics industry, injection and blow molding, metal cutting work oil, welding equipment, die-casting and machine tooling, chemical processing, pharmaceutical formulation, food and beverage processing, paper and cement processing, vacuum system, X- , power supplies and power stations, analytical equipment, semiconductors, air conditioning and compressed gas. They are also used to cool very hot special items like MRI and laser machines, and in hospitals, hotels and campuses.
Coolers for industrial applications can be centered, where a single chiller serves some cooling, or decentralized needs in which each app or machine has its own chiller. Each approach has its advantages. It is also possible to have a combination of centralized and decentralized cooling, especially if the cooling requirements are the same for some applications or point of use, but not all.
Decentralized chillers are typically small in size and cooling capacity, typically from 0.2 to 10 short tons (0.179 to 8.929 ton lengths; 0.181 to 9.072 t). Centralized chillers generally have capacities ranging from ten tons to hundreds or thousands of tons.
Cold water is used to cool and remove air humidity in medium to large commercial, industrial, and institutional facilities (CII). The water cooler can be cooled with water, air-cooled, or cooled evaporatively. Air-cooled chillers combine the use of cooling towers that enhance the thermodynamic effectiveness of refrigerants compared to air-cooled coolers. This is caused by the rejection of heat at or near the temperature of the air bulb bulb than the higher dry bulb temperature, sometimes much higher. Evaporatively cooled coolers offer higher efficiency than air-cooled coolers but lower than water-cooled coolers.
Air-cooled chillers are usually intended for indoor installation and operation, and cooled by a separate condenser water loop and connected to an outdoor cooling tower to dissipate heat into the atmosphere.
Water cooled and evaporatively cooled chillers are intended for outdoor installation and operation. Air-cooled engines are directly cooled by ambient air which is mechanically circulated directly through the engine condenser coil to release heat to the atmosphere. Machines that are cooled evaporatively are similar, unless they implement a water mist over the condenser coil to assist in cooling the condenser, making the engine more efficient than traditional air-cooled engines. No remote cooling tower required with either air cooled or evaporatively cooled chillers.
If available, cold water is available in nearby water bodies can be used directly to cool, replace or add cooling towers. The deep water source cooling system in Toronto, Ontario, Canada, is an example. It uses cold lake water to cool the coolant, which in turn is used to cool city buildings through the district cooling system. Water is again used to warm the city's potable water supply, desired in this cold climate. Each time the refrigerant heat rejection can be used for productive purposes, in addition to the cooling function, very high thermal effectiveness is possible.
Steam compression chiller technology
There are four basic types of compressors used in vapor compression refrigeration: Reciprocating compression, scroll compression, screw-driven compression, and centrifugal compression are all mechanical engines that can be powered by electric motors, steam, or gas turbines. They produce their cooling effects through reverse-Rankine cycles, also known as vapor compression. With evaporative cooling heat rejection, their performance coefficients (COPs) are very high; usually 4.0 or more.
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- COP
The current vapor compression chiller technology is based on the "reverse-rankine" cycle known as vapor compression. See the attached diagram that outlines the main components of the chiller system.
Main components of chiller:
The coolant compressor is basically a pump for cooling gas. The capacity of the compressor, and hence the chiller cooling capacity, is measured in kilowatt input (kW), horsepower input (HP), or volumetric flow (m 3 /h, ft 3 /h). The mechanism for compressing refrigerant gas varies between compressors, and each has its own application. Common cooling compressors include reciprocating, scroll, screws, or centrifuges. This can be powered by an electric motor, a steam turbine, or a gas turbine. The compressor can have an integrated motor from a particular manufacturer, or an open drive - allowing connections to other types of mechanical connections. Compressors can also be Hermetic (welded closed) or semihermetik (bolted together).
In recent years, the application of variable-speed drive (VSD) technology has increased the efficiency of chillers vapor compression. The first VSD was applied to centrifugal compressor coolers in the late 1970s and has become the norm as energy costs have increased. Now, VSD is being applied to rotary screw and scroll technology compressor.
The condenser can be cooled with air, water-cooled, or evaporated. The condenser is a heat exchanger that allows heat to migrate from cooling gas to water or air. Air cooled condenser is made from copper tube (for refrigerant flow) and aluminum fins (for airflow). Each condenser has a different material cost and they vary in efficiency. With evaporative cooling condensers, their performance coefficients (COPs) are very high; usually 4.0 or more.
Expansion devices or refrigeration meter devices (RMD) restrict the flow of liquid refrigerant which causes a decrease in pressure that partially evaporates the refrigerant; This evaporation absorbs heat from nearby liquid refrigerant. The RMD is located just before the evaporator so that the cold gas in the evaporator can absorb heat from the water in the evaporator. There is a sensor for RMD at the evaporator outlet side that allows RMD to adjust the refrigerant flow based on chiller design requirements.
Evaporator can be either plate or shell type and tube type. Evaporator is a heat exchanger that allows heat energy to migrate from the water stream into the refrigerant gas. During the change of the remaining liquid state into gas, the refrigerant can absorb large amounts of heat without changing the temperature.
How absorption technology works
The thermodynamic cycle of the absorption chiller is driven by a heat source; This heat is usually sent to the chiller through steam, hot water, or burning. Compared to electric-powered chillers, recharge chillers have very low electrical power requirements - very rarely above the combined consumption of 15 kW for both solution pumps and refrigerant pumps. However, the heat input requirement is large, and its COP is often 0.5 (single effect) to 1.0 (double effect). For the same tonnage capacity, the absorption chiller requires a much larger cooling tower than a steam compression chiller. However, the absorption of chillers, from an energy efficiency standpoint, excels where cheap, low-grade heat or waste heat is readily available. In a very sunny climate, solar energy has been used to operate chillers absorption.
A single effect absorption cycle uses water as a refrigerant and lithium bromide as an absorbent. It is a strong affinity that these two substances have one another that makes the cycle work. The whole process takes place in a vacuous hollow. Industrial chiller technology
Industrial coolers usually come complete, packaged, closed-loop systems, including chiller units, condensers, and pumping stations with recirculation pumps, expansion valves, non-existent flow stops, internal cold water controls. The internal tank helps keep the water temperature cool and prevents the temperature spikes from occurring. The closed-loop industry refrigerant circulates clean or clean cooling fluids with additive conditions at constant temperature and pressure to improve the stability and reproducibility of water-cooled engines and instruments. Water flows from the chiller to the point of application usage and returns.
If the water temperature difference between the inlet and outlet is high, then a large external water tank will be used to store cold water. In this case the cold water is not directly from the chiller to the application, but goes to an external water tank that acts as a kind of "buffer temperature." The cold water tank is much larger than the internal water that flows from the external tank to the application and the hot water returns from the application back to the external tank, not to the chiller.
The less common open-loop industrial coolant controls the temperature of the liquid in an open tank or container by constantly recirculating it. The liquid is taken from the tank, pumped through the chiller and returned to the tank. In the cooling water industry is the use of water cooling rather than air cooling. In this case the condenser does not cool the hot refrigerant with ambient air, but uses water cooled by the cooling tower. This development allows the reduction of energy requirements by more than 15% and also enables significant reduction in chiller size, due to the small surface area of ​​the water-based condenser and the absence of fan. In addition, the lack of fan allows a significant reduction in noise levels.
Most industrial coolants use cooling as a medium for cooling, but partly depends on more simple techniques such as air or water flowing over a coil containing coolants to regulate the temperature. Water is the most common coolant used in chillers, although a cooling mixture (mostly water with a cooling additive to increase heat dissipation) is often used.
Selection of industrial chiller
Important specifications to consider when looking for a cooler for the kumond industry include total lifecycle costs, resources, IP chiller rating, chiller cooling capacity, evaporator capacity, evaporator materials, evaporator type, condenser material, condenser capacity, ambient temperature, motor fan type, , internal pipe material, number of compressors, type of compressor, number of refrigerator circuits, cooling requirements, liquid discharge temperature, and COP (ratio between cooling capacity in RT and energy consumed by all chillers in KW). For medium to large chillers this should range from 3.5 to 7.0, with higher values ​​means higher efficiency. Chiller efficiency is often determined in kilowatts per refrigeration ton (kW/RT).
Key pump specifications to be considered include process flow, process pressure, pump material, elastomers and mechanical shaft seal materials, motor voltages, motor power classes, IP motor ratings and pump ratings. If the cold water temperature is lower than -5 Â ° C, then a special pump should be used to pump high concentrations of ethylene glycol. Other important specifications include the size of the internal water tank and the material and full load current.
Control panel features to consider when choosing between industrial cooling include local control panel, remote control panel, fault indicator, temperature indicator, and pressure indicator.
Additional features include emergency alarm, hot gas bypass, city water transfers, and casters.
The removable coolant is also an option for dispersal in remote areas and where conditions may be hot and dusty.
Refrigerant
A vapor compression chiller uses refrigerant internally as its working fluid. Many refrigerant options are available; when choosing a chiller, application cooling temperature requirements and cooling coolant characteristics must be matched. Important parameters to consider are temperature and operating pressure.
There are several environmental factors concerning refrigerants, and also affect future availability for chiller applications. This is a major consideration in intermittent applications where a large chiller can last for 25 years or more. Potential ozone depletion (ODP) and global warming potential (GWP) of refrigerants need to be considered. ODP and GWP data for some of the more common vapor compression refrigerants (noting that many of these refrigerants are highly flammable and/or toxic):
R12 is an ODP reference. CO 2 is a GWP reference
Refrigerants used in chillers are sold in Europe especially R410a (70%), R407c (20%) and R134a (10%).
See also
References
External links
- Basic Chiller Glossary
- Chiller Energy Consumption Calculator (requires Java)
Source of the article : Wikipedia
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