英文
How Air Conditioners Work and energy conservation technology research
Abstract: An air conditioner is basically a refrigerator without the insulated box. It uses the evaporation of a refrigerant, like Freon, to provide cooling. The mechanics of the Freon evaporation cycle are the same in a refrigerator as in an air conditioner.
Keywords: water towers 、weather-resistant、 compressor、energy conservation
When the temperature outside begins to climb, many people seek the cool comfort of indoor air conditioning. Like water towers and power lines, air conditioners are one of those things that we see every day but seldom pay much attention to. Wouldn't it be nice to know how these indispensable machines work their magic? In this article, we will examine air conditioners -- from small to huge -- so you know more about what you're seeing!
The Many Faces of Cool
Air conditioners come in various sizes, cooling capacities and prices. One type that we see all the time is the window air conditioner.
Window air conditioners are an easy and economical way to cool a small area. Most people who live in suburban areas usually have one of these in their backyard:
If you live in an apartment complex, this is probably a familiar sight: Most businesses and office buildings have condensing units on their roofs, and as you fly into any airport you notice that warehouses and malls may have 10 or 20 condensing units hidden on their roofs:
And then if you go around back at many hospitals, universities and office complexes, you find large cooling towers that are connected to the air conditioning system:
Even though each of these machines has a pretty distinct look, they all work on the same principles. Let's take a closer look.
The Basic Idea
An air conditioner is basically a refrigerator without the insulated box. It uses the evaporation of a refrigerant, like Freon, to provide cooling. The mechanics of the Freon evaporation cycle are the same in a refrigerator as in an air conditioner. According to the Merriam-Webster Dictionary Online, the term Freon is generically "used for any of various conditioner. According to the Merriam-Webster Dictionary Online, the term Freon is generically "used for any of various nonflammable fluorocarbons used as refrigerants and as propellants for aerosols."
This is how the evaporation cycle in an air conditioner works (See How Refrigerators Work for complete details on this cycle):
1.The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas (red in the diagram above).
2.This hot gas runs through a set of coils so it can dissipate its heat, and it condenses into a liquid.
3.The Freon liquid runs through an expansion valve, and in the process it evaporates to become cold, low-pressure Freon gas (light blue in the diagram above).
4.This cold gas runs through a set of coils that allow the gas to absorb heat and cool down the air inside the building.
Mixed in with the Freon is a small amount of a light weight oil. This oil lubricates the compressor.
Window Units
A window air conditioner unit implements a complete air conditioner in a small space. The units are made small enough to fit into a standard window frame. You close the window down on the unit, plug the unit in and turn it on to get cool air. If you take the cover off of an unplugged window unit, you will find that it contains:
A compressor
An expansion valve
A hot coil (on the outside)
A chilled coil (on the inside)
A control unit
The fans blow air over the coils to improve their ability to dissipate heat (to the outside air) and cold (to the room being cooled).
BTU and EER
Most air conditioners have their capacity rated in British thermal units (BTU). Generally speaking, a BTU is the amount of heat required to raise the temperature of one pound (0.45 kg) of water 1 degree Fahrenheit (0.56 degrees Celsius). Specifically, 1 BTU equals 1,055 joules. In heating and cooling terms, 1 "ton" equals 12,000 BTU.
A typical window air conditioner might be rated at 10,000 BTU. For comparison, a typical 2,000-square-foot (185.8 m2) house might have a 5-ton (60,000-BTU) air conditioning system, implying that you might need perhaps 30 BTU per square foot. (Keep in mind that these are rough estimates. To size an air conditioner for your specific needs, contact an HVAC contractor.)
The energy efficiency rating (EER) of an air conditioner is its BTU rating over its wattage. For example, if a 10,000-BTU air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 BTU/1,200 watts). Obviously, you would like the EER to be as high as possible, but normally a higher EER is accompanied by a higher price.
Is the higher EER is worth it?
Let's say that you have a choice between two 10,000-BTU units. One has an EER of 8.3 and consumes 1,200 watts, and the other has an EER of 10 and consumes 1,000 watts. Let's also say that the price difference is $100. To understand what the payback period is on the more expensive unit, you need to know:
1.Approximately how many hours per year you will be operating the unit
2.How much a kilowatt-hour (kWh) costs in your area
Let's say that you plan to use the air conditioner in the summer (four months a year) and it will be operating about six hours a day. Let's also imagine that the cost in your area is $0.10/kWh. The difference in energy consumption between the two units is 200 watts, which means that every five hours the less expensive unit will consume 1 additional kWh (and therefore $0.10 more) than the more expensive unit.
Assuming that there are 30 days in a month, you find that during the summer you are operating the air conditioner:
Since the more expensive unit costs $100 more that means that it will take about seven years for the more expensive unit to break even.
See this page for a great explanation of seasonal energy efficiency rating (SEER).
Split-system Units
A split-system air conditioner splits the hot side from the cold side of the system。
The cold side, consisting of the expansion valve and the cold coil, is generally placed into a furnace or some other air handler. The air handler blows air through ducts. The hot side known as the condensing unit, lives outside the building. The unit consists of a long, spiral coil shaped like a cylinder. Inside the coil is a fan, to blow air through the coil, along with a weather-resistant compressor and some control logic. This approach has evolved over the years because it is low-cost, and also because it normally results in reduced noise inside the house (at the expense of increased noise outside the house). Besides the fact that the hot and cold sides are split apart and the capacity is higher (making the coils and compressor larger), there is no difference between a split-system and a window air conditioner.
In warehouses, businesses, malls, large department stores, etc., the condensing unit normally lives on the roof and can be quite massive. Alternatively, there may be many smaller units on the roof, each attached inside to a small air handler that cools a specific zone in the building.
Let's take a look now at a chilled-water air conditioner.
Chilled-water System
In larger buildings and particularly in multi-story buildings, the split-system approach begins to run into problems. Either running the pipe between the condenser and the air handler exceeds distance limitations (runs that are too long start to cause lubrication difficulties in the compressor), or the amount of duct -work and the length of ducts become unmanageable. At this point, it is time to think about a chilled-water system.
In a chilled-water system, the entire air conditioner lives on the roof or behind the building. It cools water to between 40 and 45 F (4.4 and 7.2 C). This chilled water is then piped throughout the building and connected to air handlers as needed. There is no practical limit to the length of a chilled-water pipe if the system can be got well - insulated.
Whenever you walk behind a building and find a unit that has large quantities of water running through a plastic mesh, you will know you have found a cooling tower!
In many office complexes and college campuses, cooling towers and air conditioning equipment are centralized, and chilled water is routed to all of the buildings through miles of underground pipes.
Based on dynamic load track central air-conditioning system entire closed loop energy conservation technology research.
1. introductions
The energy conservation may say is the building character automatic control system starting point and the home to return to. It is well known, in the intelligent construction, HVAC (heating, ventilates and air conditioning) the system consumes to have to occupy the building consumption total energy enormous partial proportions, approximately about 50% ~60%. Specially cold: East the unit, the cooling tower, the circulating water pump and the air conditioning unit, the new atmosphere unit, all are consumes energy the big household. Therefore really has essential develops one effective air-conditioning system energy conservation method, especially uses is in improves in the existing building air-conditioning system automation the aspect. DDC (Directdigitalcontr01) the direct of numerical control, is a structure simple operation easy control device, it may borrow by the connection switches over the equipment to make the systems control along with the load change, like the air conditioning cold water circulatory system, the air conditioning box frequency conversion automatic amount of wind adjustment and the cooling tower radiation ventilator frequency conversion holds controls and so on, may let an air-conditioning system more effective revolution, like this, not only brings the very big economic efficiency for the estate management, moreover also may cause the system to move under a better operating mode, thus lengthens the equipment the service life as well as achieved provides goal of the comfortable air conditioning environment and the energy conservation.
The general building commonly used air-conditioning system has CAV, VAV, VWV and so on, respectively has differently holds controls the way, all may use DDC to control.
1 decides the amount of wind system (ConstantAirVolume, is called CAV).
Decides certainly the amount of wind system the amount of wind which blows out for the air conditioner certainly, provides coldly (is warm) the gas which the air conditioning region needs. When air conditioning region load variation, then changes the blast temperature to deal with in the room to shoulder, and achieves the maintenance indoor temperature to the comfortable area request. The commonly used central air-conditioning system is AHU (air conditioner) and the cooling water pipe system (the FCU system). These two generally decides the amount of wind (CAV) to supply the air conditioning area, in order to deal with in the room the partial loads change, decides the amount of wind system in AHU to change warm by the air conditioner blows of processes, controls in the general FCU system by cold water valve ON/OFF adjusts the blast temperature.
2 changes the amount of wind system (VAV)
Changes the amount of wind system (VarlableAirVolume, is called VAV) is the air conditioner (AHU or FCU) may move changes the amount of wind. The commonly used central air-conditioning system is AHU (air conditioner) and the cooling water pipe system FCU system. These two generally decides the amount of wind (CAV) to supply the air conditioning area, in order to deal with in the room the partial loads change, decides the amount of wind system in AHU to change warm by the air conditioner blows of processes, controls in the general FCU system by cold water valve ON/OFF adjusts the blast temperature. However these two has wasted the massive energys on the blast system. Because in long-term low load time the air feeder also carries out the entire amount of wind revolution to consume the electricity, this not only is not easy to maintain in the stable room humidity the condition, also wastes the massive blasts revolution energy. Changes the amount of wind system is aims at the blast system to consume the electricity shortcoming the energy conservation countermeasure. Changes the amount of wind system to be possible to divide into two kinds: One kind is in the AHU wind tube system air conditioning adaptable amount of wind system (AHU □the VAV system); One kind is in the FCU system room wind adaptable amount of wind system (the FCU-VAV system). The AHU-VAV system will be blows of in the entire wind tube system the temperature to be fixed, but adjusts the air feeder to deliver the amount of wind the way to deal with in the room the air conditioning load change. The FCU-VAV system is fixed cold water supplyment , but FCU installs in the room does not have the section to change the power controller to change delivers the amount of wind, that is changes FCU the heat change rate to adjust in the room the load variation. These two ways penetration amount of wind adjustment reduces the air feeder the power consumption, simultaneously also may increase the heat source machine the operating efficiency to save the heat source to consume the electricity, therefore may simultaneously obtains the energy conservation effect in the blast and the heat source two aspects.
3 changes the current capacity system (VWV)
So-called changes the current capacity system (VariableWaterVolume, is called VWV), is enhances the heat source machine by the certain water temperature supply air conditioner the efficiency, but changes by the special water pump delivers the water volume, while convenient achieves saves the effect which the water pump uses electricity. Changes the water volume system to depend on the water pump to the water pump system energy conservation efficiency the control mode and the VWV use proportion but different, whether there is the general VWV control mode section speed change (SP) and the bidirectional valve control mode. Above three kind of air-conditioning system is the present building air conditioning most often the system which designs. The central air conditioning control also is the pipeline, the fitting, the valve body or the valve centralism hypothesis control fluid provides the air conditioning. Therefore effectively combines the central air conditioning control namely to be able the active control to consume energy, the design conforms with the energy conservation the air-conditioning system.
In recent years, the our country majority of areas, in particular southeast the coastal area summer the air conditioning energy consumption suddenly was rising, the air conditioning uses electricity the tendency which increases sharply to cause the electrical network power supply to be intense. Statistics have indicated, our country every year the burning hot season air conditioning consumed the electricity to occupy 1/3 in recent years which the entire society uses electricity, the massive electrical energies swallow by the industry and the civil construction air conditioning, in particular large-scale construction central air-conditioning system, like each kind of commercial construction (office, market, hospital, hotel and so on) central air conditioning because its space big, person current capacity many, operation time long, management complex characteristic, causes the movement energy consumption to be quite high, the commercial construction air conditioning energy consumption nearly occupies its total energy consumption 50%. The central air conditioning design capacity is according to the biggest load computation, but in a major part building year only has several dozens days time central air conditioning to be at the biggest load condition. The central air conditioning cold load throughout is in during the dynamic change, like every day sooner or later, each season in turn, every year samsara, the environment and the humanities condition, real-time will be affecting the central air conditioning cold load. General, the cold load undulates in 5 ~ 60% scope, the majority building every year at least 70% is in this kind of situation. But the majority central air conditioning actually opening machine capacity far is smaller than the installed capacity, if take the most greatly cold load as the maximum work rate actuation, creates between the actual need cold load and the maximum work rate output contradiction, actually creates the huge energy waste, the national economy and the society develops for brings the very tremendous influence. This has brought the stern topic for the central air conditioning energy conservation control, also gives the general energy conservation control domain the worker brought enormously has displayed the talent the space.
The power load gap increases, the electric power supply tense aspect with difficulty obtains in recent years relaxes. Therefore, energy conservation in particular electricity saving, not only has the significant social significance moreover to have the urgent practical significance. Positively studies the development promotion green environmental protection new air conditioning technology and the equipment, the suppression air conditioning energy consumption increases, has become the building warmly to pass air conditioning domain urgent and the popular research topic. The dependence technology innovation, the system innovation, the energy conservation falls consumes, enhances the energy use efficiency, guaranteed are least in the "energy consumption, in the environmental pollution smallest" foundation, realizes the "energy conservation first, structure many Yuan, environment friendly" energy developmental strategy.
In our telecommunication production, air conditioning energy conservation supervisory work weaker, the energy waste phenomenon is serious, therefore strengthens air conditioning the maintenance management and the technological transformations, may achieve the energy conservation the goal.
Looked from the air conditioning pressure enthalpy chart that, only has the movement in the best operating mode and the condition, can display air conditioning the biggest refrigeration quantity, achieves the air conditioning energy conservation the goal. If the inflation valve oil stops up seriously, carries on the clean using the absolute ethyl alcohol, again severely newly installs; Loses the adjustment function the expansion valve to be supposed to replace. The air conditioning energy conservation, our maintenance department should from the movement cost, the maintenance maintenance aspect angle carry on the consideration.
2. air conditioning energy conservation system research survey
1) through the load control, achieves the energy conservation goal. (a) The burning hot season new atmosphere load occupies the entire cold load 25-40%, reduces the new atmosphere load, reduces the new atmosphere energy consumption, the choice smallest essential new amount of wind, also can achieve the goal. But the new amount of wind smallest supply on the one hand the country had the standard, moreover the new amount of wind insufficient will affect the air quality, will endanger the human body health. (b) Outside the optimized construction the surrounding protection structure energy conservation design, uses the heat preservation thermal insulation material technology, reduces the air conditioning load, the realization construction energy conservation, but simultaneously also causes the building cost rise, the promotion to receive the certain limit.
2) gathers can the air conditioning. Gathers coldly through the ice, avoids the daytime to use electricity the peak, at night stores up the air conditioning freezing water refrigeration, daytime does not start the air conditioning main engine only to use the aqueous system to circulate. This method itself certainly does not conserve energy the province electricity, but optimized the electrical network power supply, to already implemented the time sharing electrovalence the area, played "to economize does not conserve energy" the role, had the area promotion significance.
3) water source heat pump. Is opposite says to the air and the soil, the water is the most ideal spatial transfer cold heat source, the water source heat pump also therefore has the environmental protection, is highly effective, the energy conservation and so on the multitudinous merit, but our country water source heat pump engineering research is not very mature, compares with some developed countries also has the certain disparity. At the same time, the water source heat pump although has very many merits, but receives the geology, the environment, the policy and so on the limit quite is also big, this caused the water source heat pump to be restricted in an our country more widespread application.
4) in the central air-conditioning system individually consumes energy the equipment energy conservation transformation. (a) Air blower and water pump general frequency changer velocity modulation energy conservation, this is at present uses more technologies. This method simple practical, electricity saving effect obvious, but product and so on water pump, air blower is the system auxiliary engine partially, occupies the overall system energy consumption approximately is 40%, therefore the excavation space is limited. (b) The refrigeration main engine, the refrigeration unit's power consumption holds the very big share in the air-conditioning system, saves this part of consuming energy is the entire air-conditioning system economy movement key. At present generally all uses reduces the indoor temperature standard, enhances the cold water temperature and so on the measure realization refrigeration main engine energy conservation.
Above several methods deficiency has only considered the partial energy conservation, but had not considered from the overall system overall situation.
5) the dynamic load track energy conservation control system take the entire central air-conditioning system as a body, unceasingly changes the condition according to the air conditioning area load, through changes in the main engine and the circulatory system various parameters movement change situation, the lock following load change, realizes in meets the load need under the premise the prompt quota supplies cold quantity, namely achieves "according to must supply", basically achieved "does not lag, are not many for, many gives" the goal. This method not only compared with the permanent current capacity water pump gentle breeze machine has realized the auxiliary engine largest scale energy conservation, moreover optimized the main engine movement operating mode, might achieve the overall system conserved energy 15-35%. This is this topic research key point.
3. dynamic loads tracks energy conservation control plan
The traditional central air-conditioning system adjustment plan is: Uses the permanent current capacity pattern or the heat sink side permanent current capacity but the load side changes the current capacity pattern, the system must shoulder is according to the biggest load, the worst meteorological condition and the worst use working conditions designs, when actual moves 50% above time, the system must shoulder all below 50%, the existence has the enormous energy dissipation. Also when shoulders Q when the change, the traditional system movement parameter simply cannot achieve the synchronized adjustment, the lag adjustment method besides passively increase the unloading through the main engine, nearly no other controls method.
This research topic will abandon the former control plan, will recognize, the servo-control system theory, the intelligence control system theory take the model as the foundation, will unify with the central air conditioning main engine refrigeration technology and the cold intermediary circulatory system control, take the frequency conversion technology as the assistance method, the realization central air conditioning entire system whole coordination movement and the overall performance optimization. This research is the air conditioning energy conservation new idea, has represented the energy conservation technology recent development tendency.
1) circulatory system energy conservation: By the system angle, through to the terminal load parameter, the central air conditioning main engine, the auxiliary engine movement operating mode change, the gathering temperature, the pressure and so on the many kinds of coefficient of variation, then through the load move computation, the change system freezing water current capacity, the cooling water current capacity and the cooling tower air blower amount of wind adapts the air conditioning load change, simultaneously causes the main engine movement operating mode throughout to be in optimized in the best operating point. Generally when full load pumping machine needs the full speed movement, has not conserved energy the space, but uses the redundant technology and the frequency conversion technology unifies, the proportioning pump and the variable displacement pump coordinate,it is the truths.To freezes the aqueous system to use the best output energy control. When the ambient temperature, the air conditioning terminal load changes, Optimized the main engine movement pattern each group freezing water for the backwater temperature, the temperature difference, the differential pressure and the current capacity also along with it change, these parameters which the flowmeter, the differential-pressure pickup and the temperature sensor examines delivers to the intelligent controller, the real-time data and the system historyperformance data which the controller basis gathers, the real-time idea figures out the refrigeration quantity which the terminal air conditioning load needs, as well as each group freezing water for the backwater temperature, the temperature difference, the differential pressure and the current capacity best value, and to this adjusts various frequency changers output frequency, the control freezes the water pump the rotational speed, Changes its current capacity to cause the freezing aqueous system for the backwater temperature, the temperature difference, the differential pressure and the current capacity movement the optimum value which produces in the controller.Because the freezing aqueous system has used the output energy dynamic control, the realization air conditioning host frozen intermediary current capacity follows the terminal load the demand supply, causes the air-conditioning system in each kind of load situation, all can both guarantee terminal user's comfortableness, and maximum limit has saved the system energy consumption.The cooling water system uses the best hot transfer efficiency control. The cooling water and the cooling tower air blower system uses the best transfer efficiency control. When the ambient temperature, the air conditioning terminal load changes, central air conditioning main engine load factor along with it change, main engine condenser best hot transformation temperature also along with it change. The intelligent controller basis gathers the real-time data and the system history performance data, calculates the main engine condenser the best hot transformation temperature (inflection point temperature) and the cooling water is best, the inlet temperature, and by this adjustment cooling water pump and the cooling tower air blower frequency changer output frequency, the control cooling water pump and the cooling tower air blower rotational speed, the dynamic adjustment cooling water current capacity and the cooling tower air blower amount of wind, causes the cooling water to enter, the outlet temperature approaches the optimum value which the intelligent controller produces, thus guaranteed the central air conditioning main engine is at under the best transfer efficiency condition to move as necessary.
Because the cooling water system uses the best transfer efficiency control, had guaranteed the central air conditioning main engine in the full load and in the partial load situation, is at the best active status, throughout maintains the best energy use factor (namely the COP value), thus reduced the air conditioning main engine energy consumption, simultaneously because the cooling water pump and the cooling tower air blower frequently in are lower than under the fixed load to move, also maximum limit saved the cooling water pump and the cooling tower air blower energy consumption.
2) auxiliary engine energy conservation: Each kind pumps the kind (freezing to pump, cold water pump, air blower and so on) the movement energy conservation. Uses has the space vector control the frequency conversion velocity modulation way, changes the proportioning pump the variable displacement pump. Auxiliary engine energy conservation many to 40%
3) optimizes the auxiliary engine movement pattern: Generally when full load pumping machine needs the full speed movement, has not conserved energy the space, but uses the redundant technology and the frequency conversion technology unifies, the proportioning pump and the variable displacement pump coordinate, the optimized movement pattern, may cause the auxiliary engine unit to synthesize the energy conservation.
4) multi- parameters non-linearity control: This system for multi- parameters, when changes, the nonlinear system, take the computer as the control method, designs a set to have from seeks the stable security control system which the superior auto-adapted intelligent control, the function consummates
This central air conditioning dynamic load track energy conservation control system, with the central air-conditioning system necessary use, may realize the central air-conditioning system highly effective energy conservation, the effect is remarkable. After the theoretical calculation, compares with the permanent current capacity central air-conditioning system, whole year the average electricity saving rate may reach 20%-30%. This project technology content is high, is the collection warmly passes the air conditioning technology, the refrigeration technology, the intelligent control theory and the computer control technology is a body central air conditioning highly effective energy conservation system.
4. systems characteristics
1) entire closed loop: The central air conditioning main engine, the auxiliary engine, the circulatory system and so on took the whole constitution energy conservation control system, seeks one kind of best control rule, causes the central air conditioning main engine, the cold intermediary current capacity system all along with to shoulder Q the change to change, is for the purpose of satisfying the air conditioning area comfortableness to have to shoulder under the Q premise, realization overall system greatest degree energy conservation.
2) moves stably, safe: Optimized the main engine movement pattern, may solve the main engine to open stops the question, reduces the surge current, reduces the electrical network demand capacity; Uses softly opens stops with the low frequency movement water pump, the air blower, avoids opening stops attacks the electrical network and reduces the equipment machinery to wear, lengthens the useful life of equipment.
3) long-distance control: Through long-distance communication connection and computer connection, realization long-distance control, running status visible.
4) system adaptability strong: This electricity saving system may with the new clothing central air-conditioning system or with the old attire central air-conditioning system necessary use, does not change the original system the installment, the system connection is simple, the electricity saving system increase and the unloading cuts conveniently, does not have the impact. This system area is small, the overall system movement does not need to nurse, the low noise, not to have the unusual smell; Conserves energy, the environmental protection high is good; Does not produce the deleterious substance, not good has not affected to the environment.
5) forecasts equipment system invests the market, if every year has will surpass 200 sets of products completely to install is bigger than 50,000 m2 in the floor space in the commercial construction central air conditioning engine room, it saves the electric quantity to be equal to every year newly built 50,000 kW power plant, descrease the peak will use electricity to the summer electrical network also plays certainly alleviates the role, truly will realize the society sustainable coordinated development.
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