空调专业毕业设计英文论文翻译

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冷水机组毕业设计外文翻译

英文翻译Chilled Water Systems[1]Chilled water systems were used in less than 4% of commercial buildings in the U.S. in 1995. However, because chillers are usually installed in larger buildings, chillers cooled over 28% of the U.S. commercial building floor space that same year (DOE, 1998). Five types of chillers are commonly applied to commercial buildings: reciprocating, screw, scroll, centrifugal, and absorption. The first four utilize the vapor compression cycle to produce chilled water. They differ primarily in the type of compressor used. Absorption chillers utilize thermal energy (typically steam or combustion source) in an absorption cycle with either an ammonia-water or water-lithium bromide solution to produce chilled water.Overall SystemFigure 4.2.2 shows a simple representation of a dual chiller application with all the major auxiliary equipment. An estimated 86% of chillers are applied in multiple chiller arrangements like that shown in the figure (Bitondo and Tozzi, 1999). In chilled water systems, return water from the building is circulated through each chiller evaporator where it is cooled to an acceptable temperature (typically 4 to 7°C) (39 to 45°F). The chilled water is then distributed to water-to-air heat exchangers spread throughout the facility. In these heat exchangers, air is cooled and dehumidified by the cold water. During the process, the chilled water increases in temperature and must be returned to the chiller(s).The chillers shown in Figure 4.2.2 are water-cooled chillers. Water is circulated through the condenser of each chiller where it absorbs heat energy rejected from the high pressure refrigerant. The water is then pumped to a cooling tower where the water is cooled through an evaporation process. Cooling towers are described in a later section. Chillers can also be air cooled. In this configuration, the condenserwould be a refrigerant-to-air heat exchanger with air absorbing the heat energy rejected by the high pressure refrigerant.Chillers nominally range in capacities from 30 to 18,000 kW (8 to 5100 ton). Most chillers sold in the U.S. are electric and utilize vapor compression refrigeration to produce chilled water. Compressors for these systems are either reciprocating, screw, scroll, or centrifugal in design. A small number of centrifugal chillers are sold that use either an internal combustion engine or steam drive instead of an electric motor to drive the compressor.[1]节选自James B. Bradford et al. “HVAC Equipment and Systems”.Handbook of Heating, Ventilation, and Air-Conditioning.Ed. Jan F. Kreider.Boca Raton, CRC Press LLC. 2001FIGURE 4.2.2 A dual chiller application with major auxiliary systems (courtesy of Carrier Corporation).The type of chiller used in a building depends on the application. For large office buildings or in chiller plants serving multiple buildings, centrifugal compressors are often used. In applications under 1000 kW (280 tons) cooling capacities, reciprocating or screw chillers may be more appropriate. In smaller applications, below 100 kW (30 tons), reciprocating or scroll chillers are typically used.Vapor Compression ChillersTable 4.2.5 shows the nominal capacity ranges for the four types of electrically driven vapor compression chillers. Each chiller derives its name from the type of compressor used in the chiller. The systems range in capacities from the smallest scroll (30 kW; 8 tons) to the largest centrifugal (18,000 kW; 5000 tons).Chillers can utilize either an HCFC (R-22 andR-123) or HFC (R-134a) refrigerant. The steady state efficiency of chillers is often stated as a ratio of the power input (in kW) to the chilling capacity (in tons). A capacity rating of one ton is equal to 3.52 kW or 12,000 btu/h. With this measure of efficiency, the smaller number is better. As seen in Table 4.2.5, centrifugal chillers are the most efficient; whereas, reciprocating chillers have the worst efficiency of the four types. The efficiency numbers provided in the table are the steady state full-load efficiency determined in accordance to ASHRAE Standard 30 (ASHRAE, 1995). These efficiency numbers do not include the auxiliary equipment, such as pumps and cooling tower fans that can add from 0.06 to 0.31 kW/ton to the numbers shown (Smit et al., 1996).Chillers run at part load capacity most of the time. Only during the highest thermal loadsin the building will a chiller operate near its rated capacity. As a consequence, it is important to know how the efficiency of the chiller varies with part load capacity. Figure 4.2.3 shows a representative data for the efficiency (in kW/ton) as a function of percentage full load capacity for a reciprocating, screw, and scroll chiller plus a centrifugal chiller with inlet vane control and one with variable frequency drive (VFD) for the compressor. The reciprocating chiller increases in efficiency as it operates at a smaller percentage of full load. In contrast, the efficiency of a centrifugal with inlet vane control is relatively constant until theload falls to about 60% of its rated capacity and its kW/ton increases to almost twice its fully loaded value.FIGURE 4.2.3 Chiller efficiency as a function of percentage of full load capacity.In 1998, the Air Conditioning and Refrigeration Institute (ARI) developed a new standard that incorporates into their ratings part load performance of chillers (ARI 1998c). Part load efficiency is expressed by a single number called the integrated part load value (IPLV). The IPLV takes data similar to that in Figure 4.2.3 and weights it at the 25%, 50%,75%, and 100% loads to produce a single integrated efficiency number. The weighting factors at these loads are 0.12, 0.45, 0.42, and 0.01, respectively. The equation to determine IPLV is:Most of the IPLV is determined by the efficiency at the 50% and 75% part load values. Manufacturers will provide, on request, IPLVs as well as part load efficiencies such as those shown in Figure 4.2.3.FIGURE 4.2.4 Volume-pressure relationships for a reciprocating compressor.The four compressors used in vapor compression chillers are each briefly described below. While centrifugal and screw compressors are primarily used in chiller applications, reciprocating and scroll compressors are also used in smaller unitary packaged air conditioners and heat pumps.Reciprocating CompressorsThe reciprocating compressor is a positive displacement compressor. On the intake stroke of the piston, a fixed amount of gas is pulled into the cylinder. On the compressionstroke, the gas is compressed until the discharge valve opens. The quantity of gas compressed on each stroke is equal to the displacement of the cylinder. Compressors used in chillers have multiple cylinders, depending on the capacity of the compressor. Reciprocating compressors use refrigerants with low specific volumes and relatively high pressures. Most reciprocating chillers used in building applications currently employ R-22.Modern high-speed reciprocating compressors are generally limited to a pressure ratio of approximately nine. The reciprocating compressor is basically a constant-volumevariable-head machine. It handles variousdischarge pressures with relatively small changes in inlet-volume flow rate as shown by the heavy line (labeled 16 cylinders) in Figure 4.2.4. Condenser operation in many chillers is related to ambient conditions, for example, through cooling towers, so that on cooler days the condenser pressure can be reduced. When the air conditioning load is lowered, less refrigerant circulation is required. The resulting load characteristic is represented by the solid line that runs from the upper right to lower left of Figure 4.2.4.The compressor must be capable of matching the pressure and flow requirements imposed by the system. The reciprocating compressor matches the imposed discharge pressure at any level up to its limiting pressure ratio. Varying capacity requirements can be met by providing devices that unloadindividual or multiple cylinders. This unloading is accomplished by blocking the suction or discharge valves that open either manually or automatically. Capacity can also be controlled through the use of variable speed or multi-speed motors. When capacity control is implemented on a compressor, other factors at part-load conditions need to considered, such as (a) effect on compressor vibration and sound when unloaders are used, (b) the need for good oil return because of lower refrigerant velocities, and (c) proper functioning of expansion devices at the lower capacities.With most reciprocating compressors, oil is pumped into the refrigeration system from the compressor during normal operation. Systems must be designed carefully to return oil to the compressor crankcase to provide for continuous lubrication and also to avoid contaminating heat-exchanger surfaces.Reciprocating compressors usually are arranged to start unloaded so that normal torque motors are adequate for starting. When gas engines are used for reciprocating compressor drives, careful matching of the torque requirements of the compressor and engine must be considered.FIGURE 4.2.5 Illustration of a twin-screw compressor design (courtesy of CarrierCorporation).Screw CompressorsScrew compressors, first introduced in 1958 (Thevenot, 1979), are positive displacement compressors. They are available in the capacity ranges that overlap with reciprocating compressors and small centrifugal compressors. Both twin-screw and single-screw compressors are used in chillers. The twin-screw compressor is also called the helical rotary compressor. Figure 4.2.5 shows a cutaway of a twin-screw compressor design. There are two main rotors (screws). One is designated male (4 in the figure) and the other female (6 in the figure).The compression process is accomplished by reducing the volume of the refrigerant with the rotary motion of screws. At the low pressure side of the compressor, a void is created when the rotors begin to unmesh. Low pressure gas is drawn into the void between the rotors. As the rotors continue to turn, the gas is progressively compressed as it moves toward the discharge port. Once reaching a predetermined volume ratio, the discharge port is uncovered and the gas is discharged into the high pressure side of the system. At a rotation speed of 3600 rpm, a screw compressor has over 14,000 discharges per minute (ASHRAE, 1996).Fixed suction and discharge ports are used with screw compressors instead of valves, as used in reciprocating compressors. These set the built-in volume ratio — the ratio of the volume of fluid space in the meshing rotors at the beginning of the compression process to the volume in the rotors as the discharge port is first exposed. Associated with the built-in volume ratio is a pressure ratio that depends on the properties of the refrigerant being compressed. Screw compressors have the capability to operate at pressure ratios of above 20:1 (ASHRAE, 1996). Peak efficiency is obtained if the discharge pressure imposed by the system matchesthe pressure developed by the rotors when the discharge port is exposed. If the interlobe pressure in the screws is greater or less than discharge pressure, energy losses occur but no harm is done to the compressor.Capacity modulation is accomplished by slide valves that provide a variable suction bypass or delayed suction port closing, reducing the volume of refrigerant compressed. Continuously variable capacity control is most common, but stepped capacity control is offered in some manufacturers’ machines. Variable discharge porting is available on some machines to allow control of the built-in volume ratio during operation.Oil is used in screw compressors to seal the extensive clearance spaces between the rotors, to cool the machines, to provide lubrication, and to serve as hydraulic fluid for the capacity controls. An oil separator is required for the compressor discharge flow to remove the oil from the high-pressure refrigerant so that performance of system heat exchangers will not be penalized and the oil can be returned for reinjection in the compressor.Screw compressors can be direct driven at two-pole motor speeds (50 or 60 Hz). Their rotary motion makes these machines smooth running and quiet. Reliability is high when the machines are applied properly. Screw compressors are compact so they can be changed out readily for replacement or maintenance. The efficiency of the best screw compressors matches or exceeds that of the best reciprocating compressors at full load. High isentropic and volumetric efficiencies can be achieved with screw compressors because there are no suction or discharge valves and small clearance volumes. Screw compressors for building applications generally use either R-134a or R-22.译文冷水机组1995年，在美国，冷水机组应用在至少4％的商用建筑中。

暖通空调专业-毕业设计外文翻译

Refrigeration System Performance using Liquid-Suction Heat ExchangersS. A. Klein, D. T. Reindl, and K. BroWnellCollege of EngineeringUniversity of Wisconsin - MadisonAbstractHeat transfer devices are provided in many refrigeration systems to exchange energy betWeen the cool gaseous refrigerant leaving the evaporator and Warm liquid refrigerant exiting the condenser. These liquid-suction or suction-line heat exchangers can, in some cases, yield improved system performance While in other cases they degrade system performance. Although previous researchers have investigated performance of liquid-suction heat exchangers, this study can be distinguished from the previous studies in three Ways. First, this paper identifies a neW dimensionless group to correlate performance impacts attributable to liquid-suction heat exchangers. Second, the paper extends previous analyses to include neW refrigerants. Third, the analysis includes the impact of pressure drops through the liquid-suction heat exchanger on system performance. It is shoWn that reliance on simplified analysis techniques can lead to inaccurate conclusions regarding the impact of liquid-suction heat exchangers on refrigeration system performance. From detailed analyses, it can be concluded that liquid-suction heat exchangers that have a minimal pressure loss on the loW pressure side are useful for systems using R507A, R134a, R12, R404A, R290, R407C, R600, and R410A. The liquid-suction heat exchanger is detrimental to system performance in systems using R22, R32, and R717.IntroductionLiquid-suction heat exchangers are commonly installed in refrigeration systems With the intent of ensuring proper system operation and increasing system performance.Specifically, ASHRAE(1998) states that liquid-suction heat exchangers are effective in:1) increasing the system performance2) subcooling liquid refrigerant to prevent flash gas formation at inlets to expansion devices3) fully evaporating any residual liquid that may remain in the liquid-suction prior to reaching the compressor(s)Figure 1 illustrates a simple direct-expansion vapor compression refrigeration system utilizing a liquid-suction heat exchanger. In this configuration, high temperature liquid leaving the heat rejection device (an evaporative condenser in this case) is subcooled prior to being throttled to the evaporator pressure by an expansion device such as a thermostatic expansion valve. The sink for subcoolingthe liquid is loW temperature refrigerant vapor leaving the evaporator. Thus, the liquid-suction heat exchanger is an indirect liquid-to-vapor heat transfer device. The vapor-side of the heat exchanger (betWeen the evaporator outlet and the compressor suction) is often configured to serve as an accumulator thereby further minimizing the risk of liquid refrigerant carrying-over to the compressor suction. In cases Where the evaporator alloWs liquid carry-over, the accumulator portion of the heat exchanger Will trap and, over time, vaporize the liquid carryover by absorbing heat during the process of subcooling high-side liquid.BackgroundStoecker and Walukas (1981) focused on the influence of liquid-suction heat exchangers in both single temperature evaporator and dual temperature evaporator systems utilizing refrigerant mixtures. Their analysis indicated that liquid-suction heat exchangers yielded greater performance improvements When nonazeotropic mixtures Were used compared With systems utilizing single component refrigerants or azeoptropic mixtures. McLinden (1990) used the principle of corresponding states to evaluate the anticipated effects of neW refrigerants. He shoWed that the performance of a system using a liquid-suction heat exchanger increases as the ideal gas specific heat (related to the molecular complexity of the refrigerant) increases. Domanski and Didion (1993) evaluated the performance of nine alternatives to R22 including the impact of liquid-suction heat exchangers. Domanski et al. (1994) later extended the analysis by evaluating the influence of liquid-suction heat exchangers installed in vapor compression refrigeration systems considering 29 different refrigerants in a theoretical analysis. Bivens et al. (1994) evaluated a proposed mixture to substitute for R22 in air conditioners and heat pumps. Their analysis indicated a 6-7% improvement for the alternative refrigerant system When system modifications included a liquid-suction heat exchanger and counterfloW system heat exchangers (evaporator and condenser). Bittle et al. (1995a) conducted an experimental evaluation of a liquid-suction heat exchanger applied in a domestic refrigerator using R152a. The authors compared the system performance With that of a traditional R12-based system. Bittle et al. (1995b) also compared the ASHRAE method for predicting capillary tube performance (including the effects of liquid-suction heat exchangers) With experimental data. Predicted capillary tube mass floW rates Were Within 10% of predicted values and subcooling levels Were Within 1.7 C (3F) of actual measurements.This paper analyzes the liquid-suction heat exchanger to quantify its impact on system capacity and performance (expressed in terms of a system coefficient of performance, COP). The influence of liquid-suction heat exchanger size over a range of operating conditions (evaporating and condensing) is illustrated and quantified using a number of alternative refrigerants. Refrigerants included in the present analysis are R507A, R404A, R600, R290,R134a, R407C, R410A, R12, R22, R32, and R717. This paper extends the results presented in previous studies in that it considers neW refrigerants, it specifically considers the effects of the pressure drops,and it presents general relations for estimating the effect of liquid-suction heat exchangers for any refrigerant.Heat Exchanger EffectivenessThe ability of a liquid-suction heat exchanger to transfer energy from the Warm liquid to the cool vapor at steady-state conditions is dependent on the size and configuration of the heat transfer device. The liquid-suction heat exchanger performance, expressed in terms of an effectiveness, is a parameter in the analysis. The effectiveness of the liquid-suction heat exchanger is defined in equation (1):Where the numeric subscripted temperature (T) values correspond to locations depicted in Figure 1. The effectiveness is the ratio of the actual to maximum possible heat transfer rates. It is related to the surface area of the heat exchanger. A zero surface area represents a system Without a liquid-suction heat exchanger Whereas a system having an infinite heat exchanger area corresponds to an effectiveness of unity.The liquid-suction heat exchanger effects the performance of a refrigeration system by in fluencing both the high and loW pressure sides of a system. Figure 2 shoWs the key state points for a vapor compression cycle utilizing an idealized liquid-suction heat exchanger on a pressure-enthalpy diagram. The enthalpy of the refrigerant leaving the condenser (state 3) is decreased prior to entering the expansion device (state 4) by rejecting energy to the vapor refrigerant leaving the evaporator (state 1) prior to entering the compressor (state 2). Pressure losses are not shoWn. The cooling of the condensate that occurs on the high pressure side serves to increase the refrigeration capacity and reduce the likelihood of liquid refrigerant flashing prior to reaching the expansion device. On the loW pressure side, the liquid-suction heat exchanger increases the temperature of the vapor entering the compressor and reduces the refrigerant pressure, both of Which increase the specific volume of the refr igerant and thereby decrease the mass floW rate and capacity. A major benefit of the liquid-suction heat exchanger is that it reduces the possibility of liquid carry-over from the evaporator Which could harm the compressor. Liquid carryover can be readily caused by a number of factors that may include Wide fluctuations in evaporator load and poorly maintained expansiondevices (especially problematic for thermostatic expansion valves used in ammonia service).（翻译）冷却系统利用流体吸热交换器克来因教授,布兰顿教授, , 布朗教授威斯康辛州的大学–麦迪逊摘录加热装置在许多冷却系统中被用到，用以制冷时遗留在蒸发器中的冷却气体和离开冷凝器发热流体之间的能量的热交换.这些流体吸收或吸收热交换器,在一些情形中，他们降低了系统性能, 然而系统的某些地方却得到了改善. 虽然以前研究员已经调查了流体吸热交换器的性能, 但是这项研究可能从早先研究的三种方式被加以区别. 首先，这份研究开辟了一个无限的崭新的与流体吸热交换器有关联的群体.其次，这份研究拓宽了早先的分析包括新型制冷剂。

空调专业毕业设计外文翻译--工程热力学和制冷循环

附录B 英文翻译THERMODYNAMICS AND REFRIGERATION CYCLES THERMODYNAMICS is the study of energy, its transformations, and its relation to states of matter. This chapter covers the application of thermodynamics to refrigeration cycles. The first part reviews the first and second laws of thermodynamics and presents methods for calculating thermodynamic properties. The second and third parts address compression and absorption refrigeration cycles, two common methods of thermal energy transfer.THERMODYNAMICSA thermodynamic system is a region in space or a quantity of matter bounded by a closed surface. The surroundings include everything external to the system, and the system is separated from the surroundings by the system boundaries. These boundaries can be movable or fixed, real or imaginary. Entropy and energy are important in any thermodynamic system. Entropy measures the molecular disorder of a system. The more mixed a system, the greater its entropy; an orderly or unmixed configuration is one of low entropy. Energy has the capacity for producing an effect and can be categorized into either stored or transient forms.Stored EnergyThermal (internal) energy is caused by the motion of molecules and/or intermolecular forces.Potential energy (PE) is caused by attractive forces existing between molecules, or the elevation of the system.mgzPE=(1)wherem =massg = local acceleration of gravityz = elevation above horizontal reference planeKinetic energy (KE) is the energy caused by the velocity of molecules and is expressed as22m VKE=(2)whereV is the velocity of a fluid stream crossing the system boundary.Chemical energy is caused by the arrangement of atoms composing the molecules.Nuclear (atomic) energy derives from the cohesive forces holding protons and neutrons together as the atom’s nucleus.Energy in TransitionHeat Q is the mechanism that transfers energy across the boundaries of systems with differing temperatures, always toward the lower temperature. Heat is positive when energy is added to the system (see Figure 1).Work is the mechanism that transfers energy across the boundaries of systems with differing pressures (or force of any kind),always toward the lower pressure. If the total effect produced in the system can be reduced to the raising of a weight, then nothing but work has crossed the boundary. Workis positive when energy is removed from the system (see Figure 1).Mechanical or shaft work W is the energy delivered or absorbed by a mechanism, such as a turbine, air compressor, or internal combustion engine.Flow work is energy carried into or transmitted across the system boundary because a pumping process occurs somewhere outside the system, causing fluid to enter the system. It can bemore easily understood as the work done by the fluid just outside the system on the adjacent fluid entering the system to force or push it into the system. Flow work also occurs as fluid leaves the system.Flow work =pv (3)where p is the pressure and v is the specific volume, or the volume displaced per unit mass evaluated at the inlet or exit.A property of a system is any observable characteristic of the system. The state of a system is defined by specifying the minimum set of independent properties. The most common thermodynamic properties are temperature T, pressure p, and specific volume v or density ρ. Additional thermodynamic properties include entropy, stored forms of energy, and enthalpy.Frequently, thermodynamic properties combine to form other properties. Enthalpy h is an important property that includes internal energy and flow work and is defined as≡(4) pvh+uwhere u is the internal energy per unit mass.Each property in a given state has only one definite value, and any property always has the same value for a given state, regardless of how the substance arrived at that state.A process is a change in state that can be defined as any change in the properties of a system. A process is described by specifying the initial and final equilibrium states, the path (if identifiable), and the interactions that take place across system boundaries during theprocess.A cycle is a process or a series of processes wherein the initial and final states of the system are identical. Therefore, at the conclusion of a cycle, all the properties have the same value they had at the beginning. Refrigerant circulating in a closed system undergoes acycle.A pure substance has a homogeneous and invariable chemical composition. It can exist in more than one phase, but the chemical composition is the same in all phases.If a substance is liquid at the saturation temperature and pressure,it is called a saturated liquid. If the temperature of the liquid is lower than the saturation temperature for the existing pressure, it is called either a subcooled liquid (the temperature is lower than the saturation temperature for the given pressure) or a compressed liquid (the pressure is greater than the saturation pressure for the given temperature).When a substance exists as part liquid and part vapor at the saturation temperature, its quality is defined as the ratio of the mass of vapor to the total mass. Quality has meaning only when the substance is saturated (i.e., at saturation pressure and temperature).Pressure and temperature of saturated substances are not independent properties.If a substance exists as a vapor at saturation temperature and pressure, it is called a saturated vapor. (Sometimes the term dry saturated vapor is used to emphasize that the quality is 100%.)When the vapor is at a temperature greater than the saturation temperature, it is a superheated vapor. Pressure and temperature of a superheated vapor are independent properties, because the temperature can increase while pressure remains constant. Gases such as air at room temperature and pressure are highly superheated vapors.FIRST LAW OF THERMODYNAMICSThe first law of thermodynamics is often called the law of conservation of energy. The following form of the first-law equation is valid only in the absence of a nuclear or chemical reaction.Based on the first law or the law of conservation of energy for any system, open or closed, there is an energy balance asNet amount of energy Net increase of stored=added to system energy in systemor[Energy in] – [Energy out] = [Increase of stored energy in system]Figure 1 illustrates energy flows into and out of a thermodynamic system. For the general case of multiple mass flows with uniform properties in and out of the system, the energy balance can be written=-++++-+++∑∑W Q gz V pv u m gz V pv u m out out in in )2()2(22 []system i i f f gz V pv u m gz V pv u m )2()2(22++-++ (5)where subscripts i and f refer to the initial and final states,respectively.Nearly all important engineering processes are commonly modeled as steady-flow processes. Steady flow signifies that all quantities associated with the system do not vary with time. Consequently,0)2()2(22=-+++-++∑∑W Q gz V h m gz V h m leavingstream all entering stream all (6)where h = u + pv as described in Equation (4).A second common application is the closed stationary system for which the first law equation reduces to[]system i f u u m W Q )(-=- (7)SECOND LAW OF THERMODYNAMICSThe second law of thermodynamics differentiates and quantifies processes that only proceed in a certain direction (irreversible) from those that are reversible. The second law may be described in several ways. One method uses the concept of entropy flow in an open system and the irreversibility associated with the process. The concept of irreversibility provides added insight into the operation of cycles. For example, the larger the irreversibility in a refrigeration cycle operating with a given refrigeration load between two fixed temperature levels, the larger the amount of work required tooperate the cycle. Irreversibilities include pressure drops in lines andheat exchangers, heat transfer between fluids of different temperature, and mechanical friction. Reducing total irreversibility in a cycle improves cycle performance. In the limit of no irreversibilities, a cycle attains its maximum ideal efficiency. In an open system, the second law of thermodynamics can be described in terms of entropy asdI s m s m dS e e i i T Q system +-+=δδδ(8)wheredS = total change within system in time dt during process systemδm s = entropy increase caused by mass entering (incoming)δm s = entropy decrease caused by mass leaving (exiting)δQ/T = entropy change caused by reversible heat transfer between system and surroundings at temperature TdI = entropy caused by irreversibilities (always positive)Equation (8) accounts for all entropy changes in the system. Rearranged, this equation becomes []I d dS s m s m T Q sys i i e e -+-=)(δδδ (9)In integrated form, if inlet and outlet properties, mass flow, and interactions with the surroundings do not vary with time, the general equation for the second law isI ms ms T Q S S out in revsystem i f +-+=-∑∑⎰)()(/)(δ (10)In many applications, the process can be considered to operate steadily with no change in time. The change in entropy of the system is therefore zero. The irreversibility rate, which is the rate of entropy production caused by irreversibilities in the process, can be determined by rearranging Equation (10):∑∑∑--=surrin out T Q ms ms I )()( (11) Equation (6) can be used to replace the heat transfer quantity.Note that the absolute temperature of the surroundings with which the system is exchanging heat is used in the last term. If the temper-ature of the surroundings is equal to the system temperature, heat istransferred reversibly and the last term in Equation (11) equals zero.Equation (11) is commonly applied to a system with one mass flow in, the same mass flow out, no work, and negligible kinetic or potential energy flows. Combining Equations (6) and (11) yields []surr inout in out T h h s s m I ---=)( (12)In a cycle, the reduction of work produced by a power cycle (or the increase in work required by a refrigeration cycle) equals the absolute ambient temperature multiplied by the sum of irreversibilities in all processes in the cycle. Thus, the difference in reversible and actual work for any refrigeration cycle, theoretical or real, operating under the same conditions, becomes∑+=I T W W reversible actual 0 (13)THERMODYNAMIC ANAL YSIS OFREFRIGERATION CYCLESRefrigeration cycles transfer thermal energy from a region of low temperature T to one of higher temperature. Usually the higher-T R temperature heat sink is the ambient air or cooling water, at temperature T 0, the temperature of the surroundings.The first and second laws of thermodynamics can be applied to individual components to determine mass and energy balances and the irreversibility of the components. This procedure is illustrated in later sections in this chapter.Performance of a refrigeration cycle is usually described by a coefficient of performance (COP), defined as the benefit of the cycle (amount of heat removed) divided by the required energy input to operate the cycle:Useful refrigerating effectCOP ≡Useful refrigeration effect/Net energy supplied from external sources (14)Net energy supplied from external sources For a mechanical vapor compression system, the net energy supplied is usually in the form of work, mechanical or electrical, and may include work to the compressor and fans or pumps. Thus,net evapW Q COP = (15)In an absorption refrigeration cycle, the net energy supplied is usually in the form of heat into the generator and work into the pumps and fans, ornet gen evapW Q Q COP += (16)In many cases, work supplied to an absorption system is very small compared to the amount of heat supplied to the generator, so the work term is often neglected.Applying the second law to an entire refrigeration cycle shows that a completely reversible cycle operating under the same conditions has the maximum possible COP. Departure of the actual cycle from an ideal reversible cycle is given by the refrigerating efficiency:tev R COP COP)(=η (17)The Carnot cycle usually serves as the ideal reversible refrigeration cycle. For multistage cycles, each stage is described by a reversible cycle.工程热力学和制冷循环工程热力学是研究能量及其转换和能量与物质状态之间的关系。

暖通空调专业毕业设计外文翻译

空调设计外文翻译---印度暖通空调与冰箱工业走向世界

India HVAC&R Goes GlobalThe total market size in 2008 for the HVAC&R industry in India was approximately $2.5 billion. That year, India produced roughly 5 million refrigerators, 2.5 million room air conditioners, packaged air conditioners of various capacities, and packaged chillers of reciprocating, scroll, screw and absorption types.Other HVAC&R products manufactured in India include air-handling units, fan-coil units, refrigeration systems for cold rooms and freezer rooms; low-temperature brine chillers for industry; and commercial refrigeration equipment for food stores and supermarkets. The following stories describe some Indian companies that are making their mark internationally.Heat Pumps in DenmarkThermax absorption heat pumps and chillers are finding increasing acceptance with European and U.S. clients that want energy-efficient equipment. Businesses are demanding systems that can reduce carbon emissions and help cope with global warming.Over the last decade, Thermax has worked in optimizing energy use in Denmark by installing absorption heat pumps for centralized heating, which is a reverse application of centralized cooling with absorption chillers. Hot water from a central generation facility is used for space heating in town buildings. The heating companies reduce the energy intensity at generating centers by tapping low-grade heat from other sources such as geothermal heat from sandstone aquifers or waste heat from town incinerators.Since its first installation in 1999, Thermax absorption heat pumps are operating in several district heating installations. Recently, the company is fulfilling an order for a 3.4 MW steam absorption chiller to be installed in downtown Copenhagen as part of a district cooling project. The total capacity of the plant is 15 MW, which uses the output of the Thermax chiller, free cooling using seawater and ammonia chillers. The plant will save approximately 2,500 tons (2268 Mg) of carbon dioxide per year.In Spain, Thermax has commissioned chillers in hotels and office buildings that run on water heated by solar panels. Clients elsewhere in Europe also use Thermax chillers that work on exhaust gas from fuel cells or excess steam from old boilers that use wood waste.In the United Kingdom, large retailer Tesco has installed Thermax chillers at twostores as part of a plan to reduce its carbon footprint through various measures, including using energy-saving devices. The chillers use water from the cogeneration system that Tesco has installed for generating power.In the United States, a 1,100 kW test engine installed at a plant of a leading plastics manufacturer in Ohio generated a great deal of waste heat. Thermax harnessed this waste heat to drive an absorption chiller. Waste heat is converted to energy savings as chilled water from this system is used for process cooling in the plant. More than 150 business customers in the United States are gaining from energy profits and green reputations by installing Thermax chillers. Recently, the University at Albany-State University of New York，replaced its old, inefficient cooling system with a 1,400 ton (4924 kW) chiller that works on hot water. The university has gained 35% energy efficiency with substantial savings in operating and maintenance costs. The Henry Ford Museum in Detroit and Colorado School of Mines in Golden, Colo., also have Thermax chillers.Under a recent strategic agreement, Trane, a leading global indoor comfort systems and service provider for the North American market, will source and distribute Thermax chillers.Heat Wheels in AustraliaWhat do a hospital in Australia, a university in Florida, a high-tech commercial building in Dubai, a church in Brazil, the Olympic stadium and airport in Beijing and an indoor swimming pool in Tasmania have in common? The indoor air quality provided by DRI, Desiccant Rotors International, is a heat wheel manufacturer in Delhi. A flagship company of the Pahwa Enterprises, it is the largest privately held HVAC group in India.King Edward Memorial Hospital (KEM) in Perth, Australia, is a renowned, state-owned health-care provider for women,with more than 400 beds and a large staff of specialists. KEM is geared to provide the highest standards of health care and patient servicing, where indoor air quality plays a vital role. The original HVAC installation carried out 30 years ago was ahead of its time. It incorporated heat recovery wheels (HRW) to save energy and provide better indoor air quality. The wheels were imported from the United States and the aluminum substrate was supplied in 20 segments. With the passage of time, the substrate disintegrated and fell off in all four wheels. As a result, the wheels became non-operational and KEM Hospital and the authorities had a tough time finding a supplier that could supply newwheels in sections that could pass through the doorways without breaking down the walls of the AHU room. They also had difficulty finding an installer who could dismantle the old steel frames, also in sections, so the building could remain intact.Fortunately, DRI, through its Australian agent agreed to custom manufacture a five-segment wheel in its factory, ship it to the site, install and commission the new wheel, all under the supervision of a local consultant. With the completion of the retrofit project, KEM Hospital’s indoor air quality improved. Among other projects DRI has done are the Beijing Olympics; Pacific Controls, which is Dubai’s first green building; and the second tallest building in China, which is the 450 m (1,476 ft) tall Nanjing Green Land Square, which are all equipped with Ecofresh wheels produced in Delhi.Other DRI facts:• Largest global producer of enthalpy wheels;• World’s only AHRI and Eurovent certified rotors manufacturer;• Integrated rotor manufacturing facility;• World-class rotor (enthalpy as well as desiccant) test facility;• Sales network spread over India, U.S., Brazil, Europe, UAE,Turkey, Africa, China, Malaysia, Philippines, Japan, Korea and Australia; and• Awarded AHRI certification performance award for achieving a 100% success rate for seven consecutive years.Heat Pumps in EuropeBlue Star began exporting drinking water coolers to the Gulf countries in the Middle East as early as 1974. The large stainless steel storage tank design of the coolers was suitable for India and the Gulf countries where city water supply was intermittent. Although local buyers initially resisted buying Blue Star coolers, with improved quality and timely deliveries the company’s sky-blue water coolers became visible at every mosque and school in Dubai and Kuwait.In the early 1990s, Blue Star made large investments in new plant, machinery, technology and R&D for HVAC&R products to handle the growing market within the country. In 1999, the company started exporting ducted air conditioners of up to 7.5 ton (26 kW) capacity, as well as window and split room ACs. A substantial part of these products were specially designed for an American company; prototypes were built and tested in India and the U.S., to suit the needs of the U.S. manufacturer for the Middle East market. Labeled with the U.S. brand name, but with the words “Madein India,” customers no longer hesitated to buy such products. As many as 170,000 unitary products were sold within a few years.Buoyed by this success in the Middle East, the American company decided to enter the European market with its brand and once again chose Blue Star to design ductable heat pumps for this market, using R-407C refrigerant (instead of R-22 in the Middle East) with a sleek appearance, compact footprint, stringent safety and noise requirements. Eleven thousand units have been shipped to Europe.With $500,000 in exports in 1999, today the company has nearly $25 million in exports and ships drinking water coolers, ducted split ACs and heat pumps, and air-handling units, fan coil units, scroll chillers, screw chillers, close control packaged ACs, as well as special units for the telecom market. A large number of distributors and business partners help the company to cater to the growing market in various neighboring countries. With an increased R&D spending, Blue Star plans to ship more products to the international market.Coolers in EuropeAir-cooled fluid coolers (ACFC) are as the radiator in your car, helping to keep the engine cool, by circulating cooling water through the engine jacket and the radiator. They are larger in cooling capacity and are used in captive power plants to cool the diesel engines or gas turbines that drive the electric generators.With scarcity of water and shortage of electric power in most parts of the developing world, International Coil Ltd (ICL) of Delhi has developed ACFCs to cool the jackets of diesel engines or gas turbines running generators in 8 MW power plants or larger capacity with multiples of 8 MW, used by industry to run their plants, instead of cooling towers, which consume large amounts of water.With hundreds of installations of ACFCs in India, millions of cubic meters of water are being saved, proving them to be a good environment-friendly solution. Certified by AHRI, these ACFCs can also be supplied with Heresite coating to reduce corrosion in saline atmospheres. Internationally reputable manufacturers of power plants running on diesel engines or gas turbines including Rolls Royce of England, MAN of Germany, Wartsila of Finland and Cummins of the U.S., have signed OEM agreements with ICL to use ACFCs on their supplies of generators to most parts of the developing world.MEP Contracting in Middle EastIn the early 1970s, the Middle East embarked on ambitious plans ofmodernization and building construction.With a small domestic population, the region depended heavily on construction labor from the Indian subcontinent, which is only a few hours away by air. Arab and European companies with offices in the Gulf lured experienced Indian HVAC engineers with salaries three to four times higher than salaries prevailing in India, free company cars, petrol cheaper than water and no income tax. Voltas, being one of the largest HVAC companies, suffered crippling manpower losses that took time to replenish with the help of freshly graduated engineers.In a way, these events turned out to be a blessing in disguise, because Arab employers were so impressed with Indian engineering skills that many of them started doing business with Voltas in joint ventures, which took on large HVAC contracts initially and then went in for complete electro-mechanical projects, including electrical and plumbing.HVAC for Queen Mary IIThe experience gained from work in the Gulf States and contacts established with international suppliers all over the world of equipment and accessories, including piping, sheet metal, and insulation, led to Voltas’s ambition to take on the world.So, Voltas bid and won contracts in 30 countries and three continents, including the HVAC contract for Hong Kong Airport and the largest luxury liner ever built, Queen Mary II, while it was under construction in a French port.The company is part of the $62.5 billion Tata Group and is the number two air-conditioner brand in the country. The firm manufactured the first room air conditioner in 1954. It has overseas offices in Dubai, Abu Dhabi, Qatar, Bahrain, Singapore and Hong Kong.Author：Hiru M. JhangianiNationality：IndiaOriginate from：Air Conditioning and Refrigeration Journal of 24 (2004) 55-60印度暖通空调与冰箱工业走向世界2008年，印度的暖通空调与冰箱工业的市场总量为25亿美元。

暖通空调毕业设计翻译题目

INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int.J.Energy Res.2005;29:471–483Published online 14March 2005in Wiley InterScience ().DOI:10.1002/er.1065Multi-fault detection and diagnosis of HVAC systems:an experimental studySung-Hwan Cho 1,Young-Ju Hong 1,Won-Tae Kim 2and M.Zaheer-uddin 3,n ,y1Building Energy Research Center,KIER,71-2Jang-Dong Yousung-Gu Taejeon 305-343,Korea 2Department of Bio-Mechanical Engineering,Kongju National University,Chungnam,340-702,Korea 3Building Civil &Environmental Engineering,Concordia University,Montreal,Canada H3G 1M8SUMMARYThe objective of this study is to detect faults due to multiple element failures in HVAC systems occurring concurrently.To classify and detect single as well as multiple faults,measurements were made of supply air temperature,OA-damper position,supply fan pressure,indoor temperature and airﬂow rate in a variable air volume heating ventilating and air conditioning test facility.Experimental results show that three types of patterns emerge in the analysis of multi-fault problems.To solve the multi-fault problem,a new strategy based on pattern classiﬁcation and the use of residual ratios is presented.It is shown that the residual ratio can be used to diagnose and accurately identify and detect multiple-faults occurring in HVAC systems.Copyright #2005John Wiley &Sons,Ltd.KEY WORDS :FDD (fault detection and diagnosis);VAV (variable air volume);neural network;HVAC system;single-fault;multiple-fault1.INTRODUCTIONHVAC systems in buildings have become increasingly larger and complex.As such they require close monitoring to evaluate their performance with respect to energy eﬃciency and equipment operation.The increasing complexity has made it very diﬃcult to detect the causes,locations and eﬀects of faults in various parts of building systems.Faults whether they occur in HVAC equipment,instrumentation or control loops contribute to higher energy consumption,could shorten equipment life,and degrade indoor environment.Therefore,a fault detection technology is necessary that detects performance deterioration quickly and accurately so that a faster remedial action could be taken to improve indoor environment and ensure reliability and safety of the system.Many initial studies on HVAC systems have applied rule based diagnosis methods (Liu and Kelly,1998)to detect faults.Some other studies have used rule-based and statistical methodsReceived 25March 2004Accepted 30June 2004Copyright #2005John Wiley &Sons,Ltd.yE-mail:zaheer@cbs-engr.bcee.concordia.canCorrespondence to:M.Zaheer-uddin,Building Civil &Environmental Engineering,Concordia University,Montreal,Canada H3G 1M8.(Anderson et al.,1998).In Chen and Braun (2000)a fault diagnosis method based on optimal control theory is presented.Norford proposed a fault diagnosis technique based on the usage of electric power.Chen and Braun (2001)applied an FDD technique to develop a method for diagnosing and detecting faults in packaged air-conditioners.The use of knowledge-based methods to detect faults in HVAC systems,which are applied to actual buildings,has grown in recent years such as the work done by Katipamula et al .(1999),House et al .(1999).Also,Lee et al .(1996)used a prediction based model for detecting AHU faults.He trained a neural network to recognize the fault patterns.Recently,more reliable fault detection methods have been developed.These methods use residuals that are insensitive to outer disturbances and have high ﬁdelity in terms of identifying the fault patterns.In this study,we are interested in exploring a pattern diagnosing method for detecting single element fault or combined faults involving multiple elements both of which occur in HVAC systems.To this end,ﬁrst a single fault replication was done in which signals from outdoor air damper,indoor supply temperature sensor,indoor temperature sensor,airﬂow rate sensor and supply blower were used.Also multiple faults were replicated by applying faults in two elements at a time.The following element combinations were used in multiple fault experiments:supply temperature sensor and outdoor air damper;supply temperature sensor and supply ﬂow rate;and supply temperature sensor and supply fan.2.EXPERIMENTAL TEST FACILITYExperiments were conducted in a test room housed in an environmental chamber (EC)test facility (Figure 1).The EC is a multi-purpose research and test facility.It is used to conduct comprehensive and controlled experiments such as evaluation of HVAC control strategies,energy eﬃciency,thermal performance of building envelopes and fault detection and diagnostic studies.The test facility consists of a main chamber and a three ﬂoor level attached space.On these three ﬂoors several test rooms are built.The overall dimensions of the test facility are given in Table I.The test facility can simulate diﬀerent outdoor weather conditions for conducting diﬀerent tests irrespective of time of the year or seasons.For example,any temperature between À25to 508C can be created using a pre-selected rate of temperature increase/or decrease to simulate typical outdoor weather conditions.A complete list of thermal parameter speciﬁcations of the EC are given in Table II.Several diﬀerent test rooms were built in the EC on the ﬁrst and second ﬂoors.The layout of test rooms is depicted in Figure 2and the overall dimensions of the test rooms are summarized in Table III.As shown in Figure 2the test facility consists of four diﬀerent rooms.These include:an experimental room for performance monitoring and control of radiant ﬂoor heating systems (ONDOL in Figure 2);an experimental room for evaluating energy eﬃciency of heating/cooling systems;an indoor environment and thermal comfort room;and an HVAC test room for the study of FDD and control strategies.The HVAC test room can also be used to evaluate performance of under-ﬂoor air conditioning (UFAC)systems,variable air volume (VAV)systems and monitoring of indoor air quality (IAQ).The results presented in this paper are based on the tests conducted in the HVAC test room shown in Figure 2.A schematic diagram of the variable air volume air handling Unit (AHU)and the location of sensors/actuators and controllers used in the fault detectionCopyright #2005John Wiley &Sons,Ltd.Int.J.Energy Res .2005;29:471–483S.-H.CHO ET AL.472and diagnosis experiments are shown in Figure 3.The AHU is a variable air volume unit which can vary the airﬂow rates in the system by modulating the fan speed via a pressure controller.Similarly,a return air fan is made to track the supply air fan while maintaining a constant air ﬂow diﬀerence.The two other control loops used included a discharge air temperature control loop and an outdoor,return and exhaust damper control loop.The speciﬁcations of the AHU and the operating range of temperatures and air ﬂow conditions are depicted in Table IV.In the FDD experiments conducted the supply air temperature was varied as a function of room load and the room air temperature was maintained at a chosen set-point by regulating the air ﬂow rate to theroom.Figure 1.Environmental chamber test facility.Table I.Overall speciﬁcations of the test facility.3over ground Chamber 1ﬂoor:4.5m Attached 136.08m 22ﬂoor:3.6m Sizefacility249.48m 23ﬂoor:3.6mCapacity 1,428.8m 2Structure Steel-frame,ferro-concrete PurposeResearch &experiment Air conditioning Central air conditioningControl methodComputer based automatic controlCopyright #2005John Wiley &Sons,Ltd.Int.J.Energy Res .2005;29:471–483DETECTION AND DIAGNOSIS OF HVAC SYSTEMS473Table II.Operating range of the environmental chamber.ParameterCapacityTemperature control range À25–508C (DB)Temperature decrease rate 0–88C h À1decrease Temperature increase rate 20–108C h À1increase Humidity control rangeChamberDew point temperature 68C Æ18C at 158C (DB)Dew point temperature 108C Æ28C at 248C (DB)Dew point temperature20–308C Æ18C at 158C (DB)Experimental test room40–80%(RH)Figure yout of experimental test rooms.Table III.Dimensions of experimental test rooms.Construction Concrete Total area 70.38m 2Area1ﬂoor Experimental room for Ondol 3.0m Â5.1m=15.3m 2Experimental room for equipment 3.9m Â3.0m=11.7m 22ﬂoorExperimental room for environment 3.0m Â2.1m=6.3m 2ExperimentalroomforHVAC6.9m Â3.0m=20.7m 2Copyright #2005John Wiley &Sons,Ltd.Int.J.Energy Res .2005;29:471–483S.-H.CHO ET AL.474DETECTION AND DIAGNOSIS OF HVAC SYSTEMS475AO : Analog outputAI : Analog inputFigure3.Schematic diagram of AHU and control system.Table IV.Operating conditions in AHU–HVAC test room.Component Operation rangeIndoor condition Summer:248C(75.28F)Outdoor condition Summer:308C(868F)Supply fan Max:1000CMH(0.278m2/s)Min:200CMH(0.055m2/s)Return fan Max:900CMH(0.25m2/s)Min:200CMH(0.055m2/s)Cooling coil Capacity:13,608kcal/h(4.5HP)Condenser:9,072kcal/h(3HP)4,536kcal/h(1.5HP)Inlet cooling water temp:78COutlet cooling water temp:138C Heating coil Max.electric demand:10kWControl method:P,PI,PID and manual Mixing damper Control method:P,PI,PID and manual Supply set pressure45mmAq(448Pa)3.FAULT DIAGNOSIS THEORYThe methods for diagnosing the faults in HVAC systems comprise of both fault detection and fault diagnosis.To detect faults,it isﬁrst necessary to deﬁne and classify what constitutes a fault.This is usually referred as fault pattern classiﬁcation.Several methods are used to analyse and diagnose faults.These are:rule based diagnosis,statistical pattern recognition, neural networks and fuzzy logic.In this paper we use a model-based residual technique to detect faults.The residual is the diﬀerence between value of the state with no fault and its value with fault.These residuals are normalized and the pattern of the normalized residuals is used to Copyright#2005John Wiley&Sons,Ltd.Int.J.Energy Res.2005;29:471–483detect the faults.In this study,the following residuals were deﬁned and used in the fault diagnosis analysis:R OD ¼OD N ÀOD F ð1ÞR TI ¼TI N ÀTI F ð2ÞR SFR ¼SFR N ÀSFR F ð3ÞR ST ¼ST N ÀST F ð4ÞR SF ¼SF N ÀSF Fð5ÞEquations (1)–(5)show residuals relative to normal states and failed states (outdoor air damper,indoor temperature sensor,supply ﬂow rate sensor and supply fan).The normalized residuals were computed by dividing the residuals with the highest residual in its class using the following equation:R T ¼T N ÀT FT N ÀT F j j MAX ð6ÞIn the above equations,the subscripts are deﬁned as follows:OD=outdoor air damper,IT=indoor temperature sensor,SFR=ﬂow rate sensor,ST=supply temperature,SF=fan output,N=no fault state,and F=fault state.In this paper we have used the normalized residual patterns as inputs to train neural networks.The trained neural network is used to identify the residual patterns and recognize the fault according to a predeﬁned fault classiﬁcation scheme.4.EXPERIMENTAL METHODSeveral elements of HVAC systems often fail during day-to-day operation.Among these sensors,actuators,and fans are the most common elements that fail or give erroneous signals.In order to develop a robust fault diagnosis and detection technique,we have conducted several experiments in which faults were simulated and diagnosis analysis were performed to verify if the faults can be identiﬁed accurately.To this end,we consider a VAV–AHU operation by focusing attention on the following four elements:outdoor air damper (OD),indoor temperature (IT)sensor,supply ﬂow rate (SFR)and supply fan (SF).During typical operation of HVAC systems in buildings these elements may fail one at a time (single fault)or more likely they will fail concurrently in several combinations (multiple faults).The tests were conducted by simulating winter weather conditions in the EC.The outdoor temperature simulated was 58C corresponding to a typical mild day in winter.The VAV–AHU was controlled by a central energy management control system.The operating conditions of the VAV system were set as follows:supply air pressure set-point=440Pa,supply air temperature=368C;room temperature set-point=228C;outdoor damper open posi-tion=30%.A series of experiments were conducted in which a single fault was applied one at a time.The single fault classiﬁcation scheme used in the tests is deﬁned in Table V.The other sets of experiments conducted were to simulate multiple faults.These faults were characterized byCopyright #2005John Wiley &Sons,Ltd.Int.J.Energy Res .2005;29:471–483S.-H.CHO ET AL.476DETECTION AND DIAGNOSIS OF HVAC SYSTEMS477Table V.Fault type classiﬁcation.Type Variable Description Single fault OD Outdoor damperIT Indoor temperature sensorSFR Supply fanﬂow rateST Supply temperature sensorSF Supply fanMultiple fault ST+OD Multiple occurrenceST+SFR Multiple occurrenceST+SF Multiple occurrencesimultaneous failures of two elements.These are also deﬁned in Table V.An energy management control system was programmed to generate the phenomena similar to actual faults.The elements were set to cause fault magnitudes of10%from their original no fault settings.The faulty signals with10%error were applied to outdoor air damper and temperature sensor.Also the output signals of supplyﬂow rate sensor and the supply fan were increased by about10%in order to replicate fault state.5.RESULTS AND DISCUSSIONS5.1.Performance characteristics of the systemFigure4shows the outputs of each element such as supply temperature,heater power consumption,ﬂow rate and damper opening that were monitored during the tests involving single and multiple faults.The time evolutions of the outputs under single and multiple faults were compared.Figures4(a)and4(b)show the outputs from the ST sensor operating in single fault mode(Figure4(a))and multi-fault mode(Figure4(b)).The multiple fault modes were generated using diﬀerent combinations of ST+OD,ST+SFR or ST+SF elements.From these twoﬁgures,it can be seen that supply air temperature increases at the beginning of fault and reaches a constant level in10min whether it is a single fault in ST or a combined fault due to ST+OD,ST+SFR or ST+SF combinations.From these results it can be reasoned that faults due to OD,SFR and SF elements have very limited impact when combined with the single fault in ST.Figure4(c)shows the heater power consumption caused by single fault in ST sensor and in outdoor damper.In contrast Figure4(d)shows the heater power under the inﬂuence of combined faults in ST+OD,ST+SFR or ST+SF elements.A comparison of heater power in two cases shows that single fault power consumption tends to be added causing higher heater power consumption in multiple fault operation.Similarly the supply fan pressure responses under single and multiple faults are depicted in Figures4(e)and4(f),respectively.These two responses are identical meaning a fault in supply air temperature does not have any inﬂuence on the supply fan output Therefore,combined fault in ST and SF gives the same output response as the single SF fault response.Figure4(g)showsﬂow rate changes caused by single fault in SFR and combined fault due to ST+SFR.The former generates higher airﬂow rate than the latter.Figure4(h)shows the Copyright#2005John Wiley&Sons,Ltd.Int.J.Energy Res.2005;29:471–483S u p p l y a i r T e m p e r a t u r e ('C )102030405060708090H e a t p o w e r (k W )0102030405060708090Elapsed Time (minutes)Elapsed Time (minutes)S u p p l y F a n O u t p u t (%)01020304050607080900102030405060708090S u p p l y F a n O u t p u t (%)Elapsed Time (minutes)Elapsed Time (minutes)(a)(c)(d)(e)(f)Figure 4.Pattern analysis in the case of single and multiple faults:(a)ST -(single fault);(b)ST -(multiple fault);(c)Heater power -(single fault);(d)Heater power -(multiple fault);(e)Fan pressure -(single fault);(f)Fan pressure -(multiple fault);(g)SFR in single and multiple fault;and (h)VAV Damper in single fault.Copyright #2005John Wiley &Sons,Ltd.Int.J.Energy Res .2005;29:471–483S.-H.CHO ET AL.478output of VAV damper due to the single faults in ST sensor and SFR sensors.When supply temperature fault occurs,the output value reduces so that VAV damper shows 40%open position.When single fault due to SFR sensor occurs,damper opening increases progressively so that VAV damper opens to 50%of its full open position.These results make it possible to divide the combined faults into the following three cases.First,the measurement from a single faulty element is very nearly the same as that of the measurement from two faulty elements combined (case 1).Second,when a faulty output measurement in one element is combined with another faulty measurement from a second element,the ﬁnal measurement value is higher than single fault output (case 2).Third,fault occurring at an element does not have any eﬀect on the fault of other elements (case 3).Case 1is characterized by similarity between combined fault and single fault.The combined fault in ST+OD follows this type (Figures 4(a)and 4(b)).Case 2shows that combined fault is the sum of the single fault values.This type of fault is shown by combined faults in ST+SFR (Figures 4(c)and 4(d)).Case 3shows that fault of single element does not inﬂuence the combined fault.This type of fault is depicted as combined ST+SF fault in Figures 4(e)and 4(f).5.2.Diagnostic analysis of single and multiple-fault(s)Table VI shows the raw data,residuals,normalized values and resulting patterns of each fault both in single and multiple fault modes.The raw data is the output value of each faulty element,and the residual value is the diﬀerence between fault state and normal state.Normalized value is the residual value of each element divided by maximum residual value,using the normalized Equation (6).By using these normalized values the fault patterns were created.The normalized residual magnitudes greater than 0.5were set equal to1,and those with magnitudes less than 0.5were assigned a value of 0.5.2.1.Single fault diagnosis .A number of studies have shown the use of residual patterns in detecting single mode faults.Since,each fault gives a distinct residual pattern,these patterns areElapsed Time (minutes)Elapsed Time (minutes)0102030405060708090S u p p l y F l o w R a t e (C M H )354045505560V A V D a m p e r (%)(g)(h)Figure 4.Continued.Copyright #2005John Wiley &Sons,Ltd.Int.J.Energy Res .2005;29:471–483DETECTION AND DIAGNOSIS OF HVAC SYSTEMS479used to identify the faults.We have also analyzed the single mode fault patterns obtained in our experiments.These patterns are shown in Table VII.It is apparent that the residual patterns are unique to each fault category.These patterns were used as inputs to train a neural network.The trained neural network was tested to check its validity in identifying the faults.These results are shown as neural network outputs in Table VII.5.2.2.Multiple fault diagnosis .The residual results presented in Table VI also show some startling diﬀerences compared to single fault residuals.For example,the heater power residual in combined ST+OD fault mode is about 35%greater than the single fault ST residual.On the other hand,in the combined fault involving ST+SF and single fault in SF the magnitude of SF residual remains the same.Table VI.The data,residuals,normalized values and patterns in single/multiple faults.DATA Fault Heater (kW)VAVD (%)ST (8C)SF (%)SFR (CMH)Raw dataNormal 1.82045.0136.2968.18317.53OD 2.32547.0235.9568.42330.92IT 1.85640.7536.0166.72277.19SFR 1.76448.5136.3467.86391.50ST 2.45744.7139.5868.13312.85SF 1.75445.0535.8661.71316.02ST+OD 2.80344.4539.8668.37317.97ST+SFR 2.44045.7639.7668.33375.431ST+SF 2.35144.6339.6661.58321.64ResidualOD 0.505 2.01À0.340.2513.40IT 0.036À4.26À0.27À1.46À40.34SFR À0.056 3.050.05À0.3273.97ST 0.638À0.30 3.29À0.05À4.68SF À0.0660.04À0.42À6.47À1.51ST+OD 0.983À0.56 3.570.190.44ST+SFR 0.6200.76 3.470.1657.90ST+SF 0.531À0.37 3.37À6.59 4.16Normalized OD 0.514À0.47À0.090.040.18valueIT 0.037 1.00À0.08À0.22À0.55SFR À0.056À0.820.01À0.05 1.00ST 0.6490.070.92À0.01À0.06SF À0.067À0.01À0.12À0.98À0.02ST+OD 1.0000.13 1.000.030.01ST+SFR 0.631À0.180.970.020.78ST+SF 0.5410.090.94À1.000.06PatternOD 10000IT 01000SFR 11001ST 10100SF 01010ST+OD 10100ST+SFR 10101ST+SF111Copyright #2005John Wiley &Sons,Ltd.Int.J.Energy Res .2005;29:471–483S.-H.CHO ET AL.480When normalization is done on the basis of these residuals,however,we note that in the case of ST+SFR,SFR has additional normalization value of1as compared to single fault residual in ST sensor.Similarly,in the case of ST+SF,SF has additional normalization value1 compared to the normalized residuals from the ST sensor.Furthermore,we also note that if a combined fault in ST+OD occurs,it cannot be distinguished from single fault in ST sensor. This is evident by looking at Table VIII.When a neural network is trained using such residual patterns,it cannot distinguish single fault from a multiple fault since the same input to the neural network must identify two distinct outputs.In such cases the neural network fails to identify the fault conclusively.To deal with this type of situations,we propose the use of residual ratios.For example,the combined fault can be detected by using the ratio of heater power residual and supply temperature sensor residual.For instance in the case of single fault due to ST sensor,the heater power consumption residual is0.638kW and supply temperature residual is 3.298C.In the case of combined fault in OD and ST sensor,heater power consumption is0.983kW and supply temperature residual is3.578C.The residual ratios of heater power consumption to the output value of supply temperature in the cases of single fault and combined fault were computed as shown below.RR j STfault¼R STR powerST¼3:290:638¼5:75ð7aÞTable VII.Normalized patterns for AHU single fault diagnosis used in ANN training.Neural network inputHeat VAV ST SF SFR Neural network output Fault diagnosis 00000100000Normal10000010000Outdoor damper fault 010********Indoor temperature sensor fault 010********Supplyﬂowrate sensor fault 10100000010Supply temperature sensor fault 00010000001Supply fan fault Table VIII.Normalized patterns for AHU multi fault diagnosis used in ANN training.Neural network inputHeat VAV ST SF SFR Neural network output Fault diagnosis 00000100000000Normal10000010000000Outdoor damper fault 01000001000000Indoor temperature sensor fault 01001000100000Supplyﬂowrate sensor fault 10100000010000Supply temperature sensor fault 00010000001000Supply fan fault 10100000000100ST+OD fault 10101000000010ST+SFR fault 10110000000001ST+SF faultCopyright#2005John Wiley&Sons,Ltd.Int.J.Energy Res.2005;29:471–483DETECTION AND DIAGNOSIS OF HVAC SYSTEMS481RR j ST þODfault ¼R ST R power ST þOD ¼3:570:983¼3:63ð7b ÞThe residual ratios are respectively,5.75and 3.63in each of the two cases.When a combined fault and a single fault have the same pattern,we propose comparison of residual ratios (Table IX)in order to conclusively identify the fault.From the residual ratios computed from Equations (7a)and (7b)we note thatRR j STfault ¼R ST Rpower ST>5:0ð8a ÞRR j ST þODfault ¼R ST R power ST þOD55:0ð8b ÞWhen fault pattern is the same,and if RR ST which is the residual ratio of R ST and R power is greater than 5.0,it can be classiﬁed as a single fault.If RR ST+OD is less than 5.0,it can be identiﬁed as a combined fault.In other words,the magnitude of the residual ratio in multi-fault always remains smaller than single-fault residual ratio.This pattern was noted consistently at three diﬀerent fault rates of 10,15and 20%as shown in Table IX.Thus,these results show that pattern diagnosis using residual ratios is a useful technique in uniquely identifying single and multiple faults in HVAC systems.6.CONCLUSIONSA pattern diagnosis method for detecting single fault or combined fault occurring in HVAC systems is developed.Based on experimental results and analysis of the residual data from both single and multiple fault modes the following conclusions are oﬀered.(1)Multiple fault pattern diagnosis analysis is necessary for more accurate diagnosis offaults in HVAC systems.(2)It was found that the multiple fault patterns fall in three distinct categories.First,thereexist a group of faults,which show similar residuals in single as well as multi fault modes.In the second category of the faults the combined fault residuals were found to be sum of the individual fault residuals.In the third category of faults,the single fault outputs had no inﬂuence on the combined faults.(3)It is shown that residual ratio is a good indicator of isolating and detecting faults,whichshow similar residual patterns in single and multi-faults in HVAC systems.Table IX.Residuals,residual ratios in single and multiple fault modes.Fault Fault rate (%)Heater (kw)VAVD (%)ST (‘C)SF (%)SFR (CMH)Residual ratioST 100.638À0.30 3.29À0.05À4.68 5.75Single 150.769À2.28 5.29À0.70À40.34 6.88fault 200.851À1.097.03À0.38À34.448.26ST+OD 100.983À0.56 3.570.190.44 3.63Multiple 15 1.304À2.74 5.00À0.15À51.28 3.83fault202.406À1.097.302.37À39.343.30Copyright #2005John Wiley &Sons,Ltd.Int.J.Energy Res .2005;29:471–483S.-H.CHO ET AL.482DETECTION AND DIAGNOSIS OF HVAC SYSTEMS483NOMENCLATUREF=ﬂow sensorHeat=heater power(kW)IT=room temperature(8C)OD=outdoor damper opening(%)OT=outdoor air temperature(8C)R=residualRR=residual ratioSF=supply fan temperature(8C)SFR=supply airﬂow rate(CMH)ST=supply air temperature(8C)VAVD=VAV damper opening(%)SubscriptF=faultMAX=maximumN=no faultREFERENCESAnderson D,Grave L,Reinert W,Kreider JF,Dow J,Wubbrna H.1998.A quasi-real-time expert system for HVAC Systems.ASHRAE Transactions95:954–960.Chen B,Braun JE.2000.Simple fault packaged air conditioners.Proceedings of the Purdue University.West Lafayette, U.S.A.,July25–28,321–328.Chen B,Braun JE.2001.Simple rule based methods for fault detection and diagnosis as applied to packaged air conditioners.ASHRAE Winter Meeting,Atlanta,GA.House JM,Lee WY,Shin DR.1999.Classiﬁcation techniques for fault detection and diagnosis of an air-handling unit.ASHRAE Transactions105:1087–1097.Katipamula S,Pratt RG,Shassin DP,Taylor ZT,Gouwri K,Brambley MR.1999.Automated fault detection and diagnosis for outdoor-air ventilation systems and economizer:methodology and results fromﬁeld tests.ASHRAE Transactions105:555–567.Lee WY,House JM,Park C,Kelly JE.1996.Fault diagnosis of an air-handling system using artiﬁcial neural network.ASHRAE Transactions102:540–549.Liu ST,Kelly GE.1998.Rule-based diagnostic method for HVAC fault detection.Proceedings of Simulation Conference 89,Vancouver.Norford L,Little R.1993.Fault detection and load monitoring in ventilation systems.ASHRAE Transactions99: 590–602.Copyright#2005John Wiley&Sons,Ltd.Int.J.Energy Res.2005;29:471–483。

暖通空调专业外文翻译 --空调系统

英文文献Air Conditioning SystemsAir conditioning has rapidly grown over the past 50 years, from a luxury to a standard system included in most residential and commercial buildings. In 1970, 36% of residences in the U.S. were either fully air conditioned or utilized a room air conditioner for cooling (Blue, et al., 1979). By 1997, this number had more than doubled to 77%, and that year also marked the first time that over half (50.9%) of residences in the U.S. had central air conditioners (Census Bureau, 1999). An estimated 83% of all newhomes constructed in 1998 had central air conditioners (Census Bureau, 1999). Air conditioning has also grown rapidly in commercial buildings. From 1970 to 1995, the percentage of commercial buildings with air conditioning increased from 54 to 73% (Jackson and Johnson, 1978, and DOE, 1998).Air conditioning in buildings is usually accomplished with the use of mechanical or heat-activated equipment. In most applications, the air conditioner must provide both cooling and dehumidification to maintain comfort in the building. Air conditioning systems are also used in other applications, such as automobiles, trucks, aircraft, ships, and industrial facilities. However, the description of equipment in this chapter is limited to those commonly used in commercial and residential buildings.Commercial buildings range from large high-rise office buildings to the corner convenience store. Because of the range in size and types of buildings in the commercial sector, there is a wide variety of equipment applied in these buildings. For larger buildings, the air conditioning equipment is part of a total system design that includes items such as a piping system, air distribution system, and cooling tower. Proper design of these systems requires a qualified engineer. The residential building sector is dominatedby single family homes and low-rise apartments/condominiums. The cooling equipment applied in these buildings comes in standard “packages” that are often both sized and installed by the air conditioning contractor.The chapter starts with a general discussion of the vapor compression refrigeration cycle then moves to refrigerants and their selection, followed by packaged Chilled Water Systems。

空调节能技术中英文对照外文翻译文献

中英文对照资文翻译空调节能技术的研究1、引言节能可以说是楼宇自动控制系统的出发点和归宿。

众所周知，在智能建筑中HV AC (采暖、通风和空调)系统所耗费的能量要占到大楼消耗的总能量的极大部分比例，大致在50%~60%左右。

特别是冷冻机织、冷却塔、循环水泵和空调机组、新风机组，都是耗能大户。

所以实有必要发展一种有效的空调系统节能方法，尤其用是在改善现有大楼空调系统自动化上方面。

DDC(Dircctdigitalcontrol)直接数字化控制，是一项构造简单操作容易的控制设备，它可借由接口转接设各随负荷变化作系统控制，如空调冷水循环系统、空调箱变频自动风量调整及冷却水塔散热风扇的变频操控等，可以让空调系统更有效率的运转，这样不仅为物业管理带来很大的经济效益，而且还可使系统在较佳的工况下运行，从而延长设备的使用寿命以及达到提供舒适的空调环境和节能之目的。

一般大楼常用的空调系统有CA V、V A V、VWV等，各有不同操控方式，都可以用DDC控制。

（1）定风量系统(CA V)定风量系统(ConstantAirV olume，简称CA V)定风量系统为空调机吹出的风量一定，以提供空调区域所需要的冷(暖)气。

当空调区域负荷变动时，则以改变送风温度应付室内负荷，并达到维持室内温度度于舒适区的要求。

常用的中央空调系统为AHU(空调机)与冷水管系统(FCU系统)。

这两者一般均以定风量(CA V)来供应空调区，为了应付室内部分负荷的变动，在AHU定风量系统以空调机的变温送风来处理，在一般FCU系统则以冷水阀ON/OFF控制来调节送风温度。

（2）变风量系统(V A V)变风量系统(VarlableAirV olume，简称V A V)即是空调机(AHU或FCU)可以调变风量。

常用的中央空调系统为AHU(空调机)与冷水管系统FCL系统。

毕业设计英语翻译

2Screw Compressor GeometryTo be able to predict the performance of any type of positive displacement compressor it is necessary to have a facility to estimate the working chamber size and shape at any point in its operating cycle. In the case of screw compressors this implies the need to be able to define the rotor lobe profiles, together with any additional parameters needed for the rotor and housing geometry to be fully specified. A set of subprograms which can compute the lobe profiles and the complete geometry of the working space of a screw machine of almost arbitrary design has been developed. The default version is a new asymmetric profile, called Demonstrator, which can model any realistic combination of numbers of lobes in the main and gate screw rotors. However, any other known or even a completely new profile can be generated, with little or no modification of the code. Such profiles must, of course, satisfy geometrical constraints in order to obtain a realistic solution.螺杆式压缩机的几何结构为了能够预测任何类型的容积式压缩机的性能，在工作周期的任何时候用一个工具来评估工作腔大小和形状是有必要的。

暖通空调系统专业外文翻译

暖通空调系统专业外文翻译英文文献Air Conditioning SystemsAir conditioning has rapidly grown over the past 50 years from a luxury to a standard system included in most residential and commercial buildings In 1970 36 of residences in the US were either fully air conditioned or utilized a room air conditioner for cooling Blue et al 1979 By 1997 this number had more than doubled to 77 and that year also marked the first time that over half 509 of residences in the US had central air conditioners Census Bureau 1999 An estimated 83 of all new homes constructed in 1998 had central air conditioners Census Bureau 1999 Air conditioning has also grown rapidly in commercial buildings From 1970 to 1995 the percentage of commercial buildings with air conditioning increased from 54 to 73 Jackson and Johnson 1978 and DOE 1998Air conditioning in buildings is usually accomplished with the use of mechanical or heat-activated equipment In most applications the air conditioner must provide both cooling and dehumidification to maintain comfort in the building Air conditioning systems are also used in other applications such as automobiles trucks aircraft ships and industrialfacilities However the description of equipment in this chapter is limited to those commonly used in commercial and residential buildings Commercial buildings range from large high-rise office buildings to the corner convenience store Because of the range in size and types of buildings in the commercial sector there is a wide variety of equipment applied in these buildings For larger buildings the air conditioning equipment is part of a total system design that includes items such as a piping system air distribution system and cooling tower Proper design of these systems requires a qualified engineer The residential building sector is dominatedby single family homes and low-rise apartmentscondominiums The cooling equipment applied in these buildings comes in standard packages that are often both sized and installed by the air conditioning contractor The chapter starts with a general discussion of the vapor compression refrigeration cycle then moves to refrigerants and their selection followed by packaged Chilled Water Systems11 Vapor Compression CycleEven though there is a large range in sizes and variety of air conditioning systems used in buildings most systems utilize the vapor compression cycle to produce the desired cooling and dehumidification This cycle is also used for refrigerating and freezing foods and for automotive air conditioning The first patent on a mechanically drivenrefrigeration system was issued to Jacob Perkins in 1834 in London and the first viable commercial system was produced in 1857 by James Harrison and DE SiebeBesides vapor compression there are two less common methods used to produce cooling in buildings the absorption cycle and evaporative cooling These are described later in the chapter With the vapor compression cycle a working fluid which is called the refrigerant evaporates and condenses at suitable pressures for practical equipment designsThe four basic components in every vapor compression refrigeration system are the compressor condenser expansion device and evaporator The compressor raises the pressure of the refrigerant vapor so that the refrigerant saturation temperature is slightly above the temperature of the cooling medium used in the condenser The type of compressor used depends on the application of the system Large electric chillers typically use a centrifugal compressor while small residential equipment uses a reciprocating or scroll compressorThe condenser is a heat exchanger used to reject heat from the refrigerant to a cooling medium The refrigerant enters the condenser and usually leaves as a subcooled liquid Typical cooling mediums used in condensers are air and water Most residential-sized equipment uses air as the cooling medium in the condenser while many larger chillers use water After leaving the condenser the liquid refrigerant expands to a lowerpressure in the expansion valveThe expansion valve can be a passive device such as a capillary tube or short tube orifice or an active device such as a thermal expansion valve or electronic expansion valve The purpose of the valve is toregulate the flow of refrigerant to the evaporator so that the refrigerant is superheated when it reaches the suction of the compressor At the exit of the expansion valve the refrigerant is at a temperature below that of the medium air or water to be cooled The refrigerant travels through a heat exchanger called the evaporator It absorbs energy from the air or water circulated through the evaporator If air is circulated through the evaporator the system is called a direct expansion system If water is circulated through the evaporator it is called a chiller In either case the refrigerant does not make direct contact with the air or water in the evaporatorThe refrigerant is converted from a low quality two-phase fluid to a superheated vapor under normal operating conditions in the evaporator The vapor formed must be removed by the compressor at a sufficient rate to maintain the low pressure in the evaporator and keep the cycle operating All mechanical cooling results in the production of heat energy that must be rejected through the condenser In many instances this heat energy is rejected to the environment directly to the air in the condenser or indirectly to water where it is rejected in a cooling tower With someapplications it is possible to utilize this waste heat energy to provide simultaneous heating to the building Recovery of this waste heat at temperatures up to 65°C 150°F can be used to reduce costs for space heatingCapacities of air conditioning are often expressed in either tons or kilowatts kW of cooling The ton is a unit of measure related to the ability of an ice plant to freeze one short ton 907 kg of ice in 24 hr Its value is 351 kW 12000 Btuhr The kW of thermal cooling capacity produced by the air conditioner must not be confused with the amount of electrical power also expressed in kW required to produce the cooling effect21 Refrigerants Use and SelectionUp until the mid-1980s refrigerant selection was not an issue in most building air conditioning applications because there were no regulations on the use of refrigerants Many of the refrigerants historically used for building air conditioning applications have been chlorofluorocarbons CFCs and hydrochlorofluorocarbons HCFCs Most of these refrigerants are nontoxic and nonflammable However recent US federal regulations EPA 1993a EPA 1993b and international agreements UNEP 1987 have placed restrictions on the production and use of CFCs and HCFCs Hydrofluorocarbons HFCs are now being used in some applications where CFCs and HCFCs were used Having an understanding of refrigerants can helpa building owner or engineer make a more informed decision about the best choice of refrigerants for specific applications This section discusses the different refrigerants used in or proposed for building air conditioning applications and the regulations affecting their use The American Society of Heating Refrigerating and Air Conditioning Engineers ASHRAE has a standard numbering systemfor identifying refrigerants ASHRAE 1992 Many popular CFC HCFC and HFC refrigerants are in the methane and ethane series of refrigerants They are called halocarbons or halogenated hydrocarbons because of the presence of halogen elements such as fluorine or chlorine King 1986 Zeotropes and azeotropes are mixtures of two or more different refrigerants A zeotropic mixture changes saturation temperatures as it evaporates or condenses at constant pressure The phenomena is called temperature glide At atmospheric pressure R-407C has a boiling bubble point of –44°C –47°F and a condensation dew point of –37°C –35°F which gives it a temperature glide of 7°C 12°F An azeotropic mixture behaves like a single component refrigerant in that the saturation temperature does not change appreciably as it evaporates or condenses at constant pressure R-410A has a small enough temperature glide less than 55°C 10°F that it is considered a near-azeotropic refrigerant mixture ASHRAE groups refrigerants by their toxicity and flammability ASHRAE 1994 Group A1 is nonflammable and least toxic while Group B3 isflammable and most toxic Toxicity is based on the upper safety limit for airborne exposure to the refrigerant If the refrigerant is nontoxic in quantities less than 400 parts per million it is a Class A refrigerant If exposure to less than 400 parts per million is toxic then the substance is given the B designation The numerical designations refer to the flammability of the refrigerant The last column of Table com shows the toxicity and flammability rating of common refrigerantsRefrigerant 22 is an HCFC is used in many of the same applications and is still the refrigerant of choice in many reciprocating and screw chillers as well as small commercial and residential packaged equipment It operates at a much higher pressure than either R-11 or R-12 Restrictions on the production of HCFCs will start in 2004 In 2010 R-22 cannot be used in new air conditioning equipment R-22 cannot be produced after 2020 EPA 1993bR-407C and R-410A are both mixtures of HFCs Both are considered replacements for R-22 R-407C is expected to be a drop-in replacement refrigerant for R-22 Its evaporating and condensing pressures for air conditioning applications are close to those of R-22 Table com However replacement of R-22 with R-407C should be done only after consulting with the equipment manufacturer At a minimum the lubricant and expansion device will need to be replaced The first residential-sized air conditioning equipment using R-410A was introduced in the US in 1998 Systems usingR-410A operate at approximately 50 higher pressure than R-22 Table com thus R-410A cannot be used as a drop-in refrigerant for R-22 R-410A systems utilize compressors expansion valves and heat exchangers designed specifically for use with that refrigerantAmmonia is widely used in industrial refrigeration applications and in ammonia water absorption chillers It is moderately flammable and has a class B toxicity rating but has had limited applications in commercial buildings unless the chiller plant can be isolated from the building being cooled Toth 1994 Stoecker 1994 As a refrigerant ammonia has many desirable qualities It has a high specific heat and high thermal conductivity Its enthalpy of vaporization is typically 6 to 8 times higher than that of the commonly used halocarbons and it provides higher heat transfer compared to halocarbons It can be used in both reciprocating and centrifugal compressorsResearch is underway to investigate the use of natural refrigerants such as carbon dioxide R-744 and hydrocarbons in air conditioning and refrigeration systems Bullock 1997 and Kramer 1991 Carbon dioxide operates at much higher pressures than conventional HCFCs or HFCs and requires operation above the critical point in typical air conditioning applications Hydrocarbon refrigerants often thought of as too hazardous because of flammability can be used in conventional compressors and have been used in industrial applications R-290 propane has operatingpressures close to R-22 and has been proposed as a replacement for R-22 Kramer 1991 Currently there are no commercial systems sold in the US for building operations that use either carbon dioxide or flammable refrigerants31 Chilled Water SystemsChilled water systems were used in less than 4 of commercial buildings in the US in 1995 However because chillers are usually installed in larger buildings chillers cooled over 28 of the US commercial building floor space that same year DOE 1998 Five types of chillers are commonly applied to commercial buildings reciprocating screw scroll centrifugal and absorption The first four utilize the vapor compression cycle to produce chilled water They differ primarily in the type of compressor used Absorption chillers utilize thermal energy typically steam or combustion source in an absorption cycle with either an ammonia-water or water-lithium bromide solution to produce chilled water32 Overall SystemAn estimated 86 of chillers are applied in multiple chiller arrangements like that shown in the figure Bitondo and Tozzi 1999 In chilled water systems return water from the building is circulated through each chiller evaporator where it is cooled to an acceptable temperature typically 4 to 7°C 39 to 45°F The chilled water is then distributed to water-to-air heat exchangers spread throughout the facility In theseheat exchangers air is cooled and dehumidified by the cold water During the process the chilled water increases in temperature and must be returned to the chiller sThe chillers are water-cooled chillers Water is circulated through the condenser of each chiller where it absorbs heat energy rejected from the high pressure refrigerant The water is then pumped to a cooling tower where the water is cooled through an evaporation process Cooling towers are described in a later section Chillers can also be air cooled In this configuration the condenserwould be a refrigerant-to-air heat exchanger with air absorbing the heat energy rejected by the high pressure refrigerantChillers nominally range in capacities from 30 to 18000 kW 8 to 5100 ton Most chillers sold in the US are electric and utilize vapor compression refrigeration to produce chilled water Compressors for these systems are either reciprocating screw scroll or centrifugal in design A small number of centrifugal chillers are sold that use either an internal combustion engine or steam drive instead of an electric motor to drive the compressorThe type of chiller used in a building depends on the application For large office buildings or in chiller plants serving multiple buildings centrifugal compressors are often used In applications under 1000 kW 280 tons cooling capacities reciprocating or screw chillers may be moreappropriate In smaller applications below 100 kW 30 tons reciprocating or scroll chillers are typically used33 Vapor Compression ChillersThe nominal capacity ranges for the four types of electrically driven vapor compression chillers Each chiller derives its name from the type of compressor used in the chiller The systems range in capacities from the smallest scroll 30 kW 8 tons to the largest centrifugal 18000 kW 5000 tons Chillers can utilize either an HCFC R-22 and R-123 or HFC R-134a refrigerant The steady state efficiency of chillers is often stated as a ratio of the power input in kW to the chilling capacity in tons A capacity rating of one ton is equal to 352 kW or 12000 btuh With this measure of efficiency the smaller number is better centrifugal chillers are the most efficient whereas reciprocating chillers have the worst efficiency of the four types The efficiency numbers provided in the table are the steady state full-load efficiency determined in accordance to ASHRAE Standard 30 ASHRAE 1995 These efficiency numbers do not include the auxiliary equipment such as pumps and cooling tower fans that can add from 006 to 031 kWton to the numbers shownChillers run at part load capacity most of the time Only during the highest thermal loads in the building will a chiller operate near its rated capacity As a consequence it is important to know how the efficiency of the chiller varies with part load capacity a representative data for theefficiency in kWton as a function of percentage full load capacity for a reciprocating screw and scroll chiller plus a centrifugal chiller with inlet vane control and one with variable frequency drive VFD for the compressor The reciprocating chiller increases in efficiency as it operates at a smaller percentage of full load In contrast the efficiency of a centrifugal with inlet vane control is relatively constant until theload falls to about 60 of its rated capacity and its kWton increases to almost twice its fully loaded valueIn 1998 the Air Conditioning and Refrigeration Institute ARI developed a new standard that incorporates into their ratings part load performance of chillers ARI 1998c Part load efficiency is expressed by a single number called the integrated part load value IPLV The IPLV takes data similar to that in Figure com and weights it at the 25 50 75 and 100 loads to produce a single integrated efficiency number The weighting factors at these loads are 012 045 042 and 001 respectively The equation to determine IPLV isMost of the IPLV is determined by the efficiency at the 50 and 75 part load values Manufacturers will provide on request IPLVs as well as part load efficienciesThe four compressors used in vapor compression chillers are each briefly described below While centrifugal and screw compressors are primarily used in chiller applications reciprocating and scrollcompressors are also used in smaller unitary packaged air conditioners and heat pumps34 Reciprocating CompressorsThe reciprocating compressor is a positive displacement compressor On the intake stroke of the piston a fixed amount of gas is pulled into the cylinder On the compression stroke the gas is compressed until the discharge valve opens The quantity of gas compressed on each stroke is equal to the displacement of the cylinder Compressors used in chillers have multiple cylinders depending on the capacity of the compressor Reciprocating compressors use refrigerants with low specific volumes and relatively high pressures Most reciprocating chillers used in building applications currently employ R-22Modern high-speed reciprocating compressors are generally limited to a pressure ratio of approximately nine The reciprocating compressor is basically a constant-volume variable-head machine It handles various discharge pressures with relatively small changes in inlet-volume flow rate as shown by the heavy line labeled 16 cylinders Condenser operation in many chillers is related to ambient conditions for example through cooling towers so that on cooler days the condenser pressure can be reduced When the air conditioning load is lowered less refrigerant circulation is required The resulting load characteristic is represented by the solid line that runs from the upper right to lower leftThe compressor must be capable of matching the pressure and flow requirements imposed by the system The reciprocating compressor matches the imposed discharge pressure at any level up to its limiting pressure ratio Varying capacity requirements can be met by providing devices that unloadindividual or multiple cylinders This unloading is accomplished by blocking the suction or discharge valves that open either manually or automatically Capacity can also be controlled through the use of variable speed or multi-speed motors When capacity control is implemented on a compressor other factors at part-load conditions need to considered such as a effect on compressor vibration and sound when unloaders are used b the need for good oil return because of lower refrigerant velocities and c proper functioning of expansion devices at the lower capacities With most reciprocating compressors oil is pumped into the refrigeration system from the compressor during normal operation Systems must be designed carefully to return oil to the compressor crankcase to provide for continuous lubrication and also to avoid contaminating heat-exchanger surfacesReciprocating compressors usually are arranged to start unloaded so that normal torque motors are adequate for starting When gas engines are used for reciprocating compressor drives careful matching of the torque requirements of the compressor and engine must be considered35 Screw CompressorsScrew compressors first introduced in 1958 Thevenot 1979 are positive displacement compressors They are available in the capacity ranges that overlap with reciprocating compressors and small centrifugal compressors Both twin-screw and single-screw compressors are used in chillers The twin-screw compressor is also called the helical rotary compressor A cutaway of a twin-screw compressor design There are two main rotors screws One is designated male and the other female The compression process is accomplished by reducing the volume of the refrigerant with the rotary motion of screws At the low pressure side of the compressor a void is created when the rotors begin to unmesh Low pressure gas is drawn into the void between the rotors As the rotors continue to turn the gas is progressively compressed as it moves toward the discharge port Once reaching a predetermined volume ratio the discharge port is uncovered and the gas is discharged into the high pressure side of the system At a rotation speed of 3600 rpm a screw compressor has over 14000 discharges per minute ASHRAE 1996 Fixed suction and discharge ports are used with screw compressors instead of valves as used in reciprocating compressors These set the built-in volume ratio the ratio of the volume of fluid space in the meshing rotors at the beginning of the compression process to the volume in the rotors as the discharge port is first exposed Associated with thebuilt-in volume ratio is a pressure ratio that depends on the properties of the refrigerant being compressed Screw compressors have the capability to operate at pressure ratios of above 201 ASHRAE 1996 Peak efficiency is obtained if the discharge pressure imposed by the system matches the pressure developed by the rotors when the discharge port is exposed If the interlobe pressure in the screws is greater or less than discharge pressure energy losses occur but no harm is done to the compressor Capacity modulation is accomplished by slide valves that provide a variable suction bypass or delayed suction port closing reducing the volume of refrigerant compressed Continuously variable capacity control is most common but stepped capacity control is offered in some manufacturers machines Variable discharge porting is available on some machines to allow control of the built-in volume ratio during operation Oil is used in screw compressors to seal the extensive clearance spaces between the rotors to cool the machines to provide lubrication and to serve as hydraulic fluid for the capacity controls An oil separator is required for the compressor discharge flow to remove the oil from the high-pressure refrigerant so that performance of system heat exchangers will not be penalized and the oil can be returned for reinjection in the compressorScrew compressors can be direct driven at two-pole motor speeds 50 or 60 Hz Their rotary motion makes these machines smooth running andquiet Reliability is high when the machines are applied properly Screw compressors are compact so they can be changed out readily for replacement or maintenance The efficiency of the best screw compressors matches or exceeds that of the best reciprocating compressors at full load High isentropic and volumetric efficiencies can be achieved with screw compressors because there are no suction or discharge valves and small clearance volumes Screw compressors for building applications generally use either R-134a or R-22中文译文空调系统过去 50 年以来空调得到了快速的发展从曾经的奢侈品发展到可应用于大多数住宅和商业建筑的比较标准的系统在 1970 年的美国 36 的住宅不是全空气调节就是利用一个房间空调器冷却到1997年这一数字达到了 77在那年作的第一次市场调查表明在美国有超过一半的住宅安装了中央空调人口普查局1999 在1998年83的新建住宅安装了中央空调人口普查局 1999 中央空调在商业建筑物中也得到了快速的发展从 1970年到1995年有空调的商业建筑物的百分比从54增加到 73 杰克森和詹森1978建筑物中的空气调节通常是利用机械设备或热交换设备完成在大多数应用中建筑物中的空调器为维持舒适要求必须既能制冷又能除湿空调系统也用于其他的场所例如汽车卡车飞机船和工业设备然而在本章中仅说明空调在商业和住宅建筑中的应用商业的建筑物从比较大的多层的办公大楼到街角的便利商店占地面积和类型差别很大因此应用于这类建筑的设备类型比较多样对于比较大型的建筑物空调设备设计是总系统设计的一部分这部分包括如下项目例如一个管道系统设计空气分配系统设计和冷却塔设计等这些系统的正确设计需要一个有资质的工程师才能完成居住的建筑物即研究对象被划分成单独的家庭或共有式公寓应用于这些建筑物的冷却设备通常都是标准化组装的由空调厂家进行设计尺寸和安装本章节首先对蒸汽压缩制冷循环作一个概述接着介绍制冷剂及制冷剂的选择最后介绍冷水机组11 蒸汽压缩循环虽然空调系统应用在建筑物中有较大的尺寸和多样性大多数的系统利用蒸汽压缩循环来制取需要的冷量和除湿这个循环也用于制冷和冰冻食物和汽车的空调在1834年一个名叫帕金斯的人在伦敦获得了机械制冷系统的第一专利权在1857年詹姆士和赛博生产出第一个有活力的商业系统除了蒸汽压缩循环之外有两种不常用的制冷方法在建筑物中被应用吸收式循环和蒸发式冷却这些将在后面的章节中讲到对于蒸汽压缩制冷循环有一种叫制冷剂的工作液体它能在适当的工艺设备设计压力下蒸发和冷凝每个蒸汽压缩制冷系统中都有四大部件它们是压缩机冷凝器节流装置和蒸发器压缩机提升制冷剂的蒸汽压力以便使制冷剂的饱和温度微高于在冷凝器中冷却介质温度使用的压缩机类型和系统的设备有关比较大的电冷却设备使用一个离心式的压缩机而小的住宅设备使用的是一种往复或漩涡式压缩机冷凝器是一个热交换器用于将制冷剂的热量传递到冷却介质中制冷剂进入冷凝器变成过冷液体用于冷凝器中的典型冷却介质是空气和水大多数住宅建筑的冷凝器中使用空气作为冷却介质而大型系统的冷凝器中采用水作为冷却介质液体制冷剂在离开冷凝器之后在膨胀阀中节流到一个更低的压力膨胀阀是一个节流的装置例如毛细管或有孔的短管或一个活动的装置例如热力膨胀阀或电子膨胀阀膨胀阀的作用是到蒸发器中分流制冷剂以便当它到压缩物吸入口的时候制冷剂处于过热状态在膨胀阀的出口制冷剂的温度在介质空气或水的温度以下之后制冷剂经过一个热交换器叫做蒸发器它吸收通过蒸发器的空气或水的热量如果空气经过蒸发器在流通该系统叫做一个直接膨胀式系统如果水经过蒸发器在流通它叫做冷却设备在任何情况下在蒸发器中的制冷剂不直接和空气或水接触在蒸发器中制冷剂从一个低品位的两相液体转换成在正常的工艺条件下过热的蒸汽蒸汽的形成要以一定的足够速度被压缩机排出以维持在蒸发器中低压和保持循环进行所有在生产中的机械冷却产生的热量必须经过冷凝器散发在许多例子中在冷凝器中这个热能被直接散发到环境的空气中或间接地散发到一个冷却塔的水中在一些应用中利用这些废热向建筑物提供热量是可能的回收这些最高温度为65℃ 150°F 的废热可以减少建筑物中采暖的费用空调的制冷能力常用冷吨或千瓦千瓦来表示冷吨是一个度量单位它与制冰厂在 24小时内使1吨 907 公斤的水结冰的能力有关其值是351千瓦12000 Btuhr 空调的冷却能力不要和产生冷量所需的电能相互混淆21 制冷剂的使用和选择直到20世纪80年代中叶制冷剂的选择在大多数的建筑物空调设备中不是一个问题因为在制冷剂的使用上还没有统一的的标准在以前用于建筑物空调设备的大多数制冷剂是氟氯碳化物和氟氯碳氢化物且大多数的制冷剂是无毒的和不可燃的然而最近的美国联邦的标准环保署 1993a环保署 1993b 和国际的协议 UNEP1987 已经限制了氟氯碳化物和氟氯碳氢化物的制造和使用现在氟氯碳化物和氟氯碳氢化物在一些场合依然被使用对制冷剂的理解能帮助建筑物拥有者或者工程师更好的了解关于为特定的设备下如何选择制冷剂这里将讨论不同制冷剂的使用并给出影响它们使用的建筑空调设备和标准美国社会的供暖制冷和空调工程师学会 ASHRAE 有一个标准的限制系统表 com 用来区分制冷剂许多流行的氟氯碳化物氟氯碳氢化物和氟碳化物的制冷剂是在甲烷和乙烷的制冷剂系列中因为卤素元素的存在他们被叫作碳化卤或卤化的碳化氢例如氟或氯Zeotropes 和azeotropes 是混合二种或更多不同的制冷剂一种zeotropic混合物能改变饱和温度在它在不变的压力蒸发或冷凝这种现象被称温度的移动在大气压力下R-407 C的沸点沸腾是–44 °C – 47° F 和一个凝结点露点是–37°C –35°F 产生了7°C的温度移动 12°F 一个azeotropic 混合物的性能像单独成份制冷剂那样它在不变的压力下蒸发或冷凝它们的饱和温度不会有少许变化R-410有微小的足够温度滑动少于55 C10°F 可以认为接近azeotropic混合制冷剂ASHRAE组制冷剂 com 根据它们的毒性和易燃性 ASHRAE1994 划分的A1组合是不燃烧的和最没有毒的而B3组是易燃的和最有毒的以空气为媒介的制冷剂最高安全限制是毒性如果制冷剂在少于每百万分之400是无毒的它是一个A级制冷剂如果对泄露少于每百万分之400是有毒的那么该物质被称B级制冷剂这几个级别表示制冷剂的易燃性表 com 的最后一栏列出了常用的制冷剂的毒性和易燃的等级因为他们是无毒的和不燃烧的所以在A1组中制冷剂通常作为理想的制冷剂能基本满足舒适性空调的需求在A1中的制冷剂通常用在建筑空调设备方面的包括 R-11R-12R-22R-134a和R-410AR-11R-12R-123和R-134a是普遍用在离心式的冷却设备的制冷剂R-11氟氯碳化物和R-123 HCFC 都有低压高容积特性是用在离心式压缩机上的理想制冷剂在对氟氯碳化物的制造的禁令颁布之前R-11和R-12已经是冷却设备的首选制冷剂在已存在的系统维护中现在这两种制冷剂的使用已经被限制现在R-123 和 R-134a都广泛的用在新的冷却设备中R-123拥有的效率优势在 R-134a之上表 com 然而R-123有 B1安全等级这就意谓它有一个比较低的毒性而胜于R-134a如果一个使用R-123冷却设备在一栋建筑物中被用当使用这些或任何其他有毒的或易燃的制冷剂时候标准 15 ASHRAE1992 提供安全预防的指导方针制冷剂22 属于HCFC在多数的相同设备中被用也是在多数往复和螺旋式冷却设备和小型商业和住宅的集中式设备中的首选制冷剂它可以在一个更高的压力下运行这一点要优于R-11或R-12中的任何一个从2004开始HCFCs的制造将会受到限制在2010年R-22不能在新的空调设备中被使用 2020年之后R-22不允许生产环保署1993bR-407C和R-410A是 HFCs的两种混合物两者都是R-22的替代品R-407C预期将很快地替换R-22在空调设备中它的蒸发和冷凝压力接近R-22 com 然而用R-407C来替换R-22应该在和设备制造者商议之后才能进行至少润滑油和膨胀装置将需要更换在1998年第一个使用R-410A的空调设备的住宅在美国出现使用R-410A的系统运作中压力大约比R-22高50 表 com 因此R-410A不能够用于当作速冻制冷剂来替代 R-22R-410A系统利用特定的压缩机膨胀阀和热交换器来利用该制冷剂氨广泛地被在工业的冷却设备和氨水吸收式制冷中用它具有可燃性并且分毒性等级为B因此在商业建筑物中使用受到限制除非冷却设备的制造工厂独立于被冷却的建筑物之外作为制冷剂氨有许多良好的品质例如它有较高的比热和高的导热率它的蒸发焓通常比那普遍使用的卤化碳高6到8倍而且氨和卤化碳比较来看它能提供更高的热交换量而且它能用在往复式和离心式压缩机中天然制冷剂的使用例如二氧化碳 R-744 和碳化氢在空调和制冷系统中的使用正在研究之中二氧化碳能在高于传统的HCFCs或HFCs的压力下工作和在超过临界点的典型的空调设备中工作人们通常认为碳化氢制冷剂易燃且比较危险但它在传统的压缩机中和有的工业设备中都可以被使用R-290 丙烷都有接近R-22的工作压力并被推荐来替代R-22 Kramer 1991 目前在美国没有用二氧化碳或可燃的制冷剂的商业系统用于建筑部门31冷水机组1995年在美国冷水机组应用在至少4％的商用建筑中而且由于制冷机组通常安装在较大的建筑中在同一年里制冷机组冷却了多于28％的商用建筑的地板空间DOE1998在商用建筑中普遍采用五种型式的制冷机往复式螺杆式旋涡式离心式和吸收式前四种利用蒸汽压缩式循环来制得冷冻水它们的不同主要在于使用的压缩机种类的不同吸收式制冷机在吸收循环中利用热能典型的是来自蒸汽或燃料燃烧并利用氨－水或水－锂溴化物制得冷冻水32总的系统大约86％的制冷机和表所示的一样用在多台制冷机系统中Bitondo和Tozzi1999在冷冻水系统中建筑物的回水通过每个蒸发器循环流动在蒸发器中回水被冷却到合意的温度典型的为4～7℃－39～45℉然后冷冻水通过各设备传送到水－空气换热器在换热器中空气被冷冻水冷却和加湿在这个过程中冷水的温度升高然后必须回送到蒸发器中制冷机组是冷水机组水通过每个机组的冷凝器循环在冷凝器中水吸收了来自高压制冷剂的热量接着水用水泵打到冷却塔中水通过蒸发而降温冷却塔将在后一部分讲述冷凝器也可以是空冷式的在这种循环中冷凝器应是制冷剂－空气热交换器空气吸收来自高压制冷剂的热量制冷机组名义制冷量为30～18000kw8～5100tons在美国出售的大部分制冷机组是用电的利用蒸汽压缩制冷循环来制得冷冻水在设计中这种系统所使用的压缩机也有往复式螺杆式旋涡式和离心式一小部分的离心式制冷机利用内燃机或蒸汽机代替电来启动压缩机在建筑中所使用的制冷机组类型根据应用场所来确定对于大的办公室建筑或制冷机组需服务于多个建筑时通常使用离心式压缩机在所需制冷量小于1000kw280tons时使用往复式或螺杆式制冷机组较合适在小的应用场合若低于100kw30tons时使用往复式或旋涡式制冷机组33蒸汽压缩式制冷机四种电启动的蒸汽压缩式制冷机组的名义制冷量范围每种制冷机以所使用的压缩机类型来命名各种系统的制冷能力范围从最小的旋涡式30kw8tons到最大的离心式18000kw5000tons制冷机可使用HCFCsR22R123或HFCsR－134a制冷剂制冷机的效率通常用输入功用kw表示与制冷量用tons表示的比值表示1tons 的制冷量等于352kw或1200btu／h用这种方法衡量效率其数值越小越好离心式制冷机的效率最高而往复式是这四种类型中效率最低的表中所提供的效率是根据ASHRAE Standard30ASHRAE1995在稳定状态下测得满负荷时的效率这些效率中不包括辅助设备的能耗比如泵冷却塔的风机而这些设备可以增加006～。

暖通空调专业毕业设计外文翻译3

外文翻译（1）Refrigeration System Performance using Liquid-Suction Heat ExchangersS. A. Klein, D. T. Reindl, and K. BroWnellCollege of EngineeringUniversity of Wisconsin - MadisonAbstractHeat transfer devices are provided in many refrigeration systems to e xchange energy betWeen the cool gaseous refrigerant leaving the evaporator and Warm liquid refrigerant exiting the condenser. These liquid-suction or suction-line heat exchangers can, in some cases, yield improved system performance While in other cases they degrade system performance. Although previous researchers have investigated performance of liquid-suction heat exchangers, this study can be distinguished from the previous studies in three Ways. First, this paper identifies a neW dimensionless group to correlate performance impacts attributable to liquid-suction heat exchangers. Second, the paper extends previous analyses to include neW refrigerants. Third, the analysis includes the impact of pressure drops through the liquid-suction heat exchanger on system performance. It is shoWn that reliance on simplified analysis techniques can lead to inaccurate conclusions regarding the impact of liquid-suction heat exchangers on refrigeration system performance. From detailed analyses, it can be concluded that liquid-suction heat exchangers that have a minimal pressure loss on the loW pressure side are useful for systems using R507A, R134a, R12, R404A, R290, R407C, R600, and R410A. The liquid-suction heat exchanger is detrimental to system performance in systems using R22, R32, and R717.IntroductionLiquid-suction heat exchangers are commonly installed in refrigeration systems With the intent of ensuring proper system operation and increasing system performance.Specifically, ASHRAE(1998) states that liquid-suction heat exchangers are effective in:1) increasing the system performance2) subcooling liquid refrigerant to prevent flash gas formation at inlets to expansion devices3) fully evaporating any residual liquid that may remain in the liquid-suction prior to reaching the compressor(s)Figure 1 illustrates a simple direct-expansion vapor compression refrigeration system utilizing a liquid-suction heat exchanger. In this configuration, high temperature liquid leaving the heat rejection device (an evaporative con denser in this case) is subcooled prior to being throttled to the evaporator pressure by an expansion device such as a thermostatic expansion valve. The sink for subcoolingthe liquid is loW temperature refrigerant vapor leaving the evaporator. Thus, the liquid-suction heat exchanger is an indirect liquid-to-vapor heat transfer device. The vapor-side of the heat exchanger (betWeen the evaporator outlet and the compressor suction) is often configured to serve as an accumulator thereby further minimizing the risk of liquid refrigerant carrying-over to the compressor suction. In cases Where the evaporator alloWs liquid carry-over, the accumulator portion of the heat exchanger Will trap and, over time, vaporize the liquid carryover by absorbing heat during the process of subcooling high-side liquid.BackgroundStoecker and Walukas (1981) focused on the influence of liquid-suction heat exchangers in both single temperature evaporator and dual temperature evaporator systems utilizing refrigerant mixtures. Their analysis indicated that liquid-suction heat exchangers yielded greater performance improvements When nonazeotropic mixtures Were used compared With systems utilizing single component refrigerants or azeoptropic mixtures. McLinden (1990) used the principle of corresponding states to evaluate the anticipated effects of neW refrigerants. He shoWed that the performance of a system using a liquid-suction heat exchanger increases as the ideal gas specific heat (related to the molecular complexity of the refrigerant) increases. Domanski and Didion (1993) evaluated the performance of nine alternatives to R22 including the impact of liquid-suction heat exchangers. Domanski et al. (1994) later extended the analysis by evaluating the influence of liquid-suction heat exchangers installed in vapor compression refrigeration systems considering 29 different refrigerants in a theoretical analysis. Bivens et al. (1994) evaluated a proposed mixture to substitute for R22 in air conditioners and heat pumps. Their analysis indicated a 6-7% improvement for the alternative refrigerant system When system modifications included a liquid-suction heat exchanger and counterfloW system heat exchangers (evaporator and condenser). Bittle et al. (1995a) conducted an experimental evaluation of a liquid-suction heat exchanger applied in a domestic refrigerator using R152a. The authors compared the system performance With that of a traditional R12-based system. Bittle et al. (1995b) also compared the ASHRAE method for predicting capillary tube performance (including the effects of liquid-suction heat exchangers) With experimental data. Predicted capillary tube mass floW rates Were Within 10% of predicted values and subcooling levels Were Within 1.7 C (3F) of actual measurements.This paper analyzes the liquid-suction heat exchanger to quantify its impact on system capacity and performance (expressed in terms of a system coefficient of performance, COP). The influence of liquid-suction heat exchanger size over a range of operating conditions (evaporating and condensing) is illustrated and quantified using a number of alternative refrigerants. Refrigerants included in the present analysis are R507A, R404A, R600, R290,R134a, R407C, R410A, R12, R22, R32, and R717. This paper extends the results presented in previous studies in that it considers neW refrigerants, it specifically considers the effects of the pressure drops,and it presents general relations for estimating the effect of liquid-suction heat exchangers for any refrigerant.Heat Exchanger EffectivenessThe ability of a liquid-suction heat exchanger to transfer energy from the Warm liquid to the cool vapor at steady-state conditions is dependent on the size and configuration of the heat transfer device. The liquid-suction heat exchanger performance, expressed in terms of an effectiveness, is a parameter in the analysis. The effectiveness of the liquid-suction heat exchanger is defined in equation (1):Where the numeric subscripted temperature (T) values correspond to locations depicted in Figure 1. The effectiveness is the ratio of the actual to maximum possible heat transfer rates. It is related to the surface area of the heat exchanger. A zero surface area represents a system Without a liquid-suction heat exchanger Whereas a system having an infinite heat exchanger area corresponds to an effectiveness of unity.The liquid-suction heat exchanger effects the performance of a refrigeration system by in fluencing both the high and loW pressure sides of a system. Figure 2 shoWs the key state points for a vapor compression cycle utilizing an idealized liquid-suction heat exchanger on a pressure-enthalpy diagram. The enthalpy of the refrigerant leaving the condenser (state 3) is decreased prior to entering the expansion device (state 4) by rejecting energy to the vapor refrigerant leaving the evaporator (state 1) prior to entering the compressor (state 2). Pressure losses are not shoWn. The cooling of the condensate that occurs on the high pressure side serves to increase the refrigeration capacity and reduce the likelihood of liquid refrigerant flashing prior to reaching the expansion device. On the loW pressure side, the liquid-suction heat exchanger increases the temperature of the vapor entering the compressor and reduces the refrigerant pressure, both of Which increase the specific volume of the refr igerant and thereby decrease the mass floW rate and capacity. A major benefit of the liquid-suction heat exchanger is that it reduces the possibility of liquid carry-over from the evaporator Which could harm the compressor. Liquid carryover can be readily caused by a number of factors that may include Wide fluctuations in evaporator load and poorly maintained expansiondevices (especially problematic for thermostatic expansion valves used in ammonia service).（翻译）冷却系统利用流体吸热交换器克来因教授,布兰顿教授, , 布朗教授威斯康辛州的大学–麦迪逊摘录加热装置在许多冷却系统中被用到，用以制冷时遗留在蒸发器中的冷却气体和离开冷凝器发热流体之间的能量的热交换.这些流体吸收或吸收热交换器,在一些情形中，他们降低了系统性能, 然而系统的某些地方却得到了改善. 虽然以前研究员已经调查了流体吸热交换器的性能, 但是这项研究可能从早先研究的三种方式被加以区别. 首先，这份研究开辟了一个无限的崭新的与流体吸热交换器有关联的群体.其次，这份研究拓宽了早先的分析包括新型制冷剂。

空调工程设计英语

空调工程设计英语精选英文空调工程设计英语：Air Conditioning System Engineering DesignI. IntroductionIn today's rapidly evolving construction industry, the design of an efficient and sustainable air conditioning system is paramount. This document outlines the comprehensive engineering design for a new air conditioning system, focusing on meeting the specific requirements of the project while ensuring optimal performance, energy efficiency, and environmental friendliness.II. Project OverviewThe proposed air conditioning system is intended for a commercial office building located in a hot and humid climate. The building houses various offices, conference rooms, and common areas, with a total floor area of approximately 10,000 square meters. The system must provide comfortable indoor temperatures and humidity levels while minimizing energy consumption and noise levels.III. Design Criteria1. Temperature Control: Maintain indoor temperatures between 22°C and 26°C.2. Humidity Control: Maintain relative humidity levels between 40% and 60%.3. Air Quality: Ensure good indoor air quality by providing adequate ventilation and filtration.4. Noise Levels: Keep noise levels below 40 dB in office areas and 50 dB in commonareas.5. Energy Efficiency: Optimize system design for maximum energy savings.IV. System Design1. Air Conditioning Units: Select high-efficiency split-system air conditioners with variable refrigerant flow (VRF) technology. These units provide precise temperature and humidity control while minimizing energy usage.2. Ductwork: Design an efficient ductwork system with minimal bends and leaks to ensure optimal airflow and reduce energy losses.3. Outdoor Condensers: Locate outdoor condensers in a shaded and well-ventilated area to improve efficiency.4. Air Handling Units (AHUs): Install AHUs with high-efficiency filters and fans to maintain good indoor air quality and noise levels.5. Controls: Implement a sophisticated Building Automation System (BAS) to monitor and control the air conditioning system. This system should include temperature sensors, humidity sensors, and control valves to ensure precise temperature and humidity control.6. Energy Recovery Ventilators (ERVs): Install ERVs to recover energy from exhaust air and reduce the energy required for ventilation.V. Environmental Considerations1. Energy Efficiency: Use energy-efficient components and equipment to minimize energy consumption.2. Sustainability: Consider using renewable energy sources such as solar panels orgeothermal energy to further reduce energy usage.3. Environmentally Friendly Materials: Select materials that have low environmental impact and are recyclable or biodegradable.VI. Safety Measures1. Electrical Safety: Ensure all electrical components and wiring are properly grounded and protected against overcurrent and short circuits.2. Fire Safety: Install fire detectors and sprinkler systems in critical areas to mitigate the risk of fire.3. Maintenance Access: Provide adequate space and access for regular maintenance and repairs to ensure the system's reliability and longevity.VII. ConclusionThe proposed air conditioning system design meets the specific requirements of the project while incorporating the latest in energy efficiency and environmental sustainability. By using high-efficiency components and equipment, we aim to provide a comfortable indoor environment while minimizing energy consumption and environmental impact.中文对照翻译：空调系统工程设计一、简介在当今快速发展的建筑业中，gao效和可持续的空调系统的设计至关重要。

空调英语作文初中带翻译

However, there are also some drawbacks to air conditioning. One of the main concerns is the environmental impact of air conditioning systems, particularly their energy consumptionand greenhouse gas emissions. In addition, air conditioning can be expensive to install and maintain, and can also contribute to a phenomenon known as the "heat island effect", where urban areas become significantly warmer than rural areas due to the large number of air conditioning units and other heat-generating sources.
The main advantage of air conditioning is that it provides relief from the heat. In hot weather, air conditioning can make indoor spaces much more comfortable, allowing people to work, sleep, and relax without feeling sweaty and uncomfortable. Air conditioning can also improve indoor air quality by filtering out pollutants and allergens, which is especially beneficial for people with respiratory issues.

空调功能1000字英语作文

空调功能1000字英语作文英文回答：Air conditioning is a vital technology that provides comfort and improves indoor air quality in homes, offices, and other indoor spaces. It works by removing heat and humidity from the air, creating a cooler, more pleasant environment. Here's how an air conditioner works:Refrigeration cycle: Air conditioners use arefrigeration cycle to cool the air. The system consists of four main components: a compressor, a condenser, an expansion valve, and an evaporator. The refrigerant, whichis a special fluid that changes from liquid to gas and back, circulates through these components.Compressor: The compressor is the heart of the air conditioner. It compresses the refrigerant gas, increasing its pressure and temperature.Condenser: The compressed refrigerant gas then flows to the condenser, which is usually located outdoors. The condenser coils release heat into the outside air, cooling the refrigerant and turning it back into a liquid.Expansion valve: The liquid refrigerant passes through an expansion valve, which reduces its pressure and temperature. This causes the refrigerant to expand and evaporate.Evaporator: The expanded refrigerant flows to the evaporator, which is located inside the air handler. The evaporator coils absorb heat from the indoor air, cooling it. The refrigerant then evaporates and flows back to the compressor, completing the cycle.Air distribution: The cooled air is then distributed throughout the space by a fan. The fan may be located in the air handler or in a separate unit.Humidity control: Air conditioners also help to control humidity by removing moisture from the air. When the humidair passes over the cold evaporator coils, the water vapor condenses and is collected in a drain pan.Types of air conditioners: There are various types of air conditioners available, each with its own advantages and disadvantages:Window units: Window units are standalone units thatfit into a window frame. They are relatively inexpensive and easy to install, but they are not as efficient as other types of air conditioners and can be noisy.Central air conditioners: Central air conditioners consist of an outdoor unit and an indoor air handler. The outdoor unit houses the compressor and condenser, while the indoor unit circulates the cooled air. Central air conditioners are more efficient than window units and provide better temperature control, but they are more expensive to install and maintain.Split systems: Split systems are similar to central air conditioners, but they have a smaller outdoor unit and amore compact indoor air handler. Split systems are more flexible than central air conditioners and can be installed in spaces where a traditional central air conditioner would not fit.Portable air conditioners: Portable air conditionersare free-standing units that can be moved from room to room. They are less efficient than other types of air conditioners, but they are a good option for temporary cooling or for spaces that do not have central air conditioning.Benefits of air conditioning:Comfort: Air conditioners provide a comfortable indoor environment by cooling the air and removing humidity.Improved indoor air quality: Air conditioners help to improve indoor air quality by removing allergens, dust, and other particles from the air.Increased productivity: Studies have shown that airconditioning can increase productivity in offices and other workplaces.Reduced energy consumption: Modern air conditioners are highly efficient and can help to reduce energy consumption.Conclusion:Air conditioning is a vital technology that provides comfort, improves indoor air quality, and increases productivity. There are various types of air conditioners available, each with its own advantages and disadvantages. Choosing the right air conditioner for your needs will depend on factors such as the size of the space, the climate, and your budget.中文回答：空调的工作原理。

空调改造工程英语作文

空调改造工程英语作文Air Conditioning Renovation Project。

With the continuous development of society, people's living standards have been greatly improved. In order to create a comfortable living environment, many families have installed air conditioners. However, with the increase in electricity prices, the cost of using air conditioners has also increased. Therefore, it is necessary to carry out air conditioning renovation projects to reduce energy consumption and save costs.The air conditioning renovation project mainly includes the following aspects: optimizing the layout of air conditioners, improving the insulation of buildings, and replacing old air conditioning equipment with new and energy-saving ones.Firstly, optimizing the layout of air conditioners can effectively reduce energy consumption. The placement of airconditioners should be reasonable and scientific. The air outlet should be placed in a location where it can be evenly distributed. The air inlet should be placed in a location where it can be easily ventilated. In addition, the air conditioner should be placed in a location where it is not exposed to direct sunlight or strong winds, which can reduce the energy consumption of the air conditioner.Secondly, improving the insulation of buildings can also reduce energy consumption. The insulation of walls, roofs, and floors should be improved to prevent heat lossin winter and heat gain in summer. The use of insulation materials with good insulation performance can effectively reduce the energy consumption of air conditioners.Finally, replacing old air conditioning equipment with new and energy-saving ones is an effective way to reduce energy consumption. The new air conditioning equipment has higher energy efficiency and lower energy consumption. In addition, the use of intelligent control technology can also effectively reduce energy consumption.In conclusion, the air conditioning renovation project is an important measure to reduce energy consumption and save costs. It can not only create a comfortable living environment but also contribute to the protection of the environment. Therefore, we should actively carry out air conditioning renovation projects to achieve energy conservation and emission reduction.。

空调上的作文英语

空调上的作文英语Title: The Impact of Air Conditioning on Modern Living。

Introduction:Air conditioning has become an integral part of modern life, revolutionizing our comfort levels in bothresidential and commercial spaces. Its invention has notonly changed our physical environment but has alsoinfluenced our daily routines, productivity, and even societal structures. In this essay, we will delve into the multifaceted impact of air conditioning on modern living.Enhanced Comfort and Productivity:One of the most obvious benefits of air conditioning is the enhancement of comfort levels. Whether it's scorching heat or freezing cold outside, air conditioning systemsallow us to maintain a comfortable indoor temperature year-round. This comfort directly contributes to increasedproductivity, as individuals can focus better in a controlled environment. Studies have shown that workplaces with optimal temperature control experience higher employee satisfaction and efficiency.Health and Well-being:Beyond comfort, air conditioning also plays a significant role in maintaining health and well-being. In regions with extreme climates, air conditioning helps prevent heat-related illnesses such as heat stroke and dehydration during hot summers. Moreover, air filtration systems within AC units improve indoor air quality by removing pollutants, allergens, and airborne pathogens, thus reducing the risk of respiratory issues and allergies.Social Dynamics and Economic Impact:The widespread adoption of air conditioning has reshaped social dynamics and economic structures. In the past, cities in warmer climates experienced seasonal migrations as people sought relief from the heat. However,with the prevalence of air conditioning, these cities have become more habitable year-round, leading to demographic shifts and urbanization. Additionally, industries such as tourism, hospitality, and entertainment have flourished in regions where air conditioning has made it comfortable for visitors.Energy Consumption and Environmental Concerns:While air conditioning provides numerous benefits, it also poses challenges, particularly concerning energy consumption and environmental impact. Air conditioning accounts for a significant portion of electricity usage in many countries, especially during peak summer months. The reliance on fossil fuels to generate electricity for cooling purposes contributes to greenhouse gas emissions and exacerbates climate change. Therefore, there is a growing emphasis on developing energy-efficient cooling technologies and promoting sustainable cooling practices to mitigate environmental damage.Technological Advancements and Innovation:Advancements in air conditioning technology have led to more energy-efficient and environmentally friendly systems. Innovations such as variable refrigerant flow (VRF) systems, evaporative cooling, and smart thermostats allow forprecise temperature control and reduced energy consumption. Furthermore, ongoing research focuses on alternative refrigerants with lower global warming potential, as wellas integrating renewable energy sources such as solar power into air conditioning systems.Cultural Perceptions and Lifestyle Changes:The availability of air conditioning has influenced cultural perceptions and lifestyle choices. In regionswhere air conditioning is widespread, outdoor activities during the hottest parts of the day have become less common, as people prefer to stay indoors where it's cooler. Additionally, the expectation of air conditioning in public spaces such as malls, restaurants, and transportation has become ingrained in modern society, shaping consumer preferences and urban planning decisions.Conclusion:In conclusion, air conditioning has profoundly impacted modern living in various ways, from enhancing comfort and productivity to shaping social dynamics and economic structures. While it offers undeniable benefits, it also presents challenges related to energy consumption and environmental sustainability. Moving forward, it is imperative to strike a balance between enjoying the comforts of air conditioning and mitigating its negative consequences through technological innovation, energy conservation, and responsible usage practices.。

空调上的作文英语

空调上的作文英语Title: The Significance of Air Conditioning in Modern Life。

Air conditioning has become an indispensable aspect of modern life, offering not just comfort but also playing a crucial role in various aspects of our daily existence. From maintaining optimal indoor temperatures to preserving perishable goods, the significance of air conditioning cannot be overstated.Firstly, air conditioning contributes significantly to enhancing human comfort. In regions with extreme climates, such as scorching summers or freezing winters, air conditioning systems regulate indoor temperatures, creating a pleasant environment for occupants. This comfort is not only conducive to productivity but also essential for health, as excessive heat or cold can lead to various adverse health effects. Therefore, air conditioning ensures that individuals can work, study, and rest comfortablyirrespective of the outdoor weather conditions.Moreover, air conditioning plays a vital role in promoting public health and well-being. By controlling indoor humidity levels and filtering out pollutants, air conditioning systems help improve indoor air quality. Thisis particularly beneficial in urban areas where pollution levels can be high, leading to respiratory problems andother health issues. Additionally, in healthcare facilities, air conditioning is essential for maintaining sterile environments, preventing the spread of airborne pathogens, and facilitating the recovery of patients.Furthermore, air conditioning is indispensable in various commercial and industrial settings. In sectors such as food production, pharmaceuticals, and data centers, maintaining specific temperature and humidity levels is critical for preserving product quality and ensuring operational efficiency. For example, refrigeration systemsin supermarkets and warehouses keep perishable goods fresh, reducing food waste and supporting food supply chains. Similarly, in manufacturing processes, precise temperaturecontrol provided by air conditioning systems is essential for maintaining product quality and meeting regulatory standards.In addition to its practical applications, air conditioning also has broader societal implications. Access to air conditioning is often viewed as a marker of socio-economic development, with disparities in access reflecting underlying inequalities. In many parts of the world, vulnerable populations, including the elderly, children, and low-income individuals, may lack access to adequate cooling, exposing them to heat-related risks during heatwaves. Addressing these disparities requires not only improving infrastructure but also implementing policies to ensure equitable access to air conditioning services.However, alongside its benefits, air conditioning also presents environmental challenges. The energy consumption associated with air conditioning systems contributes to greenhouse gas emissions and exacerbates climate change. Additionally, the refrigerants used in many air conditioning units are potent greenhouse gases themselves,further contributing to global warming. Addressing these environmental impacts requires a shift towards more energy-efficient technologies, as well as the adoption of alternative refrigerants with lower global warming potential.In conclusion, air conditioning plays a multifaceted role in modern life, offering comfort, promoting health, and supporting various economic activities. However, its widespread adoption also poses environmental challengesthat need to be addressed. By recognizing the significance of air conditioning and implementing sustainable practices, we can ensure that it continues to enhance our lives while minimizing its environmental footprint.。

高中英语作文Air-conditioner空调

高中英语作文|Air-conditioner 空调高中英语作文|Air-conditioner 空调无论是在学校还是在社会中，大家或多或少都会接触过作文吧，作文是一种言语活动，具有高度的综合性和创造性。

那么问题来了，到底应如何写一篇优秀的作文呢？以下是小编精心整理的高中英语作文|Air-conditioner 空调，供大家参考借鉴，希望可以帮助到有需要的朋友。

Air-conditioner is a kind of machine used at home, at the office or in the shopping hall and any other places.空调是一种供居家，办公，商场以及其他场所使用的电器。

It is designed to change the air temperature and humidity within an area.它是用来改变某一区域内的空气温度和湿度的。

Air-conditioner is used for cooling and sometimes heating depending on the air properties at a given time to create more favourable conditions.空调是用来降温或升温的.，它是根据特定时间的空气性质来创造更适合的条件的。

It's frequently used during in the hot summer. In the north of China, it's used for heating in the cold winter.空调在炎热的夏天使用频率最高。

在中国的北方，空调在寒冷的冬天用来升温。

I like air-conditioner in the summer days and nights.夏天我喜欢日夜吹空调。

Once it turns on, the cool air will spread all over the room and I don't want to leave there anymore.只要一打开它，凉快的空气就会散布整个房间，我就再也不想离开房间了。

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J.M. Choi, Y.C. Kim
Received 28 February 2பைடு நூலகம்01
*
Department of Mechanical Engineering, Korea University, Anam-dong, Sungbuk-ku, Seoul 136-701, South Korea
* Corresponding author. Tel.: +82-2-3290-3366; fax: +82-2-921-5439. E-mail address: yongckim@korea.ac.kr (Y.C. Kim).
0360-5442/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 3 6 0 - 5 4 4 2 ( 0 1 ) 0 0 0 9 3 - 7
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J.M. Choi, Y.C. Kim / Energy 27 (2002) 391–404
pump will degrade performance and deteriorate system reliability [1,2]. Therefore, the heat pump should be charged with an optimum amount of refrigerant in order to operate with high performance over its lifetime. However, it is difﬁcult to determine the optimum charge due to its dependency on operating parameters and expansion devices of the heat pump. Proper selection and operation of an expansion device is the most important factor from a standpoint of capacity and system control. Expansion devices that have been widely used in heat pumps such as capillary tubes, short tube oriﬁces, and thermostatic expansion valves (TXV) are being gradually replaced with electronic expansion valves (EEVs), due to an increasing focus on comfort, energy conservation with environmentally safe refrigerants and application of a variable speed compressor [3,4]. Each expansion device may regulate refrigerant ﬂow differently under improper or proper charging conditions. Thus, it is necessary to have selection and design guides for the EEV to achieve proper system control and high performance. Nowadays, most heat pump systems are designed to have a small receiver or even no receiver, to make compact systems and reduce refrigerant charge amounts. Generally, a system with a small receiver can cause ﬂash gas in a liquid line, and often produces instability in system operation and ﬂow control [5]. Therefore, adequate matching between refrigerant charge and an expansion device is essential. Houcek and Thedford [1] conducted tests at three charging conditions: Ϫ23%, nominal, and +23% of nominal charge. They showed that the system capacity and energy efﬁciency ratio (EER) were reduced at outrange of nominal charge conditions. Stoecker et al. [2] compared the performance of an air conditioner with a capillary tube and TXV when the system was charged based on the manufacturer’s guidelines. The test results showed that the seasonal coefﬁcient of performance (COP) with the TXV was higher than that with the capillary tube. Domingorena [6] demonstrated that the heating capacity and COP became lower with a reduction of refrigerant charge. Farzard and O’Neal [7,8] also reported refrigerant charging effects on the performance of a heat pump with a capillary tube, short tube oriﬁce, and TXV. It was found that the TXV system showed a small variation of the COP according to refrigerant charge but a strong dependence on the outdoor temperature. Most of the previous studies related to effects of refrigerant charge were focused on the heat pump with capillary tubes, short tube oriﬁces, and TXVs. Due to several beneﬁts of EEV such as a wide coverage of ﬂow rate, precise control and reduction of superheat hunting, the EEV has been widely applied in inverter type heat pumps as well as multi-type heat pump systems. However, studies on control characteristics of the EEV by considering the refrigerant charge are very limited in the open literature. A comprehensive study on the effects of refrigerant charge in a heat pump having an EEV as an expansion device is required, to enhance system performance and to achieve proper capacity modulation. In this study, a water-to-water heat pump is tested to investigate the effects of refrigerant charge on performance in a steady state, cooling mode operation with expansion devices of capillary tube and EEV. The characteristics of the heat pump with the EEV are compared with those with the capillary tube in terms of refrigerant charge. In addition, the effects of outdoor conditions are analyzed.
Abstract For inverter heat pumps and multi-type heat pumps, conventional expansion devices such as capillary tubes, short tube oriﬁces, and thermostatic expansion valves (TXVs) are being gradually replaced with electronic expansion valves (EEVs) because of the increasing focus on comfort and energy conservation. In this study, the effects of off-design refrigerant charge on the performance of a water-to-water heat pump are investigated by varying refrigerant charge amount from Ϫ20% to +20% of full charge in a steady state, cooling mode operation with expansion devices of capillary tube and EEV. The characteristics of the heat pump with an EEV are compared with those with a capillary tube. The capillary tube system is more sensitive to off-design charge as compared with the EEV system. Cooling capacity and COP of the EEV system show little dependence on refrigerant charge, while those are strongly dependent on outdoor conditions. In general, for a wide range of operating conditions the EEV system shows much higher performance as compared with the capillary tube system. The performance of the EEV system can be optimized by adjusting the EEV opening to maintain a constant superheat at all test conditions. 2002 Elsevier Science Ltd. All rights reserved.

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空调工程设计英语

空调英语作文初中带翻译

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空调改造工程英语作文

空调上的作文英语

空调上的作文英语

高中英语作文Air-conditioner空调

冷水机组毕业设计外文翻译

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