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    2 ENG . KHALED OSSAILY

    E-mail: [email protected]

    Chiller Efficiency Chiller efficiency is measured in Kilowatts per ton (Kw/Ton) of coolingproduced. The higher the Kw/Ton, the lower the heat transfer efficiency andthe higher the cost to produce a ton of cooling.

    Chiller Log Sheet A sheet on which specific chiller readings are documented.

    Chiller Manufacturer The company that built the chiller, i.e., York, Trane, Carrier, McQuay, etc.The manufacturer name is typically prominently displayed on the chillercontrol panel or technical documentation.

    Chiller Stall A chiller stalls when the refrigerant is no longer moving through thecompressor and there is no cooling effect. All shaft work is being convertedinto heat in the compressor that may lead to permanent damage.

    Chiller Startup The chiller manufacturers recommendation on startup including pre-heating

    the compressor oil temperature prior to chiller startup.Chiller Surge When the refrigerant flows backwards through the compressor wheel every

    few seconds until the pressure builds up and the refrigerant moves forwardagain. This is even more dangerous than a stall because it reverses loads ofthrust bearings in the compressor shaft.

    Chiller Vane

    (Inlet Guide Vanes)Chiller vanes are used to control the capacity of the compressor. As the inletguide vanes start to close, they change the gas entry angle to the impellerand reduce gas flow and compressor capacity. As the vanes near the closedposition, they throttle the refrigerant flow.

    Closed Loop

    The evaporator side of the chiller system, closed to the atmosphere.

    Compressor A mechanical device where the refrigerant is compressed from a lowerpressure and lower temperature to a higher pressure and higher temperature.The compressor maintains a low pressure in the evaporator by continuallyremoving refrigerant vapors. This low pressure, low temperature vapor isthen compressed into a higher pressurize, hot refrigerant vapor which leavesthe compressor and travels to the condenser. The motor in the compressor isthe main consumer of energy in the chiller system. The energy used by thecompressor is dependent on the pressure increase. The head pressure dividedby the suction pressure or the condenser pressure divided by the evaporator

    pressure expresses this. If the compressor operates out of its original design,it will effect the energy consumption.

    CompressorErosion/Corrosion

    Damage to the bearings and impeller caused by poor lubrication, low oillevels or operating conditions such as liquid refrigerant carryover into thecompressor system.

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    E-mail: [email protected]

    Compressor Motor Amps The energy used to power the refrigerant cycle in a chiller system. The inputenergy is dependent upon the pressure increase in the compressor. The headpressure divided by the suction pressure or the condenser pressure dividedby the evaporator pressure determines it.

    Compressor Oil

    TemperatureCompressor oil temperature is the temperature of the oil in the compressorbearing lubrication system. This temperature is predetermined bymanufacturers specifications.

    Condensation The process a vapor goes through to change phase from vapor to a liquid.

    Condenser Heat exchanger where the system heat is rejected and the refrigerantcondenses into a liquid. The condenser is where hot pressurized refrigerantvapors in the compressor are cooled and liquefied by cooling tower watercirculating through the tubes of the condenser. The condenser side is

    commonly referred to as the open recirculation system or open loop.

    Condenser Delta P The pressure drop between the suction side and the discharge side of achiller barrel. This pressure drop can be measured against known valuesfrom tables/charts to determine water flow through the chiller barrel. Delta Pis dependant on chiller tube ID and tube length.

    Condenser Delta T The temperature difference between the entering and leaving water throughthe chiller barrel. i.e., the entering temperature is 85F and the leavingtemperature is 95F then the delta T would be 10.

    Condenser Water GPM(Gallons Per Minute)

    The velocity of the condenser water measured in gallons per minute. All

    chiller condensers have a manufacturers design GPM flow rate.Condenser Pressure The head pressure produced in the condenser dependent on the entering

    condenser water temperature and the saturated refrigerant temperature. Thecondenser pressure can affect the refrigerant cycle and heat transfer. Thepressure correlates to saturated refrigerant temperature on apressure/temperature chart for each refrigerant type.

    Condenser Refrigerant

    Approach Temperature The refrigerant temperature minus the leaving water temperature. Therefrigerant temperature can be determined by locating the condenser (head)pressure on a pressure/temperature chart, or if the chiller control panelprovides this information.

    Condenser Water The open recirculating system connects the chiller condenser to the coolingtower system and the atmosphere. Condenser water is subject toevaporation, debris/contamination, fouling/scaling and microbio growth.

    Conditioned Fluid The fluid being acted upon by the working fluid. Example: in an airconditioning system the air is conditioned by the refrigerant (refrigerant isthe working fluid).

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    E-mail: [email protected]

    Constant Speed Drive Constant speed drives are the most common type of chiller compressormotor. They have limited ability to adjust speed based on part loadconditions.

    Contamination Any foreign object or substance not normally found in a specific location.

    Cooling Tower Where the process of heat exchange occurs by evaporation in the openrecirculating system. The cooling tower system includes tower fans, plenum,drift eliminators, fill, levelers, hot deck and cold basin. All cooling towershave a design rated delta temperature.

    Cooling TowerApproach Temperature

    The difference between the leaving water temperature and the entering airwet bulb.

    Cooling Tower Fan Fan system designed to remove the heat generated by the open recirculating

    system through evaporation.Cooling Tower Fill Designed to brake up the circulating water into smaller particles or a thin

    film. This increases the surface area of the water to enhance evaporation andheat removal.

    Cooling Tower/Condenser

    SystemThe cooling tower system includes tower fans, plenum, drift eliminators, fill,levelers, hot deck and cold basin combined with the condenser barrel andpiping making up the open loop or open recirculating system.

    Corrosion The decay and loss of a metal due to a chemical reaction between the metaland its environment. It is a transformation process in which the metal passesfrom its elemental form to a combined (or compound) form.

    Cost of Blowdown The total cost of water sent to drain/sewer, typically determined on a per1,000 gallon basis. This value can be found on the water and sewer utilitybill or from the utility company.

    Cost of Kw The cost of electricity charged by the electric and is typically $0.04 to $0.15per kilowatt depending on geographic location.

    Cost of Makeup The total cost of water added to the condenser/cooling tower system,typically determined on a per 1,000 gallon basis. This value can be found onthe water and sewer utility bill or from the utility company.

    CPLV Calculated Part

    Load Value

    The calculated Kw/Ton derived from the effect of part load and enteringcondenser water temperature on the chiller when compared to full loaddesign.

    Dead Leg A static condition that exists over a period of time in equipment or systemthat has no water flow. This condition is usually associated with lay-up andcan promote the growth of microbes and corrosion.

    Debris Anything the environment can introduce that is washed out by the toweroperations, i.e., dirt, trash, chip scale flash corrosion, bugs, broken towerfill, broken tower wood, plastic, etc.

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    E-mail: [email protected]

    Delta P The pressure drop between the discharge side and the suction side of achiller barrel. This pressure drop can be measured against design valuesprovided by the chiller manufacturer or previously developed charts by plantpersonnel to determine water flow through the chiller barrel.

    Delta T The temperature difference between the entering and leaving water throughthe chiller barrel, i.e., entering temperature is 85F, leaving temperature is95F = delta T10F. If the actual water flow is known, delta P coulddetermine a problem if the actual delta P does not match the current waterflow.

    Design Amps (Full Load) The maximum amp load on the chiller. This information can be found in thechiller technical documentation.

    Design Condenser Delta T The temperature difference between the entering and leaving water through

    the chiller barrel when the chiller is running at full load, i.e., the enteringtemperature is 85F and the leaving temperature is 95F then the delta Twould be 10. Modern high efficiency chillers are designed to run at 9.4Fdelta T at 3gpm/ton.

    Design CondenserRefrigerant Approach

    Temperature

    The difference between the condenser water out temperature and thecondenser leaving refrigerant temperature at design full load. Thisinformation can be found in the chiller technical documentation.

    Design Condenser Water

    GPMBelow is a list of design GPM ratings based on the chiller design delta T.- Entering Water Temperature: 85F- Delta T Range: 10-20F

    - Normal delta T: 10F- 3.0 GPM/Ton @ 10F delta T- 2.5 GPM/Ton @ 12F delta T- 2.0 GPM/Ton @ 15F delta T- 1.5 GPM/Ton @ 20F delta T- 5,000 Btuh/GPM @ 10F delta T- 6,000 Btuh/GPM @ 12 F delta T- 7,500 Btuh/GPM @ 15F delta T- 10,000 Btuh/GPM @ 20F delta T- ARI Condenser Fouling Factor: 0.00025 Btu/Hr.Ft2.F

    Design Entering CondenserWater Temperature The design entering condenser water temperature is typically 85F based onARI standards for chillers commissioned after 1989. This information canbe found in the chiller technical documentation.

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    E-mail: [email protected]

    Design Evaporator Chill

    Water GPMBelow is a list of design GPM ratings based on the chiller design delta T.- Leaving Water Temperature: 42-46F- 10-20F delta T- 2.4 GPM/Ton @ 10F delta T- 2.0 GPM/Ton @ 12F delta T- 1.5 GPM/Ton @ 16F delta T- 1.2 GPM/Ton @ 20F delta T- 5,000 Btuh/GPM @ 10F delta T- 6,000 Btuh/GPM @ 12F delta T- 8,000 Btuh/GPM @ 16F delta T- 10,000 Btuh/GPM @ 20F delta T- ARI Evaporator Fouling Factor: 0.00010 Btu/Hr.Ft2.F- Chilled Water Flow Range: Chiller Design Flow 10%- Chiller Tube Velocity for Variable Flow Chilled Water:

    - Minimum Flow: 3.0 FPS- Maximum Flow: 12.0 FPS

    Design Evaporator Delta T The temperature difference between the entering and leaving water throughthe chiller barrel when the chiller is running at full load, i.e., the enteringtemperature is 54F and the leaving temperature is 42F then the delta Twould be 12.

    Design Evaporator

    Refrigerant ApproachTemperature

    The difference between the evaporator chill water out temperature and theevaporator leaving refrigerant temperature at design full load. Thisinformation can be found in the chiller technical documentation.

    Design Full Load Design refers to full load conditions. Full load is a chiller running at 100%load capacity, 85F ECWT, 42-46F leaving chill water temperature and isthe rating of the manufacturer.

    Design Full Load Amps The maximum amp load on the chiller. This information can be found in thechiller technical documentation.

    Design Kw/Ton The Kw used to produce one ton of cooling when the chiller is running atfull load design (ex: 0.6). This information can be found in the chillertechnical documentation.

    Design Specifications Manufacturer tested specification when determining design to actual

    operations. This includes the chiller, cooling tower, air handlers, etc. toensure expected performance of the equipment.

    Digital Manometer Measures positive and negative air pressures in ducts, from room to room,and for taking traverses.

    Distribution Holes

    Holes in the hot deck of a cooling tower designed to evenly distribute thewater flow over the tower fill below.

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    E-mail: [email protected]

    Drift Entrained water droplets leaving the tower system. If the drift is severe,caused by missing or damaged drift eliminators, it can increase corrosion tothe fan components.

    Drift Eliminator A device that removes entrained water droplets (drift) from air leaving thetower system.

    Dry Bulb The ambient outside temperature.

    ECWT Entering Condenser Water Temperature

    Emulsification The entrainment of one substance into another, i.e., oil in water or oil inrefrigerant.

    Energy Balance Energy cannot be created or destroyed during heat transfer; therefore theamount of energy leaving the source must equal the amount reaching the

    sink.

    Entering Condenser Water

    TemperatureEntering condenser water temperature is the temperature of water enteringthe condenser.

    Enthalpy The quantity of internal energy of a body plus the product of its volume andpressure.

    Erosion The group of natural processes, including weathering, dissolution, abrasion,corrosion, and transportation, by which material is worn away.

    Evaporation The process a liquid goes through to change phase from a liquid to a vapor.

    Evaporator Heat exchanger where the system heat is absorbed and the refrigerantevaporates into a gas. By continually pulling refrigerant vapor out of theevaporator headspace, low pressure can be maintained causing therefrigerant to evaporate rapidly. Evaporation cools the refrigerant. This coldrefrigerant produces chilled water by heat transfer. The evaporator side iscommonly referred to as the closed loop system (chill water).

    Evaporator Chill Water

    GPM (Gallons per minute)The gallons of chill water going through the evaporator per minute.

    Evaporator Delta P The pressure drop between the suction side and the discharge side of achiller barrel. This pressure drop is measured against known values to

    determine the water flow GPM through the chiller barrel. Delta P isdependant on chiller tube ID and tube length.

    Evaporator Delta T The temperature difference between the entering and leaving water throughthe chiller barrel. i.e., the entering temperature is 54F and the leavingtemperature is 42F then the delta T would be 12.

    Evaporator Fouled

    and/or ScaledA film or compound, which attaches to the internal tube surface, impedingheat transfer and lowering efficiency.

    Evaporator Refrigerant The leaving water temperature minus the refrigerant temperature. The

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    E-mail: [email protected]

    Approach Temperature refrigerant temperature can be determined by locating the evaporator(suction) pressure on a pressure/temperature chart, or if the chiller controlpanel provides this information.

    Evaporator Leaving

    Refrigerant TemperatureThe temperature of the saturated leaving refrigerant is at prior to leaving theevaporator in the refrigerant cycle.

    Evaporator Pressure A vacuum measured in inches of Hg (mercury) for low-pressure chillers anda positive pressure (psig) for high-pressure chillers. This vacuum/pressurecorrelates to refrigerant temperature on a pressure/temperature chart for eachrefrigerant type.

    Evaporator Refrigerant

    LevelThe level of the liquid refrigerant in the evaporator barrel.

    Fan A device for producing a current of air in the cooling tower used to removeheat from the condenser tower system.

    Flow Rate The quantity of fluid in motion per a unit of time. Flow rate is expressed inmass per unit time or volume per unit time.

    Flute Allows the transfer of liquid refrigerant from the condenser back to theevaporator.

    Flute Frosting A problem associated with rapid movement of liquid refrigerant at lowtemperatures from the condenser to the evaporator, causing frost to form onthe flute.

    Fouled Tubes Debris or substance which impedes flow or heat transfer. Fouling can becaused by trash, chip scale flash corrosion, microbio, etc.

    Free Oil Free or floating oil on top of a liquid with a higher specific gravity.

    Full Load Design Design refers to full load conditions. Full load is a chiller running at 100%load capacity, 85F ECWT, 42-46F leaving chill water temperature and isthe rating of the manufacturer.

    Gasket Any of a wide variety of seals or packings used between matched machineparts or around pipe joints to prevent the escape of a gas or fluid.

    Gauge An instrument or device for measuring, indicating or comparing a physical

    characteristic, i.e., temperature or pressure.GPM Gallons Per Minute

    Heat When energy is added to an object or location, the motion of the moleculesincreases causing them to collide more frequently. The motion energy isconverted into heat during the collisions. As more collisions occur more heatis released and the temperature of the object or location increases.

    Heat Index The heat index is the combination of actual outside air temperature plus theaffect of relative humidity to give an apparent temperature.

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    Heat Exchanger Device that provides a practical means for the working fluid to heat or coolthe conditioned fluid efficiently with out the two fluids mixing.

    Heat of Rejection(Heat of Expansion)

    The amount of heat rejected by the refrigerant in the condenser, whichincludes compressor heat.

    Heat Sink Object or location that is at a lower temperature than the heat source andreceives the energy from the source.

    Heat Source Object or location that is at a higher temperature than other objects orlocations.

    Heat Transfer The movement of energy as heat moving from a heat source to a heat sink.

    Heat Transfer Coefficient A proportionality constant in the heat transfer rate equation derived from theconditions of the fluid motion, the tube or fin surface geometry, and other

    thermodynamic properties.

    Heat Transfer Efficiency The ability of heat to transfer from one substance to another.

    Heat Transfer Fluid Any gas or liquid used by heat exchangers to transfer heat.

    Heat Transfer Rate Amount of energy that is moved from the heat source to the sink per anamount of time. Usually stated as Btu/hr in the English measurement systemand Watts (Joules per second) in the Metric system.

    High Pressure Chiller A chiller that operates in a positive pressure for both the evaporator andcondenser (measured in psig). Some high-pressure refrigerants include R-12,R-22, R-134a and R500.

    Hot Deck The top deck of the cooling tower where the condenser water returns to thetower prior to be cooled by evaporation, also referred to as the hot basin.

    Hot Deck Distribution Holes Holes in the hot deck that distribute the flow of returning condenser waterevenly across the tower fill.

    Hot Gas Piping (Piping) A means of recirculating hot discharge refrigerant back into the evaporator.The refrigerant must pass through a pressure-reducing device (hot gasbypass valve). The purpose of hot gas bypass is to maintain a minimum gasvolume flow rate through the compressor to avoid surging or stalling duringlow load conditions. A disadvantage is that the work of compression on the

    recirculated refrigerant does not generate any refrigeration effect.

    Hot Wire AnemometerMeasures air velocity in grilles, filters, coils and ducts.

    IPLV Integrated Part

    Load ValueA single number, part-load efficiency indicator calculated using the ARImethod at standard rating conditions. Introduced in ARI Standard 550-1986,the definition of IPLV was changed in ARI Standard 550/590-1998 to moreclosely reflect actual operating experience found in the field for a singlechiller.

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    E-mail: [email protected]

    Kw/ton A kilowatt (Kw) is a measure of electrical energy. A ton is a measure ofcooling and is defined as 12,000 BTU of cooling per hour.

    Laminar Flow Smooth undisturbed flow of a fluid.

    Latent Heat Heat given off or absorbed during phase change (condensation, evaporation,solidification, melting, or sublimation).

    Lay-up The process of winterizing a tower or condenser system when not in use.

    Legionella A bacterium of the genus legionella, especially pneumophila, that can causeLegionnaires disease - an acute, sometimes fatal respiratory disease causedby and characterized by severe pneumonia, headache, and a dry cough.

    Liquid Refrigerant The compressor coolant used in the refrigerant cycle of a chiller for heattransfer.

    Liquid Refrigerant Stacking This condition occurs can be caused by mechanical failure or low headpressure in the condenser and evaporator caused by low condenser watertemperature.

    Liquid Piping Refrigerant piping from the condenser outlet to the evaporator inlet.

    Load Amp load is compared to full load and the percentage value equals the loadof the chiller. Actual amps divided by full load amps is the percentage offull load design.

    Load Swing A large or radical change in cooling load requirements, i.e., weather orbuilding operations requirements.

    Log Mean Temperature

    DifferenceA specialized average temperature difference used to determine the heattransfer rate.

    Low Pressure Chiller A chiller that operates the evaporator in a vacuum, measured in inches of Hg(mercury). In some cases relating to entering condenser water temperature,the condenser may also operate in a vacuum. Some low-pressure refrigerantsinclude R-11, R-113, R-114, R-123.

    Maintenance Practices An organized schedule of chiller and plant maintenance.

    Microbe An organism of microscopic or ultramicroscopic size.

    Non-Condensable Gasses(Air)

    Air that enters the evaporator through a vacuum leak and migrates to thecondenser (in low-pressure chillers only). This affects the condenser headpressure, condenser refrigerator approach temperature and condenser heattransfer efficiency.

    NPLV Non-standard Part

    Load ValueA single number, part-load efficiency indicator calculated using the ARImethod referenced to rating conditions other than ARI standard. The 1998standard adopted NPLV for situations when a single chiller is not intendedto operate at standard ARI rating conditions.

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    Oil Used as the lubricant in the compressor system to lubricate and protectbearings, shaft, etc.

    Oil Analysis Tests used to determine impurities and the ability of the oil to lubricate.

    Oil Change Interval The length of time between oil changes, determined by hours of operation,oil analysis, etc.

    Oil Entrainment Entrainment is another term for flow. This term is primarily used toreference the flow of oil through the system to the return.

    Open Loop The condenser/tower side of the chiller system, open to the atmosphere.

    Operating Conditions The values of temperature, flow rate, and pressure of the heat transfer fluidsas they enter and leave the heat exchanger. Used to determine the heattransfer rate for the heat exchanger.

    Part Load Chiller load conditions below full load design. Most chillers operate at partload ~99% of the time.

    Plate Exchanger A heat exchanger used to create free cooling (not using a compressor orrefrigerant to transfer heat) by running colder tower water over stainlesssteel plates which transfers heat between the closed loop to the open loop.

    Power Factor The ratio of actual power (Kw) to apparent power (kVA). Most centrifugalmotors have a power factor between 0.87 and 0.91. Additional capacitorscan be added to raise the power factor to a practical limit of 0.95. In thetable below, the closer the length of the kVA line is the the kW line the

    more efficient the user of the energy.

    Pressure Drop Amount of reduction in the pressure of a fluid between the entering andleaving pressures. The pressure drop in a chiller is dependant upon the tubeID of the tube bundle and its length. Rough surfaces or objects that are in theflow path can cause reduced pressure.

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    Pressure Gauge An instrument that measures pressure in psig, psid or psia depending on thecircumstances.

    Primary Surface Area The area that contains the working heat transfer fluid. Usually the tubes of afinned/tube heat exchanger.

    Pump A device used to circulate fluid from one location to another.

    Pump CurveThe design capacity of a pumps ability to circulate fluid.

    Pump Curve CalibrationA flow test to determine the capacity of a pumps ability to circulate fluid.

    Pressure The application of force to something by something else in direct contact

    with it.Pressure Drop The reduction in pressure between a fluid entering and leaving a closed

    system.

    Pretreatment The removal of oil and grease from new piping and chillers to ensuremaximum heat transfer. It should also lay down a passivating film to preventflash corrosion and in some cases, white rust.

    Pumpout System Pumpout systems consist of a storage tank large enough to hold the chillersentire refrigerant charge and a refrigerant pump/compressor to move therefrigerant from the chiller to the pumpout tank and back again. Its primarypurpose is for servicing the chiller.

    Purge Unit Removes non-condensable gasses (air) from the condenser barrel of thechiller. Required on all low-pressure chillers only.

    Quality The ratio of vapor mass to total mass of a substance at the substance'ssaturation temperature and pressure.

    RAT Refrigerant Approach Temperature

    Refrigerant The mechanism used by the chiller, which performs heat transfer byconverting from liquid to gas and gas to liquid at various pressures andtemperatures. Common refrigerants used in commercial HVAC are R-11, R-12, R-22, R-113, R-114, R-123, R-134a, R-500.

    Refrigerant Analysis Laboratory analysis of a refrigerant sample to determine contamination,typically oil or moisture.

    Refrigeration Effect The amount of heat absorbed by the refrigerant in the evaporator.

    Restricted Flow Restricted flow is caused by an obstruction (blockage) in system piping,chiller barrel or tower system.

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    Retrofit A retrofit is a modification to a chiller system. For example, a new stylecompressor replacing an older, less efficient style or to use a differentrefrigerant to comply with new standards. The results can affect energyefficiency.

    Rotating Vane Anemometer Measures air velocity by use of a rotating vane or fan.

    Sacrificial Anode An anode that is made of a metal, typically zinc or magnesium, that is loweron the galvanic chart so it will be sacrificed to protect the mild steel tubesheet and end bells in the chiller from galvanic corrosion.

    Seal A seal is a tight and perfect closure (as against the passage of gas or water)or a device to prevent the passage or return of gas or air into a pipe orcontainer.

    Secondary Surface Area The area that extends from the primary surface area into the fluid beingconditioned to enhance the heat transfer.

    Sensible Heat Heat that causes a change in the temperature of an object or location.

    Separation Gasket Gasket used to separate a two or more pass chiller between the inlet anddischarge of the chiller.

    Specific Heat The ratio of the quantity of heat required to raise the temperature of onepound of a substance one degree Fahrenheit to that required to raise thetemperature of one pound of water one degree, Btu/lb. For the metricsystem, the unit of mass is kilogram and the temperature scale is Celsius.

    SRB Sulfate Reducing Bacteria. SRB can cause significant localized pittingcorrosion and severe damage in the cooling tower system.

    Strainer Used to remove foreign material from the water flow. The mesh sizedetermines the size of the material/debris being removed.

    Superheat Test A superheat test is the excess of the gas suction temperature above the gassaturation temperature

    The purpose of the superheat is to ensure that liquid refrigerant does notenter the compressor.

    Typically the standard is between 10 and 20F. A high superheat value is anindication of low refrigerant levels and low superheat value is an indicationof high refrigerant levels especially when the compressor is operating at fullload.

    Suction Piping Refrigerant piping from the evaporator outlet to the compressor suctioninlet.

    Temperature Degree of hotness or coldness of an object or location measured on adefinite scale.

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    Temperature Difference Degree of change between two temperatures.

    Thermal Expansion Pressure and temperature regulation valve, located in the liquid line, whichis responsive to the superheat of the vapor leaving the evaporator coil.

    Thermal Conductivity Material property indicating how easily heat travels through material. Itdepends on the physical structure of matter at both the molecular and atomiclevel as well as the state of matter, solid, liquid, or gas.

    Thermometer Measures and evaluates temperature.

    Trans-critical Cooling Cooling by using the sub-critical and supercritical state of the refrigerant.The critical point of a substance is the temperature and pressure where the

    phase changes to what is called a "supercritical fluid" which showsproperties of both a liquid and a vapor at the same time. Only a substancethat has a critical point near the ambient temperature can be used, makingCO2 the refrigerant of choice for this process.

    Total Surface Area The sum of the primary surface area and secondary surface area.

    Tube A pipe that water flows through to transfer heat.

    Tube Bundle A group of heat exchanging tubes.

    Turbulent Flow Disturbed, chaotic flow of a fluid. The velocity at a given point varieserratically in magnitude and direction.

    Two Phase Flow Change in phase (liquid to gas, gas to liquid), due to changes in pressure ortemperature, that takes place while the fluid is circulating through the heatexchanger.

    Ultrasonic Flow Meter A device that is used to measure flow through piping.

    Vacuum A space partially exhausted by artificial means (i.e., suction measured ininches of Hg in a low pressure chiller).

    Variable Frequency Drive

    (VFD)A chiller with a variable frequency drive has a controller that monitors theoperating conditions and uses a combination of inlet guide vanes and speedcontrol. VFDs act as a soft-starter. VFDs can offer significant energysavings at part load conditions, but they typically do not run as efficiently atfull load when compared to constant speed drives.

    Vortex A mass of fluid (as a liquid) with a whirling or circular motion that tends toform a cavity or vacuum in the center of the circle and to draw toward thiscavity or vacuum bodies subject to its action.

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    VoltsThe practical meter-kilogram-second unit of electrical potential differenceand electromotive force equal to the difference of potential between two

    points in a conducting wire carrying a constant current of one ampere whenthe power dissipated between these two points is equal to one watt andequivalent to the potential difference across a resistance of one ohm whenone ampere is flowing through it. Typical chiller voltages are 460, 480, 2400or 4160. This information can be found in the chiller technicaldocumentation.

    Water Treatment Program A water treatment program provides a biocide program that minimizesmicrobiological growth along with excellent scale/corrosion protection.

    Wet Bulb The combination of outside air temperature and relative humidity, affecting

    the ability of the tower to evaporate water into the atmosphere. The higherthe relative humidity, the more difficult it is to evaporate additionalmoisture.

    Working Fluid The heat transfer fluid that changes the temperature.