HVAC Dictionary

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AcidizeWhen acid is used to remove mineral and iron deposits (scale) to restore heat transfer efficiency.

Air Balance TestA test used to measure airflow across a tower or air handler system.

Air Balancing HoodMeasures airflow from grilles and diffusers.

Amp (Ampere)The practical meter-kilogram-second unit of electric current that is equivalent to a flow of one coulomb per second or to the steady current produced by one volt applied across a resistance of one ohm.

Amp/Ohm/Volt MeterMeasures motor amperage and voltage test controls.

ARIAir Conditioning and Refrigeration Institute

Baseline DataBaseline (or historical) data is compiling past chiller logs for review.

BasinCold water reservoir in the cooling tower system.

Basin TemperatureThe actual temperature of the cold water basin in the cooling tower system.

BearingA support or guide by means of which a moving part such as a shaft or axle is positioned with respect to the other parts of a mechanism.

Bearing Oil ReservoirExcess oil used in the lubrication of the bearing system located in the compressor system.

BiocideA substance (as DDT) that is destructive to many different organisms.

BlockageBlockage is obstruction of flow, i.e., valve, debris, etc.

BoroscopeA fiber-optic camera or lens, used to inspect tube bundles or piping.

BTUBritish thermal unit. The amount of heat required to raise the temperature of 1 pound of water 1 degree Fahrenheit.

Bypass ValveA valve used to detour flow, i.e., to detour water from the hot deck to the tower basin to control tower basin temperature.

CarryoverThe movement of a fluid from one area to another. Carryover of this liquid may contaminate another liquid, causing undesired results.

Chilled WaterChilled water is the water in the closed loop (closed to the atmosphere) or evaporator system of the chiller.

Chiller(Centrifugal Chiller)A heat exchanger using air, refrigerant, water and evaporation to transfer heat (BTUs) to produce air conditioning (measured in tons). A chiller is comprised of an evaporator, condenser and compressor system.

Chiller Barrel PassesMany chillers are designed with more than one pass to maximize heat transfer. Baffels and gaskets are used to separate each pass to ensure design flow through the chiller barrel.

Chiller Design TonnageThe design capacity of the chiller measured in tons produced in an hour.

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

Chiller Log SheetA sheet on which specific chiller readings are documented.

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

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

Chiller StartupThe chiller manufacturer's recommendation on startup including pre-heating the compressor oil temperature prior to chiller startup.

Chiller SurgeWhen the refrigerant flows backwards through the compressor wheel every few seconds until the pressure builds up and the refrigerant moves forward again. This is even more dangerous than a stall because it reverses loads of thrust bearings in the compressor shaft.

Chiller Vein(Inlet Guide Veins)Chiller veins are used to control the capacity of the compressor. As the inlet guide veins start to close, they change the gas entry angle to the impeller and reduce gas flow and compressor capacity. As the vanes near the closed position, they throttle the refrigerant flow.

Closed LoopThe evaporator side of the chiller system, closed to the atmosphere.

CompressorA mechanical device where the refrigerant is compressed from a lower pressure and lower temperature to a higher pressure and higher temperature. The compressor maintains a low pressure in the evaporator by continually removing refrigerant vapors. This low pressure, low temperature vapor is then compressed into a higher pressurize, hot refrigerant vapor which leaves the compressor and travels to the condenser. The motor in the compressor is the main consumer of energy in the chiller system. The energy used by the compressor is dependent on the pressure increase. The head pressure divided by 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.

Compressor Erosion/CorrosionDamage to the bearings and impeller caused by poor lubrication, low oil levels or operating conditions such as liquid refrigerant carryover into the compressor system.

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

Compressor Oil TemperatureCompressor oil temperature is the temperature of the oil in the compressor bearing lubrication system. This temperature is predetermined by manufacturers specifications.

CondensationThe process a vapor goes through to change phase from vapor to a liquid.

CondenserHeat exchanger where the system heat is rejected and the refrigerant condenses into a liquid. The condenser is where hot pressurized refrigerant vapors in the compressor are cooled and liquefied by cooling tower water circulating through the tubes of the condenser. The condenser side is commonly referred to as the open recirculation system or open loop.

Condenser Delta PThe pressure drop between the suction side and the discharge side of a chiller barrel. This pressure drop can be measured against known values from tables/charts to determine water flow through the chiller barrel. Delta P is dependant on chiller tube ID and tube length.

Condenser Delta TThe temperature difference between the entering and leaving water through the chiller barrel. i.e., the entering temperature is 85F and the leaving temperature 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 PressureThe head pressure produced in the condenser dependent on the entering condenser water temperature and the saturated refrigerant temperature. The condenser pressure can affect the refrigerant cycle and heat transfer. The pressure correlates to saturated refrigerant temperature on a pressure/temperature chart for each refrigerant type.

Condenser Refrigerant Approach TemperatureThe refrigerant temperature minus the leaving water temperature. The refrigerant temperature can be determined by locating the condenser (head) pressure on a pressure/temperature chart, or if the chiller control panel provides this information.

Condenser WaterThe open recirculating system connects the chiller condenser to the cooling tower system and the atmosphere. Condenser water is subject to evaporation, debris/contamination, fouling/scaling and microbio growth.

Conditioned FluidThe fluid being acted upon by the working fluid. Example: in an air conditioning system the air is conditioned by the refrigerant (refrigerant is the working fluid).

Constant Speed DriveConstant speed drives are the most common type of chiller compressor motor. They have limited ability to adjust speed based on part load conditions.

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

Cooling TowerWhere the process of heat exchange occurs by evaporation in the open recirculating system. The cooling tower system includes tower fans, plenum, drift eliminators, fill, levelers, hot deck and cold basin. All cooling towers have a design rated delta temperature.

Cooling TowerApproach TemperatureThe difference between the leaving water temperature and the entering air wet bulb.

Cooling Tower FanFan system designed to remove the heat generated by the open recirculating system through evaporation.

Cooling Tower FillDesigned to brake up the circulating water into smaller particles or a thin film. This increases the surface area of the water to enhance evaporation and heat 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 and piping making up the open loop or open recirculating system.

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

Cost of BlowdownThe total cost of water sent to drain/sewer, typically determined on a per 1,000 gallon basis. This value can be found on the water and sewer utility bill or from the utility company.

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

Cost of MakeupThe 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 on the water and sewer utility bill or from the utility company.

CPLV - Calculated Part Load ValueThe calculated Kw/Ton derived from the effect of part load and entering condenser water temperature on the chiller when compared to full load design.

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

DebrisAnything the environment can introduce that is washed out by the tower operations, i.e., dirt, trash, chip scale "flash corrosion", bugs, broken tower fill, broken tower wood, plastic, etc.

Delta PThe pressure drop between the discharge side and the suction side of a chiller barrel. This pressure drop can be measured against design values provided by the chiller manufacturer or previously developed charts by plant personnel to determine water flow through the chiller barrel.

Delta TThe temperature difference between the entering and leaving water through the chiller barrel, i.e., entering temperature is 85F, leaving temperature is 95F = delta T10F. If the actual water flow is known, delta P could determine a problem if the actual delta P does not match the current water flow.

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

Design Condenser Delta TThe temperature difference between the entering and leaving water through the chiller barrel when the chiller is running at full load, i.e., the entering temperature is 85F and the leaving temperature is 95F then the delta T would be 10. Modern high efficiency chillers are designed to run at 9.4F delta T at 3gpm/ton.

Design Condenser Refrigerant Approach TemperatureThe difference between the condenser water out temperature and the condenser leaving refrigerant temperature at design full load. This information 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 Condenser Water TemperatureThe design entering condenser water temperature is typically 85F based on ARI standards for chillers commissioned after 1989. This information can be found in the chiller technical documentation.

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 TThe temperature difference between the entering and leaving water through the chiller barrel when the chiller is running at full load, i.e., the entering temperature is 54F and the leaving temperature is 42F then the delta T would be 12.

Design Evaporator Refrigerant Approach TemperatureThe difference between the evaporator chill water out temperature and the evaporator leaving refrigerant temperature at design full load. This information can be found in the chiller technical documentation.

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

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

Design Kw/TonThe Kw used to produce one ton of cooling when the chiller is running at full load design (ex: 0.6). This information can be found in the chiller technical documentation.

Design SpecificationsManufacturer tested specification when determining design to actual operations. This includes the chiller, cooling tower, air handlers, etc. to ensure expected performance of the equipment.

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

Distribution HolesHoles in the hot deck of a cooling tower designed to evenly distribute the water flow over the tower fill below.

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

Drift EliminatorA device that removes entrained water droplets (drift) from air leaving the tower system.

Dry BulbThe ambient outside temperature.

ECWTEntering Condenser Water Temperature

EmulsificationThe entrainment of one substance into another, i.e., oil in water or oil in refrigerant.

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

Entering Condenser Water TemperatureEntering condenser water temperature is the temperature of water entering the condenser.

EnthalpyThe quantity of internal energy of a body plus the product of its volume and pressure.

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

EvaporationThe process a liquid goes through to change phase from a liquid to a vapor.

EvaporatorHeat exchanger where the system heat is absorbed and the refrigerant evaporates into a gas. By continually pulling refrigerant vapor out of the evaporator headspace, low pressure can be maintained causing the refrigerant to evaporate rapidly. Evaporation cools the refrigerant. This cold refrigerant produces chilled water by heat transfer. The evaporator side is commonly 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 PThe pressure drop between the suction side and the discharge side of a chiller barrel. This pressure drop is measured against known values to determine the water flow GPM through the chiller barrel. Delta P is dependant on chiller tube ID and tube length.

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

Evaporator Fouledand/or ScaledA film or compound, which attaches to the internal tube surface, impeding heat transfer and lowering efficiency.

Evaporator Refrigerant Approach TemperatureThe leaving water temperature minus the refrigerant temperature. The refrigerant temperature can be determined by locating the evaporator (suction) pressure on a pressure/temperature chart, or if the chiller control panel provides this information.

Evaporator Leaving Refrigerant TemperatureThe temperature of the saturated leaving refrigerant is at prior to leaving the evaporator in the refrigerant cycle.

Evaporator PressureA vacuum measured in inches of Hg (mercury) for low-pressure chillers and a positive pressure (psig) for high-pressure chillers. This vacuum/pressure correlates to refrigerant temperature on a pressure/temperature chart for each refrigerant type.

Evaporator Refrigerant LevelThe level of the liquid refrigerant in the evaporator barrel.

FanA device for producing a current of air in the cooling tower used to remove heat from the condenser tower system.

Flow RateThe quantity of fluid in motion per a unit of time. Flow rate is expressed in mass per unit time or volume per unit time.

FluteAllows the transfer of liquid refrigerant from the condenser back to the evaporator.

Flute FrostingA problem associated with rapid movement of liquid refrigerant at low temperatures from the condenser to the evaporator, causing frost to form on the flute.

Fouled TubesDebris or substance which impedes flow or heat transfer. Fouling can be caused 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 DesignDesign refers to full load conditions. Full load is a chiller running at 100% load capacity, 85F ECWT, 42-46F leaving chill water temperature and is the rating of the manufacturer.

GasketAny of a wide variety of seals or packings used between matched machine parts or around pipe joints to prevent the escape of a gas or fluid.

GaugeAn instrument or device for measuring, indicating or comparing a physical characteristic, i.e., temperature or pressure.

GPMGallons Per Minute

HeatWhen energy is added to an object or location, the motion of the molecules increases causing them to collide more frequently. The motion energy is converted into heat during the collisions. As more collisions occur more heat is released and the temperature of the object or location increases.

Heat IndexThe heat index is the combination of actual outside air temperature plus the affect of relative humidity to give an apparent temperature.

Heat ExchangerDevice that provides a practical means for the working fluid to heat or cool the 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, which includes compressor heat.

Heat SinkObject or location that is at a lower temperature than the heat source and receives the energy from the source.

Heat SourceObject or location that is at a higher temperature than other objects or locations.

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

Heat Transfer CoefficientA proportionality constant in the heat transfer rate equation derived from the conditions of the fluid motion, the tube or fin surface geometry, and other thermodynamic properties.

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

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

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

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

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

Hot Deck Distribution HolesHoles in the hot deck that distribute the flow of returning condenser water evenly 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 gas bypass valve). The purpose of hot gas bypass is to maintain a minimum gas volume flow rate through the compressor to avoid surging or stalling during low 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 PartLoad ValueA single number, part-load efficiency indicator calculated using the ARI method at standard rating conditions. Introduced in ARI Standard 550-1986, the definition of IPLV was changed in ARI Standard 550/590-1998 to more closely reflect actual operating experience found in the field for a single chiller.

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

Laminar FlowSmooth undisturbed flow of a fluid.

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

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

LegionellaA bacterium of the genus legionella, especially pneumophila, that can cause Legionnaires' disease - an acute, sometimes fatal respiratory disease caused by and characterized by severe pneumonia, headache, and a dry cough.

Liquid RefrigerantThe compressor coolant used in the refrigerant cycle of a chiller for heat transfer.

Liquid Refrigerant StackingThis condition occurs can be caused by mechanical failure or low head pressure in the condenser and evaporator caused by low condenser water temperature.

Liquid PipingRefrigerant piping from the condenser outlet to the evaporator inlet.

LoadAmp load is compared to full load and the percentage value equals the load of the chiller. Actual amps divided by full load amps is the percentage of full load design.

Load SwingA large or radical change in cooling load requirements, i.e., weather or building operations requirements.

Log Mean Temperature DifferenceA specialized average temperature difference used to determine the heat transfer rate.

Low Pressure ChillerA 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 refrigerants include R-11, R-113, R-114, R-123.

Maintenance PracticesAn organized schedule of chiller and plant maintenance.

MicrobeAn organism of microscopic or ultramicroscopic size.

Non-CondensableGasses (Air)Air that enters the evaporator through a vacuum leak and migrates to the condenser (in low-pressure chillers only). This affects the condenser head pressure, condenser refrigerator approach temperature and condenser heat transfer efficiency.

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

OilUsed as the lubricant in the compressor system to lubricate and protect bearings, shaft, etc.

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

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

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

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

Operating ConditionsThe values of temperature, flow rate, and pressure of the heat transfer fluids as they enter and leave the heat exchanger. Used to determine the heat transfer rate for the heat exchanger.

Part LoadChiller load conditions below full load design. Most chillers operate at part load ~99% of the time.

Plate ExchangerA heat exchanger used to create free cooling (not using a compressor or refrigerant to transfer heat) by running colder tower water over stainless steel plates which transfers heat between the closed loop to the open loop.

Power FactorThe ratio of actual power (Kw) to apparent power (kVA). Most centrifugal motors have a power factor between 0.87 and 0.91. Additional capacitors can be added to raise the power factor to a practical limit of 0.95. In the table below, the closer the length of the kVA line is the the kW line the more efficient the user of the energy.

Pressure DropAmount of reduction in the pressure of a fluid between the entering and leaving pressures. The pressure drop in a chiller is dependant upon the tube ID of the tube bundle and its length. Rough surfaces or objects that are in the flow path can cause reduced pressure.

Pressure GaugeAn instrument that measures pressure in psig, psid or psia depending on the circumstances.

Primary Surface AreaThe area that contains the working heat transfer fluid. Usually the tubes of a finned/tube heat exchanger.

PumpA device used to circulate fluid from one location to another.

Pump CurveThe design capacity of a pump's ability to circulate fluid.

Pump Curve CalibrationA flow test to determine the capacity of a pump's ability to circulate fluid.

PressureThe application of force to something by something else in direct contact with it.

Pressure DropThe reduction in pressure between a fluid entering and leaving a closed system.

PretreatmentThe removal of oil and grease from new piping and chillers to ensure maximum heat transfer. It should also lay down a passivating film to prevent flash corrosion and in some cases, white rust.

Pumpout SystemPumpout systems consist of a storage tank large enough to hold the chillers entire refrigerant charge and a refrigerant pump/compressor to move the refrigerant from the chiller to the pumpout tank and back again. It's primary purpose is for servicing the chiller.

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

QualityThe ratio of vapor mass to total mass of a substance at the substance's saturation temperature and pressure.

RATRefrigerant Approach Temperature

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

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

Refrigeration EffectThe amount of heat absorbed by the refrigerant in the evaporator.

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

RetrofitA retrofit is a modification to a chiller system. For example, a new style compressor replacing an older, less efficient style or to use a different refrigerant to comply with new standards. The results can affect energy efficiency.

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

Sacrificial AnodeAn anode that is made of a metal, typically zinc or magnesium, that is lower on the galvanic chart so it will be sacrificed to protect the mild steel tube sheet and end bells in the chiller from galvanic corrosion.

SealA 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 or container.

Secondary Surface AreaThe area that extends from the primary surface area into the fluid being conditioned to enhance the heat transfer.

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

Separation GasketGasket used to separate a two or more pass chiller between the inlet and discharge of the chiller.

Specific HeatThe ratio of the quantity of heat required to raise the temperature of one pound of a substance one degree Fahrenheit to that required to raise the temperature of one pound of water one degree, Btu/lb. For the metric system, the unit of mass is kilogram and the temperature scale is Celsius.

SRBSulfate Reducing Bacteria. SRB can cause significant localized pitting corrosion and severe damage in the cooling tower system.

StrainerUsed to remove foreign material from the water flow. The mesh size determines the size of the material/debris being removed.

Superheat TestA superheat test is the excess of the gas suction temperature above the gas saturation temperature

The purpose of the superheat is to ensure that liquid refrigerant does not enter the compressor.

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

Suction PipingRefrigerant piping from the evaporator outlet to the compressor suction inlet.

TemperatureDegree of hotness or coldness of an object or location measured on a definite scale.

Temperature DifferenceDegree of change between two temperatures.

Thermal ExpansionPressure and temperature regulation valve, located in the liquid line, which is responsive to the superheat of the vapor leaving the evaporator coil.

Thermal ConductivityMaterial property indicating how easily heat travels through material. It depends on the physical structure of matter at both the molecular and atomic level as well as the state of matter, solid, liquid, or gas.

ThermometerMeasures and evaluates temperature.

Transcritical CoolingCooling by using the subcritical 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 shows properties of both a liquid and a vapor at the same time. Only a substance that has a critical point near the ambient temperature can be used, making CO2the refrigerant of choice for this process.

Total Surface AreaThe sum of the primary surface area and secondary surface area.

TubeA pipe that water flows through to transfer heat.

Tube BundleA group of heat exchanging tubes.

Turbulent FlowDisturbed, chaotic flow of a fluid. The velocity at a given point varies erratically in magnitude and direction.

Two Phase FlowChange in phase (liquid to gas, gas to liquid), due to changes in pressure or temperature, that takes place while the fluid is circulating through the heat exchanger.

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

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

Variable Frequency Drive (VFD)A chiller with a variable frequency drive has a controller that monitors the operating conditions and uses a combination of inlet guide vanes and speed control. VFDs act as a soft-starter. VFDs can offer significant energy savings at part load conditions, but they typically do not run as efficiently at full load when compared to constant speed drives.

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

VoltsThe practical meter-kilogram-second unit of electrical potential difference and electromotive force equal to the difference of potential between two points in a conducting wire carrying a constant current of one ampere when the power dissipated between these two points is equal to one watt and equivalent to the potential difference across a resistance of one ohm when one ampere is flowing through it. Typical chiller voltages are 460, 480, 2400 or 4160. This information can be found in the chiller technical documentation.

Water TreatmentProgramA water treatment program provides a biocide program that minimizes microbiological growth along with excellent scale/corrosion protection.

Wet BulbThe combination of outside air temperature and relative humidity, affecting the ability of the tower to evaporate water into the atmosphere. The higher the relative humidity, the more difficult it is to evaporate additional moisture.

Working FluidThe heat transfer fluid that changes the temperature.