Carrier Class 3 Air Cooled Chillers - InspectAPedia
COMMERCIALHVAC CHILLEREQUIPMENTAir-CooledChillers
Technical Development Programs (TDP) are modules of technical training on HVAC theory,system design, equipment selection and application topics. They are targeted at engineers anddesigners who wish to develop their knowledge in this field to effectively design, specify, sell orapply HVAC equipment in commercial applications.Although TDP topics have been developed as stand-alone modules, there are logical groupings of topics. The modules within each group begin at an introductory level and progress toadvanced levels. The breadth of this offering allows for customization into a complete HVACcurriculum – from a complete HVAC design course at an introductory-level or to an advancedlevel design course. Advanced-level modules assume prerequisite knowledge and do not reviewbasic concepts.Chillers are used in a variety of air-conditioning and process cooling applications. Air-cooledchillers can be used as a single piece unit or a split in various configurations. This flexibility hascontributed to their overall popularity among designers of chilled-water systems. Air-cooledchillers range in size from small capacity models to several hundred-ton models that are utilizedto cool large commercial buildings. This TDP module will cover both packaged single piece aircooled chillers as well as split system types. This TDP module will also cover the available options and accessories, the applications, as well as criteria for selecting an air-cooled chiller. 2005 Carrier Corporation. All rights reserved.The information in this manual is offered as a general guide for the use of industry and consulting engineers in designing systems.Judgment is required for application of this information to specific installations and design applications. Carrier is not responsible forany uses made of this information and assumes no responsibility for the performance or desirability of any resulting system design.The information in this publication is subject to change without notice. No part of this publication may be reproduced or transmitted inany form or by any means, electronic or mechanical, for any purpose, without the express written permission of Carrier Corporation.Printed in Syracuse, NYCARRIER CORPORATIONCarrier ParkwaySyracuse, NY 13221, U.S.A.
Table of ContentsIntroduction . 1Air-Cooled versus Water-Cooled Chillers. 2Basic Refrigeration Cycle for Air-Cooled Chillers . 4Air-Cooled Chiller Components. 5Evaporator. 5Brazed-Plate. 5Direct Expansion (DX) Shell and Tube . 6Flooded Shell and Tube . 7Evaporator Types Pros & Cons. 8Condenser . 9Compressor . 9Reciprocating . 9Scroll. 10Screw . 10Expansion Device . 11Chiller Controls . 12Compressor Starting Methods. 13Across-the-Line Starting. 13Part-Winding Starters . 13Wye-Delta Starting . 14Capacity Control . 15Energy Management . 16Chilled-Water Reset. 16Demand Limit and Duty Cycling. 17Air-Cooled Chiller Configurations . 17Single Piece Units . 17Split Systems. 18Remote Evaporator . 18Condenserless Chiller . 19Indoor Centrifugal Condenser. 20Evaporative Condenser . 20Application Topics. 21Typical Operating Limits. 21Effects of Outside Air Temperature. 21Effects of Leaving Chilled-Water Temperature. 22Variable Flow Operation, Minimum and Maximum Flow Rates . 22Recirculation and Bypass Line Piping. 23Freeze Protection Methods . 23Refrigerants Used in Air-Cooled Chillers. 26Chiller Sizing . 26Minimum Chilled-Water System Volume . 27Parallel and Series Chillers . 28Clearances and Installation . 28Options & Accessories . 29Low-Ambient Operation. 29Low Chilled-Water Temperature Option. 30Condenser Coil Corrosion Protection . 30Hydronics Packages . 32
Codes and Standards. 34Performance Related .34ARI.34ASHRAE 90.1.36Safety Related .36ASME .36UL / CSA & ETL .36NEC / CEC.37ASHRAE 15.37Selection Criteria . 38Summary. 39Work Session . 41Appendix. 44References.44Work Session Answers .46
AIR-COOLED CHILLERSIntroductionAir-cooled chillers utilize the mechanical refrigeration cycle to produce chilled water or achilled water and antifreeze mixture. They reject the building heat to the ambient with an aircooled condensing coil. Chillers are the heart of the chilled-water air-conditioning system sincethey serve the pivotalfunction of creating thecooling effect required tomaintain comfort conditions.Chillers are used in avariety of comfort airconditioning and processcooling applications. Thechilled liquid is transported by pumps and pipesthat can be connected toliterally hundreds of roomfan coils and terminals.This allows chillers to beapplied on applications Figure 1requiring many zones ofAir-Cooled Chiller Packagecontrol.Air-cooled chillers are common in modern systems and have been growing in popularitysince the 1980s, nearly doubling in the last ten years. Today, air-cooled chillers are applied onsmall to large commercial jobs and can be used in multiples to form systems reaching severalthousand tons of installed capacity.The popularity is primarily due to the all-inclusive nature of air-cooled chillers and the reduction of costs associated with eliminating cooling tower. On some models, even the hydronicaccessories, such as the pump and expansion tank, may be included, assembled, and tested fromthe factory ready to begin operation.Typical air-cooled chiller applications include schools, hospitals, retail environment, and offices. Additionally, air-cooled chillers are popular for cooling process or manufacturingoperations.This TDP will cover packaged single-piece, as well as split system air-cooled chillers. Tolearn more about water-cooled chillers, refer to TDP-623, Water-Cooled Chillers.Commercial HVAC Equipment1
AIR-COOLED CHILLERSAir-Cooled versus Water-Cooled ChillersA differentiating feature of the types of chillers is the method used to condense the refrigerantas it leaves the compressor. The two methods involve using either air-cooled or water-cooledcondensers. Air-cooled condensers employ ambient air asthe condensing medium anduse a fan to move the air overthe coil. For a given surfaceand airflow rate, the capacityof an air-cooled condenser varies with the refrigerantcondensing temperature, whichis a function of the enteringdry-bulb temperature. Shownin Figure 2 is a typical aircooled condensing temperaturebased on 95º F dry bulb ambient air.Water-cooled condensers Figure 2employ water as the condens- Air-Cooled Condensing Temperatureing medium and use a pump tocirculate the water through thecondenser and out to a cooling tower that rejects the heat to the atmosphere.Operating cost is one of the primary factors when deciding between air-cooled or watercooled chillers. Air-cooled chiller systems typically have a lower first and maintenance cost sincethey do not require a cooling tower, condenser water pumps, and associated condenser waterchemical treatment. Operating costs, however, generally favor water-cooled chillers. This is because water-cooled chillers can take advantage of lower condensing temperatures than air-cooledchillers.Air-cooled chillers have afull load kW/ton of approximately 1.25 while water-cooledchillers have a full load kW/tonof between 0.55 and 0.8kW/ton. The kW draw of thecooling tower fans and condenser water pump should beadded to the water-cooledchiller kW/ton for an evencomparison. Even after accounting for this addedauxiliary energy draw, watercooled chilled-water systems Figure 3normally have an efficiencyAir-Cooled vs. Water-Cooled Chiller Benefitsadvantage over air-cooled.Commercial HVAC Equipment2
AIR-COOLED CHILLERSAir-cooled chillersare typically available as apackage ranging up to 500tons, while packaged watercooled chillers are typicallyavailable up to 3,000 tons.Some custom water-cooledchillers go even higher incapacity.Air-cooled chillers eliminate the concerns and maintenance requirements associated with condenser watertreatment, condenser-tube cleaning, cooling tower service,tower freeze protection, and the availability and quality ofmakeup water. This reduced maintenance requirement isparticularly attractive to building owners because it canreduce overall costs. Water-cooled chillers must have acondenser water treatment program to eliminate contaminants such as bacteria and algae growth. Fouled condensertubes, not uncommon with water-cooled chilled-water systems, can also reduce chiller efficiency.Air-cooled chillers are often selected for use in systems that require year-round mechanicalcooling requirements. Air-cooled condensers have the ability to operate in below-freezingweather, and can do so without the freeze protection issues associated with operating the coolingtower in these conditions. Cooling towers often require a basin heater, or even an indoor sump,for safe operation in freezingweather. For process applications,such as computer centers that requirecooling year-round, air-cooled chillers have a distinct advantage overtheir water-cooled counterpart.Note:The primary convenience of anair-cooled chiller is that it doesnot require a cooling tower,condenser water pump, andthe associated maintenance.Figure 4Condenser water systems are not required with air-cooled chillers.Commercial HVAC Equipment3
AIR-COOLED CHILLERSBasic Refrigeration Cycle for Air-Cooled ChillersThe refrigeration cycle of an air-cooled chiller includes two important processes:1. The evaporation of the liquid refrigerant in the evaporator, which absorbs heat and lowersthe temperature of the chilled-water system2. The condensation of the refrigerant vapor in the air-cooled condenser and rejection of heatto the atmosphereIn the air-cooled chiller refrigeration cycle, water enters the evaporator (also known as thecooler) and is cooled by the colder refrigerant flowing through the other circuit inside the evaporator. The chilled water is pumped from the chiller to the building coils to provide cooling. In theevaporator, the chilled water cools the building or process load and the cycle is completed whenwarmer water flows back to the evaporator. A mixture of cold liquid refrigerant and flash gaspasses through the evaporator circuit opposite the water to be chilled.The refrigerant in the evaporator absorbs heat from thewarmer return water, evaporates to a vapor, and finally The refrigerantexits the evaporator as a superheated vapor. The super- is on the shell side of someheated refrigerant vapor then enters the suction inlet of the evaporator designs and on thecompressor. In the compressor, the refrigerant is com- tube side of others. When thepressed, raising its pressure and temperature. High refrigerant is on the tube side,pressure and temperature refrigerant gas exits the com- the evaporator is called a DXpressor, passes through the discharge line and enters the evaporator; when on the shellcondenser. While in the air-cooled condenser coil, the hot side, it is a flooded cooler.gas condenses to liquid inside the tubes as it gives up heatto the cooler outside air being drawn across the condenser coil by the condenser fans.The condensed liquidrefrigerant then leavesthe condenser and entersthe expansion device. Asthe refrigerant passesthrough the expansiondevice, its pressure andtemperature is decreasedto the point that some ofthe liquid flashes to vapor.Theexpansiondevicecontrolstheamount of flashing inorder to maintain a certain superheat to ensureno liquid droplets enterinto the compressor suction. After leaving theexpansion device, therefrigerant enters theevaporator and the cycleis repeated.Figure 5Refrigeration Cycle Components of an Air-Cooled ChillerCommercial HVAC Equipment4
AIR-COOLED CHILLERSAir-Cooled Chiller ComponentsAll air-cooled chillers are comprised of the following components: Evaporator (cooler) Condenser Compressor Expansion DeviceLet’s examine these components individually and the role of each in the air-cooled chiller.EvaporatorThree types of evaporators are used in air-cooled chillers:1. Brazed-plate2. Direct expansion (DX) shelland-tube3. Flooded shell-and-tubeThe most common choice ofevaporator design for larger screw andreciprocating chillers has been theshell-and-tube types while smallerchillers utilize brazed-plate. Shelland-tube evaporators are widely usedand they are larger and heavier thanbrazed-plate heat exchangers. Thetubes for some evaporator types mayutilize internal and/or external enhancements to promote turbulence Figure 6and create increased heat transfer beThree Types of Evaporatorstween the fluid and the refrigerant. Photos: Brazed-plate courtesy of API Heat Transfer; DX Shell-and-TubeTurbulence actually increases the heattransfer process by keeping more of the fluid in contact with the heat exchanger surface area. Onthe refrigerant side and water side, more contact means greater heat transfer and a higher efficiency rating. Enhancement of tubes typically is achieved through a rifling or finning processduring manufacturing.Brazed-PlateBrazed-plate evaporators are used on chillers up to approximately 60 tons and consist of a series of plates brazed together with every second plate turned 180 degrees. This design creates twohighly turbulent fluid channels that flow in opposite directions over a surface area with a highheat transfer coefficient and good performance characteristics. The plates are stacked so theyform a multi-layered alternating path for each fluid to travel through. Each layer or circuit islinked to an inlet and outlet via a manifold at either end.Commercial HVAC Equipment5
AIR-COOLED CHILLERSA brazed-plate evaporator offers good heat transfer for the cost. In the multiple layers, or circuits, the fluid comes into contact with the heat exchanger surface over a very large area resultingin fast heat dispersion. The smaller cross sectional area and fluted construction also adds turbulence to the fluid, further increasingthe efficiency of heat transfer. Thefluid turbulence is also present at lowheat exchanger loadings, making thebrazed-plate heat exchanger ideal forpart-load applications. Brazed-plateheat exchangers are much smallerthan their shell-and-tube counterpart.They may be as little as 25 percent ofthe size of an equivalent shell-andtube heat exchanger.Plate type heat exchangersare also used on some aircooled chiller designs as amethod of increasingperformance via an economizercircuit. The purpose is toincrease subcooling and thusincrease the overall capacity ofthe refrigeration system.Figure 7Brazed-Plate EvaporatorThis smaller size of brazed-plate heat exchangers results in a smaller overall footprint for the chiller, abenefit for both shipping and installing the chiller. Additionally, the refrigerant circuits can be designed torequire considerably less refrigerant than shell-and-tubesystems. Because the circuitry of a brazed-plate heat exchanger system holds less volume of refrigerant, fewerpounds will be needed to charge the chiller.Given the small areas of the multiple circuits, brazed-plate heat exchangers are more susceptible to being plugged. A factory-supplied or field-supplied strainer should be used to removeparticles and contaminants from entering the water circuit of the heat exchangers. The brazedplate design is not mechanically cleanable inside.Direct Expansion (DX) Shell-and-TubeIn the direct expansion evaporator, the refrigerant flows through thetubes and the water flows around thetubes in the shell section. As heat istransferred to the colder refrigerantfrom the warmer water or water / antifreeze mixture, the refrigerant in thetubes evaporates and the water iscooled. Baffles within the shell directthe water flow path over the tubescreating the turbulence that improvesheat transfer.Figure 8Direct Expansion Shell-and-Tube EvaporatorCommercial HVAC Equipment6
AIR-COOLED CHILLERSAir-cooled chillers with reciprocating and scrollcompressors typically utilize a DX evaporator design.The direct expansion type evaporator allows the oil to beswept along with the refrigerant inside the tubes to alocation on the chiller where it can be separated and returned to the oil pump thus accomplishing the requiredlubrication these compressors require.The watersideof a direct expansion evaporatormust be chemically cleaned sincemechanical cleaning of the shellis not possible due to the internalbaffling.Flooded Shell-and-TubeFlooded shell-and-tube evaporators are also called “flooded coolers.” They have water or awater/antifreeze mixture flowing through the tubes while the refrigerant is on the shell side. Theliquid refrigerant is uniformly distributed along the bottom of the cooler.Additionally, the refrigerantcharge does not have to be removedduring tube cleaning. Flooded evaporators are typically no more efficienta design than DX or brazed-plate, butthe chiller types they are used on tendto have a more efficient compressor,such as a centrifugal.On air-cooled chillers that useflooded shell-and-tube evaporators,the number of tube passes within thevessel may be changed to further inFigure 9crease the efficiency by increasingFlooded Shell-and Tube Evaporatorthe tube velocity and turbulence. Or,they may reduce the number ofpasses to decrease the pressure drop by reducing the tube velocity. Although higher pass arrangements tend to improve heat transfer, they also increase pumping horsepower for the chilledwater circuit because of the higher pressure drop. Thus, an economic balance must be struck between higher pumping horsepower and lower compressor power.Flooded Evaporator Cleaning:Since the water flowsthrough the tubes of aflooded evaporator, thewaterside can bemechanically cleaned.Brushing is a commonmethod. The ability tomechanically clean thewaterside of a flooded shelland-tube evaporator is amajor advantage of thisdesign.Figure 10Flooded Evaporator Pass ArrangementsCommercial HVAC Equipment7
AIR-COOLED CHILLERSOn DX evaporators, there are no “pass” arrangement options because the water is on theshell side. Internal to the shell, changes to thebaffling are made to accommodate greater orless water flows.Evaporator PassesThe method most utilized in selection ofheat exchanger passes is to specifyreasonable pressure drop limits andallow the manufacturer to recommend theoptimal pass arrangement for the loadand application under consideration.Evaporator Types Pros & ConsBrazed-Plate Evaporator**DX Shell-and-Tube Evaporator*Flooded Shell-and-Tube EvaporatorProSmaller footprintProLightweightProCost effective for smaller sizesConSensitive to contamination of the water circuitConNot mechanically cleanableProCost effective for small and medium sizesProFamiliarity with customers/engineersProDesign can accommodate heater cable on the shell toprevent freezing of waterConLarger footprintConNot mechanically cleanableProHigh efficiencyProMechanically cleanableConLarge footprintConDesign cannot accommodate heater cable on the shell toprevent freezing of water in tubes*Photo courtesy of Standard Refrigeration**Photo courtesy of API Heat TransferCommercial HVAC Equipment8
AIR-COOLED CHILLERSCondenserThe condenser in an air-cooled chiller is a heat exchanger that condenses the hot refrigerantgas by using cooler outside air passing over a coil. In a typical air-cooled chiller, propeller-typefans are used to draw the outdoor air over the coil. The hot, high-pressure refrigerant vapor flowsthrough the coil tubes and is condensed to a liquid. In the last portion of condenser tubing, thecondensed liquid refrigerant is then subcooled. A final portion of the condenser is used to lowerthe refrigerant temperature below the saturated condensing temperature. This is called subcooling. This increases the refrigerationeffect and increases system capacityby about 1 percent for each degree ofsubcooling provided.Altitude AdjustmentThe airflow over the condensercoil is fixed, but the density ofthe air is affected by altitude,which affects condenserperformance. Chiller selectionsoftware will ask for projectelevation to adjust the capacityaccordingly.Figure 11Condenser Design of an Air-Cooled ChillerCompressorThere are three types of compressors utilized for air-cooled chillers. They are reciprocating,scroll, and screw.ReciprocatingReciprocating compressors, like areciprocating engine, have pistons,rods, and discharge and intake valves.The valves operate on suction anddischarge pressure. Compression isachieved by trapping a fixed amountof refrigerant gas into a chamber. Forthis reason, reciprocating compressorsare positive displacement type compressors as are scrolls and screws.Reciprocating compressors were theworkhorse of the small chiller market Figure 12for decades and are still used in manySemi-Hermetic Reciprocating Compressordesigns. Multiple reciprocating compressors were often installed in aCommercial HVAC Equipment9
AIR-COOLED CHILLERSsingle chiller to provide chiller capacities of up to 400 tons. The reciprocating compressor isavailable open, semi-hermetic, or hermetic. Open compressors extend the shaft through a seal inthe crankcase for use with an external driver. Hermetic compressors have the motor and compressor contained in the same housing, typically welded and sealed. Semi-hermetic compressorsutilize a bolted housing, instead of a welded one, to facilitate repair in the field.ScrollScroll compressors have a unique compression process. A fixed scroll coupled with themovement of an orbiting scroll, ingests suction gas into pockets. As the orbiting scroll moves, thepockets of gas are compressed to an intermediate pressure. In a final orbit, the pockets reach discharge pressure and exit through the discharge port.Scroll compressors have emergedas a popular alternative to reciprocating compressors and are available inhermetic configurations in capacitiesup to 25 tons each for use in aircooled chillers. As with reciprocatingcompressors, multiple scroll compressors are often used in a single chillerdesign to meet larger capacities.Scroll compressors are 10 to 15 percent more efficient than reciprocatingcompressors and have proven to bevery reliable, primarily because theyhave approximately 60 percent fewermoving parts. Reciprocating and Figure 13scroll compressors are typically used Scroll Compressorsingly or in multiples to provide anair-cooled chiller range from approximately 10 to 400 tons.ScrewScrew compressors are widely used in medium-sized water chillers, either singly or in multiples to accomplish a chiller range from about 70 to 500 tons. As the screw rotors turn, the suctiongas is compressed. Screw compressors have one or more rotors to accomplish the compression.Like scroll compressors, screw compressors have a reliability advantage over reciprocating due tofewer moving parts. Screw compressors, as well as reciprocating and scroll compressors are positive displacement type compressors, which means they compress a fixed amount of gas in acompression chamber. Screw compressors have become popular because of excellent reliabilityand good efficiency, especially at part loads.Commercial HVAC Equipment10
AIR-COOLED CHILLERSThere are several designs of screwcompressors featuring sing
cause water-cooled chillers can take advantage of lower condensing temperatures than air-cooled chillers. Air-cooled chillers have a full load kW/ton of approxi-mately 1.25 while water-cooled chillers have a full load kW/ton of between 0.55 and 0.8 kW/ton. The kW draw of the cooling tower fans and con-denser water pump should be
Air Cooled Chiller Air Air 2 Air Air 6 AIR COOLED CHILLERS Air-cooled chillers are refrigeration machines that remove heat from cooling loads using chilled water and reject this heat into the atmosphere using refrigerant. THEY ALL HAVE fans, condenser coils, and compressors. Air-cooled chillers are used to provide cooling for human comfort and electronic equipment as well as industrial process .
Air-Cooled Chiller The use of air-cooled chillers in process and comfort cooling applications has been steadily increasing in recent years. The air-cooled chiller has evolved from a packaged product, with few options, to a fully customizable unit that can be tailored to meet specific application and job site requirements. High-efficiency air-cooled
Maximum Series portable chillers can be used on a variety of process applications that require 20 F to 80 F chilled water. MAXIMUM SERIES † Air & Water-Cooled † 1/4 to 40 Tons † 20 F to 80 F † Using Non-Ozone Depleting Refrigerants 10 ton air-cooled model 10 ton water-cooled model 2 ton water-cooled model 1 ton air-cooled model
ACH Air-Cooled, Horizontal Air Flow ACV Air-Cooled, Vertical Air Flow ACR Air-Cooled Remote Condenser WCC Water-Cooled Condenser Digit 6 — Chilled Water System P Recirculating System, Tank and Pump M Single Pass Chiller Unit (no tank and pump) Digit 7 — Cabinet Type H Horizontal Low Profile V Vertical Upright
EWY Air-cooled chiller, heat pump EWL Remote condenser chiller ERA Air cooled condensing unit EWW Water-cooled chiller, cooling only EWC Air-cooled chiller, cooling only with centrifugal fan EWT Air-cooled chiller, cooling only with heat recovery Refrigerant D R-134a P R-407c Q R-410a Capacity class in kW (Cooling) Always 3 .
Vanguard Air-Cooled V-Twin Specifications Performance Curves 14 HP Vanguard Air-Cooled V-Twin 16 HP Vanguard Air-Cooled V-Twin 15.0 5.2 Kilowatt 7.5 8.2 9.0 9.7 10.4 111.2 111.9 14.0 13.0 12.0 11.0 10.0 9.0 8.0 7.0 16.0 6.7 6.0 HP 1800 2000 2200 24002600 2800 3000 3200 3400 3600 17.0 12.7 REVOLUTIONS PER MINUTE RATED GROSS BHP MAXIMUM .
AIR-COOLED Air-Cooled chillers utilize plant ambient air to extract heat from the refrigeration circuit. Fan or blowers move the plant air across generously sized finned condenser coils to permit full rated capacity at design conditions. WATER-COOLED Water-Cooled chillers utilize a secondary plant water source such as cooling tower or city .
English A Practical Course in British English Pronunciation FREE SAMPLE Chapter 1 pdf mp3 Written & Produced at the Pronunciation Studio. 1 Introduction 2 How to use the book. 3 IPA Chart Index 1 Introduction 2 How to use the book. 3 IPA Chart Chapter/ Page Sounds Sound Comparison Spelling & Sound 1 4 - 15 5-6 Consonants 7-8 Vowels -9 ‘ghoti’ Introduction 10 Schwa 2 16 - 27 17-18 .
