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Trane SYS-APM001-EN manual Failure Recovery, System Controls, Failure recovery

Models: SYS-APM001-EN

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Failure Recovery

System Controls

Failure Recovery

With all the varied approaches available to potential customers, it sometimes seems that the main idea gets lost. People purchase chilled-water plants to reliably produce chilled water to satisfy another need, such as comfort or process cooling. Therefore, when the plant operates there must be a process in place to recover from the failure of a chilled- or condenser-water pump, cooling tower, or chiller. Failure recovery should be integral to the chilled- water plant control system. Refer to Figure 57. If the control sequence tries to start Chiller 2 and its pump, but the pump has an electrical malfunction, the sequence should immediately lock out Chiller 2 and its pump. The control system should then automatically attempt to start Chiller 3 and its pump. At the same time, the control system should send a pump malfunction alarm to the system operator.

Figure 57. Failure recovery

Chiller 3 Start

Chiller 2 Unavailable

Chiller 1 Running

Bypass Line

Return

Supply

SYS-APM001-EN

Chiller System Design and Control

95

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Trane SYS-APM001-EN manual Failure Recovery, System Controls, Failure recovery

Contents

SYS-APM001-EN Chiller System Design and ControlApplications Engineering Manual Page Mick Schwedler, applications manager Susanna Hanson, applications engineerBeth Bakkum, information designer Chiller System Design and Control2009 Trane All rights reserved PrefaceChiller System Design and Control SYS-APM001-ENContents Chilled-Water System Control Failure RecoveryCondenser-Water System Control System ControlsChiller Primary System ComponentsChiller evaporator Primary System ComponentsFigure 1. Typical vapor-compression chiller Figure 2. Flooded evaporator cut-awayPrimary System Components Effect of chilled-water temperatureEffect of chilled-water flow rate and variation Figure 3. Direct-expansion evaporator cut-awayEffect of condenser-water temperature Water-cooled condenserPrimary System Components Effect of condenser-water flow rateAir-cooled versus water-cooled condensers Air-cooled condenserMaintenance Primary System ComponentsEnergy efficiency Primary System ComponentsLow-ambient operation Primary System Components Loads1212 Midnight midnight dry bulb wetWetbulbBulbTwo-way valve load control Three-way valve load controlPrimary System Components Heat transferred from the loads can be controlled in a number of waysFace-and-bypass dampers Variable-speed pump load controlPrimary System Components Figure 6. Two-way valveChilled-water pump Chilled-Water Distribution SystemPrimary System Components Figure 8. Uncontrolled water flow with bypass damperPrimary System Components Distribution pipingPump per chiller Manifolded pumpsPrimary System Components Pumping arrangementsConstant flow system Figure 12. Constant flow systemCooling tower Condenser-Water SystemPrimary System Components Primary-secondary systemPrimary System Components Condenser-water pumping arrangementsEffect of load on cooling tower performance Effect of ambient conditions on cooling tower performanceChiller control Unit-Level ControlsPrimary System Components Figure 16. Centrifugal chiller with AFD Primary System ComponentsCentrifugal chiller capacity control Primary System Components The availability of cooler condenser water condenser-water resetSmall Chilled-Water Systems 1-2 chillers Application ConsiderationsCondensing method Application Considerations Constant flowVariable flow Number of chillers Application ConsiderationsParallel or series Part load system operationManaging control complexity Mid-Sized Chilled-Water Systems 3-5 ChillersPreferential vs. equalized loading and run-time Figure 18. Mid-sized chilled-water system schematicApplication Considerations Large Chilled-Water Systems 6+ Chillers, District CoolingFigure 19. Large chilled-water system schematic Pipe size PowerWater Creating one centralized chilled-water system takes significant foresight, initial investment, and building development with a multi-year master plan. If the initial plant is built to accommodate many future buildings or loads, the early challenge is operating the system efficiently with much lower loads than it will experience when the project is complete. The system may need to blend parallel and series configurations “Series-Counterflow Application” on page 77 to accommodate the wide range of loads the plant experiences during phased constructionLimitations of field performance testing Chiller performance testingChiller Plant System Performance ControlsGuideline 22 includes a discussion of Guidelines for system efficiency monitoringApplication Considerations 1 Full year analysis Energy and economic analysis of alternativesApplication Considerations Guidance for Chilled- and Condenser-Water Flow Rates Selecting Chilled- and Condenser-Water Temperatures and Flow RatesSystem Design Options System Design Options Chilled-Water TemperaturesStandard rating temperatures Chilled- and Condenser-Water Flow Rates Condenser-Water TemperaturesStandard rating flow conditions System Design OptionsSystem Design Options Selecting flow rates DP2/DP1 = Flow2/Flow11.85 System Design OptionsSystem Design Options The total system power is now as followsExample of coil reselection at colder temperature/reduced flow rate Coil response to decreased entering water temperatureSystem Design Options Figure 21. Chilled water system performance at part loadSystem Design Options Cooling-tower options with low flowSmaller tower Fluid ΔT, F CΔT1 = 94.2 - 78 = 16.2F or 34.6 - 25.6 = 9.0C System Design OptionsΔT2 = 99.1 - 78 = 21.1F or 37.3 - 25.6 = 11.7C Same tower, smaller approachSame tower, larger chiller System Design OptionsSystem Design Options Retrofit opportunitiesrange Reselected tower for 50% more heat rejection with 15F 8.3CSystem Design Options Cost ImplicationsSystem Design Options Misconceptions about Low-Flow RatesMisconception 1-Low flow is only good for long piping runs Consumption System Design OptionsEnergy SystemDemirchian and Maragareci12, Eley13, and Schwedler and Nordeen11 independently showed that system energy consumption can be reduced by reducing flow rates. It is interesting to note that in the systems studied, three different chiller manufacturer’s chillers were examined, yet the energy savings only varied from 2.0 to 6.5 percent. In all cases, regardless of which manufacturer’s chillers were used, the system energy consumption was reduced. In addition, Demirchian and Maragareci12, and Schwedler and Nordeen11 also noted reduced first costs System Design OptionsParallel Chillers System ConfigurationsSystem Configurations Figure 27. Series chillers Series ChillersSystem Configurations System Configurations Primary-Secondary Decoupled SystemsHydraulic decoupling bypass piping no-flow static head from the building water column, and System ConfigurationsFigure 29. Production loop System Configurations ProductionDistribution-loop benefits of decoupled system arrangement System Configurations DistributionPumping arrangements System ConfigurationsCommon CampusFigure 34. Decoupled system supply tee System ConfigurationsDecoupled system-principle of operation System Configurations Flow-based controlTemperature-sensing Figure 35. Temperature-sensingMultiple chilled-water plants on a distribution loop System Configurations Chiller sequencing in decoupled systemsAdding a chiller Subtracting a chillerFigure 36. Double-ended decoupled system System ConfigurationsPump control in a double-ended decoupled system Chiller sequencing in a double-ended decoupled system System ConfigurationsOther plant designs Variable-Primary-Flow SystemsSystem Configurations Figure 37. Variable-primary-flow systemOperational savings of VPF designs Advantages of variable primary flowSystem Configurations System Configurations Chiller selection requirementsEvaporator flow limits Dispelling a common misconceptionTo promote good heat transfer and stable control minimum flow limit System ConfigurationsFlow-rate reduction when an isolation valve System ConfigurationsManaging transient water flows Number of operating chillersSystem Configurations These descriptions should include control sequences for System design and control requirementsSystem Configurations Bypass locations System ConfigurationsAccurate flow measurement Bypass flow control Chiller sequencing in VPF systemsSystem Configurations Adding a chiller in a VPF system System ConfigurationsSequencing based on load System ConfigurationsSubtracting a chiller in a VPF system System Configurations Other VPF control considerationsSelect slow-acting valves to control the airside coils Use multiple air handlers, and stagger their start/stop timesSystem Configurations Plant configurationConsider a series arrangement for small VPF applications Assess the economic feasibility of VPF for single-chiller plantsSystem Configurations Guidelines for a successful VPF systemModerate “low ΔT syndrome” by manifolding the chilled water pumps Chiller selectionPlant configuration System ConfigurationsBypass flow Chiller sequencingChilled-Water System Variations Heat RecoveryCondenser “Free Cooling” or Water Economizer Plate-and-frame heat exchangerFigure 41. Refrigerant migration chiller in compression cooling mode Chilled-Water System VariationsRefrigerant migration Figure 42. Refrigerant migration chiller in free-cooling mode Well, river, or lake waterChilled-Water System Variations Figure 43. Water economizer piped in parallel with chillersPreferential loading - parallel arrangement Preferential LoadingChilled-Water System Variations Figure 44. Parallel preferential loading arrangementChilled-Water System Variations Preferential loading - sidestream arrangementSidestream plate-and-frame heat exchanger Figure 45. Sidestream preferential loading arrangementProduction RecoverySidestream with alternative fuels or absorption Chilled-Water System Variations Preferential loading - series arrangementSidestream system control Figure 47. Preferential loading - series arrangementSeries-series counterflow Series-Counterflow ApplicationChilled-Water System Variations Figure 48. Series-counterflow arrangementChilled-Water System Variations Unequal Chiller SizingFigure 50. Series arrangement of evaporators and condensers EvaporatorsLow ΔT Syndrome System Issues and ChallengesAmount of Fluid in the Loop Required Volume = Flow Rate × Loop TimeChiller response to changing conditions System Issues and ChallengesSystem response to changing conditions ExampleMinimum capacity required ContingencyType and size of chiller System Issues and ChallengesAlternative Energy Sources System Issues and Challenges Location of equipmentWater and electrical connections Ancillary equipmentAlternative fuel Plant ExpansionThermal storage System Issues and ChallengesApplications Outside the Chiller’s Range Retrofit OpportunitiesFlow rate out of range System Issues and ChallengesFigure 52. Temperatures out of range for equipment System Issues and Challenges Temperatures out of rangePrecise temperature control Figure 53. Precise temperature control, multiple chillers System Issues and ChallengesChiller System Design and Control SYS-APM001-ENSystem Controls Chilled water reset-raising and loweringChilled-Water System Control Chilled-water pump controlCritical valve reset pump pressure optimization System ControlsNumber of chillers to operate Minimum refrigerant pressure differential Condenser-Water System ControlSystem Controls Table 17. VFDs and centrifugal chillers performance at 90% loadCooling-tower-fan control Condenser-water temperature controlSystem Controls Figure 54. Chiller-tower energy consumption System ControlsChiller-tower energy balance Chiller-tower-pump balance System Controls Variable condenser water flowThese three energy consumers must be balanced to minimize overall energy use. This makes varying condenser water flow complex, but the strategy below has been implemented on projects Decoupled condenser-water systemSystem Controls Cooling Tower Fan Inverter Cooling Tower Water Sump Tower Water System ControlsRecirculation Pump CDWP-2 Inverter Chiller CDWP-1 Inverter Chiller Figure 56. Decoupled condenser-water systemSystem Controls Failure RecoveryFigure 57. Failure recovery Conclusion cooling tower water. See cooling water Glossarycondenser water, leaving. See cooling water pumps system Glossarytower water. See cooling water GlossaryPlant.” IDEA 88th Annual Conference Proceedings 1997 ReferencesEngineering July ReferencesASHRAE/IESNA Standard 90.1-2007 Energy Standard for Buildings Except Low-Rise Residential Buildings. ASHRAE and IESNA32 Trane Applications Engineering Group. “Thermal Storage - Understanding the Choices.” Ice Storage Systems, Engineered Systems Clinics. Trane, 1991. ISS-CLC-2 ReferencesIndex Index Index Index Page Literature Order Number TraneSYS-APM001-EN Date