Manuals / Trane / Kitchen Appliance / Water Dispenser

Trane SYS-APM001-EN Variable-speed pump load control, Face-and-bypass dampers, Two-way valve

Models: SYS-APM001-EN

1 114

Download 114 pages 32.43 Kb

Page 15

Image 15

Primary System Components

Figure 6. Two-way valve

Airflow

Two-Way

Modulating

Valve

Variable-speed pump load control

By using a pump for each coil (Figure 7), the flow may be controlled by varying the pump speed. In such systems, there may be no control valves at the coil. This can reduce both the valve and the valve installation costs, but increases coil pump and maintenance costs.

Figure 7. Variable-speed pump load control

Airflow

Variable

Speed Pump

Face-and-bypass dampers

Figure 8 shows a control variation using an uncontrolled or “wild” coil. In this system, control of the conditioned air supply is executed by face-and- bypass dampers that permit a portion of the air to bypass the coil surface. Advantages of this strategy are the elimination of control valves and improved part-load dehumidification. A disadvantage is that all the water is

SYS-APM001-EN

Chiller System Design and Control

Page 15

Image 15

Trane SYS-APM001-EN Variable-speed pump load control, Face-and-bypass dampers, Primary System Components, Two-way valve

Contents

Chiller System Design and Control Applications Engineering ManualSYS-APM001-EN Page Chiller System Design and Control Susanna Hanson, applications engineerMick Schwedler, applications manager Beth Bakkum, information designerSYS-APM001-EN Preface2009 Trane All rights reserved Chiller System Design and ControlContents System Controls Failure RecoveryChilled-Water System Control Condenser-Water System ControlChiller Primary System ComponentsFigure 2. Flooded evaporator cut-away Primary System ComponentsChiller evaporator Figure 1. Typical vapor-compression chillerFigure 3. Direct-expansion evaporator cut-away Effect of chilled-water temperaturePrimary System Components Effect of chilled-water flow rate and variationEffect of condenser-water flow rate Water-cooled condenserEffect of condenser-water temperature Primary System ComponentsPrimary System Components Air-cooled condenserAir-cooled versus water-cooled condensers MaintenancePrimary System Components Low-ambient operationEnergy efficiency dry bulb wetWetbulbBulb LoadsPrimary System Components 1212 Midnight midnightHeat transferred from the loads can be controlled in a number of ways Three-way valve load controlTwo-way valve load control Primary System ComponentsFigure 6. Two-way valve Variable-speed pump load controlFace-and-bypass dampers Primary System ComponentsFigure 8. Uncontrolled water flow with bypass damper Chilled-Water Distribution SystemChilled-water pump Primary System ComponentsManifolded pumps Distribution pipingPrimary System Components Pump per chillerFigure 12. Constant flow system Pumping arrangementsPrimary System Components Constant flow systemPrimary-secondary system Condenser-Water SystemCooling tower Primary System ComponentsEffect of ambient conditions on cooling tower performance Condenser-water pumping arrangementsPrimary System Components Effect of load on cooling tower performanceUnit-Level Controls Primary System ComponentsChiller control Primary System Components Centrifugal chiller capacity controlFigure 16. Centrifugal chiller with AFD Primary System Components The availability of cooler condenser water condenser-water resetSmall Chilled-Water Systems 1-2 chillers Application ConsiderationsApplication Considerations Constant flow Variable flowCondensing method Part load system operation Application ConsiderationsNumber of chillers Parallel or seriesFigure 18. Mid-sized chilled-water system schematic Mid-Sized Chilled-Water Systems 3-5 ChillersManaging control complexity Preferential vs. equalized loading and run-timeLarge Chilled-Water Systems 6+ Chillers, District Cooling Figure 19. Large chilled-water system schematicApplication Considerations 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 construction PowerPipe size WaterControls Chiller performance testingLimitations of field performance testing Chiller Plant System PerformanceGuidelines for system efficiency monitoring Application ConsiderationsGuideline 22 includes a discussion of Energy and economic analysis of alternatives Application Considerations1 Full year analysis Selecting Chilled- and Condenser-Water Temperatures and Flow Rates System Design OptionsGuidance for Chilled- and Condenser-Water Flow Rates Chilled-Water Temperatures Standard rating temperaturesSystem Design Options System Design Options Condenser-Water TemperaturesChilled- and Condenser-Water Flow Rates Standard rating flow conditionsSystem Design Options Selecting flow rates DP2/DP1 = Flow2/Flow11.85 System Design OptionsSystem Design Options The total system power is now as followsFigure 21. Chilled water system performance at part load Coil response to decreased entering water temperatureExample of coil reselection at colder temperature/reduced flow rate System Design OptionsFluid ΔT, F C Cooling-tower options with low flowSystem Design Options Smaller towerSame tower, smaller approach System Design OptionsΔT1 = 94.2 - 78 = 16.2F or 34.6 - 25.6 = 9.0C ΔT2 = 99.1 - 78 = 21.1F or 37.3 - 25.6 = 11.7CSame tower, larger chiller System Design OptionsReselected tower for 50% more heat rejection with 15F 8.3C Retrofit opportunitiesSystem Design Options rangeSystem Design Options Cost ImplicationsMisconceptions about Low-Flow Rates Misconception 1-Low flow is only good for long piping runsSystem Design Options System System Design OptionsConsumption EnergyDemirchian 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 Series Chillers System ConfigurationsFigure 27. Series chillers Primary-Secondary Decoupled Systems Hydraulic decouplingSystem Configurations 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 DistributionCampus System ConfigurationsPumping arrangements CommonSystem Configurations Decoupled system-principle of operationFigure 34. Decoupled system supply tee Figure 35. Temperature-sensing Flow-based controlSystem Configurations Temperature-sensingSubtracting a chiller System Configurations Chiller sequencing in decoupled systemsMultiple chilled-water plants on a distribution loop Adding a chillerSystem Configurations Pump control in a double-ended decoupled systemFigure 36. Double-ended decoupled system Chiller sequencing in a double-ended decoupled system System ConfigurationsFigure 37. Variable-primary-flow system Variable-Primary-Flow SystemsOther plant designs System ConfigurationsAdvantages of variable primary flow System ConfigurationsOperational savings of VPF designs Dispelling a common misconception Chiller selection requirementsSystem Configurations Evaporator flow limitsTo promote good heat transfer and stable control minimum flow limit System ConfigurationsNumber of operating chillers System ConfigurationsFlow-rate reduction when an isolation valve Managing transient water flowsSystem Configurations System design and control requirements System ConfigurationsThese descriptions should include control sequences for System Configurations Accurate flow measurementBypass locations Chiller sequencing in VPF systems System ConfigurationsBypass flow control Adding a chiller in a VPF system System ConfigurationsSystem Configurations Subtracting a chiller in a VPF systemSequencing based on load Use multiple air handlers, and stagger their start/stop times Other VPF control considerationsSystem Configurations Select slow-acting valves to control the airside coilsAssess the economic feasibility of VPF for single-chiller plants Plant configurationSystem Configurations Consider a series arrangement for small VPF applicationsChiller selection Guidelines for a successful VPF systemSystem Configurations Moderate “low ΔT syndrome” by manifolding the chilled water pumpsChiller sequencing System ConfigurationsPlant configuration Bypass flowPlate-and-frame heat exchanger Heat RecoveryChilled-Water System Variations Condenser “Free Cooling” or Water EconomizerChilled-Water System Variations Refrigerant migrationFigure 41. Refrigerant migration chiller in compression cooling mode Figure 43. Water economizer piped in parallel with chillers Well, river, or lake waterFigure 42. Refrigerant migration chiller in free-cooling mode Chilled-Water System VariationsFigure 44. Parallel preferential loading arrangement Preferential LoadingPreferential loading - parallel arrangement Chilled-Water System VariationsFigure 45. Sidestream preferential loading arrangement Preferential loading - sidestream arrangementChilled-Water System Variations Sidestream plate-and-frame heat exchangerRecovery Sidestream with alternative fuels or absorptionProduction Figure 47. Preferential loading - series arrangement Preferential loading - series arrangementChilled-Water System Variations Sidestream system controlFigure 48. Series-counterflow arrangement Series-Counterflow ApplicationSeries-series counterflow Chilled-Water System VariationsEvaporators Unequal Chiller SizingChilled-Water System Variations Figure 50. Series arrangement of evaporators and condensersRequired Volume = Flow Rate × Loop Time System Issues and ChallengesLow ΔT Syndrome Amount of Fluid in the LoopExample System Issues and ChallengesChiller response to changing conditions System response to changing conditionsSystem Issues and Challenges ContingencyMinimum capacity required Type and size of chillerAncillary equipment System Issues and Challenges Location of equipmentAlternative Energy Sources Water and electrical connectionsSystem Issues and Challenges Plant ExpansionAlternative fuel Thermal storageSystem Issues and Challenges Retrofit OpportunitiesApplications Outside the Chiller’s Range Flow rate out of rangeSystem Issues and Challenges Temperatures out of range Precise temperature controlFigure 52. Temperatures out of range for equipment SYS-APM001-EN System Issues and ChallengesFigure 53. Precise temperature control, multiple chillers Chiller System Design and ControlChilled-water pump control Chilled water reset-raising and loweringSystem Controls Chilled-Water System ControlSystem Controls Number of chillers to operateCritical valve reset pump pressure optimization Table 17. VFDs and centrifugal chillers performance at 90% load Condenser-Water System ControlMinimum refrigerant pressure differential System ControlsCondenser-water temperature control System ControlsCooling-tower-fan control System Controls Chiller-tower energy balanceFigure 54. Chiller-tower energy consumption Chiller-tower-pump balance System Controls Variable condenser water flowDecoupled condenser-water system System ControlsThese 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 Figure 56. Decoupled condenser-water system System ControlsCooling Tower Fan Inverter Cooling Tower Water Sump Tower Water Recirculation Pump CDWP-2 Inverter Chiller CDWP-1 Inverter ChillerFailure Recovery Figure 57. Failure recoverySystem Controls Conclusion Glossary condenser water, leaving. See cooling watercooling tower water. See cooling water pumps system Glossarytower water. See cooling water GlossaryPlant.” IDEA 88th Annual Conference Proceedings 1997 ReferencesExcept Low-Rise Residential Buildings. ASHRAE and IESNA ReferencesEngineering July ASHRAE/IESNA Standard 90.1-2007 Energy Standard for Buildings32 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 Date TraneLiterature Order Number SYS-APM001-EN