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Trane TRG-TRC016-EN manual Staggered Set Points, notes, Chilled-WaterSystem Design, period two

Models: TRG-TRC016-EN

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Staggered Set Points

period two

Chilled-Water System Design

notes

chillers piped in series

Staggered Set Points

set point =48°F[8.9°C]

set point =42°F[5.6°C]

42°F

48°F[5.6°C] [8.9°C]

52°F

[11.1°C]

Figure 46

An alternative method of controlling chillers in series involves staggering the set points of the two chillers. This results in the downstream chiller operating first and being preferentially loaded. Any portion of the load that the downstream chiller cannot meet is handled by the upstream chiller.

The example in Figure 46 shows the system operating at about 80 percent of design cooling load. As we mentioned earlier, with three-way valves at the coils, the temperature of the water returning to the chillers decreases at part load. At 80-percent load, the return-water temperature is 52°F [11.1°C], instead of the 54°F [12.2°C] at 100-percent load. The upstream chiller is partially loaded, cooling the water to the 48°F [8.9°C] set point, while the downstream chiller remains fully loaded, cooling the water the rest of the way to 42°F [5.6°C].

40	TRG-TRC016-EN

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Trane TRG-TRC016-EN manual Staggered Set Points, notes, Chilled-WaterSystem Design, period two, set point =48F8.9C

Contents

TRG-TRC016-EN Air Conditioning Clinic Chilled-WaterSystemsOne of the Systems Series 3600 Pammel Creek Road La Crosse WI BUSINESS REPLY MAILBUSINESS REPLY MAIL THE TRANE COMPANY Attn: Applications EngineeringOne of the Systems Series Comment CardResponse Card Chilled-WaterSystemsThe Trane Company Chilled-WaterSystemsOne of the Systems Series A publication of A Trane Air Conditioning Clinic PrefaceChilled-WaterSystems period four Contentsperiod two Chilled-WaterSystem Design period threeTRG-TRC016-EN Types of Water Chillers notesperiod one Types of Water ChillersTypes of Water Chillers period oneDriving Sources notesperiod one Vapor-CompressionCyclenotes Types of Water Chillersperiod one Compressor Typesnotes Types of Water Chillersperiod one Variable-SpeedDrivesnotes Types of Water ChillersTypes of Water Chillers Condenser TypesAir-Cooledor Water-Cooled notesTypes of Water Chillers MaintenanceTower maintenance Freeze protection Makeup water notesperiod one Low Ambient Operationnotes Types of Water Chillersperiod one Efficiencynotes Types of Water Chillersperiod one Comparisonnotes Types of Water Chillersperiod one Packaged Air-CooledChillernotes Types of Water Chillersperiod one Remote Evaporator Barrelnotes Types of Water Chillersperiod one Remote Air-CooledCondensernotes Types of Water Chillersperiod one Indoor Air-CooledCondensernotes Types of Water Chillersperiod one Absorption Refrigeration Cyclenotes Types of Water ChillersTypes of Water Chillers Absorption Chillers Offer ChoiceWaste heat recovery Cogeneration notesperiod one Absorption Chiller Typesnotes Types of Water Chillersperiod one Equipment Rating Standardsnotes Types of Water Chillersperiod one Part-LoadEfficiency Ratingnotes Types of Water Chillersperiod one Standard Rating Conditionsnotes Types of Water Chillersperiod one Flow Rates and Temperaturesnotes Types of Water Chillersperiod one Flow Rates and Temperaturesnotes Types of Water ChillersTypes of Water Chillers ASHRAE/IESNA Standard 90.1–1999Electric Vapor-CompressionChillers notesperiod one Water-CooledAbsorption Chillersnotes Types of Water ChillersTypes of Water Chillers ASHRAE Standard 15–1994Safety standard for refrigerating systems notesperiod two period twoChilled-WaterSystem Design Chilled-WaterSystem DesignChilled-WaterSystem Design period twoChilled-WaterSystem notesperiod two Load-TerminalControl Optionsnotes Chilled-WaterSystem Designperiod two Three-WayValve Controlnotes Chilled-WaterSystem Designperiod two Two-WayValve Controlnotes Chilled-WaterSystem Designperiod two Face-and-BypassDamper Controlnotes Chilled-WaterSystem Designperiod two Chiller Evaporator Flownotes Chilled-WaterSystem Designperiod two Single-ChillerSystemnotes Chilled-WaterSystem Designperiod two Multiple-ChillerSystemsnotes Chilled-WaterSystem DesignChilled-WaterSystem Design Single PumpParallel Configuration notesperiod two Dedicated Pumpsnotes Chilled-WaterSystem Designperiod two Figure 43 shows an example of the pump–systemcurve relationship. When both pumps are operating, the system receives 100 percent of design flow. When only one pump is operating, the intersection of the pump’s performance curve with the system curve results in about 65 percent of design flownotes Chilled-WaterSystem DesignChilled-WaterSystem Design Chillers Piped in SeriesSeries Configuration notesperiod two Equal Set Pointsnotes Chilled-WaterSystem Designperiod two Staggered Set Pointsnotes Chilled-WaterSystem Designperiod two Primary-SecondaryConfigurationPrimary-SecondaryDecoupled Configuration Chilled-WaterSystem Designperiod two Primary-SecondarySystem Rulesnotes Chilled-WaterSystem Designperiod two Production Loopnotes Chilled-WaterSystem Designperiod two Manifolded Production Pumpsnotes Chilled-WaterSystem Designperiod two Distribution LoopChilled-WaterSystem Design Primary-SecondarySystem Rules notesChilled-WaterSystem Design period twoperiod two Varying Distribution Flownotes Chilled-WaterSystem Designperiod two Multiple Distribution Pumpsnotes Chilled-WaterSystem Designperiod two A variation of the multiple-pumpconfiguration is to use separate pumps to deliver water to specific, dedicated loads. An example is a chilled-watersystem serving a college campus. Separate distribution pumps supply water to the east A, west B, and central C portions of the campus. A primary advantage of this configuration is flexibility. Expanding the system can be achieved by simply adding another distribution pump to the existing plant and connecting it to the piping that runs to the new buildingnotes Chilled-WaterSystem Designperiod two Tertiary Pumpingnotes Chilled-WaterSystem DesignChilled-WaterSystem Design Distribution Loop CharacteristicsHigher return-watertemperatures notesPrimary-SecondarySystem Rules notesChilled-WaterSystem Design period twoperiod two System Operationnotes Chilled-WaterSystem Designperiod two Deficit Flownotes Chilled-WaterSystem Designperiod two Excess Flownotes Chilled-WaterSystem Designperiod two Control of Primary-SecondarySystemnotes Chilled-WaterSystem DesignPressure-based Types of Fluid Flow MetersChilled-WaterSystem Design period twoperiod two Temperature-BasedCalculationsnotes Chilled-WaterSystem Designperiod three period threeSystem Variations System Variationsabsorption thermal storage period threeFuel Choice Options System VariationsLow-FlowSystems Chiller Efficiency ImprovementsSystem Variations period threeSystem Variations Greater Focus on System EfficiencyTrend Toward Lower Flow Rates notesperiod three Low-FlowSystemsnotes System Variationsperiod three Variable-Primary-FlowSystemsnotes System Variationsperiod three Critical VPF System Requirementsnotes System Variationsperiod three Preferential Chiller Loadingnotes System Variationsperiod three Sidestream Configurationnotes System VariationsSystem Variations Heat-RecoveryChillerHeat Recovery notesperiod three Heat-RecoveryChiller Optionsnotes System Variationsperiod three Heat-RecoveryChiller Efficiencynotes System Variationsperiod three Control of a Heat-RecoveryChillernotes System Variationsperiod three Asymmetric Designnotes System Variationsperiod three Swing Chillernotes System VariationsSwing Chiller notesSystem Variations period threeperiod three “Free” Coolingnotes System Variationsperiod three Plate-and-FrameHeat Exchangernotes System Variationsperiod three Refrigerant Migrationnotes System Variationsperiod three Application Outside Range of Chillernotes System Variationsperiod four period fourChiller-PlantControl Chiller-PlantControlnotes period fourChiller Controls Start–stop Chilled-watertemperature controlHow to optimize system efficiency What Is Important?When to turn a chiller on or off How to recover from an equipment failureperiod four Chiller Sequencingnotes Chiller-PlantControlperiod four Temperaturenotes Chiller-PlantControlperiod four Flownotes Chiller-PlantControlperiod four Capacitynotes Chiller-PlantControlperiod four Chiller Rotationnotes Chiller-PlantControlperiod four When the system consists of chillers with different capacities, efficiencies, or fuel types, the question of which chiller to turn on or off next becomes more complex. Although each system requires a complete analysis, there are some general principles that apply to most systemsnotes Chiller-PlantControlChiller-PlantControl Heat Recoverypreferentially-loaded heat-recoverychiller notesperiod four The variable-primary-flowsystem, introduced in Period Three, is designed to operate with variable flow through the chiller evaporators. Sequencing chillers in this type of system cannot be based solely on temperature, because in a properly-operatingsystem the supply- and return-watertemperatures will be nearly constant. Determining when to turn chillers on or off is not a simple task. For control stability and chiller reliability, the flow rates through the chillers, and the rate of flow change, must be kept within allowable rangesnotes Chiller-PlantControlChiller-PlantControl System Failure RecoveryFailure Recovery and Contingency Planning notesperiod four Contingency Planningnotes Chiller-PlantControlStaging-intervaltimer System TimersSystem Tuning Load-confirmationtimerperiod four Unload Before Startnotes Chiller-PlantControlperiod four Soft Loadingnotes Chiller-PlantControlperiod four Chilled-WaterSet Point Controlnotes Chiller-PlantControlperiod four System Optimizationnotes Chiller-PlantControlperiod four Chilled Water Resetnotes Chiller-PlantControlperiod four Condenser-WaterTemperaturenotes Chiller-PlantControlperiod four Control of Condensing PressureChiller-PlantControl period four Operator Training and Supportnotes Chiller-PlantControlperiod four Operator Interfacenotes Chiller-PlantControlperiod four ASHRAE Guidelinenotes Chiller-PlantControlperiod five period fiveReview Reviewnotes period fiveReview—PeriodTwo Parallel configuration Series configurationReview Review—PeriodThreeHeat recovery Asymmetric design notesnotes Review—PeriodFourChiller sequencing Failure recovery Contingency planning System tuningnASHRAE Handbook – Systems and Equipment Reviewperiod five nASHRAE Handbook – RefrigerationQuestions for Period QuizQuestions for Period Questions for Period 9Why does a variable-primary-flowVPF system require a bypass in the system?Quiz Questions for PeriodAnswers 12Sequencing 13Decreases; increases AnswersGlossary decoupled system See primary-secondarysystem GlossaryGlossary swing chiller A smaller-capacitychiller used in a multiple-chillersystem. It is alternated on and off between the larger chillers operation to serve as a smaller, incremental step of loading notesGlossary The Trane Company