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Trane TRG-TRC016-EN manual notes, Chiller-PlantControl, period four, Variable-Primary-FlowSystems

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The variable-primary-flow system, 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-operating system the supply- and return-water temperatures 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 ranges.

period four

Chiller-Plant Control

notes

Variable-Primary-Flow Systems

variable-flow
pumps
check


valves
control
valve	two-way
	two-way
	valve
	optional bypass
	withthree-wayvalve	Figure 97
		Figure 97

The variable-primary-flow system, 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-operating system the supply- and return-water temperatures 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 ranges.

Therefore, control of a variable-primary-flow system must:

nInclude a method to determine system load. Many systems measure flow rates and temperatures.

nEnsure that flow rates through the chillers are within the allowable minimum and maximum limits. Modulation of a control valve in the bypass pipe is commonly used to ensure minimum flow rates through the chillers.

nControl the rate at which the system flow rate changes, to ensure that it does not change more rapidly than the chillers can adapt. This is especially critical when turning on additional chillers.

Adequate time must be spent designing the control sequence and commissioning the system after installation, to ensure proper operation of a variable-primary-flow system.

TRG-TRC016-EN

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Trane TRG-TRC016-EN manual notes, Chiller-PlantControl, period four, Variable-Primary-FlowSystems

Contents

Air Conditioning Clinic Chilled-WaterSystems One of the Systems SeriesTRG-TRC016-EN BUSINESS REPLY MAIL BUSINESS REPLY MAILTHE TRANE COMPANY Attn: Applications Engineering 3600 Pammel Creek Road La Crosse WIComment Card Response CardChilled-WaterSystems One of the Systems SeriesChilled-WaterSystems One of the Systems Series A publication ofThe Trane Company Preface Chilled-WaterSystemsA Trane Air Conditioning Clinic Contents period two Chilled-WaterSystem Designperiod three period fourTRG-TRC016-EN notes period oneTypes of Water Chillers Types of Water Chillersperiod one Driving Sourcesnotes Types of Water ChillersVapor-CompressionCycle notesTypes of Water Chillers period oneCompressor Types notesTypes of Water Chillers period oneVariable-SpeedDrives notesTypes of Water Chillers period oneCondenser Types Air-Cooledor Water-Coolednotes Types of Water ChillersMaintenance Tower maintenance Freeze protection Makeup waternotes Types of Water ChillersLow Ambient Operation notesTypes of Water Chillers period oneEfficiency notesTypes of Water Chillers period oneComparison notesTypes of Water Chillers period onePackaged Air-CooledChiller notesTypes of Water Chillers period oneRemote Evaporator Barrel notesTypes of Water Chillers period oneRemote Air-CooledCondenser notesTypes of Water Chillers period oneIndoor Air-CooledCondenser notesTypes of Water Chillers period oneAbsorption Refrigeration Cycle notesTypes of Water Chillers period oneAbsorption Chillers Offer Choice Waste heat recovery Cogenerationnotes Types of Water ChillersAbsorption Chiller Types notesTypes of Water Chillers period oneEquipment Rating Standards notesTypes of Water Chillers period onePart-LoadEfficiency Rating notesTypes of Water Chillers period oneStandard Rating Conditions notesTypes of Water Chillers period oneFlow Rates and Temperatures notesTypes of Water Chillers period oneFlow Rates and Temperatures notesTypes of Water Chillers period oneASHRAE/IESNA Standard 90.1–1999 Electric Vapor-CompressionChillersnotes Types of Water ChillersWater-CooledAbsorption Chillers notesTypes of Water Chillers period oneASHRAE Standard 15–1994 Safety standard for refrigerating systemsnotes Types of Water Chillersperiod two Chilled-WaterSystem DesignChilled-WaterSystem Design period twoperiod two Chilled-WaterSystemnotes Chilled-WaterSystem DesignLoad-TerminalControl Options notesChilled-WaterSystem Design period twoThree-WayValve Control notesChilled-WaterSystem Design period twoTwo-WayValve Control notesChilled-WaterSystem Design period twoFace-and-BypassDamper Control notesChilled-WaterSystem Design period twoChiller Evaporator Flow notesChilled-WaterSystem Design period twoSingle-ChillerSystem notesChilled-WaterSystem Design period twoMultiple-ChillerSystems notesChilled-WaterSystem Design period twoSingle Pump Parallel Configurationnotes Chilled-WaterSystem DesignDedicated Pumps notesChilled-WaterSystem Design period twoFigure 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 flow notesChilled-WaterSystem Design period twoChillers Piped in Series Series Configurationnotes Chilled-WaterSystem DesignEqual Set Points notesChilled-WaterSystem Design period twoStaggered Set Points notesChilled-WaterSystem Design period twoPrimary-SecondaryConfiguration Primary-SecondaryDecoupled ConfigurationChilled-WaterSystem Design period twoPrimary-SecondarySystem Rules notesChilled-WaterSystem Design period twoProduction Loop notesChilled-WaterSystem Design period twoManifolded Production Pumps notesChilled-WaterSystem Design period twoDistribution Loop Chilled-WaterSystem Designperiod two notes Chilled-WaterSystem Designperiod two Primary-SecondarySystem RulesVarying Distribution Flow notesChilled-WaterSystem Design period twoMultiple Distribution Pumps notesChilled-WaterSystem Design period twoA 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 building notesChilled-WaterSystem Design period twoTertiary Pumping notesChilled-WaterSystem Design period twoDistribution Loop Characteristics Higher return-watertemperaturesnotes Chilled-WaterSystem Designnotes Chilled-WaterSystem Designperiod two Primary-SecondarySystem RulesSystem Operation notesChilled-WaterSystem Design period twoDeficit Flow notesChilled-WaterSystem Design period twoExcess Flow notesChilled-WaterSystem Design period twoControl of Primary-SecondarySystem notesChilled-WaterSystem Design period twoTypes of Fluid Flow Meters Chilled-WaterSystem Designperiod two Pressure-basedTemperature-BasedCalculations notesChilled-WaterSystem Design period twoperiod three System VariationsSystem Variations period threeperiod three Fuel Choice OptionsSystem Variations absorption thermal storageChiller Efficiency Improvements System Variationsperiod three Low-FlowSystemsGreater Focus on System Efficiency Trend Toward Lower Flow Ratesnotes System VariationsLow-FlowSystems notesSystem Variations period threeVariable-Primary-FlowSystems notesSystem Variations period threeCritical VPF System Requirements notesSystem Variations period threePreferential Chiller Loading notesSystem Variations period threeSidestream Configuration notesSystem Variations period threeHeat-RecoveryChiller Heat Recoverynotes System VariationsHeat-RecoveryChiller Options notesSystem Variations period threeHeat-RecoveryChiller Efficiency notesSystem Variations period threeControl of a Heat-RecoveryChiller notesSystem Variations period threeAsymmetric Design notesSystem Variations period threeSwing Chiller notesSystem Variations period threenotes System Variationsperiod three Swing Chiller“Free” Cooling notesSystem Variations period threePlate-and-FrameHeat Exchanger notesSystem Variations period threeRefrigerant Migration notesSystem Variations period threeApplication Outside Range of Chiller notesSystem Variations period threeperiod four Chiller-PlantControlChiller-PlantControl period fourperiod four Chiller ControlsStart–stop Chilled-watertemperature control notesWhat Is Important? When to turn a chiller on or offHow to recover from an equipment failure How to optimize system efficiencyChiller Sequencing notesChiller-PlantControl period fourTemperature notesChiller-PlantControl period fourFlow notesChiller-PlantControl period fourCapacity notesChiller-PlantControl period fourChiller Rotation notesChiller-PlantControl period fourWhen 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 systems notesChiller-PlantControl period fourHeat Recovery preferentially-loaded heat-recoverychillernotes Chiller-PlantControlThe 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 ranges notesChiller-PlantControl period fourSystem Failure Recovery Failure Recovery and Contingency Planningnotes Chiller-PlantControlContingency Planning notesChiller-PlantControl period fourSystem Timers System TuningLoad-confirmationtimer Staging-intervaltimerUnload Before Start notesChiller-PlantControl period fourSoft Loading notesChiller-PlantControl period fourChilled-WaterSet Point Control notesChiller-PlantControl period fourSystem Optimization notesChiller-PlantControl period fourChilled Water Reset notesChiller-PlantControl period fourCondenser-WaterTemperature notesChiller-PlantControl period fourControl of Condensing Pressure Chiller-PlantControlperiod four Operator Training and Support notesChiller-PlantControl period fourOperator Interface notesChiller-PlantControl period fourASHRAE Guideline notesChiller-PlantControl period fourperiod five ReviewReview period fiveperiod five Review—PeriodTwoParallel configuration Series configuration notesReview—PeriodThree Heat recovery Asymmetric designnotes ReviewReview—PeriodFour Chiller sequencing Failure recoveryContingency planning System tuning notesReview period fivenASHRAE Handbook – Refrigeration nASHRAE Handbook – Systems and EquipmentQuiz Questions for PeriodQuestions for Period 9Why does a variable-primary-flowVPF system require a bypass in the system? QuizQuestions for Period Questions for PeriodAnswers Answers 12Sequencing 13Decreases; increasesGlossary Glossary decoupled system See primary-secondarysystemGlossary notes Glossaryswing 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 The Trane Company