Trane SYS-APM001-EN manual 100

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System Controls	87
Chilled-Water System Control	87
Condenser-Water System Control	89
Failure Recovery	95
Conclusion	96
Glossary	97
References	100
Index	103

iv

Chiller System Design and Control

SYS-APM001-EN

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Contents May Page Chiller System Design and Control Preface Contents 100 Primary System Components ChillerPrimary System Components Chiller evaporatorEffect of chilled-water temperature Effect of chilled-water flow rate and variationEffect of condenser-water temperature Water-cooled condenserEffect of condenser-water flow rate Air-cooled versus water-cooled condensers MaintenanceAir-cooled condenser Packaged or Split System?Low-ambient operation Energy efficiencyLoads Air-cooled or water-cooled efficiencyThree-way valve load control Two-way valve load controlVariable-speed pump load control Face-and-bypass dampersChilled-Water Distribution System Chilled-water pumpDistribution piping Pump per chillerManifolded pumps Pumping arrangements Constant flow systemPrimary-secondary system Condenser-Water SystemCooling tower Variable-primary systemEffect of ambient conditions on cooling tower performance Condenser-water pumping arrangementsEffect of load on cooling tower performance Single tower per chillerUnit-Level Controls Chiller controlRecommended chiller-monitoring points per Ashrae Standard Centrifugal chiller capacity control Centrifugal chiller with AFDAFD on both chillers Application Considerations Small Chilled-Water Systems 1-2 chillersApplication Considerations Constant flow Variable flowCondensing method Parallel or series Application ConsiderationsNumber of chillers Part load system operationMid-Sized Chilled-Water Systems Chillers Managing control complexityPreferential vs. equalized loading and run-time Large chilled-water system schematic Large Chilled-Water Systems + Chillers, District CoolingPower Pipe sizeWater Chiller Plant System Performance Chiller performance testingLimitations of field performance testing ControlsSYS-APM001-EN SYS-APM001-EN System Design Options Guidance for Chilled- and Condenser-Water Flow RatesChilled-Water Temperatures Standard rating temperaturesSystem Design Options Condenser-Water Temperatures Chilled- and Condenser-Water Flow RatesStandard rating flow conditions System Design Options Selecting flow rates DP2/DP1 = Flow2/Flow11.85 Low-flow conditions for cooling tower Base Case Low FlowTotal system power Component Power kW Base Case Low Flow System summary at full loadCoil response to decreased entering water temperature Chilled water system performance at part loadSmaller tower Entering fluid temperature, F CCooling-tower options with low flow System designΔT2 = 99.1 78 = 21.1F or 37.3 25.6 = 11.7C Same tower, smaller approachSame tower, larger chiller Same tower, smaller approach Present Smaller ApproachRetrofit opportunities Retrofit capacity changes Larger Present Chiller Same towerCost Implications Misconceptions about Low-Flow Rates Misconception 1-Low flow is only good for long piping runsKWh SYS-APM001-EN System Configurations Parallel ChillersSystem Configurations Parallel chillers with separate, dedicated chiller pumpsSeries Chillers Series chillersPrimary-Secondary Decoupled Systems Hydraulic decouplingCheck valves System Configurations Production Production loopSystem Configurations Distribution Distribution-loop benefits of decoupled system arrangementCommon CampusTertiary or distributed Decoupled system-principle of operation Tertiary pumping arrangementTemperature-sensing Flow-based controlFlow-sensing Multiple chilled-water plants on a distribution loop Adding a chillerSubtracting a chiller Pump control in a double-ended decoupled system Double-ended decoupled systemChiller sequencing in a double-ended decoupled system Variable-Primary-Flow Systems Other plant designsAdvantages of variable primary flow Operational savings of VPF designsChiller selection requirements Dispelling a common misconceptionFlow, ft.water Flow rate Managing transient water flows Flow-rate changes that result from isolation-valve operationSystem Configurations System design and control requirements Effect of dissimilar evaporator pressure dropsAccurate flow measurement Chiller sequencing in VPF systems Bypass flow controlAdding a chiller in a VPF system Flow-rate-fluctuation examplesSubtracting a chiller in a VPF system Sequencing based on loadOther VPF control considerations Select slow-acting valves to control the airside coilsPlant configuration Consider a series arrangement for small VPF applicationsGuidelines for a successful VPF system Chiller selectionChiller sequencing Plant configurationBypass flow Airside controlCondenser Free Cooling or Water Economizer Heat RecoveryChilled-Water System Variations Plate-and-frame heat exchangerChilled-Water System Variations Refrigerant migrationRefrigerant migration chiller in free-cooling mode Well, river, or lake waterPreferential Loading Preferential loading parallel arrangementPreferential loading sidestream arrangement Sidestream plate-and-frame heat exchangerSidestream with alternative fuels or absorption Chilled-Water System VariationsPreferential loading series arrangement Sidestream system controlSeries-Counterflow Application Series-series counterflowUnequal Chiller Sizing EvaporatorsCondensers System Issues and Challenges Low ΔT SyndromeAmount of Fluid in the Loop System response to changing conditions System Issues and ChallengesChiller response to changing conditions ExampleContingency Minimum capacity requiredType and size of chiller Water and electrical connections System Issues and Challenges Location of equipmentAlternative Energy Sources Ancillary equipmentPlant Expansion Alternative fuelThermal storage Retrofit Opportunities Applications Outside the Chiller’s RangeFlow rate out of range System Issues and Challenges Temperatures out of range Precise temperature controlPrecise temperature control, multiple chillers Chilled-Water System Control Chilled water reset-raising and loweringSystem Controls Chilled-water pump controlCritical valve reset pump pressure optimization System ControlsNumber of chillers to operate VFDs and centrifugal chillers performance at 90% load Condenser-Water System ControlMinimum refrigerant pressure differential Chillers DifferenceCondenser-water temperature control Cooling-tower-fan controlChiller-tower energy balance Chiller-tower energy consumptionSystem Controls Variable condenser water flow Chiller-tower-pump balanceDecoupled condenser-water system Effect of chiller load on water pumps and cooling tower fansCDWP-2 Failure Recovery Failure recoveryConclusion Glossary Glossary Pumps systemGlossary References Plant. Idea 88th Annual Conference Proceedings 1997References Engineering July102 Index AshraeIndex 105 106 Page Trane