Trane SYS-APM001-EN manual Variable-speed pump load control, Face-and-bypass dampers

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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

9

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Contents May Page Chiller System Design and Control Preface Contents 100 Chiller Primary System ComponentsChiller evaporator Primary System ComponentsEffect of chilled-water flow rate and variation Effect of chilled-water temperatureEffect of condenser-water temperature Water-cooled condenserEffect of condenser-water flow rate Packaged or Split System? MaintenanceAir-cooled condenser Air-cooled versus water-cooled condensers Energy efficiency Low-ambient operationAir-cooled or water-cooled efficiency LoadsTwo-way valve load control Three-way valve load controlFace-and-bypass dampers Variable-speed pump load controlChilled-water pump Chilled-Water Distribution SystemDistribution piping Pump per chillerManifolded pumps Constant flow system Pumping arrangementsVariable-primary system Condenser-Water SystemCooling tower Primary-secondary systemSingle tower per chiller Condenser-water pumping arrangementsEffect of load on cooling tower performance Effect of ambient conditions on cooling tower performanceUnit-Level Controls Chiller controlRecommended chiller-monitoring points per Ashrae Standard Centrifugal chiller with AFD Centrifugal chiller capacity controlAFD on both chillers Small Chilled-Water Systems 1-2 chillers Application ConsiderationsApplication Considerations Constant flow Variable flowCondensing method Part load system operation Application ConsiderationsNumber of chillers Parallel or seriesMid-Sized Chilled-Water Systems Chillers Managing control complexityPreferential vs. equalized loading and run-time Large Chilled-Water Systems + Chillers, District Cooling Large chilled-water system schematicPower Pipe sizeWater Controls Chiller performance testingLimitations of field performance testing Chiller Plant System PerformanceSYS-APM001-EN SYS-APM001-EN Guidance for Chilled- and Condenser-Water Flow Rates System Design OptionsChilled-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 Low-flow conditions for cooling tower Base Case Low Flow DP2/DP1 = Flow2/Flow11.85System summary at full load Total system power Component Power kW Base Case Low FlowChilled water system performance at part load Coil response to decreased entering water temperatureSystem design Entering fluid temperature, F CCooling-tower options with low flow Smaller towerSame tower, smaller approach ΔT2 = 99.1 78 = 21.1F or 37.3 25.6 = 11.7CSame tower, smaller approach Present Smaller Approach Same tower, larger chillerRetrofit capacity changes Larger Present Chiller Same tower Retrofit opportunitiesCost Implications Misconception 1-Low flow is only good for long piping runs Misconceptions about Low-Flow RatesKWh SYS-APM001-EN Parallel Chillers System ConfigurationsParallel chillers with separate, dedicated chiller pumps System ConfigurationsSeries chillers Series ChillersHydraulic decoupling Primary-Secondary Decoupled SystemsCheck valves Production loop System Configurations ProductionDistribution-loop benefits of decoupled system arrangement System Configurations DistributionCommon CampusTertiary or distributed Tertiary pumping arrangement Decoupled system-principle of operationTemperature-sensing Flow-based controlFlow-sensing Multiple chilled-water plants on a distribution loop Adding a chillerSubtracting a chiller Double-ended decoupled system Pump control in a double-ended decoupled systemChiller sequencing in a double-ended decoupled system Other plant designs Variable-Primary-Flow SystemsOperational savings of VPF designs Advantages of variable primary flowDispelling a common misconception Chiller selection requirementsFlow, ft.water Flow rate Flow-rate changes that result from isolation-valve operation Managing transient water flowsSystem Configurations Effect of dissimilar evaporator pressure drops System design and control requirementsAccurate flow measurement Bypass flow control Chiller sequencing in VPF systemsFlow-rate-fluctuation examples Adding a chiller in a VPF systemSequencing based on load Subtracting a chiller in a VPF systemSelect slow-acting valves to control the airside coils Other VPF control considerationsConsider a series arrangement for small VPF applications Plant configurationChiller selection Guidelines for a successful VPF systemAirside control Plant configurationBypass flow Chiller sequencingPlate-and-frame heat exchanger Heat RecoveryChilled-Water System Variations Condenser Free Cooling or Water EconomizerRefrigerant migration Chilled-Water System VariationsWell, river, or lake water Refrigerant migration chiller in free-cooling modePreferential loading parallel arrangement Preferential LoadingSidestream plate-and-frame heat exchanger Preferential loading sidestream arrangementChilled-Water System Variations Sidestream with alternative fuels or absorptionSidestream system control Preferential loading series arrangementSeries-series counterflow Series-Counterflow ApplicationUnequal Chiller Sizing EvaporatorsCondensers System Issues and Challenges Low ΔT SyndromeAmount of Fluid in the Loop Example System Issues and ChallengesChiller response to changing conditions System response to changing conditionsContingency Minimum capacity requiredType and size of chiller Ancillary equipment System Issues and Challenges Location of equipmentAlternative Energy Sources Water and electrical connectionsPlant Expansion Alternative fuelThermal storage Retrofit Opportunities Applications Outside the Chiller’s RangeFlow rate out of range Precise temperature control System Issues and Challenges Temperatures out of rangePrecise temperature control, multiple chillers Chilled-water pump control Chilled water reset-raising and loweringSystem Controls Chilled-Water System ControlCritical valve reset pump pressure optimization System ControlsNumber of chillers to operate Chillers Difference Condenser-Water System ControlMinimum refrigerant pressure differential VFDs and centrifugal chillers performance at 90% loadCooling-tower-fan control Condenser-water temperature controlChiller-tower energy consumption Chiller-tower energy balanceChiller-tower-pump balance System Controls Variable condenser water flowEffect of chiller load on water pumps and cooling tower fans Decoupled condenser-water systemCDWP-2 Failure recovery Failure RecoveryConclusion Glossary Pumps system GlossaryGlossary Plant. Idea 88th Annual Conference Proceedings 1997 ReferencesEngineering July References102 Ashrae IndexIndex 105 106 Page Trane