System Failure Recovery | Trane TRG-TRC016-EN specification

period four

Chiller-Plant Control

notes

System Failure Recovery

▲Maintain flow of chilled water

▲Keep it simple

◆Lock out failed equipment

◆Turn on the next chiller in the sequence

▲Notify the operator

▲Allow the operator to intervene

Figure 98

Failure Recovery and Contingency Planning

In addition to normal chiller sequencing, the chiller-plant control system must react when a chiller or another piece of associated equipment fails. Failure recovery, or ensuring the reliable supply of chilled water, is a very important part of the chiller-plant control system, and is an area where many systems have fallen short. This is especially true in field-programmed systems because of the difficulty of thorough debugging.

During periods of equipment malfunction, it is important to focus on the primary goal of the system, which is to provide the required flow of chilled water to the system at the proper temperature. It seems reasonable that the simplest and most reliable failure-recovery sequence is to simply turn on the next chiller in the sequence, and not try to turn several chillers on and off in an attempt to re-optimize the system.

During an equipment failure, it is especially important to notify the operator of the status, as well as to help the operator understand where the problem is and what might be the cause. The control system must also allow the operator to easily analyze the situation and to intervene if the failure condition will exist for an extended period of time. A system that provides this information will ensure that the system itself will be maintained and operated in proper condition.

90	TRG-TRC016-EN

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Trane TRG-TRC016-EN manual System Failure Recovery, Failure Recovery and Contingency Planning

Contents

Air Conditioning Clinic Chilled-Water Systems Business Reply Mail One of the Systems Series Comment Card One of the Systems Series Publication Trane Company Preface Contents Iii Water systems Types of Water Chillers Compressor-driven heat-driven Driving Sources Vapor-Compression Water Chillers Vapor-Compression Cycle Scroll Reciprocating Helical-rotarycentrifugal Compressor Types Variable-Speed Drives Air-Cooled or Water-Cooled Condenser TypesAir-Cooled or Water-Cooled Condensing Maintenance Low Ambient Operation Efficiency Comparison Packaged or Split Components Packaged Air-Cooled Chiller Remote Evaporator Barrel Remote Air-Cooled Condenser Indoor Air-Cooled Condenser Absorption Water Chillers Absorption Refrigeration Cycle Absorption Chillers Offer Choice Single-effectdouble-effect Direct-fired Absorption Chiller Types Equipment Rating Standards Equipment Rating StandardsAir-Conditioning & Refrigeration Institute ARI Integrated Part-Load Value Iplv Part-Load Efficiency RatingNon-Standard Part-Load Value Nplv Evaporator Condenser Rating Chiller type Flow rate Standard Rating Conditions QBtu/hr = 500 ⋅ flow rate ⋅ ∆T Flow Rates and Temperatures ARI conditions Low-flow conditions Electric Vapor-Compression Chillers ASHRAE/IESNA StandardEnergy Standard Chiller type Capacity Water-Cooled Absorption Chillers Ashrae Standard Chilled-Water System Components Chilled-Water System Design Chilled-Water System Load-Terminal Control Load-Terminal Control Options Three-Way Valve Control Two-Way Valve Control Face-and-Bypass Damper Control Three-way modulating valve Chiller Evaporator FlowConstant flow is most common Variable flow is possible Single-Chiller System Redundancy Part-load efficiency Multiple-Chiller Systems Single Pump Parallel Configuration Dedicated Pumps Percent flow Chillers Piped in Series Series Configuration Equal Set Points Staggered Set Points Primary-Secondary Decoupled Configuration Primary-Secondary Configuration Bypass pipe should be free of restrictions Primary-Secondary System Rules Production Loop Manifolded Production Pumps Distribution Loop Load terminals should use two-way modulating control valves Bypass pipe should be free of restrictions Variable-speed control riding the pump curve Varying Distribution Flow Multiple Distribution Pumps Distribution Tertiary Pumping Distribution Loop Characteristics Primary-Secondary System Rules Primary-Secondary System Operation System Operation Deficit Flow Excess Flow Control of Primary-Secondary System Pressure-based Types of Fluid Flow MetersTurbine and impeller Vortex Magnetic Ultrasonic Temperature-Based Calculations Alternate Fuel Choice Electric Utility Deregulation Indirectly-coupled, gas-engine chillers Fuel Choice Options Low-Flow Systems Chiller Efficiency Improvements Trend Toward Lower Flow Rates Greater Focus on System Efficiency Low-Flow Systems Variable-Primary-Flow Systems Variable-Primary-Flow Systems Critical VPF System Requirements Preferential Loading Preferential Chiller Loading Sidestream Configuration Heat Recovery Heat-Recovery Chiller Heat-recovery Auxiliary Dual condenser Condenser Heat pump Heat-Recovery Chiller Options Mode Heat-Recovery Chiller Efficiency Unloadingwith Control of a Heat-Recovery Chiller Asymmetric Design Asymmetric DesignDifferent chiller Capacities Different chiller Swing Chiller Chiller Free Cooling Free CoolingAirside economizer Waterside economizer Plate-and-Frame Heat Exchanger Refrigerant Migration Application Outside the Operating Range of the Chiller Application Outside Range of Chiller Chiller-Plant Control Chiller Controls What Is Important? Chiller Sequencing Chiller Sequencing Temperature Flow Capacity Chiller Rotation Small electric Chiller largeelectric chiller Heat Recovery Variable-Primary-Flow Systems Failure Recovery and Contingency Planning System Failure RecoveryMaintain flow of chilled water Keep it simple Notify the operator Allow the operator to intervene Contingency Planning System Tuning System TimersLoad-confirmation timer Staging-interval timer Unload Before Start Soft Loading Chilled-Water Set Point Control System Optimization System Optimization Pros Chilled Water ResetCons Tower Condenser-Water Temperature Control of Condensing Pressure Operator Interface Operator Training and Support Operator Interface Ashrae Guideline Vapor-compression water chillers Review-Period One Load-terminal control Review-Period Two Review-Period Three Review-Period Four For more information, refer to the following references Quiz 109 Answers 111 Glossary 113 114 115 Trane Company