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For a copy of ASHRAE Guideline 22 and other ASHRAE publications, visit the ASHRAE bookstore at www.ashrae.org/ bookstore.

SYS-APM001-EN

Application Considerations

Guidelines for system efficiency monitoring

ASHRAE Guideline 22 Instrumentation for Monitoring Central Chilled-Water Plant Efficiency6 was first published in June 2008. It states:

Guideline 22 was developed by ASHRAE to provide a source of information on the instrumentation and collection of data needed for monitoring the efficiency of an electric-motor-driven central chilled- water plant. A minimum level of instrumentation quality is established to ensure that the calculated results of chilled-water plant efficiency are reasonable. Several levels of instrumentation are developed so that the user of this guideline can select that level that suits the needs of each installation.

The basic purpose served by this guideline is to enable the user to continuously monitor chilled-water plant efficiency in order to aid in the operation and improvement of that particular chilled-water plant, not to establish a level of efficiency for all chilled-water plants. Therefore, the effort here is to improve individual plant efficiencies and not to establish an absolute efficiency that would serve as a minimum standard for all chilled-water plants.

Guideline 22 includes a discussion of:

•types of sensors and data measurement devices

•calibration

•measurement resolution, accuracy, and uncertainty

•calculation methods

•example specification

•examples of measured long-term performance

Guideline 22 recommends tracking and archiving the following over the life of the plant, in addition to normal equipment operating trends. The ability to obtain this information is dependent on the instrumentation and data measurement capabilities of the system.

1Average day’s outdoor air temperature (obtain the outside air temperature every 30 minutes and find the average of these samples each day)

2Day’s high temperature

3Day’s low temperature

4Day’s high wet-bulb temperature (calculate from temperature and enthalpy)

5Chilled-water supply temperature (average, max and min if chilled-water temperature is not fixed)

6Total ton-hours (kWh) production of chilled water for the day

7Total kWh power input for each component for the day

8Average kW/ton (COP) for the plant for the day

Chiller System Design and Control

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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 temperatureWater-cooled condenser Effect of condenser-water temperatureEffect of condenser-water flow rate Packaged or Split System? MaintenanceAir-cooled condenser Air-cooled versus water-cooled condensersEnergy 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 SystemPump per chiller Distribution pipingManifolded 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 performanceChiller control Unit-Level ControlsRecommended 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 ConsiderationsVariable flow Application Considerations Constant flowCondensing method Part load system operation Application ConsiderationsNumber of chillers Parallel or seriesManaging control complexity Mid-Sized Chilled-Water Systems ChillersPreferential vs. equalized loading and run-time Large Chilled-Water Systems + Chillers, District Cooling Large chilled-water system schematicPipe size PowerWater 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 OptionsStandard rating temperatures Chilled-Water TemperaturesSystem Design Options Chilled- and Condenser-Water Flow Rates Condenser-Water TemperaturesStandard 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 DistributionCampus CommonTertiary or distributed Tertiary pumping arrangement Decoupled system-principle of operationFlow-based control Temperature-sensingFlow-sensing Adding a chiller Multiple chilled-water plants on a distribution loopSubtracting 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 ApplicationEvaporators Unequal Chiller SizingCondensers Low ΔT Syndrome System Issues and ChallengesAmount of Fluid in the Loop Example System Issues and ChallengesChiller response to changing conditions System response to changing conditionsMinimum capacity required ContingencyType and size of chiller Ancillary equipment System Issues and Challenges Location of equipmentAlternative Energy Sources Water and electrical connectionsAlternative fuel Plant ExpansionThermal storage Applications Outside the Chiller’s Range Retrofit OpportunitiesFlow 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 ControlSystem Controls Critical valve reset pump pressure optimizationNumber 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
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