OAK RIDGE NATIONAL LABORATORY Calmac Ice Storage Test Report

across manufacturersone operatingas weil.Often system performancevalues are given for onlypoint, making it difficult to predict performanceunder other operatingconditions.Electric Power Research Institute (EPRI) therefore sponsored the development ofan Ice Storage Test Facility (ISTI to permit uniform testing of commercial-size cool storageequipment of many different types. This testing serves two purposes: (1) to provide uniformperformancetest results and (2) to promote system improvements based on experimentaldata. Uniform test results will be useful to utilities in promoting their installation and use andin requestingrate incentives from public utilities eommissiom (PUCs)and to buildingdesigners in specifying appropriate equipment for their applications. The experimental datawill also be useful to equipment designers because it will describe component behavior as wellas overall system performance.The capacity of the ISTF was sized at 250 ton-h. Real-timedata acquisition and precise computer controls were included.The ISTF can be used to test dynamic, liquid recirculation, secondary fluid, and directexpansion (DX) ice makers. The simplest ice maker is a DX machine,. In a DX ice maker,the refrigerant is sent as a cold liquid into coils submerged in a tank of water.As therefrigerant passes through these coils, it absorbs heat from the water and evaporates.As therefrigerant leaves the coils, it is completely gaseous and usually slightly superheated.water in the tank is thereby chilled until it becomes frozen.TheWhen the stored cooling isneeded, the ice is melted by circulating warm water from the heat load through the ice andreturning the chilled water to the heat load. This arrangementis called an exterior meltbecause the ice is melted from the surface opposite from the surface where the ice is formed.In a secondary fluid system, the cold liquid refrigerant is sent to a heat exchangeroutside the tank of water. In this heat exchanger, a secondary fluid, typically a glycol mixture,is chilled. This secondary fluid is then sent to the tank of water where it absorbs heat fromthe water, again freezing the water in the tank. The secondary fluid can also be used toJtransfer the stored cooling to the heat load. This arrangement is called an internal melt. Thestored cooling energy can also be transferred to the heat load by using an external melt asdescribed for the DX system.A liquid recirculation system is similar to the DX system because the cold refrigerant is sent to coils submerged in the tank of water. However, in the liquid recirculation system,.the amount of refrigerant circulated through the coils is typically two to three times greaterthan in a DX s tem that. on}y a r rtinn of the refrigerant is evaporated and the coils

remain full of liquid throughouttheir length.This additional refrigerant circulation isaccomplished through the use of gravity feed or a refrigerant pump.The stored coolingenergy is transferred to the heat load using an external melt arrangement.A dynamic ice maker freezes ice using either a DX or a liquid overfeed arrangement.However, in a dynamic system, the ice is harvested on a periodic basis. This harvesting cyclereduces the ice thickness on the heat transfer surface of the chiller. After the ice isharvested, it is stored in a slush or slurry of ice and water. The water is circulated to providethe stored cooling to the heat load.This report describes the test results for an ice storage tank furnished by the CalmacManufacturing Corporation.The Calmac storage tank is both charged and discharged usinga secondary fluid or brine. The storage system and the test facility are described in Sect. 2.Section 3 describes the tests that were performed to characterize the storage s)- tem, andSect. 4 describes the analysis methods used to evaluate the performance data. The results andrecommendations are summarized in Sects. 5 and 6.

2. SYSTEM DES ON2.1 CALMAC STORAGE SYSTEMThe Calmac model 1190 ice tank is chilled by the flow of brine through 5/8-in.-ODplastic tubing, spaced roughly 1 1/2 in. (center to center) apart. These tubes are submergedin water. The brine used for these tests was a mixture of ethylene glycol and water with afreezing point of -0 F.Caimac recommends a mixture with a slightly lower ethylene glycolconcentration, and a few tests were run at its recommended concentration.The tank can befrozen nearly solid, leaving only a minimum amount of free water to fill the voids that occurnear the heat exchanger tubing when the ice first begins to melt. The Calmac ice tank isdischarged by circulating the brine through the tank and then through the desired heat load,simulated by a simple heater in the test facility. The Calmac tanks are equipped with a waterdepth sensor that can be used to infer the amount of ice stored during a charging cycle andthe state of charge during a discharge cycle.1When the Calmac tanks were filled with the specified volume of 1620 gal of water,the water level was -3 in. higher than the recommended level of 10 in. below the fill port.During the first charge cycle, a small amount of water overflowed the tank, leaving a newfully melted water level --0.7 in. lower than the initial level. Based on the volume vs waterlevel calibration for this tank, that level change amounted to - 12 gal of water. The volumeof brine in the storage system was not measured.2.2 TF ,KFFACILITYThe test facility was designed to test a wide variety of storage systems, lt includes alirefrigeration system components necessary to charge brine systems. Figure 1 shows the testfacility configuration used to test the Calmac storage tank equipped with the brine coils. Thetest facility is well-equipped with monitoring devices to measure temperature, pressure, flow,and energy use. The monitoring points shown in Fig. 1 are listed in Table 1. A clear plastictube was inserted into the tank near the tank wall (where the water usually remains unfrozen)and looped and secured outside the tank to facilitate reliable measurements of water level.Before each level measurement was recorded, the tube inside the tank was checked to be surethat it was free of ice. The measured water level reflects changes in the tank water depth

ORNL-DWG 91-2798 ETDCooling WaterTEl9FE6PE1(Condenser)PE2"l--h 2FE11JE1TElFE5.CompressorsTE20PE10TEl0Thermal Expansion.''1/TEl8TEl7vTEl2JEIOFE3e telHTEl6Unerl-- :/--- !TEl 1FE43--Brine,:: Tank:BypassJE!TEl4TEl5,PumpsFig. 1. ]ST]:: schematic for Calmac storage system.that occur during freezingloop instrumentationis describedA variabledischargedue to the differencespeedin density betweenmore fully in Appendixpump was used to circulateevaporator/chiller,brinesystem to the brine loop that chargesa refrigerantis vaporized,the desiredwide range of testing conditions,refrigerantcoils was selected.coils based on the compressorThe controlloading.these coils open and close in responsethe evaporator/chillerThe testA and Ref. 2.cycles, as is shown in Fig. 1. The evaporator/chillerfacility's refrigerationice and water.during boththe charge(see Fig. 1) connectsthe ice storageandthe testtank.In theabsorbing heat from tee brine. To accommodatea chiller with two independentsystem is designedThe thermalexpansionto the measuredwas often running under part-loadand equal-sizeto select one or both chillervalves feedingsuperheatconditions,refrigerantat the coil exit.the thermaltoBecauseexpansion

Table 1. ISTF monitoring pointsfor the brine coil systemPoint asured quantityChiller inlet flow, refrigerant, massChiller inlet flow, brineBrine pump discharge flowCompressor outlet flow, volumeCondenser inle water flowCompressor energy and powerBrine pump energy and powerHeater energy and powerCompressor discharge pressureCondenser outlet refrigerant pressureChiller inlet refrigerant pressureChiller inlet refrigerant pressureCompressor suction pressureCompressor discharge temperatureCondenser discharge temperatureChiller inlet refrigerant temperatureChiller inlet refrigerant temperatureCompressor suction temperatureHeater inlet water temperatureHeater outlet water temperatureIce tank outlet brine temperatureIce tank outlet brine temperatureIce tank inlet brine temperatureChiller outlet brine temperatureChiller inlet brine temperatureCondenser inlet water temperatureCondenser outlet water temperaturevalves exhibited a large degree of hunting during the beginning of most freeze tests. This istypical for part-loaded expansion valves, and the hunting usually stopped after -- 30 to 45 minof operation.The brine pump speed was varied to control the brine flow rate at the selectedvalue during the charge cycle.The ISTF was designed to permit testing under a wide range of controlled conditions.Two parallel compressors with part-load capabilities are used to vary the chiller capacity from15 to 95 tons. The flow of water to the condenser controls the condensing temperaturebetween 80 and 100 F. During discharge cycles, the brine pump speed, heater power, andbypass valve positions are used to control test conditions.

73. SYSTEM TE --I'SThe test plan was structured to test the storage tank's capabilities under a wide rangeof operating conditionso The compressor discharge pressure and loading and the brine flowrate were the primary variables during the charging tests. The flow rate to the heater, heaterpower, and the brine temperature exiting the heater were the control variables during thedischarge tests.The test schedule was designed to show how the storage system would respond todifferent ice-charging periods (from 8 to 16 h). The ice-discharge tests were designed tomimic different discharge periods ranging from 6 to 12 h with varying temperatureand flowrequirements at the heater. Tables 2-4 are taken from the ISTF test procedure and show thedesired testing schedule}Calmac tests.However, this procedure was in the process of revision during the(Indeed, many revisions were prompted by experience gained during theCalmac tests.) Tables 5 and 6 present a summary of the tests that were used to analyze theCalmac storage system performance.Many charging tests were run under compressor part-load conditions.Comparingactual power use to the compressor curve predictions for full-load power use underscores theTable 2. Planned charge test sequenceTest No.Test duration(h)Refrigerant flow tostorage tank"(gal/min)Brine flow tostorage tank b(gal/min)123456786610141418106MR c1.25 x MRMRMR0.8 MRMRMRMRMR1.5 x MRMRMR0.5 x MRMR2 MRMRSpecified for liquid overfeed tests only.bSpecified for secondary loop tests only.CManufacturer's recommended flow rates.iIi alii] iiii II/

Table 3. Planned discharge test sequenceTest No.Test duration(h)12345669126912TEl2( F)TEl 1( F)606060505050384545383845Table 4. Planned standby test sequenceTest No.Test duration(h)12 60 60Initial tank conditionFully frozenFully frozenhigh efficiency penalties associated with part-load operation.These penalties are discussedfurther in a companion document. 3Ice tank heat gains were measured by recording the change in ice inventory over along period of time in the absence of ali external fluid flows. The ice depletion over this timeperiod was ascribed to shell heat gains. The ambient temperaturestandby test.was noted during theBecause of the sheltered location of the test floor, the ambient conditionsshowed little variation.

Table 5. Calmac charge test summaryTest IDAverage capacity basedon brine flow andtemperaturechange(ton)Capacity ratio: brinemeasurements/tankwater depthmeasurementsBrine flowrate(gal/min)Average brinetemperatureriseacross coils a( 8.37.133% brine, water in % brine, water in 1.221.191.2033% brine, eutectic in tank01160119012301261317815aRTD specificationbNot available.CNot available.ccccof 0.5 F.

10Table 6. Calmac dischargeTest IDAverage capacitybased on brine flowand temperaturechange at tank(ton)Temperatureto load b( F)testsummaryTemperatureout load c( F)Average brineflow to tank(gal/min)33% brine, water in 402160d605050502121344325% brine, water in tank1101111002130215132020204236444725% brine, eutectic in tank0111124233% brine, eutectic in tank01180122012501292213242738384545"Data for test up until tank outlet temperatureexceeds 48 F or untilheater outlet temperatureexceeds control value, whichever occurs first.bControlled at the given value until tank outlet temperatureexceeds thisvalue. Test then continues until heater outlet temperatureis exceeded.cControlleddUnavailable.value.

114. ANALYSISThe primary concernpresentof the data analysis is to produceit in a meaningfulperformancefashion.of the ice storagesystem.AnothersystemWhile analysis of the refrigerationuseful to system designers,METHODOI )GYof the refrigerationsystem becauseThis introducesstorageit must have themuch added complexitythatredundantthatPR INGdataavailableincrease our understandingat the condenserfor each operationaland confidenceis measuredtest permitin the test results.on both the water and refrigerantsides of the heat exchanger.effect to the ice tank is measuredby both changesmeasureice inventory)flow and temperatureof therefrigerationand by the brineeffect is also measuredcalculationsFor example, the heat rejectionThe refrigerationin the water heightchange.by brine flow and temperaturesand at the ice tank, as well as by the power going to the discharge heater.of measurementsalso enablesus to more fully separatesystem from that of the refrigerationrequirementsrathertest.This collectionthe appropriateThermodynamicpropertiesby G. T. yis dictatedfor the temperatureThis duplicationof the ice storageby system controlThe data are immediately(for temperatures,pressures,powersummeduses, and flowvalues on a 5-min basis.for R-22 are calculatedand R. A. Erth and adaptedfrom a computerizedwereprovidedformatfor use at Oak Ridge Nationalby C. K. Rice and S. IC Fischer. Brine properties,temperature,at the heaterpoint every 30 s during a charge test andthan by the analysis requirements.(for flows or energy uses) or averagedrates) to representsides.system.The data are collected for each monitoringevery 15 s during a dischargethe performance(aTheat the chiller on both the brine and refrigerantThe energy available for discharge is measuredinformationsystem.system would not encounter.Thedevelopedtheand is certainlyfrom thot of the manufacturer'sfrom a commercialand tobetweencan prove enlighteningit must be distinguishedflexibility to test a wide variety of system types.4.1 DATAis to distinguishand the performancesystem performanceAlso, the test facility is differenta commercialconcernuseful informationby UnionCarbiderange of interest was extracted, sas a functionCorporation,ofand

124.2 REFRIGERATION4.2.1EFFECTStorage TankThe refrigerationeffect in the ice tank is directly measuredof the water in the tank, as was describedice is presentin Sect. 3. This measurementin the tank and when the ice is submerged,cycle. The measuredwith the reportedby recordingthe depthis reliable wheneverusual conditionsduring a chargingdensity of ice in previous local tests was 57.2 lb/ft 3, in good agreementrange of 57.2 lb/ft 3 at 0 C to 57.4 lb/ft 3 at -10 Cvolume change vs tank depthThese figures, combinedof 144 Btu/ab, produce(Ref. 6). The measuredchange in the 7 in. above the fully filled level was 21.1 gal/in.with an assumed water density of 62.4 lb/ft 3 and the heat of fusiona latent storagecapacity of 23.2 ton-h/in, change in water depth.The heat of fusion and density of the eutecticwere not experimentallymeasuredduring the tests at the ISTF. Calmac reports that the overall tank capacity should be deratedby 15% when the 28 F eutectictaken to be 19.7 ton-h/in,is used. 7 Using this factor, the latent storagechange in eutecticdepth.The stored cooling effect is also calcul

CALMAC ICE STORAGE TEST REPORT" Therese lC Stovall ABSTRACT The Ice Storage Test Facility (ISTF) is designed to test commercial ice storage systems. Calmac provided a storage tank equipped with coils designed for use with a secondary fluid system. The Caimac ice storage system was tested over a wide range of operating conditions. Measured system