MeasuredMeasured ImpactsImpacts ofof SupermarketSupermarket HumidityHumidity LevelLevel onon DefrostDefrost PerformancePerformance andand RefrigerationRefrigeration SystemSystem EnergyEnergy UseUse
ASHRAE Winter Meeting January 24, 1999
Hugh Henderson, Jr., P.E. Mukesh K. Khattar, PhD., PE CDH Energy Corp. EPRI www.cdhenergy.com www.epri.com IntroductionIntroduction
Q CollectedCollected detaileddetailed monitoredmonitored datadata continuouslycontinuously atat twotwo storesstores forfor moremore thanthan 1212 monthsmonths Q UsedUsed directdirect digitaldigital controlcontrol (DDC)(DDC) systemsystem toto collectcollect datadata everyevery 1515 minutesminutes Q TwoTwo typicaltypical supermarketssupermarkets inin thethe MidwestMidwest – Store A: 33,400 ft2, Minneapolis, MN – Store B: 50,000 ft2, Indianapolis, IN TestTest ObjectivesObjectives
Q QuantifyQuantify thethe impactimpact ofof storestore humidityhumidity onon refrigerationrefrigeration energyenergy useuse Q UnderstandUnderstand thethe factorsfactors thatthat impactimpact affectaffect energyenergy useuse – latent loads, defrost, anti-sweat heaters Q DevelopDevelop easy-to-understandeasy-to-understand rules-of-thumbrules-of-thumb toto predictpredict thethe impactimpact ofof enhancedenhanced dehumidificationdehumidification systemssystems onon refrigerationrefrigeration energyenergy useuse ImpactImpact ofof SpaceSpace HumidityHumidity
ExpectedExpected ImpactImpact ofof LowerLower HumidityHumidity::
Q ReducedReduced moisturemoisture loadload onon displaydisplay casescases (and(and compressors)compressors) Q ReducedReduced defrostdefrost energyenergy useuse andand imposedimposed refrigerationrefrigeration loadsloads Q ReducedReduced anti-sweatanti-sweat heaterheater energyenergy useuse andand imposedimposed refrigerationrefrigeration loadsloads RefrigerationRefrigeration SystemsSystems
Characteristics Store A Store B Type of System Parallel Racks Single Comp. Racks Rack A – low temp (R502) 25 Racks (R22) Racks B, C, D medium temp (R22) Number of Compressors 18 25 Number of Zones 34 45 Total Case Length 716 ft 938 ft Total Cooler/Freezer Area 2,849 ft2 3,685 ft2 Total Refrigeration Load 60 tons 80 tons Active Defrost Method Hot Gas Electric 16 zones, time terminated 16 zones, pressure terminated, 160 kW Controlled Anti-Sweat 10 kW 9 kW Heaters 22 kW total StoreStore AA
Q Minneapolis, Minneapolis, Produce
MN Deli 2 Q 33,400 ft gross Bakery Dairy area (sales area Meat Meat 77%) Prep Entrance Exit Q open 24 hours, Checkout 7 days Q Built in 1985
Frozen Food StoreStore BB
250 ft
Q Indianapolis, Storage & Stock Rooms IN Dairy Meat & Fish Frozen Food 2 Produce Q 50,000 ft gross Cooler
200 ft area (sales area Produce Pharmacy Salad 73%) Bar Cheese
Q open 24 hours, Check Out Aisles Bakery & Floral Deli Main 7 days Video Entrance Q Built in 1992 MonitoredMonitored DataData
Description Store A Store B Outdoor Air Temperature Yes Yes Outdoor Relative Humidity Yes Yes Sales Area Temperature Yes Yes Sales Area Humidity Yes Yes Frozen Food Aisle Temperature Yes - Refrigeration System Power Yes Yes (compressor racks and (racks, condenser fans, condenser fans) electric defrost ) Anti-Sweat Heater Power Yes Yes (status of controlled heaters) (total anti-sweat heater power) Display Case Temperatures Yes - Defrost Control Parameters Yes - RefrigerationRefrigeration EnergyEnergy UseUse
Store A Refrigeration System: 06/15/94 to 09/30/95
2800
STORE A: Parallel Racks 2600
60 tons 2400
2200
2000
Store B Refrigeration System: 05/15/95 to 02/15/96 1800 3500 1600 Daily RefrigerationEnergy (kWh/day) Use
3000 1400 020406080100 Daily Average Outdoor Air Temperature (F) 2500
2000
1500
Daily Refrigeration Energy (kWh/day) Use STORE B: Single Racks 1000 0 20406080100 80 tons Daily Average Outdoor Air Temperature( F) QuantifyingQuantifying thethe ImpactImpact ofof HumidityHumidity
Store B Refrigeration System: 07/20/95 to 09/20/95 3000
30% to 40% 40% to 50% 2800
2600
2400
45%
2200 35% Daily Refrigeration Energy (kWh/day) Use
2000 40 60 80 100 Daily Average Outdoor Air Temperature (F) ImpactImpact ofof HumidityHumidity onon EnergyEnergy UseUse
Q Multi-LinearMulti-Linear RegressionRegression AnalysisAnalysis ofof RefrigerationRefrigeration EnergyEnergy UseUse atat StoreStore BB::
2 KWhREF = 268.39 + 23.72•TAO + 9.88•RH, R = 0.98 <4.7> <23.0> <9.4> t-ratios
Q ImpactImpact ofof Humidity:Humidity: 9.99.9 kWh/daykWh/day perper %RH%RH Q DataData forfor periodperiod withwith stepstep changechange inin humidity…sohumidity…so therethere isis littlelittle auto-correlationauto-correlation TheThe ImpactImpact ofof TerminatedTerminated DefrostDefrost
Store A Refrigeration System: 10/15/94 to 04/15/95
Q 2100 StoreStore AA Time-Terminated Defrost Temperature-Terminated Defrost 2000 originallyoriginally usedused Savings: 69.8 kW h/day time-terminatedtime-terminated 1900 hothot gasgas defrostdefrost 1800 Q ConvertedConverted toto 1700 1600 temperature-temperature- Daily Refrigeration Energy (kWh/day)Use 1500 0 102030405060 terminatedterminated Daily Average Outdoor Air Temperature(F ) defrostdefrost DefrostDefrost AnalysisAnalysis -- StoreStore AA
Q SIMPLESIMPLE Multi-linearMulti-linear regressionregression analysisanalysis (6(6 monthsmonths ofof data):data): 2 kWhREF = 1490.2 + 8.7•TAO - 69.8•DEF,R = 88
<99> <24> <7.4> t-ratios
Q COMPLEXCOMPLEX regressionregression analysisanalysis (12(12 monthsmonths ofof data):data):
2 2 kWhREF = 1597.7 + 2.1•TAO + 0.83•TAO - DEF•(145.6 - 4.0•RH), R = 92%
<52> <2.0> <7.4> <3.8> <3.0> t-ratios
DEF = defrost dummy variable (0=time-terminated, 1=temp-terminated) DefrostDefrost AnalysisAnalysis -- StoreStore AA ((contcont.).)
Q Q ComplexComplex andand 150 simple analysis Simple (6 mo) simple analysis 100 agreeagree 69.8 kWh/day @ 22% RH 50 Q ComplexComplex analysisanalysis Complex (12 mo) 0 impliesimplies thatthat energyenergy kWh = 145.6 + 4.0•RH
-50
useuse increasesincreases byby Defrost (kWh/day) Temperature-Terminated Due to Savings 10 20 30 40 44 kWh/daykWh/day perper %% RHRH Store Humidity Level (%) withwith hothot gasgas defrostdefrost (due(due toto impactimpact ofof defrostdefrost heatheat onon load)load) Anti-SweatAnti-Sweat HeaterHeater EnergyEnergy UseUse
Q Store A Q InIn StoreStore AA thethe 250
originaloriginal electroelectro-- 200
mechanicalmechanical controlscontrols 150
werewere replacedreplaced withwith 100 Original Control Improved Control
DDCDDC controlscontrols 50 Anti-Sweat Heater Energy Use (kWh/day)
Q 0 StoreStore BB usedused 10 20 30 40 50 60 standardstandard Store Relative Humidity (%) Reduction per each % RH Store A Store B electroelectro-mechanical-mechanical Drop in Space Humidity (kWh/day per (kWh/day per %RH) %RH) Electro-Mechanical Controls 3.5 4.6 controlscontrols DDC Controls 7.8 - StoreStore BB Anti-SweatAnti-Sweat HeatersHeaters
Store B Refrigeration System: 05/15/95 to 02/15/96 500 kW h/day = 257.29 + 4.63*RH, R2 = 0.87
450
400
350 Daily AS Heater Energy Use (kWh/day)Energy Daily Use ASHeater
300 0204060 Daily Average Store Relative Humidity (%) NetNet ImpactImpact ofof HumidityHumidity
Energy Reduction Factor Store A Store B (kWh/day-%RH) Hot Gas Defrost Electric Defrost 60 tons 80 tons Moisture Load Not Determined Load Imposed by Defrost 4.0 9.9 Direct Defrost Energy Use - Load Imposed by Anti-Sweat Heaters Not Determined Direct Anti-Sweat Heater Energy Use 7.8 4.6 TOTAL 11.8 14.5 Q HotHot GasGas Defrost:Defrost: 9-129-12 kWh/day-%RHkWh/day-%RH Q ElectricElectric Defrost:Defrost: 15-1815-18 kWh/day-%RHkWh/day-%RH ComparisonComparison toto HowellHowell MethodMethod
Q CalculatedCalculated EnergyEnergy ReductionReduction FactorFactor forfor StoreStore BB byby methodmethod developeddeveloped inin ASHRAEASHRAE 596-RP:596-RP: 88 kWh/day-%RHkWh/day-%RH Q MeasuredMeasured EnergyEnergy ReductionReduction FactorFactor (without(without ASAS Heaters):Heaters): 1010 kWh/day-%RHkWh/day-%RH Q MeasuredMeasured valuevalue isis higherhigher duedue toto impactimpact ofof ASAS heatersheaters onon casecase loadload – calculated to be 2 kWh/day-%RH (assuming 2.0 kW/ton compressor efficiency) SeasonalSeasonal ImplicationsImplications
Q WhatWhat areare thethe potentialpotential savingssavings forfor enhancedenhanced dehumidificationdehumidification systems?systems? Q AssumeAssume maintainmaintain 35%35% RHRH forfor summersummer inin Indianapolis,Indianapolis, ININ – equivalent to decreasing space humidity by 15% RH for 2,000 hours/yr Q WithWith factorfactor ofof 1515 kWh/day-%RH,kWh/day-%RH, annualannual refrigerationrefrigeration savings:savings: 18,75018,750 kWhkWh.. – $700 to $2,000/yr (at $0.03 to $0.11 per kWh) ConclusionsConclusions
Q HumidityHumidity impactsimpacts refrigerationrefrigeration systemsystem energyenergy useuse byby 10-2010-20 kWh/day-%RHkWh/day-%RH inin aa averageaverage storestore Q RefrigerationRefrigeration systemsystem featuresfeatures withwith bigbig impact:impact: – anti-sweat heaters (direct & indirect) – electric defrost (direct & indirect) Q FeaturesFeatures withwith lessless impact:impact: – moisture loads & hot gas defrost