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<ul><li><p>NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. </p><p>Using Ratings Data to Predict Field Performance of Residential Water Heaters </p><p>Jay Burch National Renewable Energy Lab ARBI Water Heater Experts Meeting National Renewable Energy Laboratory September 28, 2012 </p></li><li><p>2 </p><p>Presentation Outline </p><p> Field performance vs. rated energy factors Reflects variances in use conditions vs. test conditions Models needed to extrapolate from ratings data </p><p> Simple performance models Storage tank water heaters: paradigm No model for tankless or HPWH taking existing data </p><p> Future work HPWH simple model Validation of simple tankless and HPWH model </p><p> BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>3 </p><p>Water Heater Field Data </p><p>Daily Hot Water Energy Output [kBtu/day] </p><p>Daily</p><p> Eff</p><p>icie</p><p>ncy/</p><p>Ener</p><p>gy F</p><p>acto</p><p>r [-] </p><p>0 10 20 30 40 50 60 70 80 90 100 </p><p>0 </p><p> .1</p><p> .2 </p><p> .3</p><p> .4 </p><p> .5 </p><p> .6</p><p> .7 </p><p> .8</p><p> .9 </p><p> 1 </p><p>Test load </p><p>Field load </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>From: Actual Savings and Performance of Natural Gas Tankless Water Heaters, MN Center for Energy and Environment </p><p>Gas storage tank WH Non-condensing tankless WH Condensing tankless WH </p><p>All systems fall off at low loads </p><p>Test EFs </p><p>Storage tank WH varies the most </p><p>Tankless vary the least </p><p>Field EF mostly lower than rated EF </p></li><li><p>4 </p><p>Is Discrepancy between EFfield vs. EFtest a Problem? </p><p>NO!! Efficiency naturally varies with use conditions </p><p> Rated EF holds only at rated conditions Key factor: volume of draw Other factors: Tmains, Tset, Tenv, usage profile Does not generally indicate equipment degradation </p><p> Need models to extrapolate from rating conditions There can be real degradation in the field </p><p> Storage: probably not significant (Navigant study; PGE result) Tankless: Little data, but highly likely (scale on hx w/ hard H2O) Heat pump: Likely, but little data (?) </p><p> BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>5 </p><p>Water Heater Model Types: Three levels </p><p>2 or 3 Dimensional finite element T,v fields as f(t) Design of water heater CFD: FLUENT,... </p><p>1 Dimensional finite difference Includes stratification, run-out from heavy draw, use any heat sources Accurate annual performance predictions For storage tank water heaters and tankless: TRNSYS </p><p>Algebraic Models One-node models, time-integrated energy balance Quick and dirty annual performance prediction Focus on only algebraic models for this presentation </p><p> BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>Models predict performance for any set of use conditions </p></li><li><p>6 </p><p>Key Issue: Getting Model Input Parameters </p><p>Can one get key inputs from ratings test data? Storage tank water heaters </p><p> Key parameters inferable for simulation and algebraic models Good simulation and algebraic models exist </p><p> Tankless water heaters One parameter inferable, others must be gotten elsewhere No algebraic model exists </p><p> Heat pump water heaters No parameters inferable No algebraic model exists </p><p> Solar water heaters No parameters inferable Empirical algebraic model exists </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>7 </p><p>Energy Factor Test Summary Useful ratings data (AHRI residential water heater directory) </p><p> Storage tank water heaters (STWH) </p><p> Energy Factor: EF EF = Qout,test day/Qaux,test day </p><p> Recovery Efficiency: RE RE = Qout,1draw/Qaux,1draw-recovery RE embodies conversion efficiency conv AND tank losses during draw RE is NOT MEASURED for electric STWHs, REelec .98 by fiat </p><p> Input power/capacity: Pin MISSING outputs: measured UAtotal and measured volume (BooHoo) </p><p> Tankless water heaters (TWH) EF and Qdot,gas,max (RE, given but RE EF; mdot,max given but redundant) </p><p> Heat pump water heaters (HPWH) EF (RE given but meaningless) </p><p> Test issues: </p><p> 64.3 gal drawn @ Tset = 135 oF, Tmains,in = 57.5 F 6 equal draws, one hour apart </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>Gas Storage Tank Water Heater Models </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>9 BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>Schematic Gas Tank </p><p>Cold in Hot out P/T Valve </p><p>Gas Burner/pilot </p><p>Convection loop through flue to outside and back </p><p>Key inputs </p><p>UAflue Central flue </p><p>conv </p><p>Thermal shorts UAshorts </p><p>Insulated jacket UAskin </p><p>Other inputs </p><p>Capacitance Ctank Burner power Pburner </p><p>Sum = UAtotal </p></li><li><p>10 BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>Gas Tank Model and Parameter Inference </p><p>1/UAtotal </p><p>Tenvirons </p><p>Tstore </p><p>1/mdotcp </p><p>Tmains </p><p>Ctank </p><p>Qdot,fuel </p><p>* conv </p><p>CdTtank/dt = convPaux UAtTt-env mdotcpTout-in. </p><p>Key parameters Variables Dependent variables </p><p>UAt,gas = (RE/EF1)/[Tt-env(tday/Qout,day1/(PauxEF))] conv = RE + UAt,gas(Tt-env)/Paux </p><p> XXX = rating data </p><p>* </p><p>* see backup slides at end for derivation </p></li><li><p>11 </p><p>Algebraic storage tank models </p><p>1. Predict annual performance: QStWH,yr = [Qload + Qtank-losses]/conv = [MyrcpTout-in + UAtotal(Tset Tenv)]/conv </p><p>2. Calculate EFday:* EFday = Qload,day/Qfuel,day = conv [1/(1 + UAtotalTset-env tday/MdaycpTout-in )] </p><p>* see backup slides at end for derivation </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>12 </p><p>StWH Field Data vs. Model </p><p>Daily Hot Water Energy Output [kBtu/day] </p><p>Daily</p><p> Eff</p><p>icie</p><p>ncy/</p><p>Ener</p><p>gy F</p><p>acto</p><p>r [-] </p><p>0 10 20 30 40 50 60 70 80 90 100 </p><p>0 </p><p> .1</p><p> .2 </p><p> .3</p><p> .4 </p><p> .5 </p><p> .6</p><p> .7 </p><p> .8</p><p> .9 </p><p> 1 </p><p>Test load </p><p>Field load </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>EFtest, storage tank TWH </p><p>Storage tank algebraic model </p><p>Storage tank WH data </p><p>0</p><p>0.2</p><p>0.4</p><p>0.6</p><p>0.8</p><p>0 20 40 60 80</p><p>EFin-use vs. Qload,day, Model vs. Data </p><p>Data from Actual Savings and Performance of Natural Gas Tankless Water Heaters, MN Center for Energy and Environment </p><p>.6 </p><p>Q draw [kBtu/day] </p><p>Ener</p><p>gy F</p><p>acto</p><p>r EF </p><p>day </p></li><li><p>Potential Tankless Water Heater Algebraic Models </p><p> BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>14 </p><p>Gas Tankless Schematic (Rinnai) </p><p>Exhaust Fan Gas in </p><p>Combustion chamber </p><p>X </p><p>Control valve </p><p>X X </p><p>Heat Exchanger </p><p>3 burners </p><p>Exhaust </p><p>Hot out Cold in Adapted from the Rinnai users manual </p></li><li><p>15 </p><p>Gas Tankless One-node Thermal Model </p><p>TenvTin</p><p>TTWH</p><p>mcp.</p><p>CTWH</p><p>UA</p><p>.Qgas,in</p><p>x</p><p>TenvTin</p><p>TTWH</p><p>mcp.mcp.</p><p>CTWHCTWH</p><p>UAUA</p><p>.Qgas,in</p><p>x</p><p>Simplest possible model: one mass node (multi-node model gives better results) </p><p>= system variable </p><p>= parameter From: Tankless Water Heater Burch, J, and J. Thornton </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>16 </p><p>Input-Output Method: Possible Method </p><p>From: Application of a Linear Input/ Output Model to Tankless Water Heaters Butcher, Thomas A., Ben Schoenbauer </p><p>Major issue: Requires changing the current test method (simulated use test) to another method </p><p>Not clear how to handle wide variety of tprevious </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>17 </p><p>Tankless Data and Models </p><p>Ratings data: EF, RE, Qdot,gas,max, mdot,draw,max Observe: EF RE conv Other parameters needed*: any two of hx,decay, UA, C (hx,decay = C/UA) </p><p>*use parameter tests on similar models; or calculate from units description;... </p><p>Draw data needed: tbetween-draw , tduration-draw, mdraw </p><p>Models: 1-D Simulation models: </p><p> TRNSYS one-node and multi-node </p><p> Algebraic model: presently non-existent Proposed: draw efficiency model For in-use: analyze average draws in 3 bins (hot, warm, cold start) </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>. </p></li><li><p>18 </p><p>Analysis of a Draw (One-node model) </p><p>previous draw </p><p>draw to analyze </p><p>next draw </p><p>Time </p><p>TWH Temperature </p><p>decay </p><p>Tset </p><p>Tenv </p><p>TWH Gas Flow Rate </p><p>mgas,max . </p><p>decay </p><p>TTWH </p><p>mgas . </p><p>Waste: * Gas input during ramp-up * Qwaste = mgas,max*hng tramp Useful hot water: * Only when T = Tset </p><p>draw Qto-load@Tset/(Qto-load@Tset/conv + Qwaste) = conv/(1 + conv Qwaste/ Qto-load@Tset) </p><p>. </p><p>steady state </p><p>tprev tramp tdraw </p><p>Ramp-up </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>19 </p><p>Tankless WH Simple Algebraic Performance Model </p><p> Input data Draw inputs: tlast-draw, tdraw, mdot-draw; Tmains, Tenv, Tset Tankless unit: </p><p>Ratings data: conv, mdot,fuel,max Parameter test results, or hand estimates,...: UATWH, CTWH </p><p> Derived data* decay, T@draw start, Qcharge, tramp Draw efficiency: draw = Quseful/Qinput,draw = conv{1/[1 + (convQcharge)/Quseful]} </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>* see backup slides for derivations </p></li><li><p>20 </p><p>Data &amp; Model Efficiency vs. Draw Volume, @ 5/45m Delays </p><p>0</p><p>0.1</p><p>0.2</p><p>0.3</p><p>0.4</p><p>0.5</p><p>0.6</p><p>0.7</p><p>0.8</p><p>0 0.5 1 1.5 2 2.5 3 3.5 4</p><p>5 min</p><p>50 min</p><p>data);</p><p>data);</p><p>Simple model</p><p>Simple model</p><p>Data from DEG TWH lab report </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>45 min </p></li><li><p>21 </p><p>In-use Prediction: 3 Bins of tlast-draw </p><p> Each draw is 2 gallons Three delays since last </p><p>draw: 5, 25, 480 min draw = 0.52, 0.61, 0.74 </p><p> Specified # of each delay vs. Qload,day </p><p> EFday weighted by volume at each delay time </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>0</p><p>10</p><p>20</p><p>30</p><p>40</p><p>50</p><p>60</p><p>70</p><p>1 2 3 4 5 6 7 8 9 10 11 12</p><p>Num</p><p>ber o</p><p>f dra</p><p>ws</p><p>Qto-load, day [Btu]</p><p>Draw Start Temperatures vs. Qday</p><p>Hot</p><p>Warm</p><p>Cold</p><p>0.0</p><p>0.2</p><p>0.4</p><p>0.6</p><p>0.8</p><p>Cold Warm Hot</p><p>Draw</p><p> Effic</p><p>ienc</p><p>y</p><p>Draw Efficency vs Start Temp</p></li><li><p>22 </p><p>Tankless Field Data vs. Model Da</p><p>ily E</p><p>ffic</p><p>ienc</p><p>y/En</p><p>ergy</p><p> Fac</p><p>tor [</p><p>-] </p><p>0 10 20 30 40 50 60 70 80 90 100 </p><p>0 </p><p> .1</p><p> .2 </p><p> .3</p><p> .4 </p><p> .5 </p><p> .6</p><p> .7 </p><p> .8</p><p> .9 </p><p> 1 </p><p>Test load </p><p>Field load </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>EFtest, non-condensing TWH </p><p>Non-cond. TWH </p><p>0</p><p>0.1</p><p>0.2</p><p>0.3</p><p>0.4</p><p>0.5</p><p>0.6</p><p>0.7</p><p>0.8</p><p>0 10000 20000 30000 40000 50000 60000</p><p>Simple draw model </p><p>Daily Hot Water Energy Output [kBtu/day] </p></li><li><p>Future work </p></li><li><p>24 </p><p>Future Work </p><p> Refine/validate tankless algebraic model Assuming simulated use test input data (yields conv only) </p><p> Develop algebraic model for heat pump WHs Performance from heat pump performance maps, tank </p><p>volume, electric element locations, and element/heat pump control logic </p><p> Develop user tool embodying: 1. Parameter extraction from ratings data 2. Algebraic models </p><p> BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>25 </p><p>Thank you for your attention. </p><p>Questions? </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>26 </p><p> Backup Slides </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>27 </p><p>Basic Definitions </p><p>Energy factor (EF): EF = [Qout-to-load/Qfuel,in]t </p><p>where t is integration period </p><p> EFtest: sum Qs over 24 hour period of standard test </p><p> EFfield: sum Qs over each day or over year </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>28 </p><p>Water Heater Field Data </p><p>Daily Hot Water Energy Output [kBtu/day] </p><p>Daily</p><p> Eff</p><p>icie</p><p>ncy/</p><p>Ener</p><p>gy F</p><p>acto</p><p>r [-] </p><p>0 10 20 30 40 50 60 70 80 90 100 </p><p>0 </p><p> .1</p><p> .2 </p><p> .3</p><p> .4 </p><p> .5 </p><p> .6</p><p> .7 </p><p> .8</p><p> .9 </p><p> 1 </p><p>Test load </p><p>Field load </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>From: Actual Savings and Performance of Natural Gas Tankless Water Heaters, MN Center for Energy and Environment </p><p>Gas storage tank WH Non-condensing tankless WH Condensing tankless WH </p><p>Rated EFtest EFtest applies only at test loads!!! Dont draw EFtest lines at varying loads X </p><p>X </p><p>X </p></li><li><p>29 </p><p>Gas Tank Complications </p><p>Gas Burner: Key, complex combustion process conv must be measured </p><p>Pilot: Assume pilot = conv (proven in one case) Should include in simulation models </p><p> increases overheating significantly for solar in hot climates </p><p>Central Flue: Natural convection loop </p><p> flue to outside, down/back into house, to flue Complex: UAflue subsumed in UAtank with 1-D models </p><p> Flue losses ~ 1/3 Total losses Subsumed in UAtotal </p><p> BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>30 </p><p>Deriving UAtank and conv as f(ratings data) for Gas Storage Tank Water Heater </p><p>Assume isothermal tank (one node) Write dynamic energy balance: </p><p>CdTtank/dt = convPaux UAtTt-env mdotcpTout-in. </p><p> Integrate over time t (with Tt,end = Tt,start) convQaux,t = (Mt cpTout-in + UAtTt-envt) </p><p> Use balances in definitions of EF and RE: EF Qto-load/Qaux,t = MTcpTout-in/[(Mt cpTout-in + UAtTt-envttest)/conv RE Qdraw/Qaux,recover = Qdraw/[Qdraw + (UAtTt-env)Qdraw/Pfuel,in]/conv </p><p> Solve for key parameters: UAtotal and conv UAt,gas = (RE/EF1)/[Tt-env(tday/Qout,day1/(PauxEF))] conv = RE + UAt,gas(Tt-env)/Paux </p><p> BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>Reference: J. Burch, Using Ratings Data to Derive Simulation Model Inputs for Storage-tank Water Heaters, ASES Conf. 2004. </p><p>Danger: Math slide! </p></li><li><p>31 </p><p>EFday Derivation for gas storage tank WH </p><p>EFday = Qload,day/Qfuel,day = Qload,day/[(Qload,day + Qlosses,day )/conv]] = conv (1/(1 + Qlosses,day / Qload,day ) = conv [1/(1 + UAtotalTset-env tday/MdaycpTout-in )] </p><p>Danger: Math slide! </p></li><li><p>32 </p><p>EFday Derivation for gas storage tank WH </p><p>EFday = Qload,day/Qfuel,day = Qload,day/[(Qload,day + Qlosses,day )/conv]] = conv (1/(1 + Qlosses,day / Qload,day ) = conv [1/(1 + UAtotalTset-env tday/MdaycpTout-in )] </p><p>Danger: Math slide! </p></li><li><p>33 </p><p>Derivation of the Tankless Draw Efficiency Model </p><p>Assume Tuse = Tset (i.e., if Tout,TWH &lt; Tset, wasted H2O/Q) This assumption makes derivation simple, but can be relaxed </p><p>Given: Tankless: conv, UA, C, decay (= C/UA) Draw statistics: tlast-draw, tdraw, mdot,draw Temperatures: Tmains, Tset, Tenv </p><p>Basis of the model: Solution of the one-node energy balance (exponential) </p><p>Do both during decay, charge ramp, and stead state </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p></li><li><p>34 </p><p>Derivation of the Tankless Draw Efficiency Model, cont. </p><p>1. Calculate T@start of draw Tstart = Tenv + (Tset Tenv)e-t_lastdraw/_decay </p><p>2. Calculate tcharge Calc T = (convQdot,gas,max + mdot,drawcpTmains + UATenv )/D, where D = mdot,drawcp + UA tcharge = -decayln[(Tset T)/(Tstart T)] </p><p>3. Calculate Qwaste Qwaste = mdot,drawtcharge </p><p>4. Calculate useful Qdraw Qdraw = mdot,drawcp(Tset Tmains), Mdraw = mdot,draw tdraw </p><p>5. Calculate draw efficiency: draw = Qdraw/(Qdraw + Qwaste/conv) = conv[1/(1 = convQwaste/Qdraw) </p><p>BA Hot Water Experts Meeting; 9/27/12; NREL </p><p>Danger: Math slide! </p><p>Using Ratings Data to Predict Field Performance of Residential Water HeatersPresentation OutlineWater Heater Field DataIs Discrepancy between EFfield vs. EFtest a Problem?Water Heater Model Types: Three levelsKey Issue: Getting Model Input ParametersEnergy Factor Test SummaryGas Storage Tank Water Heater ModelsSchematic Gas TankGas Tank Model and Parameter InferenceAlgebraic storage tank modelsStWH Field Data vs. ModelPotential Tankless Water Heater Algebraic ModelsGas Tankless Schematic (Rinnai)Gas Tankless One-node Thermal ModelInput-Output Method: Possible MethodTankless Data and Model...</p></li></ul>

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