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Seminar: Modeling and Simulation for Smart, Sustainable, and Resilient Cities

Join Dr. Wangda Zhuo for a seminar on modeling chiller and cooling tower performance, chiller properties, and efficiency analysis. Learn about merging chiller & cooling tower models and low-order building modeling techniques.

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Seminar: Modeling and Simulation for Smart, Sustainable, and Resilient Cities

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  1. Seminar: Modeling and Simulation for Smart, Sustainable, and Resilient Cities Dr. Wangda Zhuo. Associate Professor Building Systems Engineering, UC Boulder When: Monday 26, 4 pm Where: ECJ Building, Classroom 3.402

  2. Lecture Objectives: Finish with intro for Project 1: Chiller - Cooling towers and modeling

  3. Cooling Tower Performance Curve R TCTR Outdoor WBT from chiller TCTS to chiller Temperature difference: R= TCTR -TCTS TCTS Most important variable is wet bulb temperature TCTS = f( WBToutdoor air , TCTR , cooling tower properties) or for a specific cooling tower type TCTS = f( WBToutdoor air , R) WBT

  4. Cooling Tower Model Model which predict tower-leaving water temperature (TCTS) for arbitrary entering water temperature (TCTR) and outdoor air wet bulb temperature (WBT) Temperature difference: R= TCTR -TCTS Model: For HW 3b: You will need to find coefficient a4, b4, c4, d4, e4, f4, g4, h4, and i4 based on the graph from the previous slide and two variable function fitting procedure

  5. Modeling of Water Cooled Chiller (COP=Qcooling/Pelectric) Chiller model: COP= f(TCWS , TCTS , Qcooling , chiller properties)

  6. Modeling of Water Cooled Chiller Chiller model: Chiller data: QNOMINAL nominal cooling power, PNOMINAL electric consumption forQNOMINAL Available capacity as function of evaporator and condenser temperature Cooling tower supply Cooling water supply Full load efficiency as function of condenser and evaporator temperature Efficiency as function of percentage of load Part load: The consumed electric power [KW] under any condition of load The coefiecnt of performance under any condition Reading: http://apps1.eere.energy.gov/buildings/energyplus/pdfs/engineeringreference.pdf page 597.

  7. Combining Chiller and Cooling Tower Models Function of TCTS 3 equations from previous slide Add your equation for TCTS → 4 equation with 4 unknowns (you will need to calculate R based on water flow in the cooling tower loop)

  8. Merging Two Models Temperature difference: R= TCTR -TCTS Model: Link between the chiller and tower models is the Q released on the condenser: Q condenser = Qcooling + Pcompressor ) - First law of Thermodynamics Q condenser = (mcp)water form tower (TCTR-TCTS) m cooling tower is given - property of a tower TCTR= TCTS - Q condenser / (mcp)water Finally: Find P() or The only fixed variable is TCWS = 5C (38F) and Pnominal and Qnominal for a chiller (defined in nominal operation condition: TCST and TCSW); Based on Q() and WBT you can find P() and COP().

  9. Low Order Building Modeling Measured data or Detailed modeling Find Q() = f (DBT)

  10. For HW3a (variable sped pump efficiency) you will need Q() 20 16 12 Q [ton] Yearly based analysis: You will need Q() for 365 days x 24 hours Use simple molded below and the Syracuse, NY TMY weather file posted in the course handout section 8 Q=--27.48+0.5152*t 4 Q=-0.45 +0.0448*t 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 t [F] TMY 3 for Syracuse, NY http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/by_state_and_city.html

  11. For Austin’s Office Building Model: (Area = 125,000sf) Hours in a year kW Used for component capacity analysis Model =0 when building is off Reading assignment: http://www.taylor-engineering.com/downloads/cooltools/EDR_DesignGuidelines_CoolToolsChilledWater.pdf Chapter: 2 Number of hours

  12. Modeling of chilled water tank(stratified vs. mixing) To chiller From building Stratification To building From chiller Mixing happens if the supply temperature vary Mixing model: mcpDT/D = Qin –  Qout

  13. Stratification Dr. Jing Song’s PhD results Flow time at 20 minutes CFD domain Flow time at 1 minute

  14. Stratified model(simplified) However even if the chiller supply constant T the return water from building is not constant! From building To chiller T1 T2 Building Building T3 Tn To building From chiller For a constant T supply it is a very simple model chiller chiller Model details in “Solar Engineering of Thermal Process”

  15. Tank model Flow indicator: Building Building Flow for each node: Energy balance: chiller chiller

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