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A Chilled Water System Analysis Tool for Industrial Assessments

A Chilled Water System Analysis Tool for Industrial Assessments. Chiller System Optimization & Energy Efficiency Workshop September 2003 Presented by Michael Socks UMass Industrial Assessment Center. The Industrial Assessment Center at UMass-Amherst.

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A Chilled Water System Analysis Tool for Industrial Assessments

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  1. A Chilled Water System Analysis Tool for Industrial Assessments Chiller System Optimization & Energy Efficiency Workshop September 2003 Presented by Michael Socks UMass Industrial Assessment Center

  2. The Industrial Assessment Center at UMass-Amherst • The IAC performs no-cost, on-site energy efficiency, waste reduction, and productivity improvement assessments for small and mid-size manufacturers • Client Characteristics: 1) SIC Code 2000-3999 2) Annual energy bills of $100,000 to $2,000,000 3) Gross annual sales less than $100 million 4) Fewer than 500 employees at the plant site 5) No in-house staff to complete a similar assessment

  3. Summary of Operating Cost Reduction Measures Equipment-based Opportunities • Replace the chiller • Install NG or absorption chillers (Hybrid) • Install HX to recover condenser heat • Store thermal energy for peak use

  4. Summary of Operating Cost Reduction Measures Control-based Opportunities • Optimize chiller sequence • Raise chilled water temperature setting • Lower condenser cooling water temperature • Use variable speed capacity control • Use 2-speed or VSD control of tower fans • Use VSD control of pump flow • Use free cooling

  5. Summary of Operating Cost Reduction Measures Load-based Opportunities • Use chilled water efficiently • Distribute chilled water efficiently • Use optimal coil or heat exchanger size/design

  6. Program Introduction Purpose: Reduce the energy consumption of installed chilled water systems Goal: Create a simple but useful software tool for analyzing potential energy savings in chilled water systems

  7. Chilled Water System (Water-Cooled)

  8. Chilled Water System (Air-Cooled)

  9. Program Description Visual Basic Executable Program • User is prompted for system information • Program analyzes the existing system • User is prompted for changes to system • Program analyzes the proposed system • Program presents savings results

  10. Program Overview: Input Basic System Data: • Number of chillers (up to 5) • Chilled water supply temperature • Geographic location • Condenser cooling method (water or air)

  11. Program Overview: Input If chiller condensers are water-cooled: • Condenser cooling water supply temperature (if constant) • WB to cooling water temperature differential (if variable) • Cooling Tower Data (# towers, # cells/tower, motor hp, # motor speeds)

  12. Program Overview: Input If chiller condensers are air-cooled: • Cooling air design temperature • Average annual ambient air temperature (if indoor air is used for cooling) • DB to condenser temperature differential (if outdoor air is used for cooling)

  13. Program Overview: Input Pump Data: • Fixed or variable flow pumping • Flow rate [gpm/ton] • Nominal pump efficiency [%] • Nominal motor efficiency [%]

  14. Program Overview: Input Chiller Data: • Chiller compressor type • Chiller capacity • Chiller full load efficiency (if known) • Chiller age

  15. Program Overview: Input Energy Cost Data: • Average electricity cost [$/kWh] • Average NG cost [$/MMBtu] System Control Data: • System operating schedule • System loading schedule

  16. Program Overview: Cost Reduction Cost Reduction Measures to Consider: • Increase chilled water supply temperature • Decrease chiller condenser temperature • Upgrade to 2-speed or variable speed tower fan motors • Upgrade to variable speed pump motor control • Replace chillers (use more efficient or NG units) • Replace refrigerant • Install VSD on chiller compressor motor (centrifugal only) • Use free cooling • Sequence chillers

  17. Program Overview: Output Output Information: • Annual chiller energy consumption (kWh and/or MMBtu) and cost • Annual cooling tower energy consumption (kWh) and cost • Annual pump energy consumption (kWh) and cost • Total annual energy consumption and cost

  18. Program Overview: Output Chiller energy may be viewed by: • Chiller • Load Cooling tower energy may be viewed by: • Wet-bulb temperature group Pump energy may be viewed by: • Chiller

  19. Example Let’s run an example . . . • (3) 200 ton water-cooled chillers (centrifugal) • 44 ºF chilled water temperature • Located in Boston, Massachusetts • Condenser cooling water is held constant at 85 ºF • (1) 2-cell tower with 15 hp 2-speed motors • Chilled water flow is constant [2.4 gpm/ton] • Condenser water flow is constant [3.0 gpm/ton] • Electricity is $0.06 per kWh • Operates 24/7 and serves an air-conditioning load • Install VSDs on each chiller compressor motor

  20. Example: Input Screen

  21. Output Summary: Chillers: 2,187,676 kWh (92%) Tower: 4,768 kWh (< 1%) Pumps: 193,934 kWh (8%) Total Energy: 2,386,378 kWh Total Cost: $143,183 Example: Output Screen

  22. Operating Cost Reduction Measure: Install a VSD on each Centrifugal Compressor Motor Example: Operating Cost Reduction Opportunities Screen

  23. Savings Summary: 598,797 kWh/yr $35,928/yr Example: Savings Screen

  24. Case Study: Application Manufacturer of laminated circuit boards uses chilled water for process cooling and space conditioning Process Cooling • Laminating oven cool-down cycle • Plating fluid temperature control Space Conditioning • ~ 50,000 ft2 clean rooms • Office and manufacturing floor air conditioning

  25. Case Study: System Specs Chilled Water System Summary • (2) 250-ton helical rotary chillers (1997) • (2) 350-ton helical rotary chillers (2001) • 45ºF chilled water; 2.4 gpm/ton • 75ºF condenser water; 3.0 gpm/ton • (4) cooling towers; (3) 15-hp fans each (2-speed) • Operates 24/7 year-round • Free cooling is used when possible

  26. Case Study: System Loading Typical Loading Schedule • 20% load for 25% of year • 30% load for 25% of year • 40% load for 25% of year • 50% load for 25% of year Note: These are average system loads. Individual chiller loading will differ.

  27. Case Study: Results

  28. Case Study: Prediction vs. Actual Without Using Free Cooling • 3,478,905 kWh actual • 3,436,931 kWh predicted • Difference: 41,974 kWh (-1.2%) With Free Cooling • 489,054 kWh and $41,570 actual savings • 608,720 kWh and $51,744 predicted savings • Difference: 119,666 kWh and $10,174 (+24%)

  29. Chiller and pumping energy decrease by approximately 22% Tower energy increases by approximately 63% Case Study: Other Observations

  30. Closing Comments • The Program IS NOT intended to determine system energy use down to the kWh or MMBtu • Program IS intended to direct analysis effort toward the most promising cost reduction opportunities • I need your help to make this program better: 1) Download the program from www.ceere.org 2) E-mail questions, suggestions, errors, etc. to me at msocks@ecs.umass.edu • Any questions?

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