A Chilled Water System Analysis Tool for Industrial Assessments

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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

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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

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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

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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

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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

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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

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Chilled Water System (Water-Cooled)
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Chilled Water System (Air-Cooled)
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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

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Program Overview Input

• Basic System Data
• Number of chillers (up to 5)
• Chilled water supply temperature
• Geographic location
• Condenser cooling method (water or air)

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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)

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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)

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Program Overview Input

• Pump Data
• Fixed or variable flow pumping
• Flow rate gpm/ton
• Nominal pump efficiency
• Nominal motor efficiency

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Program Overview Input

• Chiller Data
• Chiller compressor type
• Chiller capacity
• Chiller full load efficiency (if known)
• Chiller age

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Program Overview Input

• Energy Cost Data
• Average electricity cost /kWh
• Average NG cost /MMBtu
• System Control Data
• System operating schedule
• System loading schedule

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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

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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

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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

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Example

• Lets 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

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Example Input Screen
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Example Output Screen

• Output Summary
• Chillers 2,187,676 kWh (92)
• Tower 4,768 kWh (
• Pumps 193,934 kWh (8)
• Total Energy 2,386,378 kWh Total Cost 143,183

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Example Operating Cost Reduction Opportunities
Screen

• Operating Cost Reduction Measure
• Install a VSD on each Centrifugal
  Compressor Motor

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Example Savings Screen

• Savings Summary
• 598,797 kWh/yr
• 35,928/yr

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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

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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

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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.

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Case Study Results
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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)

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Case Study Other Observations

• Chiller and pumping energy decrease by
  approximately 22
• Tower energy increases by approximately 63

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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_at_ecs.umass.edu
• Any questions?