Thomas%20Hartman,%20P.E.

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Sustainable Chilled Water Systems
By Thomas Hartman, P.E. The Hartman
Company Georgetown, Texas www.hartmanco.com
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Sustainable Chilled Water Systems

• Session Outline
• Overview New Directions Required for
  Sustainability
• Plant Issues What Equipment, What
  Configurations
• Chilled Water Distribution What Are the
  Objectives
• Summary Conclusion Questions - Discussion

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Sustainable Chilled Water Systems

• Keys in Configuring a Sustainable Chiller Plant
• BEWARE! A Lot of Traps
• Explore new directions and technologies
• Incorporate Effective Performance Measurement
• Establish Accountability

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Sustainable Chilled Water Systems
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Sustainable Chilled Water Systems

• Managing Development of a Sustainable Chiller
  Plant
• LEADERSHIP! Be Directed and In Charge
• Set Aggressive Performance Goals
• Incorporate Effective Performance Measurement
• Establish Accountability

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Sustainable Chilled Water Systems
The Equal Marginal Performance Principle
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Sustainable Chilled Water Systems
Equal Marginal Performance Principle Based Control
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Sustainable Chilled Water Systems
Characteristics of Cooling Loads for Various
Climates
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Sustainable Chilled Water Systems
Variable vs. Constant Speed Chiller Performance
The Variable Speed Difference

• While Constant Speed Chiller Efficiency is nearly
  constant between 60 100 loading, the
  Efficiency of Variable Speed Centrifugal Chillers
  increases dramatically as load falls in that
  range.
• The Efficiency of Variable Speed Centrifugal
  Chillers is more significantly improved by the
  reduction in Condensing Water Temperature.

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Sustainable Chilled Water Systems
"Natural Curve" Of VS Centrifugal Chiller
The "Natural Curve" of a variable speed
centrifugal chiller is shown as the black line.
The Natural Curve is the locus of load points at
various condenser and evaporator conditions at
which the highest operating efficiency is
achieved. To achieve optimum performance,
chillers should be sequenced such that the
on-line chillers operate as close as possible to
their Natural Curve.
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Sustainable Chilled Water Systems
Tower Approach Temperature For 3 Tower System
At lower wet bulb temperatures, the approach of
cooling towers rises due to reduced moisture
capacity of cooler air. By keeping towers on line
and slowing fans and pumps, greater air and water
volumes pass over larger surface areas per unit
energy expended to improve part load approach
temperatures, as shown in this chart. The total
power to fans and pumps is the same for the
variable speed and constant speed systems at each
condition. Note the improved approach by slowing,
not shedding towers at low loads.
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Sustainable Chilled Water Systems
Chiller Plant with Conventional Controls
Equipment is operated independently with local
PID temperature and pressure loops. Chillers and
towers are sequenced to keep on-line equipment as
fully loaded as possible. Plant optimization, if
it is applied at all, requires another level of
control that continuously resets the various
setpoints, which can reduce overall system
stability.
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Sustainable Chilled Water Systems
All-Variable Speed Demand Based Control
Equipment is connected via an integrated network
and operation is coordinated to maintain lowest
overall energy use at all load conditions using
demand based control and natural curve sequencing
of equipment. Unless incorporated as design
criteria, temperature and pressure setpoints are
not employed except as operating limits.
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Sustainable Chilled Water Systems
Network Enabled Demand Based Control Of
All-Variable Speed Chiller Plants

• Control Features
• Simple Direct Control Relationships between
  Chillers, Pumps and Tower Fans
• "Natural Curve" Sequencing of chillers
• Benefits
• Ultra-Efficient Plant Operation
• Simpler and More Stable Plant Operation
• Longer Life for Equipment and Lower Maintenance
  Costs

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Sustainable Chilled Water Systems
Sustainable Chilled Water Plants

• Ultra Efficient All-Variable speed chiller plants
  are generally configured the same conventional
  plants, but must employ new operating strategies
  to achieve efficient operation.
• Network enabled Demand Based Control provides
  ultra-efficient, simple and stable control for
  all-variable speed chiller plants.
• Implementing all-variable speed plants
  successfully requires special emphasis on
  performance

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Sustainable Chilled Water Systems
All-Variable Speed/Flow Distribution Systems

• Background Current distribution systems
• New Choices Why all-variable flow distribution
  systems work well with variable speed chillers
• Application Developing effective all-variable
  flow chilled water distribution systems.
• Scale Large scale primary/ booster all-variable
  flow chilled water distribution systems

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Sustainable Chilled Water Systems
Primary/Secondary CHW Distribution System
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Sustainable Chilled Water Systems
Variable Primary Flow CHW Distribution System
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Sustainable Chilled Water Systems
Variable Speed Pump Operation Comparison
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Sustainable Chilled Water Systems
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Sustainable Chilled Water Systems
Improving Efficiency of Variable Flow
Distribution System for Demand Based Control

• Reduce the pressure drop through chilled water
  valves. Line size valves with zero pressure drop
  at full flow are effective if they are properly
  controlled.
• Operate chilled water pumps with network control
  that reacts to actual demand for flow by the
  valves served and sequence pumps to so that
  on-line pumps operate as close as possible to
  their natural curve.

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Sustainable Chilled Water Systems
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Sustainable Chilled Water Systems
Demand Based Control Applied to Distribution
System Elements
Valve Control Multivariable "Intelligent
Iterative Control" is used whereby valve
adjustment is based on setpoint error, pump
speed, chilled water temperature, and current
valve position. Pump Control "Orifice area"
pump speed control adjusts speed based on percent
of total valve orifice area currently open and
further adjusted by the number of valves nearly
wide open. Pump Sequencing is based on "natural
curve" principle.
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Sustainable Chilled Water Systems
Demand Based Control of Variable Flow
Distribution System
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Sustainable Chilled Water Systems
Network Enabled Demand Based Control Of
All-Variable Speed Distribution Systems

• Control Features
• Line sized valves for near zero pressure drop.
• Simple and direct "Valve Orifice Area" control of
  chilled water pumps
• Distribution pumps sequence with chillers
  according to "Natural Curve"
• Benefits
• Ultra-Efficient integrated system operation.
• Simpler and more stable plant operation
• Longer life for equipment and lower maintenance
  costs

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Sustainable Chilled Water Systems
Demand Based Control of All-Variable Flow
Primary/Booster Distribution System
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Sustainable Chilled Water Systems
Sustainable Chilled Water Distribution Systems

• All-variable speed chilled water distribution
  systems are configured very similar to newer
  conventional systems, but employ new operating
  strategies.
• Network enabled iterative and demand based
  control provide ultra-efficient, simple and
  stable control for all-variable speed
  distribution systems.
• When properly configured and operated new
  technology all-variable speed chilled water
  distribution systems ensure every load served is
  satisfied while providing ultra-efficient
  operation.

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Sustainable Chilled Water Systems
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Sustainable Chilled Water Systems
Implementing All-Variable Speed Chilled Water
Systems
WHY? Achieves approximately 0.5 kW/ton overall
annual plant distribution system performance
about half the energy use of most existing
plants. Simple, stable, ultra-efficient control
with reduced system maintenance. HOW? Network
control coordinates all-variable speed equipment
for optimum operation in response to actual
demand on system. Plant is designed for direct
control among components, and distribution system
to minimize pressure drops and variations
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Sustainable Chilled Water Systems
Success With All-Variable Speed Chiller Plants

• New variable speed system technologies require
  special effort through design/construction/turnove
  r
• Owner/Designer team must work together to ensure
  all problems will be solved
• Nearly every chiller plant is a good potential
  application for all-variable speed technologies
• Focus on Performance. Let overall plant
  performance drive the selection of configuration,
  equipment and controls
• Be certain the project incorporates measurement
  and verification and accountability for achieving
  projected performance

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Sustainable Chilled Water Systems
Next Steps Toward a Sustainable Chilled Water
System

1. Instrument current facility or facilities to
   obtain actual energy used to generate and
   distribute chilled water.
2. Calculate the potential avoided costs by
   converting to an ultra-efficient all-variable
   speed chilled water system.
3. Develop cost-effective budgets, goals and target
   dates to implement a conversion to a more
   sustainable system.
4. Implement the project or projects required to
   achieve the targeted plant performance.
5. Incorporate performance verification and
   performance accountability to ensure the goals
   are achieved and maintained.

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Sustainable Chilled Water Systems
By Thomas Hartman, P.E. The Hartman
Company Georgetown, Texas www.hartmanco.com
Questions Discussion