Applications Engineering Manual
Chiller System Design and Control
SYS-APM001-EN
Page
Mick Schwedler, applications manager
Susanna Hanson, applications engineer
Beth Bakkum, information designer
Chiller System Design and Control
2009 Trane All rights reserved
Preface
Chiller System Design and Control
SYS-APM001-EN
Contents
Chilled-Water System Control
Failure Recovery
Condenser-Water System Control
System Controls
Chiller
Primary System Components
Chiller evaporator
Primary System Components
Figure 1. Typical vapor-compression chiller
Figure 2. Flooded evaporator cut-away
Primary System Components
Effect of chilled-water temperature
Effect of chilled-water flow rate and variation
Figure 3. Direct-expansion evaporator cut-away
Effect of condenser-water temperature
Water-cooled condenser
Primary System Components
Effect of condenser-water flow rate
Air-cooled versus water-cooled condensers
Air-cooled condenser
Maintenance
Primary System Components
Low-ambient operation
Primary System Components
Energy efficiency
Primary System Components
Loads
1212 Midnight midnight
dry bulb wetWetbulbBulb
Two-way valve load control
Three-way valve load control
Primary System Components
Heat transferred from the loads can be controlled in a number of ways
Face-and-bypass dampers
Variable-speed pump load control
Primary System Components
Figure 6. Two-way valve
Chilled-water pump
Chilled-Water Distribution System
Primary System Components
Figure 8. Uncontrolled water flow with bypass damper
Primary System Components
Distribution piping
Pump per chiller
Manifolded pumps
Primary System Components
Pumping arrangements
Constant flow system
Figure 12. Constant flow system
Cooling tower
Condenser-Water System
Primary System Components
Primary-secondary system
Primary System Components
Condenser-water pumping arrangements
Effect of load on cooling tower performance
Effect of ambient conditions on cooling tower performance
Primary System Components
Unit-Level Controls
Chiller control
Centrifugal chiller capacity control
Primary System Components
Figure 16. Centrifugal chiller with AFD
Primary System Components
The availability of cooler condenser water condenser-water reset
Small Chilled-Water Systems 1-2 chillers
Application Considerations
Variable flow
Application Considerations Constant flow
Condensing method
Number of chillers
Application Considerations
Parallel or series
Part load system operation
Managing control complexity
Mid-Sized Chilled-Water Systems 3-5 Chillers
Preferential vs. equalized loading and run-time
Figure 18. Mid-sized chilled-water system schematic
Figure 19. Large chilled-water system schematic
Large Chilled-Water Systems 6+ Chillers, District Cooling
Application Considerations
Pipe size
Power
Water
Creating one centralized chilled-water system takes significant foresight, initial investment, and building development with a multi-year master plan. If the initial plant is built to accommodate many future buildings or loads, the early challenge is operating the system efficiently with much lower loads than it will experience when the project is complete. The system may need to blend parallel and series configurations “Series-Counterflow Application” on page 77 to accommodate the wide range of loads the plant experiences during phased construction
Limitations of field performance testing
Chiller performance testing
Chiller Plant System Performance
Controls
Application Considerations
Guidelines for system efficiency monitoring
Guideline 22 includes a discussion of
Application Considerations
Energy and economic analysis of alternatives
1 Full year analysis
System Design Options
Selecting Chilled- and Condenser-Water Temperatures and Flow Rates
Guidance for Chilled- and Condenser-Water Flow Rates
Standard rating temperatures
Chilled-Water Temperatures
System Design Options
Chilled- and Condenser-Water Flow Rates
Condenser-Water Temperatures
Standard rating flow conditions
System Design Options
System Design Options Selecting flow rates
DP2/DP1 = Flow2/Flow11.85
System Design Options
System Design Options
The total system power is now as follows
Example of coil reselection at colder temperature/reduced flow rate
Coil response to decreased entering water temperature
System Design Options
Figure 21. Chilled water system performance at part load
System Design Options
Cooling-tower options with low flow
Smaller tower
Fluid ΔT, F C
ΔT1 = 94.2 - 78 = 16.2F or 34.6 - 25.6 = 9.0C
System Design Options
ΔT2 = 99.1 - 78 = 21.1F or 37.3 - 25.6 = 11.7C
Same tower, smaller approach
Same tower, larger chiller
System Design Options
System Design Options
Retrofit opportunities
range
Reselected tower for 50% more heat rejection with 15F 8.3C
System Design Options
Cost Implications
Misconception 1-Low flow is only good for long piping runs
Misconceptions about Low-Flow Rates
System Design Options
Consumption
System Design Options
Energy
System
Demirchian and Maragareci12, Eley13, and Schwedler and Nordeen11 independently showed that system energy consumption can be reduced by reducing flow rates. It is interesting to note that in the systems studied, three different chiller manufacturer’s chillers were examined, yet the energy savings only varied from 2.0 to 6.5 percent. In all cases, regardless of which manufacturer’s chillers were used, the system energy consumption was reduced. In addition, Demirchian and Maragareci12, and Schwedler and Nordeen11 also noted reduced first costs
System Design Options
Parallel Chillers
System Configurations
System Configurations
System Configurations
Series Chillers
Figure 27. Series chillers
Hydraulic decoupling
Primary-Secondary Decoupled Systems
System Configurations
bypass piping no-flow static head from the building water column, and
System Configurations
Figure 29. Production loop
System Configurations Production
Distribution-loop benefits of decoupled system arrangement
System Configurations Distribution
Pumping arrangements
System Configurations
Common
Campus
Decoupled system-principle of operation
System Configurations
Figure 34. Decoupled system supply tee
System Configurations
Flow-based control
Temperature-sensing
Figure 35. Temperature-sensing
Multiple chilled-water plants on a distribution loop
System Configurations Chiller sequencing in decoupled systems
Adding a chiller
Subtracting a chiller
Pump control in a double-ended decoupled system
System Configurations
Figure 36. Double-ended decoupled system
Chiller sequencing in a double-ended decoupled system
System Configurations
Other plant designs
Variable-Primary-Flow Systems
System Configurations
Figure 37. Variable-primary-flow system
System Configurations
Advantages of variable primary flow
Operational savings of VPF designs
System Configurations
Chiller selection requirements
Evaporator flow limits
Dispelling a common misconception
To promote good heat transfer and stable control minimum flow limit
System Configurations
Flow-rate reduction when an isolation valve
System Configurations
Managing transient water flows
Number of operating chillers
System Configurations
System Configurations
System design and control requirements
These descriptions should include control sequences for
Accurate flow measurement
System Configurations
Bypass locations
System Configurations
Chiller sequencing in VPF systems
Bypass flow control
Adding a chiller in a VPF system
System Configurations
Subtracting a chiller in a VPF system
System Configurations
Sequencing based on load
System Configurations
Other VPF control considerations
Select slow-acting valves to control the airside coils
Use multiple air handlers, and stagger their start/stop times
System Configurations
Plant configuration
Consider a series arrangement for small VPF applications
Assess the economic feasibility of VPF for single-chiller plants
System Configurations
Guidelines for a successful VPF system
Moderate “low ΔT syndrome” by manifolding the chilled water pumps
Chiller selection
Plant configuration
System Configurations
Bypass flow
Chiller sequencing
Chilled-Water System Variations
Heat Recovery
Condenser “Free Cooling” or Water Economizer
Plate-and-frame heat exchanger
Refrigerant migration
Chilled-Water System Variations
Figure 41. Refrigerant migration chiller in compression cooling mode
Figure 42. Refrigerant migration chiller in free-cooling mode
Well, river, or lake water
Chilled-Water System Variations
Figure 43. Water economizer piped in parallel with chillers
Preferential loading - parallel arrangement
Preferential Loading
Chilled-Water System Variations
Figure 44. Parallel preferential loading arrangement
Chilled-Water System Variations
Preferential loading - sidestream arrangement
Sidestream plate-and-frame heat exchanger
Figure 45. Sidestream preferential loading arrangement
Sidestream with alternative fuels or absorption
Recovery
Production
Chilled-Water System Variations
Preferential loading - series arrangement
Sidestream system control
Figure 47. Preferential loading - series arrangement
Series-series counterflow
Series-Counterflow Application
Chilled-Water System Variations
Figure 48. Series-counterflow arrangement
Chilled-Water System Variations
Unequal Chiller Sizing
Figure 50. Series arrangement of evaporators and condensers
Evaporators
Low ΔT Syndrome
System Issues and Challenges
Amount of Fluid in the Loop
Required Volume = Flow Rate × Loop Time
Chiller response to changing conditions
System Issues and Challenges
System response to changing conditions
Example
Minimum capacity required
Contingency
Type and size of chiller
System Issues and Challenges
Alternative Energy Sources
System Issues and Challenges Location of equipment
Water and electrical connections
Ancillary equipment
Alternative fuel
Plant Expansion
Thermal storage
System Issues and Challenges
Applications Outside the Chiller’s Range
Retrofit Opportunities
Flow rate out of range
System Issues and Challenges
Precise temperature control
System Issues and Challenges Temperatures out of range
Figure 52. Temperatures out of range for equipment
Figure 53. Precise temperature control, multiple chillers
System Issues and Challenges
Chiller System Design and Control
SYS-APM001-EN
System Controls
Chilled water reset-raising and lowering
Chilled-Water System Control
Chilled-water pump control
Number of chillers to operate
System Controls
Critical valve reset pump pressure optimization
Minimum refrigerant pressure differential
Condenser-Water System Control
System Controls
Table 17. VFDs and centrifugal chillers performance at 90% load
System Controls
Condenser-water temperature control
Cooling-tower-fan control
Chiller-tower energy balance
System Controls
Figure 54. Chiller-tower energy consumption
Chiller-tower-pump balance
System Controls Variable condenser water flow
System Controls
Decoupled condenser-water system
These three energy consumers must be balanced to minimize overall energy use. This makes varying condenser water flow complex, but the strategy below has been implemented on projects
Cooling Tower Fan Inverter Cooling Tower Water Sump Tower Water
System Controls
Recirculation Pump CDWP-2 Inverter Chiller CDWP-1 Inverter Chiller
Figure 56. Decoupled condenser-water system
Figure 57. Failure recovery
Failure Recovery
System Controls
Conclusion
condenser water, leaving. See cooling water
Glossary
cooling tower water. See cooling water
pumps system
Glossary
tower water. See cooling water
Glossary
Plant.” IDEA 88th Annual Conference Proceedings 1997
References
Engineering July
References
ASHRAE/IESNA Standard 90.1-2007 Energy Standard for Buildings
Except Low-Rise Residential Buildings. ASHRAE and IESNA
32 Trane Applications Engineering Group. “Thermal Storage - Understanding the Choices.” Ice Storage Systems, Engineered Systems Clinics. Trane, 1991. ISS-CLC-2
References
Index
Index
Index
Index
Page
Literature Order Number
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SYS-APM001-EN
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