Chiller System Design and Control
Applications Engineering Manual
SYS-APM001-EN
Page
Chiller System Design and Control
Susanna Hanson, applications engineer
Mick Schwedler, applications manager
Beth Bakkum, information designer
SYS-APM001-EN
Preface
2009 Trane All rights reserved
Chiller System Design and Control
Contents
System Controls
Failure Recovery
Chilled-Water System Control
Condenser-Water System Control
Chiller
Primary System Components
Figure 2. Flooded evaporator cut-away
Primary System Components
Chiller evaporator
Figure 1. Typical vapor-compression chiller
Figure 3. Direct-expansion evaporator cut-away
Effect of chilled-water temperature
Primary System Components
Effect of chilled-water flow rate and variation
Effect of condenser-water flow rate
Water-cooled condenser
Effect of condenser-water temperature
Primary System Components
Primary System Components
Air-cooled condenser
Air-cooled versus water-cooled condensers
Maintenance
Primary System Components
Low-ambient operation
Energy efficiency
dry bulb wetWetbulbBulb
Loads
Primary System Components
1212 Midnight midnight
Heat transferred from the loads can be controlled in a number of ways
Three-way valve load control
Two-way valve load control
Primary System Components
Figure 6. Two-way valve
Variable-speed pump load control
Face-and-bypass dampers
Primary System Components
Figure 8. Uncontrolled water flow with bypass damper
Chilled-Water Distribution System
Chilled-water pump
Primary System Components
Manifolded pumps
Distribution piping
Primary System Components
Pump per chiller
Figure 12. Constant flow system
Pumping arrangements
Primary System Components
Constant flow system
Primary-secondary system
Condenser-Water System
Cooling tower
Primary System Components
Effect of ambient conditions on cooling tower performance
Condenser-water pumping arrangements
Primary System Components
Effect of load on cooling tower performance
Unit-Level Controls
Primary System Components
Chiller control
Primary System Components
Centrifugal chiller capacity control
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
Application Considerations Constant flow
Variable flow
Condensing method
Part load system operation
Application Considerations
Number of chillers
Parallel or series
Figure 18. Mid-sized chilled-water system schematic
Mid-Sized Chilled-Water Systems 3-5 Chillers
Managing control complexity
Preferential vs. equalized loading and run-time
Large Chilled-Water Systems 6+ Chillers, District Cooling
Figure 19. Large chilled-water system schematic
Application Considerations
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
Power
Pipe size
Water
Controls
Chiller performance testing
Limitations of field performance testing
Chiller Plant System Performance
Guidelines for system efficiency monitoring
Application Considerations
Guideline 22 includes a discussion of
Energy and economic analysis of alternatives
Application Considerations
1 Full year analysis
Selecting Chilled- and Condenser-Water Temperatures and Flow Rates
System Design Options
Guidance for Chilled- and Condenser-Water Flow Rates
Chilled-Water Temperatures
Standard rating temperatures
System Design Options
System Design Options
Condenser-Water Temperatures
Chilled- and Condenser-Water Flow Rates
Standard rating flow conditions
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
Figure 21. Chilled water system performance at part load
Coil response to decreased entering water temperature
Example of coil reselection at colder temperature/reduced flow rate
System Design Options
Fluid ΔT, F C
Cooling-tower options with low flow
System Design Options
Smaller tower
Same tower, smaller approach
System Design Options
ΔT1 = 94.2 - 78 = 16.2F or 34.6 - 25.6 = 9.0C
ΔT2 = 99.1 - 78 = 21.1F or 37.3 - 25.6 = 11.7C
Same tower, larger chiller
System Design Options
Reselected tower for 50% more heat rejection with 15F 8.3C
Retrofit opportunities
System Design Options
range
System Design Options
Cost Implications
Misconceptions about Low-Flow Rates
Misconception 1-Low flow is only good for long piping runs
System Design Options
System
System Design Options
Consumption
Energy
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
Series Chillers
System Configurations
Figure 27. Series chillers
Primary-Secondary Decoupled Systems
Hydraulic decoupling
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
Campus
System Configurations
Pumping arrangements
Common
System Configurations
Decoupled system-principle of operation
Figure 34. Decoupled system supply tee
Figure 35. Temperature-sensing
Flow-based control
System Configurations
Temperature-sensing
Subtracting a chiller
System Configurations Chiller sequencing in decoupled systems
Multiple chilled-water plants on a distribution loop
Adding a chiller
System Configurations
Pump control in a double-ended decoupled system
Figure 36. Double-ended decoupled system
Chiller sequencing in a double-ended decoupled system
System Configurations
Figure 37. Variable-primary-flow system
Variable-Primary-Flow Systems
Other plant designs
System Configurations
Advantages of variable primary flow
System Configurations
Operational savings of VPF designs
Dispelling a common misconception
Chiller selection requirements
System Configurations
Evaporator flow limits
To promote good heat transfer and stable control minimum flow limit
System Configurations
Number of operating chillers
System Configurations
Flow-rate reduction when an isolation valve
Managing transient water flows
System Configurations
System design and control requirements
System Configurations
These descriptions should include control sequences for
System Configurations
Accurate flow measurement
Bypass locations
Chiller sequencing in VPF systems
System Configurations
Bypass flow control
Adding a chiller in a VPF system
System Configurations
System Configurations
Subtracting a chiller in a VPF system
Sequencing based on load
Use multiple air handlers, and stagger their start/stop times
Other VPF control considerations
System Configurations
Select slow-acting valves to control the airside coils
Assess the economic feasibility of VPF for single-chiller plants
Plant configuration
System Configurations
Consider a series arrangement for small VPF applications
Chiller selection
Guidelines for a successful VPF system
System Configurations
Moderate “low ΔT syndrome” by manifolding the chilled water pumps
Chiller sequencing
System Configurations
Plant configuration
Bypass flow
Plate-and-frame heat exchanger
Heat Recovery
Chilled-Water System Variations
Condenser “Free Cooling” or Water Economizer
Chilled-Water System Variations
Refrigerant migration
Figure 41. Refrigerant migration chiller in compression cooling mode
Figure 43. Water economizer piped in parallel with chillers
Well, river, or lake water
Figure 42. Refrigerant migration chiller in free-cooling mode
Chilled-Water System Variations
Figure 44. Parallel preferential loading arrangement
Preferential Loading
Preferential loading - parallel arrangement
Chilled-Water System Variations
Figure 45. Sidestream preferential loading arrangement
Preferential loading - sidestream arrangement
Chilled-Water System Variations
Sidestream plate-and-frame heat exchanger
Recovery
Sidestream with alternative fuels or absorption
Production
Figure 47. Preferential loading - series arrangement
Preferential loading - series arrangement
Chilled-Water System Variations
Sidestream system control
Figure 48. Series-counterflow arrangement
Series-Counterflow Application
Series-series counterflow
Chilled-Water System Variations
Evaporators
Unequal Chiller Sizing
Chilled-Water System Variations
Figure 50. Series arrangement of evaporators and condensers
Required Volume = Flow Rate × Loop Time
System Issues and Challenges
Low ΔT Syndrome
Amount of Fluid in the Loop
Example
System Issues and Challenges
Chiller response to changing conditions
System response to changing conditions
System Issues and Challenges
Contingency
Minimum capacity required
Type and size of chiller
Ancillary equipment
System Issues and Challenges Location of equipment
Alternative Energy Sources
Water and electrical connections
System Issues and Challenges
Plant Expansion
Alternative fuel
Thermal storage
System Issues and Challenges
Retrofit Opportunities
Applications Outside the Chiller’s Range
Flow rate out of range
System Issues and Challenges Temperatures out of range
Precise temperature control
Figure 52. Temperatures out of range for equipment
SYS-APM001-EN
System Issues and Challenges
Figure 53. Precise temperature control, multiple chillers
Chiller System Design and Control
Chilled-water pump control
Chilled water reset-raising and lowering
System Controls
Chilled-Water System Control
System Controls
Number of chillers to operate
Critical valve reset pump pressure optimization
Table 17. VFDs and centrifugal chillers performance at 90% load
Condenser-Water System Control
Minimum refrigerant pressure differential
System Controls
Condenser-water temperature control
System Controls
Cooling-tower-fan control
System Controls
Chiller-tower energy balance
Figure 54. Chiller-tower energy consumption
Chiller-tower-pump balance
System Controls Variable condenser water flow
Decoupled condenser-water system
System Controls
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
Figure 56. Decoupled condenser-water system
System Controls
Cooling Tower Fan Inverter Cooling Tower Water Sump Tower Water
Recirculation Pump CDWP-2 Inverter Chiller CDWP-1 Inverter Chiller
Failure Recovery
Figure 57. Failure recovery
System Controls
Conclusion
Glossary
condenser water, leaving. See cooling water
cooling tower water. See cooling water
pumps system
Glossary
tower water. See cooling water
Glossary
Plant.” IDEA 88th Annual Conference Proceedings 1997
References
Except Low-Rise Residential Buildings. ASHRAE and IESNA
References
Engineering July
ASHRAE/IESNA Standard 90.1-2007 Energy Standard for Buildings
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
Date
Trane
Literature Order Number
SYS-APM001-EN
