Air-Cooled Chiller Refrigerant Flow Control for Low Delta T Loads
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Solution Overview
Problem
Chilled water plants using air cooled chillers face inefficiencies due to low Delta T conditions, leading to increased energy consumption and reduced cooling capacity, as existing mitigation strategies like sequencing programs and variable condenser fan speeds do not fully address these issues.
Innovation Solution
The implementation of a refrigerant pump and bypass valve in parallel with the condenser and evaporator, along with power consumption feedback to control the condenser fan, and resetting the evaporator set point based on Delta T and load conditions, enhances the efficiency of air cooled chillers by preventing refrigerant stacking and optimizing refrigerant flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a refrigerant pump and bypass valve are added in parallel with the condenser and evaporator, then refrigerant stacking is prevented and system reliability is improved, but device complexity increases
Solution Approach 1:
The refrigerant flow path is segmented into multiple parallel channels: the condenser-evaporator path and the pump-bypass path. This segmentation allows independent control of refrigerant flow through each path, preventing stacking while maintaining system reliability without requiring complete system redesign
Solution Approach 2:
The bypass valve acts as an intermediary component that redirects refrigerant flow away from the condenser when stacking conditions are detected. This intermediary mechanism provides a controlled alternative path for refrigerant, preventing the harmful stacking effect while adding minimal complexity to the existing system
2Use of energy by moving object
If condenser fan speed is controlled based on power consumption feedback, then energy efficiency is improved, but control system complexity increases
Solution Approach 1:
A feedback control loop is implemented where power consumption is continuously monitored and used to adjust condenser fan speed. The controller receives power consumption signals and automatically modulates fan speed to optimize energy efficiency, creating a self-regulating system that improves performance without requiring complex external control infrastructure
Solution Approach 2:
The control system uses the chiller's own power consumption data to automatically adjust its operating parameters. The system serves itself by using internal measurements to optimize its performance, eliminating the need for external sensors or complex control algorithms while achieving improved energy efficiency
3Productivity
If the evaporator set point is reset based on Delta T and load conditions, then cooling efficiency is improved, but control complexity increases
Solution Approach 1:
The evaporator set point is made dynamic rather than fixed, automatically adjusting based on real-time Delta T measurements and load conditions. This dynamic adjustment allows the system to optimize cooling efficiency across varying operating conditions without requiring manual intervention or complex control algorithms
Solution Approach 2:
The control system changes the evaporator temperature set point parameter in response to varying load conditions and Delta T measurements. By dynamically modifying this key parameter, the system adapts to changing conditions and maintains optimal cooling efficiency without adding significant control complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the seasonal efficiency of air cooled chillers by approximately 40%, reduces energy usage, and maintains optimal operating conditions for chilled water plant components, thereby increasing their lifespan and reducing energy costs.
Implementation Method 1
A refrigerant pump and bypass valve connected in parallel feed refrigerant from the condenser to a receiver
Implementation Method 2
The condenser fan section is generally set to maintain a constant condensing temperature
Implementation Method 3
a chiller to produce chilled water, which is pumped to air handlers to cool building air
Data Source
AI summary
In an air cooled chiller, a refrigerant pump and bypass valve connected in parallel feed refrigerant from the condenser to a receiver; the pump is activated in response to condenser pressure; and the bypass is used otherwise. The condenser fan is controlled based on power consumption by the air cooled chiller that varies with ambient conditions. An evaporator set point is reset to meet load conditions. An expansion valve for the evaporator is controlled based on chilled water temperature, Delta T, or information from an air handling unit. Feedback of valve setting or position, temperature of air, valve size, and/or importance of an air handling unit is used to control the flow of chilled water. A variable pressure curve or other relationship is used with the feedback to control flow of chilled water based on the load. Refrigerant temperature is controlled based on information from the air handling unit.