High-side pressure control for transcritical refrigeration system
Solution Overview
Problem
Conventional control schemes for CO2 vapor compression systems in transport refrigeration units, which operate over a large range of heat source temperatures, fail to accurately determine the optimum high-side pressure, leading to suboptimal energy efficiency and cooling capacity due to reliance solely on heat sink temperature conditions.
Innovation Solution
The system controls high-side pressure in CO2 vapor compression systems by considering conditions on both the high-pressure and low-pressure sides, utilizing sensors to sense refrigerant conditions at various points and adjust the expansion device to achieve optimal pressure based on a combination of temperature and pressure readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional control schemes use only heat sink temperature to control high-side pressure, then the control system is simple, but energy efficiency and cooling capacity are suboptimal across large ranges of heat source temperatures
Solution Approach 1:
The control system implements feedback by continuously monitoring both high-side pressure and low-side evaporating temperature, using these measurements to dynamically adjust the expansion device and maintain optimal high-side pressure for maximum energy efficiency and cooling capacity across varying operating conditions
Solution Approach 2:
The system transitions from static pressure control based solely on heat sink temperature to dynamic pressure control that adapts in real-time to changing heat source temperatures by incorporating low-side evaporating temperature feedback and adjusting expansion device positioning accordingly
2Adaptability or versatility
If the system is designed to cover a large range of heat source temperatures, then the system has high adaptability, but single-parameter pressure control becomes insufficient
Solution Approach 1:
The control system achieves universality by designing a multi-parameter control scheme that functions effectively across the entire operating envelope from -20°F to 57°F heat source temperatures, using both high-side pressure and low-side evaporating temperature inputs to maintain optimal performance under all conditions
Solution Approach 2:
The system optimizes performance across varying temperatures by dynamically changing control parameters - specifically by adjusting the relationship between high-side pressure and low-side evaporating temperature through expansion device modulation, allowing the system to adapt to different operating conditions within the broad temperature range
Data Source
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AI summary
To accommodate a transcritical vapor compression system with an operating envelope which covers a large range of heat source temperatures, a high side pressure is maintained at a level determined not only by operating conditions at the condenser but also at the evaporator. A control is provided to vary the expansion device in response to various combinations of refrigerant conditions sensed at both the condenser and the evaporator in order to maintain a desired high side pressure.